Properties of modified phosphogypsum binder

Abstract

Phosphogypsum (PG) is common by-product of chemical fertilizers plants. However, it has limited use in local construction industry. At the same time the deposits of natural gypsum will depleted in several decades and alternative waste by-product gypsum will be required. The main disadvantage of phosphogypsum binder is the need in neutralization of harmful admixtures, aggregation of PG particles during grinding and high water demand. Therefore, there is need in modifying admixtures to facilitate the manufacturing process and achieve sufficient performance characteristics of binder. The paper reports on an investigation of the influence of composite modifying admixture, consisted of slacked lime and superplastisizer, on water-binder ratio, strength properties and peculiarities of structure forming of the binder. Compressive strength of specimens made of modified binders varied from 20 to 24 MPa and bending strength varied from 10 to 12 MPa at the age of 28 days. Per scanning electron microscope (SEM) data, the morphology of CaSO4·2H2O was not related to the type and portion of admixtures. However, at the application of optimal values of superplasticizer and slaked lime denser disposition of crystals is observed.