International Concrete Abstracts Portal

Over the last two decades, the literature has focused on using glass fiber-reinforced polymer (GFRP) bars in compression members. Nonetheless, several aspects have yet to be explored. One such aspect is the lap splicing of GFRP reinforcement. Limited research has examined the splice strength of GFRP bars in concentric compression members. None has been performed on eccentrically loaded columns with lap-spliced bars. In the current study, nine full-scale GFRP reinforced concrete columns measuring 305 mm in diameter and 1600 mm in length with splices in both compression and tension were tested under moderate, high, and extreme eccentricity. The splice lengths used were 12, 24, and 36db for each eccentricity. In addition, five similar specimens from the literature were used for comparison: two had 24 and 36db splice lengths and were tested under concentric loading; the other three had continuous bars tested under different eccentricities. The comparison was in terms of load–displacement curves, load–splice strength curves, and contribution of splice components. The experimental results were compared to the provisions provided in ACI 440.11-22 and CSA S6-25. An interaction diagram based on the recommendations of CSA S806-12 was also drawn and compared to the interaction diagram of the experimental data. Test results indicate that the end-bearing was considerable and is a critical factor, especially at moderate eccentricity. Furthermore, the columns with spliced bars showed a higher peak load than columns with continuous bars, and splice length had a positive effect on splice strength and peak load. The analysis shows that the equation in ACI 440.11-22 and CSA S6-25 is significantly conservative. The results of this research will inform the development of new and accurate design equations for economic lap splices in subsequent phases of the study. They will also encourage design codes to consider end-bearing in compression splices.

Construction technology exerts a significant influence on the bearing behavior of pile foundations. Taking an airport expansion project as the engineering background in Lanzhou City, Gansu Province, China, a comparative analysis of the bearing behaviors of dry-bored piles and slurry wall-protected bored piles through static load tests and numerical simulations was conducted. The main conclusions are as follows: Both test piles exhibit a load-settlement curve of the steep-drop type. Compared with dry-bored piles, slurry wall-protected bored piles tend to accumulate sediment at the pile base, leading to increased settlement. In addition, a mud cake tends to form along the shaft of slurry wall-protected bored piles, which restrains the mobilization of shaft friction and further exacerbates settlement. Under identical load and pile length conditions, the end-bearing resistance, degree of shaft friction mobilization, and axial force in dry-bored piles are consistently lower than those in slurry wall-protected bored piles. Different construction technologies affect the load-transfer mechanism of pile foundations. During the drilling of slurry wall-protected bored piles, the surrounding soil is infiltrated by slurry, and a mud cake is formed on the pile shaft—this not only reduces the mobilization of shaft friction but also results in a slower decay of axial force along the pile. The presence of the mud cake increases the vertical displacement of the soil around the pile tip, and the magnitude of this displacement increases with the thickening of the mud cake. Moreover, the vertical displacement of the surrounding soil decreases as the elastic modulus of the mud cake increases.

Limestone calcined clay cement (LC3) has the potential to provide high clinker replacement in cement blends while providing excellent engineering properties and durability with low environmental impact, but such blends of clinker, limestone, and calcined clay are still in the industrial trial stage in the United States (US). In this study, it is proposed that sources of calcined clay (C), Type IL portland cement (IL), and additional limestone powder (L) can be blended into a “CC·I·L” cement to speed up the implementation of LC3-like systems in the US by combining already commercially available components during concrete mixing. In this investigation, regional CC·I·L blends were prepared using ASTM C595 Type IL cements and calcined clays, replacing 20% - 30% of the cement, from suppliers in the east, west, central, and mountain areas of the US, with additional ground limestone to reach a total limestone content of up to 15% by mass of the total cementitious system. To investigate the feasibility of this approach, fresh properties, early and late age performance, and durability of pastes and mortars made with the CC·I·L blends were examined and compared to ASTM C595 standard performance requirements and performance of regionally available Type IL cements. The results showed that 30% calcined clay and 15% limestone can be used to produce CC·I·L blends in each studied region to meet the ASTM C595 strength requirements. However, gypsum adjustment up to 5.0% was necessary to address undersulfation of CC·I·L blends in some of the regional blends. The results demonstrate the feasibility of using CC·I·L in the US without intergrinding, by taking into account key design factors such as the reactivity of calcined clays, sulfate balance, performance, durability, and possible environmental impact.

Ultra-high-performance concrete (UHPC) often contains conductive steel fibers that interfere with conventional electrical durability tests, such as resistivity measurements, limiting their reliability for mixture qualification. This study proposed an accelerated chloride migration electrical (ACME) test to rapidly assess the durability of UHPC with steel fibers against chloride ingress. Four strength classes ranging from high-performance concrete to UHPC were made with three steel fiber contents (0, 1.5, and 2%) and cured under fog, steam, and precast regimens. ACME test results were compared against surface/bulk resistivity and long-term bulk diffusion measurements to assess their consistency and sensitivity to fiber content. Across mixtures ≥18 ksi, fiber inclusion had minimal influence on ACME penetration depth, and strong correlations were observed between ACME results and one-year diffusion coefficients. Based on these findings, a 7-day ACME limit for steam-cured samples is proposed as a rapid, fiber-independent acceptance criterion for qualifying the chloride penetration resistance of UHPC mixtures.

Hydrostatic pressure has a significant impact on the transportation of chloride ions in concrete, especially in underground structures and marine environments. This paper proposes a new seepage velocity model that considers the combined effects of hydrostatic pressure and initial hydraulic gradient on chloride ion transport. By combining saturated and unsaturated concrete seepage models and convection-diffusion coupled chloride ion transportation analysis, the influence of hydrostatic pressure and seepage velocity on chloride ion transport in concrete is studied. Experimental verification shows that the proposed model can accurately predict the concentration distribution of chloride ions. The analysis results indicate that the seepage velocity under hydrostatic pressure is not only positively correlated with the permeability coefficient of concrete and hydrostatic pressure, but also negatively correlated with the initial hydraulic gradient, and has a significant impact on the transient seepage characteristics of unsaturated concrete. The effect of seepage velocity on the chloride ion transportation process exhibits nonlinear characteristics. Before a critical value, seepage velocity promotes the transportation of chloride ions, while after exceeding this critical value, the influence gradually decreases. Based on this conclusion, it suggests that in the durability design of underground concrete structures, a chloride ion transportation model considering the convection-diffusion coupled effect should be adopted for a more accurate prediction on the service life of the structure.