Experimental Study On Dry Shrinkage And Crack Resistance Under Restrained Shrinkage Of Ultra High Toughness Cementitious Composites

There are some defects of normal cementitious materials,for example,higher brittleness, lower tension strength,lower toughness and easier to crack.In many projects,constructions of concrete are often destroyed or even cannot be used because of these defects.How can we find ways to control the generation and development of cracks to enhance the durability of materials? It has been paid more attention in the field of cement and concrete research for a long time.Ultra High Toughness Cementitious Composites(UHTCC),which shows the observed strain-hardening behavior and multiple cracking under the uniaxial tensile load,has excellent toughness and remarkable energy absorption ability.So,it can be considered that UHTCC will be widely used in the structures in the future.However,people also pay attention to the behavior of shrinkage and crack resistance of UHTCC.Therefore,mechanical properties test, drying shrinkage test and restrained shrinkage test are performed in the paper,with emphasis on the drying shrinkage and crack resistance of UHTCC.The major contributions are summarized as follows:(1) Though the three-point flexural test the flexural behavior of UHTCC is analysed, with comparing with cement slurry,plain concrete and fiber reinforced concrete.The results of experiment indicate that UHTCC shows the observed strain-harding behavior and ascendant distortion ability under the flexural load;the failture of UHTCC turns on plasticity with multiple cracking.(2) Drying shrinkage test is performed in the paper.The results of the test show that: drying shrinkage of UHTCC mostly takes place at early age;meanwhile the vaporing speed of water contained in the UHTCC can be played down with waterish nursing which will lead to higher ultimate drying shrinkage deformation;PVA fibre has little influence on the drying shrinkage of UHTCC.Though the theoretical analysis it can be concluded that in UHTCC repaired systems the surface cracks may be suppressed,the delamination of the interface may be minimized and the durability of structures may be improved.By non-linear fitting it is showed that hyperbolic expression can describe and forecast the drying shrinkage deformation of UHTCC clearly. (3) Through the test of flat-slab restrained shrinkage,crack resistance of UHTCC at early age was investigated.The experimental results indicated that:to some extent,PVA fiber has influence on the water evaperation of UHTCC;UHTCC begins to plastic shrinkage after casting,but the cracks which are bridged by fibers are suppressed;under high temperature and strong wind,cracks produced due to dry shrinkage developed in UHTCC.However the maximum crack width is rather small,no more than 50μm.