Analytical models for prediction of plastic cracking in very early-age concrete slab

Abstract

This thesis reviews the cause of plastic cracking, proposes analytical models for prediction of plastic cracking in early-age concrete slab, and provides several case studies. Among plastic cracking caused by various causes, this study focuses on two most commonly occurring plastic cracks; plastic settlement cracking and plastic shrinkage cracking. Considering the fact that the settlement of fresh concrete is caused by consolidation and not sedimentation, a numerical approach based on the small strain consolidation theory is introduced for the analysis of plastic settlement in concrete slabs and the validity of the approach is verified through experiments. An experiment using a non-contact laser measurement device is performed to measure the amount of settlement due to self-weight for bulk mortar; material parameters related to the settlement of mortar are estimated based on the measurement results. It is concluded that the laser measurement system suggested in this study can be utilized as an accurate and automated method for measuring bleeding, which is identical to the settlement due to self-weight. Another experiment is then performed on rebar-embedded mortar to measure the settlement distribution by location, and the influences of mixture proportions and cover depth on differential settlement are analyzed. Through correlation studies between experimental data and settlement distributions obtained by self-weight consolidation analysis, the validity of applying the consolidation theory to the analysis of plastic settlement of mortar is verified. Since plastic shrinkage cracking is basically induced from the drying surface condition of freshly placed concrete, a precise estimation for plastic shrinkage cracking is possible with an accurate calculation of the evaporation of bleed water. Accordingly, an analytical model that can predict the occurrence of plastic shrinkage cracking in concrete slabs is introduced on the basis of the balance between the amoun...