Difference between revisions of "602 - Concrete Pavement Construction"
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===[[#Acceptance of Materials|Acceptance of Materials]]=== | ===[[#Acceptance of Materials|Acceptance of Materials]]=== | ||
Revision as of 15:25, 11 March 2014
GENERAL
-Reserved-
MATERIALS
Acceptance of Materials
Before paving operations start, the paving inspector should verify that all materials that need to be incorporated in the pavement have been tested and accepted. Most materials will be stockpiled in the Contractor’s yard on the project site. Often this is also the location of the batching plant.
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When the load transfer assemblies arrive on the project site, call Region materials personnel so they can verify that the assemblies were built according to the standard plans. Notice of acceptance by Region materials personnel is the required documentation. |
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Check to see if the dowel bars and the fiber joint filler material are certified. Sampling and testing may be required. |
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After the Contractor starts to set the load transfer assemblies on the grade, they must be visually inspected for:
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The entire bar is to be coated with an approved plastic or epoxy coating to prevent corrosion, and at least two-thirds of the dowel bar’s length is to be coated with an approved material to prevent concrete from adhering to the bar. If the yellow Republic Steel Company coating is used, the dowels need not be coated. |
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Any material of uncertain origin should be piled separately and not used until it is determined that it meets specification requirements. |
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Visually inspect the handling and storage of all materials used in the concrete paving operation. |
Pavement Reinforcement
Welded wire fabric (mesh) reinforcement is accepted for use based on laboratory tests and certification that consists of a tension test, weld shear test, bend test and fabrication inspection covering gauge and spacing dimensions. Welded wire fabric is generally furnished in flat sheets and assembled in bundles of 150 sheets or less. Each bundle should have a tag bearing the manufacturer and material description, and a second tag giving the sampling agency or laboratory name. Mesh is usually sampled at the fabrication shop after fabrication, but it may be sampled at the job site. Reporting of testing is usually done within ten days. Documentation will be the notice of acceptance from the Construction and Technology lab.
Welded joints should withstand normal shipping and handling without breaking. Broken welds do not constitute cause for rejection unless the number of broken welds in a sheet exceeds 1 percent of the total number of joints in a sheet.
Thin, powdery rust and tight rust are not considered detrimental and need not be removed. When reinforcement is rusted to where the effective cross sectional area may be reduced, evidenced by an overall thick rust coating or heavy scaling, tests should be made to determine if the reinforcement conforms to the required dimensions and mechanical properties. If the reinforcing steel meets these requirements, the rust itself should not be a cause for rejection.
The pavement reinforcement should be stored off the ground. Steel mesh on the bottom of the stockpile, having contact with the ground and contaminated with dirt and grass, will be cleaned thoroughly before delivery to the paving site. A high pressure water hose will usually be required to effectively clean the mesh. If the reinforcement cannot be cleaned thoroughly, it must be rejected.
Tie Bars and Bent Bars
These items should be checked for certification, or sampled and tested when they arrive on a project.
Curing Compound
- Check certification, or sample and test each batch or lot.
- Material may be in drums or in a large tank. Inspection consists of seeing that the material is not contaminated or diluted and that it is mixed according to the manufacturer’s recommendations.
- A curing compound should not be used when stored from one construction season to the next without resampling and testing.
- Check yield of material to ensure correct coverage.
Joint Seals
At least 6 feet (1.8 m) of each size and lot of preformed neoprene joint sealer will be sampled at random and submitted to the Construction and Technology lab in Lansing.
CONSTRUCTION
Concrete Testing Procedures
Quality control testing for concrete QC/QA construction projects will be governed by the Contractor’s quality control plan. Acceptance tests on the concrete on these projects will be in accordance with the Special Provision for Furnishing Portland Cement Concrete (QA) at the frequency specified.
Concrete for non-QC/QA projects will be tested for acceptance by the inspector according to the Frequency of Test chart. The first load of each type of concrete each day will be subject to acceptance testing by the Engineer for air content, slump and temperature.
Concrete placement will not begin until the testing verifies that the concrete meets specifications. Continued testing during concrete placement will be per the testing frequency chart, or any time the inspector questions the consistency of the concrete.
Frequency of Tests
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Air |
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Slump |
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Temperature |
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Strength specimens (2 beams or 2 cylinders = 1 strength test) | ||
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Beams |
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Cylinders |
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Mold two sets of beams every day for production paving (two beams in the morning and two beams in the afternoon). Mold two sets (four beams) for each substructure unit, or every 200 cubic yards (150 cubic meters) of miscellaneous concrete. On substructure repair or rehabilitation, beams should be molded at least twice a week. These beams will be used to check the design of the mix and are therefore to be cured under moist conditions.
Additional beams may be required by the Engineer for special purposes such as early opening of pavement to traffic, removing false work, etc. If these additional beams are used to determine the strength of concrete cast in cold weather, they should be cured by the same methods used to cure the pavement or structure; that is, insulated blankets or heating and housing.
Additional strength testing may be required for opening to traffic, stripping of forms, etc., and should be cured under the same environmental conditions as the pavement structure being tested.
Sampling and Testing Concrete Time Limits
Time Limits for Sampling and Testing Fresh Concrete
Sampling Freshly Mixed Concrete ASTM C 172 (Modified for MDOT Procedures)
- Concrete samples should be representative of the entire concrete batch.
- For structure concrete being placed with a transfer bucket, take samples after more than 1/2 cubic yard (0.5 m3) has been discharged.
- If it is necessary to take samples from a stream of concrete where the concrete is being placed directly into the forms, make a representative sample by mixing several pailfuls of concrete taken from the stream.
- Pavement concrete may be sampled after the concrete is placed on the grade, if taken from two or more locations to make a composite sample.
- Placed concrete should be sampled at the discharge end of the pump.
- Since sampling from the pump discharge presents some difficulty at times, routine tests may be made on concrete samples from the pump hopper provided sufficient correlative tests have been made between the truck discharge and the pump discharge.
- When concrete appears to be out of specification, the inspector has the right to stop its placement until confirming tests are made. Sampling, in this case, is performed in a reasonable manner.
- The Contractor should be notified of the sampling plan for a particular project before operations begin.
Temperature of Freshly Mixed Concrete Test Method for Temperature of Freshly Mixed Portland Cement Concrete: ASTM C 1064
The concrete temperature should be run in conjunction with the slump and air tests. Complete the temperature measurements within five minutes after obtaining the sample.
Equipment : A thermometer readable to 1.0°F (0.5°C).
- The temperature of the freshly mixed concrete may be taken in the transporting equipment before concrete placement, in the forms or in a properly prepared sample. No matter where the temperature is taken, be sure that the sensor of the thermometer has at least 3 inches (75 mm) of concrete surrounding it.
- Gently press the concrete around the thermometer at the surface of the concrete so that the ambient air temperature does not affect the reading.
- Leave the thermometer in the freshly mixed concrete for a minimum of two minutes, or until the temperature stabilizes, and then read and record the temperature.
- Complete the temperature measurement within five minutes after obtaining the sample.
- Record the temperature of the freshly mixed concrete to the nearest 1.0°F (0.5°C).
- Clean the thermometer and replace in its case.
Slump Test Test Method for Slump of Hydraulic Cement Concrete: ASTM C 143
The slump test measures the consistency of the plastic concrete. The slump test will be started within five minutes of obtaining the sample. The concrete sample within the cone will be discarded and not used to perform another test.
Equipment: slump cone, nonabsorbent base plate, steel rod 15 inches (600 mm), scoop, ruler.
These steps apply to concrete with coarse aggregate up to 1-1/2 inch (38 mm) in size. For larger aggregate, see alternate procedures in ASTM C 143.
- Remix the concrete sample.
- Dampen the cone and place it on a flat, moist, nonabsorbent, rigid and horizontal surface. If smooth plywood is used, cover it with plastic.
- Hold the cone firmly in place and fill the container in three layers, each approximately one-third the volume of the cone. (One-third of the volume fills the cone to a depth of 2-5/8 inches (67 mm); two-thirds fills the cone to a depth of 6-1/8 inches (155 mm).
- Rod each layer 25 times.
- For the first layer, slightly incline the rod and make approximately half the strokes near the perimeter.
- On successive layers, penetrate the previous layer slightly.
- On the third layer, keep concrete mounded above the top of the mold at all times.
- Strike off the last layer with a screeding motion of the tamping rod.
- Remove any spilled concrete from the base of the cone.
- Raise the cone a distance of 12 inches (300 mm) in 5 ±2 seconds by a steady upward lift with no lateral or torsional motion.
- Complete the entire test, including rodding and measurement of slump, within 2-1/2 minutes.
- Measure the difference in the height of the cone and the displaced original center of the top surface of the concrete.
- Measure and report to the nearest 1/4 inch (6 mm).
- The test is not valid if there is decided falling away or shearing off of the concrete. Disregard the test and make a new test on another portion of the sample.
- Clean and dry the equipment.
Air Content
The air content requirement for most concrete is 5 percent to 8 percent. Check the specification requirements for the item of work being tested. Variations in concrete temperature, aggregate gradation, consistency, mixing equipment and other factors can cause fluctuations in the air content. If the air content is below the minimum specified for the concrete, the Contractor will be required to add an air-entraining admixture. The proper amount of admixture per batch will be added at the batching plant by means of an approved automatic dispenser.
The first load of each type of concrete each day will be tested for air content by the inspector. Additional tests during the day’s pour will be as per the frequency chart.
The pressure meters (Acme-Type A and Press-ur/White- Type B) are designed to show air content in percent when an operating pressure is applied. The air content determined, however, includes not only the air entrained in the concrete, but also that held within the pores of the aggregate particles. Since it is only the entrained air that is desired, it is necessary to correct the measured air content for the air held within the aggregate particles.
The pressure type air meter cannot be used to determine entrained air content in concrete using light weight or highly porous aggregates such as slag, or coarse aggregates with an aggregate correction factor of more than 0.5 percent. A Roll-a-Meter must be used with these materials.
Pressure meters also need to be calibrated for operating pressure. The instructions for calibration should be with each type of meter: Acme, Press-ur, White, etc.
Instructions for Use of the Acme Air Meter
- The calibration value of percent air, K, for a given meter and calibration cup is computed:
- K = [(V1 (vol. of cup in cc)) / (V2 (vol. of bowl in cc))] x 0.98 x 100
- Place the brass calibration cup in the meter bowl with the hole in the cup facing down and the cup resting on its three legs.
- Pour water into the bowl carefully so as to minimize the possibility of the water entering the calibration cup. Fill the bowl to nearly full.
- Place the top on bowl after wetting the gasket and bowl flange. Fill the meter to above the zero mark on the water glass.
- Close the petcock and funnel valve and pump the meter to approximate operating pressure. Incline the meter to about 30° and tap the cover to release any entrapped air adhering to the inner surface of the meter. Slowly release the pressure.
- Open the upper petcock and adjust the water level to the zero mark in the water glass. Close the petcock and pump air into the meter until the K value is read on the sight tube. Tap the pressure gauge (to stabilize) and read the gauge. This is the operating pressure, P, for this meter.
- Slowly release the pressure and check that the water level returns to the zero mark. If not, refill the water level to the zero mark and repeat steps 6 and 7.
Notes: The fixed value of 15 psi for P is no longer used. The new operating pressure, P, must be determined by calibration.
Any substitution of the pressure gauge or glass water tube will necessitate a new calibration.
Do not tilt the meter when the calibration cup has been placed in the meter for calibrating unless the meter is under pressure.
Acme and Press-ur-Meter Aggregate Correction Factor Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method: Part of ASTM C 231
Aggregate corrections factor is used when the air content is determined by the pressure meter.
The correction for air held within the particles of the aggregates should be determined at the beginning of the job and probably will be sufficiently accurate for use for the duration of the work.
Prepare proportional samples of fine and coarse aggregate in the amounts which will exactly fill the meter’s container and proceed to “box” (mix) them together.
- The aggregate correction is determined independently by applying the calibrated pressure to a sample of inundated fine and coarse aggregate in approximately the same moisture condition and proportions occurring in the concrete under test.
- Calculate the weights of fine and coarse aggregate, proportioned according to the concrete proportioning chart for the materials being used, that will exactly fill the bowl.
- Use the following example to obtain a proportioned sample of aggregates based on a 1 yd3 (1 m3) batch:
- FA = Weight of fine aggregate for test, lb. (kg)
- CA = Weight of coarse aggregate for test, lb. (kg)
- S = Volume of the bowl used in test, yd3 (m3)
- Volume of Acme Meter bowl = 0.0074 yd3 (.00566 m3)
- Volume of Press-ur-Meter bowl = 0.0093 yd3 (.00708 m3)
- B = Volume of the concrete batch 1 yd3 (1 m3)
- F* = Weight of fine aggregate in batch, 1 yd3 (1 m3) moist condition
- C* = Weight of coarse aggregate in batch, 1 yd3 (1 m3) moist condition
- FA = (S/B) x F
- CA = (S/B) x C
- FA(kg) = 0.0074 yd3 (.00566 m3) x 1212 lbs/yd3 (719 kg) = 9.0 lbs (4.0 kg)
- CA(kg) = 0.0074yd3 (00566 m3) x 1947 lbs/yd3 (1155 kg) = 14.4 lbs (6.5 kg)
- Note: For this example, the unit weight of the coarse aggregate is 1947 lbs/ft3 (1155 kg/m3) and the unit weight of the fine aggregate is 1212 lbs/ft3 (719 kg/m3).
- Mix the representative samples of coarse and fine aggregates together. Fill the bowl half full of water and slowly pour the combined aggregate into the bowl, stirring and tapping the sides of the bowl to eliminate all entrapped air.
- Follow the procedures for determination of air in freshly mixed concrete for the appropriate weight - Type A or Type B. The resulting air content is the aggregate correction factor.
- The aggregate correction factor is subtracted from the meter reading of air content for the concrete being tested.
Air Content Pressure Method (Type A) “Acme” Meter Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method: ASTM C 231
This test is performed according to ASTM C 231: Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method.
Equipment : ACME meter, scoop, rubber mallet or rubber tipped steel rod, strike-off bar, water.
- This test method may not be used with slag or other lightweight porous aggregates, or aggregates with an aggregate correction factor more than 0.5 percent.
- Predetermine the aggregate correction factor (see ASTM C 231).
- Remix the sample and dampen all the equipment, removing the excess moisture.
- Fill the bowl in three equal layers, rodding each layer 25 times and penetrating 1 inch (25 mm) into the previous layer. Rap the sides smartly 10 to 15 times with a standard mallet (rubber tipped rod) after each layer. There should be no shortage of concrete below the rim of the bowl during the rodding of the third layer. An excess of 1/8 inch (3 mm), after consolidation, is desired.
- Strike off the concrete with a metal strike-off bar. Clean the contact surface and dampen the rubber seal on the cover. Clamp on the cover.
- Add water until the site tube is half full.
- Rotate the meter on its base at a 30° angle several times, tapping the cover with a mallet.
- Bring the water level to slightly above the zero mark while lightly tapping the sides of the bowl. Adjust the water level to the zero mark by opening the lower drain valve. Close all the valves.
- Pump the pressure to the desired operating pressure (lightly tap the pressure gauge to stabilize the gauge).
- Read the apparent air content on the scale to the nearest 0.1 percent. (h1).
- Gradually release pressure while tapping the bowl.
- Record the water level (h2).
- Calculate the apparent air content (A1 = h1 - h2).
- Repeat steps 9 through 13 without adding water to obtain a second reading (A2). Reading A1 and A2 should agree within 0.2 percent.
- The average of the two readings minus the aggregate correction factor is the final air content.
- Clean and dry the equipment for storage.
Air Content Determination When Value Exceeds Scale Reading at Operating Pressure, P
When the air content cannot be read on the scale with the application of the operating pressure, P, the following procedure and formula may be used to make this determination.
- Decrease the pressure until the water level in the glass is within the readable range of the scale. This pressure will be considerably reduced from the operating pressure.
- Note the value of this reduced gauge pressure, Pr, and the simultaneous scale reading, S.
- The correct air content is obtained by multiplying the scale reading, S, by a computed factor, F.
- Factor, F, is computed as follows:
- F = (P (A1 + Pr )) / (Pr (A1 + P ))
- Where:
- P = Operating Pressure, psi
- Pr = Reduced Pressure, psi
- A1 = Atmospheric Pressure, 14.6 psi
- Air content % = S x F (minus aggregate correction factor).
Example:
At the normal operating pressure of 13.5 psi (P), you cannot read the water level on the scale.
After reducing the pressure to 10 psi, you are able to read the water level on the scale at 6.8(S).
The factor for reduced pressure at 10 psi for a meter with a normal operating pressure of 13.5 psi = 1.18(F).
Air content % = S (6.8) x F (1.18) = 8.0 percent (minus the aggregate correction factor).
In lieu of the general equation shown, the following table may be used to determine the correct air content when the value is greater than can be determined at normal operating pressure, P. Use either the 10 psi or 5 psi reduced pressure and multiply by the respective factor found in the table opposite the value of the normal operating pressure.
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Air Content - Pressure Method (Type B) Press-ur-Meter Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method: ASTM C 231
This test is performed according to ASTM C 231: Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method.
Note: These instructions are for the Press-ur-Meter. The White meter may vary slightly: see the instructions that come with the unit.
Equipment : Press-ur-Meter, scoop, steel rod, rubber mallet, strike-off bar, rubber syringe, water.
- This test method may not be used for concrete with lightweight or porous aggregate.
- Predetermine the aggregate correction factor (see ASTM C 231).
- Remix the sample and dampen all the equipment, removing the excess moisture.
- Fill the bowl in three equal layers, rodding each layer 25 times and penetrating 1 inch (25 mm) into the previous layer. Rap the sides smartly 10 to 15 times with a standard mallet or rubber tipped rod after each layer. There should be no shortage of concrete below the rim of the bowl during the rodding of the third layer. An excess of 1/16 inch (3 mm), after consolidation, is desired.
- Strike off the concrete with a metal strike-off bar. Clean the contact surfaces. Dampen the rubber seal on the cover and clamp the cover onto the bowl.
- Close the main valve between the air chamber and the bowl and open both petcocks.
- Syringe the water through one petcock until water comes out of the other petcock.
- Jar the meter gently until no air bubbles come out the petcock.
- Close the air bleeder valve, if open, and pump the pressure up to the initial pressure line (usually 2 percent to 3 percent past zero, depending upon the calibration).
- Allow a few seconds for the compressed air to cool, then adjust the meter to the initial pressure line by pumping or bleeding while tapping the gauge lightly.
- Close both petcocks.
- Open the main air valve. While holding the valve open, sharply rap the bowl, lightly tap the gauge and read the air content on the gauge.
- Subtract the aggregate correction factor from the gauge reading and record the air content.
- Clean and dry the equipment for storage.
Air Content - Volumetric Method (Roll-a-Meter) Test Method for Freshly Mixed Concrete by the Volumetric Method: ASTM 173
This test is performed according to ASTM 173: Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method. This method of determination of the air content of freshly mixed concrete may be used with any type of aggregate whether it is dense, porous or lightweight. However, it must be used for lightweight (slag type) materials.
Equipment: Roll-a-Meter, scoop, mallet and/or rubber tipped rod, strike-off bar, rubber syringe, measuring cup, water funnel, isopropyl alcohol, water.
- Remix the sample and dampen all the equipment, removing any excess moisture.
- Fill the bowl with concrete in three equal layers, uniformly rodding each layer 25 times, penetrating the previous layer approximately 1/2 inch (13 mm).
- Tap the sides of the bowl 10 to 15 times with a mallet (rubber tipped rod) after rodding each layer.
- Strike off the top layer with the strike-off bar.
- Wipe the contact surfaces clean and moisten the sealing ring. Clamp the top to the base.
- Fill the meter with water, using a funnel, and adjust the water level to the zero mark, using a syringe.
- Invert the meter and agitate 5 seconds at a time for a minimum of 45 seconds to free the concrete from the base.
- Vigorously roll the meter at a 45° angle for approximately one minute.
- Set the meter upright, jar it tightly and wait until the air rises to the top and the water level stabilizes, approximately one minute. Stabilized means no change of liquid level more than 0.1 percent.
- Repeat the rolling operation until no further drop in the water level is observed and two consecutive readings do not change by more than 0.25 percent (it may be necessary to roll the meter several times to verify that there is no further drop in the water level).
- Dispel the foam with the standard measuring cup filled with 70 percent isopropyl alcohol.
- The air content is read to the bottom of the meniscus in the neck (estimated to the nearest 0.25 percent) plus the number of cups of alcohol.
Molding Cylinders Practice for Making and Curing Test Specimens in the Field: ASTM C 31 (Cylinders)
Compression test cylinders are molded according to ASTM C 31: Standard Test Method of Making and Curing Test Specimens in the Field. Cylinders made for compressive strength need companion slump, air content and temperature tests from the same sample of concrete before molding. Cylinders made in the field will have to be transported to the Region lab within 48 hours for further curing and testing. If cylinders are not shipped to the lab within 48 hours, it will be necessary to provide moist curing at the site within 24 ±8 hours of molding. Two (2) cylinders are needed for each compressive strength test.
Equipment: Two molds per test, 6 inches x 12 inches (152 mm x 305 mm), tamping rod, scoop, mallet, wood float or trowel.
- Remix samples.
- Lightly coat mold with a form release agent and dampen other equipment.
- Fill molds in three equal layers, distributing concrete symmetrically.
- Rod each layer 25 times, penetrating the previous layer about 1 inch (25 mm) (do not strike the bottom of the mold hard).
- Tap the mold sides lightly to close voids left by the rodding.
- Strike off the top with a float or trowel.
- Clean the outside of the mold.
- Cover/cap the cylinder to prevent the loss of moisture during initial curing.
- Store undisturbed for the initial 24 ±8 hours at 60 to 80°F (16 to 27°C).
- Arrange for transportation to a Region lab.
Note: If deer tags are used for identification, bend the barbed end about 1/2 inch (12 mm) and insert it into the center of the cylinder. Fold the rest of the tag across the top of the cylinder and down the outside. Cap as per step 8.
Compression Machine for Strength Test
The testing machine must be calibrated at least every 18 months and any time it is relocated, repaired or its accuracy is in doubt.
The bearing block surface may not depart from the plane by more than 0.001 inch (0.025 mm) in any 6 inches (152 mm) and must be clean and free of debris.
Sulfur or Gypsum Caps
- Capping plates for the compression machine are designed either for sulfur of high-strength gypsum cement.
- Minimum thickness (glass 1/4 inch (6 mm) (metal 0.43 inch (11 mm).
- Minimum size 1 inch (25 mm) greater in diameter than the specimen.
- Have a surface plane of 0.002 inch (0.05 mm) in 6 inches (152 mm).
- Have no gouges, grooves or indentations greater than 0.01 inch (0.25 mm) deep, or 0.05 in2 (32 mm2) in surface area.
- The recessed area on the capping plates which receive molten sulfur or gypsum cement will not be deeper than 1 inch (25 mm).
A bulls eye or guide bar will be available and used for proper alignment of the specimen during capping.
Neoprene Caps
Neoprene caps consist of neoprene pads and steel cups.
- Pads must have a durometer hardness of 60 ± 5 and can be used a maximum of 100 times.
- Steel cups must not be more than 0.08 inch (2 mm) greater in diameter than the pads being used.
- No gouges or dents larger than 0.01 inch (0.25 mm) in depth or 0.03 in2 (32 mm2) in surface area are permitted on the outside bearing surface of the cups.
- All bearing surfaces of cups (inside and outside) will be lined to within 0.002 inch (0.05 mm).
Capping Materials
Sulphur capping material will be heated to 264 to 288°F (129 to 143°C).
Specimens capped with high-strength gypsum caps cannot be stored underwater or in a moist room.
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Compressive Strength Test Test Method for Compressive Strength of Cylindrical Concrete Specimens: ASTM C 39
- Cylinders must be kept moist between capping and testing. Cover the specimens with wet burlap while awaiting testing (caps should not be covered).
- Specimen ends must not depart from perpendicularity to the axis by more than 0.5 degrees 0.12 inch in 12 inches (3 mm in 300 mm).
- Determine the cylinder diameter by averaging two diameters measured at right angles to each other at about mid-height.
- Measure the length of the specimen to the nearest 0.002 in (0.05 mm). The length-to-diameter ratio should be greater than 1.8 but less than 2.2. If the specimen length-to-diameter ratio is less than 1.8, correct the test result obtained by multiplying by the appropriate correction factor shown:
- L/D: 1.75 1.50 1.25 1.00
- Factor: 0.98 0.96 0.93 0.87
- Wipe clean the upper and lower loading and bearing surfaces of the specimen and the testing machine.
- Place the specimen on the lower bearing block and carefully center the specimen in relation to the top spherically seated block.
- Carefully bring the top (spherically seated) block to bear so that uniform seating is obtained.
- Apply the load continuously and without shock until the specimen yields. The rate of loading the specimen must be within a range of 0.14 and 0.34 MPa per second for hydraulically operated machines. Make no adjustments in the rate of loading while the specimen is yielding rapidly just before failure.
- Calculate the compressive strength and report to the nearest 0.1 MPa. See Figure 602-2 for Concrete Cylinder/Core Compression Test Results, Form 1160B.
- Record the maximum load and note the type of failure and any defects in the making of the specimen (Figure 602-2).
Casting Flexural Strength Specimens Practice for Making and Curing Concrete Test Specimens in the Field: ASTM C 31 (Beams)
Flexural strength test beams are cast according to ASTM C 31: Standard Test Method of Making and Curing Concrete Test Specimens in the Field. Test beams may be molded at the plant or at the job site. The location of molding, curing and testing will be designated by the Engineer. Usually the plant is the preferred site, as this method avoids the need to transport the beams for curing. The average of two beams equals one strength test.
Equipment: Molds 6 in x 6 in x 21 in (152 mm x 152 mm x 533 mm), nonabsorbent base, scoop, steel tamping rod, mason’s trowel, mallet, wood float, plastic sheet to help retard evaporation.
- Clean and lightly oil the molds and place on a level, nonabsorbent surface.
- Wet the equipment, removing excess moisture, and remix the sample.
- Fill the mold in two equal layers, rodding each layer 60 times. When rodding the second layer, the rod should penetrate the first layer by about 1/2 inch (12 mm). After each layer is rodded, the mold should be spaded along the sides and end with a trowel, or other suitable tool, and the outside tapped with a mallet to consolidate the rod holes.
- Strike-off the surface of the concrete with a wood float to produce a flat, even surface.
- Cover with a nonabsorbent plate or plastic and keep damp with wet sand or wet burlap for the first 24 hours.
- Remove the molds and continue curing in damp sand, immersion in lime water or other approved method until testing, ideally at 60 to 80°F (21 to 25°C).
- Clean the equipment and re-oil the molds.
Test Method for Flexural Strength of Concrete
Note: The table of Modulus of Rupture factors which is used with this test method will produce a test result in metric units. Follow these directions carefully and note where measurements are made in metric versus English units. See Figure 602-3 for an example of Report of Modulus of Rupture, Form 1160A.
Equipment: Testing machine, jack and jack handle, anvil, ruler.
- Set up the beam testing machine on a level surface.
- Open the jack valve to release pressure and push the jack head down. Place the anvil on top of the jack and close the valve.
- Place the test specimen on its side in the machine with respect to its position as molded.
- With the clamping bar bolts in a vertical position, snug down the clamps. Care should be taken to ensure that the end of the beam is not touching the frame of the machine.
- Check the dial of the jack to make sure that the red following indicator is zeroed out. Pressure should be applied at the rate of 400 pounds per minute. It is helpful having an assistant call out 15 second intervals during which 100 pounds of pressure is applied continuously. Keep the load constant until rupture occurs.
- Take three measurements across each dimension (one at each edge and at the center) to the nearest 0.08 in (2 mm) to determine the average width and depth of the beam. Do the same to measure the average length of the beam.
- The factor for the width and depth is taken from the following table, Modulus of Rupture Factors, and multiplied by the load applied to calculate the modulus of rupture in MPa. Make out the proper documentation.
- If the 28 day test result is below the design strength, save and continue curing the beam ends for possible compression testing by Construction and Technology. Concrete data: air content, slump, temperatures and remarks, such as low curing temperature, damage in handling or lack of moist curing should be sent with the beam ends to Construction and Technology. The Contractor should be notified of low results.
Modulus of Rupture Factors
MR = LOAD (pounds) x FACTOR
This table was developed for use with beam testing devices that give a load in pounds.
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Note: Dimensions are for the beam as placed in testing machine. Place the beam to be broken on its side in the machine, with respect to its position as molded. Load is to be applied at a rate of 400lbs (180 kg) per minute by dial reading.
Concrete Test Hammer (Swiss Hammer)
The concrete test hammer may be used in place of test beams on work requiring a large number of repetitive tests. An example would be fast setting pavement patches which must be opened to traffic the day of placement. Normally, this work would entail making a number of test beams throughout the day and opening the patch when minimum strength is attained. In this case, correlations are made between the test hammer and beam test results to establish a minimum hammer reading for a given strength requirement. Patches may then be opened to traffic on the basis of the test hammer readings.
Equipment: Swiss hammer
- Test hammer readings are taken on the concrete before the molds are removed.
- Sixteen readings are taken over the entire surface of the test beam, keeping 1 inch (25 mm) from the sides of the mold.
- Drop the lowest three readings and the highest three readings and record the average of the remaining ten readings.
- Unmold the test beam and break, as indicated in Test Method for Modulus of Rupture, for its flexural strength.
- The flexural strength of the beam can now be represented by the average of the ten readings of the test hammer.
- The average of a number of test hammer readings taken over the entire surface of the slab, or at the corners of a repair patch that match the recorded reading taken on the test beam, should have the comparable flexural strength.
Unit Weight and Yield Test Method for Unit Weight, Yield and Air Content (Gravimetric) of Concrete: ASTM C 138
This method covers determination of the weight per cubic meter of freshly mixed concrete and gives formulas for calculating the yield.
Equipment: Bucket (approximately 1/2 cubic foot (0.015 cubic meters), scales, a scoop, tamping rod, strike-off plate, mallet.
- Remix the sample.
- Dampen the equipment and remove the excess moisture.
- Tare the dampened bucket to nearest 0.25 pound.
- Fill the bucket in three equal layers, rodding each layer 25 times.
- Do not forcibly strike the bottom.
- Penetrate the previous layer about 1 inch (25 mm).
- Rap the sides smartly 10 to 15 times after each rodding.
- On completion of consolidation, no substantial excess or deficiency of concrete should be present (an excess of 1/8 inch (3 mm) is optimum).
- Small quantity of concrete may be added.
- A representative portion of an excess amount of concrete may be removed with a scoop or a trowel.
- Strike-off the concrete with the plate. To best accomplish this:
- Place the plate two-thirds of the way over the top of the bucket, apply vertical pressure and withdraw the plate with a sawing motion to finish the original area covered.
- Cover the original two-thirds of the bucket with the plate and advance the whole plate with vertical pressure and a sawing motion completely across the concrete surface.
- Final screeding can be done with the inclined edge of the plate for a smooth and level surface.
- Clean the sides and bottom of the container and weigh to the nearest 0.25 pound.
- Calculate the unit weight and clean the equipment.
To assure accurate results, net weight determinations should be made on three separate measures of concrete. The weight per cubic foot (meter) of concrete will be calculated by dividing the average net weight of the concrete (in pounds) by the volume factor (in cubic feet) stamped on the rim of the measure. Contact the Construction Services Section or the Construction and Technology Concrete laboratory for equipment and help with adjustments when running a yield determination.
Example:
Volume of bucket = 0.501 cubic feet
Tare of bucket = 17.6 pounds
Concrete + bucket = 90.2 pounds
90.2 pounds - 17.6 pounds = 72.6 pounds / 0.501 = 145.2 pounds/cubic foot x (16.018307) = 2325.9 kg/m3
Instructions to Concrete Pavement Inspectors
The construction of PCC pavement is a highly mechanized operation that requires inspection of a vast quantity of material and a working knowledge of numerous types of equipment. Inspectors assigned to this work should be thoroughly familiar with the Standard Specifications, standard plans, Special Provisions, construction details and order of work.
A meeting on paving operations should be scheduled with the Contractor’s paving personnel to discuss scheduling and equipment, and to introduce the paving inspection team. The Contractor’s paving superintendent and foreman should be at this meeting.
Pavement Inspection Team
- Concrete Paving Inspector - Obtains a structurally sound pavement with the desired ride qualities. This will largely depend upon the inspector’s supervision and attention to details. Works near the center of the operation, observing the placement of concrete and reinforcement, finishing and floating of the slab. Supervises the assistants and helps them resolve any problems.
- QC testing - temperature, air, slump, test beam yield; although the actual testing may be delegated to others, unless using QC/QA specifications.
- Responsible for record keeping, documentation of pay quantities and preparation of Inspector’s Report of Concrete Placed, Form 1174A (Figure 601-7) and for maintaining communications with the concrete plant.
- Engineer - Designates a senior paving inspector to be in charge of the entire paving operation.
- Assistant(s) - Will be assigned as needed; usually one or two, depending on project size and the Contractor’s anticipated production rate. This should be discussed with the Contractor before starting paving operations.
Checking the base condition and the setting of load transfer assemblies ahead of the paving operation is usually a full-time job.
Checking straightedging, floating, edging, texturing, stenciling and curing can be a full-time job for another assistant.
Plan Review and Field Book
The proposal and plans, including the typical sections, should be reviewed by the paving inspector. Standard plans relating to the concrete paving should also be reviewed. Check the list on the plan note sheet for applicable standards.
A field book should be prepared containing the data needed for paving inspections.
- Project and surfacing limits. Station equations.
- Location and type of all monument boxes, drop inlets, manholes, catch basins, etc. to be constructed, reconstructed or adjusted within the pavement area.
- Location of ramps, added lanes, lane drops and similar locations where lane ties will need to be added or deleted.
- Stationing of expansion joints for intersections and other special locations where expansion joints will be needed (Figure 602-4). It is good practice to obtain a set of plans and mark the location of all expansion joints. Some plans will contain a joint layout sheet prepared by the designer. This sheet should be reviewed for errors and omissions.
- Increase expansion joints after September 15 (standard plans).
- Location of header joints where critical to maintain cross traffic, entrances to business places, etc.
- Areas where part-width construction or gaps for traffic are to be constructed, including limits, amount of cements and types and locations of joints.
Communication Between Plant and Street
Specifications require the Contractor to provide a communication system between the concrete plant and the paving site. Normally, the Contractor’s foreman or superintendent has a two-way mobile communication for this purpose. Results of air and slump tests should be communicated to the plant. Information can also be transmitted by the drivers of the concrete hauling units. Normally, the Contractor’s supervisor will advise the plant to stop shipping concrete when equipment breaks down or other delays occur on the paving site.
Placing and Finishing Concrete
The specifications set forth the equipment requirements necessary in the paving train. The specific equipment requirements have been greatly reduced during recent years. We are less concerned about the specific type or piece of equipment the Contractor uses and more concerned with the result. The inspector should note the trimming, placing, spreading, consolidation, finishing, texturing and curing equipment the Contractor plans to use to see if it fits the project on which it will be used. Equipment capacity and capability will not be the same on a small urban widening project as on a high production rural project. The Lansing Office concrete staff inspector will visit the project when paving starts to assist in determining equipment suitability and other related problems to get the project properly started. If there are questions about the condition and/or equipment capability, contact the Engineer.
Minimum Project Requirements
- Some method of trimming the base.
- A method of delivering and placing the concrete on the grade in a timely manner, without segregation.
- Installing the reinforcement, if required.
- Installing lane ties, if needed.
- Consolidating and finishing the concrete, straightedging and floating.
- Edging and texturing the surface.
- Curing the pavement.
- Sawing and sealing the joints.
Screeds and pan floats must be checked for proper slope adjustment.
The inspector should verify that the membrane sprayer is in working condition before paving starts. If in doubt, the Contractor should demonstrate this capability.
Check to see that the Contractor has all the necessary hand tools, such as 5 foot (1.5 m) and 10 foot (3 m) straightedges, floats, edgers and stencils.
If forms are used, they should be checked for straightness, general condition, condition of locks, etc. before form setting operations begin. These forms serve the dual purpose of containing the plastic concrete and providing a track on which most of the concrete placing and finishing equipment rides. For radii of 150 feet (45 m) or less, flexible forms will be required (see subsection 602.03 of the Standard Specifications for Construction). Review the specifications and checklist, included in this manual, for specific form and backup rail requirements.
Grade Condition
After the aggregate base or open-graded drainage course (OGDC) is placed, shaped and compacted, it is brought to final grade, usually by an automatic trimmer. This machine operates off a string line for line and grade. The string line should be checked for sags before the final cut on the aggregate base, as most slipform paving equipment runs on the aggregate base for final grade.
Aggregate Base
- Behind the grading operation, the aggregate base should be checked for thickness, elevation and proper cross section.
- Thickness is checked by digging through the aggregate and recording the depth of the hole.
- Depth should be within 3/4 inch (15 mm) of plan thickness (example: a minimum of 31/4 inch (85 mm) when 4 inches (100 mm) depth is specified).
- Elevation and cross section are determined by stretching a string line across the grade from stakes set by the instrument crew.
- Measurements are made from the string line to the grade and recorded.
- Any significant variations from the plan should be brought to the Engineer’s and Contractor’s attention.
- Any areas where the grade appears to have been disturbed should be rechecked.
- The grade should be moist when paving operations start, but there should be no puddles of standing water.
Load Transfer Assemblies
After the base is properly compacted and fine trimmed to receive the concrete load, transfer assemblies are placed at joint locations. The inspector should work closely with the Contractor’s crew while they are setting these assemblies.
The assembly itself holds the dowel bars in position so they will not move during concrete placement and consolidation.
- The distance between joints should be checked.
- The assemblies must be positioned at right angles to the centerline as shown in Figure 602-5.
- After they are properly positioned, they must be staked to the base using six pins per basket assembly.
- The basket pin must be in contact with the lower horizontal wire as shown in Figure 602-6.
After the Contractor completes staking the assembly, the inspector should check vertical alignment with the basket level to ensure that dowels are parallel with the pavement surface (Figure 602-6).
At this time, the bars should be visually checked for horizontal alignment by sighting over the tops of the bars to the previously set assemblies to see if the bars are parallel to the string line.
Even though the assemblies have been set at right angles to the string line, the bars may not be parallel to the string line due to improper fabrication of the assemblies.
After final check, cut the shipping wires.
Any apparent misalignment can usually be corrected by tapping the frame to realign the bars.
The bars should also be inspected for complete coating on at least two-thirds of the length of the bar.
If the coating is applied by hand, check the bottoms of the bars to verify that they are entirely coated and there is no excess of material on them.
Dowel Bar Inserter (DBI)
An approved mechanical device that automatically installs load transfer bars, at the required depth, and properly consolidates the surrounding concrete. The device may be used in lieu of load transfer assemblies.
When a dowel bar inserter (DBI) is used to install load transfer bars, the bars shall be placed at the same spacing as detailed for dowel bar assemblies in Standard Plan R-40 Series. The pavement shall be placed and consolidated full-depth prior to insertion of the dowel bars.
The DBI shall be capable of accurately inserting dowel bars at the joint spacing and location shown on the plans. The DBI shall be capable of inserting dowel bars into the full-depth plastic concrete at the specified location, and shall be capable of consolidating the concrete around the dowel bars such that no voids exist, without the supplemental use of hand-held vibrators.
The Contractor will take measurements of the inserted dowels relating to the specification tolerances. These measurements will be made in the presence of and provided to the Engineer when requested. It is anticipated that no more than one percent of the transverse joints will be wet checked in a day.
The alignment of the dowel bars is crucial to the life of the pavement. If a dowel or group of dowels is not perfectly aligned longitudinally with the pavement, the life of the pavement and the joints can be significantly reduced. Therefore, wet and dry depth and position alignment checks need to be performed periodically to insure the proper depth, vertical and horizontal alignment of the dowels are being provided by the paving equipment and DBI.
Any out of tolerance joints shall be marked and replaced at the Contractor’s expense. If the dowels are consistently out of tolerance with respect to alignment and/or depth, the Contractor must stop production paving and take steps to correct the alignment problems. Dowel alignment problems can be created when too much concrete, commonly referred to as head, develops in front of the paver that has the DBI mounted to it. The amount of head carried by the DBI paver must be in accordance with the DBI and paver manufacturer’s recommended depth to provide consistent proper dowel alignment.
Many other factors can contribute to dowel alignment and depth problems when using a DBI. The important thing to remember is to be sure the DBI is consistent when placing dowels throughout each day’s production. Periodic wet and dry alignment/depth checks are necessary to ensure consistency. The inspector should also make sure the Contractor is following all of the DBI manufacturer’s recommendations for the use of this equipment.
Expansion Caps
Expansion assemblies should be checked to make sure there are no voids under the expansion felt, between the ends and the forms or around the dowel bars. Expansion caps must be securely placed on opposite unwelded ends of the bars, with 1 inch (25 mm) space left between the end of the bar and the inside of the cap. When using the slipform paving method, the outside 4 inches (100 mm) of the expansion felt will be removed and replaced behind the paver.
It will be necessary for the Contractor to mark the center of the load transfer assemblies so that a saw cut can be made over these joints after the concrete has hardened. Usually, this is accomplished by setting a basket pin opposite the center of the joint outside the pavement limits. Normally, a ribbon is attached to the stake to identify its location.
When setting load transfer assemblies for a widening, do not use the previous saw cut as a method of aligning the basket unless checked for angles. Align this joint with a right angler, or the 3-4-5 triangle method described in Figure 602-5.
Production Paving Projects
Concrete will be produced in a central mix plant.
Concrete will be transported to the job site in dump trucks or agitator trucks. The allowable haul time will depend on the type of hauling unit and the concrete temperature, as stated in the Standard Specifications.
The Contractor will provide a ticket system to record the batch numbers and have someone at the dump site to pick up the tickets.
Occasionally, the inspector should pick up these tickets from the Contractor and check to see that the concrete is within the specified time limits.
Count the tickets to determine the total concrete received. Compare this to the theoretical amount required to compute the overrun or underrun. The cause of any underrun should be determined and corrections should be made immediately. Possible causes include thin pavement, narrow width of slab or improper scale readings at the concrete plant.
Mesh - Dowel Pavement
Concrete is usually deposited into a spreader. Different types are used, but all intended to spread the concrete uniformly over the grade without segregation.
Augurs, paddles or plows are used to spread the concrete across the grade.
The final spreader operation is to strike off the concrete at a predetermined elevation.
The inspector should see that concrete does not build up in the corners of the spreader box, or on the frame, and later fall into the fresh concrete.
Sometimes the spreader operator uses up his truckload of concrete but continues forward on the grade. This leaves areas along the edge of the slab that are void of concrete and should be avoided.
Dual Lane Operation
The spreading operation should be kept reasonably close to the following description so no more than 30 minutes elapse between layers of concrete, or between placing and finishing the concrete.
Tie bars are placed at the center longitudinal joint.
A lane tie bar installer is often mounted on the rear and in the center of the spreader. This device commonly consists of a wheel containing notches into which a laborer will place reinforcement bars of proper length and diameter (Standard Plan R-41 Series).
As the spreader moves forward, the wheel rotates and depresses the lane tie bars into the struck off concrete.
Bar spacing, as required to the nearest free edge, should be checked as soon as possible after paving starts.
Check the bar depth after finishing operations are complete, as they have a tendency to settle due to the vibration of paving equipment.
If reinforcement is required, it is carried on a cart spanning the pavement. It is pulled off the cart one sheet at a time and placed on the struck off concrete.
The sheets are hooked or tied together. Be sure to check the 24 inch (600 mm) overlap between sheets of reinforcement (Standard Plan R-45 Series).
After the reinforcement is spread out on the struck off concrete and tied together, it may be pushed down into the concrete by a mesh depressor. Different depressors are used, but most incorporate vibration and oscillation.
Skis or rollers are used to press the reinforcement down. The mesh depressor is usually mounted on the front of the slipform paver or finishing machine.
Alternate Method of Placing Reinforcement
Set the strike off of the spreader at the elevation of the reinforcement below the pavement surface.
The reinforcement is spread, tied together and remains on the struck off concrete until covered by concrete from a second spreader. In this operation, it is important that the two spreading operations be coordinated so the first layer of concrete is not exposed for more than 30 minutes. If a delay exceeding 30 minutes occurs, which may result in a cold joint between layers, the inspector should note the area involved and arrange for special coring.
Installing Reinforcement by Placing it on Chairs
A third method of installing reinforcement is by placing it on chairs and pouring the concrete over and through the reinforcement. As chairs are an added expense to buy and place, their use is generally limited to odd widths or other small pours, where a mesh depressor or second spreader is not practical.
After mesh placement is completed, consolidation and finishing of the concrete is accomplished either by a form riding finishing machine or slipform paver.
Slipform Pavers/Riding Finishing Machine
The slipform paver uses a lower slump concrete to minimize edge slump. Therefore, full width vibrators are necessary to eliminate all internal honeycombs. The inspector should check to see that the vibrators are working. Bubbles should be apparent around each operating vibrator.
It is important that the slipform paver, or finishing machine, has the correct concrete amount in the screed, or strike-off plates, to prevent overloading that will cause slipping of the track or drive wheels. This will result in chatter bumps on the surface. Inadequate concrete in the screed fronts will leave low spots on the surface.
Form riding finishing machines, and some slipform pavers, have two oscillating screeds that shape the surface of the concrete. For the best results, the front screeds should have about an 8 inch (200 mm) roll of concrete in front of it. The second should have a smaller roll, about 4 inches (100 mm). A slow, steady forward movement with a uniform supply of concrete in front of the finisher will produce the best surface finish. Slipform pavers are equipped with extrusion plates to form and finish the concrete. Slipform pavers are equipped with spray bars to add water as an aid to finishing. The inspector should insist that water added be kept to a minimum. It should not be added continually, but only occasionally when a minor delay has occurred, or for other similar reasons. It is better to use a slightly higher slump initially than to continually add water to the pavement surface.
If a pan float, or other mechanical float, is used behind the slipform paver or the finishing machine, it should leave the concrete surface in a substantially finished condition.
Some slipform paving machines are equipped with transverse screeds for additional floating. Tears or open areas indicate improper screed adjustments, inadequate vibration or perhaps a harsh mix. Attempts to correct the equipment should be made before changing the mix.
The edge condition should be noted immediately behind the slipform paver. Check for edge slump with the 5 foot (1.5 m) straightedge. The edgers on the paver should be adjusted to minimize edge slump. When the concrete leaves the trailing edge of the edgers, it should slump down and out to the proper width and elevation. For this reason, it is essential to maintain a uniform slump from load to load.
Check the pavement behind the paver or finisher to verify the proper width, crown and/or slope.
After machine finishing, the slab surface should be checked by the Contractor's finisher using a 10 foot (3 m) straightedge and the 5 foot (1.5 m) lap method of straightedging. Any high or low areas indicated by the straightedges are to be corrected. The areas needing correction may be hand floated, if necessary, to seal the surface. On slipform paving, the finisher should stop the straightedge about 4 to 6 inches (100 to 150 mm) from the edge to keep from slumping the edge with the added weight of the straightedge.
Concrete Pavement, Unbonded Overlay
This item is used for a situation when existing concrete pavement and shoulders are to be overlaid with a new concrete surface. The existing concrete typically undergoes Hot Mix Asphalt (HMA) or concrete joint repairs and is then overlaid with a HMA bond breaker layer before the new concrete surface is paved. A wax based white curing compound is applied at a rate of 1 gallon per 200 square feet, to the surface of the HMA bond breaker just prior to the time the new concrete overlay is paved.
Concrete Pavement, Unbonded Overlay is typically paid for by volume in cubic yards. The inspector will determine the volume of concrete used each day, based on the number of batches used for pavement and shoulders, and the nominal volume of concrete per batch. This amount will be documented by the batch ticket printouts. This item shall include all materials, labor, and equipment necessary to furnish and place the concrete mixture. Periodic wet depth checks shall be taken throughout the day to verify the pavement thickness and confirm the volume of concrete placed. Using the wet depth checks, the pavement width, and length of the day’s production, a volume of concrete placed can be computed. This volume can then be compared to the volume from the total day’s production on the Contractor’s batch tickets.
Random unscheduled daily yield checks on the volume produced by the batch plant should be performed to verify the amount of concrete produced per batch. This volumetric yield check can then be applied to all batches leaving the plant and compared to the computed total volume placed during the day’s production. The yield check should provide a simple verification of the batch ticket volume printed by the batch plant. This procedure should be part of the Contractor’s quality control plan and periodically verified through MDOT quality assurance testing where appropriate. This method of checking the volume of concrete can be used wherever concrete is being paid for by volume.
Concrete Pavement, Miscellaneous, Non-Reinforced Unbonded Overlay
This pay item shall be used for ramp reconstruction, ramp overlay, gore areas and approach areas. The quantity for miscellaneous pavement associated with overlay projects will be measured and paid for as described in the section for Concrete Pavement, Unbonded Overlay.
Grade Control
Grade control is critical when paving a concrete overlay. Overruns can be controlled by monitoring the grade of the surface the overlay is to be placed on prior to paving the bond breaker layer and the overlay. Recorded string line depth checks on the grade control prior to paving the overlay are important to monitor the volume of concrete to be placed and keep it close to the actual plan quantity.
Grade control is again the critical item for controlling Contractor material quantities, and final profiles when paving miscellaneous concrete. Smaller miscellaneous areas are typically formed prior to paving miscellaneous concrete. The forms can benefit the grade control process. However, matching the grades in approaches, and ramp gore areas can lead to pavements that do not drain properly or have a safe profile for the public. If not included in the plans, a set of detail grades should be computed and plotted prior to the beginning of the project to attempt to alleviate grade problems. The detail grades should be computed from the plan profiles for the adjacent pavement. After the detail grades are computed, they should be plotted to determine the proposed gore/approach cross sections prior to beginning the project. If the detail grades are determined prior to any paving, with the approval of the Engineer, the inspector can typically adjust the mainline and/or ramp grades to allow for a safe gore and approach pavement.
Tube Float Machine
A separate tube float is sometimes used behind the straightedging on a production paving project. The tube float machine is also equipped with a spray bar. As previously mentioned, it is important that the amount of water added by this spray bar be controlled. Any water added to the concrete surface during finishing operations will reduce the water/cement ratio that will cause surface spalling. Repeated passes of the tube float with the addition of water can generate large quantities of grout. This is used either to fill depressions in the surface or is floated off the pavement edge. If used to fill depressions, the grout shrinks as the water evaporates and the depressions remain. Grout wasted over the edge produces overhanging projections, which are undesirable. Another reason to minimize the use of the tube float is that texture made of grout will wear off at a rapid rate. Therefore, water added by the tube float and the number of passes of the float should be minimal. Usually two passes are adequate to check the surface and seal any voids.
Hand edging may be done either ahead of or behind the tube float. Final edging must be behind the tube float if grout is being wasted over the edge. Conventional edgers should be used to round the top corner. It should be left with a radius not exceeding 1/4 inch (6 mm). Edge slump should be rechecked with the 5 foot (1.5 m) straightedge behind all finishing operations. Any edge slump exceeding 3/8 inch (9 mm) should be corrected before the concrete sets. If continuing slumps of up to 1/4 inch (6 mm) occur, the Contractor should adjust the edgers on the trailing end of the side forms to eliminate the slump.
Expansion Joint Filler
During final finishing operations. The previously removed 4 inch (100 mm) end section of the expansion filler material should be replaced and the concrete consolidated around the joint filler. The expansion joint filler location should also be marked for sawing at a later date. The best method of doing this is by working from a bridge spanning the pavement. The expansion filler top is exposed in about five locations across a 24 foot (7.2 m) pavement by using a small trowel to remove the concrete. A small block is then placed on top of the expansion filler. The block should extend to the surface and be held in place by nails extending into the filler. Later the joint is sawed out from block to block (Figure 602-7).
Concrete Texturing
Following floating, the surface is to be textured longitudinally with a burlap drag. Even though the final texturing will be by metal tines, it is important that the slab be properly textured initially with burlap to give the surface a slightly roughened, gritty texture.
Usually 36 to 60 inches (900 to 1500 mm) of burlap should be in contact with the pavement surface. Two layers of burlap may be required to impart a gritty surface. The burlap should be cleaned of built-up mortar daily and replaced when it is no longer effective. It should be kept moist to avoid removing water from the concrete surface.
When slipform paving, it is better not to have the burlap drag extend over the edges, as it may cause the concrete to slump, or tear the edges.
When completing the metal tining, texturing operations shall not delay curing. Timely application of curing compound is critical to the final strength and durability of the concrete pavement. Application of the curing compound must take precedence over texturing the surface with the metal tines. If texturing has to be delayed, it will follow at a later date when the concrete has attained 28 days design compressive strength. In this case, the Contractor shall submit a plan for the Engineer’s approval for texturing the pavement after the concrete has reached the strength required to support the equipment. This work shall be at the Contractor’s expense.
The last 4 inches (100 mm), can be hand dragged by the finishers doing the edging.
A strip of artificial grass mat may be used in place of burlap. After burlapping, the surface is to be grooved transversely with a wire tine comb. Either machine or hand methods may be used. The tine grooves should be 1/8 to 1/4 inch (3 to 6 mm) deep, 1/8 inch (3 mm) wide, on about 1/2 inch (13 mm) centers. Tine marks should not be overlapped. Overlapping decreases the spacing, which results in breakage. The grooves should be one continuous pass across the entire pavement surface.
Tining Device
The tining device must be accurately adjusted to the crown and the pavement slope to ensure uniform contact between the tines and the pavement. It must also be adjusted to lift off the pavement just as the tine head reaches the edge to avoid breaking down the edges when slipform paving. Check the tining periodically to see that the operator is obtaining a uniform surface, with groove depths from 1/8 to 1/4 inch (3 mm to 6 mm). Following tining, the Contractor is to stencil the pavement 12 inches (300 mm) from the edge of the pavement so the numbers can be read in the direction of traffic.
Membrane Curing
Membrane curing compound is to be applied as soon as the free water has left the surface. Often the same machine is used for tining, curing and applying the compound. Usually this is as soon as tining is complete. However, texturing shall not delay the curing compound application. If it becomes necessary to apply the curing compound prior to texturing, the texturing must be completed after the concrete has obtained its 28 day design compressive strength.
Make sure the curing compound has been mixed according to the manufacturer’s recommendation before the compound is transferred from the drums to the tank on the curing machine.
It should be constantly re-circulated or stirred during application.
Insist on a uniform application of each of the two coats for textured surfaces. One coat is required for non-textured surfaces. Coverage is 1 gallon per 200 square feet (1 liter per 5 m2) for each coat.
The important point is to get enough material on the exposed surface to completely seal the tops, bottoms and sides of the grooves with an unbroken membrane. Timely coverage is critical to the final strength and durability of the concrete.
The slab edges should be spray cured promptly if the forms are removed before the desired strength is met.
Depending on the wind, sometimes the curing compound may have to be applied in two different directions to get proper coverage.
Header Joints
Night header joints should receive the inspector’s attention, as they are often the location of bumps in the finished pavement.
When it is anticipated that paving will resume within seven (7) days, paving is suspended on a transverse contraction or expansion joint.
An adjustable header board is staked in place in the center of the load transfer device assembly.
The header top should be left at least 1/2 inch (12 mm) below the pavement surface and the finishing equipment passed over the header.
The area adjacent to the header must be filled with fresh concrete.
Do not permit partially hardened concrete, or laitance, carried in the vibratory box to be used in this area.
Just before the finishing equipment passes over the header, the concrete adjacent to the header should be vibrated with a hand held vibrator.
It is a good idea to spread burlap or plastic over the projecting ends of the dowels to facilitate cleanup of excess concrete.
Since the header board may not match the crown of the pavement, it is a good idea to insert pieces of 1/4 inch (6 mm) Masonite behind the header board to be adjusted to the exact elevation of the finished pavement after the finishing equipment has passed over the header joint (Figure 602-8).
The finishers will now be able to straightedge the pavement up to and across the header. When slipform paving, the last 10 feet (3 m) or so of the longitudinal bulkhead joint adjacent to the header should be formed to prevent the slab from becoming over width. This over width will cause spalling of the edge when the paver is backed to the header.
Leaving the header is also an operation that needs close attention. The header board should be removed carefully to avoid damage to the green concrete.
After the concrete is placed, the header should be thoroughly vibrated to eliminate voids. As the slipform paver or finishing machine starts forward, there is a tendency for the concrete to cling to the screeds and the float pans, leaving the surface low in these areas. It is important that the Contractor straightedge this area carefully. Stretch a string line parallel to the centerline from 10 feet (3 m) behind the header to 30 feet (9 m) in front to check the header for the need of corrective work while the concrete is plastic.
Date and stationing should be stenciled in the concrete by the Contractor, on the night and morning sides of the header.
When paving is to stop for more than seven (7) days, such as at the end of the project or a seasonal shutdown, a special end-of-pour header should be used. This header is located between contraction joints. Use 1-1/4 inch (32 mm) diameter x 18 inch (450 mm) long epoxy coated deformed bars. See the Standard Plan R-39 Series for layout spacing.
Inspection During and Following Concrete Placement
Inspect the previous day’s pavement for uniformity of texturing and curing. Have areas been missed, or textured too shallow or too deep? Are there thin spots or streaks in the curing membrane? Has the edge of the slab been completely coated with curing compound? Check for any honeycomb in the edge and have it patched.
At this time, the relief sawing of the transverse joints should be complete or in progress. Look for any random cracks that would indicate sawing was not completed in a timely manner. Also, look at the relief saw cuts for excessive raveling, indicating they were sawed too soon. Check for correct depth of the saw cuts.
When sawing of the joints to final width begins, the inspector should check on the width and the depth (Standard Plan R-39 Series). Location of saw cuts for contraction joints should be over the center of the assembly. It is important that the expansion joint saw cuts be made exactly over the expansion felt. This is accomplished by sawing from block to block as explained under Finishing the Concrete. Finally, the top corner of the joint grooves are to be beveled at a 45° angle to reduce joint spalling.
The centerline longitudinal joint will be sawed within 24 hours, but not until the concrete has hardened sufficiently that no raveling or spalling occurs. All traffic must be kept off the pavement until the longitudinal joint has been sawed. Since the upper 1 inch (25 mm) of the longitudinal joint must be sawed a minimum of 1/4 inch (5 mm) wide, and the lower one-third need only be 1/8 inch (3 mm) wide, the Contractor will often use two saws operating in tandem. Sawing and sealing of the longitudinal joint are required before transverse joints are sealed (Standard Plan R-41 Series).
Before transverse joints are sealed, they should be inspected for spalls and foreign material. All spalls that extend into the support area of the neoprene must be patched with epoxy. Epoxy patching, to be successful, requires strict compliance with the specifications and the manufacturer’s instructions. The spalls must be thoroughly cleaned as per specification. The spall area must be primed with epoxy. The two components of the epoxy must be proportioned accurately by using the entire contents of both cans, or by having a volumetric dispenser. The material should be mixed by a power mixer until a uniform mixture is obtained, then blend dry sand into the epoxy. The epoxy patch should be left slightly below the pavement surface to avoid wheel load directly on the patch.
Just before installing neoprene seals, the joints should be given a final cleaning, as per specification, to remove any foreign material. A lubricant adhesive is to be applied to the joint faces. Lubricant adhesive may be applied on the neoprene seal when installing. Either hand roller or machine methods are permitted for installing the seal. However, screwdrivers or similar tools shall not be used, as the seal may be punctured by these tools. Excess lubricant adhesive must be cleaned off the top of the neoprene seal after installation because it will not allow the seal to work correctly.
The seal should be checked for stretch and compression during installation. Unroll the seal and lay it across the pavement. Mark the seal where it meets with the pavement edge. Stretch should not exceed 5 percent 14 inches for 24 foot (350 mm for 7.2 m) pavement. Compression is limited to 2 percent 5 3/4 inches for 24 foot (143 mm for 7.2 m).
When rolled curb and gutter, valley gutter, or concrete shoulder abut the pavement, the seal must be carried across the pavement and down the edge of the adjacent structure in one continuous piece. Final sealing of the joints must be delayed until the related concrete items are complete.
Hot and Cold Weather
During hot weather, additional precautions must be taken to obtain high quality pavement. Concrete placement is prohibited when the concrete temperature exceeds 90°F (32°C). Even with concrete temperature at 80°F (27°C), it may be difficult for the final finishing and texturing to be completed before the concrete hardens. Under these conditions, there is a strong desire by the Contractor’s finishers to add water to the pavement surface to lubricate their floats and straightedges. Any water added is to be in the form of mist from a fog sprayer. This limits the amount of water added and minimizes dilution of the cement paste on the concrete surface.
For hot weather conditions, the inspector can refer to Table 706-1 of the Standard Specifications for Construction. This table gives evaporation rates for conditions for paving concrete based on air temperature, concrete temperature, relative humidity, and wind velocity. If the evaporation rate exceeds 0.15 lbs/ft2/hr from the table, then the Contractor should not pave. In any combination of weather conditions, the Contractor must be able to ensure to the Department that they can prevent premature drying of the pavement surface during the paving process.
In extreme weather conditions, timely application of the curing compound is not always the complete solution to preventing premature drying of the pavement surface. Extreme weather conditions can require additional steps to aid in the prevention of premature surface drying and other adverse effects caused by hot weather. Continuous, constant temperature moist curing, covering the entire surface of the pavement with continuously wet burlap, and reducing the concrete mix temperature (cement, aggregate and/or water temperature) are examples of other options for helping reduce the impact of hot weather on concrete pavement. With the exception of continuous moist curing, the curing compound should still be applied when using these options for paving in hot weather. The Contractor’s Quality Control Plan must be reviewed before paving begins. The Quality Control Plan must contain adequate detail regarding the plan for properly curing the concrete in accordance with MDOT and American.
Protection from cold weather is the Contractor’s responsibility. Although concrete will withstand below freezing temperature due to heat of hydration, it is considered good practice to provide a protective covering of insulated blankets or straw when freezing temperatures are anticipated. When cold weather is anticipated, the pavement should be covered as soon as possible. However, the pavement must be able to support the weight of the insulating blankets or straw without damaging the surface.
If the Contractor neglects to cover the pavement in a timely manner, and the temperatures drop below freezing during the curing period, the inspector should note the areas involved and notify the Engineer. Arrangements can be made to take special cores from the area in question to determine whether or not the concrete has been damaged.
Rain Damage
Protection from damage by rain is the Contractor’s responsibility and the inspector should avoid giving the Contractor any instructions as to covering the concrete, or other protective measures. If the Contractor is unable to texture the pavement, or the texture is washed away, they will be required to groove the hardened concrete.
If serious rain damage occurs, such as breaking down of slipformed edges or erosion of the surface by water running off the pavement, repairs should be made as soon as the rain stops. Water on the surface should be carefully removed with straightedges to avoid working the water into the concrete. Fresh concrete should then be added and the surface refinished.
If the rain has damaged the curing membrane, this should be corrected by respraying the area after the rain has stopped.
Miscellaneous Paving
In addition to the main paving operation, most projects will involve some miscellaneous paving. This might be semi-production work on service roads or ramps. Other times it will involve strictly hand work at street intersections.
The quantity of paving involved will dictate the type of equipment to be used. As with production pavement, the inspector should ensure that methods and equipment proposed will ensure quality work.
Trimming the base will usually be a combination of a road grader and hand methods.
Forms are used for hand work. Radii of less than 150 feet (45 m) will require flexible forms.
Concrete may be placed without a spreader providing it can be placed without segregation. The concrete must be struck off for placement of reinforcement.
Do not permit placing of reinforcement on top of piles of concrete to be tramped into final position by workers. If it is not practical to strike off the concrete due to irregular area, the reinforcement should be placed on chairs. The proper number of chairs will be used to hold the reinforcement at the specified location.
All areas along forms and joints will be consolidated with a vibrator. The vibrator will be inserted vertically into the concrete to ensure complete consolidation and will not be used to move the concrete.
Screeding of the surface will usually be by a form-riding finishing machine or a hand-pulled vibrating strike off. Sometimes roller screeds or lightweight slipform pavers are used.
Straightedging gaps and other areas subject to high-speed traffic is important. A string line check of these areas is also helpful.
Burlapping, tine texturing and curing will normally be done with hand held equipment. Make sure tining is done in one continuous pass from edge to edge. Do not permit tining each way from centerline, as a poor appearance will result.
Applying the curing compound will be done from a bridge or by using a boom so uniform coverage can be obtained.
Concrete Shoulders
When concrete shoulders are called for on the plans, they will be constructed according to the current specifications and Standard Plan R-112 Series.
Preparation of the grade is similar to that required for pavement; shaped to the required line, grade and cross section and compacted to the required specific density. The edge of the pavement should be cleaned of any dirt or other foreign material. Shoulders adjacent to pavement will require lane ties to keep the shoulder from separating from the pavement.
Expansion joint filler is placed in line with opposite expansion joints in the pavement as per Standard Plan R-42 Series. Load transfer devices are omitted from concrete shoulders.
Just before concrete is placed, the edge of pavement and the entire base should be dampened.
See the Standard Plan R-45 Series for placement of the steel reinforcement.
Concrete is usually placed on the grade directly from hauling units. Normally a modified slipform paver will be used to strike off, consolidate and finish the shoulder concrete.
Immediately behind the machine in the finishing operation, check the surface for proper slope or crown.
Edges will be inspected for slump, thickness and to ensure that they are all free from contamination by base material.
Floating will be done only as necessary to close the surface.
Relief cuts must be sawed to the proper depth to control cracking. After curing, the joints are to be sawed to the final width and depth and sealed with the same seal as used in the pavement.
The longitudinal bulkhead joint between the pavement and the shoulder will be sawed and sealed before the transverse contracting joints are sealed.
Rumble strips will be placed according to the standard plan. This is constructed with a modified float having a corrugated surface.
Texturing is done with a burlap drag or a stiff broom.
The surface and outside edge should be coated with white membrane curing compound at a rate of 1 gallon per 200 square feet (1 liter per 5 m2).
Base Course Paving
Another type of miscellaneous paving is concrete base course. This is usually a widening placed adjacent to an existing pavement which is in need of resurfacing.
General construction methods are similar to those described above for concrete pavement. A few important differences are mentioned here.
The edge of the existing pavement may be in poor condition. Check the plans to determine if any corrective work is required on this edge before casting concrete against it.
Base course mat be either reinforced or non-reinforced. Plane-of-weakness joints may be either formed or sawed. No joint seals are required. No load transfer assemblies are used in base course. Review the Standard Plan R-42 Series for joint layout and header joints in non-reinforced base course.
Standard Plan R-45 Series indicates the reinforcement lap required (usually 24 inches (600 mm). Six hundred millimeters of reinforcement should also extend through the header joints.
Straightedge tolerance is more liberal, 3/8 inch in 10 feet (9 mm in 3m). Texturing is done by burlap drag. The surface should not be tined, as it will be difficult to clean before placing the overlay.
Cure with a transparent compound instead of white. Only one application is required at the rate of 1 gallon per 200 square foot (1 liter per 5 m2) of surface.
Opening to Traffic
Often the Contractor will want to use the new pavement as a haul road for his batch trucks at the earliest possible time, or he may want to place a wheel or track on new pavement edge to pave the adjacent lane. Other times it will be important to open an intersection or drive to traffic as soon as possible.
The inspector and Contractor should try to anticipate the need for early openings and arrange to make an extra set of beams when the concrete in question is being cast. These beams should be cured under environmental conditions similar to the pavement being cast.
The following table, excerpted from Section 104 of the Standard Specifications for Construction, indicates when equipment may be allowed on the pavement.
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Finishing Equipment |
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|
|
|
|
Load within Legal Limits (For batch-hauling only) |
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|
|
|
|
Slip-form Pavers and Paving Mixers |
|
|
|
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|
Loads up to 25 percent over Legal Limits (For batch-hauling and shoulder operations only) |
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|
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Occasional Loads up to 50 percent over Legal Limits (To complete construction activities) |
No load is to be permitted on the pavement until the centerline joint is sawed, the contraction joints relief cut, the expansion joints sawed out to full width and temporary or permanent seals installed. Curing is to be continued until a flexural strength of 550 psi (3.8MPa) has been obtained.
When job control beams are not available, the curing surface treatment film will not be broken by Contractor’s equipment or other traffic until the concrete has attained 70 percent of the anticipated minimum strength as determined from the following table.
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
|
|
|
|
|
|
|
|
|
| |
|
1
2
3
4
5
|
3
9
10
9
7
|
3
12
22
31
38
|
8
12
11
10
7
|
8
20
31
41
48
|
14
15
11
10
6
|
14
29
41
51
57
|
19
18
12
11
6
|
19
37
49
60
66
|
25
17
12
9
5
|
25
42
54
63
69
|
30
17
12
7
4
|
30
47
59
66
71
|
36
17
12
6
4
|
36
53
65
71
75
|
|
6
7
8
9
10
|
7
7
6
5
3
|
45
52
58
62
65
|
7
6
5
4
3
|
55
60
65
69
72
|
6
5
4
4
3
|
63
68
71
75
78
|
6
4
3
3
3
|
72
76
79
82
85
|
5
3
3
2
2
|
74
77
80
83
85
|
4
3
3
2
2
|
75
78
81
83
85
|
3
3
3
2
2
|
79
82
85
87
89
|
|
11
12
13
14
15
|
3
3
2
2
2
|
68
71
73
75
77
|
3
2
2
2
2
|
75
77
79
81
83
|
2
2
2
2
1
|
80
82
84
85
86
|
2
2
1
1
1
|
87
89
90
91
92
|
2
1
1
1
1
|
87
89
90
91
92
|
1
1
1
1
1
|
87
88
89
90
91
|
1
1
1
1
1
|
90
91
92
93
94
|
|
16
17
18
19
20
21
|
2
1
1
1
1
1
|
79
80
81
82
83
84
|
1
1
1
1
1
1
|
84
85
86
87
88
89
|
1
1
1
1
1
1
|
87
88
89
90
90
91
|
1
1
1
0
0
0
|
93
93
94
94
94
94
|
1
1
1
0
0
0
|
92
93
93
93
93
93
|
1
1
1
0
0
0
|
91
92
92
92
92
92
|
1
1
1
0
0
0
|
94
95
95
95
95
95
|
Street Inspector’s Report
Inspector’s Report of Concrete Placed, Form 1174A (Figure 601-6) is the primary report required of the paving inspector. It should be prepared for each day that pavement is cast. In addition to the original copy to the Engineer and a copy to the Construction Services Section, the inspector should retain a copy.
Any unusual happenings should be noted in the remarks section of the report. Often this is most important when a problem develops and the circumstances surrounding the problem are being reconstructed later. Any material accepted on the basis of visual inspection should be noted in the remarks. The back of the form should be used for sketches, when necessary, to describe any irregular areas.
In addition to the daily report, the field book prepared before the project started can be used to note additional information concerning the paving operation. Depending on the type of project, it may be necessary for the street inspector to complete an Inspector’s Daily Report, Form 1122B (Figure 601-7) documenting traffic control, equipment used or other work activities in progress.
Reports and documentation requirements should be reviewed with the Engineer before paving starts.
Keep in mind that some quantities must be documented at the time of placement while others can be checked later. An example of the former is areas where high-strength concrete is used and is to be paid for.
Inspector’s Checklist
Transporting Central Mixed Concrete
- Determine that elapsed time is within specification limits for temperature and type of hauling unit.
- Hauling units should be mortar tight.
- Trucks should be washed out as necessary to prevent buildup of hardened concrete.
Job Site Quality Control
- All testing equipment on the job before start of concrete operations: air meters, slump cone and related tools and concrete thermometer.
- Perform test according to frequency guide. May perform additional tests for control. Check Standard Specifications for consistency (slump).
- Check for supply of air entraining agent at the job site for truck mixers. Concrete shall contain 6.5 ± 1.5 percent entrained air, except 4-1/2 percent air is permitted for slumps under 1-1/2 inch (37 mm) placed by slipform methods.
Slipform Paving
- Grade, including track line, to be trimmed by autograder or other base trimmer and free of all irregularities.
- Any disturbed area to be recompacted to the specified density.
- Sight along stringline for sags, adequate supports and general condition. On tight radius ramps, stringline stakes may be required at 10 to 13 foot (3 m to 4 m) spacing.
- Depth checks on base to be taken after trimming as required.
- Use stringline to check for proper crown or cross slope from grade stakes to top of aggregate base and record on Form 1145. Inform Contractor or his representative on the job site of grade checks. Issue permit to place for placing load transfer devices as directed.
- Load transfer assemblies should be observed for coating and to make sure they are at right angles to the stringline, parallel to grade and properly spaced and pinned. Check the free end of the expansion dowel for proper space between cap and end of dowel.
- Base shall be moist at time of placing concrete.
- Spreader and pave must have proper crown setting.
- Operator of spreader must use care to avoid moving dowel bar assembly from pinned position. Equal amounts of concrete must be placed on each side of the expansion joints to avoid moving.
- Operation of spray cure machine to be verified before paving starts.
- Concrete spread to cover entire base to strike-off depth prior to placing reinforcement, unless bar chairs, rollers or mesh depressor is used.
- Mesh must not be over width or laid on skew to cause it to catch on sliding forms. Mats are to be hooked together in two places on each mat. At load transfer assemblies, each mat is to be wired across basket assembly in two places if mats are moving.
- Check reinforcement mats for proper lap and spacing from joints.
- Observe operation of lane tie bar installer. Inserted ties to be spaced as indicated in the Standard Specification, keeping inserted ties out of the load transfer assembly area. Have a field pull out test made after the first day’s pour.
- Pave to vibrate concrete full width and depth of pour. Observe vibrators frequently to see that they are all operative.
- Observe wet crown checks taken from the Contractor throughout the day.
- Measure depth of reinforcement and lane tie bars behind the paver. Mesh depressors or vibrators may cause settlement below plan depth. Check plans for proper depth.
- To get a smooth surface and minimize dragging the mesh forward, the surcharge of concrete ahead of the pave should not overload the pave and should be uniform across the grade.
- Pavement is to be checked by Contractor with 10 foot (3 m) straightedge behind paver. Look especially for dips at mesh laps.
- Edge slump should be checked frequently behind paver and again behind the texturing equipment with a 5 foot (1.5 m) straightedge.
- Machine finishing and floating should be organized to leave a minimum of hand finishing. Do not permit application of water by spray nozzles on tube float. Floats and straightedge must not be pulled over edge of slab, as edges will slump.
- Pavement is to be edged to remove any overhanging projections of concrete. Edging should be delayed as necessary to minimize edge slumping.
- Pavement surfaces to be dragged longitudinally and tined transversely by use of a wire comb.
- Observe Contractor stenciling the station numbers at the correct location and direction.
- White pigmented compound is required for curing concrete pavement, curb and gutter and sidewalk. Transparent or clear compound is required for curing concrete base course at the specified rate.
- Mechanical agitation of curing compound is required.
- For tined surfaces, curing compounds shall be applied in two applications, each at the specified rate. Check for proper yield and record.
- Curing compound shall be applied as received. No thinning is allowed.
- Enough pavement should be checked the following morning to determine the quality of workmanship. Advise the Contractor of all deficiencies. Record all findings. Mark areas for review by the Engineer.
- Where adjacent pavement lanes are constructed in separate pours, keep equipment from operating on the recently placed pavement until the pavement has attained adequate strength, as determined by test beams and table in specifications.
Form Paving
Review the items for slipform paving. In addition, the following should be checked.
- Forms are to be measured for proper height. Forms to be a minimum of 10 foot (3 m) long. Base width equal to or greater than the thickness of the pavement.
- Condition of forms checked with 10 foot (3 m) straightedge before project starts and daily as project is paved. Forms that do not meet specifications are to be rejected.
- Stringline required to establish form grade shall be sufficiently taut to eliminate sag.
- Forms to be set directly on autograder trimmed base or on base trimmed with form grader.
- Three pins of adequate length used in each form. Each form to lock to adjacent form.
- If forms are set on disturbed base, material under forms shall be tamped on both inside and outside of form.
- Top of form shall be free of mortar prior to setting.
- Forms to be oiled before each use.
- Sufficient forms shall be in place ahead of the paver so they may be checked for line and grade in advance of placing concrete. The minimum length of forms in place shall be equal to the anticipated length of pavement to be placed in 2 hours.
- Surplus base material left inside of forms is to be removed.
- Depth to base from stringline at top of forms measured and recorded.
- Vibratory strike board or screed shall be used on hand work.
- Screeds on finishing machine and/or spreader finisher adjusted to proper crown.
- Proper quantity of concrete being carried ahead of each screed.
- Vibrator must be used along forms and transverse joint. If, in the opinion of the Engineer, sufficient vibration of the concrete is attained by use of a mesh installer, the use of vibrators along the faces of the forms may be omitted. Vibrate the concrete over the load transfer assemblies.
- Observe operator of finishing machine. Care should be taken to avoid moving the premolded fiber filler in the expansion joints from the vertical position.
- Metal back-up rails are to be used to prevent damage to the previous day’s pour by flanged wheels of equipment.
- After form removal, inspect edges of pavement for honeycomb.
Sawing and Sealing Joints/Longitudinal Joints
- The longitudinal joint shall be sawed within 24 hours.
- Saw is to be equipped with guide to maintain alignment.
- Check size of saw cut 1/8 inch (3 mm x a pavement depth). Top 1 inch (25 mm) must be 1/4 inch (6 mm) wide for seal.
- Bulkhead joints must be sawed and sealed with hot pour sealant.
- Joint faces should be cleaned by sandblasting or other approved method and blown clean before sealing with hot poured sealant.
- Joint should be completely filled, but not overfilled.
- Longitudinal joints are to be sealed before transverse joints.
Transverse Joints
- A standby concrete saw is required for relief cuts.
- Two-stage sawing is required, except for slag aggregate. First stage is to be completed as soon as possible without raveling. See Standard Plan R-9 Series.
- Second stage sawing is to be done after the concrete has gained at least 30 percent of its strength. Centered over relief cut (see plans and Standard Plan R-39 Series for sizes of joint groove for type of seal being used).
- Top corners of joints are to be beveled.
- If final sawing is completed before curing period is over, joint areas are to be cured with tape or other moisture barrier.
- Temporary or permanent seals must be installed in expansion joints before construction traffic uses pavement. Construction traffic may run over contraction joints after relief sawing, and when the concrete has met minimum strength requirements.
- Joint spalls extending into the neoprene support area are to be required with epoxy before sealing.
- Repair area must be sandblasted or wire brushed then blown clean and primed.
- Use rigid forms when needed.
- Mix entire contents of both parts of epoxy or use volumetric dispenser and mix for at least 2 minutes.
- Epoxy patch placed slightly below pavement surface.
- Clean joint with oil-free compressed air before sealing. Inspect for stones or other foreign material. Must be sandblasted for hot poured rubber seal.
- Use approved lubricant-adhesive for neoprene seals.
- Measure seal for stretch before and after installing - maximum = 5 percent = 14 inches for 24 feet (350 mm for 8 m) of pavement.
- Splicing of seal is not permitted except by Special Provision.
- Top of seal should be slightly below bottom of level after installation. Seal should not be twisted.
MEASUREMENT AND PAYMENT
Pavement Coring
To determine pavement, shoulder and base course thickness and depth of reinforcement, cores shall be taken from the pavement before its final acceptance to determine the thickness of the pavement and depth of pavement reinforcement below the pavement surface according to MTM 201. Refer to subsection 602.04 of the Standard Specifications for Construction and the following flow chart (see Figure 602-9) for this determination.
Ride Quality
A specification to encourage the Contractor’s to construct the smoothest pavements possible and the method to measure the surface for smoothness.
The Contractors may use a California-type Profilograph or a GM-type Rapid Travel Profilometer to measure the pavement smoothness.
The Engineer will establish and mark the limits for Ride Quality Measurement including the POB, POE and any excluded areas.
The California-type Profilograph will produce a trace, or Profilogram, on graph paper, to a true 1:300 horizontal scale and true 1:1 vertical scale, which will be analyzed according to Michigan Test Method 204-88.
If a computerized Profilograph is used, a trace will not need to be analyzed, but should be spot checked with a blanking band.
The equipment must be calibrated before use.
Tire pressure should be 25.375 psi ± 1.015 psi (175 kPa ± 7 kPa) in the recording wheel.
The horizontal calibration will be checked by running the Profilograph over a measured 1000 foot (300 m) length which should produce a trace of 3.28 ft ± 0.118 in (1 m ± 3 mm). Calibration of the computerized version will be run over a distance of 1000 foot (300 m) and should produce a printout within ± 3.28 feet (1 m).
The vertical calibration is to be done according to the manufacturer’s specification and must be documented by the Contractor.
The GM-type Profilometer will be calibrated according to the user’s manual.
Software is provided which allows the operator to test the operation of the three buttons and computer system, along with a “bounce” test.
The vertical calibration of the laser sensor is to be done according to the manufacturer’s specification and must be documented by the Contractor.
The horizontal distance is calibrated by traveling a known distance and typing in the value on the keyboard while in the calibration mode. The continued reliability of the odometer will depend on a constant tire pressure.
The measurement/profile will be taken in the wheel tracks of each lane.
The starting position of Ride Quality using the California-type Profilograph is when the rear wheel assembly is entirely on the road surface, placing the recording wheel 16.25 feet (5 m) beyond the POB. The ending position will be when the front wheel assembly is at the POE, placing the recording wheel 16.25 feet (5 m) short of the POE. Whenever the run is stopped before the POE, the recording wheel should be placed at the same location for a restart. See Figure 602-10 for a Profilograph.
Measurement outside the POB or POE may be done to check for bumps, and will be paid as Ride Quality Measurement - Concrete.
The software for the GM-type Profilometer has been designed to simulate the same starting and ending points as the California Profilograph. Starting the measurement (GO button) at the POB will start data recording at 16.25 foot (5 m) after the POB. Ending the run (STOP button) at the POE will stop the data recording 16.25 foot (5 m) prior to the POE. Caution should be taken when stopping the GM Profilometer between the POB and POE as in daily or short runs. As the recording data will stop 16.25 foot (5 m) prior pushing the Stop button, the next run will have to be started 32.5 foot (10 m) before that same point to start the data recording at the right point. See Figure 602-11 for an example of starting and stopping points.
The California Profilograph trace will have to be reduced, using a blanking band, to segments. Bumps which exceed the limits established by Special Provision can be located by using a bump template. The computer version will analyze the ride quality and locate the bumps which must be ground.
The rapid travel Profilometer can give data in inches per mile or by a ride quality index, along with the locations of must-grind areas.
Check the proposal for pay items and adjustment table for the item of Ride Quality.
Roadways, collector distributors, ramps and turn lanes that are not covered under a ride quality specification should be evaluated for smoothness and removable bumps in one of three ways:
By using a 10 foot (3 m) straightedge as per MTM 722-97.
By using a rolling straightedge available from the Construction and Technology equipment shop.
By using the rapid travel profilometer, which is programmed to check for bumps according to the Standard Specification for these areas. Contact the Construction Services section for use of this equipment.
