International Concrete Abstracts Portal

Drilling support fluid is used to stabilize deep excavations during the construction of cast-in-place concrete foundations like drilled shafts. During concreting operations, flowable concrete, tremie-placed or pumped to the bottom of the excavation, displaces the lower-density support fluid. Reinforcement cage congestion from tight rebar spacing requires concrete to build sufficient pressure head inside the reinforcement cage before radially filling the annular cover region. Even under ideal conditions, the support fluid-concrete interface produced during radial flow has been proven to impact side shear capacity, corrosion resistance, concrete strength, and rebar bond strength. These effects largely go unnoticed. This paper compiles the findings of 13 studies conducted to highlight the impact of support fluid performance on drilled shaft construction while providing recommendations vital to the evolution of concrete placement practices in deep excavations.

This research aims to provide a theoretical foundation for the structural design of magnesium phosphate cement (MPC) in high-temperature environments and facilitate the recycling of municipal solid waste incineration bottom ash (BA). Uniaxial compression tests of BA-MPC after exposure to temperatures from 20 to 1000°C were carried out. Subsequently, the stress-strain curve, peak stress, peak strain, and deformation modulus were examined. The peak stress, peak strain, and deformation modulus, considering the influence of temperature factors, are proposed using regression analysis. Based on the continuum damage mechanics, the axial compression damage constitutive model of MPC is developed, accompanied by an analysis of its temperature damage characteristics. The results show that BA improves MPC strength and helps stabilize its deformation after exposure to high temperatures. The peak stress of MPC decreases after exposure to high temperatures, and the peak stress of BA-MPC is higher at the same temperature. At 1000°C, the peak stress of MPC ranges between 15.86 and 28.38 MPa. After high thermal exposure, the peak strain fluctuation of the MPC with BA stays small, and the deformation modulus is higher than that of the MPC without BA. The developed MPC axial compression damage constitutive model can accurately describe the stress-strain relationship of MPC under axial compression following high-temperature exposure, with a correlation coefficient greater than 0.86. The temperature damage variable of MPC rapidly accumulates in the range of 20 to 200°C. At 600°C, the temperature damage variable and the total damage variable without BA attained maximum values of 0.656 and 0.751, respectively. BA can reduce the total damage and temperature damage of MPC to a certain extent.

The determination of the static coefficient of friction between steel and concrete is essential for the design and safety of structures, particularly in systems operating under low axial stresses, such as foundation slabs supporting waste storage casks. In such applications, sliding resistance and shear transfer at the steel-concrete interface play critical roles in ensuring stability and overall structural performance. Inadequate friction at this interface can lead to sliding, reducing the structure’s capacity to resist lateral forces and potentially resulting in serviceability or safety concerns. This study presents an innovative approach to evaluate the static coefficient of friction between steel, prepared to a specific steel surface roughness level (SSPC-SP 6/NACE No. 3), and concrete with varying surface roughness profiles, including light sandblast, light to medium sandblast, medium bush hammer, and heavy sandblast finishes. Tests were performed under low normal stresses (18, 33, and 50 kPa [2.6, 4.8, and 7.6 psi]) and shear displacement rates (3, 5, 7, and 9 mm/s [0.12, 0.20, 0.28, and 0.35 in./s]). A custom test setup was developed to apply controlled displacement to a concrete block while measuring the horizontal force required to initiate sliding against the steel plate. The results indicate that the static coefficient of friction across all concrete surface roughness levels ranges from 0.68 to 0.75, with a mean value of 0.72. Statistical analysis at a 95% confidence level reveals that variations in concrete surface roughness, shear displacement rates, and applied normal stresses do not produce significant differences in the static coefficient of friction. Consequently, using concrete with light sandblast surface preparation in the field is sufficient to achieve a static coefficient of friction comparable to aggressive surface roughness profiles. These findings simplify construction practices while ensuring reliable shear transfer and sliding resistance at steel-concrete interfaces in low axial stress applications.

Prestressed concrete enables slender, economical, and durable structures, with post-tensioned (PT) precast girders widely used in bridge construction. Accurate design requires precise prediction of prestress losses, among which friction losses, arising from duct curvature, wobble, and anchorage slip, are most significant. Existing codes employ simplified exponential models, yet notable discrepancies persist between predicted and actual field values. This study presents full-scale experimental testing on PT precast girders used in Egypt’s Light Railway Transit (LRT) Project. Prestressing forces were measured using strain gauges to evaluate friction losses along tendon profiles. Results revealed that measured losses consistently exceeded code-based predictions, highlighting the influence of stress level and nonlinear variation along the tendon; factors often ignored by current provisions. Regression analysis yielded refined exponential models with improved accuracy and strong agreement with observations. The proposed refinements enhance predictive reliability and provide a foundation for updating design codes toward safer, more realistic PT concrete structures.

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.