When it comes to constructing strong concrete, the size of the coarse-grained aggregate is a major factor. Generally, smaller aggregates are used to create stronger concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates for normal strength concrete. Since fine aggregates are used to fill the voids of coarse-grained aggregates, the smaller the coarse-grained aggregates, the finer the fine aggregates should be. This article studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of different sizes and concentrations.
Recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse-grained aggregate (NCA) at 0%, 15%, 30% and 45%, with aggregate sizes ranging from 5 to 12 to 20 mm. Fresh concrete properties, such as slump, Kelly ball, compaction factor, K slump and fresh density, were tested to determine the influence of RCA size and concentration. In addition, mechanical properties were studied by performing compression, split tensile and stress-strain tests. The test results revealed that increasing the RCA concentration decreases the fresh and hardened properties of HSCs.
In fresh concrete experimentation, RAC mixes of 12 to 20 mm in aggregate size showed greater workability than aggregate mixes of 5 to 12 mm. In contrast, aggregate mixtures of 5 to 12 mm RAC had a higher compressive and split tensile strength and a higher modulus of elasticity than concrete from aggregate mixtures of 12 to 20 mm. When it comes to sustainability, the study found that RAC's smaller size range produces lower embedded CO2 (Eco) and provides a cost-effective and sustainable solution for the construction industry. Only 15-34% of zone 1 aggregates will pass a 0.6 mm screen; 35-59% of zone 2 aggregates will; 60-79% of zone 3 will; and 80-100% of zone 4 will. Once processed, aggregates are handled and stored to minimize segregation and degradation and avoid contamination. There are several reasons to specify leveling limits and maximum aggregate size, and most importantly, workability and cost.
The maximum size of a well-graded coarse-grained aggregate of a given mineralogy can have two opposite effects on the strength of normal concrete. Sand and aggregate help reduce cost and also limit the amount of shrinkage that occurs in concrete as it cures. The replacement of the calcareous aggregate (limestone) with a siliceous aggregate (sandstone), under identical conditions, resulted in a substantial improvement in the strength of the concrete. In conclusion, when it comes to creating strong concrete, smaller aggregates are key. 20mm aggregates meet the threshold for strong concrete while 40mm aggregates are used for normal strength concrete.
Additionally, using smaller size ranges for recycled aggregate concrete can provide a cost-effective and sustainable solution for construction projects.