International Concrete Abstracts Portal

Geopolymer, an inorganic polymer material, has recently gained attention as an eco-friendly alternative to Portland cement. Numerous studies have explored the potential of geopolymer as a primary structural material. This study aimed to examine the efficacy of geopolymer composites as repairing and strengthening materials rather than as structural materials. We collected and analyzed data from 782 bond strength tests and 164 structural tests including those on beams, beam-column connections, and walls. The analysis focused on critical factors affecting the bond strength of geopolymer composites with conventional cementitious concrete, and the structural behaviors of reinforced concrete members repaired or strengthened with these composites. Our findings highlight the potential of geopolymer composites for enhancing the resilience and toughness of existing damaged or undamaged concrete structures. Additionally, they offer valuable insights into the key considerations for using geopolymer composites as repair or strengthening materials, providing a useful reference for future research in this field.

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. The fly ash-based GPC (FA-based GPC) displays noticeable variability in its mechanical properties due to differences in mix design ratios and curing methods. To address this challenge, we 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 (ANN) were employed for compressive strength modeling. The developed ANN model underwent rigorous evaluation using statistical metrics such as R-values, R₂ values, and mean square 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 datasets 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 – 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.

There is a need to model the complete responses of shear-critical beams strengthened with embedded through-section (ETS) fiber-reinforced polymer (FRP) bars. Here, a strategy is proposed to integrate two separate approaches, flexural‒shear deformation theory (FSDT) for element fields and a bonding-based method for ETS strengthening, into a comprehensive computation algorithm through localized behavior at the main diagonal crack. The use of force- and stress-based solutions in the algorithm that couple fixed and updated shear crack angle conditions for analyzing the shear resistance of ETS bars is investigated. The primary benefit of the proposed approach compared to single FSDT or existing models is that member performance is estimated in both the pre-peak and post-peak loading regimes in terms of load, deflection, strain, and cracking characteristics. All equations in the developed model are transparent, based on mechanics, and supported by validated empirical expressions. The rationale and precision of the proposed model are comprehensively verified based on the results obtained for 46 datasets. Extensive investigation of the different bond‒slip and concrete tension laws strengthens the insightfulness and effectiveness of the model.

Portland cement has played a significant role in the construction of major infrastructure and building structures. However, in light of the substantial CO2 emissions associated with its production, there is a growing concern about environmental issues. Accordingly, the development of eco-friendly alternatives is actively underway. Geopolymer represents a class of inorganic polymers formed through a chemical interaction between solid aluminosilicate powder with alkali hydroxide and/or alkali silicate compounds. Concrete made with geopolymers, as an alternative to portland cement, generally demonstrates comparable physical and durability characteristics to ordinary portland cement (OPC) concrete. Research on the material properties of geopolymer concrete (GPC) has made extensive progress. However, the number of large-scale tests conducted to assess its structural performance is still insufficient. Additionally, there is a shortage of comprehensive studies that compile and analyze all the structural experiments conducted thus far to evaluate GPC’s potential. Therefore, this study aimed to compile and analyze a number of bond, flexural, shear, and axial strength tests of GPC to assess its potential as a substitute for OPC and identify its distinctive characteristics compared to OPC. As a result, it is considered that GPC can be used as a substitute for OPC without any structural safety issues. However, caution is needed in terms of deflection and ductility, and additional experiments are deemed necessary in the aspect of compressive strength of large-scale members.