What is the difference?
By Daniel Wilson, PE
Senior Consultant
Quality Control (QC) and Quality Assurance (QA) testing during construction differ in their functions; however, both are critical to the quality management process, and ultimately the owner acceptance that compliant materials have been produced and installed in compliance with the project specifications by the paving contractor. Since both asphalt and concrete pavement materials are made on the same day they are installed, QC and QA must work closely, proactively, and expeditiously so that variations or deviations are quickly identified and corrected.
Contractors, or testing companies hired by the contractors, perform QC testing to verify that the materials being produced conform to the project specifications. QC testing lets the contractor know if they are out of specification tolerances and if there is a need to make any changes to the process. Independent testing companies hired by the construction site managers or owners perform QA testing to confirm that the QC testing was performed accurately and that results are in alignment. The objective of both QC and QA testing is to ensure the owner is receiving the product they are paying for.
Both Quality Control and Quality Assurance begin early in the process before construction starts with construction management firms reviewing the Contractor’s QC plan and the material submittals for conformance to the specifications. A QC plan outlines the contractor’s steps or actions during the production of materials and construction operations. It also establishes responsible parties for specific procedures. Quality Control requires constant attention in critical areas of site work, especially for asphalt and concrete paving. For example, when the materials must meet specific requirements to withstand the expected loads placed on the pavements, QC and QA are critical to make sure the pavement will perform as designed. In addition, QA inspections deliver value to clients by promptly identifying potential issues and prompt corrective actions.
An asphalt material taken from a loaded truck headed to the paving job site is split into QC and QA samples and prepared for property testing.
A concrete test cylinder is prepared for compressive strength testing (once cured) as part of QC testing and QA verification that the results achieve the minimum strength values required by the specifications.
A third-party inspection firm that works directly for the owner is a Quality Assurance (QA) firm. This firm provides unbiased testing information to the site management team and contractors. A third-party or in-house testing company that performs tests directly for the contractor is a Quality Control (QC) firm.
A good QC program is essential in helping the contractors ensure that they are supplying materials that meet the specified project requirements and that their installation methods result in the desired end product. Specifically, the contractor’s in-house QC or hired firm will provide:
- Assembly of a QC plan.
- Concrete and asphalt mix design information.
- Aggregate gradations.
- Monitor production of materials produced and placed.
Asphalt pavement depth verified for specification compliance as part of a typical QA verification process.
A solid QA program is critical in ensuring that the contractor’s QC processes will result in quality materials delivered to the project and installed correctly. An experienced and objective third-party firm working for the owner to oversee the QA program is the best way to ensure that the materials and installation methods adhere to the project specifications. This not only makes sure that the owner gets what they are paying for now, but results in long-term value as the pavement performs and has the life expectancy intended and designed.
Temperature verification typically performed as a QC and QA check is critical to achieving proper density during hot mix asphalt pavement installation.
The owner-contracted QA firm will work directly for the construction site managers and perform testing of subgrade, aggregate, and asphalt densities, material temperature reports, compressive concrete cylinder testing, and material installation depths. Alternatively, the construction site managers may perform some tasks that do not require a specialized laboratory or equipment.
A successful project that avoids post construction disputes will result from professional site managers providing general observation and the presence of both QC and QA testing firms.