Study On Physical Modification Of NSF Type Superplasticizer By Mixing With Polycarboxylic Type Superplasticizer

NSF type superplasticizer(NSF) is widely used in the concrete engineering at present in our country. It has high water reducing rate at low dosage whether the adaptability problem with cement and high slump loss are always the point in concrete production. For the adaptability problem, various cements or superplasticizers are test to find the best. For the control of slump loss, generally some setretarder(mainly glucide) is mixed with the superplasticizer to delay the setting time of concrete. For the methods above is bothering and difficult to control, the quality of concrete is difficult to control. So it is necessary to find out some other ways to improve the performance of NSF. Polycarboxylic type superplasticizer(PC) is a new high performance superplasticizer with very high water reducing rate at low dosage. It is of the characteristics of low slump loss, little effect on setting time and clearly effect on strength rise. But for the high cost it could not be broadly used. So the PC could be considered to mix with NSF to make up its limitation and the cost is cut down. Otherwise it is helpful for the compound technique research of PC for the future. Two kinds of PC(JS and XM) and one kinds of NSF (SPF-1) are tested in this article. The best mix proportion(two-components and three-components) and dosage is found out via cement paste test and concrete test. The effects of compound dispersants on the physical performance, shrinkage, penetrability of concrete and the microstructure(formation of gel, pore structure) of hardened cement paste are studied. The adaptability status of superplasticizers on the surface of cement particle and the effect on ZETA position are analyzed. The adaptability with various cements and UEA is also discussed. The results indicate: (1) It is effective to control slump loss when NSF is mixed with some PC, but not all kind of PC is available. The initial slump decrease with the increase of the mix proportion of PC. The rational proportion of PC/NSF is 10～30wt% (2) Some deficiency of two-components mixed dispersants could be avoid via three-components mix for increase air content or viscidity of concrete. Mix with setretarder could make compound dispersants setretarder superplasticizer which could extend initial setting time up to 20h and no negative effect on late compressive strength. (3) Compound dispersants show strong dispersion force when UEA, different blending materials(exclude SF) and cements are used in concrete. Some compound dispersants could make the late shrinkage of concrete decrease remarkably which is almost the same as standard concrete at 120d as the NSF is above 32%. The penetrability resistance grade of concrete using compound dispersants is increased by several levels than that of NSF. (4) Compared with NSF, compound dispersants without air entraining agent could change the microstructure of cement paste gel such as size reduced, surface area increased, harmless pore(<200?) increased and ultimate pore radius reduced which make the cement paste gel more even and compact. (5) The impact of compound dispersants to the ZETA position(absolute value) of cement-water dispersion system is related to the kind of PC. With the increase of the mix proportion of PC, the drop speed of the ZETA position become slower. The mechanism of compound dipersants is supposed to be explained by the theory of electrostatic repulsion, and the steric hindrance is considered to delay the drop speed of ZETA position. So the slump loss become slower. (6) For the chemosynthesis of PC is affected by a lot of factors, its configuration varies a lot. Compound dipersants mixed with XM shows the better performance which is almost the same as PC(exclude compressive strength). There are still some problems with the compound dispersants mixed with JS. (7) There is big advantage in using cost of compound dispersants so its future in market is great.