Before concrete is used for construction work, it is significant to determine its quality by taking specific tests and conducting inspections. Taking tests before concreting, during concreting, and after construction will help in efficient use of concrete. Quality control enables minimization of risks and reduction of overall costs. As concrete is checked at every stage, it helps in rectification of errors at every stage. Thus, saving overall cost and ensuring quality in construction. Moreover, it ensures low repair and maintenance cost. Following stages are involved in quality control of concrete in construction projects.
The first stage of quality control of concrete involves two steps. First step includes determining specification requirements about different materials such as reinforcement, embedded fixtures, forms, excavations, and others. The second step includes control test of ingredients of concrete such as cement, water, and aggregate. The quality of cement is determined by conducting compressive strength test on cubes. The cement needs to be protected from moisture, retested every two months, and rejected if a large lump is found in bag. As the quality of concrete is impacted based on shape, durability, grading, and water absorption properties of aggregate, these properties need to be tested before the preparation of concrete. Then aggregates should be tested initially before the approval of source and tested once or twice every day to determine moisture content. The quality of water needs to be tested according to specified standards. Furthermore, chemical analysis need to be conducted and if suspended impurities are found, they should be allowed to settle down for some time.
Checking upon quality during preparation of concrete is necessary for concrete applications such as mixing, batching, compacting, laying, and others. The concrete should be carried out in laboratory with the help of materials needed on site. If weight batching is not feasible, volume batching should be carried out with proper supervision. During mixing, materials need to be poured in proper sequence and mixer need to be charged to its full capacity. The mixing time should be carried for more than two minutes. It needs to be ensured that segregation will not take place during unloading and transportation. Workability should be checked with the help of compaction factor or slump test. Concrete should be dropped from a height less than one meter. To compact concrete, vibrators should be used. The concrete needs to be protected from hot and cold weather in first few stages. Avoid concreting below 4.5 °C and above 40 °C. In case of very hot weather, cool down water and aggregates. While in case of very cool weather, heat water and aggregates.
Compression tests should be conducted on cubes of concrete once laying and compacting of concrete are carried out. The hardened concrete needs to be tested to determine whether it meets shapes, dimensions, and sizes of design specification. There should be enough concrete cover during reinforcement. However, if reinforcement is seen in the part of structure, that part should be eliminated and essential action must be taken. The concrete strength is determined by cube samples tested at 28 days. If the strength is minimum than expected, then appropriate tests should be taken. Chemical analysis of hardened concrete should be conducted and cores from structure should be cut and tested for strength.
Civil contractors in Pune as well construction companies as across India have been conducting these tests to ensure concrete used in construction is of the highest quality and there is not a contrast between the minimum required strength and mean strength of concrete mix.