Performances of compressed stabilized bricks using phosphate waste rock for sustainable construction

Abstract

Huge volumes of phosphate waste rock are generated during the extraction of sedimentary ores, and deposited around the mining site, covering large surfaces and causing many environmental problems. This study presents a cost-effective and environmentally friendly solution allowing the valorization of phosphate waste rock (PWR) to produce eco-friendly compressed stabilized earth bricks-CSEB. CSEB is one of the earthen building materials family, offering many advantages in terms of insulation and thermal properties, good mechanical performances, use of local raw materials, and low embodied energy… For the soil classification, PWR was first characterized using chemical, mineralogical, and geotechnical properties. Then, various mixtures were formulated at the laboratory scale using PWR with cement as a stabilizer and red marl employed to enhance the cohesion and brick’s consistency. The objective was to investigate the role of cement and red marls additions, curing conditions, and brick shapes on different CSEB properties. The optimal formulation that satisfied the requirements of the international standards was adapted to the pilot scale, using hollow and solid brick forms with a size of (250*125*75) mm3. The laboratory results showed that the use of 10% cement with 10% red marl seems to be the most adequate. The pilot scale findings revealed that the addition of cement and red marl improves the compressive strength that reaches 5.70 and 2.56 MPa, for hollow bricks in dry and wet states, respectively. For solid blocks, 4.51 and 2.44 MPa were obtained in both states, respectively. The obtained water absorption coefficients respect the requirements of the standards. The thermal conductivity values are acceptable; 0.44 and 0.51 W.m-1.K-1. The TCLP test of the elaborated bricks showed that the concentrations of leached contaminants (Pb, Cd, As, Cr) are below the requested limits.