Rice husk and water treatment plant sludge incorporated into soil–cement brick

Abstract

Soil–cement brick is an alternative material for construction, which enables waste recycling, resulting in the reduction of raw material extraction. Accordingly, this study evaluated by physical and chemical tests, the incorporation of rice husk, and water treatment plant (WTP) sludge in soil-cement brick, without burning these wastes in the soil mixtures (in natura). It was identified in the rice husk a content of 5500 mg kg−1 of phosphorus, 4000 mg kg−1 of nitrogen, and 280,000 mg kg−1 of lignin. The sludge had 3662 mg L−1 of COD, 2270 mg L−1 of BOD, and 7580 mg L−1 of phosphorus. This suggests the use of rice husk in natura, although the sludge presents the possibility of developing microorganisms that can cause negative effects on the material, being necessary long-term studies. Physical characterization tests were conducted according to Brazilian National Standards (NBRs) 10,836, 7181, 6459, 7180, and 7182 (Brazilian standard practices). The soil was classified as sandy, well sorted, after a physical analysis with a liquid limit (LL), plastic limit (PL), and plasticity index (PI) of 26.10%, 10.51%, and 10.59%, respectively. The sludge presented the same LL as the soil and a PL of 8.80%. The greatest amount of rice husk used was 21.43% with a resistance of 2.07 MPa, while the amount of sludge used was 35.71% with a resistance of 2.30 MPa, both after 28 days of curing.