Internal curing of cement composites using kenaf cellulose microfibers

This study investigated the applicability of kenaf cellulose microfibers (CMFs) as an internal curing agent in cement composites. The test variables were the length and mass fraction of kenaf CMFs. Two types of CMFs, approximately 400 μ m and 5 mm long respectively, were prepared by pulverizing kenaf strand fibers. The amount of CMFs varied, at 0, 0.3, 0.6, 1, 2, and 3% of the cement by weight. The internal curing of cement composites was assessed by autogenous shrinkage and internal relative humidity tests. The internal curing effects were also examined by compressive strength testing and microstructural analyses, including thermogravimetry and microscopy. Regardless of the CMF type, the use of a higher CMF ratio caused a 12∼63% reduction in autogenous shrinkage and a 3∼30% increase in relative humidity. Of the two CMF types, the shorter CMFs were more effective in reducing autogenous shrinkage due to their better dispersion and restraining effect. In contrast, a better compensation for relative humidity resulted from the longer CMFs. Both types of CMFs were effective for internal curing, considering that the mixtures with CMFs generally exhibited a good correlation between rate of addition and increases in internal relative humidity and related reductions in autogenous shrinkage.