Phosphogypsum, tropical soil and cement mixtures for asphalt pavements under wet and dry environmental conditions

Abstract Phosphogypsum (PG), a by-product of phosphoric acid, is sensitive to the variation in water content. Therefore, this paper aims to investigate the use of hemihydrate PG (HH) mixed with a fine lateritic soil (S) and cement (C) considering the mechanical and durability characteristics in wet and dry cycles. This study investigated hemihydrate PG (HH) produced in the laboratory using a thermal treatment process aiming its application in mixtures for asphalt pavement layers. The mixtures of soil with different contents of HH and cement were obtained based on previous studies and physical-chemical designs. The natural soil and mixtures were characterized by laboratory tests and compacted at a fixed energy and time after moistening (from 5–25 min). In order to carry out the durability tests, the mixtures were cured for 7 days in a wet chamber and then 12 cycles of wetting, drying and brushing were applied. Unconfined compression tests were performed after a 7-days curing process with and without immersion and after durability tests with 1, 6 and 12 cycles. The resilient modulus was found by dynamic triaxial testing for different curing times (0, 7 and 28 days) in a wet chamber. Scanning electron microscopy images were obtained to improve understanding on the changes in the behavior of the samples. Solubility tests were also performed considering soil and water quality. It is possible to conclude that the mixtures demonstrate technical viability for pavements, but solutions related to solubility must be considered to avoid environmental problems.