710 - Waterproofing and Protective Covers
Joint waterproofing is a preformed material placed at locations where a concrete joint is located below grade thus creating the potential for leaking or seepage due to infiltration through the soils. An example of a common joint that requires joint waterproofing is the joint between the abutment bridge seat and backwall.
Per specifications the membrane must be a minimum 18 inches wide. The membrane must be centered over the joint so that it extends a minimum of 9 inches on either side of the joint.
The membrane typically requires a prime coat for adhesion per manufacturer’s recommendations.
The integrity of the membrane and its waterproofing capabilities relies upon the bond between the membrane adhesive and the concrete. The membrane is to be applied within 4 hours of removing the form work at the location requiring the waterproofing. The air and concrete temperatures must be greater than 40 degrees prior to beginning surface preparation. The 4 hour requirement may be adjusted accordingly to meet the temperature limitations. The surface of the concrete must be dry, clean and free from sharp edges or intrusions. Ensure the contractor fills any surface with an MDOT approved epoxy mortar, or concrete. These patches must be cured for 24 hours prior to placement of the membrane. Abrasive blasting with compressed, oil-free air is required to remove all contaminates and prepare the surface for the membrane. The surface is to be prepared and primed 12 inches either side of the joint to accommodate the full membrane adhesion width.
Prior to backfilling, the engineer may require the contractor to demonstrate the membrane is adhered to the concrete and free from wrinkles and tears. Any tears in the membrane may be patched with additional membrane material overlapping 6 inches either side of the area to be patched.
Cover the joint with backfill as soon as practical to avoid sagging in the membrane.
Expansion Joint Waterproofing
Expansion joint waterproofing is used at locations indicated in the plans as expansion joints in the substructure, or at integral and semi-integral backwall abutment locations. Expansion joint waterproofing is applied in similar fashion to the Joint Waterproofing described above except that a bond breaker and two layers of membrane will be used.
The beveled surfaces at the expansion joint location will not receive the prime coat and will instead receive a bond breaker (bond breaker tape or equivalent material) to the face of each beveled surface next to the expansion joint to prevent adhesion of the membrane at this location. This allows for rotation, expansion and contraction of the substructure at this location without tearing the membrane. Place the bond breaker at the beveled surfaces, then prime the surface 12 inches either side of the joint. Place the membrane per the section on Joint Waterproofing described above ensuring the membrane follows the contour of the beveled surfaces. This “slack” in the membrane allows for the required expansion. A second layer of membrane must then be placed over the first layer. Prime the first layer per manufacturer’s recommendations. A bond breaker is not needed for the second coat. Apply the second layer of membrane and backfill after adhesion amongst the layers and concrete has been demonstrated.
Deck waterproofing can be done with preformed membranes which are covered by the standard specifications, or spray applied membranes which are covered by a Unique Special Provision. The pay item will tell you which one is specified for the project.
Preformed Deck Waterproofing membranes require additional preparation and consideration for long term performance. Things to consider are cleaning, patching, adhesives, placement, and overlays.
Preformed Deck Waterproofing is often placed on existing decks to enhance Hot Mix Asphalt (HMA) overlays and seal the existing superstructure from moisture and deicing chemicals. Additional preparation is required to assure the performance of adhesion, eliminate tears and holes, and to limit permeability.
The deck must be clean and relatively smooth before placing the Preformed Deck Waterproofing. Cleaning contaminates such as oil, grease and other deleterious materials is the first step. The deck should be patched with approved grout mixes as per 710.03.C. Sharp texturing and any sharp edges and bumps must be ground to aid in full contact of the adhesive and membrane, and prevent puncture. Prior to placing the membrane, the surface needs a final cleaning by sweeping and blowing or vacuuming.
When placing the Preformed Deck Waterproofing membrane make sure that a uniform coat of adhesive is placed on the substrate. The membrane placement starts at the low side of the deck and is shingle lapped to prevent water from penetrating under the edges. Place the membrane in smooth layers. The edges are to be pushed into an approved mastic to prevent leaking.
Where there are raised curbs, joints or other vertical surfaces place a strip of the Preformed Deck Waterproofing membrane up the raised edge high enough to contain the proposed overlay mix.
After placement of the Preformed Deck Waterproofing membrane, it is important to keep heavy equipment and steel drum equipment off the surface to prevent puncturing or tearing the surface. Light rubber tired equipment should also be limited. It is important to stage work in a manner that minimizes equipment being used on the prepared surface and to keep any required equipment from turning to the greatest extent possible. Steel drum rollers used for paving must stay on the paved surface and be delivered by the end of the mat where the paving began.
Placing HMA over Waterproofing Membrane
When paving HMA on a Preformed Deck Waterproofing membrane there are a couple of concerns that need to be addressed. The first is vibration on the deck. Remember that bridges were not designed to accommodate the frequency of vibratory rollers. The HMA should be static rolled only. The materials for preformed membranes are typically temperature sensitive. The manufacturer has a maximum allowable temperature for the membrane to properly function. The maximum temperatures are generally below 300 degrees Fahrenheit. The paving contractor should be notified of this prior to paving. It may be possible to use a warm mix asphalt to aid in compaction.
Shotcrete is the process of applying concrete projected at high velocity on to a vertical or overhead surface, and is applied using a “wet” or “dry” mix. Shotcrete is typically used for substructure repairs where forming and/or concrete placement by conventional means is difficult.
The standard specifications, and this portion of the Construction Manual, focuses on the “wet” method which mixes all the concrete constituents prior to introduction to the delivery hose. The Department utilizes a latex modified concrete mixture.
The “dry” method adds the water to the dry mix at the nozzle and its use is covered by a Unique Special Provision. For more information regarding the “dry” method refer to the Unique Special Provision and contact the CFS Materials Group or the BoBS Structure Construction Section.
Shotcrete equipment and materials can be difficult to calibrate and apply to the substrate. In this regard shotcreting is very dependent upon the skill of the operator or “nozzleman”. Test panels are required to demonstrate to the engineer the ability of the nozzleman to provide a satisfactory patch. The test panel should replicate the field placement in terms of thickness and steel reinforcing pattern, but be at least 3 inches thick. After test panel placement, the concrete must be kept continuously wet and above 40 degrees for at least 5 days. Five cores must then be taken from the panel and tested in accordance with subsection 710.03.D.1 of the Standard Specifications for Construction.
Prior to shotcrete placement for concrete patches all loose material must be removed from the patch. Edges surrounding the patch must be saw cut 1 inch deep. Care should be taken not to damage sound surrounding concrete during removal operations. After concrete removal, the areas to be patch must be blast cleaned with a compressed, oil-free air to remove all contaminates.
Ensure the contractor uses galvanized or epoxy coated reinforcement wire for all patches greater than 2 inches deep. The reinforcement should be placed at mid depth of the repair, or at least 1 inch from the face of the repair. Ensure the contractor uses stainless steel anchors spaced no more than 18 inches on center in each direction.
Immediately prior to shotcrete placement the patch must be wetted with the liquid latex component to be used during the shotcrete operation. Place shotcrete in several passes until the required thickness is met. Large areas may be broken down into smaller sections for placement; however, the final thickness must be achieved prior to moving to the next section. Laminations in the shotcrete should be avoided. The nozzleman must keep the nozzle 2 to 6 feet away from the surface and as near as perpendicular to the surface as possible. Do not apply shotcrete if high winds prevent proper application, the surface temperature of the concrete is less than 45 degrees, or during rain causing washouts or sloughing of the fresh concrete. Place shotcrete in accordance with section 710.03.D.3 of the Standard Specifications for Construction.
Demonstrate to the Engineer that nozzle operators are capable of applying shotcrete correctly. Use test panels simulating job conditions for each gun shooting position (down, horizontal, and overhead) required on the project. Use the same shotcrete material on the test panels as proposed for use on the project. Use a panel 2 by 2 feet square and at least 3 inches thick or the same thickness required on the project, whichever is greater. At least half of the panel area must have the same reinforcing steel pattern that is required on the project.
Keep test panels continuously moist and above 40°F for 5 days after shotcrete application. Remove at least five cores from the test panels and test for compressive strength in accordance with ASTM C39/C39M. Cut cores with a diameter of at least 3 inches meeting a length-to-diameter ratio (L/D) of at least 1.0. Adjust core strengths in accordance with ASTM C42/C42M if the L/D is less than 2.0. The average compressive strength of the cores must be at least 85% of the required compressive strength with no individual core having a compressive strength below 75% of the required compressive strength.
Take additional cores through the reinforcing steel so the Engineer can evaluate the soundness of the shotcrete behind the steel. The Engineer will examine the cored surfaces and require additional cores or sawcuts if necessary to evaluate soundness and uniformity of deposited material. The Engineer will evaluate the test panels and cores to verify that shotcrete surfaces are dense and free from laminations, voids, and sand pockets.
If applying shotcrete to protect waterproofing, perform the work immediately after the completion of waterproofing.
If using shotcrete to repair concrete members, remove unsound concrete and concrete contaminated by chemicals or oils. Saw cut and repair the edges of the area required for repair, and patch to a depth of at least ½ inch. Provide tools that will not damage sound concrete surrounding and beneath the area being removed.
Use galvanized or epoxy-coated welded wire reinforcement on repairs greater than 2 inches deep. Place the reinforcement at mid-depth of the repair and at least 1 inch below the surface. Attach the reinforcement to sound concrete with stainless steel anchoring devices spaced in a grid no greater than 18 by 18 inches. Use anchors that can support three times the weight of shotcrete allocated to each anchor.
Blast-clean the prepared area and remove traces of dirt, oil, and loose material. Follow with an oil-free air blast to remove abrasive material and dust.
Pre-wet the surface with the liquid latex component immediately before placement of shotcrete.
Balance air and material to ensure a steady flow and to prevent slugging of material, plugging, and excess rebound. Apply the shotcrete using pneumatic equipment that sprays the mix onto the prepared surface at a high enough velocity to produce a compacted dense homogeneous mass with no sagging or sloughing.
Place each layer of shotcrete in several passes over a section of the work area. Divide large expanses into smaller areas and apply shotcrete to its full thickness before moving to the next area. Avoid laminations during placement.
Keep the nozzle 2 to 6 feet from the work. Hold the nozzle as close to perpendicular to the surface as possible and never less than a 45-degree angle to the surface.
Remove rebound and overspray that does not fall clear. Do not salvage or recycle rebound and overspray.
Do not apply shotcrete under the following conditions:
- High wind preventing proper application;
- Surface temperature below 45°F; or
- Rain causing washouts or sloughing of the fresh shotcrete.
Cure shotcrete and provide temperature protection in accordance with subsection 706.03.N.3. of the Standard Specifications for Construction.
The Engineer may require cutting cores from the completed work for compression testing. If the Engineer orders tests, obtain and test at least three cores in accordance with subsection 710.03.D.1. of the Standard Specifications for Construction.