Strength properties and mechanism of phosphate-modified high alumina cement
Conventional Portland cement in CCUS(carbon capture,utilization and storage)environment has poor CO2 corro-sion resistance,which cannot meet the long-term safe storage requirements.Phosphate-modified high-alumina cement can improve the strength degradation problem of high-alumina cement,and the cement stone has high CO2 corrosion resistance.The compressive strength of the cement stone was evaluated after the addition of various types and quantities of phosphate compounds,and the influence of phosphate type and dosage on the compressive strength was analyzed.The strength mecha-nism of modified cement was revealed by combining the characteristics of mineral composition,microstructure and pore struc-ture.It is shown that the inherent properties of phosphate compounds have a substantial impact on high alumina cement.So-dium Hexametaphosphate(SHMP)is selected as the modifier material of high alumina cement,which significantly improves the compressive strength of the cement without any decline in strength during the later stages.Within the same curing period,as the dosage of SHMP increases,the compressive strength of the sodium hexametaphosphate chemically bonded(CAP)ma-terial initially rises,then declines,and eventually stabilizes.The maximum compressive strength is achieved at a SHMP dos-age of 3%.When the SHMP dosage reaches 3%,a small amount of C-A-P-H gel forms,adhering to the crystallized calcium aluminate hydrate,filling the gaps between cement particles,and forming a mesh-like structure within the cement matrix.This mesh structure strengthens the later-stage development of strength.Furthermore,SHMP inhibits the formation of calcium aluminate hydrate or converts it into C-A-P-H gel.Consequently,an increase in SHMP dosage leads to a decrease in the generation of calcium aluminate hydrate while promoting the formation of C-A-P-H gel.
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