International Concrete Abstracts Portal

As recycled concrete reaches the end of its service life, a new generation of coarse recycled aggregate (CRA) is created. Although the variables influencing the physical properties of CRA are well understood, the performance of multi-recycled coarse aggregate (MRCA) remains insufficiently explored, being essential to study how the modified properties could affect the performance of recycled concrete. This research involved five recycling cycles to evaluate the properties of MRCA and its impact on the mechanical and durability performance of concrete made with 75% MRCA. The findings indicate that water absorption, porosity, and abrasion of MRCA increase with each recycling cycle. Although the mechanical behaviour of the concretes appears to be unaffected by the number of recycling cycles, the elastic modulus is negatively impacted when MRCA is used. Furthermore, while some permeability properties are significantly influenced by each recycling cycle, both water penetration depth and resistance to sulfate attack remain largely unchanged.

Service life modeling of microbially induced concrete corrosion (MICC) is essential for assessing structural durability, optimizing maintenance, and minimizing risks in wastewater environments. ASTM C1904-20 is a recently developed biogenic benchtop method for assessing MICC that is safe, accelerated, and practical compared to conventional laboratory tests. The objective of this study is to use the benchtop test to predict the service life of concrete exposed to MICC in sewer pipes. This correlation is based on the Pomeroy model that relates the field H₂S concentrations, wastewater flow conditions, pipe and flow geometry, and the properties of the concrete. A demonstration study is provided to show how the ASTM C1904 data could be used to predict the performance of different types of concrete and antimicrobial products in realistic exposure scenarios. The projected corrosion rates in field conditions reflected the delayed and reduced corrosion rates for mixtures with antimicrobial treatment.

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.

This paper presents findings from an experimental study focused on the performance of concrete composed entirely of 100% slag aggregate, enhanced with polypropylene (PP) fibers, subjected to severe freeze-thaw cycling between -60°C and +60°C. The research employed varying fiber lengths of 19.01, 38.1, and 57.15 mm and dosages of 3, 6, and 9 kg/m³. Findings indicate that the incorporation of fibers contributes to the overall resilience of the slag aggregate concrete under freeze-thaw conditions. To evaluate freeze-thaw resistance, the coefficient of thermal expansion (CTE) was determined using the Ohio CTE method and AASHTO TP60-00. Additionally, dynamic modulus, mass loss, and flexural strength were assessed. X-ray fluorescence (XRF) analysis was performed on slag aggregates to characterize their chemical composition. Findings indicate that the incorporation of fibers, particularly at a dosage of 9 kg/m³ and a length of 57.15 mm, enhances the resilience of the slag aggregate concrete under 300 freeze-thaw conditions as specified in ASTM C666/C666M-15, leading to improved flexural strength and reduced mass loss (less than 7%). However, some fiber-reinforced concrete samples experienced up to a 26.776% decrease in flexural strength after freeze-thaw cycles. Additionally, 38.1 mm fibers at varying dosages effectively mitigated the adverse effects of freeze-thaw cycles on the concrete's thermal expansion. In contrast, concrete without fibers lost over 40% of its mass. This contribution is particularly significant given the scarcity of data on the performance of concrete entirely made up of slag aggregate and mixed with PP fibers of different lengths in extreme weather environments.

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.