Investigation on the Synergistic Behavior of Cement, Copper Slag, and Phosphogypsum in the Stabilization of Black Cotton Soil

Abstract

The current research aims at stabilizing expansive black cotton soil through the use of a ternary mixture of Ordinary Portland Cement (OPC), Copper Slag (CS),
and Phosphogypsum (PG) that might be providing good results with minimal resource utilization by the materials. The selection of the three materials was made
keeping in mind a synergistic effect that could be achieved. For instance, a) cement is the main binder, b) copper slag is a pozzolanic activator, and c)
phosphogypsum is a source of ettringite. Black cotton soil was amended with different proportions of the ternary blend and its performance was assessed through
Atterberg limits, Free Swell Index (FSI), and Unconfined Compressive Strength (UCS) tests. The optimal blend was the one that produced the highest strength and
most reduction in swelling characteristics. In fact, with the increase in the addition of the ternary stabilizer, the liquid limit and plasticity index were reduced
consistently, whereas the shrinkage limit was increased, signifying an enhancement in the volumetric stability of the soil. A substantial decrease in the free swell
index, at the level of about 73%, was achieved by the optimal blend with respect to the untreated soil. The UCS was increased by almost 375% at the optimal mix
in comparison with the untreated soil after 60 days of curing. The pozzolanic reaction and the gradual development of C‐S‐H, C‐A‐H, and ettringite phases were
the underlying reasons for this strength. These results corroborate the notion that the ternary mixture as proposed herein is a feasible and efficient method for the
stabilization of expansive black cotton soils.