International Concrete Abstracts Portal

As global demand for concrete has been forecasted to continue rising, one of the approaches toward more sustainable construction is the adoption of mixture designs that replace conventional ones. The current study contains a comparison between concrete mixtures that constitute only ordinary portland cement (OPC) and mixtures incorporating 25% OPC with a 75% replacement by supplementary cementitious materials (SCMs). The major experimental hypothesis focuses on investigating whether it is effective to use thermal treatment under moderately elevated temperatures to enhance physical and mechanical properties of concrete. Comparisons were performed using mechanical tests such as compressive strength, tensile strength, and flexural strength, and through several nondestructive physical experiments, as well as microstructural investigation using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In conclusion, the experimental results showed a mostly positive influence, observing significant enhancements after thermal treatment. However, treated concrete mixtures that constitute only OPC seem to excel in overall performance compared to those incorporating SCMs.

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 challenges of deterioration and increasing maintenance costs in steel-reinforced concrete railway sleepers emphasize the urgent need for innovative, durable, and sustainable alternatives. This study evaluated the shear strength of precast concrete sleepers prestressed with basalt fiber-reinforced polymer (BFRP) rods, using normal self-consolidating concrete (NSCC) and fiber-reinforced self-consolidating concrete (FSCC). Seven full-scale specimens, each 2590 mm (8 ft, 6 in.) in length and prestressed to 30% of the tensile strength of BFRP rods in accordance with the Canadian Highway Bridge Design Code (CHBDC), were tested to assess cracking loads, ultimate strength, bond behavior, and failure mechanisms. All tests were conducted in accordance with the American Railway Engineering and Maintenance-of-Way Association (AREMA) guidelines. The results indicate that all specimens met AREMA design load requirements without visible cracks or slippage based on a train speed of 64 km/h (40 mph), annual traffic of 40 MGT (million gross tons), and sleeper spacing of 610 mm (24 in.). Comparative analysis using CSA S806-12 (R2021) design standard and ACI 440.4R-04 (R2011) design guide revealed that predictions based on CSA S806-12 (R2021) were less conservative than those from ACI 440.4R-04 (R2011) for the shear strength of BFRP prestressed sleepers. The BFRP rods exhibited excellent tensile performance, with minimal prestress losses, and their sand-coated surface ensured efficient load transfer by preventing slippage and enhancing the bond strength. FSCC specimens demonstrated delayed cracking, enhanced crack control, and ductility compared to NSCC specimens. These findings highlight the potential of BFRP prestressed concrete sleepers, particularly when combined with FSCC, as a sustainable solution for railway infrastructure, emphasizing the need for a design code refinement for BFRP applications.

Portland Limestone Cement (PLC) has gained widespread use as the most accessible and sustainable blended cement in the market. However, in many African countries, including Ghana, the use of clay pozzolana in the concrete industry has primarily relied on Ordinary Portland Cement (OPC). In this study, PLC Type II/B-L was partially replaced with clay pozzolana at levels ranging from 10% to 50% by weight. The investigation included compressive strength testing, non-destructive evaluations using electrical surface resistivity, pulse velocity, and chloride penetration tests, targeting a characteristic strength of 30 MPa. Additionally, an environmental impact assessment based on the carbon footprint of both control and clay pozzolana concretes was conducted. The mix design followed the EN 206 standard. A total of 72 cubic moulds were produced for the strength test. The results showed that clay pozzolana concretes with between 10 and 20% replacement achieved strength values of 35 and 33 MPa, respectively, higher than the target of 30 MPa (4351.13 psi) strength at 28 days. However, mixtures with 30% to 50% replacement required extended curing periods of 60 to 90 days to reach the desired strength. At extended curing, 10-50% clay pozzolana replacement attained strength between 32 and 41 MPa. Non-destructive test results showed no direct correlation with compressive strength, confirming that different factors govern strength, resistivity, and pulse velocity. The environmental impact assessment revealed a 14 to 51% reduction in CSi and a 19 to 36% increase in CRi with 10 to 50% clay pozzolana (for CSi) and 10 to 40% (for CRi). The thermodynamic modelling also revealed that pozzolana contents below 30% primarily promoted pozzolanic reactions, enhancing performance compared to the control mix. Based on these results, 20–30% clay pozzolana replacement is recommended to ensure reliable performance, while higher levels (>30%) require further durability evaluation for long-term use.

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.