International Concrete Abstracts Portal

This study presents the development of a novel three-dimensional (3-D) assembled retaining wall block system, in which individual blocks are interconnected in the upper-lower, left-right, and front-back directions. Unlike conventional segmental block gravity walls that rely solely on horizontal shear keys between upper and lower blocks, the proposed 3-D system is designed to resist shear forces across the entire block cross-section through comprehensive mechanical interlocking. To evaluate its structural performance, direct shear tests were conducted, focusing on two key parameters: the block arrangement between the front and back sides, and the frictional resistance between the block and the foundation concrete. Experimental results demonstrated that the proposed system exhibits significantly enhanced shear strength compared to conventional retaining wall systems. Based on these findings, shear strength estimation formulas were developed to support structural design and stability assessment. The proposed 3-D block system not only improves the mechanical integrity of retaining walls but also holds potential for enhanced resilience against complex geotechnical challenges due to climate change. These results suggest that the new system provides a reliable and robust alternative for the design of segmental retaining walls requiring high shear resistance and long-term stability.

The concept of multi-generational 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-generational concrete subjected to chloride salt dry-wet cycling. After 30 dry-wet 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 dry-wet 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 mixes, 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 concrete composites with textile waste provides a sustainable path for circular construction. This paper reports the effects of the incorporation of textile-derived cellulose on the performance of cementitious composites. The study investigated the effect of the substitution of cement with micro-cellulose, 0 to 5%, on the compressive strength of cement paste. Isothermal calorimetry revealed cellulose delays initial hydration and increases the cumulative heat release over time. Chemical and microstructural analytical techniques like Thermogravimetric analysis, Nuclear Magnetic Resonance, Mercury Intrusive Porosimetry, and Scanning Electron Microscopy were employed to examine the reaction kinetics of the cement when incorporating recycled cellulose. The research findings highlighted that recycled textile cellulose notably impacts the cement paste hydration process and the properties developed. Optimal cellulose content was identified as 1% by cement weight.

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.

To improve the ductility of fiber-reinforced polymer reinforced concrete structures, the hybrid reinforcement with glass fiber-reinforced polymer (GFRP) and stainless steel (SS) is selected in this paper. Nine seawater sea sand concrete beams were designed and tested. The effects of concrete strength, effective reinforcement ratio ρ₂, and reinforcement type in the tensile zone on the flexural behavior of the beams were analyzed. The test results show that with the same concrete strength and the same effective reinforcement ratio ρ₂, the ductility of hybrid reinforced beams is higher than GFRP reinforced beams; the comparison of mid-span deflection of the GFRP bars and hybrid reinforced beams are not only depend on the reinforcement type, but also depend on the total stiffness of reinforcement before SS bars yield in the tensile zone and whether the SS bars are yielding in the tensile zone. Meanwhile, theoretical analysis was conducted for cracking moment, ultimate flexural load-carrying capacity, and mid-span deflections. A new ultimate flexural load-carrying calculation equation was proposed, which predicted the experimental values in good agreement.