Comparison of non-contact autogenous shrinkage measurements and the stress ratio of capillary stress to compressive strength

摘要

The measurement of autogenous shrinkage is a very important and fundamental step before conducting any autogenous shrinkage related research. This study investigates two non-contact autogenous measurement methods using eddy current sensor: non-contact corrugated tube method (CTM) and non-contact vertical prism method (VPM). Comparisons are made between them in terms of starting time, restraint condition, experimental operation and experimental results. In CTM measurement, the effective autogenous shrinkage is defined as the stage after the expansion stage. The corrugated tube would have a restraint effect on free deformation of cement paste inside if the axial stiffness of tube is not small enough compared to its radial stiffness. As for VPM, experimental operations are much simpler and no size effect is found so that effective studies among specimens with different sizes are allowed in this method. Meanwhile, the calculation of capillary stress is introduced and a power function correlation between capillary stress and autogenous shrinkage is found. The stress ratio (SR) of capillary stress to compressive strength is firstly proposed to analyze the tendency of autogenous shrinkage. Cement paste with lower W/C has a greater stress ratio. The evolution of SR reflects the competition between the growth of self-desiccation induced stress and the growth of pore structure strength gain. (C) 2019 Elsevier Ltd. All rights reserved.