Effect of lightweight aggregate on minimizing autogenous shrinkage in Self-Consolidating Concrete

摘要

Cracking is one of the main reasons for reduction of concrete durability, as it allows for penetration of water and aggressive chemicals leading to corrosion of rebars, deterioration and structural failure. Recently, rapid new developments in the new generation of concrete reveal the need for a better assessment of shrinkage and its effect on structural performance, as well as prevention and control of shrinkage. The shrinkage test methods that are codified in Poland (Graf-Kaufman and Amsler methods) allow for measurement of shrinkage deformation after removal of the forms, i.e. after 24 hours. In case of the new generation concrete with a low w/c ratio, the autogenous shrinkage is very important in the initial period of binding and hardening of concrete (up to 24 hours from casting). This paper presents the results of autogenous shrinkage tests for mortar and concrete. The autogenous shrinkage was tested using Auto-Shrink method. The crack resistance of concrete with regard to shrinkage deformations was tested using a ring-test method according to the ASTM Standard C 1698-09. Because autogenous shrinkage cannot be controlled by exterior curing procedures, the shrinkage tests were performed with light-weight aggregates saturated with water. Use of light-weight aggregates (LWA) allows for "interior curing" based on gradual release of water from presatutated LWA balancing interior moisture content. In addition, the effect of shrinkage reducing admixture on deformations of internally cured concrete was also tested. The test results confirmed the advantage of the considered internal curing for concrete. Internal curing can be successfully applied to concrete structures with low w/c ratio.