The impact of primary sludge from paper industry on the properties of hardened cement paste and mortar

In the paper, the impact of paper production waste (primary sludge, or PS) on the properties of cement pastes and mortars is discussed upon. Some specimens were formed with fine PS fraction that replaced a part of cement content in them (5%, 10%, 15%, or 20%); in other specimens, coarse fraction of sludge (2/4) was used and a part of content of fine filler (sand) was replaced by PS. The properties of mixtures, such as water content required for cement paste of normal consistence, the setting time, exothermic temperature, flow diameter and plunger penetration, were established. In addition, the properties of hardened mortar, such as its density, flexural strength and compressive strength, were established. The microstructure of hardened specimens was examined as well. It was found that PS retarded hydration processes and reduced exothermic temperature; in addition, it reduced the flow diameter and the plunger penetration. While assessing the properties of hardened mortar, it may be stated that 5% PS waste might be used for replacement of a part of cement content.