Research On Multifunctional Properties Of Engineered Cementitious Composites

With the rapid development of China‘s economy,the national highway network is gradually improved.However,due to the continuous increase in traffic flow between cities and the speed of vehicles,it brings cement pavement a lot of pressure.In terms of using situation of cement pavement in China,there are still many problems,such as the original design theory,imperfect of calculation method,lack of experiences in the construction and attention to maintenance,which makes many cement pavement structural damage or the early disease d ue to functional defects,seriously affects the quality of road use.Therefore,in order to real-time monitor the health status of cement pavement;provide preventive measures for potentially occurring catastrophes;prolong the service life of cement pavement,ECC is proposed to as cement pavement materials in this thesis.The ECC material with properties of self-sensing capacity,high ductility,self-healing capacity and high-early-strength(HES)can prolong the service life of cement pavement,decreases the maintenance number during service life and reduce the economy cost.The material properties of ECC,including,self-sensing,high ductility,self-healing and HES,are investigated in this paper.These research results can provide experimental and theore tical basis for the application of ECC in cement pavement.Firstly,based on the principle of resistance of concrete material itself can sense stress/strain or damage,the relationship between the change of bulk resistivity of ECC material and crack patter n under different tensile strain states was tested by using four-point probe method with high frequency alternating current(AC)in this study.The evaluation system of crack width/number and self-sensing capacity of ECC is established,providing the design basis for self-sensing ECC material.Secondly,in order to enhance the ductility of ECC material,this paper provides a new method to improve the tensile and bending properties,as well as drying shrinkage performance of ECC specimens by adding superabsorbent polymer(SAP)act as artificial defects.Meanwhile,the change of fluidity and density in ECC specimens are also analyzed.The influence of different SAP particle size and content on mechanical properties of ECC materials is investigated.Thirdly,based on the ability of SAP particles to absorb water in a high-humidity condition and release water in a low-humidity condition,the self-healing of ECC material under no water condition is studied in this paper.The evaluation system of self-healing capacity under different environmental variables and material variables is established,providing the design basis for self-healing ECC material.In addition,it is found that when the weight of SAP particle to cement is 4%,the self-healing behavior has the most effect on the recovery in mechanical properties of ECC specimen;it can accelerate the self-healing rate and promote the recovery of mechanical performance.Finally,in order to achieve rapid opening of cement pavement within a few hours after repair,meanwhile considering reduce the cost of cement pavement construction,low cost HES-ECC are developed with local ingredients based on design theory of fracture mechanics and micro-mechanics.The matrix parameters including fracture strength and fracture toughness are obtained by design sulphoaluminate cement(SAC)and silica fume.The fiber/matrix parameters including chemical bond and friction bond strength are obtained by single fiber pullout test.The designed low cost HES-ECC materials can meet the requirement of cement pavement.