EMM575-1 Leadership in Sustainable Infrastructure Leadership en Infrastructures Durables Vancouver, Canada May 31 – June 3, 2017/ Mai 31 – Juin 3, 2017 INVESTIGATION OF THE STRENGTH DEVELOPMENT USING MAGNESIUM ALKALINIZATION FOR SUBGRADE Muhammad, Nurmunira 1,3 and Siddiqua, Sumi 2 1 Graduate Student, The University of British Columbia, Okanagan, Canada 2 Assistance Professor, The University of British Columbia, Canada 3 nurmunira.muhammad@alumni.ubc.ca Abstract: The stabilization of problematic soils with chemical additives has become popular globally. Others studied the use of the magnesium chloride (MgCl 2) for improving weak soil properties, but the MgCl2 mixed with the alkaline solution as a chemical additive have not been investigated. This paper studied the factors that contribute to the strength development of silty sand, a typical subgrade soil in Kamloops BC, Canada, using the MgCl2 with different ratios of alkalinization solution (Na2SiO3/NaOH). The total of 65 samples included the untreated sample were examined using standard compaction and the unconfined compressive strength (UCS) tests under a curing period of 7, 14, 28, and 60 days. Results revealed that the chemical additive was improving the density and the compressive strength of the silty sand. This increase in strength was subjected to the formation of the new cementitious product, which was the combination of the chemical additive that filled up voids and reinforces the particles in the soil. 1 INTRODUCTION Statistically, the investment cost in maintaining and rehabilitating the road subgrade in British Columbia, Canada is extremely expensive. BCMoTI (2015) had reported in the B. C on the Move; A 10-year Transportation Plan bulletin, an additional $270 million is needed to improve the condition of provincial side roads which includes hard surfacing, gravelling base construction, dust control, shoulder widening, and other safety improvements over the next three years. Moreover, problematic soil subgrade greatly contributes a major event on the road pavement like potholes, rutting, and pumping on the road surface. Most of BC highways laid on the problematic soil such as clay, organic and silt. The selection of the best option like optimizing the pavement layer by thinning while still achieving the strong subgrade can result in reducing the material and construction cost. Many methods that can be applied to strengthen the weak subgrade but chemical stabilization method has become a vital method that most researchers were tried to applied and produce a product that is practical to the environment and cheap. The chemical stabilization process is complete when the chemical additive reacts with the soil by changing or altering the soil minerals properties and engineering properties. This process involved the cation exchange, flocculation, crystallization, and dissociation with the result in improvement of the soil strength parameters and the loading capacity (Zhu and Liu 2008). However, the proposed stabilizer agent in most research were targeting the clay soil using lime, fly ash, cement or ordinary Portland cement as the additive (Hashemi et al. 2015, Khater 2010, Saadeldin and Siddiqua 2013, Sukmak et al. 2013). Scientifically, the cement product such as the Ordinary Portland Cement (OPC) and lime is not practically safe for the environment. As for every ton of OPC prepared, the cement manufacturing process discharges almost 0.85 to 1.0 tons of carbon dioxide into the air (Davidovits 2015). The accrue discharges of CO2 may be jeopardizing the environment; hence the industry as well as the researcher