Study On The Relationship Between The Rheological Properties Of Cement Paste And The Performance Of The Self-Compacting Concrete

The self-compacting concrete(SCC)has become one of the research focuses in the field of civil engineering due to its advantages of high mobility,high durability and green environmental protection.As one kind of high performance concrete materials in the new century,SCC is widely used in many special projects such as tunnel and underground engineering,dense reinforcement structure,thin wall structure,high fine structure and so on.There are lots of studies on SCC at present,but the researches on the performance and mechanical properties of SCC in combination with the rheological theory are not sufficient.In order to meet the requirements of engineering construction and application,most concrete is usually mixed with admixtures and admixtures,such as Polycarboxylic Water reducing agent,fly ash and air entraining agent.Due to the"adsorption and dispersion" effect of Polycarboxylic Water Reducer,the ball effect of fly ash and the electrostatic repulsion of air entraining agent,the mixture ratio design of admixture and fly ash self compacting concrete and the study of its rheological properties have become more complicated.Firstly,the mix proportion of self compacting concrete is designed by using total volume method and parameter design method.Considering the matrix material in the mixture ratio,cement paste belongs to the non Newtonian fluid viscoelastic material,the evaluation of its rheological behavior is mainly two rheological parameters of plastic viscosity and yield stress.At present,most scholars believe that the rheological Bingham model is suitable for describing the rheological behavior of cement paste,so it is aimed at the incorporation of polycarboxylic acid.The apparent viscosity and shear stress of cement paste were tested by rotational rheometer.It is found that with the increase of the amount of polycarboxylic acid water reducing agent,the torque of cement base decreases,that is,the apparent viscosity and shear stress decrease with the increase of shear rate in a certain range.The yield stress and plastic viscosity of the tested samples were obtained by fitting the experimental data by Bingham model.It was found that the yield stress and plastic viscosity of most sample materials decreased with the increase of the amount of Polycarboxylic Water reducing agent.When the fly ash is mixed with cement paste,the shear thinning or thickening of the cement paste(specific performance is related to the amount of fly ash)is presented.The modified Bingham model is used to fit the plastic viscosity with the yield stress,to reflect the power law relationship between the shear stress and the shear rate,and to improve the Bingham model by using the improved model.A suitable box for workability of self compacting concrete paste is drawn by fitting the plastic viscosity and yield stress.Combined with rotating rheometer,the test and initial flow degree test of air entraining agent are tested,and the selection of external additive and fly ash is further completed.Based on the proportion of selected self compacting concrete,the performance and mechanical properties of the self compacting concrete with different admixtures and fly ash are tested and analyzed.The effects of cement ratio,polycarboxylic acid water reducer,fly ash and air entraining agent on the rheological properties and mechanical strength of self compacting concrete were compared.Through research and comparison,it is found that water binder ratio,polycarboxylate superplasticizer,fly ash and air entraining agent can help improve the rheological properties of self compacting concrete.Because of their different mechanism of action,the relationship between effects is arranged as follows:water binder ratio>polycarboxylate superplasticizer>fly ash>air entraining agent.In the project with high mobility and strength,the combination of relatively large low water binder ratio,high content polycarboxylic acid water reducing agent,low content fly ash and corresponding air entraining agent has better effect.Based on a large number of self compacting concrete slurry experimental research,this paper has a certain practical guiding value for the laboratory screening its mix proportion design,and also provides a reference for further research on the application of self compacting concrete and engineering practice.