Research On Polycarboxylic High Performance Slump Retaining Admixture

With the rapid development of infrastructure construction, the quality requirement ofcommercial concrete becomes more and more strict. The polycarboxylic high performancesuperplasticizer is widely used in the high performance concrete at present. It attached extensiveattention because of its characteristics of non-toxic, environmental protection and high waterreducing rate and it will has a widespread attention in the application but many problems comeout during the application. One of these is the slump loss while mixing with the polycarboxylicsuperplasticizer in the concrete. This problem has affected the application and development ofpolycarboxylic superplasticizer.Combining with the development of the polycarboxylic and through reasonable molecularstructure design to manufacture polycarboxylic high performance slump-retaining admixture.The materials are methyl allyl polyoxyethylene ether(TPEG), acrylic acid(AA),compoundmolecular weight modifier and modified initiator.Through the single factor analysis to explore the impact of the reaction time, the reactiontemperature, the dosage of initiator, the mole ratio of acrylic acid and methyl allylpolyoxyethylene and the dosage of themolecular weight regulator to the polycarboxylic slumpretaining admixture. Using the orthogonal design to found that the synergistic effect has greatimpact to the admixture. The order of the factors to the admixture is as follows: the mole ratio ofacrylic acid and methyl allyl polyoxyethylene＞the dosage of the molecular weight regulator＞the dosage of initiator＞the reaction temperature＞he reaction time. And get the optimizedreaction conditions: the reaction temperature is60℃, the reaction time is2h, the mole ratio ofacrylic acid and methyl allyl polyoxyethylene is2:1, the dosage of initiator is0.84%and thedosage of the molecular weight regulator is0.28%。Through the concrete slump and the loss test, compressive strength test, cement adaptabilitytest and stability test found that there is rarely slump and expansion loss after90minutes. At thesame time, the admixture has no side effect to the early strength of concrete and can increase thelater strength of concrete. Throught the concrete comparison of most cement sold in Wuhan, itshows that the admixture has optimum adaptability. Meanwhile the admixture shows no delayedcoagulation and has good storage stability. It can be widely used in projects.Using infrared spectroscopy(IR) to characterize the molecular structure of thepolycarboxylic slump retaining admixture and obtain the ideal molecular structure of theadmixture combining with the synthetic materials. Discussing the mechanism of thepolycarboxylic slump retaining admixture and concluded that space steric hindrance of thesdmixture plays a leading role.