Effect of mix design on restrained shrinkage of concrete

Abstract

The impetus for this research came from a project that involved the reconstruction of Twelve bridge decks in Tabriz, East Azerbaijan, IRAN that was completed in the summer of 2009. Shortly after construction was completed, shrinkage cracks were observed on 8 of the 12 bridge decks. Such cracking can cause long term durability problems by facilitating chemical ingress and moisture penetration that may aggravate problems such as alkali-silica reaction and corrosion of the reinforcing steel [1]. Shrinkage cracks can also increase deterioration caused by cyclic loadings. Any of these problems can decrease the service life of a bridge deck [1]. The mixture used in the bridge decks had a w/c+p ratio of 0.33 and contained 26.2% fly ash (Class F). Although the mixture was not intended to be a high performance concrete (HPC) mixture, it did have characteristics similar to HPC mixtures. As the use of HPC becomes more common, studies on the effect of pozzolanic materials and the ability of admixtures to reduce concrete shrinkage are needed to ensure durability of the structures. This paper presents results from an experimental study conducted to determine how certain mixture proportion parameters influence concrete shrinkage. In particular, the free shrinkage of concrete mixtures with varying amounts of fly ash, shrinkage reducing admixture (SRA), expansive cement, and fibers were studied.