International Concrete Abstracts Portal

The composition of OPC changed in North America with the addition of ground limestone in 2004 (since the adoption of ASTM C150-04a), which reacts to form carboaluminate hydration products. This paper discusses the potential influence of limestone addition on porosity, pore connectivity, formation factor, and electrical properties of cementitious systems. The carboaluminate reaction products can result in a system with limestone that has an equivalent water-to-powder ratio (w/p) that is approximately 0.07 lower than the system without limestone (occurring at the minimum porosity). When reactive alumina is added to the system, a greater amount of limestone reacts, and a reduction in porosity occurs. The carboaluminate phases impact the transport properties of mixtures to a greater extent for mixtures with moderately low w/p and aluminous SCMs. This has implications on standards and specifications, which are based on historic research and testing using cements not containing limestone, and therefore would have a higher porosity and lower formation factor than cements manufactured in the US after approximately 2004 at the same w/p.

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 stresses1. 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 of 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.

This paper presents the effectiveness of various reinforcing schemes in the end zones of prestressed concrete bulb-tee girders. The default girder, provided by a local transportation agency, includes C-bars and spirals intended to control cracking, and is analyzed using three-dimensional finite element analysis. The formulated models are used to evaluate the breadth of end zones, strain responses, cracking patterns, damage amounts, and splitting forces, depending upon the configuration of the end-zone reinforcement. The number of C-bars is not influential in developing strand stress along the girder. The maximum principal stresses exceed the conventional limit within h/4 of the girder end, where h is the girder depth; however, the 3h/4 limit adequately encompasses the stress profiles, particularly in the web of the girder. The maximum tensile strain in the concrete varies with the elevation of the girder, and the inclined strands cause local compression in the C-bars, while spiral strains are independent of the number of bars. By positioning the C-bars, the vertical strain of the concrete decreases by more than 15.9%, which can minimize crack formation. Whereas the short-term crack width of the girder may not be an immediate concern, its long-term width is found to surpass the established limit of 0.18 mm (0.007 in.). In this regard, multiple C-bars should be placed to address concerns about undesirable cracking. The splitting cracks in the girder, resulting from the strand angles and eccentricities, can be properly predicted by published specifications within the range of 0.2h to 0.7h, beyond which remarkable discrepancies are observed in comparison with a refined approach. From a practical perspective, two to three No. 6 or No. 7 C-bars spaced 150 mm (6 in.) apart are recommended in the end zones alongside welded wire fabric.

Engineered cementitious composites (ECC) represent a significantinnovation in construction materials due to their exceptionalflexibility, tensile strength, and durability, surpassing traditionalconcrete. This review systematically examines the composition,mechanical behavior, and real-world applications of ECC, with afocus on how fiber reinforcement, mineral additives, and micromechanical design improve its structural performances. The present study reports on the effects of various factors, including different types of mineral admixtures, aggregate sizes, fiber hybridization, and specimen dimensions. Key topics include ECC’s strain hardening properties, its sustainability, and its capacity to resist crack development, making it ideal for high-performance infrastructure projects. Additionally, the review discusses recentadvancements in ECC technology such as hybrid fiber reinforcementand the material’s growing use in seismic structures. The paper also addresses the primary obstacles, including high initial costs and the absence of standardized specifications, while proposing future research paths aimed at optimizing ECC’s efficiency and economic viability.

Design codes base the behavior of the shear-friction interface on two models: the basic shear friction model and the cohesion plus friction model. These models have been developed using steel as the reference reinforcing material and they have extended to design provisions when using glass fiber-reinforced polymer (GFRP) materials. However, when using GFRP reinforcement, where yielding does not happen, a different ultimate limit state needs to be introduced. Accordingly, additional data and analysis are required to validate and improve the proposed models and to verify what implications they have on design when specifying GFRP materials. In this research, a study was conducted based on previous experimental data on the contribution of GFRP bars to the mechanism of shear transfer by using the pushoff test. Through a multiple linear-regression analysis, a mathematical model introducing new parameters that accurately capture the behavior of this material with respect to shear-transfer phenomena in concrete structures is presented in this paper. The findings of this study provide new insights into the behavior of the shear-friction mechanism with GFRP reinforcement, suggesting potential updates for current design codes and guide specifications.