Utilization of Recycled Concrete Powder as Cement Replacement or Filler in Masonry Mortar

Portland cement is the most energetically demanding component among all cement-based materials. It not only consumes high levels of energy, but also is one of the important CO2 emission sources in the world. So any efforts to reduce the consumption of cement can lead to lower environmental pollution. One way to handle this problem is using recycled powders (remained at construction and demolition waste recycling sites) as a partial replacement of cement. According to the literature, recycled concrete powders can be successfully used as cement replacement or filler in cement-based products. This strategy can lead to consumption of construction waste recycling products as well as reduction in the greenhouse emissions. However, due to lower hydration activity of recycled concrete powder compared to cement, utilization of it in masonry mortars seems more practical as opposed to concrete. In this research three different groups of mortar mixes were designed. The first group consisted of mixes in which 25%, 50% and 75% of the total ordinary Portland cement were replaced with recycled concrete powder. In the second group, 10% and 15% silica fume were replaced with ordinary Portland cement, and finally in the third one, both 10% and 15% silica fume was used in mixes containing 25% recycled concrete powder. The results of physical (both fresh and hardened states) and mechanical tests showed that utilizing 10% or 15% silica fume in mortar containing 25% recycled concrete powder can lead to a similar or even better physical and mechanical performance compared to reference mix.