Experimental Study On Flexural Fatigue Properties Of UHTCC-FGC Beams

Concrete, with the advantages of low price and easily accessibility of its raw materials, is widely used in civil engineering construction. But the brittle characteristic of concrete, especially under tensile stress is one of its major limitations. The formation and evolution of cracks in concrete structure will reduce its stiffness and durability. With the properties of high ductility and pseudo strain-hardening behaviour, Ultra high toughness cementitious composites(UHTCC) is an ideal material to replace concrete to compress its brittle failure.The ultimate tensile strain of UHTCC is about3%～7%, and the average width of UHTCC can be controlled below100μm-sometimes even below40μm. However the wide use of UHTCC is limited by its high cost, thus it’s reasonable to use it to replace concrete in the key parts of a structure. Previous monotonic experimental results have shown that the failure of UHTCC-FGC beams (i.e. functionally graded composite beams crack-controlled by UHTCC) occurs with the formation of multiple cracks, thus leading to higher deformability and load carrying capacity of UHTCC-FGC beams than reinforced concrete.This research which is financially supported by Natural Science Foundation of China (No.51008270) and Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20100101120058) focuses on mechanical performances of UHTCC-FGC beams under fatigue loading. A total of13beams including4plain concrete beams and9UHTCC-FGC beams were casted, and the stress level is set between0.7and0.9. The constant ratio of minimum stress to maximum stress is set to0.2to avoid any impact and slip between the loading machine and the specimens during testing. All the specimens will be subjected to sinusoidal cyclic loading at2Hz and4Hz frequency. During the experiments, the fatigue life, deformability and loading capacity of UHTCC-FGC beams will be measured and recorded. Meanwhile, the development of cracks and the failure pattern of UHTCC-FGC beams during the test will be observed at the same time.