International Concrete Abstracts Portal

A slag-based zero-cement concrete (ZC) was newly developed as an alternative, eco-friendly material to Portland cement concrete. To investigate the bond performance between ZC and steel reinforcing bars, lap splice tests were conducted for ZC beams. Fourteen beams (two cementitious normal concrete (NC) beams and twelve ZC beams) were tested at the ages of 6 days (45 MPa (6.53 ksi)) and 28 days (60 MPa (8.7 ksi)). For steel reinforcement, Grade 600 MPa (87.0 ksi) reinforcing bars were used. The test parameters included the concrete type, concrete strength (i.e., concrete age), reinforcing bar diameter, concrete cover thickness, ratio of actual lap splice length to required lap splice length, and use of stirrups. The test results showed that the performance of ZC beams was comparable to that of the counterpart NC beams in terms of moment–deflection relationship, damage mode, and reinforcing bar stress at the peak load. This result indicates that the bond performance of ZC was equivalent to that of NC with identical compressive strength. The bar development length specified in current design codes safely predicted the reinforcing bar stress of the ZC beams at failure: current design codes are applicable to the reinforcing bar development length design of ZC members.

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.

Ultra-high-performance geopolymer concrete (UHP-GPC) can exhibit high to exceptional strength. Given the importance of UHP-GPC’s mechanical properties, prediction of its 28-day compressive strength (fc′) remains insufficiently explored. This study predicts UHP-GPC’s fc′ based on alkali-activated materials, sand, fiber volume, and water-geopolymer binder and alkali activator ratios. Advanced statistical modeling and a spectrum of ensemble machine learning (ML) algorithms including random forest (RF), gradient boosting (GB), extreme gradient boosting (XGB), and stacking are used to predict UHP-GPC’s strength. The derived models reveal the significance of fiber, slag, and sand as the most significant factors influencing the 28-day fc′ of UHP-GPC. All the ML models demonstrate higher precision in forecasting fc′ of UHP-GPC compared to statistical modeling, with R2 peaking at 0.85. Equations are derived to predict the strength of UHP-GPC. This paper reveals that UHP-GPC with superior mechanical properties can be designed for further sustainability.

Slag-based zero-cement concrete (ZC) of high strength (60 MPa [8.70 ksi]) was developed as an eco-friendly construction material. In the present study, to investigate the structural behavior of precast columns using ZC, cyclic loading tests were performed for five column specimens with reinforcement details of ordinary moment frames. Longitudinal reinforcement was connected by sleeve splices at the precast column-footing joint. The test parameters included the concrete type (portland cement-based normal concrete [NC] versus ZC), construction method (monolithic versus precast), longitudinal reinforcement ratio, and sleeve size. The test results showed that the structural performance (failure mode, strength, stiffness, energy dissipation, and deformation capacity) of the precast ZC columns was comparable to that of the monolithic NC and precast NC columns, and the tested strengths agreed with the nominal strengths calculated by ACI 318-19. These results indicate that current design codes for cementitious materials and sleeve splice of longitudinal reinforcement are applicable to the design of precast ZC columns.