International Concrete Abstracts Portal

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.

Past researchers have concentrated on the durability characteristics of textile-reinforced cementitious composites with quartz and silica sand. However, to make it easily available for construction, this study explores the durability characteristics of cementitious composites (CC) with the available manufactured sand before applying it to textile reinforcement. It is more important to study the durability characteristics as the main aim of application is to construct thin structures without coarse aggregate. Thus, the durability and microstructural characteristics of basalt fiber (BF)-reinforced fine-grained CC incorporated with ground granulated blast-furnace slag (GGBS) as a partial substitution of cement (BFRFGC) were studied. The CC were exposed to different exposure conditions, such as acidic environment, alkaline environment, and elevated temperature. Then, their visual appearance and change in weight and strength were studied as per the codal provisions at several exposure ages. In addition, microstructural studies were also performed at different exposure conditions and were compared with the specimens before exposure. The BFRFGC showed 61.93% and 27.58% lower strength and weight change than controlled fine-grained CC (CFGC) under extreme conditions (that is, exposure to sulfuric acid). Also, the results from microstructural studies reveal that BF and BFRFGC are resistant to all these conditions. Subsequently, BFRFGC has superior resistance under various exposure conditions and excellent durability characteristics.

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.

Lightweight concrete (LWC) finds wide-ranging applications inthe construction industry due to its reduced dead load, good fireresistance, and low thermal and acoustic conductivity. Lightweightgeopolymer concrete (LWGC) is an emerging type ofconcrete that is garnering attention in the construction industryfor its sustainable and eco-friendly properties. LWGC is producedusing geopolymer binders instead of cement, thereby reducing thecarbon footprint associated with conventional concrete production.However, the absence of standard codes for geopolymer concreterestricts its widespread application. To address this limitation,an investigation focused on developing a new mixture design forLWGC by modifying the existing ACI 211.2-98 provisions has beencarried out. In this study, crucial parameters of LWGC, such asalkaline-binder ratio (A/B), molarity, silicate/hydroxide ratio, andcuring temperature, were established using machine learning techniques. As a result, a simple and efficient method for determining the mixture proportions for LWGC has been proposed.

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.