Technical note
Interface shear strength properties of geogrid-reinforced steel slags using a large-scale direct shear testing apparatus

https://doi.org/10.1016/j.geotexmem.2020.04.001Get rights and content

Highlights

  • Large scale direct shear tests on geogrid-reinforced LFS and EAFS blends.

  • Biaxial geogrid provides higher interface strength than the triaxial geogrid.

  • Beneficial application of such waste materials in pavement construction is proved.

Abstract

This research evaluates the shear strength properties of unreinforced and geogrid-reinforced ladle furnace slag (LFS), electric arc furnace slag (EAFS) and a blend comprising 50% LFS and 50% EAFS (LFS50+EAFS50) using the large direct shear testing apparatus (DST). The large DST results of unreinforced steel slags indicated that LFS had the lowest shear stress ratio at the peak shear strength among all samples, while LFS50+EAFS50 samples (both unreinforced and reinforced) demonstrated the highest shear stress ratio amongst the tested samples. A higher apparent cohesion value was achieved with the inclusion of biaxial geogrid in LFS and EAFS samples as compared to the triaxial geogrid interface. The observed behavior can be attributed to the larger aperture size of the biaxial geogrid compared to the triaxial geogrid leaving more void planar space for a direct interaction between slag particles. In contrast, the apparent cohesion of LFS50+EAFS50 without a geogrid interface was high and did not change significantly with the insertion of geogrid. Given, the range of internal friction angles for ordinary soils, studied slag by-products achieved internal friction angles in excess of 59° (with no geogrid interface) and these significant values proved highly beneficial application for these waste materials in pavement construction.

Introduction

Industrial waste materials are by-products from the manufacturing process with no residual values. Population growth, high worldwide demand for construction materials, scarcity of natural resources and the vast stockpiles of wastes accumulating at landfills are currently some of the main issues in developing and developed countries. Access to virgin materials to support the major cities’ infrastructure development is becoming increasingly difficult and costly, hence the recycling and re-use of waste materials are considered as a popular alternative for governments and key decision maker authorities. To date, several attempts have been made by researchers to evaluate the engineering properties of various recycled and waste materials, with the intention of being able to substitute commonly used natural quarry materials in major infrastructure construction projects (Arulrajah et al., 2017; Maghool et al., 2017; Mirzababaei et al., 2013; Smolar et al., 2016).

Steel is an important construction material that has the ability to be recycled indefinitely. In 2016 alone, nearly 1600 million metric tons (mt) of steel were recycled and reused, a significant increase from 500 mt in the 1960s (Maghool et al., 2016). Similar to waste materials generated by other industrial processes, steelmaking has its own by-products, termed as slag. The production of one ton of steel generates approximately 200 kg–400 kg of slag, depending on the manufacturing technique and type of furnace used. The World Steel Association (2016) reported more than 400 million tons of iron and steel slag is generated per annum worldwide. In the past decade, significant amounts of slag were successfully utilized as a construction material, mostly by the cement and concrete manufacturing sectors (Guo and Shi, 2014). There are currently no re-use options for certain types of slags, such as ladle furnace slag (LFS), which is a disposal concern to steelmaking companies and environmentalists due to its high lime content.

There are two main methods for steel production including steelmaking in basic oxygen furnaces and scrap-based steel making in electric arc furnaces (Heidrich and Woodhead, 2010). This research focuses on electric arc furnace by-products, which uses electrical energy, fluxes and 100% steel scrap to produce steel. The electric arc furnace generates two types of slag at various stages of the steelmaking process from steel scraps; electric arc furnace slag (EAFS) and ladle furnace slag (LFS). The recycling of one ton of steel scrap in the electric arc furnace generates about 140 kg of EAFS and 40 kg of LFS (Maghool et al., 2016).

Various studies on utilizing EAFS in different applications have been reported, on aspects such as the aggregates durability, skid resistance, cementitious properties, high permeable micro-fabric and excellent particle interlocking. EAFS has been previously used in asphalt mixing and concrete manufacturing process (Dippenaar, 2005; Meiling et al., 2017; Mohi ud Din and Mir, 2019; Oluwasola et al., 2015; Pasetto and Baldo, 2010). In contrast, most of the reports on engineering characteristics of LFS have been limited to the use of this by-product as a stabilizer, after processing it to a powder form, due to its high lime content and cementitious characteristics (Manso et al., 2013; Serjun et al., 2013). However, the main drawback of processing LFS to powder and converting it to a useful product, is that this operation (weathering, grinding, etc.) is costly, can quickly damage the fine sieves due to the cementitious properties of LFS and is not entirely an eco-friendly process. The geo-environmental and fundamental geotechnical properties of LFS and EAFS as unbound road construction materials was studied by Maghool et al. (2016) and Sudla et al. (2018) and it was recommended that these by-products are suitable as aggregates in roadwork applications (i.e. based on Australian standards), causing no harm to the environment. Furthermore, a long-term assessment of chemicals released from steel slag has been studied by Chaurand et al. (2007) and Dayioglu et al. (2018), and the results reported have indicated that the long-term leaching release of trivalent Chromium (Cr(III)) as one of the main ingredients of steel is insignificant and not categorised as a toxic constituent as it remains in the same form during the leaching process. However, it is vital to investigate the environmental impact of using steel slag in roadwork projects based on different international regulations.

Slag aggregates are subjected to both compression (at the top) and tension (at the bottom) when used as base material. The tensile strength of slag aggregates can be improved with geosynthetic reinforcement (Horpibulsuk and Niramitkornburee, 2010; Suddeepong et al., 2020). The interface shear strength between compacted material and geosynthetic is the typical failure mode of the reinforced material considering the stress level applying to pavement layer (Chai et al., 2002; Zhang et al., 2015).

The primary purpose of this paper is to further evaluate the interface shear strength characteristics of unreinforced and geogrid-reinforced LFS, EAFS and their mixture, as this aspect has not been studied before. Therefore, the re-use of such industrial waste materials in construction applications will result in a sustainable and cost-effective alternative for the waste management of steel by-products, provided that the advanced engineering properties of these materials are comparable to those of traditional quarry materials.

Section snippets

Materials and methods

The EAFS and LFS samples for this research were provided by a major steel recycling company located in Melbourne, Australia. EAFS is generated at the beginning of the steelmaking process in the electric arc furnace, where the steel scrap is smelted and purified using respectively electricity and fluxes. The high temperature of 1600 °C and lime addition as a flux assists in the removal of silicate and phosphorus materials from the molten steel and also shapes the EAFS slag. The red-hot steel is

Results and discussion

Table 3 presents a summary of engineering characteristics of LFS, EAFS and LFS50+EAFS50. Fig. 1 shows the particle size gradation curve of the steel slags along with ASTM lower and upper limits for pavement materials. Both LFS and LFS50+EAFS50 met the requirements of ASTM standard (ASTM, 2007) to be used as type I materials in pavement applications. LFS was classified as having the gradation of a silty sand (SM), EAFS as a well-graded gravel (GW) and LFS50+EAFS50 as a poorly graded gravel with

Conclusions

The LFS, due to the high lime content and cementitious nature, achieved a high shear strength. EAFS, given its high-quality, durability, skid resistance, cementitious properties, highly permeable and excellent particle interlocking, was found to be a very high-quality aggregate. Due to the interlocking shape of its particles, EAFS sample performs as a rock mass in the high confining pressures, which was confirmed by the DST. The LFS50+EAFS50 mixture was prepared to improve the engineering

Acknowledgements

The second and last author acknowledge the financial support from the National Science and Technology Development Agency under Chair Professor program (P-19-52303).

References (42)

  • AS

    Soil Chemical Tests—Determination of the pH Value of a Soil—Electrometric Method. Australian Standard 1289.4.3.1

    (1997)
  • AS

    Particle Density and Water Absorption of Coarse Aggregate - Weighing-In-Water Method. Australian Standard 1141.6.1

    (2000)
  • AS

    Particle Density and Water Absorption of Fine Aggregate. Australian Standard 1141.5

    (2000)
  • AS

    Soil Strength and Consolidation Tests—Determination of Permeability of a Soil—Constant Head Method for a Remoulded Specimen. Australian Standard 1289.6.7.1

    (2001)
  • AS

    Soil Strength and Consolidation Tests—Determination of Permeability of a Soil—Falling Head Method for a Remoulded Specimen. Australian Standard 1289.6.7.2

    (2001)
  • AS

    Soil Compaction and Density Tests - Determination of the Dry Density/moisture Content Relation of a Soil Using Modified Compactive Effort. Australian Standard 1289.5.2.1

    (2003)
  • ASTM

    Standard Test Method for Particle-Size Analysis of Soils. ASTM Standard D422

    (1963)
  • ASTM

    Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASTM Standard D2487

    (2006)
  • ASTM

    Standard Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine

    (2006)
  • ASTM

    Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table, D4253

    (2006)
  • ASTM

    Standard Specification for Materials for Soil-Aggregate Subbase, Base, and Surface Courses

    (2007)
  • Cited by (35)

    • Production of biocement using steel slag

      2023, Construction and Building Materials
    • Effect of particle regularity on the shear response of geogrid-granular material interface under cyclic normal loading

      2023, Transportation Geotechnics
      Citation Excerpt :

      Furthermore, the interlocking mechanism of the reinforced soil interface is also influenced by loading conditions, such as static normal and cyclic normal loading. Under static normal loading, Maghool et al. [19] analysed the effects of biaxial and triaxial geogrids on steel slags under different constant normal loading. Han et al. [20] analysed the appropriate geogrid aperture size and interface shear failure modes.

    View all citing articles on Scopus
    View full text