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.

In the Netherlands, the existing reinforced concrete solid slab bridges require assessment for shear. Skewed slab bridges form a subset of this category. Previous experiments showed that stresses concentrate in the obtuse corner, which becomes governing for shear, and that the shear capacity in skewed members is reduced. The presented series of experiments studies the shear capacity of reinforced concrete slabs under concentrated loads. In total, five skewed slabs are tested, resulting in 15 shear experiments. The parameters that are studied are the skew angle, the reinforcement layout, the distance between the load and the support, and loading near the obtuse or acute corner. The results are compared to existing calculation methods and recommendations for determining the acting shear stress and shear capacity, which lead to reasonable results. Ultimately, the insights of these experiments can be used for the assessment of existing skewed slab bridges.

Controlling deflections in reinforced concrete (RC) flexural members under service loads is a serviceability requirement prescribed by design codes, such as the ACI CODE-318. Serviceability requirements are challenged by productivity requirements, such as faster construction and longer span demands, among others. This paper summarizes a parametric analysis conducted to estimate long-term deflections of one-way RC slabs. The objective of this study is to assess the effect of geometrical, concrete, and construction parameters on the long-term deflections of one-way RC slabs. The effect of these parameters on immediate deflections is also analyzed. Results of this study show that increasing the slab thickness and the area of tension reinforcement proved to be the most effective strategies for reducing both immediate and long-term deflections of one-way RC slabs. Additionally, the results of the parametric study highlight the relative influence of each studied parameter in controlling deflections.

This study presents a comprehensive field investigation into the long-term behavior of unbonded post-tensioned (PT) concrete flat slabs using Smart Strands embedded with fiber Bragg grating (FBG) sensors. The monitoring program was conducted in a real-world building in Seoul, Korea, spanning over five and a half years and capturing continuous prestressing force and deflection measurements at multiple slab locations. Results revealed that approximately 5% of nominal strength of tendon prestress losses occurred within the first year, stabilizing thereafter, and that deflection patterns were significantly influenced by slab position and construction activities. Comparison with analytical models showed strong alignment, with ACI CODE-318-25 time-dependent coefficients accurately predicting long-term deflections after the early-age period. This study contributes valuable long-term data, validating design codes and guidelines and enhancing understanding of the time-dependent behavior of PT concrete structures.

This paper summarizes the results of an experimental study investigating interface shear resistance through slant shear tests. A total of 54 tests were conducted on 6 x 12 in. (150 x 300 mm) cylinders with inclined cold joints. Five key test parameters were investigated: cold joint inclination, interface roughness, variation in concrete compressive strength between layers, casting age difference, and aggregate size. The test results demonstrated that the most influential parameters affecting interface shear resistance were interface roughness, casting age difference between layers, and aggregate size. Conversely, cold joint inclination and variations in compressive strength between layers were identified as comparatively less influential factors. A comprehensive analytical study was conducted including the comparison of five current design codes. A modified approach is proposed for calculating the interface shear resistance, compatible with current design codes’ expressions. The proposed approach was validated using the experimental results generated from this study and a database of 124 slant shear test results from different research programs. Overall, the proposed approach resulted in more accurate estimations for the interface shear resistance, particularly for specimens with intermediary levels of amplitude at the interface.