Properties Of Plastic Concrete Under Uniaxial And Triaxial Compressive Stress

Plastic concrete is made of bentonite, clay, cement, sand, gravel and water, which is flexible engineering material. In order to use it in cutoff walls extensively, researches were carried on parameters which affected the properties of plastic concrete, such as water cement ratio, unit water, cement, and the relation between unit water and the other parameters was established by 7 plastic concrete mixes tests. Mechanical properties of plastic concrete under uniaxial and triaxial stress were focused using uniaxial compression test, triaxial and true triaxial one, cyclic loading one and permeability one. Main researches were carried on as following:1. Basic mechanical properties of plastic concrete under uniaxial stress(1) Properties under uniaxial compressive stress. Research has been done on the factors influencing strength of plastic concrete, e.g. loading rate, specimen shape, age and constituent. When uniaxial compressive strength of plastic concrete is over 2.0 MPa, the rate should be 0.1 MPa/s, when less than 2.0 MPa, the rate be 0.05MPa/s.(2) Elastic modulus. Elastic modulus of plastic concrete is focused on the influence with specimen shape, standard measurement distance, age and constituent. The result shows that the specimen of 150mm×150mm×300mm, full-lengthed measurement standard stance, should be selected in testing elastic modulus of plastic concrete without preloading. The formula for E can choose the two points of 0.3 and 0.7 times of peak strength on the ascending section in the stress strain curve.(3) Constitutive relation. Stress-strain curve of plastic concrete under uniaxial compressive stress is studied with specimen shape, age, standard measurement distance and constituent. Constitutive equation of plastic concrete under uniaxial compressive stress is established in ascending segment and descending one.2 Mechanical properties of plastic concrete under triaxial compressive stress(1) Mechanical properties under conventional triaxial stress. Main researches are carried on strength and stress strain curve of plastic concrete under conventional triaxial stress. The result shows that strength of plastic concrete increases greatly with confining pressure, and they are established on the relation between the strength of plastic concrete and uniaxial compressive one, confining pressure, and the relation between secant modulus and uniaxial compressive strength, elastic modulus, confining pressure. Furthermore, the constitutive equation under triaxial stress is presented.(2) Mechanical properties under true triaxial stress. Strength of plastic concrete is focused in two kinds of true triaxial tests. The result shows plastic concrete strength increases greatly with lateral pressures, when one of lateral pressure is constant, the strength increases with increases of the other lateral one in the one kind of true triaxial tests. And plastic concrete strength increases more with the increases of the initial lateral pressure, it can reach 4-6 times of uniaxial compressive one in the other kind of true triaxial test.Volume strain and peak one are focused under two kinds of true triaxial tests. The result shows that there is dilatancy for plastic concrete in the one kind of true triaxial test with constant lateral pressure, and the onset of dilatancy increases withσ2 for the constant a3. Peak strain is 0.005-0.015 in the uniaxial compression test, but it can be 0.02-0.05 in the first kind of true triaxial test, and it can be 0.062-0.093 in the second kind of true triaxial test.(3) Deformation characteristics during prepeak and post peak zones. Researches on relations between deformation characteristics and stress state during prepeak zone are carried on. The deformation behaves mainly elastically, when plastic concrete occurs under uniaxial compression test and true triaxial compression one with constant lateral displacement. And elastic modulus is used to represent the plastic concrete deformation characteristics during the prepeak zone. The deformation behaves mainly plastically, when plastic concrete occurs under triaxial compression tests with constant lateral pressure. Secant modulus has been used to assess plastic concrete deformation in the conditions.Researches on relations between deformation characteristics and stress state during postpeak zone are carried on. According to D2 (D2=E1.5ε/E0.3), stress strain curve of plastic concrete behaves as following during post peak zone: (4) Failure criterion. Failure criterion has been studied by Griffith theory and Mohr-Coulomb rules according to plastic concrete conventional triaxial test. Failure criterion in octahedron stress is brought out on terms of plastic concrete true triaxial test.3 plastic concrete mechanical properties under uniaxial cyclic loading testPlastic concrete mechanical properties under 4 kinds of cyclic loading tests is concerned. The equation between peak strength under cyclic loading test and one under uniaxial directly loading test, the maximal stress during cyclic loading is presented. Plastic loop and stress-strain curve of cyclic loading of plastic concrete is analysized.4 Permeability of plastic concretePlastic concrete permeability is studied by comparative permeability test and permeability test in soil mechanics. The result shows that comparative permeability test is good, and the other is bad. The water pressure should be 0.5MPa, and the time be 12h in the comparative permeability test. The modified method of calculation of permeability coefficient is presented.5 Mixes design of plastic concreteParameters are proposed in order to get required strength plastic concrete, including water cement ratio, water, cement and sand ratio.6 Applied of plastic concrete cutoff wall in engineering practiceDesign is analysized on Zhaikou reservoir in Henan province by 3-D FEM. The result shows that plastic concrete cutoff wall can be used in the project, and C10 concrete below 40m and 5MPa plastic concrete for upper segment, and design indexes of plastic concrete are suggested.