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Concrete, the construction industry’s most utilized construction material, has transformed the environment and the modern built-up lifestyle. Although concrete is a first-rate supplier to the carbon footprint, it is imperative for buildings to display sustainable characteristics. Scholars have explored techniques to lessen the carbon footprint and the way to put into effect strategic waste control plans in which waste is reused. This study explores the dual benefits wherein concrete ingredients are replaced through abandoned waste which reduces the unwanted waste materials that have a substantial carbon footprint and thus results in the recycling of waste as part of a sustainable economic system. In this study, timber ash is utilized as a partial substitute for sand and cement, crumb rubber and waste glass as a partial substitute for sand, recycled concrete, and waste glass as a substitute for gravel. Characteristics studies were done to check the influence of each waste replacement on the modulus of elasticity of concrete. More than sixty-five combinations of waste have been examined to attain the modulus of elasticity of concrete. A total of about 200 concrete cylinders were cast to provide at least three cylinders for each generated data point. Three different ASTM standards were utilized to determine the modulus of elasticity of each mix. Four mixes comprising of the combination of two waste materials and two mixes comprising of the combination of three waste materials replacing natural materials were determined to exhibit an equal or superior modulus of elasticity of the control mix of 25 GPa.

Concrete, the most consumed man-made material worldwide, has shaped the environment and the modern world. Even though concrete is a major contributor to the carbon footprint, it is indispensable for building the sustainable world of tomorrow. Researchers have been exploring ways to reduce the carbon footprint and to implement strategical waste management plans in which wastes are repurposed. Pollution has been a challenge for almost all countries, especially with the increase in the release of greenhouse gases in the atmosphere and the emissions resulting from wastes in unmanaged landfills. Additionally, the areas available for landfills have become scarce. Daily all around the world, generated are wastes such as wood ash, waste glass, used tires, construction debris, and demolition wastes. These wastes usually accumulate in landfills for years, as they are mostly nondecomposable. This research explores a solution to this twofold problem in which concrete components are replaced by wastes and by-products, which in return reduces the need for raw materials that have a significant carbon footprint and repurposes wastes as part of a circular economy. In this research, wood ash is used as a partial replacement of cement and sand, fine crushed glass and crumb rubber as partial replacements of sand, and crushed glass and recycled concrete aggregates as partial replacements of gravel. The optimum eco-friendly structural concrete mix was determined to be the combined mix consisting of 5% wood ash as a partial replacement of cement; 20% wood ash, 20% fine crushed glass, and 2% crumb rubber as partial replacements of sand; and 5% crushed glass and 50% recycled concrete aggregates as partial replacements of coarse aggregates. By mass, the recycled waste materials constituted 32% of the mix, translating into 34% of its volume. Additionally, identified were mixes that may be used for structural applications.

In this study, the efficacy of strengthening of reinforced concrete (RC) beams in shear by utilizing high-performance fiber-reinforced concrete (HPFRC) was explored. The shear strengthening was achieved by epoxy bonding of prefabricated HPFRC strips or plates onto the beams. The beams were strengthened utilizing two different strengthening schemes: (i) plates side strengthening (ii) vertical strips applied at shear critical sections. The behavior of the two configurations was compared to the behavior of non-shear reinforced and shear-reinforced RC beams. The high-performance concrete (HPC) utilized contains 1.5% of steel fibers per volume of HPC mortar and is known as HPFRC. Parameters determined were the flexural strength and compressive strength of HPFRC mortar. The obtained results revealed that HPFRC realized a 28-day flexural strength of 20 MPa and a compressive strength of 108 MPa. Moreover, HPFRC strengthened RC beams experienced an increased in strength capacity of about 50% for plates and 36% for vertical strips compared to the RC beams with no stirrups. The results for HPFRC strengthened beams with plates were superior compared to those of the stirrup-reinforced beams, whereas the results of HPFRC strips strengthened beams were almost identical to the stirrup-reinforced beams. Also observed, was an improvement in the ductility of the beams with the best results achieved when employing HPFRC plates and strips.HighlightsShear Strengthening of RC beams by HPFRC plates utilizing two methods.Precast HPFRC plates bonded by epoxy adhesive and anchored.Continuous shear strengthening resulted in high-capacity enhancement and ductility.

This paper presents the outcomes of a comprehensive experimental investigation aimed at characterizing the in-plane shear strength of Unreinforced Masonry (URM) wallettes subjected to diagonal compression. The study focuses on the strengthening of these wallettes using precast Ultra-High Performance Concrete (UHPC) diagonal strips, externally bonded onto the wall substrates through high-strength epoxy mortar. Twenty-three wallettes, each measuring 1000 mm × 1000 mm × 70 mm, were meticulously constructed and subjected to in-plane diagonal compression. Among these, eighteen wallettes underwent strengthening utilizing various configurations of UHPC, with a key emphasis on variables such as UHPC strip width and thickness, substrate nature, and corner confinement with enlarged UHPC rectangular plates. Findings from the experimental program highlighted the significant influence of UHPC retrofit parameters on the wallettes performance. Notably, corner confinement emerged as an effective strategy against premature toe crushing failure, enhancing the wallettes ability to withstand higher in-plane compressive loads. While UHPC strip width exhibited moderate impact, UHPC strip thickness emerged as a dominant factor. Increasing strip width from 100 to 250 mm yielded an approximate 8% shear strength improvement, whereas doubling strip thickness from 10 to 20 mm led to a substantial 27% enhancement. Notably, enhanced strip width demonstrated pronounced benefits in terms of ductility and energy dissipation capacity. Excessive UHPC retrofit thickness induced brittle failure despite escalating shear strength. Conversely, thinner UHPC retrofits achieved a favorable balance between strength, ductility, and energy dissipation. Wallettes retrofitted with 5 mm UHPC exhibited an impressive 2.36-fold shear strength increase compared to reference walls, while those with 10 mm and 20 mm UHPC retrofits experienced 2.14 and 2.78-fold improvements, respectively. Furthermore, the manner of UHPC application significantly influenced the strengthening system's behaviour. For identical strengthening layouts, the direct bonding of UHPC onto masonry substrates resulted in a 25% increase in shear strength compared to UHPC bonding onto plaster overlays.

A comprehensive research project was undertaken to evaluate the effect of styrene butadiene rubber (SBR) latex admixture on washout loss and bond strength of underwater concrete (UWC) designated for repair applications. Three UWC series possessing low to high stability levels that incorporate 5 to 15% SBR, by binder mass, were tested. A 1.5 m (4.93 ft) long specially designed channel was developed to enable the UWC to free fall from the outlet of a V-funnel apparatus, flow along an inclined surface submerged in water, then spread onto a horizontal concrete surface. Results show that underwater casting leads to reduced pulloff strengths caused by washout loss and aggregate segregation that weaken in-place properties. The incorporation of SBR was particularly efficient to reduce washout loss and improve adhesion between the repair overlay and substrate. Regression models enabling the prediction of residual bond strengths from the UWC rheological properties, washout loss, and polymer content are established. Keywords: pulloff strength; rheology; styrene butadiene rubber (SBR) latex; underwater concrete; washout loss.

The Czochralski manufacturing process has been observed to result in small periodic and undesirable undulations in the crystal diameter under certain conditions. There appear to be critical values for the height-to-diameter ratio of the crucible, the rotational velocity, and possibly the crucible temperature, which govern the appearance or nonappearance of these undulations. Many papers have been published on this phenomenon, and attempts to circumvent it have been proposed. Basically, the reduced buoyancy of the colder fluid directly under the crystal interface causes a “lava-lamp” circulation which can, under the right (wrong, from a manufacturing point of view) circumstances be reversed, causing a periodic fluctuation of the temperature at the crystal interface; and the remelting-resolidifying produces the diameter undulations. The fluctuations were analyzed by the perturbation theory, applied to the non-linear governing equations. However, the linearized equations did not predict any oscillatory phenomena. At this point, it was recognized that the oscillations had strongly non-linear characteristics and are impervious to quantitative analysis by linearization techniques. A rigorous analytic solution of the equations for the linearized rotational fluid velocity (the other velocity components are zero to first-order) and temperature was performed, using mode-matching to handle the competing boundary conditions at the top of the melt (Dirichlet under the crystal, versus free surface beyond the crystal). Basically, one expresses the eigenfunction expansion of the solution (of the time-Laplace-transformed equations) directly under the crystal, with the Dirichlet condition at the top, in terms of the (unknown) solution at the intermediate radius (under the outer rim of the crystal); then one expresses the eigenfunction expansion of the solution under the free surface similarly; then one imposes the constraints that the two solutions match smoothly at the interface. Both solutions involve non-homogeneous partial differential equations in the Laplace domain due to the initial conditions, requiring invocation of (eigenfunction expansions of) the Green's functions; the latter will mismatch at the interface, so the imposed smoothness requires compensating for this mismatch. The details of this compensation have apparently not been considered in previous work. Additionally, other researchers have reported increased accuracy in mode-matching computations when the number of modes considered in each sub-region is different; a rationale for this phenomenon is offered.