Synergic Action of Fly Ash In TernaryMixtures of High-Performance Concrete

Abstract

The scope of this work is to quantify the synergic action of fly ash when mixed with other pozzolans, through the performance of microstructural and durability parameters of high-performance concrete (HPC). Eleven mixture proportions were tested with fly ash, rice husk ash and silica fume in binary and ternary mixtures, with cement substitution, in mass, from 10% to 50%. The following tests related to HPC durability were made: axial compression strength, elasticity modulus, shrinkage, total chloride content, Cl-/OH- ionic relationship, water penetration and accelerated carbonation. Some microstructural parameters were determined such as bound water, amount of C-S-H, remaining (C3S + C2S) and C-H. The results were calculated related to the unitary mass of cement, compared to each other in compressive strength equality of 70 MPa. Practically all the variables linked to the durability presented better performance in the ternary mixtures, than the arithmetic sums of the respective binary mixtures and this behavior is validated with microstructural evidence. It is suggested that the fly ash has a synergic action in ternary mixtures, probably due to the higher dispersion of the cement grains, similar of plasticizing mixture action, resulting in additional nucleation sites and larger amounts of hydration products. A synergic action model of fly ash in ternary mixtures is provided.