Effect of pre-wetted lightweight aggregates on residual stress development and stress relaxation in restrained concrete ring specimens

Abstract

With the continuous progress of concrete technology, concrete with the low water-to-cement (w/c) ratio is utilized extensively. Concrete suffers significant shrinkage due to the high self-desiccation at early age. When shrinkage of concrete is hindered by the restraint, the tensile stress will develop and cause the generation of cracks. For reducing the shrinkage, internal curing (IC) has been employed in concrete by introducing the additional water which can be preserved in pre-wetted lightweight aggregates (LWAs). Although a number of studies focus on the results from autogenous and drying shrinkage, the result of the effect of IC with LWAs on the performance of concrete with low w/c ratio is still limited. In present study, the investigations on the stress relaxation and time to cracking of concrete with the different proportions of pre-wetted LWAs (0%, 10%, 30%, and 50% by the volume replacement of normal weight coarse aggregates) were conducted by the restrained ring test. Results obtained from tests were shown as follows: (1) the strain of steel ring decreased with the increase of the proportion of pre-wetted LWAs; (2) the maximum residual stress of concrete mixture decreased with the increase of the proportion of pre-wetted LWAs; (3) the relaxed stress of concrete mixture decreased with the increase of the proportion of pre-wetted LWAs at the different age; (4) the stress rate of concrete mixture decreased with the increase of the proportion of pre-wetted LWAs; (5) although the concrete mixture with the 50% proportion of pre-wetted LWAs cracked at the earliest age, the time to cracking was postponed when the proportion of pre-wetted LWAs increased from 0% to 30%.