International Concrete Abstracts Portal

Advancements in AI and computational models have significantly enhanced the predictability of concrete performance by leveraging extensive datasets. Recently, machine learning models have been developed to predict concrete’s compressive strength based on its mixture proportions. However, these models treat supplementary cementitious materials (SCMs) as a categorical (as opposed to quantitative) parameter and do not account for the significant impact of the SCM reactivity on concrete’s strength development. In this study, we assembled a dataset of binary (cement-SCM) mixtures, incorporating SCM reactivity measured by the R3 (ASTM C1897) test. Utilizing a random forest machine learning model, we demonstrated that integrating SCM reactivity significantly enhances the model's predictive performance with the fewest input parameters (w/cm, SCM/cm, SCM R3 heat, Agg/cm, cement CaO%). Further, we implemented a multi-objective Bayesian optimization framework to assist in the mixture proportioning of low-carbon low-cost concrete utilizing cement(s) and SCM(s) available to a concrete producer. This framework proposes concrete mix designs to meet a target 28-day compressive strength while minimizing cost and CO2 emissions, by leveraging SCMs with varied reactivity levels. The proposed mix designs were further validated with experiments. The work demonstrates how to avoid model extrapolation and erroneous predictions by utilizing a multi-dimensional convex envelop algorithm. Overall, the outcomes of this work provide a valuable tool for the concrete industry which can be expanded to predict and incorporate other metrics of concrete performance (e.g., workability, durability) and develop optimized mix designs accordingly.

This paper proposes new procedures for determining allowable loads for power-actuated fasteners that are consistent with ASCE/SEI 7-22. Thirty new load test data sets for single fasteners in shear and tension and fastener groups in shear are analyzed statistically. The current ICC-ES AC70-2021 procedure yields allowable loads that are quite variable, even negative, and very sensitive to “reject-as-outlier” decisions. In addition, ICC-ES AC70 procedures to determine allowable loads can currently not be clearly linked to the reliability requirements of ASCE/SEI 7-22. Monte Carlo simulation demonstrates that the proposed simplified method, derived from the described detailed method, is robust for sample sizes as small as 10 specimens. It yields allowable fastener loads that are 10 to 25% greater than those obtained using the current ICC-ES AC70 procedure yet are typically 60 to 90% of the actual allowable fastener loads, derived from the described detailed method to assess allowable loads in line with ASCE/SEI 7-22 reliability requirements. The new provisions are extended to cases where the coarse aggregate hardness in the test specimens differs from that in the structure, which is not addressed in ICC-ES AC70.

This paper presents the implications of variable bond for the behavior of concrete beams with glass fiber-reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded reinforcing bars, which are intended to represent sequential bond damage. Conforming to published literature, three shear span-depth ratios (av/d) are taken into account: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the reinforcing bar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the av/d from 1.5 to 3.7, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams by up to 40.2%, and the slippage of the partially bonded reinforcing bars dominates their flexural stiffness. Compared with the case of the beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of reinforcing bar stress is dependent upon the av/d and, in terms of using the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of reinforcing bar stresses with bond damage when subjected to arch and beam actions.

This study investigated the flexural behavior and seismic connection performance of precast lightweight aggregate concrete shear walls (PLCWs) using the relative emulation evaluation procedure specified by the Architectural Institute of Japan (AIJ). Six PLCW specimens connected through a bolting technique were prepared and tested under constant axial and cyclic lateral loads. In addition, three companion shear walls connected through the most-used spliced sleeve technique for precast concrete members were prepared to confirm the effectiveness of the bolting technique for the seismic connection performance. The main parameters were the concrete type (all-lightweight aggregate [ALWAC], sand- lightweight aggregate [SLWAC], and normalweight concrete [NWC]); the compressive strength of the concrete; and the connection technique. The test results showed that none of the specimens connected through the conventional spliced sleeve technique reached the allowable design drift ratio specified by the AIJ, indicating that the spliced sleeve is an unfavorable technique for obtaining a seismic connection performance of PLCWs equivalent to that of cast-in-place reinforced concrete shear walls. However, the specimens made of ALWAC or NWC and connected through the bolting technique not only reached the allowable design drift ratio specified by the AIJ but also satisfied the requirements of the seismic connection performance (lateral loads and allowable error at yield displacement) within the allowable design drift ratio. Consequently, the displacement ductility ratio of the specimens connected through the bolting technique was 1.52 times higher than those for the specimens connected through the conventional spliced sleeve technique, respectively. This difference was more prominent in the specimens made of ALWAC than in those made of SLWAC or NWC. Thus, the use of the bolting technique as a wall-to-base connection in shear walls can effectively achieve a seismic connection performance equivalent to that of cast-in-place shear walls while maintaining the medium-ductility grades.

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.