# Electrically Conductive Roller-Compacted Concrete (RCC) Containing BOFS, Steel Fiber, and Steel Shaving

Authors: Danial Nasr; Ehsan Bavafa
Journal: Advances in Civil Engineering
 (2023)

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## Abstract

In this study, the feasibility of using steel fibers and steel shavings in roller-compacted concrete containing coarse basic oxygen furnace slag aggregate was investigated in order to improve its mechanical properties and to produce an electrically conductive and environment-friendly concrete. For this purpose, various samples containing 0.4, 0.7, and 1% of steel fiber and 3, 5, and 7% of steel shaving were fabricated. The compressive strength, indirect tensile strength, electrical resistance, and specific density tests were conducted on the samples. The results demonstrated the positive effect of steel fiber and the destructive effect of steel shaving on the compressive and tensile strengths of RCC containing BOFS. The results of the electrical resistance test showed a more positive effect of steel shaving than steel fiber in the conductivity of RCC samples. Regarding the specific gravity results, the natural aggregate replacement with BOFS as well as steel fiber and steel shaving resulted in an increase in the specific gravity of the mixtures. Utilizing the both steel fiber and steel shaving can compensate the unfavorable properties on the RCC containing BOFS.


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## Body

## 1. Introduction

As the cost of bitumen and asphalt pavement construction continues to rise, there is a growing demand for alternative materials that can improve the mechanical and physical properties of concrete used in road construction [1]. Roller-compacted concrete (RCC) pavement is an increasingly popular option for medium to high volume traffic due to its cost-effectiveness and longer lifespan when compared to other pavement types such as Portland cement concrete (PCC) and asphaltic pavements.RCC is a type of concrete with very low-workability (zero Vee-Bee tests) that its water content is lower than that of conventional concrete. In RCC, natural and synthesized aggregate or a combination of both can be used. One of the new materials that can be used in pavements is basic oxygen furnace slag (BOFS) which is the by-products of the steel manufacturing process that contains the nonmetallic blend of materials such as silicate, calcium, calcium ferrite, calcium oxide, iron oxide, aluminum oxide, and magnesium oxide [2]. Some favorable properties of BOFS are high abrasion resistance, high shear strength, and low cost. The use of BOFS as an aggregate replacement in RCC to pave roads can prevent damage to the environment [3] and in countries with a low area and difficulty in the provision of aggregate, the use of BOFS for pavement construction is a logical solution. One of the most suitable methods for using the waste and preventing the deposition of the product in nature would be using in cement and asphalt concrete [4]. Despite the advantages of BOFS in the pavement construction, there is still limited research on its use as an aggregate replacement in RCC. Therefore, there is a need for further investigation on the feasibility and potential benefits of using BOFS in the RCC pavement.Another issue to be addressed is the problem of ice formation on the surface of road and airport pavement. Ice formation causes delays and reduces road safety, and at airports, it can lead to flight delays and millions of dollars in damage [5]. Chemical deicing and salts can also be harmful to concrete pavements and the environment, reducing the pavement’s longevity [6]. To address this problem, an electrically conductive concrete (ECC) was developed based on the Canadian National Research Council method, which creates thermal energy when a voltage is connected to it, making it useful for melting snow and ice on the pavement [7, 8].Several investigations have been performed to address the issue. Research conducted by Abdualla et al. aimed to investigate the effectiveness of the hot pavement system (HPS) in melting ice and snow on airport pavement surfaces under various winter weather conditions. Using the data collected and the performance of the slabs, under real weather conditions, the ECON-based HPSs can distribute heat in the slab and have the ability to melt the ice and snow under different winter conditions [5]. In another study, Abdualla et al. examined and identified the requirements of an electrically conductive concrete (ECON) system to be high performance and cost-effective. A small sample of the heated conductive concrete system was designed and optimized with ECON at Iowa State University and then tested to determine its efficiency. The results demonstrated that energy consumption was lower than that of the ECON prototype [9].Zhang et al. sought to address the issue of thermal cracking in overwintering layers of roller-compacted concrete (RCC) dams. To achieve this, the researchers designed a novel type of hydraulic concrete, referred to as electrically conductive roller-compacted concrete (ERCC). The investigation cantered around the electro-thermal properties of ERCC, with a focus on its resistivity and its capacity to regulate temperature distribution and reduce the likelihood of cracking. In addition, the mechanical and compaction properties of ERCC were evaluated, and the superiority of the roller compaction method was demonstrated. The study results revealed that ERCC has considerable potential as a material for overwintering layers in RCC dams located in extremely cold regions, presenting a more adaptable and intelligent solution for temperature control. This innovative approach represents a significant breakthrough in the field of RCC dam engineering, and it could pave the way for more efficient and durable dam construction in the future [10].In another study, the use of ground granulated blast-furnace slag (GGBFS) and BOFS on the mechanical properties of RCC was addressed. The research results showed that RCC containing the BOFS could not produce higher compressive strength than conventional RCCs, but the replacement of 25% of natural aggregate with BOFS yielded the highest resistance in comparison with other aggregate replacement percentages and fulfilled the requirements of RCCP. However, replacing the GGBFS as the filler with a natural one was not recommended [11].In a study, the addition of carbon fiber to RCC was investigated to produce electrically conductive concrete. After producing the samples, the 3.7 volts electrical current to the samples was applied, and the temperature of the slab surface during the test was measured. It was concluded that the concrete temperature containing 1% and 2% carbon fiber with the implementation of an AC current of 3.75 V increased from 10°C to 11.7°C after 200 minutes. Also, the results of compressive and tensile strength tests of the samples indicated an increase in their resistances [12].Chang and Chai evaluated the effect of adding steel fibers to concrete. They performed fracture and fatigue tests on the samples. It was concluded that adding 1 to 1.5 volumetric per cent of steel fibers to concrete can increase the amount of passed charge about 2–2.5 times [13].Qasrawi investigated the influence of steel slag and recycled concrete aggregate in conventional concrete. In the study, steel slag and recycled materials were replaced partly or totally by a natural concrete aggregate. According to the results of the study, the addition of steel slag increased the mechanical properties of concrete [3].In a study, Chunlin et al. replaced the natural concrete aggregate with rubber particles and steel slag. The results represented that the mechanical strength of concrete containing steel slag is acceptable, although the flexural strength is slightly lower than that of conventional concrete [14].Yehia and Tuan made the construction of conductive concrete containing steel shaving, steel fiber, and carbon powder and used it on the deck of the bridge to test its deicing characteristics. It was concluded that the implementation of a thin coating layer of conductive concrete and the connection of the electric current to the bridge deck could prevent surface ice formation. The cost of energy used to defrost is estimated to be about $0.6 to $0.8 per square meter. Moreover, the mechanical strength of concrete met AASHTO and ASTM standards requirements [6].Devi and Gnanavel evaluated the influence of replacement of steel slag instead of coarse and fine natural aggregate on the mechanical and durability properties of concrete. The compressive strength, tensile strength, bending strength, and durability tests performed on the samples. The results showed that the partial replacement of fine-andcoarse-grained aggregate with steel slag increases compressive, tensile and flexural strengths [15].According to a study, steel slag was replaced with a natural aggregate in concrete to enhance the mechanical properties of concrete under fire exposure conditions. The samples were exposed to a temperature of upto 800°C at the age of 56 days. The results of the compressive strength and other characteristics were examined, and it was observed that the slag could improve the strength of the concrete against fire upto 400°C [16].In order to improve the mechanical properties of roller-compacted concrete (RCC) containing coarse blast furnace slag (BOFS) aggregate and to develop electrically conductive and environmentally-friendly concrete, this study investigates the feasibility of incorporating steel fibers and steel shavings into the concrete mix. To achieve this objective, various concrete samples were fabricated with steel fiber percentages of 0.4%, 0.7%, and 1% per the total volume of the concrete mixture and steel shaving percentages of 3%, 5%, and 7% per the volume of fine aggregate. The mechanical properties of the samples were evaluated through compressive strength and indirect tensile strength tests, while electrical resistance and specific density tests were conducted to assess the electrical conductivity and density of the concrete, respectively.


## 2. Materials

### 2.1. Aggregate

Natural aggregate constitutes about 75% to 85% of concrete and significantly affects its properties in both the fresh and hardened states. The size of the aggregate must comply with the ASTM C33 standard, and in roller-compacted concrete (RCC), it affects the performance, quality, density, and segregation. The physical properties of the aggregate also impact the resistance, modulus of elasticity, thermal properties, and durability of the hardened concrete [17]. To achieve the desired surface quality, the nominal maximum size of the coarse-grain aggregate should be limited to 19 mm. The fine-andcoarse-grinded aggregate can be either natural or crushed aggregate or a mixture of both. The crushed aggregate is preferred for RCC as it requires less energy for compaction and generally results in less segregation and higher flexural strength. The crushed aggregate used in this research is sourced from Isfahan limestone mines, and its physical characteristics and gradation are given in Table 1 and Figure 1, respectively.Table 1
Physical properties of aggregate.
PropertyStandardFine gravelCoarse gravelNominal maximum aggregate sizeASTM-C1364.7519Los angles abrasion (%)ASTM-C131—16.0Bulk density (g/cm3)ASTM-C1272.7102.680SSD density (g/cm3)ASTM-C1272.7302.716Water absorption (%)ASTM-C1270.580.53Clay lump (%)ASTM-C1420.0170.01Figure 1
Grading of aggregate.


### 2.2. Cement

The choice of cement type is an essential aspect of RCC fabrication, as it can significantly affect the material’s properties and performance. Type I or II Portland cement and F or C grade Fly ash are commonly used in the production of RCC pavements. To ensure quality and reliability, the Portland cement must meet the ASTM C150 [18] standard requirements, which ensure that it meets specific chemical and physical characteristics. However, Portland cement type III (early hardening) is typically not used in RCC due to the lack of sufficient time to work with the concrete. In the present study, Portland cement Type II of Ardestan Cement Factory in Isfahan was utilized. Tables 2 and 3 provide detailed information on the chemical and physical characteristics of the cement, respectively. The careful selection of cement type and adherence to standard requirements is crucial in achieving the desired properties and performance of RCC.Table 2
Chemical analysis of cement.
ComponentPercentageSiO222.0Fe2O33.82AL2O35.00MgO1.90CaO64.00SO31.50K2O0.49Na2O0.25L.O.I1.0Table 3
Physical properties of cement.
Blaine (cm2/gr)Setting time (min)Compressive strength (kg/cm2)InitialFinal3 days7 days28 days3000 ± 5095 ± 5150 ± 10>170>275>370


### 2.3. Water

The quality and requirements of water used in RCC are critical factors that can impact the material’s overall strength and durability. The ASTM C1602 [19] standard sets out the specifications for the quality of water to be used in RCC, which is similar to the requirements for ordinary concrete. It is essential to ensure that the water used is free from contaminants and impurities that could negatively affect the RCC’s properties. In addition to the quality of the water used, the amount of water must also be carefully controlled during the RCC fabrication process. The Vee-Bee test is typically used to determine the low-workability range for RCC, which requires that the amount of water used be restricted to achieve the desired workability while maintaining the optimal strength and durability of the material. Careful attention to the quality and quantity of water used is crucial in producing high-quality, reliable RCC that meets the required performance standards.


### 2.4. Basic Oxygen Furnace Slag

This research project utilized BOFS from Isfahan Steel Company as the primary raw material. The use of BOFS as a partial replacement for natural coarse-grain aggregate was a key element of the experimental design, with the exception of the control sample (RCC-P0). Tables4 and 5 provide a detailed overview of the physical and chemical properties of the BOFS utilized in this study. The BOFS material was carefully selected based on its quality and consistency to ensure that the resulting RCC would meet the required standards for strength, durability, and other critical performance factors. As a by-product of the steelmaking process, BOFS has proven to be an effective and sustainable alternative to traditional coarse-grain aggregates, reducing the environmental impact of RCC fabrication while maintaining its structural integrity. The physical and chemical properties of the BOFS were thoroughly examined and characterized to ensure that the resulting RCC would meet the desired specifications and performance standards.Table 4
Technical specification of slag.
PropertyStandardCoarse gravelNominal maximum aggregate sizeASTM-C13619Los Angles abrasion (%)ASTM-C13118.0Bulk density (g/cm3)ASTM-C1272.710SSD density (g/cm3)ASTM-C1273.25Water absorption 24 h (%)ASTM-C1271.50Table 5
Chemical analysis of BOFS.
ComponentPercentageSiO211.22FeO12.26AL2O30.73MgO2.15P2O52.35MnO5.02K2O0.01Na2O0.02CaO50.11TFe15.39


### 2.5. Steel Fibers

Steel reinforced concrete is a composite material made of cement, crushed aggregate, water, and a certain percentage of steel fibers that are evenly dispersed in various directions. The addition of steel fibers to concrete has been found to increase bending strength, compressive strength, shear strength, and cracking resistance, as well as the conductivity and thermal conductivity of the concrete [20], and also increases the conductivity of the concrete. This study focuses on using steel fibers to improve the mechanical properties of RCC and to enhance its electrical conductivity, thermal conductivity, and resistance to electrical flow, as shown in Figure 2. The steel fibers used in this study are double-hooked with a length of 35 mm and meet other specifications as outlined in Table 6.Figure 2
Steel fibers used in this study (a) separately and (b) in the mixture.
(a)(b)Table 6
Properties of steel fibers.
PropertyValueFiber diameter (mm)0.8Tensile strength (MPa)1150Elongation (%)<3Length (mm)35Specific gravity7.69Aspect ratio43.74


### 2.6. Steel Shaving

Steel shavings have been increasingly used as an additional component in reinforced concrete to enhance its electrical conductivity and reduce its electrical resistance. In this study, steel shavings were incorporated along with steel fibers in various volumetric percentages of the fine aggregate to improve the electrical properties of the concrete. The steel shavings were obtained from CK45 steel and had a uniform length within the range of 7–9 mm which is presented in Figure3. They were thoroughly mixed with other components of the concrete to ensure even distribution. The effect of different volumetric percentages of steel shavings, in combination with steel fibers, on the electrical conductivity and other properties of RCC are presented in the subsequent sections.Figure 3
Steel shaving used in this study.


## 2.1. Aggregate

Natural aggregate constitutes about 75% to 85% of concrete and significantly affects its properties in both the fresh and hardened states. The size of the aggregate must comply with the ASTM C33 standard, and in roller-compacted concrete (RCC), it affects the performance, quality, density, and segregation. The physical properties of the aggregate also impact the resistance, modulus of elasticity, thermal properties, and durability of the hardened concrete [17]. To achieve the desired surface quality, the nominal maximum size of the coarse-grain aggregate should be limited to 19 mm. The fine-andcoarse-grinded aggregate can be either natural or crushed aggregate or a mixture of both. The crushed aggregate is preferred for RCC as it requires less energy for compaction and generally results in less segregation and higher flexural strength. The crushed aggregate used in this research is sourced from Isfahan limestone mines, and its physical characteristics and gradation are given in Table 1 and Figure 1, respectively.Table 1
Physical properties of aggregate.
PropertyStandardFine gravelCoarse gravelNominal maximum aggregate sizeASTM-C1364.7519Los angles abrasion (%)ASTM-C131—16.0Bulk density (g/cm3)ASTM-C1272.7102.680SSD density (g/cm3)ASTM-C1272.7302.716Water absorption (%)ASTM-C1270.580.53Clay lump (%)ASTM-C1420.0170.01Figure 1
Grading of aggregate.


## 2.2. Cement

The choice of cement type is an essential aspect of RCC fabrication, as it can significantly affect the material’s properties and performance. Type I or II Portland cement and F or C grade Fly ash are commonly used in the production of RCC pavements. To ensure quality and reliability, the Portland cement must meet the ASTM C150 [18] standard requirements, which ensure that it meets specific chemical and physical characteristics. However, Portland cement type III (early hardening) is typically not used in RCC due to the lack of sufficient time to work with the concrete. In the present study, Portland cement Type II of Ardestan Cement Factory in Isfahan was utilized. Tables 2 and 3 provide detailed information on the chemical and physical characteristics of the cement, respectively. The careful selection of cement type and adherence to standard requirements is crucial in achieving the desired properties and performance of RCC.Table 2
Chemical analysis of cement.
ComponentPercentageSiO222.0Fe2O33.82AL2O35.00MgO1.90CaO64.00SO31.50K2O0.49Na2O0.25L.O.I1.0Table 3
Physical properties of cement.
Blaine (cm2/gr)Setting time (min)Compressive strength (kg/cm2)InitialFinal3 days7 days28 days3000 ± 5095 ± 5150 ± 10>170>275>370


## 2.3. Water

The quality and requirements of water used in RCC are critical factors that can impact the material’s overall strength and durability. The ASTM C1602 [19] standard sets out the specifications for the quality of water to be used in RCC, which is similar to the requirements for ordinary concrete. It is essential to ensure that the water used is free from contaminants and impurities that could negatively affect the RCC’s properties. In addition to the quality of the water used, the amount of water must also be carefully controlled during the RCC fabrication process. The Vee-Bee test is typically used to determine the low-workability range for RCC, which requires that the amount of water used be restricted to achieve the desired workability while maintaining the optimal strength and durability of the material. Careful attention to the quality and quantity of water used is crucial in producing high-quality, reliable RCC that meets the required performance standards.


## 2.4. Basic Oxygen Furnace Slag

This research project utilized BOFS from Isfahan Steel Company as the primary raw material. The use of BOFS as a partial replacement for natural coarse-grain aggregate was a key element of the experimental design, with the exception of the control sample (RCC-P0). Tables4 and 5 provide a detailed overview of the physical and chemical properties of the BOFS utilized in this study. The BOFS material was carefully selected based on its quality and consistency to ensure that the resulting RCC would meet the required standards for strength, durability, and other critical performance factors. As a by-product of the steelmaking process, BOFS has proven to be an effective and sustainable alternative to traditional coarse-grain aggregates, reducing the environmental impact of RCC fabrication while maintaining its structural integrity. The physical and chemical properties of the BOFS were thoroughly examined and characterized to ensure that the resulting RCC would meet the desired specifications and performance standards.Table 4
Technical specification of slag.
PropertyStandardCoarse gravelNominal maximum aggregate sizeASTM-C13619Los Angles abrasion (%)ASTM-C13118.0Bulk density (g/cm3)ASTM-C1272.710SSD density (g/cm3)ASTM-C1273.25Water absorption 24 h (%)ASTM-C1271.50Table 5
Chemical analysis of BOFS.
ComponentPercentageSiO211.22FeO12.26AL2O30.73MgO2.15P2O52.35MnO5.02K2O0.01Na2O0.02CaO50.11TFe15.39


## 2.5. Steel Fibers

Steel reinforced concrete is a composite material made of cement, crushed aggregate, water, and a certain percentage of steel fibers that are evenly dispersed in various directions. The addition of steel fibers to concrete has been found to increase bending strength, compressive strength, shear strength, and cracking resistance, as well as the conductivity and thermal conductivity of the concrete [20], and also increases the conductivity of the concrete. This study focuses on using steel fibers to improve the mechanical properties of RCC and to enhance its electrical conductivity, thermal conductivity, and resistance to electrical flow, as shown in Figure 2. The steel fibers used in this study are double-hooked with a length of 35 mm and meet other specifications as outlined in Table 6.Figure 2
Steel fibers used in this study (a) separately and (b) in the mixture.
(a)(b)Table 6
Properties of steel fibers.
PropertyValueFiber diameter (mm)0.8Tensile strength (MPa)1150Elongation (%)<3Length (mm)35Specific gravity7.69Aspect ratio43.74


## 2.6. Steel Shaving

Steel shavings have been increasingly used as an additional component in reinforced concrete to enhance its electrical conductivity and reduce its electrical resistance. In this study, steel shavings were incorporated along with steel fibers in various volumetric percentages of the fine aggregate to improve the electrical properties of the concrete. The steel shavings were obtained from CK45 steel and had a uniform length within the range of 7–9 mm which is presented in Figure3. They were thoroughly mixed with other components of the concrete to ensure even distribution. The effect of different volumetric percentages of steel shavings, in combination with steel fibers, on the electrical conductivity and other properties of RCC are presented in the subsequent sections.Figure 3
Steel shaving used in this study.


## 3. Mix Design and Tests

Two methods are commonly used for making laboratory samples of RCC concrete. In the first method, the sample is poured into the mold and compressed on a vibration table under an overweight according to ASTM C1176 [21]. In the second method, the specimen is constructed in a multilayer and compacted with the application of a Marshall Hammer according to ASTM D1557 [22]. The Marshall Hammer can compact samples and produce a similar density compared to the samples taken from the field compacted RCC pavement.In this study, cylindrical molds with a diameter of 150 mm and a height of 300 mm were used to compact the RCC samples in four layers using a Marshall Hammer. For the first layer, the materials were poured into the mold, and a 14.5 cm steel plate was placed on top of the aggregate. Then, 40 blows were applied by a 4.5 kg hammer falling from a height of 45 cm. The other three layers were similarly compacted. After compaction, the specimens were left in the mold for a day and then removed and kept in water for 28 days to ensure complete hydration of the concrete. This method of sample preparation allowed for consistent and reliable results in testing the mechanical and electrical properties of the RCC samples.


### 3.1. Mix Proportion

The volumetric method was chosen for this study due to the higher specific gravity of the added materials, including slag, steel fibers, and steel shavings, compared to the natural aggregate. This method ensures that the proportion of each component is accurately measured by volume. In this study, steel fibers were added at volumetric percentages of 0.4, 0.7, and 1% of the total aggregate, while steel shavings were added at volumetric percentages of 3, 5, and 7% of the fine aggregate. The mix designs for all samples are presented in detail in Table7. The precise amounts of each component were carefully calculated to ensure optimal performance and economy of the final RCC. The mix designs were formulated to achieve the desired strength and durability properties while also considering the cost-effectiveness of the final product. The use of the volumetric method for proportioning the components of RCC is essential to ensure the accurate and efficient production of high-quality and cost-effective materials.Table 7
The characteristics of RCC mix design used in the study.
RCC sampleNatural coarse aggregate (kg/m3)BOFS coarse aggregate (kg/m3)Natural fine aggregate (kg/m3)Steel fiber (%)Steel shaving (%)Water (kg/m3)Cement (kg/m3)RCC-P08300119000114.0300BOFS01022119000116.1BOFS-F0.40101811840.40114.3BOFS-F0.70101511800.70112.5BOFS-F101012117710110.2BOFS-S301022115303115.9BOFS-S501022113005115.7BOFS-S701022110607115.4BOFS-F0.4-S30101811490.43114.3BOFS-F0.4-S50101811250.45114.1BOFS-F0.4-S70101811010.47113.9BOFS-F0.7-S30101511450.73112.6BOFS-F0.7-S50101511210.75112.3BOFS-F0.7-S70101510970.77112.1BOFS-F1-S301012104113111.2BOFS-F1-S501012101815111.0BOFS-F1-S70101299417110.5


### 3.2. Compressive Strength Test

To test the compressive strength of the RCC samples, cylindrical specimens with a diameter of 150 mm and a height of 300 mm were prepared in accordance with the ASTM C39 [23] standard. In total, three samples were taken from each mix design to ensure accuracy and reliability of the test results. After casting and compaction, the samples were left to cure in water for 28 days to attain maximum strength. The compressive strength was then tested using a hydraulic compression machine, and the average value of the three samples was recorded. The results of the compressive strength tests for all the samples are presented in Figure 4. It should be noted that compressive strength is an essential parameter for evaluating the ability of RCC to withstand compressive loads and is an important factor in designing RCC pavements.Figure 4
Compressive strength test.


### 3.3. Split Tensile Strength Test

The indirect tensile stress (ITS) of RCC samples was evaluated using the IDT test method according to the ASTM C496 [24] standard, which involved applying a uniform compressive force of 50 mm per minute to cylindrical samples of 150 × 300 mm after 28 days of water curing (Figure 5). At least four replicate samples were evaluated for each mix design to ensure the accuracy and reliability of the results. During the test, a vertical compressive force was applied, which resulted in tensile tension in the horizontal direction. The ITS value was calculated using the following equation:(1)ITS=2PπDt,where P, D, and t represent the peak load until failure in Newtons, the diameter in centimeters, and the thickness in centimeters, respectively. The study was conducted using the observed average diameters and thicknesses, and no adjustments were made to the readings acquired from the test instrument. At least four replicate samples were evaluated for each of the mix designs to ensure the accuracy and consistency of the results. The ITS values obtained from the test were used to evaluate the performance of the RCC samples with different mix designs.Figure 5
Tensile strength test.


### 3.4. Specific Gravity

The specific gravity of a material is an important factor that can affect its properties, such as compressive strength, durability, and workability. Since the specific gravity of slag and steel fibers and shavings is different from that of natural stone, it was expected that the specific gravity of the mix designs would be altered compared to ordinary RCC. Therefore, in this study, a specific gravity test was performed for all of the mix designs. Initially, the specimens’ saturated surface-dry weight was measured, and then, the weight of each sample under water was determined using an Arashmidus scale. The SSD specific gravity of the samples was calculated based on these measurements. The results of the specific gravity test provided useful information for evaluating the mix designs’ properties and helped to ensure that the required specifications were met.


### 3.5. Electrical Resistance

To perform the electrical resistivity test on all samples, a thin layer of cement paste was used to make a proper contact between the concrete sample surface and two copper metal electrodes. The sample was in the form of a wet cylindrical shape, as shown in Figure6. The electrodes were then connected to a 3.75-volt AC power supply, and the current passing through each sample was measured during the test. The electrical resistance of the cylindrical sample was calculated using the following equation:(2)R=VI,where R is the apparent resistance in ohms, V is the voltage in volts, and I is the current in amperes. When a current passes through concrete without conductive components, it must go through aggregate or cement paste, which has a very high electrical resistance and cannot easily pass the current. However, when conductive materials such as steel fibers and steel shavings are added to the concrete, they can easily pass the current through the material due to their connection with each other and with the concrete matrix (Figure 6). As the charge passes through the concrete, the specimen acts as a thermal element and its temperature begins to increase. After measuring the apparent resistance of each sample using equation (2), the specific electrical resistance of the concrete was calculated using the following equation for all specimens:(3)ρ=RAL=VAIL=1Conductivity,where ρ is specific electrical resistivity (Ω.m), R is apparent resistance (Ω), A is the cross section of the sample (m2), and L is the height of sample (m).Figure 6
Electrical resistance test.


## 3.1. Mix Proportion

The volumetric method was chosen for this study due to the higher specific gravity of the added materials, including slag, steel fibers, and steel shavings, compared to the natural aggregate. This method ensures that the proportion of each component is accurately measured by volume. In this study, steel fibers were added at volumetric percentages of 0.4, 0.7, and 1% of the total aggregate, while steel shavings were added at volumetric percentages of 3, 5, and 7% of the fine aggregate. The mix designs for all samples are presented in detail in Table7. The precise amounts of each component were carefully calculated to ensure optimal performance and economy of the final RCC. The mix designs were formulated to achieve the desired strength and durability properties while also considering the cost-effectiveness of the final product. The use of the volumetric method for proportioning the components of RCC is essential to ensure the accurate and efficient production of high-quality and cost-effective materials.Table 7
The characteristics of RCC mix design used in the study.
RCC sampleNatural coarse aggregate (kg/m3)BOFS coarse aggregate (kg/m3)Natural fine aggregate (kg/m3)Steel fiber (%)Steel shaving (%)Water (kg/m3)Cement (kg/m3)RCC-P08300119000114.0300BOFS01022119000116.1BOFS-F0.40101811840.40114.3BOFS-F0.70101511800.70112.5BOFS-F101012117710110.2BOFS-S301022115303115.9BOFS-S501022113005115.7BOFS-S701022110607115.4BOFS-F0.4-S30101811490.43114.3BOFS-F0.4-S50101811250.45114.1BOFS-F0.4-S70101811010.47113.9BOFS-F0.7-S30101511450.73112.6BOFS-F0.7-S50101511210.75112.3BOFS-F0.7-S70101510970.77112.1BOFS-F1-S301012104113111.2BOFS-F1-S501012101815111.0BOFS-F1-S70101299417110.5


## 3.2. Compressive Strength Test

To test the compressive strength of the RCC samples, cylindrical specimens with a diameter of 150 mm and a height of 300 mm were prepared in accordance with the ASTM C39 [23] standard. In total, three samples were taken from each mix design to ensure accuracy and reliability of the test results. After casting and compaction, the samples were left to cure in water for 28 days to attain maximum strength. The compressive strength was then tested using a hydraulic compression machine, and the average value of the three samples was recorded. The results of the compressive strength tests for all the samples are presented in Figure 4. It should be noted that compressive strength is an essential parameter for evaluating the ability of RCC to withstand compressive loads and is an important factor in designing RCC pavements.Figure 4
Compressive strength test.


## 3.3. Split Tensile Strength Test

The indirect tensile stress (ITS) of RCC samples was evaluated using the IDT test method according to the ASTM C496 [24] standard, which involved applying a uniform compressive force of 50 mm per minute to cylindrical samples of 150 × 300 mm after 28 days of water curing (Figure 5). At least four replicate samples were evaluated for each mix design to ensure the accuracy and reliability of the results. During the test, a vertical compressive force was applied, which resulted in tensile tension in the horizontal direction. The ITS value was calculated using the following equation:(1)ITS=2PπDt,where P, D, and t represent the peak load until failure in Newtons, the diameter in centimeters, and the thickness in centimeters, respectively. The study was conducted using the observed average diameters and thicknesses, and no adjustments were made to the readings acquired from the test instrument. At least four replicate samples were evaluated for each of the mix designs to ensure the accuracy and consistency of the results. The ITS values obtained from the test were used to evaluate the performance of the RCC samples with different mix designs.Figure 5
Tensile strength test.


## 3.4. Specific Gravity

The specific gravity of a material is an important factor that can affect its properties, such as compressive strength, durability, and workability. Since the specific gravity of slag and steel fibers and shavings is different from that of natural stone, it was expected that the specific gravity of the mix designs would be altered compared to ordinary RCC. Therefore, in this study, a specific gravity test was performed for all of the mix designs. Initially, the specimens’ saturated surface-dry weight was measured, and then, the weight of each sample under water was determined using an Arashmidus scale. The SSD specific gravity of the samples was calculated based on these measurements. The results of the specific gravity test provided useful information for evaluating the mix designs’ properties and helped to ensure that the required specifications were met.


## 3.5. Electrical Resistance

To perform the electrical resistivity test on all samples, a thin layer of cement paste was used to make a proper contact between the concrete sample surface and two copper metal electrodes. The sample was in the form of a wet cylindrical shape, as shown in Figure6. The electrodes were then connected to a 3.75-volt AC power supply, and the current passing through each sample was measured during the test. The electrical resistance of the cylindrical sample was calculated using the following equation:(2)R=VI,where R is the apparent resistance in ohms, V is the voltage in volts, and I is the current in amperes. When a current passes through concrete without conductive components, it must go through aggregate or cement paste, which has a very high electrical resistance and cannot easily pass the current. However, when conductive materials such as steel fibers and steel shavings are added to the concrete, they can easily pass the current through the material due to their connection with each other and with the concrete matrix (Figure 6). As the charge passes through the concrete, the specimen acts as a thermal element and its temperature begins to increase. After measuring the apparent resistance of each sample using equation (2), the specific electrical resistance of the concrete was calculated using the following equation for all specimens:(3)ρ=RAL=VAIL=1Conductivity,where ρ is specific electrical resistivity (Ω.m), R is apparent resistance (Ω), A is the cross section of the sample (m2), and L is the height of sample (m).Figure 6
Electrical resistance test.


## 4. Results and Discussion

### 4.1. Compressive Strength

The compressive strength test results are presented in Figure7. The results indicate that replacing the coarse aggregate with slag slightly decreases the compressive strength of concrete compared to the control samples. This could be attributed to the low glass content and high iron oxide content of the basic oxygen furnace steel slag, which limits the formation of calcium silicate hydrate (C-S-H) gel and, therefore, reduces its pozzolanic activity with Portland cement. However, the addition of steel fibers to the concrete leads to a significant improvement in compressive strength, with the strength improving greatly as the percentage of steel fibers increases. On the other hand, replacing the fine aggregate with steel shavings causes a remarkable reduction in the compressive strength of concrete compared to the control samples. This may be due to the difficulty of dispersing the steel shavings in the cement mortar and the lack of pozzolanic reaction between steel shavings and cement paste, as steel shavings are metallic in nature and lack the chemical properties necessary to undergo a pozzolanic reaction. Nevertheless, the incorporation of steel fibers into samples containing steel shavings compensates for the strength reduction, and with a higher percentage of steel fibers, the strength loss reduces and approaches the level of the fiber-reinforced concrete samples without steel shavings.Figure 7
Compressive strength of 28 days cured specimens.


### 4.2. Indirect Tensile Strength

The results of the indirect tensile strength test are presented in Figure8. The BOFS sample showed a slight decrease in tensile strength compared to the control sample, which may be due to the lower pozzolanic reaction between the cement paste and BOFS aggregate. On the other hand, the addition of steel fibers to RCC samples resulted in higher tensile strength, with the sample containing 1% of steel fibers exhibiting the highest strength (4.5 MPa). The split tensile strength decreased slightly with the replacement of steel shavings, which could be attributed to the lower pozzolanic reaction between the cement paste and BOFS aggregate. However, the addition of 0.7% and 1% of fibers increased the tensile strength compared to the control sample. For the samples containing steel shavings with 0.7% and 1% of steel fibers, the introduction of higher percentages of steel shavings resulted in a strength loss. This could be due to the lack of or weaker transmit region around the steel shavings, resulting in a reduction in tensile strength. Furthermore, the strength compensation of steel fibers decreased.Figure 8
Split tensile strength of 28 days cured specimens.


### 4.3. Electrical Resistance

Figures9 and 10 depict the electrical resistance and specific electrical resistance, respectively, of the RCC samples. As seen in the figures, the BOFS sample exhibits higher electrical resistivity than the control sample. This can be attributed to the lower pozzolanic activity and weaker transmit region of the slag aggregate, which outweighs any positive effects of the high iron oxide content on electrical resistance.Figure 9
Electrical resistance.Figure 10
Specific electrical resistance.Upon adding 0.4% of steel fibers to the concrete mix, a sharp drop in electrical resistance is observed, which slightly decreases with higher percentages of steel fibers. In contrast, the addition of steel shavings leads to a significant reduction in electrical resistance in the RCC samples. In samples containing 1% steel fibers with varying percentages of steel shavings, the electrical resistance is slightly lower compared to samples with only steel shavings. Notably, the samples containing 0.7 and 1% of steel fibers with 7% of steel shavings exhibit a sharp decrease in electrical resistance and a significant increase in concrete conductivity when compared to the control sample. This is likely due to the presence of more electrically conductive compounds, namely, steel fibers and shavings, which create a network of conductive pathways throughout the material. This network facilitates the flow of electricity through the concrete, leading to a decrease in electrical resistance and an increase in conductivity.


### 4.4. Bulk Specific Gravity

In Figure11, the bulk specific gravity of various mixtures is presented. It is observed that the specific gravity of all the samples is higher than the control sample. The addition of the slag aggregate to the concrete results in an increase in the specific gravity compared to the control sample. This can be attributed to the higher specific gravity of slag than conventional natural materials. Moreover, specimens that were solely made up of steel shavings or steel fibers exhibited a higher specific gravity than the control sample and the BOFS specimen, as steel has a high specific gravity. In composite samples, the specific gravity continued to increase with the addition of fibers and steel shavings. Furthermore, it was observed that a higher percentage of steel fibers led to a higher specific gravity.Figure 11
Specific gravity.


## 4.1. Compressive Strength

The compressive strength test results are presented in Figure7. The results indicate that replacing the coarse aggregate with slag slightly decreases the compressive strength of concrete compared to the control samples. This could be attributed to the low glass content and high iron oxide content of the basic oxygen furnace steel slag, which limits the formation of calcium silicate hydrate (C-S-H) gel and, therefore, reduces its pozzolanic activity with Portland cement. However, the addition of steel fibers to the concrete leads to a significant improvement in compressive strength, with the strength improving greatly as the percentage of steel fibers increases. On the other hand, replacing the fine aggregate with steel shavings causes a remarkable reduction in the compressive strength of concrete compared to the control samples. This may be due to the difficulty of dispersing the steel shavings in the cement mortar and the lack of pozzolanic reaction between steel shavings and cement paste, as steel shavings are metallic in nature and lack the chemical properties necessary to undergo a pozzolanic reaction. Nevertheless, the incorporation of steel fibers into samples containing steel shavings compensates for the strength reduction, and with a higher percentage of steel fibers, the strength loss reduces and approaches the level of the fiber-reinforced concrete samples without steel shavings.Figure 7
Compressive strength of 28 days cured specimens.


## 4.2. Indirect Tensile Strength

The results of the indirect tensile strength test are presented in Figure8. The BOFS sample showed a slight decrease in tensile strength compared to the control sample, which may be due to the lower pozzolanic reaction between the cement paste and BOFS aggregate. On the other hand, the addition of steel fibers to RCC samples resulted in higher tensile strength, with the sample containing 1% of steel fibers exhibiting the highest strength (4.5 MPa). The split tensile strength decreased slightly with the replacement of steel shavings, which could be attributed to the lower pozzolanic reaction between the cement paste and BOFS aggregate. However, the addition of 0.7% and 1% of fibers increased the tensile strength compared to the control sample. For the samples containing steel shavings with 0.7% and 1% of steel fibers, the introduction of higher percentages of steel shavings resulted in a strength loss. This could be due to the lack of or weaker transmit region around the steel shavings, resulting in a reduction in tensile strength. Furthermore, the strength compensation of steel fibers decreased.Figure 8
Split tensile strength of 28 days cured specimens.


## 4.3. Electrical Resistance

Figures9 and 10 depict the electrical resistance and specific electrical resistance, respectively, of the RCC samples. As seen in the figures, the BOFS sample exhibits higher electrical resistivity than the control sample. This can be attributed to the lower pozzolanic activity and weaker transmit region of the slag aggregate, which outweighs any positive effects of the high iron oxide content on electrical resistance.Figure 9
Electrical resistance.Figure 10
Specific electrical resistance.Upon adding 0.4% of steel fibers to the concrete mix, a sharp drop in electrical resistance is observed, which slightly decreases with higher percentages of steel fibers. In contrast, the addition of steel shavings leads to a significant reduction in electrical resistance in the RCC samples. In samples containing 1% steel fibers with varying percentages of steel shavings, the electrical resistance is slightly lower compared to samples with only steel shavings. Notably, the samples containing 0.7 and 1% of steel fibers with 7% of steel shavings exhibit a sharp decrease in electrical resistance and a significant increase in concrete conductivity when compared to the control sample. This is likely due to the presence of more electrically conductive compounds, namely, steel fibers and shavings, which create a network of conductive pathways throughout the material. This network facilitates the flow of electricity through the concrete, leading to a decrease in electrical resistance and an increase in conductivity.


## 4.4. Bulk Specific Gravity

In Figure11, the bulk specific gravity of various mixtures is presented. It is observed that the specific gravity of all the samples is higher than the control sample. The addition of the slag aggregate to the concrete results in an increase in the specific gravity compared to the control sample. This can be attributed to the higher specific gravity of slag than conventional natural materials. Moreover, specimens that were solely made up of steel shavings or steel fibers exhibited a higher specific gravity than the control sample and the BOFS specimen, as steel has a high specific gravity. In composite samples, the specific gravity continued to increase with the addition of fibers and steel shavings. Furthermore, it was observed that a higher percentage of steel fibers led to a higher specific gravity.Figure 11
Specific gravity.


## 5. Conclusion

In this study, the feasibility of using steel fibers and steel shavings in RCC containing coarse BOFS aggregate was investigated in order to improve its mechanical properties and to produce electrically conductive and environmentally-friendly concrete. The following conclusions can be drawn based on the compressive, tensile, electrical resistivity, and specific gravity of the various mixtures:(1)
The use of BOFS in RCC as coarse aggregate alone is not enough and cannot achieve the mechanical properties required for RCC, but its compressive strength can be increased by adding steel fibers to RCC. The use of steel fibers reinforces the RCC samples and the compressive strength of concrete increases. However, the steel shavings have a destructive effect on compressive strength, but with a combination of steel fibers, this destructive effect reduces.(2)
The addition of BOFS aggregate and steel shavings replacement causes a reduction in the tensile strength of the RCC, which can be compensated by adding steel fibers that might be due to a weaker transmission region around steel shavings BOFS aggregate which results in a reduction in tensile strength.(3)
The high levels of iron oxide in BOFS aggregate have little effect on the electrical resistance of concrete samples. Adding the steel fibers and shavings alone can reduce the electrical resistance of the RCC, and when used simultaneously, the electrical resistance of the concrete made with 0.7% and 1% of steel fibers with 7% of steel shavings decreases dramatically.(4)
The BOFS aggregate, steel fibers, and shavings, when added to the concrete, result in an increase in the bulk specific gravity.(5)
Considering all the test results, it can be concluded that BOFS concrete samples containing 0.7% steel fibers along with 7% of steel shavings result in comparable and better performance in terms of compressive and tensile strengths, while producing significantly lower electrical resistivity in comparison with the control mixture.In summary, the findings of this study indicate that the use of steel fibers and steel shavings in RCC containing BOFS aggregate can improve its mechanical properties, make it electrically conductive, and maintain its environmental friendliness. Therefore, the use of these materials is a feasible and practical solution for the production of RCC with improved properties, which can be used in various applications, such as pavements and dam constructions.



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*Source: 6036906-2023-03-17.xml*