Effect Of Casting Temperature And Curing Regime On Mechanical Properties And Durability Of Concrete
Omar S. Baghabra Al-Amoudi, محمد مصلح الدين, محمد ناصر
كلية تصاميم البيئة-جامعة الملك فهد للبترول والمعادن · السعودية
Under hot weather concreting, the primary cause of shorter service life of concrete structure is cracking. Cracking of concrete is noted in many structures of the Arabian Gulf where the environmental condition is characterized as hot weather. It could initiate a number of detrimental processes that are known to be harmful to the long-term concrete performance. High concrete temperature at the time of placement is one of the reasons of concrete degradation, especially under hot and arid environments. The cause of concrete deterioration is also ascribed to the high differential between the fresh concrete temperature and the ambient temperature.To overcome the adverse effects of hot weather and to produce good quality concrete, many local building regulatory authorities and international codes of practice including the Saudi building code limit the maximum allowable fresh concrete temperature to 35C. However, there is no data to validate this limit. Further, the applicability of this limit to blended cement concretes needs to be evaluated.This study was carried out to evaluate the effect of water to cement ratio, casting temperature and curing regimes on the compressive and split tensile strength, pulse velocity, depth of water penetration and plastic and drying shrinkage strain of plain and blended cement concretes. The blended cements studied were fly ash (FA), very fine fly ash (VFFA), silica fume (SF), ground granulated blast furnace slag (GGBFS) and natural pozzolan (NP) and used at the following replacements: at 30, 10, 7, 70 and 20%, respectively, by weight of plain cement. The plain and blended cement concrete specimens were cast at temperatures of 25, 32, 38 or 45C and cured under moist condition, covering with wet burlap or applying a curing compound. Plain concrete specimens were prepared with a w/c ratio of 0.3, 0.4 or 0.45 while blended cement concretes were prepared with a constant water to cementitious materials ratio of 0.4.Results of this investigation indicated that the optimum casting temperature for OPC and SF cement concretes was 32C while that for VFFA, FA, GGBFS and NP cement concretes it was 38C. Further, moist curing was noted to be the most efficient curing regime for strength and pulse velocity development as well as for enhancing the durability followed by curing by covering with wet burlap and applying a curing compound, in decreasing order of importance. However, the application of a curing compound exhibited higher efficiency in reducing the plastic and drying shrinkage strain compared to curing by covering with wet burlap or plastic sheet. Based on the data developed in this study, the optimum concrete mixture temperatures for plain and blended cement concretes for hot weather conditions were presented. In addition, correlations between test properties and concrete mix parameters were developed along with the relationships among test properties.