Recycling of waste river sludge into unfired green bricks stabilized by a combination of phosphogypsum, slag, and cement

Abstract

The current study is taken an attempt to reuse the waste river sludge (WRS) with high moisture content in the production of cost-effective unfired green bricks. For this purpose, hemihydrate phosphogypsum (HPG) was innovatively applied to dehydrate WRS, and different consecutive dosages of Ordinary Portland cement (OPC), sodium metasilicate (SMS) and pozzolanic waste materials like ground granulated blast-furnace slag were mixed with WRS. The observed results indicated the excellent performance of unconfined compressive strength (UCS) of the brick specimens that was obtained around 31 MPa employing the combinations 6: 4 of WRS and HPG along with the 16% slag and 4% OPC. Water absorption resisting capacity and UCS of this hard mixture satisfied the requirements of the Chinese standard. Moreover, the scanning electron microscopic (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) corroborated the strength development properties of bricks through progressing the microstructures along with calcium silicate hydrate (CSH) and ettringite minerals formations. The result of this study indicated that the unfired green bricks comprising the mixtures mentioned above are economical viable. Furthermore, the utilization rate of waste materials in the optimal ratio can reach 96%. Therefore, the outcomes of this research might be a potential application in the field of sludge treatment for manufacturing the cos-effective green bricks.