Geotechnical Properties and Microstructure of Lime-Fly Ash-Phosphogypsum-Stabilized Soil

Abstract

The use of industrial waste as a potential stabilizer of marginal construction materials is cost effective. Phosphogypsum and fly ash are industrial wastes generated in very large quantities and readily available in South Africa. In order to explore the potential stabilization of vastly abundant expansive soil using larger quantity phosphogypsum waste as a potential modifier, composites with a mixture of lime-fly ash-phosphogypsum-basic oxygen furnace slag were developed. However because of the presence of radionuclide, it was necessary to treat the phosphogypsum waste with mild citric acid. The effect of the acid treatment on the geotechnical properties and microstructure of expansive soil stabilized with phosphogypsum-lime-fly ash-basic oxygen furnace slag (PG-LFA-BOF) paste was evaluated, in comparison with the untreated phosphogypsum. Expansive soil stabilized with acid-treated PG-LFA-BOF paste exhibited better geotechnical properties; in particular, the high strength mobilized was associated primarily with the formation of various calcium magnesium silicide and coating by calcium silicate hydrate and calcium aluminate hydrate. The soil microstructure was improved due to the formation of hydration products. The stabilized expansive soil met the specification for road subgrades and subbase. Stabilization of expansive soils with phosphogypsum, fly ash, and basic oxygen fly ash does not only improve engineering properties of soil but also provides a solution in relation to disposal and environmental pollution challenges.

The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil

“…When lime [ 2 ] or carbide slag [ 3 , 4 ] is used as a soft soil stabilizer, its stabilization mechanism originates from the ion-exchange reaction, pozzolanic reaction, and carbonation reaction between calcium hydroxide and soil particles. Industrial slag [ 5 , 6 ], fly ash [ 7 , 8 ], natural pozzolans [ 9 ], zeolite [ 10 ], municipal solid waste incineration fly ash [ 11 ], and other pozzolanic materials can also be applied to a stabilizer. The activated silica and alumina contained in these pozzolanic materials undergo a pozzolanic reaction in the alkaline environment of calcium hydroxide.…”

“…In some studies, gypsum [ 8 ], recycled bassanite [ 12 ], or phosphogypsum [ 7 ] was added into cement and lime to form a new compound stabilizer, which significantly increases the formation amount of ettringite (AFt) crystals in hydration products. AFt crystals are recognized as unfavorable products in concrete due to their high expansiveness, which induces concrete cracking when they are formed [ 13 ].…”

Utilization of Cementitious Material from Residual Rice Husk Ash and Lime in Stabilization of Expansive Soil

“…In recent years, as environmental protection issues have drawn increasing attention, scholars have started to use various types of solid wastes as additives for expansive soil stabilization [12], such as fly ash [13], blast furnace slag [14,15], cement kiln dust [16,17], waste foam particle [18], alkali residue [19], and so on. Sometimes, some wastes can also be mixed with cementitious material during stabilization of expansive soil, for example, fly ash and lime [20,21], bagasse ash and lime [22], natural volcanic ash and lime [23], phosphogypsum and lime [24], ground granulated blastfurnace slag and lime [25], iron tailing sands, and calcium carbide slag [26]. ese mixtures can achieve better results than cementitious material alone.…”

Modification of Lime-Fly Ash-Crushed Stone with Phosphogypsum for Road Base

“…A large amount of it is normally discarded to the environment without any treatment leading to environmental contamination. It has been well documented that PG is an effective modification material for stabilizing special soil and improving the base (or subgrade) behaviors in roadway engineering [2][3][4][5][6]. Studies have been shown that PG alone is not sufficient for road construction.…”