| Magnesium Phosphate Cement(MPC)is an inorganic cementitious material.Compared with traditional Portland cement,it has many unique advantages.Such as,it has the ability to set and harden in severe cold environment,super early strength,good bonding performance,good volume stability.MPC has a good application in the field of rapid repair of building structures,and it is also very suitable for rapid construction,emergency repair and reinforcement in severe cold environments.Therefore,in order to expand the wider application of engineered cementitious composites(ECC)in the field of rapid repair and in low temperature environments.In this experiment,magnesium phosphate cement was used to develop an ultra-high ductility magnesium phosphate cement-based composite(MPCECC)that has both the advantages of MPC and the strain hardening characteristics of engineering cement-based composites.And the MPCECC is used to combine with CFRP,which has the advantages of light weight,high strength and corrosion resistance,to investigate the bond properties of the composite interface.The main conclusions are as follows:(1)In this experiment,MPCECC with significant strain hardening was developed.The specific ratio is:the mass ratio of magnesium to phosphorus is 1.4,the particle size of quartz sand is 150-180 mesh,the water-solid ratio is 0.14,the sand-to-binder ratio is 0.2,and the content of fly ash is 40%,and the fiber volume content is 2.0%.The ultimate tensile strain is 7.1%,the ultimate tensile stress is 4.73MPa,and the compressive strength is 39.91 MPa.SEM test shows that the micro-morphology of this ratio matrix is very dense,and the failure of the dog-bone axial tensile specimen is the fiber pull-out failure.In addition,low temperature curing reduces the ultimate tensile stress and compressive strength of MPCECC,but the strain hardening performance does not decrease significantly.At the curing age of seven days,MPCECC exhibited significant strain hardening performance,while the strain hardening performance decreased slightly when the curing age was 28 days.(2)The test shows that the strain hardening indices(strength index PSHσ and energy index PSHJ)have great correlation with ultimate tensile strain.Focusing on the experimental data and the MPCECC data developed by our research group using PVA fibers,the relationship between the strain hardening indices and the ultimate tensile strain is fitted,and based on this,a design and evaluation method for magnesium phosphate cement-based composites was established.(3)The concrete matrix strength(C30,C40,C50)and MPCECC thickness had no significant effect on the composite interface bearing capacity.The interfacial bearing capacity of the concrete substrate treated with high-pressure water gun spraying and the epoxy glue brushed after spraying is higher than that of the chisel group.In addition,the composite interface in which MPCECC is used as a binder to cover CFRP also has a high interface bearing capacity.(4)The slippage of the composite interface with MPCECC layer under load is larger than that of the specimen without MPCECC layer.And the slip value also increases with the increase of MPCECC thickness.In addition,the introduction of MPCECC significantly increased the effective bonding length of CFRP.The effective bonding length also increased with the increase of MPCECC thickness.The control group of the roughened concrete interface at the high-pressure water gun has a higher shear stress level,and with the increase of MPCECC thickness,the maximum shear stress increases.(5)The introduction of MPCECC makes the fracture energy of the composite interface increase significantly.With the increase of the thickness of the MPCECC layer,the fracture energy of the composite interface also increases gradually.Sanding the CFRP surface with sandpaper is also beneficial to the improvement of the fracture energy of the composite interface.In addition,the fracture energy of composite interface also increased with age increasing from 14 days to 28 days. |
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