Frost testing of high strength concrete:: frost salt scaling at different cooling rates

The effects of variation of cooling rate and time at minimum temperature on frost deterioration of concrete have been investigated on three non-air-entrained concrete and one air-entrained concrete. It was found that at an equal number of freeze/thaw cycles, the frost/salt scaling increased when reducing the rate of cooling for the non-air-entrained concretes. A slow cooling rate produced more scaling at comparable periods in the frozen condition, compared to a rapid cooling rate and variable time at minimum temperature. Air-entrained concrete with very good frost/salt durability showed no clear effect of freeze/thaw cycle variations. Measurements of resonance frequency at prolonged cycling for two of the concretes (same binder, with/without air) showed that for the air-entrained concrete, the internal cracking was increased by increasing the rate of cooling. For the non-air-entrained concretes, the internal cracking was severe for all types of cycles. Measurements of absorption during the tests revealed increased absorption with increased damage and a strong correlation between absorption and internal cracking. The scaling was found to accelerate when internal cracking increased. The two types of deterioration (scaling and cracking) therefore appear to be connected in tests where both cracking and scaling occur. The results of this investigation illustrate an important difference between frost/salt scaling and internal cracking: scaling increased with a reduced rate of cooling, whereas internal cracking increased with an increased rate of cooling.