Mechanical Behavior And Design Method For Reactive Powder Concrete Beams

At 1993, a new cement-based material Reactive Powder Concrete (RPC) was proposed by Pierre Richard, which is composed of quartz sand, cement, active mineral admixture, super plasticizer, steel fiber and water in a certain mix proportion and curing condition. It is believed to have a promising application prospect because of its many excellent properties such as high strength, high toughness and high durability.Because of the special composition, RPC is different from normal concrete in mechanical properties. Consequently, the analysis methods of bearing capacity, stiffness and deflection of RPC members are also different. In addition, plastic internal force redistribution of statically indeterminate beam plate made of RPC has its distinct characteristics. So it is necessary and meaningful to study the optimal proportion and mechanical properties of RPC and to investigate the mechanical behavior and design method of RPC simple support beams and continuous beams. The main work in this paper is as follows:At first, The influence rules of composition dosage on strength and fluidity of RPC were researched by 59 groups of preparation tests. The test results indicate that the water-to-binder is the most critical influencing factor for performance of RPC. The strength of RPC increases and the fluidity of RPC decreases with the decrease of water-to-binder. The fluidity of RPC decreases with the increase of dosage of quartz sand, silica fume and steel fiber and it increases with the increase of dosage of slag in certain limit. There are saturation points in the relation curves of RPC strength and the dosage of silica sand, silica fume, slag. Strength increases as the rise of dosage of steel fiber in the limit of 1%~4%. Strength of RPC is higher by autoclave curing which working temperature is 200oC and pressure is 1.5 MPa than other curing method because RPC contains active materials such as silica fume, slag which activity can be stimulated by autoclave curing. The preliminary design formula of RPC mix proportion is proposed on the basis of test results and bo wromi formula. The design formula provides reference for mix proportion of RPC.Second, The axial compressive strength, axial tensile strength, strain corresponding to the peak stress, elastic modulus, poisson ratio and stress-strain relationship are determined through the compressive test of RPC prism which is 100mm×100mm×300mm and tensile test of RPC prism which is 60mm×60mm×400 mm. The equations of compressive and tensile stress-strain curves are fitted based on the test curves. The tests indicate that the elastic modulus is 4.12×104 N/mm 2, poisson ratio is 0.22, strain corresponding to the peak compressive stress is 3560μεand strain corresponding to the peak tensile stress is 249με, the ultimate strain corresponding to 0.5 f c is 5500με. The strain corresponding to the peak compressive stress and the ultimate strain corresponding to 0.5 f c are larger than normal concrete (the strain corresponding to the peak compressive stress of normal concrete is about 2440με, when its strength is same as the RPC in this paper), The compressive stress-strain curve is in elastic stage when stress is less than 0.6~0.7 f c.Third, The test of six reinforced reactive powder concrete simple support beams was completed. The test results indicates that the plastic influence coefficient increases linearly with the increase of reinforcement ratio which is less than 4.3%, and the calculation formula of plastic coefficient of RPC beam which is related to the reinforcement ratio and section height is proposed referring to the calculation method of the influence of section height on plastic coefficient in Concrete Structure Design Code. Based on the equation of RPC tensile stress-strain relation curve, the contribution of RPC in tensile region is 15%~40% of total resistance when the reinforcement ratio is 0.2%~10%. The reduction factor of RPC tensile stress, which is needed by calculation of cross section bending capacity of RPC beam, is derived on the basis of assumption that the tensile stress is uniformly distributed and the point of resultant force is at the center of tensile region. The calculation formulas of stress of tensile rebar and compressive stress of RPC under working load are derived through the compressive strain of cross section of pure bending section, the equation of compressive stress-strain curve of RPC and the strain of tensile rebar of crack section. Consequently, the formulas of stiffness and crack of RPC beam are presented.At last, Five two-span reinforced reactive powder concrete continuous beams were fabricated and tested with one point load applied at each mid span. During the test, the mechanical behavior at the stage of cracks, yielding of the steel bar both in the critical section of intermediate support and mid span and ultimate limit state were investigated. Because the ultimate compressive stain at compressive edge of RPC beam, which is no less than 5500με, is higher than the ultimate compressive strain of normal concrete, the plastic process of plastic hinge of RPC continuous beam is longer than the normal concrete continuous beam and the plastic rotation angle of RPC continuous beam is larger than the normal concrete continuous beam. Therefore, the amplitude of moment redistribution of RPC continuous beam is significantly increased. In this paper, the length of equivalent plastic hinge is derived for the design state and ultimate state based on the test results, and the calculation formula of the moment modification coefficient is proposed, in which the independent variables are plastic deflection and relative height of compressive region. The results provide basis for plastic design of RPC continuous beam.