International Concrete Abstracts Portal

Due to the excellent deformation coordination ability and permeability, bentonite has been widely introduced to modify concrete in underground geotechnical engineering. However, the underlying mechanism for bentonite modification remains unexplored. A series of experiments was performed to clarify the modification mechanism of bentonite. The results showed that all strengths decreased upon bentonite addition, while high toughness was achieved. The micro-test results revealed that bentonite promotes the dissolution of calcium hydroxide (CH) and the nucleation of calcium silicate hydrate (C-S-H) in the interfacial transition zone (ITZ). The hydration products produced by the reactive ions and ultrafine bentonite particles continuously reduced the porosity and Ca/Si ratio in ITZ, strengthened the interface bonding, and controlled the coalescence of microcracks. Inversely, bentonite particles tend to adsorb large amounts of water and hinder the available water from accessing cement grains, which results in an increased porosity and slower hydration progress of cement grains. The loose microstructure cannot be compensated for by reinforced interfacial bonding and inevitably results in the deterioration of mechanical performance in composites.

This study investigates the bonding behavior of large-diameter steel bars (D43 and D57) embedded in concrete using pull-out tests coupled with acoustic emission (AE) monitoring. These large bars, commonly used in nuclear containment structures from the 1970s, were compared with conventional steel bars (D19 and D32) across three concrete strength levels. All tests were performed under displacement-controlled loading using an MTS testing machine. Results indicate that ACI 408R provisions remain valid for large-diameter reinforcing bars. The test results showed that when specimens reached ultimate bond stress, the D57 bar developed only 12 to 16% of its yield strength, whereas the D19 bar reached at least 70%. AE monitoring effectively captured the debonding process, and cumulative AE hit counts correlated with the strain energy released at each loading stage, offering insight into bond failure mechanisms.

This study investigates the structural performance improvement when bond beams are included in stack bond walls. Nine 4.0 m x 2.4 m x 0.20 m masonry walls were tested under out-of-plane and axial loads. The walls were constructed in three configurations: running bond, stack bond without bond beams, and stack bond with bond beams, following TMS 402/602 standard. Results show similar failure patterns and crack formation between running bond and stack bond walls, but stack bond walls with bond beams exhibited distinct behavior. Stack bond walls with bond beams showed slightly higher out-of-plane flexural capacity compared to running bond walls, with a difference ranging from 4 to 5%. These findings provide valuable insights for evaluating the structural performance of concrete masonry walls with different bonding patterns. This study suggests a potential revision to the Canadian (CSA S304) masonry design standard, potentially lifting restrictions on stack bond masonry wall construction.

This study investigated the shear bond behavior, with and without optimized interfaces, between conventional and geopolymer steel fiber–reinforced concretes. Sixteen prismatic and eight cylindrical composite specimens were cast with interface inclination angles of 45° and 27°, respectively. In prisms, the inclined interface area was varied: eight were optimized by 50% to balance compressive and shear stresses, allowing a more accurate determination of cohesion and friction coefficients under steel fiber effects. Fiber volume fractions of 0.0, 0.5, 1.0, and 1.5% were tested, and the influence of epoxy at the interface was also assessed. Optimized prisms exhibited adhesive failure along the interface, matching the internal friction angle, whereas non-optimized prisms showed cohesive failure with a friction angle deviating from the interface. Increasing fiber content improved performance, especially when combined with epoxy. A new bond shear strength model is proposed, incorporating friction, cohesion, and fiber effects.

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.