International Concrete Abstracts Portal

This paper presents the behavior of anchorage zones, also known as end zones, with discrete reinforcing bars and continuous meshes. To examine the implications of various reinforcing schemes on the capacity, cracking, and failure of end zones, 50 block specimens are loaded, and their responses are analyzed. Test parameters include the types of reinforcing bar materials (steel and glass fiber-reinforced polymer, (GFRP)) and the configurations of the reinforcing bars and steel meshes (single and multiple placements). In terms of load-carrying capacity, the specimens embedded with the GFRP rebars outperform those with the steel reinforcing bars and meshes by 14.0%. The post-peak load drop of the blocks with the steel and GFRP reinforcing bars is analogous due to distributed axial stresses in the unreinforced concrete region, differing from the abrupt drop observed in the specimens with the steel meshes that intersect the concrete in orthogonal directions. While concrete splitting originates from local tension generated near the axial compression, the location of cracking is dominated by the path of stress trajectories related to the number of reinforcing bars, which is not recognized in the case of the meshed specimens. The pattern of the isostatic lines of compression clarifies the development of bursting forces that cause cracking in the concrete. A two-stage analytical model is formulated to predict the magnitude of bursting forces and determine the effects of several parameters on the response of the end zones. The applicability of existing design expressions is assessed, and the need for follow-up research is delineated.

The use of recycled plastic aggregate in cement-based materials has emerged as a promising strategy to reduce plastic waste and promote sustainable construction. However, the inherent hydrophobicity of plastic surfaces poses a significant challenge by limiting their bonding with the cement matrix. This review critically examines five major surface treatment methods, such as coating, oxidation, silane, plasma, and radiation, to enhance the compatibility of recycled plastic aggregates in cementitious composites. Coating with materials such as waterglass, slag powder, or acrylic resins improved compressive strength by up to 78% depending on the coating type. Oxidation using hydrogen peroxide or calcium hypochlorite increased hydrophilicity and improved strength by approximately 10%–30%, while excessive treatment with NaOH-hypochlorite mixtures reduced strength by up to 60%. Silane treatment significantly enhanced surface bonding, resulting in improved mechanical properties. Plasma treatment demonstrated high efficiency, reducing contact angles from ~108° to 44.0° within 30 seconds. Radiation treatment using gamma rays and microwaves increased surface roughness and strength, with gamma irradiation at 100–200 kGy leading to substantial improvements in compressive strength and surface morphology. To the authors’ knowledge, this is the first review to systematically compare the effectiveness, mechanisms, and limitations of these surface treatments specifically for recycled plastic aggregates in cement-based materials. This review also highlights the practical challenges of scaling such treatments, including energy demand, chemical handling, and cost, and identifies future directions such as bio-based coatings and nanomaterial functionalization. The findings provide critical insight into optimizing surface treatments to improve the mechanical performance, durability, and sustainability of concrete incorporating plastic aggregates, supporting their broader adoption in sustainable construction practices.

The durability of reinforced concrete is often compromised by chloride penetration, leading to corrosion of reinforcing steel and reduced structural strength. To improve the sustainability and longevity of concrete structures, it is crucial to model and predict chloride permeability (CP) accurately, thereby minimizing the time and resources required for extensive experimental testing. This paper presents a proof-of-concept study applying Artificial Neural Networks (ANN) to predict CP in concrete structures. The model was trained on a small but carefully controlled experimental dataset of 10 concrete mixtures, considering four key parameters: water-to-cementing materials ratio, silica fume content, cementing materials content, and air content. Despite the limited dataset size, which constrains generalizability and statistical robustness, the ANN captured nonlinear relationships among the input parameters and CP. The comparison between experimental and simulated CP values showed reasonable agreement, with errors ranging between –242 and 420 Coulombs. These results establish the trustworthiness and reliability of the proposed model, providing a valuable tool for predicting CP and informing the design of durable and sustainable concrete structures.

CO2 mineralization in concrete enhances cement hydration by reacting with calcium-rich materials, forming nano-scale calcium carbonate that fills micro-pores. This study explores CO2-mineralized concrete performance, produced using a two-step mineralization process. Concrete with 0.2% CO2 by cement weight exhibited significantly higher compressive strength, increasing by 18.78%, 19.27%, and 20.63% at 7, 28, and 56 days, respectively. Isothermal calorimetric analysis confirmed increased heat evolution in CO2-mineralized cement paste, while X-ray diffraction and scanning electron microscopy revealed calcium carbonate formation and more ettringite volume. The higher strength gain due to CO2 mineralization is used to leverage the cement content. A comparative study reveals that CO2-mineralized concrete with 7.5% reduced cement content achieves equivalent strength and durability to conventional concrete, reducing carbon emissions by 8% while significantly lowering cost per unit strength and enhancing sustainability and performance.

Ultra-high-performance concrete (UHPC) is composed of a high volume fraction of binder and steel fibers, and a very low water content, resulting in enhanced strength and ductility, along with higher cost and environmental impacts. This study develops a UHPC mixture amenable to three-dimensional (3-D) printing, with 30% of cement (by mass) replaced with a combination of replacement materials. The proportioned UHPC mixture with 1.5% fiber volume fraction demonstrates 28-day compressive strengths of > 120 MPa (17.4 kips), and limited anisotropy when tested in the three orthogonal directions. Furthermore, 3-D printed layered composites are developed where UHPC (with and without fiber reinforcement) and conventional concrete layers are synergistically used in appropriate locations of the beam so as to achieve mechanical performance that is comparable to 3-D printed UHPC sections. Such manufacturing flexibility offered by 3-D printing allows conserving resources and attaining desirable economic and environmental outcomes, as is shown using life cycle and techno-economic analyses (LCA/TEA). Experimental and theoretical analysis of load carrying capacity and preliminary LCA/TEA show that >50% of the fiber-reinforced UHPC beam volume (in the compression zone) can be replaced with conventional concrete, resulting in only a <20% reduction in peak load carrying capacity, but >35% reduction in cost and >20% reduction in CO2 emissions. These findings show that targeted layering of different materials through 3-D printing enables the development and construction of 3-D-printed performance-equivalent structural members with lower cost and environmental impacts.