INFLUENCE OF THE COMPOSITION OF REACTIVE POWDER ALKALINE-ACTIVATED SLAG PORTLAND CEMENT CONCRETE ON THE EVOLUTION OF ITS PROPERTIES

Abstract

The influence of the composition of alkali-activated reactive powder concretes (RPC) and other factors on the genesis of their properties is established. It was shown that an increase in the binder content in the composition caused an increase in strength, and the dependence of strength on the sand content at all stages of hardening is almost direct at water-cement ratio £ 0.35. Optimization of sand granulometry allowed to improve the rheological properties of the mixture and to increase the strength by 5...6%. The effect of increasing the OPC within 5...45% in the mixture with ground granulated blast furnace slag (GGBFS) on the strength of RPC is ambiguous - in the early stages (up to 3 days) it causes an acceleration of strength gain, but in the long term, composition with 5% OPC and 95% GGBFS has the highest strength. Shrinkage deformations decrease with an increase of OPC/GGBFS  ratio and part of fine aggregate. The introduction of an optimal amount of dispersed calcite additive allows to reduce the shrinkage deformations. The admixtures allow regulating the initial setting times within 19...118 min. The performed work resulted in obtaining high-strength, ultra-rapid-hardening, alkali-activated cement reactive powder concrete of strength class C80/95 with high early strength (52.3 MPa at 1 d; 76.3 MPa at 2 d; 85.0 MPa at 3 d), high crack resistance (compressive strength / flexural strength ratio = 5.3…5.9), reduced shrinkage (0.5…0.6 mm/m), stable performances, and technologically acceptable setting times. In terms of early strength gain, the designed ultra-rapid-hardening RPC significantly surpasses concretes based on alumina cement, super-rapid-hardening portland cement and low-water-demand cement, while having acceptable shrinkage. Considering the high physical, mechanical, operational and special characteristics, the obtained RPC can be classified as high performance concrete.