Experimental Investigation of the Effects of Curing Temperature and Amount of Silica Fume on Properties of Reactive Powder Concrete Made from Local Materials

The curing ambient temperature and the amount of Silica Fume are the effective factors on the mechanical properties of reactive powder concrete (RPC). In this research, the effects of the curing ambient temperature and also the effects of the amount of silica fume on reactive powder concrete have been investigated. The autoclave device has not been used so that these concretes can be used in different environments as in-situ concreting. The prepared specimens were cured by immersion in water. To investigate effects of the curing ambient temperature, specimens were cured in water at three temperatures of 27, 60, and 80°C and were tested for compressive, tensile, and flexural strength at the age of 3, 7, and 28 days. The results show that the curing ambient temperature has a significant effect on the early strength of RPC, which increases strength at high temperatures. In the curing in water, it was found that 60°C is an optimum temperature; Because the specimens with the curing ambient temperature of 80°C show higher compressive, tensile, and bending strengths, but the increase in strengths compared to the curing ambient temperature of 60°C is very small. The compressive strength of the specimens cured in the water pool with temperature of 80°C has increased by 43.7%, 43.5%, and 25.9% at the ages of 3, 7, and 28 days, respectively, compared to the specimens cured at temperature of 27°C; Also, the increases in bending strength in the mentioned cases are equal to 51.5, 53.4 and 25.8% respectively. Similar results are also observed in tensile strength. In the next step, to study the effect of the changes in the amount of silica fume, five concrete mixtures with different amounts of silica fume were produced. These values were considered as a percentage of cementitious material (cement + silica fume) of 0, 10, 15, 25, and 35%. The specimens made in this step were only cured in a water pool with temperature of 27°C at the ages of 3, 7, and 28 days and were tested for compressive, tensile, and bending strength. It should be noted that at this stage, cementitious material (cement + silica fume) is fixed and is equal to 1008 kg / m3 of RPC. The results indicate that the replacement of silica fume has increased the strengths, but the optimal value is in the range of 15 to 25%. The compressive strength of the specimens with 25% replacement of silica fume at the ages of 3, 7, and 28 days has increased compared to the specimens with 10% replacement of silica fume by 66.3%, 40.9%, and 64.0%, respectively. These increases are equal to 100.8, 93.8 and 107.7 percent, respectively, compared to the specimens with zero percent replacement (without silica fume)