Effect of iron industry slags on the geotechnical properties and mineralogy characteristics of expansive smectite clay

Expansive clayey soils, which are predominantly distributed throughout the world, have complicated behavior. Heaving and settling in these soils may pose considerable problems and severe damage to structures that come into their contact or constructed out of them and consequent distress to people if not adequately taken care of. Granulated blast furnace slag (GBFS) and basic oxygen furnace slag (BOS) are two types of by-product materials resulting from the manufacture of iron that are produced in large amount throughout the world. The proper disposal of such byproducts is one of the major issues for environmentalists since leaving them to the environment directly may cause health problems. Hence, the aim of this study is to investigate the potential use and effectiveness of expansive soils treatment using GBFS and BOS. To achieve the objectives, the admixtures were added to the clay smectite samples in proportion of 0 to 30% by weight and tests of the pH value, electrical conductivity (EC) measurement, Atterberg limits, swelling, unconfined compression strength (UCS) and X-ray diffraction analysis were performed on those samples at different curing period (i.e. 1, 3, 7, 14, 28, 45 and 90 days). Lime as a conventional additive was also used to evaluate the performance of GBFS and BOS. The results reveal that in the limited curing condition (i.e. less than 3 days) and with the addition of 20% slag, the swelling could be eliminated mainly due to the short term reactions (i.e. cation exchange and osmotic pressure increasing). On the other hand, based on the X-ray graphs it was found that with appropriate curing (more than 7 days) and due to the growth of the cementation compounds such as calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH), especially in samples containing BOS, the needed slag to control heave potential will be declined up to 4 times. The presented results indicate that highly expansive clayey soils can be stabilized satisfactorily by lime and following adequate curing due to development of the pozzolanic reaction. Beside, with a further increase in the lime content, the pozzolanic activity can not continuously take place and the excessive addition of lime caused a reduction in the mechanical capacity. On the other hand, the samples containing slag show a progressive increase in the strength with increasing the additive content and could overcome the difficulties associated with the use of lime. For example, the USC of smectite sample with 30% BOS and after 90 days of curing was almost 12 times higher than the untreated sample. However, in the presences of GBFS due to lower solubility and limitation of pozolanic activity the lower change was observed. The The macro and micro level experiments results of this study indicate that the utilization of iron and steel slags especially basic oxygen furnace slag (BOF) is a good alternative for lime stabilization which reduces the cost of soil treatment project and help the management of these byproducts.