The reuse of LFS in roadwork construction will significantly reduce the demand of natural quarry aggregates and will possibly divert huge amount of these waste ...
Sixth International Conference on Geotechnique, Construction Materials and Environment, Bangkok, Thailand, Nov. 14-16, 2016, ISBN: 978-4-9905958-6-9 C3051
GEOTECHNICAL PROPERTIES OF LADLE FURNACE SLAG IN ROADWORK APPLICATIONS
Farshid Maghool1, Arul Arulrajah2, Suksun Horpibulsuk3 and Yan-Jun Du4 Department of Civil and Construction Engineering, Swinburne University of Technology, Australia; 3 School of Civil Engineering, Suranaree University of Technology, Thailand; 4 Institute of Geotechnical Engineering, Southeast University, China 1,2
ABSTRACT Ladle Furnace Slag (LFS) is an industrial waste from steelmaking process, generated during the final stage in ladle refining furnace. LFS samples were sourced from a steelmaking company in Victoria, Australia. This paper reports on the results of a geotechnical and chemical evaluation on LFS to assess the viability of using this byproduct in roadwork constructions. A comprehensive suits of engineering tests was undertaken comprising moisture content, specific gravity, particle size analysis, hydrometer, organic content, flakiness index, Los Angeles (LA) abrasion, hydraulic conductivity, modified compaction, pH, Unconfined Compression Strength (UCS) and California Bearing Ratio (CBR). In addition, the chemical composition of LFS sample was assessed using X-ray Fluorescence analysis (XRF). The engineering properties of LFS were then compared with typical quarry materials. The chemical composition results indicate that LFS contains high amount of calcium. Thus, the effect of 0, 7 and 28 days of curing on the strength of unbound LFS was investigated using UCS test. The specimens with 7 and 28days curing had higher UCS value than uncured samples attributed to high lime content and hydration process. From an engineering perspective, LFS was found to be suitable material to substitute typical quarry material in roadwork applications. The reuse of LFS in roadwork construction will significantly reduce the demand of natural quarry aggregates and will possibly divert huge amount of these waste from landfills and stockpiles. Possible applications of unbound LFS in road pavement are also discussed. Keywords: Ladle Furnace Slag, Pavement Base, Unconfined Compression Strength, Industrial Waste INTRODUCTION Waste materials are universally described as byproducts of Commercial, industrial, building and demolition activities that do not have any value [1]. Due to the recent enforcement of more stringent environmental regulations all around the world, recycling and reuse of waste materials has become very critical. Steel has been known as the one of the world’s most recyclable materials. Annually, more than 1400 million tonnes of steel is manufactured worldwide [2]. The steelmaking process generates an industrial by-product termed as slag. In Australia alone, the annual production of steel slag is reported to be around 2.4 million tonnes [3]. In the past decade, noticeable amount of slags was effectively utilized as cementitious and noncementitious construction materials. More than 60% of the utilized slags in Australia was granulated blast furnace slag, which is really popular among cement and concrete companies [4]. However, there are currently limited studies and reuse options for particular types of slag including LFS. LFS is formed during the secondary steelmaking process in the ladle refining furnace. In this stage, the
molten refined steel is poured out of the furnace and the resulting product on the bottom of the ladle is known as LFS. On average the production of one tonne of steel in steelmaking plants results in 30 to 50 kg of LFS [5]. Limited research on engineering and geotechnical properties of LFS have been conducted up to the present time. Serjun et al. [6] graded LFS as a low quality material due to its fine grain size, adverse leaching potential and expansive behavior. Manso et al. [7] indicated LFS can be a valuable by-product after it has been turned into a dusty product and its expansive characteristics could be reduced in this form. Manso et al. [8] studied the behavior of soils stabilized with LFS and found similar results of the same soils after mixing with lime. This research also suggested that UCS value was significantly increased in the soils blended with LFS powder while the plasticity index and free swelling behavior of soils can be reduced. Serjun [6] stated that LFS has the potential to be used as a supplementary cementing material in numerous civil and construction applications due to its cementitious hydraulic properties.
GEOMATE- Bangkok, Nov. 14-16, 2016
The use of industrial wastes as roadwork construction materials will be an optimistic outcome for the waste management hierarchy, provided that the use takes into account the required environmental and engineering considerations [9]. The limited knowledge on the relevant engineering and geotechnical properties of unbound LFS is main obstacle for using these materials in roadwork applications. An extensive suite of engineering and chemical testing were undertaken on LFS to evaluate the feasibility of using these steel slag aggregates as road construction materials. MATERIALS AND METHODS Samples for this research were collected from the top of various LFS stockpiles from a steelmaking plant in Victoria, Australia. LFS is well-graded grey material and produced during the secondary steelmaking process in the ladle refining furnace. LFS was poured out from the ladle furnace in a liquid-state and then is cooled down from 1600°C to room temperature [7]. To obtain a representative sample for laboratory testing, LFS samples were properly mixed, split and sieved through a 20mm sieve.
CBR, UCS and hydraulic conductivity samples were prepared and compacted under modified compaction effort at optimum moisture content to reach at least 98% of maximum dry density. Three sets of sample were prepared for each of these tests. The CBR samples were then soaked for 4 days with a surcharge mass of 4.5 kg on top. The swelling of the CBR samples were measured during the 4 days of soaking using a dial gauge supported by a metal tripod. UCS samples were compacted in five layers of predetermined mass in a spilt mold with an internal diameter 100 mm and effective height of 200 mm. To evaluate the effect of curing on mechanical properties of unbound LFS, two extra sets of UCS samples were prepared and cured in a humid chamber with a minimum humidity of 95% and temperature control of 25°C for 7 and 28 days. Table 1 Chemical composition of LFS. Chemical compounds Fe2O3 CaO SiO2 MgO MnO2 Cr2O3 TiO2 SO3 P 2O 5 K 2O Al2O3
Weight (%) 35.233 24.899 22.934 8.633 5.827 0.954 0.498 0.498 0.466 0.059 non-detected
RESULTS AND DISCUSSION
Fig. 1 presents the LFS sample appearance after passing through a 20 mm aperture sieve. It is evident from the photo that LFS sample in this study contains some electric arc furnace slag and natural aggregates from the manufacturing site plant. The chemical composition of LFS samples were assessed using Xray Fluorescence analysis (XRF). The natural moisture content of LFS was also determined using drying oven set at 105°C. A series of laboratory evaluations was conducted to assess the engineering properties of the LFS comprising particle size distribution [10], hydrometer [11], organic content [12], flakiness index [13], particle density and water absorption [14]-[15], pH [16], modified compaction [17], LA abrasion [18], Hydraulic conductivity [19], CBR [20] and UCS [21], according to relevant established Australian and American standards.
100 90
Percentage Passing (%)
Fig. 1 LFS sample appearance.
Chemical composition results of LFS are reported based on 100% normalization of oxide compounds and presented in Table 1.
LFS - Sieve analysis
80 70
LFS - Hydrometer
60 50 40 30 20 10 0 0.001
0.01
0.1
1
Particle Size (mm) Fig. 2 Particle size distribution plot of LFS.
10
100
GEOMATE- Bangkok, Nov. 14-16, 2016
Table 2 Engineering properties of LFS. Engineering parameters Natural moisture content (%) Clay content (%) Silt content (%) Sand content (%) Gravel content (%) USCS natation Organic content (%) Particle density: fine (kN/m3) Particle density: coarse (kN/m3) pH Flakiness index (%) LA abrasion loss (%) Hydraulic conductivity (m/s) Maximum dry density (Mg/m3) Optimum moisture content (%)
LFS 2 kN/m3) and very close to the values previously reported for electric arc furnace slag [23]. The pH values of samples indicate that LFS is alkaline by nature. The flakiness index of LFS was found by separating the flaky particles and was noted to be approximately 30. Table 3 Strength properties of LFS. Strength properties CBR (%) Swell (CBR) (%) UCS_ no curing (MPa) UCS_7 days curing (MPa) UCS_28 days curing (MPa)
LFS 156-165
