Free and restrained early-age shrinkage of mortar: Influence of glass fiber, cellulose ether and EVA (ethylene-vinyl acetate)

Abstract

The objective of this paper is to present a new testing method for investigating early-age (i.e. between 0 and 24 h after mixing) shrinkage of cement-based material. Whatever the free or restrained conditions, the plastic shrinkage is caused by the evaporation of water from the surface of fresh concrete. Free plastic shrinkage was investigated by optical instrumentation system. It can thus be measured the average shrinkage before and/or very early after the setting process. In addition to this value, the optical system provides a measurement of the deformation field to assess the degree of heterogeneity of shrinkage at the surface of the sample during the drying. The restrained shrinkage tests are performed using an active restrained system. The testing apparatus, based on a ring test, is presented with its own computer-controlled closed loop. This technique provides quantitative information about stress development that may be used to assess the potential for cracking in thin cement-based materials subjected to drying. As first results, the influence of the mix design (cellulose ether, EVA and glass fiber) has also been investigated: reducing of cellulose ether quantity in mix-design, modifies the kinetic and level of early-age shrinkage. The use of EVA decreases the overall shrinkage but does not reduce the heterogeneity of surface shrinkage. However we obtained with EVA, a decrease in the internal residual stress. The glass fiber reduces shrinkage and also reduces the heterogeneity of the surface shrinkage. However at a low rate of incorporation of glass fibers, no reduction of internal residual stress is obtained.