Experimental Research on Microstructure and Physical‐Mechanical Properties of Expansive Soil Stabilized with Fly Ash, Sand, and Basalt Fiber

Abstract

Expansive soil is a source of risk to the foundations or subgrade engineering. Stabilization of expansive soil is imperative for practical engineering. A series of laboratory experiments were performed to analyze the physical-mechanical properties and microstructures of stabilized soil. Three stabilizers used in this study are fly ash, sand, and basalt fiber. Different percentages of fly ash (0, 5, 10, 15, and 20%), sand (0, 8, 16, and 24%), and basalt fiber (0 and 0.4%) were added by weight into natural soil. Experimental results indicate that the optimum moisture content of stabilized soil increases with the increase of fly ash content for a given sand content, whereas the maximum dry density shows a decreasing trend. The variation trend of optimum moisture content and maximum dry density turns reverse with the increase of sand content for a given fly ash content. Plasticity index is decreased by both increasing fly ash content and sand content. It is found that the maximum unconfined compressive strength and optimum growth rate of strength are obtained by selected mixtures of 10% fly ash, 8% sand, and 0.4% basalt fiber contents. As the analysis of complementary effect suggests, most of the mixt treatments applied in this study have produced good results associated with the strength enhancement of expansive soil. In line with the results of SEM tests, the connection among clay particles has been enhanced through the generation of hydration products (C-S-H and AFt) of fly ash. The filling effect of sand has increased the integrality and compactness of stabilized soil. Moreover, the gripping effect between fibers and soil particles notably improves the strength of stabilized soil. The effect of sand on reinforced soil with 0.4% basalt fiber increases the interfacial force between fibers and soil particles.

On the Recent Trends in Expansive Soil Stabilization Using Calcium‐Based Stabilizer Materials (CSMs): A Comprehensive Review

“…When acetylene is burnt, calcium carbon residue (CCR) is produced. It is deleterious in nature but rich in lime [138] content; therefore, it can be used to modify the properties of expansive soils [169]. e stabilization with CCR achieves better results than with lime from the viewpoint of economy and environment [170].…”

Effect of Basalt Fiber Addition on Static‐Dynamic Mechanical Behaviors and Microstructure of Stabilized Soil Compositing Cement and Fly Ash

“…e principle of cement stabilization is similar to the above explanations. With the addition of more cement or fly ash into stabilized soil, the unreacted cement or fly ash particles kept inside stabilized soil are the main reason of the gentle variation phase in Figures 5 and 6 [38]. In addition, it is easily found that the curing period is another important factor to affect the mitigation of swelling-shrinkage properties of stabilized soil.…”

“…erefore, the lower value of plasticity index indicated that the expansive soil with lower swelling behavior. e reduction of plasticity can be explained with the cation exchange reaction and the flocculation of clay particles [2,4,38]. e addition of chemical stabilizers such as fly ash and cement may cause the happening of cation exchange process and flocculation reaction inside stabilized soil, which can make the internal structure of soil specimen more aggregated and flocculated [2].…”

“…When the fly ash content increases to 15% or 20%, the unconfined compressive strength exhibits a decreasing trend compared with the stabilized soil sample with 5% cement and 10% fly ash. With the inclusion of fly ash into stabilized soil, the pozzolanic reactions and the occurrence of flocculation are the main reasons to improve unconfined compressive strength of stabilized soil [9,38].…”

“…us, the unconfined compressive strength of stabilized soil significantly enhanced with the fly ash content of 10%. However, because fly ash itself has no cohesion [9], the unreacted fly ash particles remained inside the soil structure directly caused the reduction in cohesive force among particles [38]. Consequently, the unconfined compressive strength of stabilized soil showed a downward trend under the experimental condition of excess fly ash content (FA � 15% or FA � 20%).…”