The effect of heat-treated boron derivative waste at 600 °C on the mechanical and microstructural properties of cement mortar

Turkey holds 73% of the world's boron deposits. 25.3% of the total deposits are tincal ore and located in Eskişehir Kırka region. During the production of 1 million tons of borax pentahydrate (Na2O·2B2O3·5H2O) from tincal ore, approximately 900.000 tons of solid boron derivative waste generated in a year. The boron derivative waste is stored in waste ponds and causes both economic and environmental problems. The main purpose of this study is to utilize the waste in a widely used material, like cement mortar. For this purpose, first, detailed thermal and mineralogical characterization of the waste was carried out and the heat treatment temperature was determined accordingly as 600 °C. Subsequently, the effects on the cement mortar were investigated by replacing boron derivative waste with cement in weight ratios of 5%, 15%, and 25%. Also, waste-incorporated cement paste samples were prepared with the same replacement ratios to investigate the changes in phase compositions. Compression tests were conducted for all mortars at 7th, 28th and 90th day. Incorporation of waste by the ratio of 5% provided higher strength value (52 MPa) than reference mortar (51 MPa) at the 90th day. For early ages, the strength ratio values were varied from 55% to 94% depending on both the incorporation ratio and the age of the sample. After the compression tests, samples were characterized by XRD analysis and microstructural analysis were conducted for both mortar and paste samples in order to understand the effects of waste replacement on the microstructural evaluation. For strength point of view, heat treated waste is practical to be utilized in the production of cement mortar by 25 wt%.