Chemical Admixtures in Low-Carbon Cement and Concrete System

【Author】

Etsuo Sakai;Masahiro Miyauchi;Daiki Atarashi;

【Abstract】

<正>Chemical admixture is very useful for higher performance of concrete and production of high fluidity concrete and high strength concrete etc..In addtion,chemcal admixture is also improtant for the reduction of CO_2 in the cement and concrete field For recycling system of using retarder,the testing system of cement in sludge water has been proposed A part of the sludge water in which the hydration of the cement was stopped by the addition of sodium gluconate is sampled,and Mg(NO_3)2.6H_2O is added,the hydration of the cement that had been stopped is started.The rate of heat liberation of this sludge water is measured for up to about 10 hours by using of conduction calorimeter.The rate of heat liberation curves for 24 hours,or the heat liberation,is predicted using of hydration model.From this method,it is possible to evaluate the amount of cement remaining in the sludge water.In this method,even if cement is replaced with sludge solids at the ratio of 5-10%,the properties of the concrete are virtually unchanged compared with concrete with no sludge.CaF_2 was used as mineralizer.When excessive KF is added,3 times the dosage of superplasticizer are needed,in order to ensure the same fluidity as when no KF is added Regardless of the type of superplasticizer,the specific surface area of hydrated sample increases,and the amount of superplasticizer adsorbed increases by adding of KF.Ultra fine particles which may be CaF_2 in gel form are generated so the specific surface area increases and the amount of superplasticker increases.The completely different adsorption behaviour of superplasticizers onto ordinary Portland cement(OPC) and blast furnace slag(BFS) is caused by the molecular structure of superplasticizers used PC-superplasticizer with a high ratio of side chains has been slightly adsorbed onto cement,but is adsorbed onto BFS to which Ca~(2+) is adsorbed so the fluidity of high volume slag cement paste in which BFS particles are mainly dispersed is improved.By ensuring durability for a long period of time,the life of cementitious materials and the service life of structures can be extended,thus, reducing the environmental load At normal water/cement ratios,the dispersing effect is related to the adsorption of superplasticizer or the size of the molecule,the dispersion action of particles being greater the larger the amount of adsorption and the larger the molecule.However,at low water/powder ratios,the relationship between the amount of adsorption and the size of the molecule to the fluidity of the paste has the opposite tendency.The paste with superplasticizer which the amount of adsorption was small and the size of the molecule was small is observed the best fluidity.It is necessary for non-adsorbed polymer in the liquid phase to be greater than a certain amount in high strength or high durable cement and concrete. Originality This paper describes our researches and important results into chemical admixtures for low-carbon cement and concrete system.In recycling system of sludge water using retarder,the utility of this system is described and the evaluation method of the amount of cement remaining in the sludge water with sodium gluconate has been proposed by using of Mg(NO_3)2·H_2O,conduction calorimeter and the hydration model.For mineralizer,the influence and the action mechanism of fluoride ion on the fluidity of cement paste with PC-superplasticizer was clarified.In blended cement,it is clear that the adsorption behaviour of superplasticizers onto OPC and BFS is caused by the molecular structure of superplasticizers.The optimum molecular structure of PC-superplasticizer for blended cement was proposed.In blended cement such as high volume slag cement with low OPC clinker,adsorption is mainly to BFS rather than OPC, so superplasticizer with a high ratio of side chains is considered to be useful.For fluidity of high strength cement paste that is high durable cement paste at low water powder ratio,it was clarified that non-adsorbed superplasticizer is necessary in liquid phase.

【Keywords】

chemical admixtures;;low carbon cement and concrete;;retarder;;superplasticizer;;molecular structure

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