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In the present work, the effect of early‐strengthening of reinforced concrete (RC) beam specimens using layers of ultra‐high performance concrete (UHPC) on their performance against reinforcement corrosion was examined. A number of fifteen RC beam specimens were prepared, one beam specimen uncorroded and unstrengthened was considered as a control beam, two beams were corroded and unstrengthened, and twelve corroded and strengthened beam specimens that were divided into two groups. RC beam specimens of the first group were corroded continuously to cause total theoretically targeted mass losses of the steel rebars and then strengthened using UHPC layers. RC beams of the second group were also corroded to the same degrees but in two steps. In the first step, the beams were corroded to cause a portion of targeted theoretical mass losses. Then the beams were strengthened in the same way as the beams of the first group and then subjected to second‐step accelerated reinforcement corrosion to achieve finally the same degrees of total theoretical mass losses as that of the first group. The corroded and strengthened beam specimens were exposed to flexural testing, and then the corroded rebars extracted from the beams were used to conduct gravimetric tests to determine the actual values of the mass losses due to accelerated corrosion. The gravimetric and flexural tests' results were used mainly to observe the influence of early‐strengthening on the actual mass loss and the flexural behavior of the tested beam specimens. Results showed a significant reduction in the values of the actual mass loss and better flexural behavior due to the early‐strengthening of the corroded beams. An analytical model, developed and validated using the data collected from the experimental tests, can be utilized to predict the ultimate load‐carrying capacities of the corroded strengthened RC beam specimens. [ABSTRACT FROM AUTHOR]

There is an increasing trend towards using recycled aggregate (RA) in concrete due to the shortage of high quality natural aggregates. The use of RA in concrete results in the conservation of natural resources, protects the environment and encourages sustainable construction. Though some studies have been conducted on the use of recycled aggregate concrete (RAC), the effect of mixture composition on its properties has not been well addressed. In the reported study, the effect of mixture composition, namely cement content and water/cement ratio and the proportion of RA on the mechanical properties of RAC was evaluated, with the intention of developing varying grades of RAC. As reported in earlier studies, the properties of RAC were generally inferior to that of normal aggregate concrete (NAC). Notwithstanding this, RAC with acceptable mechanical properties can be produced utilizing RA, for example RAC with low strength can be used in non‐structural applications. The construction industry should be encouraged to use RAC in building construction; as its use will lead to technical, economic and environmental benefits. Further, the use of RAC will lead to a sustainable development of the construction industry, particularly in regions that lack good quality natural aggregates. Based on the data developed in the reported study, the following quantities of RA are recommended to produce RAC: (i) 20% to produce low strength (20–30 MPa) concrete, (ii) 40% to produce medium (30–50 MPa) concrete and high strength (more than 50 MPa) concrete. Mathematical correlations between the mechanical properties of RAC with varying mix design parameters, such as cement content and water cement ratio and the quantity of RA, are also reported. These correlations can be used to predict the properties of RAC prepared with other proportions of RA and mix design parameters. [ABSTRACT FROM AUTHOR]

This computational investigation focused on numerical modeling of the shear behavior of ultra‐high‐performance concrete (UHPC) beams reinforced longitudinally with high‐strength rebars and ordinary‐strength steel (stirrups). Nonlinear three‐dimensional finite element model, using the concrete damaged plasticity model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC concrete beams within a commercial finite element software package ABAQUS 6.13. This investigation included the effects of various parameters; shear span‐to‐effective depth ratio (a/d), volume fraction of steel fibers, Vf, longitudinal reinforcement ratio, ρ, and stirrups spacing, s, on shear behavior of UHPC beams. Numerical results compared with previously obtained experimental results in terms of shear force–midspan deflection and cracking‐propagation behaviors. The results showed that finite element analysis predicted the shear behavior of UHPC beams in good agreement with the experimental data and predicted the response of the beam with variation in various parameters with a good accuracy. [ABSTRACT FROM AUTHOR]