Water absorption and water/fertilizer retention performance of vermiculite modified sulphoaluminate cementitious materials

This paper investigated the effects of vermiculite on water absorption, water/fertilizer retention and basic physicochemical properties of sulphoaluminate cementitious materials for plant growing applications. Vermiculite was utilised to partially replace sulphoaluminate cement (SAC) for the preparation of a cementitious material with enhanced water absorption capacities and water/fertilizer retention properties which are essential for plant growing in a cement-based environment. Mercury intrusion porosimetry (MIP) and thermal analysis (TG-DSC) were employed to characterize the effects of vermiculite on the porosity and hydration products of hardened SAC-based pastes for plant growing. Hydration heat-evolution was introduced for the hydration process of SAC-based materials. Experimental results showed that SAC based materials delivered the best performance at a 20 wt% vermiculite content. At this SAC replacement level, the water absorption rate of hardened SAC-based paste increased by 95.3% while the water retention capacity of the SAC-based hardened paste increased 13% at 120 h. In addition, other property enhancements were measured including reduction of the fertilizer pervasion rate by up to 15.3 wt%, a 0.45 drop in the pore fluid alkalinity and the early-age compressive strength of up to 35.1 MPa.