International Concrete Abstracts Portal

This research establishes a systematic methodology for selecting a migratory corrosion inhibitor (M-CoI) as a repair strategy for reinforced concrete structures exposed to aggressive environments. Conducted in two phases, Phase 1 involves corrosion testing in pore solutions to evaluate inhibitor efficacy, while Phase 2 examines the percolation ability of M-CoIs in different concrete systems and the performance of M-CoI in RC with corroded reinforcing bars. The findings reveal that the efficiency of the compounds as repair measures is significantly lower than their preventive performance, primarily due to the presence of corrosion products on the steel surface. Additionally, the effectiveness of the M-CoIs is influenced by their concentration and form at the reinforcing bar level; specifically, 4-Aminobenzoic acid (ABA) achieved maximum concentration in its purest form, whereas Salicylaldehyde (SA) and 2-Aminopyridine (AP) reached the reinforcing bar in lower concentrations. Importantly, the study highlights that compounds effective in pore solution may not perform well in concrete, underscoring the necessity of considering the intended application, preventive or repair, when selecting inhibitors. Thus, a comprehensive approach involving both pore solution testing and migration ability assessments is essential for optimal corrosion protection in reinforced concrete.

Engineered cementitious composites (ECC), a prominent innovation in the realm of concrete materials in recent years, contain a substantial amount of cement in their composition, thereby resulting in a significant environmental impact. To enhance the environmental sustainability of ECC, it is plausible to substitute a large portion of cement in the composition with fly ash, a by-product of coal-fired power plants. In recent years, there has been increased research in ECC containing high-volume fly ash (HVFA) binders and its wider application in construction practices. In this particular context, it becomes imperative to review the role of the HVFA binder in ECC. This review first examines the effects of incorporating an HVFA binder in ECC on fiber dispersion and fiber/matrix interface behavior. Additionally, mechanical properties, including the compressive strength, tensile behavior, and cracking behavior under loading, as well as durability performances of HVFA-based ECC under various exposure conditions, are explored. At last, the review summarizes the research needs pertaining to HVFA-based ECC, providing valuable guidance for future endeavors in this field.

The production of carbonated aggregates from Class F fly ash (FA) is challenging due to its low calcium content, typically less than 10%. This study investigates the production of carbonated alkali-activated aggregates using FA and calcium carbide sludge (CCS). Sodium hydroxide was used as an activator and examined the effects of autoclave treatment on the properties of these aggregates. The optimal mixture, comprising 70% FA and 30% CCS, achieved a single aggregate strength of >5 MPa in autoclave carbonated (AC) aggregates, comparable to the strength obtained after 14 days of water curing in without autoclave carbonated (WAC) aggregates. Both AC and WAC aggregates exhibited a bulk density of 790 to 805 kg/m³ and CO₂ uptake of 12.5% and 13.3% in AC and WAC aggregates, respectively. FE-SEM and FT-IR analysis indicated the formation C-A-S-H gel in noncarbonated aggregates, while calcite and vaterite, along with N-A-S-H gel, formed in carbonated aggregate. Concrete incorporating AC and WAC aggregates exhibit compressive strengths of 39 and 38 MPa, with concrete density of 2065 kg/m³ and 2085 kg/m³, respectively. Furthermore, AC and WAC aggregate concrete showed a reduction in CO₂ emission of 18% and 31%, respectively, compared to autoclave noncarbonate (ANC) aggregate concrete. These findings highlight the potential of producing carbonated alkali-activated aggregates from FA and CCS as sustainable materials for construction applications.

Geopolymer concrete (GPC) is a progressive material with the capability to significantly reduce global industrial waste. The combination of industrial by-products with alkaline solutions initiates an exothermic reaction, termed geopolymerization, resulting in a carbon-negative concrete that lessens environmental impact. Fly ash (FA)-based GPC displays noticeable variability in its mechanical properties due to differences in mixture design ratios and curing methods. To address this challenge, the authors optimized the constituent proportions of GPC through a meticulous selection of nine independent variables. A thorough experimental database of 1242 experimental observations was assembled from the available literature, and artificial neural networks (ANNs) were employed for compressive strength modeling. The developed ANN model underwent rigorous evaluation using statistical metrics such as R-values, R2 values, and mean squared error (MSE). The statistical analysis revealed an absence of a direct correlation between compressive strength and independent variables, as well as a lack of correlation among the independent variables. However, the predicted compressive strength by the developed ANN model aligns well with experimental observations from the compiled database, with R2 values for the training, validation, and testing data sets determined to be 0.84, 0.74, and 0.77, respectively. Sensitivity analysis identified curing temperature and silica-to-alumina ratio as the most crucial independent variables. Furthermore, the research introduced a novel method for deriving a mathematical expression from the trained model. The developed mathematical expressions accurately predict compressive strength, demonstrating minimal errors when using the tan-sigmoid activation function. Prediction errors were within the range of –0.79 to 0.77 MPa, demonstrating high accuracy. These equations offer a practical alternative in engineering design, bypassing the intricacies of the internal processes within the ANN.

In this study, a chloride adsorption test was performed to depict the chemical evolution of pore solution for cement hydration. It was found that the amount of chloride adsorbed by the AFm phase and the calcium-silicate-hydrate (C-S-H) phase decreased with the increasing pH of the pore solution. The stability of Friedel’s salt tended to decrease with the increasing pH of the pore solution. Notably, in the C-S-H phase, the decrease in the amount of chloride adsorption resulting from an increase in the pH level was larger when the Ca/Si ratio was higher. Based on these works, multiple regression analysis was performed to examine the correlation between the chloride adsorption density of cement hydrates and the experimental variables involved, including the pH of the pore solution and the amount of chloride-ion penetration. The pH of the pore solution was predicted based on cement hydration and pore-chemistry theories, and these results were combined with the experimental results, considering the changing chemical characteristics of the pore solution during each temporal stage of cement hydration. The amount of chloride-ion adsorption in fly ash (FA) and granulated blast-furnace slag (GBFS) was larger than in ordinary portland cement (OPC) due to the decreased pH of the pore solution resulting from the consumption of calcium hydroxide.