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.

Brittle punching failures in flat plates are precluded by ensuring adequate shear strength. Typically, this is achieved by adding shear reinforcement in the design. This paper presents an experimental and analytical study of flat plates to investigate load-resisting mechanisms associated with stirrup addition. The experimental program includes four isolated flat plates with parametric variations tested under monotonic punching loads. In terms of normalized shear strength, improvements of 22% and 29% were observed in flat plates with different layouts of stirrups, respectively, when compared with the reference specimen without stirrups. The role of longitudinal and shear reinforcements in punching resistance of flat plates was assessed through strain observations. Based on test findings, a physics-based analytical procedure for punching capacity estimation is proposed and verified using a database of 72 isolated flat-plate specimens. The proposed method provided reasonably accurate capacity estimates with an overall mean test-to-estimated capacity ratio of 1.06 and a low coefficient of variation (COV) of 13%. These estimates are also compared with capacity predictions using ACI 318-19 guidelines, which resulted in an overall mean capacity ratio of 1.58 with a COV of 22%. Based on experimental and analytical results, modifications to ACI 318-19 two-way shear provisions are suggested by incorporating the key parameters in shear strength estimations, which improved the prediction accuracy to a mean of 1.25 with a COV of 13%.

Nuclear power plants use reinforced concrete shear walls with flanges for lateral load-resisting systems. The present study investigated the shear-friction strength of reinforced concrete walls with flanges by testing eight wall specimens under cyclic lateral loading. The test parameters were the flange length, flange configuration, wall thickness, interface roughness, and load direction. The test results showed that vertical reinforcing bars in the flanges, as well as the web, increased the shear-friction strength of the walls. However, due to the premature punching failure at the web-flange joint, the contribution of the thin flange was limited. Further, the shear-friction strength of the symmetric flanged wall was identical, regardless of the load direction: the shear-friction strength of the flanged wall was determined by the total vertical reinforcing bars placed in the web and flange. The tested shear-friction strengths, including previous test results, were compared with the predictions of current design methods. Including the flange contribution in the current design methods improved the prediction of test results compared to the case neglecting the flange contribution.

Laboratory tests of deep, lightly reinforced concrete members without shear reinforcement demonstrate that the nominal shear stress at failure decreases with increasing depth and with decreasing tension longitudinal reinforcement ratio. Design procedures for one-way shear strength in ACI 318-19 incorporate these effects, but result in relatively low design shear strengths for members with both large depth and low reinforcement ratio. To better understand the effects of depth and longitudinal reinforcement on shear strength, tests were conducted on beams with varying depth, a relatively low ratio of high-strength longitudinal reinforcement, and with either no shear reinforcement or minimum shear reinforcement. Loads were applied slowly and monotonically and included concentrated loads plus self-weight. Beam supports were either point supports, as in a beam, or uniformly distributed, similar to some foundation reactions. The test results demonstrate size and longitudinal reinforcement effects and suggest that a lower-bound unit shear strength may be applicable for the design of members with both large depth and low reinforcement ratio.

The bond property between deformed bars and concrete plays a significant role in the safety of construction. Numerous database-dependent empirical models are proposed to evaluate the bond behavior without considering the effect of additional confinement, whose application range is quite limited as a result of unstable accuracy. In this paper, a new model was established based on the thick-walled cylinder model and fictitious crack theory, which can predict bond strength and bond-slip response with fiber-reinforced polymer (FRP)-steel confinement. The effects of various factors on the bond behavior such as concrete strength, concrete cover, reinforcing bar diameter, bar surface geometry, and FRP/steel confinement were comprehensively discussed. According to radial crack radius, the radial stress and displacement induced on bond interface can be calculated, and thus analytical formulae of bond strength and slip were respectively developed in conjunction with deformed bar surface geometry. Finally, a new analytical model was proposed, which can simulate the bond-slip curves of the specimens with different confinement levels, covering unstrengthened, FRP-strengthened, stirrup-strengthened, and FRP-stirrup dually strengthened specimens. Compared with existing models, the proposed model can provide better agreement with existing test results.