International Concrete Abstracts Portal

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.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio reinforced concrete (RC) shear walls when designed using normal-strength reinforcement (NSR) versus high-strength reinforcement (HSR). Such studies demonstrated that the use of HSR has the potential to address several constructability issues in nuclear construction practice by reducing the required steel areas and subsequently reinforcing bar congestion. However, the response of nuclear RC shear walls (that is, aspect ratios of less than 1) with both HSR and axial loads has not been yet evaluated under ground motion sequences. As such, most nuclear design standards restrict the use of HSR in nuclear RC shear wall systems. Such design standards do not also consider the influence of axial loads when the shear-strength capacity of such walls is calculated. To address this gap, the current study investigates the influence of axial load on the performance of nuclear RC shear walls with HSR when subjected to ground motion sequences using hybrid simulation testing and modeling assessment techniques. In this respect, two RC shear walls (that is, W1-HSR and W2-HSR-AL) with an aspect ratio of 0.83 are investigated. Wall W2-HSR-AL had an axial load of 3.5% of its axial compressive strength, whereas Wall W1-HSR had no axial load. The test walls were subjected to a wide range of ground motion records, from operational basis earthquake (OBE) to beyond design basis earthquake (BDBE) levels. The experimental results of the walls are discussed in terms of their damage sequences, cracking patterns, ductility capacities, effective periods, and reinforcing bar strains. The test results were then used to develop and validate a numerical OpenSees model that simulates the seismic response of nuclear RC shear walls with different axial load levels. Finally, the experimental and numerical results were compared to the current ASCE 41 backbone model for RC shear walls. The experimental results demonstrate that Walls W1-HSR and W2-HSR-AL showed similar crack patterns and subsequent shear-flexure failures; however, the former had wider cracks relative to the latter during the different ground motion records. In addition, the axial load reduced the displacement ductility of Wall W2-HSR-AL by 18% compared to Wall W1-HSR. Moreover, the ASCE 41 backbone model was not able to adequately capture the seismic response of the two test walls. The current study enlarges the experimental and numerical/analytical database pertaining to the seismic performance of low-aspect-ratio RC shear walls with HSR to facilitate their adoption in nuclear construction practice.

Current design assumptions for precast, prestressed concrete piles embedded in cast-in-place (CIP) pile caps or footings vary across states, leading to inconsistencies in engineering practices. Previous studies suggest that short embedment lengths (0.5 to 1.0 times the pile diameter) can develop approximately 60% of the bending capacity of the pile, with full fixity potentially achieved at shorter embedment lengths than current design specifications due to confinement stresses. This study experimentally evaluates 10 full-scale pile-to-cap connection specimens with varying embedment lengths, aiming to investigate the required development length for full bending capacity. The findings demonstrate that full bending capacity can be achieved at the pile-to-pile cap connection with shallower embedment than code provisions, challenging existing design standards and highlighting the need for more accurate guidelines for bridge foundation design.

Reinforced concrete members derive flexural strength from reinforcing steel, which acts together with the concrete to mobilize the required capacity. Design standards stipulate mandatory norms that must be complied with during the design process. Non-compliance with these provisions can increase the risk of corrosion, compromising the safety and integrity of the structure. Concrete protects the reinforcing steel against corrosion, but it can also become a contributing factor when its microstructure is poor due to non-compliance with these norms. Assessing the residual flexural capacity is essential for making informed decisions regarding repair or demolition. The proposed model in this paper enables computation of the reduction in flexural strength based either on gravimetric mass-loss percentage or on measured corrosion current density. A design chart is also proposed to facilitate practical application, enabling engineers to assess residual capacity and decide on repair or demolition.

Inverse analysis methods proposed by current standards for extracting the tensile properties of tension-hardening cementitious materials from indirect tension tests (e.g., flexural prism tests) are considered either cumbersome and can only be performed by skilled professionals 1,2 or apply to certain configurations and specimen geometries. Significant discrepancies are reported between the results of direct tension tests (DTT or DT tests) and inverse analysis methods. This has eroded confidence in flexural tests as a method of characterization of tension-hardening Ultra-High Performance Concrete (UHPC) and has motivated its abandonment in favor of DT testing. Additional concerns are size sensitivity, variability, and lack of robustness in the results of some methods. However, DT tests are even more difficult to conduct, and results are marked by notable scatter. This is why some codes allow for bending tests at least for quality control of UHPC. To address the limitations of the bending tests in providing an easy and quick method for reliable estimation of the tensile characteristic properties of UHPC, a new practical method is developed in this paper, based on a Forward Analysis (FA) of third-point bending tests. A unique aspect of the approach is that it considers the nonlinear unloading that occurs in the shear spans of the prism after strain localization in the critical region. The method was used to derive charts for direct estimation of the tensile properties from quality control bending tests, for the commonly used flexural specimen forms and material types. The goal of the study is to provide a practical alternative in the characterization of tension-hardening UHPC materials. Results obtained using the proposed FA method are in good agreement with the tensile response from DT tests. However, it is noted that due to the presence of a strain gradient in bending tests and the larger strain gauge lengths employed in some DT tests, the strain values at localization from DT tests tend to be more conservative.