Improving the frost resistance of road concrete through complex modification of the cement stone structure

Abstract

Deterioration of cement concrete pavements under alternate freezing and thawing in the presence of chloride deicing agents proceeds through two partly independent channels. The first one relates to the volume and connectivity of capillary pores in the cement stone, the second one is governed by the geometry of the entrained air system and is described by the spacing factor. In mix design both channels are adjusted separately, so the joint effect of complex modification remains quantitatively undefined. The aim of the study is to separate the contribution of each channel to the increase in the number of freeze-thaw cycles and to obtain a computational relation linking frost resistance with two measurable structural parameters. An author's power-law model of the cycle number has been developed; its parameters were estimated by ordinary least squares over six model mixes containing air-entraining, superplasticizing, pozzolanic and organosilicon hydrophobizing admixtures, and the increment was decomposed by the chain substitution method. The elasticity of the cycle number with respect to the spacing factor equals minus 0,68, and with respect to open capillary porosity minus 0,52. Four-component modification raises the cycle number from 118 to 412, with 49,5% of the increment provided by the reduction of the spacing factor from 0,52 to 0,16 mm, 40,5% by the decrease of capillary porosity from 7,80 to 3,80%, and the remaining 10,0% by surface hydrophobization. The obtained ratio of contributions indicates that the main reserve for raising the frost resistance of road concrete lies in the geometry of the air phase; at an attainable capillary porosity of 4,30% the F2300 grade is reached only when the spacing factor falls below 0,21 mm.