Frost susceptibility of concrete in near-saturated states

A new model was proposed to provide a basic understanding of the freezing mechanism of pore water in concrete in near-saturated states. The model, which is also called the two-stage model, is based on the plastic ice theory of capillary freezing and melting of pore water;This model is able to explain the abrupt drop in frost resistance as saturation increases to a near-saturated state that Powers\u27 hydraulic pressure hypothesis can not. It is suggested that concrete will suffer far greater stresses in this state because of the occurrence of the second stage bulk-ice-initiated freezing, which results in the extrusion of ice to the exterior of the concrete. It is also suggested that the volume of extruded ice, which can be measured by dilatometry, is proportional to these stresses;The objectives of this research are two-fold. The first is to investigate the applicability of the proposed model. Second, based on the understanding of the freezing mechanism of pore water in concrete, is to introduce a quicker, simpler, and more economical method of predicting frost resistance of concrete without relying on the tedious and expensive standard freeze-thaw testing method;Mortar samples subjected to dilatometric measurements indicated quite good agreement with the proposed model;A systematic study of the dilatometric expansion upon freezing as a function of saturation level, the rate of water uptake, and the permanent expansion of mortar samples after subjecting them to 60 freeze-thaw cycles, at a cooling rate of 15°C per hour, showed that the dilatometric expansion upon freezing combined with the rate of saturation could potentially be used to evaluate the frost susceptibility of mortars. Significant changes were observed in the pore structure of the samples upon freeze-thaw cycling, but they are not consistent enough to evaluate frost damage;Similar conclusions were reached from the results of a series of experiments with concrete samples;A simple test method is proposed to predict performance of concrete. It consists of immersing 1[superscript]\u27\u27 diameter by 1[superscript]\u27\u27 high core samples in water for a specified period of time and measuring their dilatometric reversible expansions upon freezing at -20°C