Commentary - Special Provision for Quality Control and Acceptance of Portland Cement Concrete 12SP604(B)
Over the past three years, the department has implemented a series of revisions to the title frequently used special provision (FUSP). The primary basis for change to the department’s historical standard specifications described in Sections 604 and 605 of the Standard Specifications for Construction is to separate contractor administered quality control (QC) from department (MDOT) administered quality assurance (QA-Acceptance). Additionally, revisions were also made in efforts to better define both the contractors and departments respective roles and responsibilities toward improving quality, not only with respect to concrete sampling testing, but also with regard to the holistic concrete construction process.
The following items are some of the significant key aspects included in this special provision. Reference to the page number of the FUSP is noted in parenthesis.
- The contractor must administer their QC program independent of the MDOT (QA) acceptance program. (page 1)
- Both the contractor and the department (Engineer) must conduct independent startup testing of the fresh concrete prior to discharge of the concrete onto the grade or into the forms.
- Percent-within-limits (PWL) analysis for payment applies only to mainline concrete pavements, concrete shoulders, miscellaneous concrete pavement (including ramps) and concrete pavement overlays. Temporary concrete paving applications, however, should not be analyzed using PWL.
- A significant change from the prior revision of the FUSP is that the quality index analysis using PWL will no longer apply to bridge decks.
- Since concrete bridge approaches are considered reinforced concrete elements, which are designed and constructed similar to a bridge deck, they should be sampled, tested, and analyzed for payment according to the provisions for non-PWL application.
- The intent of the specification is to administer PWL only when sufficiently large continuous quantities of concrete of the same job mix formula (JMF) and application are being placed in a timely manner to accommodate the required number of sublots for statistical-based PWL analysis. Although it may not be feasible in all cases, it is preferred that when setting up the limits for each production lot (approximately 5 sublots) of paving concrete, a focus should be toward closing out the lot at (preferably) the end of each paving day. Partitioning the paving operation for the project into reasonable and representative production lots should be done well in advance of paving, with consideration for the contractor’s anticipated daily production.
- Concrete applications other than those associated with (permanent) paving items, described above, are to be considered non-PWL and should be sampled, tested, and analyzed for payment according to the provisions for non-PWL application.
- The Concrete Quality Initiative pay item establishes a budgeted amount to cover the potential five (5) percent maximum positive pay adjustment for the concrete paving items associated with PWL. Concrete Quality Initiative does not apply for non-PWL concrete applications.
- It is the contractor’s responsibility to ensure that complete and continual QC is being administered throughout the entire duration of the project. (page 4)
- The contractor is required to develop a project-specific QC Plan. The QC plan is intended to be a roadmap for the project, which is to say that it should describe how, when, and where the contractor will administer the necessary control of their processes throughout all phases of construction in order to deliver a quality end product that will meet specification requirements. The QC Plan is not limited solely to sampling and testing of the concrete. Rather, it should also include discussion of the entire concrete construction process. Items that should be considered (where applicable) in the QC Plan are listed starting on page 4 of the FUSP. The QC Plan is to be submitted to the Engineer a minimum 10 working days prior commencement of related work. The Engineer will have 5 working days from receipt of the QC Plan to make any comments and respond to the contractor regarding the acceptability of the QC Plan. The contractor must not be authorized to begin concrete placement until the Engineer accepts the QC Plan. Keep in mind that the QC Plan is a living document in the sense that in the event of changing site conditions, the contractor and the Engineer can agree to justified changes, which should then be reflected in submittal of a revised QC Plan to the Engineer for review and acceptance. The revised QC Plan then becomes the new roadmap for the contractor to guide their quality-based processes control. (pages 4-6)
- The contractor is required to designate a QC Administrator for the project. The QC Administrator must have full authority and responsibility for implementation of QC for the project. If issues arise at any time that may not be in alignment with proper QC or in defiance of the QC plan, the Engineer must first notify the QC Administrator of the observed deficiencies. If the QC Administrator fails to take immediate corrective action in efforts to resolve the issue, the Engineer must issue a Notice of Noncompliance with Contract Requirements (Form 1165). A Notice to Resume Work (Form 1165) will then be issued when the necessary corrective action has been taken to bring the work back into conformance with specification requirements. (pages 6, 13, and 19)
- It is important that the contractor maintain complete daily records and reports of all QC tests and inspections. Further, the specification requires that the QC records are to be furnished to the Engineer for their review and files within 24 hours after the date covered by the record. A consequence to the contractor for untimely submittal of these QC documents is that acceptance of the work will be withheld, and also eligibility for PWL dispute resolution will be forfeited for all concrete work associated with the delinquent records and reports. (page 6)
- The individuals performing QC testing for the contractor are not required to be Michigan Concrete Association (MCA) Level I certified technician. However, the QC testers must demonstrate that they are proficient and capable of sampling and testing the fresh concrete according to the applicable standard test methods prior to beginning work. Keep in mind that if the contractor opts to employ non-certified testers, the contractor forfeits all rights to dispute resolution consideration in the event there is a discrepancy between contractor QC and department QA administered test results. Also, the Engineer should contact the QC Administrator if the contractor QC tester is shown to be incompetent relative to proper fresh concrete sampling and testing techniques. If the QC Administrator fails to take immediate corrective action, the Engineer should then issue a Notice of Noncompliance with Contract Requirements (Form 1165). Regardless of whether or not the contractor elects to employ the services of an MCA Level I certified testing technician, they are still obligated to perform the necessary physical testing of the fresh concrete to ensure that it meets specification requirements prior to discharge onto the grade or into the forms. (pages 7 and 12-13)
- Similar to field testing, the QC laboratory selected by the contractor must also demonstrate that they are equipped, staffed, calibrated, and managed to perform the necessary testing of the concrete according to the applicable standard test methods.
- Mix designs and JMFs must be submitted to the Engineer a minimum of 10 working days prior to the anticipated date of concrete placement. (page 10)
- The Engineer then has up to 5 working days from receipt to review the contractor’s submittal and respond with any comments or objections. (page 10)
- The mix design review should verify that all of the materials to be used in the concrete are from approved sources, the trial batch information is complete, and that the physical characteristics or the fresh and hardened concrete meet the specification requirements for the grade of concrete. (page 10)
- The mix design submittal must also include certification along with test data showing that the fine aggregate to be used in the concrete mixture has been tested and meets the requirements for alkali-silica reactivity (ASR). Testing of the fine aggregate (either ASTM C1260 – 14-day Mortar Bar Test, or ASTM C1293 – one-year Concrete Prism Test) must be conducted by an independent testing laboratory. Independent laboratory test reports for the fine aggregate are valid for two years after completion of testing. If ASR testing of the fine aggregate is not available, as described above, the JMF must include replacement of the Portland cement with 25 to 40 percent slag cement or fly ash. Testing of the JMF for resistance to ASR must then be conducted according to Method 3 (ASTM C1567 – 14-day Mortar Bar Test). Again, ASR independent laboratory test reports submitted as part of Method 3 evaluation are valid for two years provided all of the materials included in the proposed JMF are the same (and from the same source) as what are represented by the Method 3 ASR test report. (page 9)
- ASR testing of the fine aggregate or JMF is not required for concrete pavement repair or temporary concrete pavement applications. (page 9)
- If the concrete mix design is specified as either a Grade P1M or DM, the mix design documentation must also include the necessary test data for optimization of the aggregates, as described in Appendix 1 of the special provision. (page 7)
- There are two ways that concrete mixes may be provided for the project; contractor provided mixes and Department provided mixes. (pages 10-12)
- o Contractor Provided Mixes – The contractor is responsible for all mix design development and laboratory verification testing. Four methods of verification are as follows: (page 11)
- Method 1 – Trial Batch. Method 1 verification is for new JMFs that do not have any historical record of being used on a prior MDOT project. Method 1 concrete mixes are starting from scratch and require that a full suite of laboratory trial batch tests be conducted and submitted to the Engineer for review in order to determine whether or on the JMF conforms to specification requirements.
- Method 2 – Same Mix. Method 2 verification is used to evaluate the documentation for the JMF, based on the successful historical MDOT project performance for the exact JMF using the same sources and proportions of materials (aggregates, cementitious materials, admixtures). Verification test results for the JMF must reference the historical project where successful performance was attained and must also contain all fresh and hardened concrete trial batch information presented at the time the mix was originally developed through Method 1 – Trial Batch.
- Method 3 – Similar Mix. Method 3 verification is similar to Method 2 with the exception that substitution of the coarse and intermediate aggregates are permitted provided the proposed aggregates are of the same geologic type traceable to the original aggregates used in the original Method 1 verified JMF. Verification test result documentation is required along with the calculations showing the adjustments to the mixture proportions, including yield adjustment calculations, based on the differing physical properties of the substituted aggregates.
- Method 4 – Annual Verification. The Engineer may accept a concrete JMF from a concrete producer that is not specific to a project provided all of the materials specified in the JMF have not changed. This annual verification of a particular concrete plant’s JMF is valid for one year, but may be carried over to the next construction season if a project is being constructed over multiple years. Written certification must be provided to the Engineer that the same materials used prior will also be used in the upcoming season. Method 4 examples could include mixture proportion sheets generated by the Central Office (CFS) Concrete Laboratory.
- o Department Provided Mixes – Concrete mixes that would fit in this category would be ones specified for the project that are provided either in the Standard Specifications for Construction (such as LMC and SFMC mixtures) or as part of a standalone special provision. (page 12)
- Concrete materials change over time and adjustments must periodically be made in order to achieve the required fresh and hardened concrete properties. This is why a concrete mix design (and its accompanying JMF documentation) is valid only for two years from its original date of inception through trial batch. This applies for contractor, as well as department provided mixes. In other words, for contractor provided mixes, the maximum lifespan for any particular concrete JMF would be two years before the mix would have to be again verified via Method 1 – Trial Batch. For mixes that are generated by the Central Office (CFS) Concrete Laboratory, the physical properties for the fine and coarse aggregate are updated annually by MDOT. Therefore, new mixture proportion sheets should be requested by the region staff annually, if needed.
- Regardless of the method of verification, ASR testing of the fine aggregate or JMF is required.
- Both the contractor and the Engineer must conduct independent startup sampling and testing of the fresh concrete for temperature, slump, and air content.
- Prior to startup, the contractor must provide and locate the proper number of curing facilities throughout the project capable of housing both QC and QA 28-day compressive strength test specimen. The contractor is responsible for maintaining the proper curing environment inside each curing facility for the entire duration of initial curing (the first 48 hours immediately after molding test specimens). The contractor is also responsible for the security of the curing facilities and their content. Requirements for contractor provided curing facilities can be found in subsections c.5.E and d.2.C of the special provision. (page 12)
- The stability of the entrained air system has been shown to be critical relative to long-term durability of the concrete. Excessive air loss in concrete may be a result of either adverse interactions between the air entraining admixture and other chemical additives, improper mixing, or simply a result of the effectiveness of the chemical additives as the concrete temperature fluctuates. A concrete mixture may perform quite well when tested in the laboratory at a concrete temperature of 70° F, but may very well fail to meet specification requirements in the field when discharged from the hopper at 90° F. The consequence of inheriting a poorly entrained air-void system in the hardened concrete is often not felt until several years later, which is observed in terms of premature distress as a result of freeze-thaw damage. As part of the contractor’s required battery of QC tests, concrete that is either slipformed or pumped must be checked before and after the pump or paver to verify the stability of the entrained air system as follows:
- o At least once each week of production, or whenever the QC tests have shown that the QC action limits have been exceeded,
- o Whenever the concrete pump is relocated, and whenever there is a significant change in the boom angle of the pump.
- o If the air loss is greater than 2.0 percent, the contractor must suspend operations and make the appropriate adjustments to the mix or operations to reduce the air loss. (pages 12-13)
- The concrete must be rejected if it arrives at the jobsite and either the maximum slump is exceeded (too wet) or concrete temperature exceeds 90° F (too hot). It is not appropriate to permit a load of concrete to be pulled aside and mixed for an extended period of time with intend toward driving excess water from the mix. Excessive revolutions beyond the normal mixing breaks down the aggregates and potentially corrupting the entrained air-void system. Further, additional mixing creates heat, which may further increase the concrete temperature. (page 13)
- If it is observed that the contractor’s QC testing and oversight is not sufficient enough to adequately control the quality of the concrete construction, the Engineer should notify the contractor’s QC administrator, which may result in the contractor having to modify the QC plan and step up QC testing and oversight in efforts to maintain better control of quality. (page 13)
- When the contractor develops their QC plan, they should design their program in such a manner to provide them advanced warning when the uniformity of the concrete may be deviating, prompting corrective action in efforts to restore the quality. These intermediate limits (that would be a trigger for the QC Administrator to take immediate corrective action) are called “action limits”.
- The “suspension limits” are also referred to as specification limits. For example, suspension limits for air content of fresh concrete are when field testing reports less than 5.0- or greater than 8.5 percent. The contractor may choose to establish their action limits at 5.5- and 8.0 percent. In other words, they are documenting that they will take action to investigate the cause and make the necessary adjustments to their concrete for subsequent loads to ensure continuous compliance before it gets to the point where MDOT will suspend work. If the contractors QC test results exceed the suspension limits (specification limits), they must suspend work and take the appropriate corrective action to restore the quality to acceptable levels. (pages 13-14)
- The Engineer may permit reduced QC testing for small incidental quantities described in subsection c.5.G of the special provision. Reduced contractor QC is not the same as reduced QA (acceptance) for small incidental quantities. The contractor is still responsible for their quality control (QC). However, for small incidental quantities, the Engineer may permit the contractor to utilize the services of the concrete producer to share in the concrete QC sampling and testing provided the concrete producer has the required qualified staff on site, or available when needed, to cover the QC activities associated with sampling and testing of the concrete. Keep in mind, however, that the contractor is still responsible for maintaining all QC oversight for the project, according to their approved QC plan, regardless of whether or not the Engineer approves reduced QC for the small production quantities. Further, please note paragraph 2 of subsection c.5.G of the special provision, which limits the total project quantity of concrete eligible for reduced QC testing to 100 cubic yards for the item of work. This is to prevent instances where the contractor could argue that all concrete items for an entire project meet small incidental quantity criteria, thus creating the situation where the contractor may try to excuse himself of any QC obligation for the entire project. It would not be appropriate to permit reduced QC oversight for an item of work staged with daily placements of curb and gutter less than 20 cubic yards but having a total project quantity for that item of several hundred cubic yards. (pages 14-15)
- It is the Engineer’s responsibility for all QA (acceptance) for the project. In other words, the contractor QC test results are not to be used for acceptance of the work. (page 15)
- The Engineer is required to develop a project-specific QA Plan. The QA plan is intended to be a roadmap for acceptance of the concrete, which is to say that it should describe how and at what frequency QA sampling and testing will be administered for each item of work in efforts to ensure that the appropriate payment, penalty, or remedial action is being administered to meet specification requirements. (page 15)
- This QA plan is to be provided to the contractor a minimum 5 working days prior commencement of related work. The QA plan should then be discussed at the pre-production meeting and any comments or proposed changes should then be documented. (page 15)
- All QA testing must be performed by a current MCA Level I certified concrete technician (regardless of whether the tester is an MDOT or consultant employee). Whenever there is aggregate sampling and testing on the project, it must be performed by an MCAT certified aggregate technician. (page 15)
- A very important aspect of acceptance is the upfront correlation between the department’s and the contractor’s air meters. The intent for correlation is to ensure that the air meters and concrete thermometers used to test the concrete for QC and QA on any given day of production are functioning properly. What is of equal importance is that the QC and QA testing technicians are also conducting the tests according to the proper test methods and procedures. Side by side correlation testing must be conducted prior to the first concrete placement and also whenever there is a change in testing equipment and/or testing personnel. If there are questions regarding differences between the test results attained by the QC and QA, it is advisable for the QC and QA concrete technicians to conduct a correlation. The necessary action should be taken (which may include requesting an IAT) in order to ensure that both the QC and QA test are being conducted in the proper manner and the test results are in reasonable correlation (air content within 1.0 percent, temperature within 2 degrees F). (page 15)
- Both the contractor and the department must conduct independent startup sampling and testing of the fresh concrete for temperature, slump, and air content. Since startup testing is not part of the random QA sampling and testing protocol, 28-day compressive strength test specimens are not required to be molded during startup testing of the concrete. (page 16)
- The concrete application will dictate how the concrete placement will be partitioned for representative sampling, testing, and ultimate analysis for payment. It is important to keep in mind that only concrete having the same grade, mix design, JMF and same specified fresh properties (slump, air content) may be combined into a common production lot. For example, if the grade of the concrete pavement is the same (eg. Grade P1) but the application is different (eg. hand formed miscellaneous pavement versus slipformed mainline pavement having different specified fresh concrete properties), the concrete for each of these applications is not the same JMF and, therefore, must be set up and analyzed independently. Another consideration would be the timeliness of placement. The objective is to complete the production lot as timely as practical in efforts to complete the analysis for payment. Ideally, it is recommended to close out each production lot at the end of each respective day of placement. Realistically, it is suggested that a production lot be set up with the objective of completing concrete placement and closing it out within a week, at most. Holding the production lot open much longer than that serves not only to delay the disposition of the payment to the contractor, but also raises the likelihood that the concrete represented by each subsequent sublot could be quite different in terms of fresh properties compared to the concrete sampled and tested during initial placements of the production lot. (page 16)
- There are three categories that can be used to accept the concrete, as follows:
- o PWL Applications. Acceptance of concrete using percent-within-limits (PWL) is limited to concrete pavements only (except for temporary concrete pavements). However, keep in mind that there must be a sufficient amount of concrete being placed in a timely manner in order to truly perform a statistically-based PWL analysis. The Engineer should exercise common sense when deciding when and where to apply PWL for very small or intermittent concrete pavement placements. For instance, a concrete pavement placement consisting of a total 50 cubic yards placed over a several week time period may not be an appropriate PWL candidate. On the other hand, 50 cubic yards, or more per day of concrete pavement being placed for five consecutive days could reasonably constitute completion of a production lot, and therefore, could potentially be candidate for PWL analysis. Each day of production would then represent an individual sublot. For large mainline concrete paving projects, a single day’s production of concrete (eg. 2500 cubic yards) could constitute a production lot. Each day’s production would then be subdivided into five approximately equal sublots of 500 cubic yards each in volume. A random number would then be generated for each sublot to pinpoint the precise location within that respective sublot where the QA sample is to be taken. (pages 16-18)
Concrete pavements evaluated using PWL are the only applications that require the sampling locations to be determined using the random number method. The following steps should be followed to establish PWL sample locations:
- Generate a list of random numbers prior to the pre-production meeting.
- The Engineer and the contractor’s QC administrator are to sign each sheet of random numbers at the pre-production meeting. In efforts to eliminate any perception of bias, it is important
- Make a copy of the signed random number sheets for the MDOT field inspector and place the originals in the project file. These original sheets are to be retained as part of the permanent project files. The contractor does not receive a copy at this time.
- A copy of the random number sheets may be given to the contractor, upon their request, at the completion of the project.
- Determine the size and limits of each production lot of paving based on the anticipated quantity of pavement concrete to be placed.
- Subdivide the production lot into five (5) approximate equal size sublots.
- Refer to Section 1.06 “Random Sampling for Quality Control/Quality Assurance Projects” of the Materials Quality Assurance Procedures (MQAP) Manual for guidance on how to set up a random sampling schedule for concrete paving. Examples of how to determine sampling locations, based on random numbering, are included herein.
- o Non-PWL Applications. All other concrete applications with exception to permanent pavement are to be sampled and analyzed according to non-PWL provisions There may be occasional instances when small or intermittent volumes of concrete pavement could potentially be candidate for acceptance using non-PWL application protocol. The Engineer can make this determination at the project level, which should be based on site conditions. (page 18)
The random sampling method is not required for non-PWL applications. However, it may be a practical means to set up a random sampling schedule for larger volume concrete placements, such as bridge substructure units or bridge decks. The random sampling method may not be as practical for small volume concrete placements. In the case of smaller volume placements, representative sampling may be more applicable. A general sampling frequency of at least one sampling approximately every 50 cubic yards is a starting point. However, a minimum of one sample is required to be taken each day of concrete placement, regardless of the size of the placement. For simplicity, a suggested sampling strategy could be to base the sampling rate on individual structural element (eg. minimum one sampling for each footing, pier column, pier cap, etc…), using the above approximate 50 cubic yard quantity threshold to determine the number of samplings within each structural element. In general, considerations for sampling of the concrete for non-PWL applications should be based on the project-specific site conditions, as determined by the Engineer, in efforts to ensure that all of the concrete is reasonably represented by tests. However, keep in mind that it is not in the best interest of the department to establish sampling frequencies which either over- or under-samples the concrete. Over-sampling may be considered a poor use of staff resources; whereas, under-sampling could potentially jeopardize federal-aid participation.
- o Small Incidental Quantities. The intent of establishing the small incidental quantities category for concrete acceptance is to provide a way for the Engineer to evaluate non-structural and non-pavement related concrete elements without having to conduct the full battery of testing for the fresh concrete. Keep in mind that QA (acceptance) testing of small incidental quantities is not the same as reduced QC testing. Regardless of the volume of concrete being placed, QC is the responsibility of the contractor, while QA is the sole authority of the department. It is important to retain this separation of responsibility and authority. The maximum single day threshold for small incidental quantity QA and reduced QC consideration is limited to 20 cubic yards. However, the maximum total project quantity of concrete that can be considered for reduced QC testing is limited to 100 cubic yards (eg. five-20 cubic yard placements). There is no maximum total project quantity threshold for QA testing of small incidental quantities. The minimum frequency for QA small incidental quantity placements should be as follows:
- Daily QA testing (minimum) of the fresh concrete properties (slump, temperature, air content of fresh concrete),
- Weekly sampling for 28-day compressive strength,
- Interim visual inspection during concrete placement to provide the necessary assurance that the quality standards are being met for the application.
Keep in mind that the contractor is still required to conduct independent QC testing, regardless of the application, in order to ensure that they are maintaining continual control of their operations. It is not acceptable for the contractor to forego their QC testing responsibilities in lieu of any offers that they may extend to piggyback onto the department’s QA. (page 18)
- Historically, QA sampling and testing was often conducted at the concrete plant. However, in efforts to capture the final in-situ properties of the concrete as placed on the grade or in the forms, sampling and testing is now required to be conducted as near the point of final discharge as practical. Worker safety should always be considered. Samples for QA should not be taken at the batch plant or before discharge from the concrete pump (with exception to tremie concrete). If discharged directly onto the grade or into the forms, the concrete sample should be taken from the grade and transported to a safe location for testing using a wheelbarrow. (page 17)
- If the concrete is being discharged from a ready mix truck, the truck that has been selected for sampling should be permitted to discharge one-third of its load prior to sampling. (page 17)
- When taking the QA sample, the contractor is not permitted to make adjustments to the concrete mixture (slump, air content) prior to taking the QA sample unless similar adjustments were made as a normal part of QC for prior and subsequent loads of concrete representing the concrete placement. In other words, special consideration should not be given to the concrete selected for QA testing in efforts to ensure it meets specification requirements prior to sampling, testing, and molding of the test cylinders. (page 17)
- Two QA strength test cylinders are to be molded for each sampling associated with non-PWL applications (non-paving). Four cylinders are to be molded for each sublot sampling associated with PWL applications (paving); two samples for 28-day QA testing and two samples that are to be retained in the cure tank in the event of dispute resolution. (page 18)
- It is the responsibility of the contractor to provide and maintain the necessary number of curing facilities to ensure that the QA strength test cylinders are in the proper environment during the initial curing period (maximum 48 hours of field curing prior to the transporting to the laboratory for final curing). It is not the responsibility of the department personnel to take on the duties of maintaining the initial curing facilities. This point must be conveyed to the contractor at the pre-placement meeting and the contractor should not be permitted to begin concrete placement until the proper initial curing facilities are in place and properly functioning. Further, the contractor is ultimately responsible for the security of the curing facilities and their content throughout the entire duration which they are in use. (page 19)
- In order to ensure continual chain of custody for all QA strength test cylinders, it is very important that the curing facilities be designed in a manner that the QA samples are secured against theft and tampering using a department-provided padlock. Only the Engineer is allowed physical access to the QA strength test cylinders. The contractor is not permitted to hold a duplicate key. Do not take this point for granted. Federal aid could be forfeited if it is shown that the chain of custody for the QA samples was compromised by leaving them unattended in a non-MDOT secured curing facility. (page 19)
- Transport the QA strength test specimens to the department designated testing laboratory for final curing no sooner than 8 hours after final set of the concrete (final set is normally 4 to 6 hours after concrete placement, but may vary depending on mix design), but not later than 48 hours after molding. Ensure that the individual assigned to transport the QA test cylinders is (1) an MDOT-authorized transporter, (2) trained in the proper transport procedures, and (3) equipped with the proper transporting devices necessary to protect the cylinders against damage. The total transport time must not exceed 4 hours.
- It is recommended that the region testing laboratory coordinate with the project office and individuals assigned to transport the QA test specimens to maintain a checklist and records of initial/final curing, transport time, and chain of custody for the QA test specimens.
- The analysis for pay factor and price adjustment is to be completed within 7 working days after completion of 28-day compression testing for the production lot. (page 20)
- o For PWL applications (paving), the PWL worksheet is to be used to complete the quality index analysis. The PWL worksheet can be found under the Manuals & Guides tab located on the Construction Field Services page of the InsideMDOT intranet or public website.
- Make sure that the proper PWL worksheet revision is being used to calculate the pay factor and price adjustment. The proper version of the PWL worksheet will have a revision date in its file name corresponding with the FHWA approval date for the special provision included in the project proposal.
- Save the PWL worksheet to your computer prior to entering data.
- Positive price adjustment (quality initiative) applies only for PWL applications.
- Positive price adjustment (quality initiative) calculations are based on a maximum five (5) percent of the contractors bid price for the concrete pavement (Conc Pavt, Shoulder) pay item. There should be no manual conversion (or back-calculation) of the pay unit from square yards to cubic yards (or visa versa) when determining the quantity of pavement that represents either the quality initiative price adjustment calculation or the total allowable quality initiative dollar amount for the item. The budgeted amount has been pre-determined by the designer, which was based on five (5) percent of the Engineer’s Estimate unit price for the concrete paving item times (x) the plan quantity for the project. All quality initiative price adjustments for concrete pavement items (with exception to concrete overlays) are to be based on a direct adjustment (ADJ) calculation to the standard square yard pay unit for the production lot. For concrete overlay applications, the pay item (Conc Pavt, Ovly, Furnishing and Placing) should be used to determine quality initiative price adjustment, based on a direct adjustment (ADJ) calculation to the cubic square yard pay unit for the production lot.
- Do not separate the cost of the concrete from the contractor bid price for the item of work prior to performing the quality index analysis. The contractor may argue that the contractor’s price per cubic yard of concrete should be the only dollar amount subject to penalty, but then argue the contrary in the event of quality initiative incentive payment. All adjustments are based on the contractor bid price for the item of work associated with the concrete.
- Keep in mind that subsection d.4.C of the special provision requires that both pay factors (PFs and PFac) be 100.00 or greater for the production lot to be eligible for positive price adjustment (quality initiative). This is to safeguard against the manipulation of one quality index parameter in order to influence the pay factor of the other (eg. driving the air content down to the lower specification limit threshold in efforts to maximize the compressive strength). The PWL worksheet will flag this and make the appropriate adjustment to the overall lot pay factor (OLPF).
- Dispute resolution for 28-day compressive strength applies only for PWL applications. Provisions for dispute resolution are located in subsections d.6 and d.7 of the special provision. (page 24)
- Since the air content of the concrete is measured while the concrete is still in its plastic state, the appropriate time to engage in dispute of the air content test results is during initial concrete placement. It is very important that this up-front correlation of the contractor’s QC and the department’s QA air tests be verified, as described in subsection d.1.B of the special provision. (page 15)
- o For non-PWL applications (non-paving), the pay factor and price adjustment are to be calculated by hand according to subsection d.5 of the special provision. There is no spreadsheet available for non-PWL pay factor and price adjustment calculations. (page 22)
- An addition that was made to the price adjustment calculations for non-PWL applications is the inclusion of a graduated pay factor for the air content of fresh concrete (PFac). Subsection d.5.B of the special provision describes the requirements. (page 23)
- If the 28-day compressive strength for concrete associated with non-PWL applications fails to achieve the lower rejection limit, the Engineer may elect to require additional evaluation of the rejectable concrete associated with the failing test results as described in subsections d.5.A and d.9.B of the special provision. (pages 23 and 27)
If the air content of fresh concrete is below 5.0, or above 8.5 percent, the Engineer should refer to subsections d.5.B of the special provision, which provides guidance for further action as described in options (1) and (2). (page 23)
For small incidental quantities, there is no concrete strength or air content related price adjustment associated with the item provided the concrete has met the acceptable quality level. The weekly 28-day strength test results described in d.2.B(3) of the special provision should, however, be noted on each Inspector’s Daily Report associated with the small production quantity placed during that week. (page 18)