Technical Measures To Reduce The Viscosity Of UHPC Mixtures

Ultra-high performance concrete has good mechanical properties and durability and is an important research direction for the sustainable development of concrete technology.Ultra-high-strength and high-performance concrete has complex composition and high viscosity,which is an important factor restricting its development and application.There is currently a lack of research on technical measures to reduce the viscosity of UHPC blends.The research on the technical measures to reduce the viscosity of UHPC can provide the basis and theoretical guidance for the design of UHPC,which is of great significance for the promotion and application of UHPC.Based on the above background and significance,this paper mainly focuses on the problem of excessive UHPC viscosity,and adopts various technical measures to reduce the viscosity of UHPC blends.First of all,the characterization method of the viscosity of the paste and the main influencing factors of the viscosity were studied to find the method suitable for the characterization of the viscosity,and the influence of the main influencing factors on the viscosity,and then the basic measures for viscosity reduction were determined.The types and proportions of the viscosity reducer and defoamer mixed to reduce the viscosity of UHPC mixes were obtained;different types of inert mineral admixtures were incorporated to reduce the viscosity of the pastes,and the ratios and viscosity reductions were incorporated according to the water film layer theory.Mechanisms have been studied.The coarse aggregates were used to replace part of the fine aggregates to reduce the viscosity of the blends.The effects of SSA and slurry thickness on the viscosity of the blends were analyzed.Finally,the regularity and mechanism of the influence of the mixing ratio of long and short steel fibers on the rheological properties of UHPFRC were studied,and the influence rule of steel fiber factor(k)on the rheological parameters and mechanical properties of UHPCFRC was discussed.The results showed that:1)T200 can reflect the change trend of UHPC mixture viscosity.Under the water-binder ratio of 0.162-0.203,the viscosity calculation model using Chidiac can better reflect the change of the viscosity of the UHPC mix.With the increase of admixture dosage,the viscosity decreases first and then increases.The additive content of admixture at low water-to-rubber ratio has a more obvious effect on the viscosity of the slurry,and the admixture of admixture is an important factor in the viscosity of the slurry.The lower,the more obvious the effect of steel fiber on the viscosity of the paste.2)The influence on the viscosity and mechanical properties of the matrix should be considered when selecting the defoamer.The incorporation of inert mineral materials can reduce the viscosity of UHPC mixes.The reduction of the specific surface area of the system and the ball effect of the particles are the main reasons for the viscosity reduction.3)Thickness of slurry layer,SSA and close bulk density can better reflect the influence of aggregate on the viscosity of UHPC mix.Appropriately increase the aggregate particle size,the specific surface area of the system decreases,and the thickness of the particle slurry layer increases,which will increase the UHPC fluidity and reduce the UHPC viscosity.The best quality ratio of coarse-grained aggregates to replace fine-grained aggregates is between 0.2 and 0.4.With the increase of substitution ratios,particle sizes and close packing densities,the UHPC blends are more prone to agglomeration,resulting in UHPC mixing.The viscosity of the compound increases.4)When the partial replacement ratio of 6 mm steel fiber to 13 mm and 19 mm steel fiber is 0.75,the mixture has the largest fluidity and the smallest viscosity.With the increase of the k value,the viscosity first decreased and then increased,the fluidity increased first and then decreased;the k value and the compressive strength and flexural strength showed a good linear growth relationship.In summary,we have found a method to measure viscosity,a combination of viscosity-reducing admixtures and defoamers;using a variety of inert mineral admixtures,and summarized the mechanism of viscosity reduction;found the impact of aggregate-matched UHPC viscosity.Laws and mechanisms;By reducing the UHPC viscosity through the combination of long and short steel fibers,the influence of steel fiber factor(k)on UHPC performance is given.It provides a reference for the study of reducing the viscosity of UHPC mix,and has certain engineering application value and theoretical guidance significance.