Simultaneous influences of nanomaterial and fiber reinforcement on enhancing the mechanical performance of geopolymerstabilized soft clayey soils

Abstract

This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer (GP) through the optimized inclusion of nano-metakaolin (NM) and polypropylene fiber. The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes. To this end, binders including lime alone, LG (slag-based geopolymer), LGNM (nano-modified LG with NM) and LGNMF (LGNM/fiber) mixture were separately added to soft soil samples. The fabricated composites were then subjected to a set of macro and micro level tests. The results indicated that, adding LG binary with a 20% NM replacement can lead to a significant increase (by nearly 21 times) in soil strength and a remarkable decline (about 70%) in the compression index. In fact, NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric, which staggeringly improve the soil hydromechanical attributes. It was also observed that raising the curing temperature will effectively augment the polymerization kinetics, leading to a substantial increase (~2 times) in the soil solidification process. However, the stabilized composites containing NM may reveal a brittle nature under more intense stress. Such a potential drawback seems to be resolved by the integration of fibers within the matrix. LGNM combined with fiber would boost (≥10 times) the energy absorption capacity of the soil, notably enhancing its residual strength. Overall, LGNMF may not only feature a broader range of benefits (inc. economic, technical, environmental) compared to traditional binders but also promote the ductility of the GP materials.

1. Introduction

Soft and weak clayey soils may exhibit very high compressibility and low shear strength, and thus are often unsuitable for geotechnical structures and/or geo-environmental projects [1–3]. To address the limitations of problematic soils, one initial approach is to replace them with suitable materials. However, this solution may present its own economic and environmental challenges.

Chemical stabilization is one of the popular methods introduced many years ago in order to stabilize problematic soil. In this case, adding binders can improve the interfacial bonds among the soil particles by creating cementitious compounds, thereby boosting both strength and compressibility of the soil [4]. Conventional binders (inc. cement and lime) have been widely utilized to address the challenges associated with soft clayey soils, even if these materials may show limited efficiency in certain conditions such as at the presence of high sulfate dosages and/or in cold environments [5, 6]. Moreover, the production of cement and lime is generally associated with adverse environmental impacts (e.g., CO2 emissions) and high energy consumption. Thus, in recent years, numerous studies have been performed to develop alternative amendments to reduce production costs, energy consumption and environment impacts while enhancing the geotechnical properties of the stabilized soils [3, 7, 8].

Nowadays, the use of nano-scale materials (e.g., nano-zeolite, nano-SiO2, nano-CaCO3, nano-metakaolin, etc.) as partial replacements for traditional binders has attracted increasing interest in the field of soil modification. This is owing to remarkable pozzolanic activity and high pore-filling properties of these nano-materials, which can not only improve the mechanical and especially durability attributes of composites but also reduce the global demand for cement, thereby decreasing greenhouse gas emissions [6, 9]. While the utilization of nano-zeolite and nano-SiO2 has recently attracted the attention of researchers [10, 11], the relatively high production costs of these ultra-fine pozzolanas may limit their application and promotion in soil modification; however, among the proposed nano-materials, the cost of nano-metakaolin (NM) production is often lower [12]. Additionally, NM is more unstable, making it react faster when incorporated into the cementitious matrix [13]. Furthermore, as PEREZ-CORTES and ESCALANTE-GARCIA [14] reported, while the NM-based geopolymer (GP) containing 100% NM is better than cement, as to CO2 emissions only, the produced GP with NM<70% outperforms the cement-based materials in various indicators including environmental...