Effect of mineral admixtures on coefficient of thermal expansion of concrete and cement paste

Change in the concrete temperature causes the expansion of the concrete to become tensile stress. The risk of concrete cracking decreases with decreasing coefficient of thermal expansion (CTE) under temperature changes. In this research, in order to investigate the effect of mineral admixtures on the coefficient of thermal expansion, concrete and cement paste samples containing silica fume, metakaolin and slag with a constant ratio of water to cement materials and the amount of cement materials have been made, and compressive strength, total porosity, Pore size distribution and coefficient of thermal expansion of the samples have been examined. The results indicated that CTE of reference concrete had a descending trend up to 60 days, and diminished by 12%, after which it remained constant. On the other hand, in the slag-containing concrete, after 60 days, the descending trend started and declined by 10% up to 120 days. For the concrete containing silica and metakaolin, at the very early ages, it had 14% less CTE as compared to reference concrete, while with the ageing of the sample, its CTE dropped by around 8%. Across all concretes, reduction of CTE was associated with lowered total porosity. Utilize the experimental data, a model for predicting the coefficient of thermal expansion of concrete at different ages is presented using concrete thermal expansion coefficient at 7-day age. In the following, the relationship between CTE and compressive strength, total porosity and the average diameter of pores has been investigated, which has the highest correlation between the coefficient of thermal expansion and the diameter of pores.