Improving efficiency of calcium oxide expansive additives by polylactic acid film

Abstract

Calcium oxide-based expansive additive (CEA) has the disadvantages of a too-fast reaction rate when mixed with water and lower storage stability when exposed to the atmosphere, which reduces its expansion efficiency for shrinkage-compensating concrete. This paper introduces a modification technology by encapsulating CEA particles with polylactic acid (PLA) polymer to form a protective membrane. Experimental results indicate that the encapsulating PLA membrane could build an inductive period in the hydration process of CEA and delay the initiation of hydration when mixed with water, thus effectively reducing the invalid hydration of CEA during the plastic stage. Restrained and free deformation testing results demonstrate that the expansion of the cement paste incorporating modified CEA increases by 25% and 35% over that of the paste with the original CEA, respectively. The weathering rate, assessed under conditions of 25°C and 60% humidity to evaluate the storage stability, was slowed down by 30%. This paper offers an original method to improve the expansion efficiency of additives so that sufficient varieties of polymer can be utilised.