Bridge Answer Man column: Making sure bridge materials are strong |

Bridge Answer Man column: Making sure bridge materials are strong

Work continues through the winter on the Grand Avenue bridge project.
Klaus Kocher | Colorado Department of Transport

Quality assurance and quality control are two large parts of the Grand Avenue bridge project.

In the context of products used for construction, quality assurance procedures carried out by the Colorado Department of Transportation exist to assure the quality of all materials on CDOT projects is in accordance with Title 23 of the Code of Federal Regulations and the Federal Highway Administration. On the project level, that means sampling, testing and inspecting materials, products and work to assure conformance with plans and specifications are being met.

With more than 7,000 cubic yards of structural concrete involved among the two bridges and retaining walls, sampling and testing concrete is a quality assurance process that is routinely performed both on and off the project on a daily basis. Concrete is tested before, during and after being delivered to the project.

On the project, personnel sample and test the delivered concrete to determine air content, slump and unit weights. Samples are also placed into small cylindrical molds and are tested at a particular age (28 days being the project standard) to determine compressive strength values, which can be used to estimate the structure’s in-place concrete strength or to verify the specified mix design strength. These types of test procedures are part of CDOT’s quality assurance procedures.

Quality control or process control is a routine part of the supplier’s and contractor’s system of procedures to monitor, assess and adjust production to ensure the final product will meet the specified level of quality for the project. Quality control procedures are geared towards adjusting and monitoring variability of the materials to achieve the required end product.

Prior to delivering concrete to the project, the supplier routinely tests the concrete. Before this has even occurred, aggregates, cement, fly ash and other admixtures have been tested for various requirements as well. During placement, quality control procedures are followed by personnel responsible for finishing concrete. Properly consolidating concrete and minimizing aggregate segregation are two important finishing aspects.

The project may have up to five or more personnel on site during concrete pours directly responsible for quality assurance and quality control efforts. This requires CDOT, the contractor and supplier personnel, who are all working to ensure there is not out-of-specification concrete as deficiencies can cost considerable time and money or require corrective actions.

Quality assurance and quality control is imperative to building the traffic and pedestrian bridges in Glenwood Springs. The safety and longevity of the new bridges for generations to come is the end goal.

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