Abstracts:The use of fiber-reinforced polymer (FRP) fabrics as reinforcement in concrete offers several advantages, such as high tensile strength, corrosion resistance, and light weight. This paper presents experimental and mechanical studies on the flexural behaviors of FRP fabric reinforced ultra-high-performance concrete (UHPC) panels. Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) fabrics were investigated. Mechanical properties of GFRP and CFRP fabrics, high-strength mortar, and UHPC containing micro steel fibers were experimentally evaluated. The interfacial properties between the FRP fabric and cementitious matrix were characterized using push-pull tests. The flexural performance of panels with different reinforcement configurations was experimentally evaluated. The use of GFRP or CFRP fabric enhanced the flexural properties of UHPC panels, but did not lead to any increase in the flexural strength for the panels made with high-strength mortar. A mechanical analysis is performed to understand and predict the flexural behavior of the FRP fabric reinforced UHPC panels. The proposed fabric reinforced UHPC panel is demonstrated to be promising for the development of lightweight, high-performance permanent formwork system. Such formwork can be potentially used in accelerated construction of critical infrastructure with enhanced crack resistance and extended service life.

Abstracts:Obtaining the mesostructure of concrete from X-ray computed tomography (CT) requires segmentation of the data into distinct phases, a process complicated by the limited contrast between aggregates and mortar matrix. This paper explores the possibility to add baryte or hematite into the concrete mixture to enhance the contrast between cement paste and aggregates in CT, thus allowing for a semi-automatic segmentation. Raw and segmented CT images of plain and modified concrete mixtures are obtained and compared to assess the validity of the proposed approach. Characterization tests are also performed in order to ensure that the concrete characteristics are not appreciably affected by the presence of the enhancers.

Abstracts:RAC produced with crushed recycled aggregate (RA) is regarded as an environmental friendly material, while its high water demand, high mortar content and low modulus have restricted its application. Scattering-filling coarse aggregate (SFCA) process was applied to prepare the recycled aggregate concrete with promoted performance. With the reference of conventional concrete and the scattering-filling natural aggregate (SFNA) concrete, the influences of ratio, type, size and moisture state of RA on mechanical and durable properties of scattering-filling recycled aggregate (SFRA) concrete were investigated. The results indicate that SFCA process could improve the compressive strength, elastic modulus, and reduce the drying shrinkage and chloride penetration. The frost resistance of SFRA is comparable with the conventional concrete. With 10–20 mm scattering-filling aggregate of RA, SFCA concretes get more significant improvement on elastic modulus and anti-permeability; Higher water content of RA worsen the performance of recycled aggregate concrete (RAC) for water in the RA weakening ITZ; Furthermore, image processing analysis and microhardness indicated that SFCA process improve the properties by increasing the homogeneity of aggregate distribution and improving ITZ between the aggregate and cement paste in RAC. SFCA process provides an economic method to produce high-quality recycled aggregate concrete and an efficiently approach to the utilization of recycled concrete aggregate from Construction and Demolition waste.

Abstracts:In this study, compression tests of longitudinally cracked concrete were conducted to clarify the effect of existing crack on reduction of compressive strength and compressive fracture energy. In the specimens, one or two longitudinal cracks were introduced mechanically before compression loading. The experimental parameters were set to specimen shape, size, height to diameter ratio, coarse aggregate size, number of existing crack and the width. Based on experimental evidences, it was clarified that the reduction of both compressive strength and compressive fracture energy due to existing crack was dependent on crack width and those reduction tendencies are clearly influenced by coarse aggregate size without the effect of other parameters. Moreover, in order to discuss the reduction mechanism, compression tests focused on the effect of crack shape such as wave height and length were also conducted. In the specimens, imitation of existing cracks were embedded for neglecting the effect of damage near crack. As a result, it was found that the crack shape was significant for the reduction of concrete strength and compressive fracture energy. Finally, compressive strength reduction model in association with maximum crack width and maximum coarse aggregate size was proposed.