When it comes to constructing strong concrete, the size of coarse-grained aggregates is a primary factor. Generally, smaller aggregates are needed for stronger concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates meeting the threshold 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 finer the 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 experimentation with fresh concrete, RAC mixes with an aggregate size of 12 to 20 mm showed greater workability than aggregate mixtures 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 aggregate mixtures of 12 to 20 mm of concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces lower embedded CO2 (Eco) and provides a cost-effective and sustainable solution for the construction industry. Air entrainment is a mixture that is added to the mixture during production to help the mixture withstand the damaging effects of freeze-thaw cycles. Coarse-grayed aggregates with a size of 20 mm or less are commonly used for most concrete constructions.
Observations and field tests can be used to check the quality of aggregates and choose the right aggregate to produce concrete. The selection of good quality coarse-grated aggregates is essential for the production of concrete that meets the desired strength and durability requirements. Leveling limits and maximum aggregate size are specified because these properties affect the amount of aggregate used, as well as cement and water requirements, workability, pumpability, and concrete durability. The classification of an aggregate is determined by a sieve analysis, which is the distribution of particles of granular materials among various sizes, generally expressed in terms of cumulative percentages greater or less than a series of sieve opening sizes (or the percentages between certain ranges of openings of sieve). With the same cement content and consistency, concrete mixes containing larger aggregate particles require less mixing water than those containing smaller aggregates. For medium strength concrete, 40mm aggregates are best; however, for high strength concrete, 20mm is ideal.
Sand and aggregate help reduce cost and also limit the amount of shrinkage that occurs in concrete as it cures.
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