Influence of Polyepoxysuccinic Acid on Solid Phase Products in Portland Cement Pastes

The influence of polyepoxysuccinic acid（PESA）on the solid phase products in hydrated Portland cement pastes was investigated by isothermal calorimetry,X-ray diffraction（XRD）,^29Si and ^27Al nuclear magnetic resonance（NMR）.The results indicated that PESA bonds Ca^2＋ions in pore solution to prevent portlandite formation,and also combines with Ca^2＋ions on the surface of silicate minerals to prolong the control time of phase boundary reaction process,leading to the retardation of silicate mineral hydration.Meanwhile,the interlayer Ca^2＋ions in Jennite-like structure bridging PESA and C-S-H gels prevent silicate tetrahedron and aluminum tetrahedron from occupying the sites of bridging silicate tetrahedron,which causes the main existence of dimer in C-S-H structure,deceases the degree of Al^3＋substituting for Si^4＋and promotes the transformation from 4-coordination aluminum to 6-coordination aluminum.Furthermore,the-Ca^＋chelating group from reacting PESA with Ca^2＋ions combines easily with SO4^2-ions,resulting in transformation from ettringite,AFm to TAH（Third aluminum hydrate）.However,with the higher addition of PESA,it will bridge the excess PESA by Ca^2＋ions to form a new chelate with ladder-shaped double chains structure,which not only reduces the amount of PESA bonding Ca^2＋ions,but also decreases its solidifying capability for SO4^2-ions,leading to the transformation from TAH to AFm or ettringite.Meanwhile,at later hydration,the inhibition effect of PESA on cement hydration is weakened,and the transformation degree from TAH to AFm is higher than that to AFt with the addition of PESA.