MECHANICAL PROPERTIES OF LOW-CARBON CONCRETE USING FLY ASH AND BLAST-FURNACE SLAG IN LOW WATER-CEMENTITIOUS MATERIAL RATIO

Abstract

Recently, it is necessary to reduce CO₂ emissions in terms of environmental impact reduction. Concrete generates extremely large environmental impact. In material manufacturing, cement is a material that especially emits the largest amount of CO₂ among other materials of concrete. An effective means of reducing CO₂ is considered to replace a part of ordinary portland cement with fly ash and blast-furnace slag. However, concrete of high replacing rate of the admixture is considered to decrease strength development of concrete at an early age and increase autogenous shrinkage of concrete. Therefore, it is realistic for reducing CO₂ emissions to use versatile cement with relatively-low replacing rate of the admixture. In this study, low-carbon concrete using fly ash and blast-furnace slag for low water-cementitous material ratio（W/B＝0.30）have been measured on compressive strength, pore size distribution, autogenous shrinkage and resitance to shrinkage cracking. In addition, the effect of the reduction of CO₂ emissions in comparison to difference of the water-cementitous material ratio（W/B＝0.30 and 0.40）is verified. From the abovementioned test results, regardless of curing condition and the combination of the admixture replacing ratio, the compressive strength of concrete at the age of 91 days obtains the same performance of concrete without the admixture. Also, the effect of the reduction of CO₂ emissions is almost the same regardless of the water-cementitous material ratio. Furthermore, the concrete manufacturing of low environmental impact is the range of an appropriate water-cementitous material ratio.