Research On The Properties Assessment And Sustainable Structural Design Of Ultra-High Performance Concrete With Low Cement Content

As a new type of structural material,Ultra-High Performance Concrete(UHPC)is famous for its high strength,low porosity,and excellent durability,which has a wide range of potential applications in the future.Due to the removal of the coarse aggregate,the cement content of UHPC ranges from 800 kg/m3 to 1100 kg/m3,which is three or four times than that of normal concrete.Such large amount of cement not only requires substantial amounts of energy to produce and releases large amounts of carbon dioxide,but also deviate from the "energy-saving and sustaianble" principles in our country.As such,how to produce UHPC with less cement and lower emission while providing the equivalent properties and satisfying the substantial requirements of the construction field in our country remains an open issue.Meanwhile,due to the use of steam and pressure curing togher with silica sand and powder,the cost of UHPC is relatively high.As such,the produce of UHPC with low cost is a new research topic.On the other hand,the reason that UHPC have been not widely used can be attrributed to the lack of comparision of structural scheme design and muli-objective sustainable structural design.Only comparing UHPC with normal strength on a structural scale can make full use of advantages of UHPC in terms of its cost and sustainabiltiy.Therefore,based on the mix design optimization and particle packing,the aim of this paper is to:(1)design and produce Ultra-High Performance Concrete with low cement;(2)assess and predict the UHPC properties.(3)use NSC(Normal Strength Concrete),HPC(High Performance Concrete)and UHPC with and without SCMs(Supplementary Cementitious Materials)as comparison and alternatives together with muli-objective sustainable structural design.The content of this paper is as follows:1.Based on the analysis of the physical properties such as particle size distribution,surface area,particle shape and the chemical properties such as oxide composition,phase composition and amorphous content,a new method of how to choose cement alternative material is proposed.The choose of material of this study is based on this method.Meanwhile,starting with the optimal packing theory and particle size distribution calculation,based on the Funk and Dinger theory,a new mix design method of UHPC wit low cement is proposed by using supplementary cementitious materials such as fly ash(FA),limestone powder(LP),rice husk ash(RHA)and silica fume(SF).The mix design of this research is based on the formulation of optimization curve by setting target value,adjusting variables,settting constraints and solving equations through Excel Solver Tool programming.The value of distribution modulus is choosen to be 0.23 in the Funk and Dinger to design UHPC with low cement.It is validated to be the the optimal solution to the best flowability and mechanical of UHPC with low cement.2.Under the normal temperature curing and by using normal sand as aggregate,the supplementary cementitious materials composed of fly ash,limestone powder,silica fume and rice husk ash in different proportions(up to 50%)are used to produce UHPC.The flowability of UHPC was investigated by calculating the superplitisizer conetent.The hydration degree of UHPC was investigated by testing the heat evolution rate,total heat and calcium hydroxide content.The pore structure of UHPC was evaluated by nitrogen adsorption method.The microstructure of UHPC was examined by scanning electron microscopy(SEM).The flexural and compressive strength was investigated at 7,28,90,and 365 days.The equivalent factor(k-value)of binary material and optimum proportion of these material in UHPC was proposed based on experimental result.3.Based on the experimental result,an artificial neural networks(ANN)model was constructed to evaluate the possibility of predicting the compressive strength of UHPC with low cement.The model composed of 11 input variables which contained:the mass of sand,cement,water,coarse aggregate,fly ash,silica fume,superplasticiser,water to cement-equivalent ratio,aggregate to cement-equivalent ratio,fine aggregate ratio,the difference between the minimum and maximum value of aggregate.The comparison between the predicted results and trial data were given by evaluating the root mean square error(RMSE),mean absolute percentage error(MAPE)and absolute fraction of variance(R2).4.An ontology-based approach supporting multi-perspectives sustainable structural design was proposed by using Ontology,SWRL rules and Ontology Development 101 rules on the Protege.A comprehensive knowledge base for multi-perspective structural design across different sectors is developed,which includes classes,relationship and properties by using CommonKAD method.The knowledge base has been validated and a full building case study was used to demonstrate its practical use;where NSC,HPC and UHPC different type of materials with and without SCMs are used as comparison and alternatives.The approach combines sustainability and cost with safety knowledge and provides multi-perspectives solutions considering safety,low carbon and cost.It demonstrates a new way of working for structural engineer to achieve ultimate sustainable design by using UHPC materils up to structural scale.