Geopolymer-stabilized soils: influencing factors, strength development mechanism and sustainability.

What is it about?

This paper presents the strength and micro-structural characteristics of high plasticity expansive clay stabilized with ordinary Portland cement (OPC) and geopolymers. Furthermore, sustainability aspects such as cost-efficiency, energy consumption and eco-efficiency of the OPC and geopolymer-stabilized soils were compared. The experimental results revealed that the geopolymer-stabilized soils exhibit higher strength and sustainability performance than the OPC-stabilized soils. This study also explores the developed machine learning prediction models of the geopolymer soils’ unconfined compressive strength (UCS) based on experimental data from current research and previous literature. Linear regression (LR), K-nearest neighbour (KNN), random forest (RF), random forest with random search hyperparameter optimization (BRRF) and random forest with grid search hyperparameter optimization (BGRF) were used as part of ensemble algorithms to predict stabilized soils UCS. Eight parameters such as liquid limit (LL), plasticity index (PI), ground granulated blast furnace slag (S) content, fly ash (FA) content, the molarity of NaOH (M), activator to binder ratio (A/B), Na/Al and Si/Al were used as input to predict UCS of geopolymer soils. The following metrics were used to assess the models’ predictive ability for compressive strength: coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE) and mean square error (MSE). The BRRF model has a good potential to predict the UCS of geopolymer soils, according to the findings of its testing (MAE = 0.27, MSE = 0.21, RMSE = 0.46, R2 = 0.99) and training (MAE = 0.78, MSE = 1.48, RMSE = 1.23, R2 = 0.96) phases. According to the RF model's feature importance study, slag content and liquid limit were found to influence forecasting compressive strength, while fly ash content has the least influence.

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Why is it important?

Soil is used as a construction material widely across the globe for various purposes; some soils are having very poor properties in nature which should be engineered before utilization. Expansive clays are proved to be extremely problematic due to their nature of exhibiting high level of volumetric variations according to changes in the water content [Citation1,Citation2]. When they absorb water, they expand or gain volume; when water is removed, they contract or lose volume [Citation3]. Therefore, in field clayey soil layers, swelling and shrinkage alternately occur in rainy and summer seasons. Therefore, civil engineering projects erected on expansive clays suffer severe cracking that causes significant financial loss [Citation4]. The impact of expansive soils on civil engineering infrastructures has resulted in significant financial losses globally, amounting to millions of dollars in damages [Citation4]. Therefore, the economic harm brought on by expanding soils is equivalent to the combined harm brought on by many or all-natural disasters.

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