Synthesis and effect of polycarboxylate superplasticizer-contained silica-matrix-microcapsules on the flow behavior of cement paste

Polycarboxylate superplasticizer (PCE) is one of the most widely-used chemical admixture in concrete, which is generally added during the mixing stage of concrete. However, part or major of the PCEs would be consumed during the initial rapid hydration resulting in the reduce of efficiency. Encapsulation of PCEs is an effective strategy to inhibit the undesired effects. However, due to retarding effect, low loading rate (high dosage required), and large capsule size ( 101-102 mu m), most of the polymer and inorganic shell materials are not beneficial for the mechanical strength of concrete. Herein a type of silica matrix-microcapsule containing PCE were synthesized by the hydrolytic condensation of silane in an water/oil (W/O) emulsion. The loading rate could achieve 70 wt% based on the total weight of capsule. The size, specific surface area of the capsule could be well-regulated, which enabled the tunning of the release process within hours in simulated pore solution. Microcapsules containing PCE can significantly enhance the fluidity retention property of cement paste. The capsules also promote hydration due to silica, which could react with Ca(OH)2 and yield calcium silicate hydrate gel. The strength of mortar showed that capsule improved the mechanical properties of mortar.