Geopolymer Recycled Aggregate Concrete: From Experiments to Empirical Models

Abstract

Ordinary cement concrete is a popular material with numerous advantages when compared to other construction materials; however, ordinary concrete is also criticized from the public point of view due to the CO2 emission (during the cement manufacture) and the consumption of natural resources (for the aggregates). In the context of sustainable development and circular economy, the recycling of materials and the use of alternative binders which have less environmental impacts than cement are challenges for the construction sector. This paper presents a study on non-conventional concrete using recycled aggregates and alkali-activated binder. The specimens were prepared from low calcium fly ash (FA, an industrial by-product), sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and recycled coarse aggregate. First, influences of different factors were investigated: the ratio between alkaline activated solution (AAS) and FA, and the curing temperature and the lignosulfonate superplasticizer. The interfacial transition zone of geopolymer recycled aggregate concrete (GRAC) was evaluated by microscopic analyses. Then, two empirical models, which are the modified versions of Feret’s and De Larrard’s models, respectively, for cement concretes, were investigated for the prediction of GRAC compressive strength; the parameters of these models were identified. The results showed the positive behaviour of GRAC investigated and the relevancy of the models proposed.

Analyzing the mechanical performance of fly ash-based geopolymer concrete with different machine learning techniques

“…The contents of coarse and fine aggregates did not seem to have a significant effect on strength. This trend was in line with the findings of previous studies, where it was reported that the interface transition zone (ITZ), morphology and particle size distribution of the aggregates was more influential in strength development than their contents [30,54]. Finally, Table 7 elucidates the effect of pre-curing on the compressive strength of FA-based geopolymer concrete, revealing the role pre-curing plays in improving the minimum, average and maximum strength values of all data sets.…”

“…However, the dynamic increase factor obtained from the constitutive model presented in this study was not consistent with the experimental results. Le et al [30] used the modified Feret and De Larrard models to predict the compressive strength of FA-based geopolymer recycled aggregate concrete. Compared with Feret's model, which requires a modification that replace the parameter for cement (C) with the parameter for binder (B) to ensure reasonable prediction accuracy, De Larrard's model only needs to determine the parameters of natural and recycled aggregates in advance to get satisfactory prediction results.…”

Durability Performance of Geopolymer Concrete: A Review

“…Figure 17 shows the scanning electron micrographs of the geopolymer concrete samples exposed to 200, 800, and 1000 • C. At 200 • C, the microstructures of the geopolymer concrete sample are characterized by a dense and intact morphology with little pore spaces (Figure 17a,b). Similarly, dense and flat microstructures were observed in fly-ash-based geopolymer concrete researched by Zhao et al [79] and Le et al [80]. Zhao et al [79] further discovered that that the dense microstructure of the geopolymer concrete remained intact after an exposure to 400 • C. After an exposure to 800 • C, however, some thermal micro-cracks could be seen in the microstructures of the geopolymer concrete samples (Figure 17c,d).…”

“…At 200 °C, the microstructures of the geopolymer concrete sample are characterized by a dense and intact morphology with little pore spaces ( Figure 17 a,b). Similarly, dense and flat microstructures were observed in fly-ash-based geopolymer concrete researched by Zhao et al [ 79 ] and Le et al [ 80 ]. Zhao et al [ 79 ] further discovered that that the dense microstructure of the geopolymer concrete remained intact after an exposure to 400 °C.…”

Geopolymer-Based Artificial Aggregates: A Review on Methods of Producing, Properties, and Improving Techniques

“…Therefore, some alternatives have been made towards minimizing the direct utilization of natural sources for aggregates as well as reducing environmental concern regarding increases in by-products with limited landfills available, which will consequently lead to pollution of the environment. Further initiatives to mitigate the depletion of natural resources include the introduction of recycled aggregates and artificial aggregates, which encourages the recycling of waste materials [ 15 , 24 , 25 ].…”