In this investigation, mortar samples with no pozzolanic material or with 5, 10, 15, 20% silica fume, 30, 50 and 70% ground granulated blast furnace slag were subjected to heat cycles between room temperature for 5 hours and 65 °C for 7 hours to study the effects of temperature variations during summer in the Middle East on the mortar samples. Two heat cycles were applied every day for 90 days. The effect of the heat cycles on moisture loss, compressive strength, ultrasonic pulse velocity and drying shrinkage was assessed. The percentage moisture loss was 7.3 % for OPC mortar or 9.2, 9.7, 10.7 and 11.1 for the 5, 10, 15 and 20% silica fume mortars, respectively, and 11.1, 12.8 and 13.7 % for the 30, 50 and 70% GGBS mortars, respectively by the end of the heat cycles. The increased moisture loss due to the inclusion of pozzolanic materials was explained in light of the current understanding of the effect of silica fume and ground granulated blast furnace slag on the hydration reactions and microstructure of the mortars. The heat cycles reduced the compressive strength in all but the 5 and 10% silica fume mortars, in which pozzolanic reactions were probably resumed after the samples were placed in the ovens. The loss in ultrasonic pulse velocity for the 10% silica fume and 30 and 50% ground granulated blast furnace slag mortars was 5.6, 54.2 and 9.8% lower than that observed in the Ordinary Portland cement mortar, respectively. However, unlike the other mortars, the 10% silica fume mortar lost most of its pulse velocity after more than 28 days in the heat cycles. The maximum observed shrinkage for the 5, 10, 15 and 20% SF mortars was 120, 300, 320 and 480% higher than the Portland cement mortar, respectively. The corresponding increase in shrinkage was 280 and 600% for the 30 and 50 GGBS mortars, respectively. The continued swelling during the heat cycles of the 70% slag mortar may be due to its severe cracking, leading expansion by heating. The observed shrinkage values for pozzolanic mortars after exposure to heat cycles are excessive and there is a need to monitor if moisture reabsorption from humidity or rain would alleviate shrinkage in real structures constructed in the Middle East. |
