Stabilization of highly decomposed peat soil: mechanical, physicochemical, and microscopic examination

Commonly used soil stabilization methods often overlook the degree of decomposition in peat soil. Highly decomposed peat exhibits lower strength and higher acidity than slightly decomposed peat due to the breakdown of cellulose and hemicellulose into humic acids. This study employed corrosion-resistant aluminate cement, phosphogypsum (PG), and manufactured sand to stabilize highly decomposed peat soil. Unconfined compressive strength (UCS) and shear tests were conducted to evaluate the effectiveness of the stabilization, while microstructural analyses were performed to investigate the underlying mechanisms. An optimal dosage of 15% PG, 30% aluminate cement, and 30% manufactured sand increased the UCS of highly decomposed peat soil by 22 times, from 10.2 kPa to 221.0 kPa, and increased cohesion by 4.2 times, from 16.3 kPa to 67.9 kPa. Furthermore, the stabilized peat soil exhibited early strength development under the optimal dosage: after just 3 days of curing, the strength reached 61% of the strength achieved after 90 days. Adding PG and aluminate cement raised the pH from 5.48 to above 9.0, meeting the minimum requirement for hydration reactions. PG promoted ettringite formation, which filled pores and densified the microstructure, while calcium carbonate formed through the carbonation of hydration products further enhanced compactness through both filling and bonding effects. These findings highlight the proposed method as a practical and effective solution for stabilizing highly decomposed peat soil.