Research On Tensile Mechanical Performance And Temperature Effect Of Strain Hardening Cement-based Composite

In the study of SHCC, researchers find uniaxial tension testing the most directand reliable method to examine whether SHCC can present its strain hardeningcharacteristic. Some fiber reinforced composites are able to show this phenomenonunder bending or other forces, while they show strain softening under uniaxial tension.The stress-strain curve under uniaxial tension is characteristic curve of SHCC. Basedon the above, the experiments are done on the influence of diverse materials, variousmixes, different curing ages and damage of elevated temperature and freeze-thaw onthe properties of SHCC under uniaxial tension, the ability of controlling cracks ofSHCC is researched at the same time. The primary coverage is as follows:(1) Mixing fly ash in SHCC can improve the interface feature between fiber andmatrix effectively, decrease the interface cohesion between fiber and matrix,strengthen SHCC’s stain hardening characteristic. In the experiment, two kinds of flyash, Grade I and Grade II, are chosen to study the effect of fly ash on the properties ofSHCC under uniaxial tension. Results indicate that compared with Grade II, SHCCmixed with Grade I has higher strength and better strain hardening ability.(2) As for fine aggregates in SHCC, some researchers choose river sand, whilethe majorities have the alternative of quartz sand referring to the abroad. Therefore,the influence of type and particle size of sand on the properties of SHCC underuniaxial tension is a new task to study. The experiments are done on the influence ofriver sand and different particle size of quartz sand on the properties of SHCC. Thecrack width under uniaxial tension is tested as well. Results reveal that SHCC mixedwith quartz sand has higher strength and better capability to control crack. Thesmaller the particle size of quartz sand is, the better the effect will be.(3) The mixture of silica fume can improve strength of SHCC material, but itsinfluence on strain hardening characteristic and capability of controlling crack is atopic for further study. During uniaxial tension tests on SHCC with different dosageof silica fume, the cracking behavior under different strain is observed and analyzed. Results reveal that mixing silica fume can improve the strength a lot, while thedeformability changes a little, but it takes adverse effect on capability of controllingcrack.(4) Uniaxial tension tests are done on SHCC at various curing ages, which are3d,7d,14d,28d respectively. Results indicate that the strength at first crack increaseswith rising curing age, while the ductility of SHCC decreases.(5) Elevated temperature can accelerate hydration reaction in matrix and improveSHCC’s strength, but its influence on strain hardening characteristic and capability ofcontrolling crack is a research topic in this thesis. After uniaxial tension tests onspecimens damaged by Elevated temperature, the conclusion can be drawn that SHCCusing quartz sand is sensitive to change of temperature, the strength at first crackincreases with rising temperature. Uniaxial tension tests are done on SHCC at variousElevated temperature, which are20℃，50℃，80℃，100℃respectively, to studycapability of controlling crack under different strain. Results indicate that the averagecrack width of SHCC damaged by elevated temperature under ultimate situation is notup to80μm.(6) Uniaxial tension tests are done on SHCC after suffering0,50,100,150,200,300freeze-thaw cycles respectively. The conclusion can be drawn that SHCC remainsgood ductility though the tensile strength decreases a little.