Effects And Mechanisms Of Retarders And Superplasticizers On The Fluidity And Strength Of The Sulphoaluminate Cement Pastes

Both retarder and superplasticizer used in the cement pastes is one of the methods to improve the fluidity and reduce the fluidity loss. Because of the serious fluidity loss and shouter setting time of sulphoaluminate cement, two kinds of retarders such as citric acid(CA) and sodium gluconate(SG) were respectively added into the cement pastes or mortar containing β-naphthalenelfonic acid-based superplasticizer(BNS), aminosulfonic acid-based superplasticizer(AS) and polycarboxylate acid-based superplasticizer(PC) to study the effects of retarder on the fluidity, setting time and the strength.The results showed that the fluidity of cement pastes increased with increasing the dosage of superplasticizer; the fluidity improved, the fluidity loss reduced and the effects of sodium gluconate was better when the two kinds of retarders admixture is within 0.03% ~ 0.15%. Furthermore, when the dosage of retarder was increased, the longer the setting time and the lower the strength. Ultraviolet spectrophotometry, zeta potential, X-ray diffraction analysis(XRD) and scanning electron microcopy analysis(SEM) were used to analyze via the examinations of the adsorption properties, electrokinetic properties, intensity peaks and microstructure of the ettringite. The results indicated as follows:(1) as the superplasticizers increased and the hydration time extended, the adsorption quantity of the superplasticizers were also increased.(2) The electrokinetic properties were in good agreement with the fluidity of the cement pastes.(3) The results of XRD show that the ettringite in the paste was decreased when CA or SG was added into the cement with three superplasticizers.(4) The results of SEM show that the adding of three superplasticizers make the hydration products of ettringite was acicular structure at 7d. when two retarder mixed into three kinds of high efficiency water reducing agent to the cement paste separately, both CA and SG inhibited the growth and the crystailization of ettringite in water slurry, and it is a columnar structure at 7d.