Hydration products and microstructural properties analysis of magnesium phosphate cement comprising with industrial residues

Abstract

Cavities, micro-cracks and micro-pores are formed in the microstructures of magnesium phosphate cement (MPC) due to the rapid hydration process. For increasing the structural solidity, formation of secondary minerals is necessary through filling the micro-cracks and micro-pores. In addition, existence of optimum level of intermediate crystals increases the microstructural density as well as strength performance of MPC compounds. To attain the high-quality microstructures of MPC for water stability, present study added four different pozzolanic properties based industrial by products namely fly ash (FA), silica fume (SF), bauxite (BX) and phosphogypsum (PG) were introduced by means of their optimum dosages. The 1d aged SEM micrographs with high magnifications shown that free particles of magnesia and phosphate salts reacted with the used all supplementary cementitious materials and formed huge secondary crystals. In addition, presence of intermediate crystals was detected by EDS and X-ray diffraction tests in the powder specimens at 1d age, which are Enstatite, Mullite, Lizardite, Berlinite, kaolinite, kyanite, CSH and ettringite. It has been noted from crystallinity analytical results that MPC specimens comprising with BX and PG including FA exposed the higher intermediate crystal amounts around 34.3% and 41.6% at 1d; 49% and 47.6% at 28d, respectively. In the similar way, amorphous contents were significantly reduced with the passages of hydration ages. Furthermore, all the nominated blends with SCMs unveiled the well heat resistance and lost structural water at higher temperature as compared to control mix. The outcomes of present research might be applicable to design MPC matrices for higher strength and water structures.