Inorganic Chemicals Industry >
Effect of phosphogypsum modified by lime-cement-fly ash on physical properties of cement
Received date: 2022-02-18
Online published: 2022-12-19
Lime，cement and fly ash were used to modify phosphogypsum，the solubility of sulfate in modified phosphogypsum was determined，and the effects of undisturbed phosphogypsum and modified phosphogypsum on the physical properties of cement were compared，and the effects of phosphogypsum on the hydration products of cement at different ages before and after modification were analyzed with X-ray diffraction（XRD） and scanning electron microscopy（SEM）.The results showed that the pH value of modified phosphogypsum gradually was increased with the increase of lime admixture，and when the lime admixture was 4%（mass fraction），the pH of phosphogypsum was 12.22，the soluble phosphorus and fluorine in phosphogypsum were transformed into insoluble phosphorous salts and calcium fluoride.With the increase of cement and fly ash content，the solubility of modified phosphogypsum was decreased.When the lime content was 4%，the cement content was 10%，and the fly ash content was 10%，the mass concentration of sulfate radical in the filtrate obtained by soaking the modified phosphogypsum in water for 8 hours after 7 d of curing was 0.30 g/L，which was 81.8% lower than the mass concentration of sulfate radical in the filtrate obtained by soaking the unmodified phosphogypsum in water for 8 hours.Compared with the cement paste with unmodified phosphogypsum，the water cement mass ratio of the cement paste with modified phosphogypsum was reduced from 0.41 to 0.38，the initial setting time and final setting time were shortened by 34.6% and 27.2% respectively，and the 28 d compressive strength was increased by 21.1%.After the modification of phosphogypsum with lime，cement and fly ash，the generated hydraulic products such as hydrated calcium silicate and ettringite were wrapped on the surface of gypsum particles，which reduced the dissolution rate of sulfate in water，reduced the impact on tricalcium aluminate in cement，and made the internal structure of hardened body become dense，and the mechanical properties were significantly improved.
Key words： phosphogypsum; modification treatment; dissolution rate; cement; physical property
Bin GUI , Hong CHEN , Lin YANG , Hongjie WANG , Jianxin CAO . Effect of phosphogypsum modified by lime-cement-fly ash on physical properties of cement[J]. Inorganic Chemicals Industry, 2022 , 54(12) : 92 -98 . DOI: 10.19964/j.issn.1006-4990.2022-0064
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