Water treatment waste as supplementary cementitious material

Abstract

The increase in demand for treated water causes the generation of waste from its process - Water Treatment Plant Sludge - WTS, to rise gradually. Alternatives are needed for the reuse of this waste in other chains, with Civil Construction being a segment that incorporates waste in techniques and products. This sludge is composed of soils that incorporate lime and aluminates in the phase of physical treatment of water. This work exposes the viability of using water treatment sludge with secondary cementitious potential, where sludge sample was calcined at 750 °C for three hours. Tests were produced comparing the finely ground calcined material with blast furnace slag. The results of X-ray diffractogram analysis showed that the material formed with calcination is metakaolinite. Thermogravimetric analyses indicated that the temperature plateau and the applied energy rate (calcination time) provided adequate dehydroxylation of the residue in the range of 507 °C to 580 °C. The effective pozzolanic was evaluated in the methods of Brazilian standards under the performance for compression with partial replacement of cement by 25%. The test results showed a high pozzolanic strength of WTS, close to the minimum standards required (90%) by the methods used, reaching 89% of the reference strength with the 100% calcined material sample and 92% and 96% obtained with WTS samples mixed with 32% and 50% of blast furnace slag, respectively. Demonstrating the technical feasibility of using the waste as a supplementary cementitious material in the incorporation of cement and in the production of mortars and concretes. The results obtained also expose that this waste can be used in low environmental impact concrete technology - LC3 for example, to be further studied in future research.