Development of Cost-Effective Self-Consolidating Concrete Incorporating Fly Ash, Slag Cement, or Viscosity-Modifying Admixtures

摘要

Self-consolidating concrete (SCC) in the fresh state is known for its excellent deformability, high resistance to segregation, and use, without applying vibration, in congested reinforced concrete structures characterized by difficult casting conditions. Such a concrete can be obtained by incorporating either mineral admixtures such as fly ash (FA) and slag cement or viscosity-modifying admixtures (VMAs). The use of VMAs has proved very effective in stabilizing the rheology of SCC. Commercial VMA currently available in the market is costly and increases the price of such a concrete. Research to produce an economical SCC with desired properties was conducted over the last few years with the use of mineral admixtures or use and development of a cost-effective VMA. This paper presents the comparative performance of SCCs manufactured with FA, slag cement, and various VMAs based on fresh and mechanical properties and also on cost. Twenty-one concrete mixtures were investigated. FA SCC mixtures had cement replacement of 40, 50, and 60%, while slag cement SCC mixtures had 50, 60, and 70% replacement. The water-cementitious material ratios (w/cm) ranged from 0.35 to 0.45. Three different VMAs including Welan gum (WM), a commercial one named COM, and a new saccharide-based VMA named A were used in VMA SCC mixtures with w/cm of 0.45. Tests were carried out on all mixtures to obtain fresh properties such as viscosity and stability as well as mechanical properties such as compressive strength. The influence of percentages of FA or slag cement, w/cm, dosage of high-range water-reducing admixture, dosages of air-entraining agent, and types of VMA on the properties of SCC were critically reviewed. The results showed that an economical SCC with desired properties could be successfully developed by incorporating FA, slag cement, or VMA. Three different economical mixtures were identified from FA, slag cement, and VMA-based SCC satisfying the targeted strength of 35 MPa. These mixtures included FA with 50% replacement, slag cement with 60% replacement, and a mixture with new VMA A with a w/cm of 0.45. It was found that these SCC could replace the control concrete and could be more economical (30 to 40% in case of FA and slag cement). The new VMA A was found to develop a SCC with better fresh and hardened properties and at significantly lower cost compared with its commercial counter parts―COM and WM. Although the VMA SCC with new A-VMA was slightly costlier than those with FA and slag cement, it was more resistant to segregation and had higher early strength development.