Research on the Main Properties of Cementitious Mortars Prepared with High-Fe₂O₃-Content Raw Drinking Water Treatment...

Drinking water treatment sludge (DWTS) is a typical by-product of drinking water treatment plants. Concerns are growing about how to deal with big amounts of this sludge generated globally. One of the ways is to reuse DWTS as a supplementary material in cementitious systems and thus reduce landfill disposals. For our studies, we used DWTS containing more than 52% Fe₂O₃. The DWTS was taken from a water treatment plant in Vilnius, Lithuania. This work aimed to find potential applications of unprocessed DWTS in cementitious systems as a supplementary material that changes the physical and mechanical properties of the final product. Tests were performed with cementitious mortars where the binder was replaced with DWTS (from 0% to 12.5%). Local raw materials such as Portland cement CEM I 42.5R and sand 0/4 were used in the tests. Water absorption, absorption kinetics, and mechanical strength tests were conducted, and predictive freeze-thaw resistance was estimated. The heat release rate and open-closed porosity were also measured. The results showed that DWTS impacts the hydration of cementitious mortars, lowers their density (from 2122 kg/m³ to 1954 kg/m³), as well as compressive strength (from 41.78 MPa to 24.76 MPa) and flexural strength (from 6.24 MPa to 4.07 MPa), and increases total porosity (from 28.1% to 34.6%) and closed porosity (from 9.1% to 14.9%). The lowest toughness value of 6.08 was recorded in the 12.5% DWTS sample. From our conducted research, it could be observed that raw DWTS potentially changed the porosity parameters of cementitious mortars. This resulted in an incremental improvement in durability and an improvement in the hardness of cementitious mortars. A higher content of raw DWTS changed the colour (to reddish) of cementitious mortars, due to its higher Fe₂O₃ content (up to 53%). All of the above-mentioned properties allowed the designing of cementitious landscape products with a wider range of colours.