Compsotition Design Of UHPC Based On Physical And Chemical Packing Effects At The Whole Material Scale

Ultra-high performance concrete(UHPC)is an emerging cement-based composite,which has ultra-high strength and durability,and thereby exhibites a wide application prospect and value in civil engineering.Different from ordinary concrete,the basic design principle of UHPC is to realize its compact microstructure on the basic of denser particle packing theory and add steel fibres for the martrix enhancement.Therefore,designing the mixture of UHPC scientifically and reasonably is the key to develop excellent performance of UHPC materials.However,the research on the mixture design method of UHPC is relatively limited,which is obviously not conducive to the development and application of the basic theory of UHPC.To solve the problem,based on the denser packing theory,this paper considers the physical and chemical effects of different ingredients on the packing system,including solid particle materials,steel fibres and liquid materials,and proposes corresponding optimizated mix-design methods.Based on the above,a method and theory of optimized composition design of UHPC based on physical and chemical effects incorporating all ingredients are proposed.The research content and main results are as follows:(1)Aiming at the problem that the design method of solid particle ingredients in UHPC system is not clear enough and the performance of designed UHPC can not be predicted,based on MAA particle stacking model and artificial intelligence technology,an optimized mixture design method of solid ingredients in UHPC system is proposed.Firstly,the performance prediction model of UHPC based on genetic algorithm based artificial neural network(GA-ANN)is established,and it is proved that the model has excellent applicability and prediction accuracy(R~2>0.9),which can be applied to the performance prediction and mixture design of UHPC.Meanwhile,a UHPC performance prediction software with good user interface is developed based on the established model.Then,a mixture design method of UHPC solid particles is proposed by combining MAA model and GA-ANN technology:MAA model is used to preliminatively design the proportion of solid particles;after that,according to the performance requirements,the GA-ANN based prediction software is used to further optimize the proportion of solid ingredients.Overall,this method can effectively design UHPC materials with high compactness,which expandes the application of artificial intelligence technology in the UHPC field.(3)Aiming at the interference and influence of steel fibres in UHPC packing system,an optimized mixture design approach for UHPC fibres is presented,based on MAA particle packing model and equivalent diameter thoery of steel fibres.Firstly,the equivalent diameter of the steel fiber is determined based on the comparison of the effect of sieving substitute particles on the wet packing density of UHPC by replacing the steel fibres with equal volume.After that,the steel fibres are incorporated into the MAA model in the form of equivalent diameter to design UHPC,and the macro/micro performance is evaluated and analyzed.The results show that the steel fibres commonly used in UHPC system(D=0.2 mm,L=13 mm,)can be incorporated into the MAA model in the form of 5.65mm particles.In addition,undrlying the approach presented herein,the negative effect of steel fibres on the packing structure of UHPC could be minimized it reveals and their positive role of the matrix reinforcement can be given full play.Thus,the UHPC composites with dense packing structure and excellent compressive strength(171MPa)are developed.(3)Aiming at the problem that the influence of liquid materials on UHPC packing system is not considered in the current UHPC design methods,an optimal design method of liquid phase composition of UHPC is proposed based on MAA particle packing model and water film thickness(WFT)theory.The specific design procudure is explained as follows:First,the water film thickness is added to the surface of solid particles and then incorporated into the MAA model to determine the proportion of solid particles;then,the proportion of liquid components(water and superplasticizer)is determined by solving equations;finally,the complete mixture is determined and the corresponding UHPC material is prepared.At the same time,the performance of the designed UHPC material is evaluated to verify the feasibility of the proposed method.The results show that water and superplasticizer can significantly improve the WFT of UHPC.In addition,the designed UHPC has a dense structure at both macro and micro scales,which ensures its excellent mechanical properties.Finally,some new insights are proposed to understand the development of UHPC microstructure and strength by combining centroplasm effect,water film theory and particle packing theory.It is proved that the liquid phase components can be incorporated into the UHPC packing system by the form of water film thickness.In summary,this paper proposed a method for the optimized composition design of UHPC based on physical and chemical effects incorporating all ingredients,which perfects the basic design theory in the UHPC field,and is beneficial to promote the high efficiency and fine development of UHPC.In the future,the project can be futher studied based on the discipline overlapping,such as the artificial intelligence technology,visual design software,which could further improve the design theory of UHPC.