Experimental study of the mechanical properties and shrinkage of self-compacting concrete with binary and ternary mixes of fly ash and limestone filler

Abstract

Self-compacting concrete’s (SCC’s) particular need for self-compacting, i.e. to achieve a high passing and filling ability, deformability capacities and a high resistance to segregation, necessarily requires the reduction of the volume of coarse aggregate and the increase of the volume of ultrafine materials and admixtures (mainly superplasticisers). The increase in the volume of ultrafine materials mentioned, achieved exclusively at the cost of the cement, would have, as main effects, the significant increase of the overall cost of SCC, of its hydration heat and potential effects on properties such as shrinkage and cracking. Consequently, significant amounts of mineral additions are usually incorporated, in replacement of part of the cement to improve the workability properties, reduce the production of hydration heat and reduce the overall cost. Mainly because it needs to incorporate significant quantities of ultrafine materials (cement and mineral additions), SCC has great potential for the use of these sub-products, such as fly ash (FA), or other commercial products, such as limestone filler (LF), as partial replacement of cement. However, the use of significant quantities of mineral additions (also necessary to ensure self-compactability), with the consequent increase in the paste volume and decrease in the coarse aggregate, will alter the SCC’s microstructure and lead to a change in shrinkage and mechanical properties. It is therefore essential to investigate and demonstrate the applicability of large quantities of these additions (in both binary and ternary mixes), mainly due to the existing regulation limitations related to their use in blended cements and as direct replacement of cement in the production of concrete mixes. To this end, an experimental programme was conducted to evaluate the effect of large quantities of FA and LF in binary and ternary mixes on the mechanical properties and shrinkage of SCC. This study focuses essentially on the evaluation of compressive strength in cubic and cylindrical moulds, splitting tensile strength, the secant and dynamic elastic modulus and, finally, shrinkage. A detailed analysis of the results and their comparison with both reference values and with results of other authors is performed. For that purpose, a total of 11 SCC mixes were produced: 1 with cement (C) only; 3 with C + FA in 30, 60 and 70% replacement by volume (fad); 3 with C + LF in 30, 60 and 70% fad; and finally, 4 mixes with C + FA + LF in combinations of 10–20, 20–10, 20–40 and 40–20% fad.