The effects of urea on strength gaining of fresh concrete under the cold weather conditions

•Effects of urea on the compressive strength of concrete exposed to cold weather investigated.•Workability of concrete was improved.•Urea provides protection against freezing in the plastic state concrete.

Objective: The study focused on the application of urea to the cold weather concreting. One of the advantages of this method is to simplify curing after concrete placement at low temperatures; only an anti-evaporation sheet is necessary to keep fresh concrete wet until finishing of concrete curing.Method: Urea is used at level of 6% by weight of cement dosage in the mixtures. After casting, one group of concrete samples were cured in the different deep freezes at -5, -10, -15, -20 °C for 7, 14 and 28 days and then the same samples were cured in water for 7, 14 and 28 days in accordance with ASTM C 192. Compressive strength of hardened concrete was determined according to ASTM C 39.Results: At -5 °C and -10 °C the admixture’s positive effect is evident but at -15 °C and -20 °C the same effect was not achieved when compared to mixes without antifreeze admixtures. As a result at cold weather concreting, urea can be an effective alternative to the other precautions up to -5 °C without any protections. In this paper Scanning Electron Microscopic (SEM) observations also helped to explain the effect of Urea on concrete under cold weather conditions.