| This dissertation is focused on mechanical performance of fiber reinforced lightweight concrete. Lightweight concrete is used extensively by the building construction industry as non-structural wall panels, bricks and architectural exterior finishing. Since its mechanical properties are considerably lower than regular concrete, structural use (as load bearing structural member) of lightweight concrete is limited. Lately, reinforcing concrete with short fibers becomes popular. This is because of the recent advancements in micromechanics of fiber reinforced composites that lead to development of High Performance Fiber Reinforced Concrete (HPFRC). HPFRC is strong, ductile, and tough. In this study, we have successfully developed high performance fiber reinforced lightweight concrete (HPFRLWC) that maintains high strength, high ductility, and excellent toughness. At the same time, the densities of the HPFRLWC can be made between 1.6 to 0.8 g/cm3, representing 35 to 75 percent reduction from normal weight concrete. This study provides a framework for the design of high performance fiber reinforced lightweight concrete based on fracture mechanics based approach.; The study divided in to three phases. The first phase was to theoretically determine a fiber volume fraction to have ductile lightweight concrete. Prediction of fiber volume fraction was made using a theory involving fracture toughness of matrix, material and mechanical properties of fiber, and friction bond strength between fibers and the matrix. Second phase was to confirm theory of prediction fiber volume fraction for pseudo-ductility was true. It was confirmed that 1.5 percent polyvinylalcohol (PVA) is satisfactory to have strain hardening in the mortar, lightweight aggregate (Cenosphere), and aerated concrete composites. It is also confirmed that pseudo-strain hardening is highly related to the fracture toughness of the matrix. Pseudo-ductility was achieved by using 1.5 percent PVA fibers for the matrix compositions with a fracture toughness of 0.4 MPa-m1/2 (440 psi-in1/2 ). Flexural behavior of the matrix having fracture toughness more than mentioned was dominated by the fiber rupture. The composite was failed in the first cracking stress without presentation of ductility. The third and final phase was to evaluate mechanical properties of HPFRLWC regarding material properties. In this phase, basic effect of material properties on the flexural, compressive and fracture behavior was studied. Test results extracted that with a determined mix design, a material which is considerably ductile and as strong as concrete yet much lighter than concrete is produced. |
