International Concrete Abstracts Portal

This paper presents findings from an experimental study focused on the performance of concrete composed entirely of 100% slag aggregate, enhanced with polypropylene (PP) fibers, subjected to severe freeze-thaw cycling between -60°C and +60°C. The research employed varying fiber lengths of 19.01, 38.1, and 57.15 mm and dosages of 3, 6, and 9 kg/m³. Findings indicate that the incorporation of fibers contributes to the overall resilience of the slag aggregate concrete under freeze-thaw conditions. To evaluate freeze-thaw resistance, the coefficient of thermal expansion (CTE) was determined using the Ohio CTE method and AASHTO TP60-00. Additionally, dynamic modulus, mass loss, and flexural strength were assessed. X-ray fluorescence (XRF) analysis was performed on slag aggregates to characterize their chemical composition. Findings indicate that the incorporation of fibers, particularly at a dosage of 9 kg/m³ and a length of 57.15 mm, enhances the resilience of the slag aggregate concrete under 300 freeze-thaw conditions as specified in ASTM C666/C666M-15, leading to improved flexural strength and reduced mass loss (less than 7%). However, some fiber-reinforced concrete samples experienced up to a 26.776% decrease in flexural strength after freeze-thaw cycles. Additionally, 38.1 mm fibers at varying dosages effectively mitigated the adverse effects of freeze-thaw cycles on the concrete's thermal expansion. In contrast, concrete without fibers lost over 40% of its mass. This contribution is particularly significant given the scarcity of data on the performance of concrete entirely made up of slag aggregate and mixed with PP fibers of different lengths in extreme weather environments.

Ultra-high-performance concrete (UHPC) is composed of a high volume fraction of binder and steel fibers, and a very low water content, resulting in enhanced strength and ductility, along with higher cost and environmental impacts. This study develops a UHPC mixture amenable to three-dimensional (3-D) printing, with 30% of cement (by mass) replaced with a combination of replacement materials. The proportioned UHPC mixture with 1.5% fiber volume fraction demonstrates 28-day compressive strengths of > 120 MPa (17.4 kips), and limited anisotropy when tested in the three orthogonal directions. Furthermore, 3-D printed layered composites are developed where UHPC (with and without fiber reinforcement) and conventional concrete layers are synergistically used in appropriate locations of the beam so as to achieve mechanical performance that is comparable to 3-D printed UHPC sections. Such manufacturing flexibility offered by 3-D printing allows conserving resources and attaining desirable economic and environmental outcomes, as is shown using life cycle and techno-economic analyses (LCA/TEA). Experimental and theoretical analysis of load carrying capacity and preliminary LCA/TEA show that >50% of the fiber-reinforced UHPC beam volume (in the compression zone) can be replaced with conventional concrete, resulting in only a <20% reduction in peak load carrying capacity, but >35% reduction in cost and >20% reduction in CO2 emissions. These findings show that targeted layering of different materials through 3-D printing enables the development and construction of 3-D-printed performance-equivalent structural members with lower cost and environmental impacts.

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.