عنوان مقاله [English]
Over the past decades, the production of cement as a key material in concrete has been increasing due to the need of civil works to this vital construction material. However, the production process of cement is costly and, more importantly, is not environmentally-friendly due to the emission of huge amount of carbon dioxide ($CO_2$) in the atmosphere. Reducing cement consumption in concrete through partial substitution by inexpensive eco-friendly materials can effectively reduce the emission of greenhouse gases. Calcium carbonate ($CaCo_3$) widely available as a waste material during wastewater treatment process can be one of those materials. In this paper, the effects of $CaCo_3$ covered by nano-carbon layers on the mechanical as well as durability properties of concrete are experimentally investigated. In the first phase, the effect of cement substitution by $CaCo_3$ covered by nano-carbon layers on the early strength of high-strength concrete is evaluated to determine a reasonable range
of substitution for the second phase. The influence of partial cement substitution by these particles on the compressive strength in different ages, tensile strength, flexural strength, water absorption capacity, and electrical resistivity of concrete is investigated in the second phase. The results indicate that due to the presence of $CaCo_3$ particles, the compressive strength of concrete remains more or less constant even with reducing the amount of cement in concrete. Based on the result obtained in this research, up to 7 percent of cement content in concrete can be substituted by $CaCo_3$ particles covered by nano-carbon layers without remarkable reduction in mechanical properties of hardened concrete. Bearing in mind that reducing the amount of
$Co_2$ emission is remarkably essential for our environment, using these particles as a partial cement substitution is an effective way to decrease cement consumption in the construction industry, and hence, to reduce the emission of this gas.