Shear behaviour of lightweight concrete beams strengthened with CFRP composite

This paper presents the experimental results obtained from lightweight and normal concrete beams with closed and U-shaped configurations of epoxy bonded Carbon FRP (CFRP) reinforcement in order to compare the shear resisting mechanisms between lightweight and normal concrete beams. The experimental results show that the CFRP can successfully be applied in the strengthening of lightweight concrete beams and the shear strength gained due to CFRP reinforcement for lightweight samples is less than the normal weight concrete samples while the mode of failures are the same. In contrast, diagonal shear cracks propagate through the lightweight aggregate compared to cracks around normal aggregate in the concrete matrix. Furthermore, the numerical study shows that the design guidelines to estimate the CFRP contribution, which do not differentiate the concrete types, overestimate the U-shaped CFRP contribution on lightweight concrete beams where the effective bond length of CFRP could not be achieved due to lower tensile strength of lightweight concrete

Pulse velocity assessment of early age creep of concrete

Creep of concrete can have damaging effects by inducing deformations that may contribute or eventually lead to cracks, which influence concrete durability, steel reinforcement exposure to corrosion, and aesthetic damage to architectural buildings. This research investigated the early age creep deformation in concrete samples made with normal, lightweight (Lytag), recycled concrete, and recycled asphalt aggregates using ultrasonic pulse velocity measurements. Creep was achieved by applying a load corresponding to 30% of the strength of concrete to 100 × 250 mm prisms. The compressive load was applied from 24 h after mixing and up to 27 days. The results and analysis of measurements obtained for stress development, specific creep (creep strain per unit stress), and ultrasonic pulse velocity measured up to 27 days after load application are presented. Empirical models that allow the assessment of creep of concrete using ultrasonic pulse velocity measurements are also presented. Early age specific creep is higher for recycled asphalt aggregate than Lytag aggregate and recycled concrete aggregate concretes, which are higher than gravel concrete. Measurements of ultrasonic pulse velocity could be used to determine creep but further work to refine this technique is required