A Clay-Based Geopolymer in Loess Soil Stabilization

Influence of environmental stresses on the durability of slag-based alkali-activated cement crusts for wind erosion control

Wind erosion is a significant environmental challenge in arid and semi-arid regions, and artificial crust creation on the soil surface has emerged as an effective approach to mitigate this phenomenon. Various methods of crust formation have been proposed to combat wind erosion in these regions. However, a comprehensive study assessing the durability of these crusts against environmental stresses has been lacking. Hence, the primary objective of the present study is to address this critical issue by evaluating the erodibility and surface strength of alkali-activated slag crusts in response to various environmental stressors. These stressors encompass ultraviolet radiation, heating and cooling cycles, wetting and drying cycles, and freezing and thawing cycles. Through wind tunnel tests, erosion rates were measured under different wind velocities and saltation bombardment conditions, while penetrometer tests were conducted to analyze surface strength. The results demonstrate that alkali-activated cementation produced robust crusts, exhibiting an impressive reduction of over 99.9 % in erosion rates compared to untreated samples. However, the introduction of environmental stresses led to a fivefold increase in erosion rates. Freeze and thaw cycles had the most detrimental effect on the alkali-activated cement crusts while heating and cooling cycles had a relatively minor impact. The wetting and drying cycles and UV radiation ranked second and third, respectively, in terms of their destructive effects on crust erodibility. Despite the observed effects, the crusts maintained their efficiency even when subjected to severe environmental stresses. Notably, the erosion rate of the treated crusts after enduring the most severe studied stress, that is five freeze and thaw cycles, was over 250 times lower than that of the untreated samples.

Wind erosion control using alkali-activated slag cement: Experimental investigation and microstructural analysis

This paper aims to mitigate wind erosion of soil by employing alkali-activated slag. Wind tunnel tests were conducted on soil samples treated with varying percentages of slag at different wind speeds (7, 14, 21, and 28 m/s) and under a sand bombardment condition. In the absence of saltating particles, the erodibility ratios of the alkali-activated slag-treated samples with weight percentages of 1%, 2%, 4%, and 6% to the untreated sample at the highest wind speed (i.e., 28 m/s) correspond to 0.19%, 0.10%, 0.08%, and 0.06%, respectively. Moreover, in the presence of saltating particle bombardment, these samples exhibited erodibility reductions of 98.5%, 98.8%, 99.4%, and 99.6% compared to the untreated sample. The strength of the formed crusts, determined by penetrometer tests, increased significantly for the treated samples, ranging from 1300 to 6500 times greater than the untreated sample. The complementary analysis using x-ray diffraction and field emission scanning electron microscopy revealed the formation of albite and anorthite crystals along with the formation of calcium aluminosilicate hydrate, sodium aluminosilicate hydrate, and calcium silicate hydrate gels in the cementation process. Overall, the study highlights the effectiveness of alkali-activated slag in forming strong crusts that provide substantial protection against wind erosion, resulting in a significant decrease in wind erodibility.

Study on the relationship between permeability coefficient and porosity, the confining and osmotic pressure of attapulgite-modified loess

This study investigated attapulgite-modified loess as an efficient and cost-effective method for creating an impermeable liner for landfills in regions with scarce clay resources. Laboratory permeability tests were conducted using a flexible wall permeameter to determine the permeability of compacted loess and attapulgite mixtures under varying osmotic conditions. The relationship between the permeability coefficient, attapulgite dosage, radial pressure, and osmotic pressure was analyzed. Nuclear magnetic resonance and scanning electron microscopy were also used to observe the microstructure of the modified loess. The results showed that attapulgite dosage significantly reduced the permeability coefficient, but the effect became limited when the content surpassed 10%. The decrease of the permeability coefficient of the modified loess is mainly due to the filling of pores between the loess by attapulgite, which makes the pore size and throat size of the modified loess smaller. The modified loess displayed a sheet structure that contributed to an increased permeability coefficient due to increased radial pressure. This study provides valuable insights into using attapulgite-modified loess as a material for landfill lining in regions with scarce clay resources.

The Effects of Soil Porosity and Mix Design of Volcanic Ash-Based Geopolymer on the Surface Strength of Highly Wind Erodible Soils

Surface stabilization of loose, non-cohesive, and fine soils has always been a challenging task for geotechnical engineers. These soils show meager mechanical behavior and are very vulnerable to wind erosion. Many attempts have been made to combat wind erosion of soils. These attempts, including a variety of soil surface amendment methods, have faced complications in terms of financial efficacy, reduced long-term behavior at elevated temperatures, and limitations in stabilization of a wide range of soil types. The application of geopolymers for surface stabilization is a novel approach, which has its own challenges in terms of selecting an appropriate precursor type, mix design, and preparation method. This study evaluated the challenges of using volcanic ash (VA)-based geopolymer, through the 1 Phase (1P) method for stabilization of two silty and sandy soils. A series of uniaxial compressive strength (UCS) and penetrometer tests were performed on cylindrical specimens and soil surface-treated samples, respectively, to evaluate the resistance of treated samples with different porosities. Moreover, the rheological behavior of geopolymer paste having various binder-to-activator ratios is discussed. The available rheological characteristics of geopolymer in this study fit well with the Bingham model. It was found that, despite the minimal crust thickness formed on the topsoil, significant surface resistance is acquired. The results show notable performance of the 1P method for surface amendment of both the silty and sandy soil samples.

Potential of Soil Stabilization Using Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash via Geopolymerization Method: A Review

Geopolymers, or also known as alkali-activated binders, have recently emerged as a viable alternative to conventional binders (cement) for soil stabilization. Geopolymers employ alkaline activation of industrial waste to create cementitious products inside treated soils, increasing the clayey soils’ mechanical and physical qualities. This paper aims to review the utilization of fly ash and ground granulated blast furnace slag (GGBFS)-based geopolymers for soil stabilization by enhancing strength. Previous research only used one type of precursor: fly ash or GGBFS, but the strength value obtained did not meet the ASTM D 4609 (<0.8 Mpa) standard required for soil-stabilizing criteria of road construction applications. This current research focused on the combination of two types of precursors, which are fly ash and GGBFS. The findings of an unconfined compressive strength (UCS) test on stabilized soil samples were discussed. Finally, the paper concludes that GGBFS and fly-ash-based geo-polymers for soil stabilization techniques can be successfully used as a binder for soil stabilization. However, additional research is required to meet the requirement of ASTM D 4609 standard in road construction applications, particularly in subgrade layers.

Research and Application of Slag–Nanosilica Stabilizer for Silt Subgrade

With the rapid development of construction and road engineering, the accumulation of silting waste soil is becoming more and more serious. In order to recycle the silt, a new type of stabilizer was developed in this study to improve its mechanical properties and applicability on roads. The optimal ratio of stabilizer components was determined by orthogonal test and grey correlation analysis. The effects of stabilizer on the macroscopic mechanical properties of silt were investigated by unconfined compressive strength (UCS) test and split test. The water stability test and freeze–thaw cycle test were carried out to study the durability and road performance of stabilized soil. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods were used to study the effect of the stabilizer on the microstructure and mechanism of silt. The results showed that the optimal mixture ratio of the new type of stabilizer was quicklime: nanosilica: slag = 32:3:65. Adding 10% stabilizer is a reasonable and effective method to strengthen silt, which has the characteristics of high strength and strong durability in the early period. The addition of stabilizer will result in hydration reaction, pozzolanic reaction, and cation exchange on the surface of soil particles with silt, which will enhance the intermolecular force of soil particles, reduce the porosity of soil, and strengthen the connection between soil particles.

Soil Erosion: Dust Control and Sand Stabilization

This Special Issue on soil erosion invites novel and original articles based on physical and chemical theories, field and laboratory experimental, soil analyses, and/or statistical and mathematical modeling that advance our knowledge on dust control and sand stabilization.