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In concrete beam design, the shear capacity of the concrete beam is of great interest because shear failure is associated with an abrupt failure mode that undermines the flexural performance of the beam. Recently, because of the increasing cost of natural resources and environmental concerns, the use of recycled aggregate (RA) in construction is becoming the standard practice. However, the effects of recycled aggregates on the shear strength of concrete have not been fully examined. In this study the effects of RA on concrete shear strength are studied experimentally by performing flexural tests on 20 RA concrete beams with various combinations of span-to-depth ratios (a/d ¼ 1 . 50, 2 . 50, 3 . 25), longitudinal reinforcement ratios (s ¼ 0 . 53%, 0 . 83%, 1 . 61%) and RA replacement ratios (0%, 30%, 50%, 100%). The test results indicate that the concrete shear strength diminishes by up to 30% at 100% replacement ratio compared with the natural aggregate concrete. The shear strengths of the RA concrete beams are also compared with those obtained from the existing models for natural aggregate concrete and some design considerations in using the recycled aggregate concrete are discussed. NotationA b section area of beam (m 2 ) A s steel rebars area (mm 2 ) a/d shear span-to-depth ratio b w , h, d width, depth and effective depth of beam (mm) E c elastic modulus (GPa) E s modulus of elasticity of rebars (GPa) f ck specified concrete compressive strength (MPa) f su specified tension strength of rebar (MPa) f y specified yield strength of rebar (MPa) P c early transverse tension crack load (kN) P cr initial critical shear crack load (kN) P cu ultimate shear load (kN) V cr shearing strength in early shear crack (kN) V u ultimate shearing strength (kN) r principal rebar ratio r/r b relative rebar ratio

This article presents the results of an experimental and analytical study on the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally reinforced with steel spirals. The experimental work was carried out by testing twenty-four 150 Â 300 mm 2 concrete cylinders subjected to pure compression with various confinement ratios and types of confining material. The test results show that the compressive response of concrete confined with both FRP and steel spirals cannot be predicted by summing the individual confinement effects obtained from FRP and steel spirals. This is largely attributable to differences in the inherent material properties of FRP and steel. A new empirical model to predict the axial stressstrain behavior of concrete confined with FRP and steel spirals is proposed. Comparisons between experimental results and theoretic predictions show agreement.

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The objective of this study was to investigate the potential use of sand washing waste as filler for epoxy resin mortar. The mechanical properties of four series of mortars containing epoxy binder at 10, 15, 20, and 25 wt. % mixed with sand blended with sand washing waste filler in the range of 0–20 wt. % were examined. The compressive and flexural strength increased with the increase in epoxy and filler content; however, above epoxy 20 wt. %, slight change was seen in strength due to increase in epoxy and filler content. Modulus of elasticity also linearly increased with the increase in filler content, but the use of epoxy content beyond 20 wt. % decreased the modulus of elasticity of the mortar. For epoxy content at 10 wt. %, poor bond strength lower than 0.8 MPa was observed, and adding filler at 20 wt. % adversely affected the bond strength, in contrast to the mortars containing epoxy at 15, 20, 25 wt. %. The results indicate that the sand washing waste can be used as potential filler for epoxy resin mortar to obtain better mechanical properties by adding the optimum level of sand washing waste filler.

Cracking of concrete over time, is a natural phenomenon. Longer service life of concrete structures is desirable. Self-healing concrete using bacteria, which could form CaCO 3 crystals for crack sealing, has promised benefits to reduce cost for concrete maintenance, because cracks could be autonomously repaired without human intervention. However, because of harsh concrete internal environment render the effectiveness depending on the bacteria viability within concrete. In this study, expanded clay (EC) was used as a carrier, to protect bacteria (Lysinibacillus boronitolerans YS11) from the harsh environment during the process. Existence of bacteria inside EC was observed using electron microscopy. When exposed to bacterial solution of 1.0 × 10 9 cells/mL, bacterial density within EC reached approximately 0.82 × 10 7 cells/g of dry EC. Extent of bacterial viability within EC, submerged to solution containing 1.0 × 10 8 cells/mL, was 53.6% of free bacteria solution containing 1.0 × 10 7 cells/mL, as measured with fluorescein diacetate assay. When rate of calcium carbonate formation was measured with Ca 2+ disappearance, rates were comparable between bacteria within EC (submerged to bacterial solution containing 1.0 × 10 8 cells/mL) and free bacteria (1.0 × 10 7 cells/mL). This finding indicates that bacteria with EC is very active for generation of CaCO 3 within EC. All experimental results suggest that EC may be an adequate bacteria carrier for self-healing concrete.

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The biaxial flexural strength of a concrete panel can be evaluated by two different methods: the centrally loaded round panel test (ASTM C 1150) and the recently proposed biaxial flexure test (BFT). Twenty-six tests, with 13 specimens for each test method, were performed to verify the effect of the different test methods on the biaxial flexural strength of concrete. A finite-element analysis of the specimens of two test methods showed that the biaxial flexure test set-up allows a larger area with a uniform biaxial stress on the bottom surface around the centre of the specimen than the ASTM C 1550 set-up, indicating that the difference in the test results is attributable to the volume effects. The test results showed that the biaxial flexure test method gives a more reliable biaxial flexural strength with a 25% lower coefficient of variation than that from the ASTM C 1550.