Influences of phosphate tailings on hydration and properties of Portland cement

• Influences of phosphate tailings (PTS) mainly arise from the dilution effect.
• The dissolution of phosphorus from PTS has a slight retarding effect on hydration.
• Dedolomitization causes a slight expansion and no significant strength recession.
• The study exhibits the feasibility to utilize PTS in Portland cement as filler.

Phosphate tailings, which mainly consist of dolomite particles, are solid wastes produced from mining and beneficiating operations of phosphate rock. The use of phosphate tailings in Portland cement as filler is helpful to reduce the carbon emission and relieve other environmental problems caused by its large accumulation. Influences of phosphate tailings on hydration, properties of Portland cement and volume stability due to possible dedolomitization are investigated. Phosphate tailings affect setting time, strength and drying shrinkage mainly through the dilution effect. A small part of phosphorus dissolves from the tailings during the early stage of hydration, and the dissolved phosphorus extends the induction period, reduces the main heat peak by the precipitation mechanism. The dedolomitization of phosphate tailings takes place with the presence of alkalis but causes no significant volume expansion and strength recession.