Strength-maturity index behavior of high performance cementitious mortar exposed to early hot curing conditions

The performance of mortar or even concrete primarily depends upon the type and ratio of its ingredients, additives and curing conditions. The important part of this research emphasis to draw the consequences on strengths of high performance mortar, when it is subjected to a high environment temperature during the first hours of setting time of cement mortar. On Summer season in Mosul/Iraq, according to what was obtained records for 50 years ago of Mosul city from the Department of Meteorology in Nineveh, the mean environment temperature is approximately 40°C during the day hours. This temperature was dependent in the present research, as extreme conditions, to be exposed to High Performance Cementitious Mortar (HPCM) and extended to 5 hours of its early curing period. The present experimental research was aimed to determine the effect of this temperature on the strength-maturity index response of high performance mortar. For this purpose, HPCM is at a ratio of 1 cement: 2.25 sand: 0.38 water, incorporating with three different levels of polycarboxylic-ether super-plasticizer (SP) (i.e., 0.5%, 1.0%, and 1.5%) of cement weight, and two percentages of adding Micro-Silica Fume (MSF) (i.e., 0%, and 7%) replaced with cement. The compressive strength of HPCM under the effect of early high curing temperature was studied at different ages (namely, 7,14, and 28 days). The test results demonstrated that when mortar is exposed to high temperature of 40°C for the first 5 hours of curing process, a negative consequence is resulted, especially, the later age strength decreases significantly compared to that at normal curing conditions. The negative consequence is not caused by the difference in degree of hydration, it is caused by the uneven distribution and pragmatic expansion of hydration products due to the high curing temperature. Incorporating of silica fume can effectively agitate this negative consequence, where, the 28-day compressive strength of super-plasticized mortar, exposed to high temperature, reduces by about (6, 16, 15, and 14 %) for superplasticizer levels of (0, 0.5, 1.0, and 1.5 %), respectively. Comparatively, when 7% MSF is added to the mortar, the negative effect on compressive strength increases to (20, 23, 18, 16%) for superplasticizer levels of (0, 0.5, 1.0, and 1.5 %), respectively compared to standard curing condition. A 0.5 % content of SP is the appropriate level for optimizing all HPCM properties for mixes without Micro-Silica Fume (MSF), w