XIAO Jie, LIU Jing, XIANG Jia-jun, LIU Zhao-hui, LIU Cai-zhuang, RONG Ya-peng, LIU Zhi-yong, CHANG Jin, ZHANG Hong-ri, HE Jian-gang
A response surface model based on response surface methodology (RSM) was established to investigate the feasibility of using fluidized industrial-solid-waste solidified loess in roadbed engineering. Granulated blast furnace slag powder (GBFS), circulating fluidized bed desulphurization fly ash (CFBFA), and flue gas desulphurization gypsum (FGD) were used as the influencing factors, and the 7 and 28 d unconfined compressive strengths (UCS) of specimens were used as the response values. This study examined the influence of various solid waste materials on the strength of fluidized solidified loess when 10% ordinary Portland cement (OPC) was incorporated into the curing agent. The mixing ratio of the curing agent was optimized, and the hydration mechanism of the strength formation was analyzed using X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis-derivative thermogravimetry, and scanning electron microscopy. The results show that with an increase in the amount of GBFS and a decrease in the amount of CFBFA, the UCS at 7 and 28 d increases significantly, and the interaction between GBFS and CFBFA significantly influences the UCS. With an increase in the FGD dosage, the 7 d UCS first increases and then decreases, whereas the 28 d UCS decreases. The effect of the interaction between FGD and GBFS on the UCS changes from significant to nonsignificant as the curing age increases from 7 to 28 d, whereas the interaction with CFBFA has the opposite effect. On the basis of the optimal ratio determined using RSM, the strength requirements and raw material costs were considered. At a binder-soil ratio of 0.15 and a water-solid ratio of 0.51, the recommended dosages of GBFS, CFBFA, and FGD are 43%-50%, 25%-32%, and 8%-15%, respectively. At the beginning of the reaction, OH- released via OPC hydrolysis and Ca2+ and SO42- dissolved from FGD can stimulate volcanic ash activities on the surfaces of GBFS and CFBFA. This promotes the formation of ettringite (AFt) and calcium silicate (aluminum) acid (C—S—(A)—H), which binds loess particles and fills interparticle pores, increasing the 7 d UCS of the test specimens. In the later stage of the reaction, GBFS and CFBFA continue to dissolve Ca2+, [SiO4]4-, and [AlO4]5- to undergo volcanic ash reactions, generating additional C—S—H to fill structural pores and cracks and further increasing the 28 d UCS of the specimen. In practical engineering applications, fluidized solidified loess prepared by adjusting the ratio of curing-agent raw materials or binder-soil ratio can fully satisfy the strength requirements of general abutments, culvert backfills, and general highway subgrades.