International Concrete Abstracts Portal

The term “mass concrete” characterizes a specific concrete condition that typically requires unique considerations to mitigate extreme temperature effects on a structure. Mass concrete has historically been defined by the physical dimensions of a massive concrete element with the intent of identifying when differential temperatures may induce early-onset cracking, leading to reduced service life. More recently, in addition to differential temperature considerations, extreme upper temperature limits have been imposed by the American Concrete Institute to prevent long-term concrete degradation. Studies dating back to 2007 show shafts as small as 48 in. (1.2 m) in diameter can exceed both differential and peak temperature limits; in 2020, augered cast-in-place piles as small as 30 in. (0.76 m) in diameter exceeded one or both limits. This suggests the term “mass concrete” is misleading when considering today’s high-early-strength or high-performance mix designs. This study applies numerical modeling coupled with field measurements to investigate the effects of concrete mix design, drilled shaft diameter, and environmental conditions on heat energy production and temperature. Further, the outcome of this study focuses on developing criteria that combine the effects of both size and cementitious material content to determine whether unsafe temperature conditions may arise for a given drilled shaft design.

This study comprehensively investigates the development of ambient-cured self-compacting geopolymer concrete (SCGC) based on the chemical composition of binder and alkaline activator. Five factors of the chemical composition of binder and alkaline activator, each with four levels, are used to evaluate and optimise the workability and compressive strength of the high-strength SCGC. The designed SCGC mixes provided sufficient workability properties and compressive strength between 28 MPa [4061 psi] and 70.3 MPa [10196 psi]. It was found that the SCGC mix with a binder content of 600 kg/m³ [37.4 lb/ft³], a CaO/(SiO₂+Al₂O₃) mass ratio of 0.55, a Na2O/binder mass ratio of 0.11, a SiO₂/Na₂O mass ratio of 1.2, and Na₂O/H₂O mass ratio of 0.35 was the optimum mix, which achived slump flow of 770 mm [30.3 in.], 28-day compressive strength of 70.3 MPa [10196 psi], and final setting time of 80 min. The CaO/(SiO₂+Al2O₃) ratio in binders, binder content, and Na₂O/binder mass ratio have been found to be the most influential factors on the workability and compressive strength of ambient-cured SCGC. Microstructure analysis of SCGC mixes showed that the increase in the CaO/(SiO₂+Al₂O₃) ratio promoted the formation of calcium-aluminate-silicate-hydrate (C-A-S-H) gels and enhanced the compressive strength by filling voids and creating a compact and dense microstructure.

This paper proposes a series of empirical modifications to an existing three-step analytical model used to derive the cyclic shear capacity of circular reinforced concrete (RC) columns considering corrosive conditions. The results of 16 shear-critical RC columns, artificially corroded to various degrees and tested under quasistatic reversed cyclic loading, are used for model verification. The final model is proposed in a piecewise damage-state format relative to the measured damage of the steel reinforcement. New empirical decay coefficients are derived to determine the degraded material properties based on an extensive database of over 1380 corroded tensile tests. An additional database of 44 corroded RC circular piers is collected to assist in the modification of ductility-based parameters. Compared to the shear-critical test specimens, the model results indicate that the peak shear capacity can be predicted well across a range of deterioration severities (0 to 58.5% average transverse mass loss), with a mean predictive ratio of ±8.60%. As damage increases, the distribution of the corrosion relative to the location of the shear plane becomes a critical performance consideration, increasing predictive variance.

Concrete, a highly energy-intensive material, contributes approximately 10% of global carbion dioxide (CO2) emissions. To address this issue, incorporating industrial residues in concrete production has emerged as a viable solution, reducing natural resource consumption and lowering the CO2 footprint. Using bauxite residues in concrete has proven to be an environmentally friendly and sustainable approach. In this study, cement mass was partially replaced with bauxite residues (at 5%, 10%, 15%, and 20%), with variations in residue diameter (300 μm, 600 μm, and 2 mm) and in liquid form. The concrete’s workability, air content, density, mechanical strength, elasticity, Poisson’s ratio, and porosity were assessed with each replacement percentage. The study revealed that bauxite residues can effectively replace up to 20% of cement in a concrete mixture. Although their use slightly affects the fresh properties of concrete, it significantly enhances its mechanical properties. With this approach, a sustainable and eco-friendly concrete without compromising its performance can be created.

Chloride threshold values for steel reinforcing bars in reinforced concrete under the effect of varying temperatures and extended long-term conditions in hot climate are investigated. This investigation covers a gap in the current codes, including ACI 318, where the effect of temperature on the chloride threshold is not addressed. A total of 96 concrete specimens reinforced with carbon steel reinforcing bars sourced from two manufacturers were cast with different chloride contents and exposed to four temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F) for a period of more than 2 years. The chloride threshold values were determined based on corrosion potential, corrosion rate, and mass loss at the end of the exposure period. The results of the three techniques showed a consistent trend of significant dependency of the chloride threshold value on temperature. The average water-soluble chloride threshold values based on mass loss were found to be 0.77%, 0.72%, 0.47%, and 0.12% by weight of cement for temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F), respectively. These findings are significant as they showed a dramatic drop in the chloride threshold values at high temperature. This research highlights the need for reassessment of ACI Code limits considering hot climate.