Use of CFB bed ash and recycled aggregates in making non-portland cement concrete

• Main Authors: Ting-chun Shaw, 蕭定群
• Other Authors: Wei-hsing Huang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/56938715314952006442

碩士 === 國立中央大學 === 土木工程研究所 === 98 === Circulating Fluidized Bed boiler (CFB) bed ash is the by-product of the CFB desulfurization process, and has been proved to be a potential material for replacement of portland cement as a cementitious material. In this study, CFB bed ash was used as an alkali substances to activate the pozzolanic reaction of blast furnace slag such that the activated slag can be used as cementitious materials in making concrete. Mortar specimens made with various proportions of CFB bed ash and slag were tested for their compressive strength, volume stability and durability. Also, recycled concrete aggregate (RCA) and industrial waste slag sand were evaluated to replace natural coarse and fine aggregates, respectively, for the possibility of producing a non-portland cement concrete. Test results indicate that the combination of 20% CFB ash and 80% slag produces adequate compressive strength satisfying the ASTM C 150 requirements on strength of Portland cement. On the other hand, it is suggested that the amount of CFB used be less than 20%, so as to avoid generating over-expansion due to the high content of SO3 in CFB bed ash. In addition, it was found that the incorporation of CFB ash helps reducing the shrinkage resulting from the high amount of slag as cementing material. And the combination exhibits excellent sulfate-resisting capability also. Concrete mixes proportioned using 25% electric-arc furnace slag in replacement of fine aggregates showed increases in compressive strength, while the use of 50% RCA in replacement of natural coarse aggregate showed reduced compressive strength. The shortcoming of using CFB ash in activating slag as cementitious material is that it caused delayed setting time. Various chemical admixtures were tested for improving the setting time of the mixes in question. It was found that, at an appropriate amount, the use of alkali activator would speed up the setting time of slag-CFB bed ash cementing system. To conclude, the combination of slag-CFB bed ash along with recycled aggregates shows great potential of non-portland cement green concrete.