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Properties and characterization of green one-part geopolymer activated by composite activators

Ma, Cong, Zhao, Bin, Guo, Shenglai, Long, Guangcheng, Xie, Youjun
Journal of cleaner production 2019 v.220 pp. 188-199
alkalinity, calcite, calcium carbonate, cement, compression strength, environmental impact, heat, polymers, porosity, sodium carbonate
One-part geopolymer similar to conventional Portland cement by just adding water is a new type of green cementitious material. Na2SiO3-anhydrous is an excellent powder activator for preparing one-part geopolymer, but its CO2-e emission and alkalinity are very high. In this study, the Na2CO3 was used to replace a portion of Na2SiO3-anhydrous, and the properties of one-part geopolymer with composite activators were investigated systematically. The possible influencing mechanism of the complex use of activators in one-part geopolymer was proposed. Test results indicate that the replacement level of Na2CO3 has slight impact on the fluidity and increases the final setting time significantly. This is directly related to the initial heat release rate and the type of network structures formed. The compressive strength decreases with increasing the Na2CO3 content. On the one hand, the quantity of gelatinous products reduces and calcite is produced as the new phase after replacing Na2SiO3-anhydrous by Na2CO3. On the other hand, the gathering of calcite and low-crystalline CaCO3 in some regions leads to the generation of many large micro-cracks, which explains the change in the porosity of the unfavorable pores. Judged from the cost per MPa and total CO2-e emission for a cubic meter of cementitious materials, one-part geopolymer activated by composite activators is cleaner than that activated by single Na2SiO3-anhydrous or Na2CO3. This study provides a guidance for preparing one-part geopolymer with lower alkalinity and potential environmental impact.