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 geopolymer concrete (UHP-GPC) can exhibit high to exceptional strength. Given the importance of UHP-GPC’s mechanical properties, prediction of its 28-day compressive strength (fc′) remains insufficiently explored. This study predicts UHP-GPC’s fc′ based on alkali-activated materials, sand, fiber volume, and water-geopolymer binder and alkali activator ratios. Advanced statistical modeling and a spectrum of ensemble machine learning (ML) algorithms including random forest (RF), gradient boosting (GB), extreme gradient boosting (XGB), and stacking are used to predict UHP-GPC’s strength. The derived models reveal the significance of fiber, slag, and sand as the most significant factors influencing the 28-day fc′ of UHP-GPC. All the ML models demonstrate higher precision in forecasting fc′ of UHP-GPC compared to statistical modeling, with R2 peaking at 0.85. Equations are derived to predict the strength of UHP-GPC. This paper reveals that UHP-GPC with superior mechanical properties can be designed for further sustainability.

Slag-based zero-cement concrete (ZC) of high strength (60 MPa [8.70 ksi]) was developed as an eco-friendly construction material. In the present study, to investigate the structural behavior of precast columns using ZC, cyclic loading tests were performed for five column specimens with reinforcement details of ordinary moment frames. Longitudinal reinforcement was connected by sleeve splices at the precast column-footing joint. The test parameters included the concrete type (portland cement-based normal concrete [NC] versus ZC), construction method (monolithic versus precast), longitudinal reinforcement ratio, and sleeve size. The test results showed that the structural performance (failure mode, strength, stiffness, energy dissipation, and deformation capacity) of the precast ZC columns was comparable to that of the monolithic NC and precast NC columns, and the tested strengths agreed with the nominal strengths calculated by ACI 318-19. These results indicate that current design codes for cementitious materials and sleeve splice of longitudinal reinforcement are applicable to the design of precast ZC columns.

To reduce CO2 emissions of concrete, a slag-based zero-cement concrete (ZC) of high strength (60 MPa [8.70 ksi]) was developed. In the present study, cyclic loading tests were conducted to investigate the seismic performance of full-scale interior precast beamcolumn joints using the new ZC. One monolithic portland cementbased normal concrete (NC) beam-column joint and two precast ZC beam-column joints were tested. The test parameters included concrete type, fabrication method, and beam bottom bar anchorage detail. The structural performance was evaluated, including the strength, deformation capacity, damage mode, and energy dissipation. The test results showed that the structural performance of the precast ZC beam-column joints could be equivalent, or superior, to that of the monolithic NC beam-column joint. Although the reinforcement details of the ZC joints do not satisfy the seismic design requirements of special moment frames in ACI 318-19, the seismic performance of the ZC joints satisfied the requirements of ACI 374.1-05 and AIJ 2002 Guidelines.

This research focuses on developing a mixture design for highstrength geopolymer concrete (HSGPC) complying with the highstrength concrete criteria mentioned in Indian standards. This study focuses on optimizing the content of alkaline activators and binders proportionately. The compressive strength of different proportions of geopolymer mortar was carried out meticulously to determine the optimal proportions of solution-binder (S/B) and sodium silicatesodium hydroxide (SS/SH) ratios. The aforementioned ratios were optimized using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) analysis for further calculation. The mixture proportions for Grades M70, M80, M90, and M100 were determined and verified through experimental validation. To assess the suggested mixture design, a slump test was conducted to quantify the workability, subsequently followed by the evaluation of compressive strength after 24 hours, 7 days, and 28 days. After achieving the desired workability, promising compressive strength was observed as 76, 89, 93, and 104 MPa at 28 days. Finally, the mechanism of strength increment was investigated using various characterization techniques, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energydispersive spectroscopy (EDS). The SEM/EDS analysis of the HSGPC proves the dense microstructures of different gel formations. The proposed mixture design procedure falls under the target strength-based method category. It has successfully yielded a strength of 104 MPa for ground-granulated blast-furnace slag (GGBS)-based geopolymer concrete incorporating coarse and fine aggregates.