Efficiency of cement content and of compactness on mechanical performance of low cement concrete designed with packing optimization

The unavoidable concern with developing sustainable materials in the construction sector has led to the attempts to reduce the content of Portland cement in structural concrete mixtures. Thus, the main objective of this research was to develop low cement concrete (LCC), maximizing the replacement rate of cement by additions and/or reducing the amount of binder through combining the design parameters of concrete, such as water/cement, water/binder, and compactness, without compromising the specified mechanical performance and consistency. The mix-design and characterization of various LCC mixtures were developed, considering two amounts of powder in the binder paste, 350 and 250 kg/m(3), being the first with very plastic consistency and the latter with dry consistency and low cohesion, due to the reduced proportion of water and binder. These were combined with large spectrum of cement replacement rates, through adding fly ash and limestone filler, as well as with different compactness levels, and with the variation of aggregates proportions. The concrete mixtures were characterized in fresh and hardened states, in terms of consistency, compressive, tensile and flexural strengths and the Young's modulus. Results revealed that a lower amount of powder in the binder paste leads to lower consistency and cohesion. However, it is possible to improve the workability if a powder content up to 350 kg/m(3) is adopted. Thanks to the optimized combination of Portland cement, fly ash and limestone filler additions, and the granulometric optimization and the use of superplasticizer, it is possible to produce LCC with good workability, stability, and mechanical performances, thus mitigating the limitation of using high content of fly ash as partial substitute for cement. The characterization of the mechanical strengths and the Young's modulus revealed that is possible to substantially reduce the Portland cement content of LCC mixtures, up to about 50%, being however possible to increase that replacement rate up to 70%, assuming simultaneously an adequate performance for structural purposes. The variation of aggregates proportioning, which is controlled by different granulometric curves, revealed high influence both on consistency and on Young's modulus. (C) 2020 Elsevier Ltd. All rights reserved.