Expermental Research Of Auxiliary Plastic Effect Of Concrete Retarder

Concrete superplasticizer and retarder are often compounded to use. In compounded additives, the action of retarder is mainly to prevent the hydration of cement, leading to longer setting time of concrete and reducing slump loss of concrete. Besides these fuctions, the author points out that under the stimulation of superplasticizer small molecule retarters with little water-reducing effect or no water-reducing effect has obvious auxiliary plasticizing effect. In the meantime the compatibility of three element system of cement-superplasticizer-retarder is exsited.By adopting the cement paste experiments based on the standard GB50119—2003, the compatibility of three element system of cement-superplasticizer-retarder and the auxiliary plasticizing effect of retarter were systematically investigated, which included two types of superplasticizer such as sulphnated formaldehyde condensate and sodium-sulfanilate-phenol formaldehyde condensate, and four types of retarter such as sodium tripolyphosphate, sodium gluconateby ,citric acid and white sugar. The obtained results showed that when the dosage of superplasticizer was low or the compatibility of superplasticizer with cement used was bad , the auxiliary plasticizing effect of retarter was more. Among the four types of retarter, the compatibility of sodium gluconate with two element system of cement-superplasticizer was best, and its auxiliary plasticizing effect was also most obvious.Based on the standard GB/T8076-1997, the auxiliary water-reducing rates of sodium tripolyphosphate, sodium gluconate and calcium lignosulphnate compounded with naphthalence-based and ammonia-based superplasticizer, were investigated. The results showed that for cement-retarder system the water-reducing rates of sodium tripolyphosphate and sodium gluconate were much less while that of calciumlignosulphnate was about 8%. but when being compouned with superplasticizer, the auxiliary water-reducing rate of sodium tripolyphosphate was about 7%~9%, slightly less than that of calcium lignosulphnate under the same condition;the auxiliary water-reducing rate of sodium gluconate was about 8%~11%, slightly more than that of calcium lignosulphnate.By adopting the cement paste experiments, the influence of types of gypsum on the auxiliary plasticizing effect of retarder was investigated. The obtained results showed that for anhydrite used, the auxiliary plasticizing effect of retarder was obvious;whatever types of gypsum used as to setting time adjusting agent of cement, the auxiliary plasticizing effect of sodium gluconate was best obvious.