Resistance of phosphogypsum cement pozzolanic compositions against the influence of water

Abstract

The reprocessing of freshly removed extractive hemihydrate phosphogypsum into hydraulic composite phosphogypsum cement pozzolana (PGCP) binder using mechanical activation is analyzed in this work. In order to increase the effectiveness of the dealing with phosphogypsum reprocessing problem and to lower the energy consumption required for the production of binding materials from phosphogypsum, physical mechanical and water resistance properties of the PGCP binder with less amount (10 %) of cement (PGCP(10)) were analyzed and compared with the properties of conventional PGCP binder, where the amount of cement is 20 % (PGCP(20)). The PGCP binder with pozzolana additives of two types – carbonate opoka and microsilica are analysed. Fresh wet hemihydrate phosphogypsum, cement and pozzolana additive were mechanically activated together and from resulting mixture the samples were formed by vibrating. Compressive strength of PGCP(10) samples after 28 days was 26 MPa – 29 MPa, after 4 months – 30 MPa – 32 MPa, PGCP(20) – 32 MPa – 35 MPa and 36 MPa – 42 MPa accordingly. It is found, that hardened PGCP(10) are also quite resistant to short-term (2 days) impact of water (softening coefficient was 0.91 – 0.94, however, its resistance to long-term impact of water is significantly less than PGCP(20). PGCP with microsilica is more strength and more resistant to impact of water than PGCP with opoka. Both, PGCP with opoka, as well as the ones with microsilica, are resistant to the formation of ettringite. However, the primary ettringite and high amount of carbonates, found in the PGCP with opoka, stimulates the formation of thaumasite at low positive temperature and humidity.