Drying shrinkage of conrete samples exposed to extreme hot weather

Drying shrinkage is of great importance to concrete engineers, especially when dealing with hot climates. High ambient temperatures and low humidity accelerate evaporation of moisture from concrete resulting in increased drying shrinkage when compared to normal or cool climates. However, when dealing with the real environment (daily and seasonal weather factors variations), the matter becomes complex. While some factors will increase shrinkage and therefore result in contraction, other daily or seasonal factors may reverse such an effect. To explore the effect of mixing time and season of cast on normal strength concrete (NSC), two concrete mixes were cast and tested in real environment of Alain city (interior region in the UAE). Each mix was cast twice, once in summer and once in winter. The samples were cast, cured and kept in the outdoor environment. All samples were cured for three days after which they were left exposed to the environment. Shrinkage was then immediately measured. The effect of mixing duration was also investigated. Samples were cast after 20 minutes, 40 minutes and 60 minutes from the start of mixing. Plain OPC, and OPC/microsilica combinations were used. Mixing was carried out by a certified ready mix plant. The results indicated that while significant effect of season of casting was evident, no significant influence of mixing duration was apparent on drying shrinkage of concrete.