Experimental Study On True Triaxial Compression Of Self-compacting Concrete

Self-compacting concrete has high fluidity,high anti-segregation and high filling in terms of working performance.It can fill every corner without vibration and rely on its own gravity,and can achieve the advantages of full compaction,so it is widely used in engineering.And engineering of reinforced concrete and concrete filled steel tubular members are constraint effect,and the self-compacting concrete is another level of complexity-materials constitute the impact on the effect of restraint,such as whether the self-compacting concrete paste volume content is higher effect on the characteristic of confined concrete crack expansion and axial stress-strain relationship.Therefore,further research and exploration are needed.In this paper,the active confinement effect of self-compacting concrete with different slurry volume contents under true triaxial compression is studied.Study different paste volume content（34%,36%,40%）,and different lateral confining pressure（including conventional triaxial pressure and true triaxial pressure）for confined concrete mechanics performance,（including failure pattern,the axial stress-strain curve,the axial stress and horizontal strain curve and volume strain,axial strain curve,etc.）.The experimental research in this paper includes the following contents:（1）A simple test device is designed to realize the true triaxial compression test,which overcomes the problems of the existing true triaxial compression test equipment,such as the complex principle,high development cost,scarce number of test equipment and high research threshold.The device needs to be used with ordinary hydraulic servo press,axial direction provided by the ordinary hydraulic servo press maximum principal compressive stress,horizontal two perpendicular to the first load component connection hydraulic jack and oil control system respectively,and make the cube specimens of two sets of relative horizontal surface by stress are mutually independent and constant,can realize the true triaxial pressure.The fluctuation of the lateral confining pressure was recorded in this test,and the test data showed that the lateral confining pressure was stable and fluctuated less during the loading process.The axial displacement meter and horizontal displacement meter are set,which can record the deformation of cube specimen in the process of true triaxial compression,and directly analyze the strength and deformation characteristics of concrete under true triaxial compression.（2）Under uniaxial compression,the compressive strength and peak strain of concrete specimens decrease gradually with the increase of the volume content of slurry.In general,the concrete presents"brittle"failure with the increase of the volume content of slurry.Under conventional triaxial compression loading,the peak stress and peak strain of confined concrete increase linearly with the increase of confining pressure.Under true triaxial compressive loading,the minimum principal compressive stress₁ is kept unchanged,and only the intermediate principal compressive stress₂ is increased.The compressive strength of concrete also increases,but the increase in strength is not obvious.An effective constraint requires both minimum and intermediate principal compressive stresses to be increased.The minimum principal compressive stress₁ of concrete is the same,and the softening stage of the curve is basically the same.The decreasing trend of the softening stage has a great weight depending on the magnitude of the minimum principal compressive stress₁,while the change of the intermediate principal compressive stress₂ has little effect on it.Self-compacting concrete under the true triaxial pressure,the volume with the increase of axial strain present a compressed before the expansion of the law,and with the increase of the content of paste volume of axial loading of tiny cracks in the concrete slurry under the constraints by lateral confining pressure,develop more slowly in the slurry,the volume expansion of concrete specimens more slowly.Under different confining pressures,there are three types of failure of concrete specimens:columnar failure,oblique shear failure and compression flow failure.（3）In the conventional triaxial compression,based on Popovics scholars’complete stress-strain curves for the uniaxial compression of ordinary concrete,Zhou et al.By introducing the parameters of lateral confining pressure into Popovics’model and combining with the characteristics of stress-strain curve of true triaxial compression of self-compacting concrete in the softening stage in this paper,a stress-strain curve model suitable for the characteristics of self-compacting concrete is established,which mainly corrects the peak stress and peak strain of confined concrete.In addition,the original model curve has the same downward trend in the softening stage,and the shape coefficient related to the constraint stress is added,so that the model curve changes with the confining pressure in the softening stage under different confining pressures.In the case of true triaxial compression,the equivalent confining pressure defined by Yu et al.,is quoted,and the equivalent confining pressure is brought into the above model,thus the stress-strain curve under true triaxial compression can be described.（4）Some typical concrete failure criteria are verified,and the characteristic values of true triaxial compressive strength of different parameters in this paper are put into the failure criteria of Ottosen scholars and Guo-Wang,so as to calculate the failure criteria parameters of self-compacting concrete with different slurry volume contents in this paper.