Effects of Fly Ash Contents on Durability Properties of No-Cement Eco-Binder Concrete

• Main Authors: Chih-Yang Chen, 陳致仰
• Other Authors: Ta-Peng Chang
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/96769396384515982607

碩士 === 國立臺灣科技大學 === 營建工程系 === 104 === The cementitious material of the No-Cement Eco-Binder Concrete is composed of three powders, circulating fluidized bed combustion (CFBC) fly ash, ground granulate blast furnace (GGBF) slag and Class F fly ash. This research addressed the effects of various amounts of Class F fly ashes on the durability property of such concrete. The compositions of CFBC ash, anhydrous gypsum and lime, react with water to produce ettringite (Aft) and calcium silicate hydrate (C-S-H) gel to provide the concrete strength, but excessive amount will produce expansion resulting in unstable concrete volume and the reduction of the durability of concrete. This study used a fixed water-cementitious material (w/cm) ratio of 0.3, and five proportions of fly ash with (0%, 10%, 20%, 30%, 50%), and two proportions of CFBC ash (15%, 25%) to replace the slag powder to make the concrete, from which the engineering properties of fresh, hardened, and durability were studied to investigate the resulting effects due to the addition of various amounts of fly ash. The results of study show that: (1) Fresh properties. When the amount of replacement of fly ash increases from 0 to 20%, the values of slump and slump flow increase by the ranges from 1.85% to 3.7% and from 2.8% to 22.4%. When the replacement ratio increases to 30% and 50%, the values of slump and slump flow decrease by the ranges from 8% to 10.2% and from 27.4% to 28.9%. The optimal value of fly ash replacement to have good workability is from 10% to 20%. (2) Engineering properties. At fixed amount of 15% of CFBC ash together with the increase of fly ash from 0% to 50%, the compressive strengths of 28 days and 56 days reduced by 7.04% to 4.77%. When the replacement amount of fly ash from 0% to 30%, the ultrasonic pulse velocities of 28 days and 56 days decreased by 0.3% to 1.34%. The ultrasonic pulse velocity with 50% of fly ash lower was lower than that of 0% by 0.01%. The coefficient of thermal conductivities at 28 days and 56 days increased by 20.1% and 10.7% when the increase of fly ash from 0% to 50%. (3) Durability properties. The rapid chloride tests result show that, at age of 56 days with 10% and 20% of fly ash additions, the amount of charge decreased by 34.3% and 31.4%, respectively. When the addition of fly ash increased to 30% and 50%, the amount of charge increased by 42 % and 169%, respectively. At the fixed amount of 15% of CFBC ash with the amount of fly ash replacement from 0% to 50%, the amount of electrical resistivity of 28 days and 56 days increased by 3.52% and 17.2%. When the amount of fly ash increased and under curing pressure for 48 and 72 hours, the carbonation depth increased by 200%~282.6%. Two mixtures with the lowest and second lowest corrosions were (a) 25% replacement of CFBC ash and (b) 15% replacement of CFBC ash and 20% replacement of fly ash, respectively, having the values of only 8.4% and 11.9% of those of the OPC.