Strength Concrete Shrinkage Cracking

Shrinkage cracking is a critical problem in concrete construction. In recent years, various mineral admixtures such as fly ash, blast furnace slag, silica fume along with superplasticizers have been used to produce concrete with high strength and durability. But no systematic study has been done on volume stability of high-strength concrete (HSC) and the cracking problems become more serious in engineering practice. So it very important to research on shrinkage cracking of HSC.The paper presents a systematic study on characteristics and influencing factors of HSC. The result shows that the tests, which are used in this paper, including ring test and free shrinkage test, could do well in evaluating the shrinkage-cracking potential of HSC. USC is more sensitive to shrinkage cracking than normal concrete. The combined effects of higher free shrinkage lower specific creep and higher modulus of elasticity resulted in early cracking for USC. The paper presents an analytic model of factors that influence shrinkage tracking of USC.The influence of water binder ratio (w/b) and mineral admixtures on the shrinkage cracking of HSC are investigated, The smaller the w/b, the more serious the shrinkage cracking. Incorporating with fly ash could reduce the tendency of shrinkage cracking of HSC, due to reducing the free shrinkage effectively, and the opposite trend is found when silica fume is added to concrete. Fine blast furnace slag powder could increase the shrinkage potential of USC, although it could not increase the free shrinkage of concrete obviously.Several measures are tested for reducing the shrinkage cracking potential of HSC. It was found that polypropylene fiber could not prevent the crack opening due to its lower modulus of elasticity. Steel fiber could reduce the shrinkage cracking obviously because of its higher modulus of elasticity ~nd binder strength. The expansive agent UEA-H could compensate shrinkage remarkably, so it could reduce the tendency of shrinkage cracking significantly. USC with shrinkage reducing admixture (SRA) have lower tendency ef shrinkage cracking due to its lower free shrinkage.