Effect Of Mineral Admixture On The Compatibility Between Alite-Sulphoaluminate Cement And Superplasticizers

This paper studied about adsorption characteristics of polynaphthalene sulfonatesuperplasticizer （FDN） or aminosulfonic acid-based superplasticizer （AS） on the surface ofcalcium sulphoaluminate, the hydration mixture and alite-sulphoaluminate cement. This paperalso studied about the influence of mineral composition and mineral admixture on adsorptioncharacteristics of superplasticizers, using the laboratory and the commercial madealite-sulphoaluminate cement. Water demand of normal consistency, fluidity and fluidity-loss,hydration properties, setting time and compressive strength of cement with the addition ofFDN or AS were detected. Effect of slag or fly ash on the compatibility betweenalite-sulphoaluminate cement and superplasticizers were also investigated.The results showed that the adsorption amount of superplasticizers on different hydrationsystems were detected by ultraviolet-visible absorption spectrometry. The adsorption amountand maximum adsorbed amount of FDN or AS on the hydration mixture in the hydratedsystem was more than theC4_A3S mineral with the same adsorption time, and these two kindsof hydration systems had much stronger adsorptive capacity than C₃S and C2S. With certainC₃S amount, as the amount ofC4_A3S increased, the adsorption amount and maximumadsorption amount of FDN or AS on cement increased observably, and the maximumadsorption amount was1.2to2.5times of Portland cement. The adsorption amount andmaximum adsorption amount of FDN or AS on slag and fly ash were smaller, and fly ash hadmuch stronger adsorptive capacity than slag. With the addition of mineral admixture intocement, as the amount of mineral admixture increased, the adsorption amount and maximumadsorption amount of superplasticizers on cement decreased.The content ofC4_A3S mineral had observable influence on the workability of cement.With the amount ofC4_A3S increased, water demand of normal consistency and waterreducing ratio of cement increased, the initial fluidity of cement paste was similar, but thefluidity-loss decreased faster. The compatibility between cement and superplasticizers couldbe improved by using mineral admixture. The influence of slag was better than fly ash, andthe more slag were added, the less fluidity-loss decreased. The maximum adsorption amount of FDN or AS and fluidity corresponding of cement paste showed an inverse relation.With the addition of superplasticizer into cement, the disperse state of cement particlesand hydration products improved obviously, and the formation of early hydration productsdelayed. After24h hydration, the inhibition of the superplasticizer disappeared gradually, andthe hydration products increased. Moreover, AFt and the hydration calcium silicate matchedbetter. There was obviously improved densification of hydrated cement pastes’ microstructure.With the addition of mineral admixture, the amount of early hydration products decreased,and thus the hydration rate of heat and the heat release quantity decreased.As for pure alite-sulphoaluminate cement, with the increased amount ofC4_A3S, thesetting time was shorter, the early compressive strength was higher, but the development ofthe later compressive strength was slow. With the addition of FDN or AS into cement, thesetting time was extended, but the strength of every age increased. The influence of AS on thestrength of cement was better than FDN.With the addition of slag into cement, the initial and final setting time were extended, asthe content of slag increased,3d’s compressive strength decreased obviously. The decreasedrange of7d’s and28d’s strength was smaller. With the increased amount ofC4_A3S, thestrength of every age improved obviously. As the content of fly ash increased, the initial andfinal setting time delayed, and the strength of every age decreased. When the content of flyash was40%, the early strength decreased dramatically. However, the strength of every ageincreased observably by using FDN or AS, especially for the early days, the influence of ASwas better than FDN, and that of slag was better than fly ash.With the addition of both fly ash and slag into cement, the dominant complementationeffect could be developed. When the addition ratio of slag and fly ash was3:1, the strength ofcement was similar as cement with the addition of only slag, which was much higher thancement with the addition of only fly ash. The increased influence of AS on composite systemwas also observable.