Section 6: Quality Control/Quality Assurance
In addition to providing step-by-step procedures for Contractors and Fabricators, this manual is also meant to provide Quality Control (Contractor) and Quality Assurance (Owner) inspectors with the knowledge needed to ensure that appropriate repair solutions are selected and implemented. Each procedure in Chapter 3 of this manual includes detailed instructions on each individual facet of the repair.
Proper attention to and implementation of each step in the repair process is critical to successful application. The first step is ensuring that the contractor is using approved materials. Correct proportioning and mixing is also critical. A common mistake is for Contractors to “eyeball” or guess at proper proportions when using multi-part mixes. Inspectors should verify that Contractors are measuring, either by volume or weight, all individual components prior to mixing. In almost all cases the Contractor should utilize an acceptable form of mechanical mixing; hand mixing is not acceptable. It is not possible to put a sufficient amount of energy into mixing when doing so usinga shovel, trowel, or by hand. In small applications a small “jiffy” type paddle and mixer are often sufficient. When using larger quantities of cementitious repair material a mortar or volumetric mixer is more appropriate.
Application varies significantly with repair type and material. Refer to the applicable section in Chapter 3.
Another frequent problem leading to premature failure of repairs, especially cementitious materials, is inadequate curing. Improper curing often leads to cracking very early in the life of the repair. The best (and easiest) curing method is to leave the forms in place when using form-and-pour applications. In those cases only a small amount of moist curing is required in the small areas used to place the concrete. Ponding is also an excellent method of curing but is typically impractical in most repair scenarios. Many manufacturers include instructions for application of curing membranes. However, continuous moist curing is typically preferable to curing membranes. When using wet mats it is imperative that the mats be kept moist during the entire curing interval. In cases where membrane curing is approved, the Contractor must use material that is preapproved by TxDOT and is acceptable to the repair material supplier.
Since curing requirements vary significantly depending on the type of material and the manufacturer, it is important that curing methods adhere to the technical product literature for the specific material being utilized. As noted above, moist curing is the preferred method for most cementitious patch materials. However, moist curing can actually harm some patch materials, such as those that contain magnesium phosphate. Again, the Contractor must adhere to the requirements for the specific material being applied.
Contractor’s Responsibilities (QC):
- Anchor: #KIAOGXLU
- It is the Contractor’s responsibility to use repair materials specified in the Contract Documents and this manual. For materials in which there are lists of materials available through TxDOT’s DMS and MPL process, the Contractor should only use products that have been preapproved. Any deviation from the originally proposed and approved materials must be approved by the Engineer in writing. When in doubt, contact the Bridge Division or Construction Division for guidance on whether a proposed material is acceptable. Anchor: #DUSXOYUG
- Store materials on jobsite according to material supplier’s requirements, preventing direct exposure to sunlight and moisture. Materials exceeding their shelf lives may not be used. Anchor: #ESGNPRMX
- When required by the Contract, perform a trial repair or mockup to demonstrate acceptable performance and installation methods. Anchor: #IQUUMMGX
- Ultimately, quality is the Contractor’s responsibility. If the Contractor feels that any of the procedures outlined in this manual or in the contract plans could lead to unacceptable performance, they must inform the Engineer of those concerns in writing prior to commencing work. In such cases, the Engineer will work collaboratively with the Contractor to come to an agreeable solution.
Owner’s Responsibilities (QA):
- Anchor: #JNEMKVOE
- Check materials to ensure that they are appropriate for the given application. Material should either be on one of TxDOT’s preapproved lists or approved by the Engineer prior to use. Anchor: #LHECBEAU
- Ensure that the Contractor is following the procedures outlined in this manual and as shown on the plans for material selection, preparation, implementation, curing, and any other steps crucial to the performance of the concrete repair. Procedures may need to be altered for varying weather conditions (excessive heat or cold, rain, high wind, etc.). Anchor: #XOEREPYU
- Verify that all damaged material has been removed and that the remaining surface is clean and sound before the Contractor proceeds with repair material installation. Anchor: #XUBIRFIO
- Confirm that repair material performance is acceptable through visual observations and nondestructive testing. Patch material should not exhibit cracking. One of the easiest and most effective tests is to sound the repair material using firm (but not destructive) blows with a hammer. When repair material has debonded from the substrate there is generally a distinctive hollow sound when the material is struck. Defective repair material must be removed and replaced. Anchor: #EFKOMTFN
- In some cases, the Contractor may opt to perform nondestructive or destructive testing when there is a question about whether a repair is performing adequately. Often such testing will involve taking cores for petrographic analysis. Though a Contactor may use an independent consultant or lab for performing forensic or petrographic investigations, ultimately TxDOT will decide whether a repair is acceptable.