The three major steel manufacturing factories in Jordan dump their byproduct, steel slag, randomly in open areas, which causes many environmental hazardous problems. This study intended to explore the effectiveness of using fine steel slag aggregate (FSSA) in improving the geotechnical properties of high plastic subgrade soil. First soil and fine steel slag mechanical and engineering properties were evaluating. Then 0%, 5%, 10%, 15%, 20%, and 25% dry weight of soil of fine steel slag (FSSA) were added and mixed into the prepared soil samples. The effectiveness of the FSSA was judged by the improvement in consistency limits, compaction, free swell, unconfined compression strength, and California bearing ratio (CBR). From the test results, it is observed that 20% FSSA additives will reduce plasticity index and free swell by 26.3% and 58.3%, respectively. Furthermore, 20% FSSA additives will increase the unconfined compressive strength, maximum dry density, and CBR value by 100%, 6.9%, and 154%. By conclusion FSSA had a positive effect on the geotechnical properties of the soil and it can be used as admixture in proving geotechnical characteristics of subgrade soil, not only solving the waste disposal problem.
The byproduct of steel manufacturing in Jordan, steel slag, is dumped randomly in open areas, which causes many environmental hazardous problems. The three steel factories in Jordan are daily generating from 15–20 tons of steel slag. Most of the steel slag production in Jordan is utilized in the cement industry and has never been used in any other fields due to the lack of research in these fields [
It is recognized that swelling of expansive soils may cause significant distress and severe damage to overlying structures. Documented evidence of extensive damage caused by soil expansion is available from different countries in the world. In some locations, the estimated damage cost attributed to soil expansion exceeds the cost of damages from natural disasters such as floods, tornadoes, hurricanes, and earthquakes [
Steel slag, a byproduct of steel manufacturing, is produced during the separation of molten steel from impurities in steel-making furnaces. The slag evolves as a molten liquid and is composed of a complex solution of silicates and oxides that solidifies upon cooling. Steel slag is a recycled material that can be useful in the construction industry. For example, in 2002, 50 million metric tons of steel slag was estimated to be produced worldwide [
Mainly as a granular road base or as an aggregate in construction applications, steel slag aggregate (SSA) has been successfully used in the Middle East under hot weather conditions [
Yadu and Tripathi [
The specimens were subjected to durability index and UCC strength tests. The samples were prepared with a maximum stabilizer dosage of 16% and five different combinations of lime and GGBS were adopted with GGBS replacing lime in increments of 4% in each successive combination. The samples were molded at three different moisture contents at their MDD to study the effect of placement water content. The investigation revealed that 4% lime with 12% GGBS produced the highest strength and durability out of all the combinations. The strength of the stabilized soil increased with decrease in lime content and increase in GGBS content in the mix, thereby giving a clear indication of better performance of lime-industrial waste combinations when compared to pure lime or pure industrial waste stabilization. It is evident that strength of lime-clay systems was hugely dependent on the GGBS component which increases the density and permeability of the system by forming cementitious gels.
Obuzor et al. [
Rao and Sridevi [
Moreover, a number of trial road sections with slag in unbound base course were constructed, while a comparison research carried out between layers containing steel slag as an aggregate and layers with crushed stone [
The main focus of the current study is to evaluate the effectiveness of added FSSA to stabilize and enhance the performance characteristics of the medium-plastic subgrade soil.
The study soil sample used in this research was obtained from Irbid city in the northern part of Jordan. To characterize the studied soil sample, grain size distribution (Sieve analysis, hydrometer analysis) according ASTM D 422-2007, Atterberg limits according to ASTM D 4318-10 and specific gravity according to ASTM D 854-14 tests were performed. Soil sampling, preparing, and testing were done according to ASTM [
Physical characteristics and Atterberg limits of the considered soil.
Property | Soil |
---|---|
Gravel (%) | 0.0 |
Sand (%) | 11.6 |
Silt (%) | 50.1 |
Clay (%) | 38.3 |
Liquid limit (%) | 62.4 |
Plastic limit (%) | 28.5 |
Plasticity index (%) | 33.9 |
Specific gravity | 2.72 |
Activity | 0.89 |
Grain size distribution of the soil.
Fine steel slag aggregate (FSSA) was obtained from the United Iron and Steel Manufacturing Company, Amman. FSSA passing the diameter 4.75 mm (sieve #4) was used in this study. Table
Physical characteristics of fine steel slag aggregate.
Physical characteristics | Value |
---|---|
Gravel (%) | 0.0 |
Sand (%) | 96.2 |
Silt (%) | 3.8 |
Clay (%) | ⋯ |
Liquid limit (%) | Nonplastic |
Coefficient of uniformity (cu) | 9.0 |
Coefficient of curvature (Cc) | 1.78 |
Specific gravity | 3.205 |
Angularity (%) | 58 |
Absorption (%) | 4.5 |
Chemical composition of fine steel slag aggregate.
Chemical characteristics | Cr | Ni | Fe | Zn | Pb | Cu | Cd |
---|---|---|---|---|---|---|---|
Value (%) | 0.063 | 0.004 | 0.019 | 0.021 | 0.0 | 0.0 | 0.0 |
Grain size distribution of the fine steel slag.
The soil sample used in this research was dried at 105°C in a drying oven and then passed through sieve number 4 (4.75 mm in diameter) to obtain a uniform distribution. Fine steel slags with amount of 0, 5, 10, 15, 20, and 25% by dry weight of the soil were added and mixed with dry soil to obtain a homogeneous mixture. The standard proctor compaction test according ASTM D-698, 1994, was done for all FSSA mixed sample, to obtain the optimum water content and maximum dry density values which needed to prepare the samples for use in free swell and unconfined compressive strength tests for each FSSA additive percentage. Table
Mix proportions used in preparing samples.
FSSA (%) | Max. dry density (g/ | Optimum water content (%) | Dry soil mass (g) | FSSA (g) | Required water (g) | Final mix proportion |
---|---|---|---|---|---|---|
0.0 | 1.622 | 16.9 | 1000 | 0.0 | 169 | 1000 g (dry soil) + 0.0 g (FSSA) + 169 g (water) |
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5.0 | 1.641 | 15.1 | 1000 | 50 | 151 | 950 g (dry soil) + 5.0 g (FSSA) + 151 g (water) |
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10.0 | 1.648 | 13.7 | 1000 | 100 | 137 | 900 g (dry soil) + 100 g (FSSA) + 137 g (water) |
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15.0 | 1.692 | 13.1 | 1000 | 150 | 131 | 850 g (dry soil) + 150 g (FSSA) + 131 g (water) |
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20.0 | 1.734 | 12.8 | 1000 | 200 | 128 | 800 g (dry soil) + 200 g (FSSA) + 128 g (water) |
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25.0 | 1.766 | 12.2 | 1000 | 250 | 122 | 750 g (dry soil) + 250 g (FSSA) + 122 g (water) |
Each soil-additive mixture was passed through sieve number 40 (0.425 mm in diameter) and then liquid limit (LL) and plastic limit (PL) tests were done according to ASTM D 4318-00, 1994. Liquid limit (LL) is defined as the water content, in percent, at which a part of soil is placed in a standard cup and then cut by a groove of standard dimensions will flow together at the base of the groove for a distance of 13 mm (1/2 in.) when subjected to 25 shocks from the cup being dropped 10 mm in a standard Casagrande liquid limit apparatus operated at a rate of two shocks per second. The plastic limit (PL) is the water content, in percent, at which a soil can no longer be deformed by rolling into 3.2 mm (1/8 in.) diameter threads without crumbling.
The procedure used to perform the free swell tests is based on the procedure recommended by ASTM D 4829 standard. All the test specimens are compacted to maximum dry density and optimum water content using a mold of 70 mm diameter and 20 mm height. After 24 hours of curing under a 7 kPa pressure. The soil specimen starts swelling and vertical displacements are recorded until the expansion is completed and no vertical movement is observed. Vertical displacements are plotted against time. Free swell ratio or free swell percentage is defined as the ratio between the initial and final height of the sample.
The unconfined compressive strength test method was used to evaluate the shear strength parameters of the samples with additives. The samples were molded in stainless steel tubes of 76 mm height and 38 mm diameter and compressed to the desired compaction characteristics of each additive level. The samples were removed from the tubes and tested directly with a rate 1 mm/min. The unconfined compressive strength test was performed in according to ASTM D2166/D2166M-13 standards.
The CBR test method is used to evaluate the potential strength and bearing capacity of a subgrade soil, subbase, and base course material for use in road and airfield pavements. Two samples are usually prepared for CBR tests; one is tested directly after sample preparation, to simulate the normal field conditions, and the other after soaking in water for 96 hours to simulate the worst conditions in the field. According to ASTM D-1883-99, the test is carried out under a seating pressure of 4.5 kg and a penetration speed of 1.27 mm/sec. The CBR specimens are prepared by a standard mold with an internal diameter of 152.4 mm (6 inches) and a height of 177.8 mm (7 inches). In this study, specimens were compacted at the optimum moisture content determined by standard proctor tests. Three specimens were compacted in 5 layers using 10 blows, 25 blows, and 75 blows, as recommended by ASTM D-1883-99, part 7.2, and then tested without soaking in water. The CBR value is calculated according to the following formula:
Liquid limit and plastic limit tests were conducted on each sample prepared with 0, 5, 10, 15, 20, and 25% of the FSSA additive. The liquid limits (LL), plastic limits (PL), and plasticity indices (PI) are shown in Figure
Variation of Atterberg limits with FSSA contents.
Standard proctor compaction (ASTM D-698, 1994) was conducted on the samples with different percentage of FSSA content (0, 5, 10, 15, 20, and 25%). The compaction curves of samples with and without the additive of FSSA are presented in Figure
Compaction curves of samples with the FSSA additive.
The soil used in this research is classified as CH soil and consists of quartz as a major mineral constitute with smectite as a minor mineral and trace amounts of the minerals illite, calcite, dolomite, and kaolinite. These clay minerals, which have negatively charged surfaces, attract to the positive ions in the void by electrostatic attraction, leading to a concentration of ions near the diffuse double layer (DDL). The intersection or overlap of DDLs causes repulsive forces to arise between the particles; these forces cause the free swelling [
Effect of the FSSA additive content on the free swell.
FSSA content (%) | 0.0 | 5.0 | 10.0 | 15.0 | 20.0 | 25.0 |
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Free swell amount (%) | 5.15 | 4.80 | 4.60 | 3.00 | 2.15 | 1.65 |
Free swell percentage versus time for samples with different FSSA contents.
The variation in unconfined compressive strength with FSSA content is shown in Figure
Effect of the FSSA additive content on the unconfined compressive strength and strain at failure.
FSSA content (%) | 0.0 | 5.0 | 10.0 | 15.0 | 20.0 | 25.0 |
| ||||||
Unconfined compressive strength (kPa) | 142.95 | 196.41 | 209.54 | 270.30 | 310.12 | 285.11 |
Strain at failure (%) | 7.24 | 5.26 | 3.95 | 3.68 | 3.42 | 2.50 |
Stress shear strength versus strain for samples with different FSSA contents.
In this study, three samples were prepared for CBR tests at the same moisture content. Each sample was compacted with a different number of blows (10, 25, and 75) as recommended by ASTM D-1883-99, part 7.2, note 3, since the maximum dry density was determined from compaction in the 4 in. (101.6 mm) mold; it is necessary to compact specimens, using 75 blows per layer. The CBR tests were conducted directly (without soaking in water). Table
CBR values of the three samples of soil without additives.
Number of blows | Water content (%) | Dry density (g/ | CBR (%) |
---|---|---|---|
10 | 16.9 | 1.573 | 6.0 |
25 | 16.9 | 1.664 | 9.1 |
75 | 16.9 | 1.723 | 13.5 |
(a) Relationship between resistance and penetration for soil without additives. (b) CBR value for soil without additives.
Table
CBR values of the three compaction efforts samples of soil with FSSA additives.
FSSA content (%) | Number of blows | Water content (%) | Dry density (g/ | CBR (%) |
---|---|---|---|---|
5.0 | 10 | 15.1 | 1.6080 | 6.2 |
25 | 15.1 | 1.666 | 9.6 | |
75 | 15.1 | 1.742 | 15.9 | |
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10.0 | 10 | 13.7 | 1.618 | 7.2 |
25 | 13.7 | 1.669 | 11.3 | |
75 | 13.7 | 1.768 | 17.9 | |
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15.0 | 10 | 13.1 | 1.621 | 9.3 |
25 | 13.1 | 1.686 | 13.4 | |
75 | 13.1 | 1.797 | 19.6 | |
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20.0 | 10 | 12.8 | 1.664 | 12.0 |
25 | 12.8 | 1.708 | 16.0 | |
75 | 12.8 | 1.809 | 20.0 | |
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25.0 | 10 | 12.2 | 1.704 | 11.5 |
25 | 12.2 | 1.784 | 16.3 | |
75 | 12.2 | 1.834 | 19.7 |
(a) Relationship between resistance and penetration for soil with 5% FSSA additives. (b) CBR value for soil with 5% FSSA additives.
(a) Relationship between resistance and penetration for soil with 10% FSSA additives. (b) CBR value for soil with 10% FSSA additives.
(a) Relationship between resistance and penetration for soil with 15% FSSA additives. (b) CBR value for soil with 15% FSSA additives.
(a) Relationship between resistance and penetration for soil with 20% FSSA additives. (b) CBR value for soil with 20% FSSA additives.
(a) Relationship between resistance and penetration for soil with 25% FSSA additives. (b) CBR value for soil with 25% FSSA additives.
CBR values correspond to maximum dry density for FSSA additive content.
This research focuses on the effect of stabilizing high plastic subgrade soil by adding FSSA. From the test results, the following conclusions can be drawn: Liquid limit, the plastic limit, and the plasticity index decrease as FSSA content increases. For example at 20% of FSSA content, the soil changes from high plasticity clay (CH) to low plasticity clay (CL). As the FSSA increases, the maximum dry density increased and the optimum water content decreased. The free swell percentage decreases from 5.15% for 0.0% FSSA content to 2.15% for 20% FSSA content. This decreasing in free swell percentage makes the soil more stabilizing from civil engineering view. The unconfined compressive strength increases and the strain at failure decreases as the FSSA content was increased up to 20%. The effect of 20% FSSA on compressive strength is more than the other percentage. The unsoaked CBR value increases from 6.9% for soil with 0.0% FSSA to 17.5% at 20% FSSA content. According to Bowles [
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank Mr. Saleem Hatamleh and Mr. Mohammad Shafique of Civil Engineering Laboratories at Hashemite University for their help in carrying out the experimental tests.