Utilization of fly ash with and without secondary additives for stabilizing expansive soils: A review

Expansive soil dual behavior (swell/shrink) exhibits high compressibility and volumetric instability against the frequent moisture imbalance, rendering premature failure of lightweight structures. The present research highlighted the geotechnical behavior of expansive soil treated with industrial waste pozzolanic fly ash (FA) materials. Fly ash, a leftover from coal burning in power plants is considered a problematic solid waste globally. The typical disposal technique for fly ash can lead to the degradation of flora and fauna and contamination of fertile land. However, numerous research studies reveal that fly ash can be used to effectively strengthen the geoengineering properties, including physical, chemical, and biological. This paper critically reviews past research on the efficiency of fly ash as a soil stabilizer in enhancing the mechanical behavior of expansive soils. The effect of varying dosages and types of fly ash in soil mixture on the Atterberg limits, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and swell potential is critically reviewed through a series of geotechnical and microstructural characterization tests. The addition of varying percentages of fly ash (25–40%) to expansive soil shows an improvement in plastic behavior (up to 30–33%), compressive shear strength (40–48%), penetration resistance (52–55%) with least swelling (42–48%), and compressibility (36–40%) of fly ash-soil. Furthermore, the volumetric stability (swell/shrink) of clayey soil is attributed to mineral alteration and chemical compositions due to active pozzolanic reactions. This study may prove to be very effective in devising an alternative stabilizer to address the dual nature problems associated with expansive soil.