Improving the pore structure of perforated cenospheres for better internal curing performance

Abstract

The pore structure of internal curing agents can significantly influence their effectiveness in reducing the autogenous shrinkage of cementitious materials with low w/b ratios. Optimization of their pore structures is meaningful, whereas it is rarely concerned. This study demonstrates that the pore structure of the perforated cenosphere can be adjusted to achieve a better internal curing performance. Increasing the etching duration can expose the own pores of cenospheres at an etching concentration of 0.7 M, gradually increasing the porosity of the perforated cenospheres. A higher etching solution concentration can significantly increase both size and number of the perforating holes. The results of the desorption properties test showed that more porous perforated cenospheres released up to about 90 % of the carried water to the surrounding environment at a higher rate, thereby achieving better effectiveness in reducing the autogenous shrinkage of low w/b cement mortars. An optimal etching condition that an etching duration of 15 min and a concentration of etching solution of 0.7 M were confirmed to prepare perforated cenospheres to almost eliminate the autogenous shrinkage of cement mortars. In addition, it is confirmed that a non-volatile acid, oxalic acid, can be used to replace hydrochloric acid to prepare the etching solution for cenospheres.