The Research On Composites Material Of Densified Strain Hardening Cementitious Composite For Strengthening Concrete Structures

Strain Hardening Cementitious Composites(SHCC)has exhibit tensile strain hardening similar with metal material and multiple fine cracks.This material offers superior performance over other reinforcement material for reinforced concrete.Due to the issues of SHCC with low Young's modulus and tensile strength,RC structure's ultimate bearing capacity using SHCC strengthening were not obvious,so densified Strain Hardening Cementitious Composite(DSHCC)were developed using the densification method.The selection of new compositions and optimizing was based on the fresh characteristics properties and uniaxial tensile test,air permeability tests and shrinkage behavior tests;then tests and theoretical analysis were carried out to find the effectiveness of applying DSHCC for bending and shear resistance of RC beams.Therefore the main research contents of this paper are as follows:1.Experimental study on the mix proportion and the basic mechanical properties of DSHCCMix proportion tests of DSHCC were carried out according to fresh characteristics and mechanical property.Firstly SHCC and UHPC were compared with material mix proportion and mechanical property,then based on DSP theory,approximate range of new material have been developed.Water cement ratios and silica/binder ratios and so on were established based on workability property test.The choosing of PVA fiber ratio was mainly depended on tensile mechanical properties for repairing demand.Finally the compressive strength and elastic modulus of the material are obtained by axial compression test.Compared with SHCC materials,the mechanical properties of DSHCC materials have been greatly improved,and the tensile and compressive strengths and Young's modulus has been raised by 38%,56%,and 59%respectively.DSHCC layer can make the ductility of strengthened RC beams increase 40%and 100%2.Experimental study on permeability and shrinkage of DSHCCDSHCC has excellent anti-permeability with combination diagram method including Torrent pressure method and the combination of Wenner resistivity method.Research on shrinkage properties of materials,the water cement ratio,silica fume content,fiber content and curing conditions of four parameters on the material shrinkage effect,It was proposed to increase the fiber content and expansion agent,and improve the curing conditions to control concrete shrinkage.3.Experiment and theoretical analysis on flexural behavior of RC beams strengthened with DSHCCThe experimental results show that the DSHCC reinforced beams the first crack load,yield load and ultimate load was improved than those of composite mortar reinforced beam,and durability of RC beams was greatly improved because of DSHCC behavior of formatting multiple fine cracking.The tests also found that with the strengthening layer thickness increases,the ductility of the strengthened beams got worse because of the crack interface layer which causes DSHCC to strengthen the top layer of stress concentration,then local stress exceed the ultimate tensile strength and premature fracture,the strengthened beams cause brittle failure.Deformation capacity was greatly improved by a small amount of steel in DSHCC,which enhance the ductility of the strengthened beams.Experiments and numerical analysis for RC beams with the reinforced DSHCC strengthened was carried out,which show the strengthened beams flexural performance;the calculated values and tests was compared.Finally a simplified formula for calculating the ultimate bearing capacity of RC beams strengthened with DSHCC was proposed in this study.4.Experimental Study and theoretical analysis on Shear Performance of Strengthened RC Beams with DSHCCSix test beams in two groups which are respective with shear span ratios of 3.2 and 2.2 are studied;the differences of the shear failure mode,bearing capacity,deformation and fracture distribution between RC beam and DSHCC strengthened beam were analyzed;Based on finite element analysis and the Truss-Arch theory,a simplified ultimate shear strength formula of the DSHCC strengthened beam is derived and verified by the test results.This investigation proves that the DSHCC is also an excellent material for shear strengthening and the proposed simplified ultimate shear strength formula will give reference for the design of DSHCC strengthened beams.A simplified ultimate shear strength formula of the DSHCC strengthened beam is derived and verified by the test results.