Flexural Performance Of Reinforced High-strength Lightweight Aggregate Concrete Beams

Concrete bridges have advantages such as cheap construction cost, nice durability and adaptability, better integrate. But the great deadweight is its defect. High-strength Lightweight Aggregate Concrete (HSLWAC) have light weight-high strength, thermal insulation, good earthquake resistant performance, high durability and remarkable economic benefits characteristic, its application on bridge engineering, tall buildings and marine engineering increases day by day. And it's also an environmental protection building materials. This preeminence will be highlight as the sustainable development strategy was carried out.The most existing study materials on LWAC were aim at regular strength grade (below LC40). Concrete at this strength grade is no more suits for load bearing structures of wide span concrete bridges. The study on high-strength LWAC But the study on the mechanics properties of high-strength LWAC members is scarce in our country. This limits the proper and wide use in bridge engineering. The study work on Specified Density Concrete (SDC) has not been carried on. Base on the flexural tests included 6 reinforced high-strength LWAC beams (48.5MPa≤F_cu≤72.1MPa) and 1 reinforced normal-weight concrete (NC) beam, this paper study these beams flexural mechanical properties. This paper contains such research result as following:1. Introduce the study status in the field of LWAC and SDC, and their application and development state in bridge engineering. The research achievement of LWAC components and SDC components were summarized. Author list some questions of LWAC components, and present the significance and study content of this paper.2. Through the flexural tests of 11 beams, the ultimate flexural load, deflection, ductility, crack patterns, failure modal of reinforced high-strength LWAC beams and reinforced SDC beams were studied. The test results showed that Reinforced high-strength LWAC beams show strong brittleness at destruction. SDC beams and NC beam have the similar failure modal. But their cleavage depth at compressive region is less than high-strength LWAC beams. Deflection of LWAC beams is greater than SDC beams and NC beam, and deflection of SDC beam is close to NC beam's. Ductility of test beams decrease as the increasing of reinforcement ratio and concretestrength. The deflection-ductility indexes Hj of reinforced high-strength LWAC beam without stirrup and compression reinforcement is smaller than NC beam in this test.3. The ratio of LWAC beams' crack resistant load (Ncr) and ultimate load (Nu) range from 14.56%—38.15%. And this ratio of SDC beams range from 12.50% — 33.85 %. The crack width and crack spacing of high-strength LWAC beam are smaller than SDC beam and NC beam with same reinforcement ratio and approximately concrete compressive strength. This show that the crack resistance ability of high-strength LWAC beam is better than NC beam.4. According to the Code Specification for Design of Lightweight Aggregate Concrete Structures (JGJ 12-99), the resistance moment plastic index of cross sectionis y=1.75. But the crack resistant moments of high-strength LWAC beams calculated by the value is obvious larger than the test value. To high-strength LWAC beam with rectangular section, this paper advice the basic value of resistance moment plastic index of cross section ym= 1.50. And it should take the section high into account. The crack resistant moments calculated by Equation (5-2) are more approximate to the experimental cracking moment than by the code JGJ 12-99.5. Based on the test data analysis and theoretical derivation, the formulas of the maximum crack width and stiffness for high-strength LWAC beams under short term load are provided in this paper. These formulas not only embody the mechanics properties of flexural high-strength LWAC beams, but also link up the calculate modal of the code JGJ 12-99. The calculate results by these formulas are close to the test values, and they could be referenced by the high-strength LWAC engineering application.No matter considering from the advance of bridgework technology, the materials science development and the execution sustainable development strategy, high-strength LWAC have become the most importance development direction of high-strength and high performance concrete. It will supply a new development chance for large span concrete bridges. This paper conducted the systemic study and research on the flexural mechanics properties of reinforced high-strength LWAC beams and reinforced high-strength SDC beams under short term load. The calculate methods of crack resistant moment, the maximum crack width and stiffness which suit for high-strength LWAC beams were supplied. The research achievements of this paper provide useful reference for the application of high-strength LWAC and SDC in large span bridgeworks.