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.