Lightweight magnesium phosphate cement composites with struvite recovered from wastewater
A feasibility study was performed to utilize struvite, in combination with magnesium oxide (MgO), to develop magnesium phosphate cement. The struvite was a wastewater by-product from a sewage treatment plant in British Columbia, Canada. To achieve MgO-phosphate reactivity in water, two types of recycled struvite were used: heated struvite and newberyite (i.e. rehydrated struvite). A more common phosphate source, Potassium Dihydrogen Phosphate (KDP) was also adopted and replaced in different proportions by recycled struvite. Perlite was incorporated to produce lightweight composites for building applications at different strength-density ratios. Microstructural/chemical analyses were complemented with compressive strength tests at different ages. Reactivity with MgO was achieved for both heated struvite and newberyite. The main reaction product was cattite but reactivity of less soluble newberyite was lower. KDP had the fastest reaction leading to the formation of K-struvite. The lightweight composites achieved up to 90% of their strength in 7 days.