Influence of the cement fineness on strengths of cement pastes containing high phosphorus slag

Mechanical grinding was used to increase the specific surface area of cement in order to increase the dosage of phosphorus slag (PS) in Type P·O 42.5 cement. X-ray diffraction, hydration heat, and scanning electron microscopy were used to analyze the hydration process of cement containing PS. The results show that the increase of fineness of cement can obviously improve the mechanical property of PS cement pastes. When specific surface area increased to 460 m²/kg, the flexural strength and compressive strength of cement mortars mixed with 40% PS for 3 and 28 days are 3.77, 17.6, 9.89, and 52.0 MPa, respectively, still meeting the strength requirements of Type P·O 42.5 cement. The PS admixture can effectively lower the hydration heat of cement. Phosphorus slag delayed the hydration process of cement, inhibited the formation of ettringite and contributed a low strength of mortars for 3 days curing. The degree of hydration of PS at the early ages was low, leading to a poor interface between PS particle and cement matrix.