The effect of antifreeze additives on fresh concrete subjected to freezing and thawing cycles

•Effects of calcium nitrate and urea on the fresh concrete properties are investigated.•Calcium nitrate has shown a positive effect on freeze–thaw durability.•Urea was less effective than calcium nitrate in freeze–thaw deterioration.•When urea and calcium nitrate added, concrete internal structure is improved.•The effect on antifreeze agents has increased with increasing of freeze–thaw cycles.

This study focused on the effect of antifreeze additives on the microstructural changes and physical and mechanical properties of fresh concrete subjected to freezing–thawing cycles produced by cold weather. For this purpose, antifreeze additives, urea and calcium nitrate, were used at the level of 6% by weight of cement dosage and were compared with control samples. After casting, one group of control samples was cured in moist curing conditions for 1 day and then cured in lime-saturated water at 23 ± 1 °C for 28 days. Another group of controls, urea and calcium nitrate mixtures, were subjected to freezing–thawing cycles 1, 3, 5, 7, 10, 15 and 28 times. Scanning electron microscopic (SEM) images, ultrasonic pulse velocity (UPV), water absorption and compressive strength tests were conducted. The results showed that the lowest water absorption value after 28 freezing–thawing cycles was 5.8% for the calcium nitrate mixes. The 28-day compressive strength of the control, calcium nitrate and urea mixes subjected to freezing–thawing 28 times was reduced by 72.0%, 27.8% and 52.9% compared to those of the control samples cured in lime-saturated water at 23 ± 1 °C for 28 days. The SEM images showed that the samples containing calcium nitrate had a more compact and denser micro-structure compared to urea and the control.