Frost-Salt Influence on Cement Concrete

The article explores hypotheses concerning frost-induced damage in concrete under alternating freezing and thawing conditions, and examines methods for improving the frost resistance of road cement concretes. It is shown that the primary causes of frost damage in road concrete include the freezing of water in pores and capillaries, loosening of the surface layer, subsequent abrasion, and early layer-by-layer structural destruction that penetrates deeper into the concrete mass. When a pore or capillary is filled with water, ice formation generates stress in the microvolume of cement concrete due to pressure from growing ice crystals on the pore walls. This pressure is initially transmitted to the remaining liquid phase, which does not freeze at –18 °C, as the crystallization of pure ice enriches the remaining liquid with alkalis or salts. Consequently, the impact of temperature cycling is exacerbated by additional effects from salt solutions. The article presents research on the influence of concrete composition incorporating the plasticizer «FM 21» and varying levels of entrained air on the density, strength, and frost resistance of cement concretes. It is demonstrated that under freeze–salt exposure with NaCl, salts are deposited in the pores and defects of the concrete structure. Experiments confirm that salt crystallization initially leads to densification of structural layers, followed by a rapid loss of strength and gradual concrete degradation as crystallization pressure increases. Thus, the study concludes that frost damage to road concretes during operation results from a combined effect of hydraulic pressure from water and crystallization pressure from ice and salts. It is proposed that frost resistance can be enhanced by increasing the density of concrete’s structure at all levels. Existing concrete mix design techniques can achieve such density by reducing the water-to-cement (W/C) ratio through the use of modern superplasticizers, decreasing cement paste porosity via powdered microstructure modifiers, and lowering capillary porosity by using cements with active mineral additives.