This paper reviews the methods adopted to produce high-performance concrete (HPC) and ultrahigh-performance concrete (UHPC). The chronological development of these concretes in terms of their constituents, mixture proportions, mixing protocols, and particle packing models from selected literature are presented. The paper highlights the earliest techniques that were used to obtain cementitious materials with high strength and durability, including pressure mixing and heat curing. The paper also covers the work done on HPC and UHPC since the late 1990s and summarizes the current state of the art. Numerous mixture proportions to attain target compressive strengths between 100 and 200 MPa are presented. Higher compressive strengths are achieved with denser mixtures (with practically achievable maximum particle packing densities, i.e., interparticle pores are minimized). In other words, particle packing density is a major attribute in the achievement of low porosity, flowability, durability, and reduced defects in concrete. Therefore, models, theories, and trial methods to achieve a higher packing density in concrete are presented.
1 September 2020 in Construction and Building Materials
The electrochemical corrosion parameters, such as corrosion potential, corrosion current density, and the Tafel constants are necessary inputs for the corrosion modeling in reinforced concrete. Literature shows large variability in their values, whereas the data are scarce for the carbonated concrete. This paper presents a range of corrosion parameters for the active steel in carbonated and the passive steel in noncarbonated concrete. Forty‐eight singly reinforced concrete cylinders were cast, of which 24 were carbonated and the others were sound samples. Potentiodynamic polarization curves were obtained at three different scan rates and extrapolated to extract the corrosion parameters. To validate these parameters, a macrocell corrosion system was simulated using FEM‐based Comsol multiphysics® software. The numerical results were compared to two experimental studies. A natural dispersion in the values of corrosion parameters for both active and passive steels was observed. The average Stern–Geary constant was 54 and 47 mV for active and passive steels, respectively. Numerical simulations with the obtained parameters predicted the macrocell corrosion in partially carbonated concrete with a high accuracy. The presented values of corrosion parameters in this study could help researchers and engineers to simulate the corrosion phenomena in concrete accurately.
1 April 2021 in Journal of Composites for Construction
This paper addresses the durability of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) laminates under natural and saline environments in the Arabian Gulf. Beam specimens were conditioned under sunlight and saline water for 180, 360, and 730 days and tested under four-point bending until failure. The load–deflection curves, strains, failure modes, ductility, and stiffness of the exposed beams were evaluated. The CFRP-strengthened specimens exhibited a 67% higher ultimate load capacity than control specimens after 28 days and up to 51% and 71% higher load capacity than control specimens after two years of direct sunlight and saline water exposure, respectively. No pronounced loss in strength and stiffness or damage to the epoxy was observed. Failure modes were transformed from cohesive to adhesive due to saline water exposure, whereas sunlight-exposed samples exhibited no failure-pattern change, and failures remained cohesive or interfacial. For design and analysis, environmental strength reduction factors are proposed and compared to current industry guidelines. Thus, CFRP-strengthened laminates can endure and perform effectively when subjected to severe environments of high salinity, temperature, and humidity.