Mechanical and compressibility characteristics of a soft clay stabilized by slag-based mixtures and geopolymers

Abstract

In the present study, industrial wastes such as Granulated Blast Furnace Slag (GBFS) and Basic Oxygen Furnace Slag (BOFS) activated with calcium oxide (CaO) and medium reactive magnesia (MgO) are used for chemical stabilization of a soft clay. This environmentally friendly approach can eliminate the hazards associated with improper waste disposal and reduce greenhouse gas emissions generated by cement production. To this end, various amounts of additives (ranging from 2.5 to 20%) with the activator:slag ratio of 1:3 are added to kaolinite clay and cured at two temperatures of 20 and 45°C. A series of laboratory tests, including pH, Electrical Conductivity (EC), one-dimensional consolidation, Unconfined Compressive Strength (UCS), are conducted on the stabilized samples. The increasing temperature causes a faster formation of cementitious products and a higher UCS value, as confirmed by the SEM micrographs and XRD analysis, particularly in the case of MgO-BOFS (MB) and CaO-BOFS (CB) samples with the UCS values of 4 and 4.7 MPa after 90 days of curing, respectively. Furthermore, the MB- and CB-stabilized clay samples show a better compressibility characteristic compared to the MgO-GBFS (MG) and CaO-GBFS (CG) blends. To further enhance the activity of the additives and to prepare a slag-clay based geopolymers, two types of alkaline solutions at various Na2SiO3:NaOH ratios are added to the mixtures at the final step. In addition, the energy absorption capacity (Eu) and the secant modulus (E50) of the optimum blends are determined to assess the toughness and stiffness of the samples. The results indicate that the UCS values of the MB and CB samples increase up to 7.41 MPa and 8.44 MPa after 90 days of curing, respectively, when the Na2SiO3:NaOH ratio is 80:20. Generally, the use of slag-clay based geopolymers, particularly BOFS, is very effective to address the problems associated with the soft soil and the optimum mixtures are successful in decreasing settlements and enhancing compressive strength of the soft soil, which can be considered for use as a pavement base material.