Improving the shrinkage/strength property of high-strength mortar containing clinoptilolite zeolites by phosphoric acid treatment

Clinoptilolite zeolite serves as internal curing agents upon pre-wetting, but suffers from strength reduction. To address the adverse effect and enhance the shrinkage mitigation efficiency, present study focused on the pretreatment of zeolite with phosphoric acid (PA). Autogenous/drying shrinkage and the internal relative humidity were evaluated by means of integrated shrinkage measurement device. Results indicate that PA pretreatment of zeolite enhanced the compressive strength of mortar in comparison with the traditional deionized water absorbing method. It could also be reflected by the improved hydration heat release. Both autogenous and drying shrinkage was greatly mitigated by up to 65 % under PA modification. Porous zeolite particles acted as internal water reservoir to compensate for water loss, extending the duration of saturation period inside high-strength mortar. The size and volume of internal pores in zeolite particles were responsible for the moisture control based on the calculated pore radius. Additionally, an increased surface tension of zeolite particles with higher concentration of phosphoric acid contributed to lower RH. The shrinkage/strength ratio (μm/m/MPa) implies that 0.5 M PA treatment for zeolite contributes the best to the properties of high-strength mortar, manifested by the most compact microstructure under the scanning electron microscope. • Shrinkage was mitigated by up to 65 % incorporating PA modified zeolite. • The duration of saturation period was extended in zeolite-contained mortar. • Critical pore radius was increased for internal curing with the addition of zeolite. • 0.5 M PA optimized the shrinkage/strength ratio of high-strength mortar.