Studies On Mechanical Properties Of Strain Hardening Cementitious Composites(SHCC) And Structural Analysis Of SHCC Pipes

The existing cement concrete pipes can satisfy the basic requirements for water supply and drainage engineering.But they possess less crack resistance and potential for steel or steel wire corrosion,which lead to the leakage of pipeline and even pipe explosion accidents during the service period.Multi-matrix composite pipes(MMCP)composing of resin matrix composite lining,steel tube,cement matrix structural layer and prestressed glass fiber reinforced resin layer will contribute to the solution of these problems.In MMCP,mechanical properties of different materials have great diversity.For example,the low ductility of normal cementitious materials can’t correspond with the high ductility of steel and glass fiber reinforced resin.Thus,the cement matrix structural layer is one of the weakest components in MMCP.Because of the structural complexity of MMCP,strain hardening cement-based composites(SHCC)as the cement matrix structural layer in MMCP is investigated in this dissertation,To implement the application for SHCC in MMCP,the preparation and mechanical properties of SHCC,the structural performances of SHCC pipeline,theoretical analysis of SHCC pipes,and finite element modeling of SHCC pipes based on concrete damage plastic model(CDP)are studied.The main results are as follows:(1)The main factors affecting tensile mechanical properties of SHCC and their mechanisms were discussed systematically.The influence of different ratio of fly ash to cement,different grading of fine quartz sand,different PVA fibers(length,surface oiling treatment)and cured in different conditions(curing period,standard curing and steam curing)on SHCC tensile properties under direct tension was revealed,and then the optimal mixing proportion to prepare SHCC was determined.The process of multiple cracking in SHCC could be monitored by means of digital image correlation(DIC)technique.It was found that most of the fine cracks were stable in the process of tension,that is,the width of crack kept stable.However,the width of crack which was developed into the main crack eventually increased with the increase of stress and strain during the hardening phase.(2)Structural performances for steel reinforced SHCC pipes(RSHCCP),SHCC pipes(SHCCP),steel reinforced cement mortar pipes(RMP)and plain cement mortar pipes(MP)with the same pipe diameter were analyzed upon the three-edge bearing test(TEBT).These four kinds of pipes were tested during monotonic loading and cyclic loading.Then,variations in deflection,strain and width of cracks of the crown,the springline and the invert of pipes with increasing load were observed.It was verified that RSHCCP was a new type of semi-rigidity concrete pipe with thin-wall,high strength and high deformation rate.Meanwhile,the criterion to classify semi-rigid pipe was put forward,that is,the ratio of soil stiffness and pipe ring stiffness was more than 10 and less than 96.(3)The theoretical analysis model for calculating RSHCCP’s bearing capacity has been established.Then the bending moment of the crown and the bearing capacity were obtained by the model.The analytical results were consistent with the test results.The theoretical model was used to design the minimum wall thickness of RSHCCP.(4)Finite element analysis model was established incorporated with concrete damage plasticity model,the stress-strain relationship of SHCC and tension/compression cycle test results of SHCC.This model was used to analyze the damage developing process,bearing capacity,deformation rate of RSHCCP.The simulated results were in agreement with the test results.