Effect of Phosphogypsum Content and Humid-heat Curing on the Mechanical Properties of Excess-sulfate Phosphogypsum Phosphorus Slag Cement

Abstract

To solve the problems of low early strength and slow strength development of excess-sulfate phosphogypsum phosphorus slag cement (EPPSC), humid-heat curing (HHC) was used to improve the mechanical properties of EPPSC. Different contents of phosphogypsum (PG) and phosphorus slag were introduced into the system. The mass changes of the samples before and after curing were compared. The compressive strengths of the samples under HHC were measured and compared with those under standard curing (SC), respectively. The hydration mechanism of EPPSC under HHC conditions was investigated by XRD and SEM. The experimental results show that the strength of the EPPSC after 24 h of HHC is comparable to that of standard curing after 28 d, which can reach more than 30 MPa. The later strength of the specimens subjected to HHC is also improved. The suitable curing temperature is 60–70 °C, the suitable curing time is 12–24 h, and the suitable PG dosage is 30%–50%. The EPPSC can obtain the compressive strength as 43.6 MPa at 28 d and 63.0 MPa at 90 d, while the problems of low early strength and slow strength development can be improved. HHC accelerates the formation of C-S-H gel and the growth of ettringite (AFt) crystals by promoting the dissociation of granulated blast furnace slag and phosphorus slag. At the same time, the growth and densification of gypsum crystals in PG-enriched areas form the PG microaggregate, enhancing the system’s cementing ability, thus improving the overall performance of EPPSC materials.

Keywords

phosphogypsum / phosphorus slag / cementitious material / humid-heat curing

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