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<p>The composite cementitious system of phosphogypsum (PG) and ground granulated blast furnace slag (GGBS) (CSPS) is a ternary combination system composed of PG, GGBS and alkaline activators. Its strength comes from the combined activation of GGBS by PG and alkaline activators, resulting in the formation of a large amount of calcium (alumino) silicate hydrate (C-(A)-S-H) gel and ettringite (AFt). This study aims to investigate the differences in the strength development of the curing agent pastes and solidified sludge soils when using ordinary Portland cement (OPC) or quicklime as alkaline activator in CSPS. The mechanical properties and the underlying microscopic mechanisms are investigated by unconfined compressive strength (UCS) tests, pH and electrical conductivity (EC) evaluation, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) tests. The test results indicate that OPC demonstrates more pronounced strength enhancement while quicklime helps to establish a highly alkaline environment, facilitating the processes of chemical reactions and hardening in curing agent pastes. The curing agent consisting of PG, GGBS and OPC (PSC) is significantly affected by the initial water content and pH of sludge, &#xa0;whereas the curing agent consisting of PG, GGBS and quicklime (PSL) shows better solidification effect on the sludge with high water content and exhibits greater engineering applicability. Besides, there are a large number of overlapping pores and unreacted PG in PSC-solidified soil, while PSL-solidified soil exhibits a high density, with a significant amount of C-(A)-S-H gel and AFt filling the pores and strengthening the interparticle bonding strength. Therefore, compared to OPC, the strong alkaline environment provided by quicklime more effectively promotes pozzolanic and hydration reactions when solidifying high water content sludge with CSPS, supplying sufficient C-(A)-S-H gel and AFt to fill the pores and bond the particles in solidified sludge soil.</p>

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Effect of alkaline activators on sludge solidification by composite cementitious system of phosphogypsum and slag

  • 期刊论文

  • 发表日期：

    2026年2月25日

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  • Shuang Han,
  • Yunzhi Tan,
  • Xianqiao Wu,
  • De’an Sun,
  • Jun Wu,
  • Hui Li

摘要

The composite cementitious system of phosphogypsum (PG) and ground granulated blast furnace slag (GGBS) (CSPS) is a ternary combination system composed of PG, GGBS and alkaline activators. Its strength comes from the combined activation of GGBS by PG and alkaline activators, resulting in the formation of a large amount of calcium (alumino) silicate hydrate (C-(A)-S-H) gel and ettringite (AFt). This study aims to investigate the differences in the strength development of the curing agent pastes and solidified sludge soils when using ordinary Portland cement (OPC) or quicklime as alkaline activator in CSPS. The mechanical properties and the underlying microscopic mechanisms are investigated by unconfined compressive strength (UCS) tests, pH and electrical conductivity (EC) evaluation, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) tests. The test results indicate that OPC demonstrates more pronounced strength enhancement while quicklime helps to establish a highly alkaline environment, facilitating the processes of chemical reactions and hardening in curing agent pastes. The curing agent consisting of PG, GGBS and OPC (PSC) is significantly affected by the initial water content and pH of sludge,  whereas the curing agent consisting of PG, GGBS and quicklime (PSL) shows better solidification effect on the sludge with high water content and exhibits greater engineering applicability. Besides, there are a large number of overlapping pores and unreacted PG in PSC-solidified soil, while PSL-solidified soil exhibits a high density, with a significant amount of C-(A)-S-H gel and AFt filling the pores and strengthening the interparticle bonding strength. Therefore, compared to OPC, the strong alkaline environment provided by quicklime more effectively promotes pozzolanic and hydration reactions when solidifying high water content sludge with CSPS, supplying sufficient C-(A)-S-H gel and AFt to fill the pores and bond the particles in solidified sludge soil.