International Concrete Abstracts Portal

This study investigates how flexural moments at the locations of drilled cores influence the compressive strength of cores. Reinforced concrete slabs were subjected to three-point loading, and cores were extracted from locations with varying levels of the internal bending moment. Additional cores and push-out cylindrical specimens were extracted from companion control slabs that were not loaded. The coarse aggregate type (natural or recycled concrete aggregate) was another variable in the slabs. A total of 129 drilled cores, 100 mm in diameter, were tested. The results showed that the flexural moments at the locations where cores were extracted reduced the compressive strength of the cores by 7% on average, even in locations where the flexural moments did not exceed the value of the experimentally observed cracking moment. They also showed that the strength of cores extracted from recycled aggregate concrete is weaker than that of standard 28-day moulded cylinders.

This study evaluated the performance of recycled brick-concrete aggregate concrete (RB-CAC) incorporating both recycled brick aggregate (RBA) and recycled concrete aggregate (RCA). It further examined the reinforcement effects of polypropylene macrofibers (PPMF) on the composite and assessed its mechanical properties and frost resistance. The results showed that incorporating 15% RBA reduced the compressive and splitting tensile strengths of concrete by less than 20%, while the peak load decreased by 28.8%. Fiber incorporation effectively mitigated compressive strength degradation and significantly enhanced tensile strength, with the optimum fiber dosage at 0.9% by volume. However, RBA incorporation reduced frost resistance, resulting in a 37.6% strength loss and a 40.6% mass loss after 100 freeze-thaw cycles. In contrast, a 0.6% fiber admixture improved frost resistance, reducing strength loss and increasing the relative dynamic elastic modulus by 26.7%. Finally, the study established a frost-resistance durability prediction model based on PPMF and RBA content.

The concept of multi-generation concrete recycling is increasingly relevant as many existing recycled concrete structures near the end of their service lives. This study examines the performance variation and recyclability of multi-generation concrete subjected to chloride salt drying-and-wetting cycling. After 30 drying-and-wetting cycles, natural aggregate concrete, designed with three different strength grades, was crushed to produce the first generation of recycled fine aggregate, which was then used to prepare the second generation of concrete. This second generation was subjected to the same drying-and-wetting cycling and subsequently crushed to yield a second generation of recycled fine aggregate. The results demonstrate a significant decline in the performance of the second generation of concrete, with an average compressive strength reaching only 89.52% of the first generation. Notably, the performance deterioration was more pronounced in lower-strength mixtures, which exhibited increased porosity, greater mass loss, and deeper chloride penetration. Both generations of recycled fine aggregate met the standards for Class III aggregate; however, some properties of the recycled fine aggregate derived from higher- strength concrete qualified for Class II aggregate status. Additionally, a regression analysis model was developed to predict the attenuation coefficients for the third generation of concrete with design strengths of 30, 45, and 60 MPa, yielding coefficients of 56.84%, 67.75%, and 71.72%, respectively. This study underscores the potential for multi-generational use of recycled fine aggregates and highlights the importance of selecting appropriate design strengths to enhance durability and recyclability in chloride-rich environments.

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—coating, oxidation, silane, plasma, and radiation—to enhance the compatibility of recycled plastic aggregates in cementitious composites. Coating with materials such as water glass, 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 to 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 degrees within 30 seconds. Radiation treatment using gamma rays and microwaves increased surface roughness and strength, with gamma irradiation at 100 to 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 amount of recycled concrete powder (RCP) experiences an exponential increase due to the construction and demolition activities associated with buildings and infrastructure. To enhance the reactivity and use of RCP, this study investigated the effect of thermal (calcination), inorganic (calcium hydroxide [CH]), organic (diethanolisopropanolamine [DEIPA]), and synergistic activation on the strength development of RCP-cement (RCP-C) pastes. The microstructure of hardened pastes was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). The results indicated that the optimal compressive and flexural strengths were achieved when pastes were activated by calcination at 700°C for 30 minutes, followed by inorganic and organic activation using CH and DEIPA as activators successively. The compressive (flexural) strength at 1, 3, and 28 days increased by 42% (26.9%), 27.0% (18.6%), and 25.5% (16.3%), respectively, compared to the control group. The microstructure analysis revealed that the enhancement mechanism can be attributed to a thermal-inorganic-organic synergistic activation.