The Development And Property Of Compound Shrinkage Reducing Admixture For Concrete

The shrinkage cracking of concrete is an important problem in the academic and engineer circles. With the development of modern concrete technology, the use of high strength concrete with low water-to-cement (w/c) ratio has been observed to undergo significant shrinkage cracking in recent years. The early age cracks which is a critical problem in terms of durability is more vulnerable to happen. The presence of cracks creates a free path for deleterious substances that may lead to premature deterioration and the reduction of the structure service life. Because of the durability problem of concrete, a large number of construction projects can’t be used, cause huge economic losses. Restrained shrinkage can be a cause of cracking in concrete. If the tensile strength is lower than the stress level caused by restrained to movement, in particular at early ages, shrinkage cracks occurs. There are many kinds of methods to reduce and control shrinkage cracking of concrete. One solution to reduce the potential for shrinkage cracking is to incorporate a Shrinkage Reducing Admixture (SRA) in concrete mixtures. Shrinkage Reducing Admixtures are being increasingly used in concrete construction. SRA, composed by surfactants, work by reducing the surface tension of the pore fluid which in turn reduces the capillary stress developed and the shrinkage of concrete. In this paper, a compound shrinkage reducing admixture is developed to reduce early age shrinkage of concrete. The physical properties of SRA and the influence of SRA on cement-based materials have been studied for giving more reliable experimental data and theoretical reference for future engineering application.In this paper, with the consideration of chemical structure and function mechanism, a high performance and low cost compound shrinkage reducing admixture, based on combination principle of surfactant, was developed. The physical properties of SRA also have been studied.The microstructure of the cement paste was determined by Scanning Electron Microscopy (SEM), and the effects of SRA on the microstructure of cement hydration production products were studied. Results show that paste containing SRA shows a delayed hydration. Working performance and mechanical properties of mortar or concrete with or without SRA were studied, results show that SRA has a certain negative effect on the mechanical properties of cement-based materials. The effect of SRA on the shrinkage and cracking behaviors of cement based materials have been studied through the concrete cracking experiment, early age and long age shrinkage experiment of concrete and mortar. Results show that SRA effectively reduces the shrinkage of cement based materials, and resulted in a significant decrease in restrained shrinkage cracking of concrete. The appearance time of exothermic peak can be delayed, and the peak value as well as the hydration heat of cement can be lowered by adding the SRA. The cement hydrate reaction with SRA is steady and SRA reduces the risk of temperature shrinkage cracking. When the mix content of SRA is1.7%, SRA can reduce the shrinkage of mortar by up to80%at3d and50%at28d, the24h shrinkage of concrete by up to55%. We also find that SRA has good compatibility with superplasticizer.