Adsorption Mechanism of Polycarboxylate-Based Superplasticizer in CFBC Ash-Portland Cement Paste

宋远明¹，GUO Chuanchuan¹，QIAN Jueshi²，LIU Yiquan³，CAO Aizhi¹

1. School of Environmental and Materials Engineering, Yantai University2. School of Materials Science and Engineering, Chongqing University3. School of Civil and Environmental Engineering, Nanyang Technological University

摘 要：Circulating fluidized bed combustion（CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of "invalid adsorption site" of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion（PCC） fl y ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fl uidity of CFBC ash-Portland cement paste is lower than that of the PCC fl y ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor fl owability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.

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