Enhancing concrete performance through iron slag substitution: analysis of mechanical, durability and microstructural studies

Abstract

The coarse aggregate was replaced with iron slag by weight from 10 to 60% with 10% variations, and the self-compacting concrete samples were analyzed after 28 days of curing in water. This study assesses concrete sample flexural strength, splitting tensile strength, ultrasonic pulse velocity (UPV), acid resistance, surface water absorption, compressive strength, electrical resistance, and capillary water absorption. Additionally, the SEM (Scanning Electron Microscopy) analysis was performed to assess the microstructure level of the cement concrete mix. The samples with iron slag substituted at 20%, 40%, and 60% show greater compressive, flexural, and splitting tensile strengths (about 18.4%, 28.6%, and 16.9% higher) than the control samples. Moreover, adding coarse aggregate containing 10, 20, 30 and 40% of higher strength at compression was achieved with iron slag.

Keywords:
Coarse aggregate; Iron slag aggregate; Durability; mechanical strength; Self-compacting concrete

1. INTRODUCTION

In the modern day, concrete is a building material widely used in construction. On the other hand, the traditional ingredients utilized in its manufacturing create serious environmental problems. Industrial waste materials that fulfil code requirements and have qualities similar to conventional materials should be used in concrete to enhance sustainability in the building sector [¹]. The overuse of natural resources for building poses a challenge to the sustainability of natural sand and gravel. On the other hand, disposing of industrial waste on land ruins ecosystems and magnifies environmental issues. Many academics are studying the disposal of industrial waste in the building sector to minimize the consumption of natural resources and manage solid industrial waste [²]. A vast array of waste products is now being disposed of into the environment by several industries. Dolomite residual powder, Steel slag, copper slag, granite sawing waste, marble powder, foundry sand, ladle furnace slag, perlite powder, iron slag, glass, spent brick and ceramic waste, weld slag, red mud, spent garnet sand, rubber waste, plastic waste are some of these waste materials [³]. These leftover components may partially replace gravel, cement, and sand with conventional and self-restraining concrete [⁴].

The building industry may improve concrete construction’s durability and functionality while reducing environmental issues using these waste materials. Superplasticizers and compounds that change viscosity are added, and standard materials are used to create self-compacting concrete (SCC). Notable qualities of this kind of concrete include high resistance to segregation in its fresh form, outstanding workability, and extraordinary passing ability. Granted that SCC has a lower aggregate content than NVC (Normally Vibrated Concrete), the aggregates are nevertheless essential in defining the qualities of the concrete once it has hardened and become fresh [⁵]. A move toward more environmentally friendly methods has been observed in the concrete industry lately as alternative materials are used more frequently to produce SCC. Adding self-compacting concrete made from industrial waste and by-product materials has been the subject of extensive research [⁶]. The results of these studies have shown that the microstructure, overall durability, and mechanical properties of the concrete are improved when these materials are added in specific proportions.

Partially substituting cement and aggregate, iron slag is one of these wastes and by-product products. Every year, the iron and steel industries in different parts of the world create large amounts of iron slag. Every year, seventeen thousand tons of iron slag (IS) are produced in India [⁷]. Iron slag is very frequently liable in open spaces close to populated areas, endangering the lives of nearby inhabitants. On the other hand, the disposal issue of iron slag is ideally addressed by using it in concrete production. Given the ongoing expansion in iron slag production, it is necessary and appropriate to integrate iron slag into the concrete rather than discard it. Many academics have focused on replacing sand in concrete with iron slag as an additional ingredient. Concerning strength and microstructural characteristics, substituting iron slag for aggregate in the SCC example has shown encouraging results [⁸]. Studies showed that the shielding characteristics against point sources of 60Co and 137Cs increase when these materials are used in place of aggregates [⁹]. Additionally, adding these minerals to concrete helps strengthen it. Also, slag aggregate-containing concretes have the potential to be a more affordable option than radiation-shielding composites [¹⁰], and previous studies focused on iron slag concrete’s technical characteristics and capacity to lessen urban runoff pollutants [¹¹].

This article illustrated that this concrete requires less money for mixing and implementation than ordinary concrete. It is advised to collect urban runoff and improve the state of cities with minimal vehicular volumes. Existing researchers used copper and iron slag instead of concrete particles. The results of this study show that adding these components to concrete can enhance its mechanical qualities [¹²]. Instead of focusing on aggregates, researchers examined the mechanical properties of various concentrations of iron slag [¹³]. The parameters studied were modulus of elasticity, splitting tensile strength, flexural strength, slump flow, V-funnel, U-box, and L-box. These article’s findings demonstrate that adding iron slag to SCC can enhance its flexural, splitting tensile and compressive strengths, among other qualities. Researchers used fine aggregate instead of iron slag in SCC in a different investigation. This investigation also looked at how concrete’s characteristics are impacted by nano-silica. Also, the study demonstrated the enhanced compressive strength of samples treated at an early age (7 days) with iron slag [¹³]. Slag concretes have several benefits for building, making them an excellent option for various building materials. Slag concretes’ longevity and resistance to chemical assaults offer long-lasting structural integrity in areas where moisture and possible soil pollutants are an issue, such as basement walls and foundations [¹⁴]. They guarantee these essential construction components can endure environmental pressures, safeguarding the entire building. Slag concretes increase pavement longevity, lowering maintenance costs and rising pavement lifespan. In addition, slag concretes are a preferred option due to their resistance to corrosion and low maintenance requirements in infrastructure projects like marine structures, bridges, and tunnels, during which exposure to extreme temperatures is inevitable [¹⁵]. This promotes the fundamental components of the constructed surrounding’s durability and sustainability.

This effort aimed to evaluate iron slag’s potential as a natural alternative for coarse aggregate. Iron slag was used as a natural coarse aggregate alternative in the following concrete samples: 0%, 10%, 20%, 30%, 40%, 50%, and 60%. Concrete sample curing took place in water for 28 days. There were numerous experimental tests carried out, such as Acid resistance, Capillary water absorption, Compressive strength, Micro-scale analysis, Flexural strength, L-box, Electrical resistance, Slump flow, Ultrasonic pulse velocity (UPV), Surface water absorption, V-funnel, splitting tensile strength using scanning electron microscopy (SEM). The iron slag substituted in samples with 20%, 40%, and 60% has been shown to have greater compressive, flexural, and splitting tensile strengths (about 18.4%, 28.6%, and 16.9% higher, respectively) than control samples. Furthermore, samples subjected to the acid environment showed enhanced compressive strength and reduced mass loss when 10 to 40% of iron slag was replaced with coarse aggregates, as opposed to control specimens.

2. MATERIALS AND METHODS

2.1. Cement

Based on ASTM C150 [¹⁶], type 2 Portland cement is used in this article. The XRD (Rietveld technique) identified Portland cement’s chemical and physical characteristics and stages. The findings are shown in Table 1. Noteworthy is the use of X-ray fluorescence (XRF) studies to evaluate the Portland cement’s chemical properties.

Table 1
Properties of Type II Portland cement.

S. NO.	CHEMICAL PROPERTIES	VALUE IN %	PHYSICAL PROPERTIES	VALUE
1.	SiO2	25.27	Absorption of water	–
2.	Al2O3	7.03	Density	3048 kg/m3
3.	Fe2O3	6.21	Surface area	310 m2/kg
4.	CaO	65.77	Autoclave Expansion	0.1%
5.	MgO	0.41		26% in 3 days
6.	K2O	0.93	Compressive Strength	30 MPa in 7 days
7.	Na2O	0.64		44 MPa in 28 days
8.	SO3	1.31	Setting time	90 min (Initial)
9.	Loss of Ignition	1.12		150 min (Final)
10.	C3S	52.82	–	–
11.	C2S	18.24	–	–
12.	C3A	8.31	–	–
13.	C4AF	10.02	–	–
14.	Gypsum	5.33	–	–

2.2. Limestone powder (LSP)

In this investigation, 95% pure LSP was used. Table 2 lists the limestone powder’s physical and chemical characteristics. It should be noted that X-ray fluorescence (XRF) analysis was used to assess the chemical characteristics of the powdered limestone.

Table 2
Properties of limestone powder.

S. NO.	CHEMICAL PROPERTIES	VALUE IN %	PHYSICAL PROPERTIES	VALUE
1.	SiO2	0.12	Absorption of water	0.1%
2.	Al2O3	0.05	Density	2598 kg/m3
3.	Fe2O3	0.01	Surface area	1678 m2/kg
4.	CaO	54.20	Calcium carbonate	95%
5.	MgO	0.62	–	–
6.	K2O	0.04	–	–
7.	Na2O	0.04	–	–
8.	SO3	0.01	–	–
9.	Loss of Ignition	42.8	–	–

2.3. Natural coarse and fine aggregate

Table 3 presents the features of coarse and fine particles seen in nature in compliance with ASTM C128-07 [¹⁷], ASTM C29-09 [¹⁸] and ASTM C127-07 [¹⁹]. Crushed boulders from Isfahan City, Iran, were used to create the largest diameter of the coarse particles is 19 mm. Figure 1 shows how the iron slag and natural aggregates are graded.

Table 3
Properties of iron slag and natural aggregates.

TYPE OF COMPONENT	APPEARANCE	SPECIFIC GRAVITY	WATER ABSORPTION (%)
Coarse Aggregate	Grey	2.78	0.34
Fine aggregate	Light Grey	2.52	1.10
Iron Slag	Black and Glassy	3.27	0.21

Figure 1
Size distribution of (a) fine aggregate and (b) Iron slag/coarse aggregates with IS standard limits..

2.4. Iron slag

The principal waste generated by the steel industry is referred to as iron slag. In Figure 1, the iron slag aggregate used in this study is shown visually. The substance’s 3340 kg/m³ specific gravity, the iron slag, has a water absorption rate of 0.24%. The iron slag’s grain size distribution is seen in Figure 1, which has particle sizes ranging from 4.75 to 19 mm. 5.72% Fe₂O₃, 4.3% Al₂O₃, 21.85% CaO, 2.5% MgO, and 8.3% SiO₂ make up the main constituents of these materials.

2.5. Superplasticizer (SP)

Using a high-range water reducer based on polycarboxylic ether (HRWR), P10-3R, the workability of new cement mortar has been improved. ASTM C494 [²⁰] states that Table 4 displays the superplasticizer’s characteristics.

Table 4
Properties of superplasticizer.

TYPE OF PROPERTY	QUALITY STANDARDS	RESULTS OBTAINED
pH	5 – 7.5	6.8
Density	0.9 – 1.2	1.1
Colour	–	Brown
Chlorine	<2400	790

2.6. Sample preparation, testing, and curing

Concrete cubes with 100 × 100 × 100 mm size and Cylinders with 150 × 150 × 150 mm in size were used for this study. The compressive strength of the concrete cubes has been conducted at a loading rate of 0.1 to 0.2 MPa/s in the compressive strength testing machine. For flexural strength the loading rate of 0.01 to 0.1 MPa/s and for Tensile strength, the loading rate of 0.1 to 0.2 MPa/s has been adopted. Seven distinct mix designs were created, with iron slag substituted for natural coarse stones ranging from 0% to 60%. SCC-0, SCC-10, SCC-20, SCC-30, SCC-40, SCC-50, and SCC-60 were the names given to these mix designs. The control group was made by replacing the coarse aggregates with 0% iron slag (SCC 0) and 60% iron slag (SCC 60). Moreover, a 0.9% HRWR (High-Range Water-Reducing) Additives were used for cement weight. The ratio of cement to water was the same in each combination, it should be noted. Table 5 provides specifics about the blends and their amounts. The curing process of concrete is crucial for ensuring that it achieves its intended strength, durability, and resistance to environmental factors. Proper curing helps maintain adequate moisture, temperature, and time conditions necessary for the chemical reactions within the concrete mix to progress effectively. In this study, the curing of concrete specimens has been done for 28 days in clean water. After 28 days of curing the sample was taken from the water and dried in the sunlight for experimental investigations.

Table 5
SCC details and its mix proportions.

MIX COMPONENTS (kg/m3)	SCC 0	SCC 10	SCC 20	SCC 30	SCC 40	SCC 50	SCC 60
Cement	335	335	335	335	335	335	335
Limestone powder	105	105	105	105	105	105	105
Superplasticizer (kg)	3	3	3	3	3	3	3
Fine Aggregate	950	950	950	950	950	950	950
Coarse Aggregate	820	740	660	575	490	410	330
Iron Slag	0	80	160	240	320	400	490
W/C ratio (%)	0.5	0.5	0.5	0.5	0.5	0.5	0.5
Iron Slag (%)	0	10	20	30	40	50	60

2.7. Testing of concrete specimens

2.7.1. Fresh concrete tests

The SCCs’ viability was evaluated using various tests per the code’s specifications. EFNARC code guidelines [²¹] were followed in conducting the slump flow test, V-funnel test, and L-box test (Table 6).

Table 6
EFNARC standards for SCC.

SLUMP VALUE TEST		V – FUNNEL TEST		L–BOX TEST
CLASSES OF SLUMP FLOW	OBSERVED VALUE (mm)	CLASSES OF VISCOSITY	OBSERVED VALUE IN SECONDS	CLASSES OF PASSING ABILITY	BLOCKING RATIO (h2/h1)
SF 1	550 – 650	VF 1	≤8	PA 1	≥ 0.8 (2 bars)
SF 2	660 – 750	VF 2	9 – 25	PA 2	≥ 0.8 (3 bars)
SF 3	760 – 850

2.7.2. Hardened concrete tests

A compressive strength test was conducted on the issues’ materials to ensure compliance with the relevant norms and regulations. In addition to the ultrasonic pulse velocity testing, further tests were performed on electrical resistance, capillary water absorption, flexural strength, split tensile strength, and acid resistance. The strength test results and the iron slag are shown in Figure 2. Under BS: Part 116 [²²], three 100 mm cubic specimens were used for the compressive strength test. Testing was done with a loading rate of 2.5 kN/s following a 28-day curing period. Three cylindrical specimens underwent a 28-day water curing period before being subjected to the split tensile strength test. Following ASTM C496 [²³] criteria, a loading rate of 2.1 kN/s was used during the test. Treated beams of 500 mm × 100 mm × 100 mm each were used for the bending strength test, which followed the guidelines of ASTM C78’s [²⁴] three-point bending formula. Two 100 mm cubic samples were used in surface water absorption tests conducted by BS: Part 122 [²⁵]. ASTM C597 [²⁶] was followed to conduct ultrasonic pulse velocity testing. Tests of electrical resistance, capillary water absorption and acid resistance were also carried out in the research articles correspondingly [²⁷, ²⁸].

Figure 2
(a) Iron slag, (b) Compressive, (c) Flexural and (d) Split tensile strength of concrete test..

3. RESULTS AND DISCUSSIONS

3.1. Properties of fresh concrete

3.1.1. Slump value test

Figure 3 illustrates how employing iron slag affects concrete slumps. Concretes have slump values between 658 and 764 mm. As seen in Figure 3, the slump value of concrete has grown dramatically as the volume of slag in the concrete has increased. Comparing the concrete mixes with 10, 20, 30, 40, 50, and 60% iron slag to the manage sample, the slump values improved by 3.51%, 5.32%, 7.90%, 10.79%, 13.22%, and 16.2%, respectively. The explanation for the rise in the cement-to-water ratio and the free water available in the concrete might be attributed to the reduced ability of slag grains to absorb water. This will cause more concrete slumps. According to the EFNARC classification [²⁹], concrete compositions containing 0–50% steel slag are classified as SF2. On the other hand, the SF3 group would include the sample that included 60% iron slag. Increasing iron content in SCC can enhance workability through improved packing density, reduced internal friction, favorable changes in rheology, contributions to cementitious reactions, and increased mix stability. Each of these factors plays a role in ensuring that the SCC remains flowable and cohesive without segregation or bleeding, which are critical for maintaining the quality and performance of the concrete in structural applications. Concretes with more significant percentages of slag can be used to produce structural elements, including beams with varying cross-sections, where concrete must flow, according to the findings of the slump test. Some slag kinds may lower concrete’s slump value fractured and uneven surfaces [³⁰].

Figure 3
Slump value of SCC mixes..

3.1.2. L-box

The L-box ratio values are shown in Figure 4 for each design with varying amounts of coarse iron slag. Concretes made with steel slag as coarse aggregate at a proportion ranging from 0 to 60% had blocking ratios (h1/h2) between 0.87 and 0.98. Concrete’s capacity to pass through rebar generally improves with increased iron slag content and the L-box ratio. In comparison to the control design, the h1/h2 parameter value increased by 2.3%, 3.45%, 6.93%, 9.21%, 11.5%, and 12.64%, respectively, for designs containing iron slag with 10 to 60% of coarse aggregate replacements. All iron slag-based concretes meet the EFNARC classification [²⁹] requirements for passing and filling, and they are all classified as PA1 materials. The inadequate water absorption by the coarse iron slag particles and glassy texture have decreased the concrete’s viscosity and raised the water-to-cement ratio, making it easier for the concrete to flow through the rebars’ compactness. The slag particles’ sharp angular form and higher blocking likelihood cause the passing ability to develop slower in increasing volumes. The L-box ratio and passing ability are increased when slag is used instead of natural coarse aggregates. Because slag is heavier than natural aggregates in concrete [³¹], researchers asserted that adding 60–80% iron slag to concrete instead of natural aggregates causes a drop in passing capacity [³²].

Figure 4
L box values of SCC..

3.1.3. V-Funnel test

The V-Funnel test results for concrete samples with coarse aggregate content ranging from 0 to 60% are shown in Figure 5. Between 3.96 and 6.1 seconds was the range of durations for each concrete sample to pass through the funnel. All mix designs showed quicker funnel test passage times than the control design, as iron slag was often substituted as coarse aggregate. This is because the iron slag grains’ form and angularity made it challenging for the concrete to flow down the funnel. It should be noted that the test revealed no signs of volatility or segregation, suggesting that the viscosity of the concrete mixture was suitable. The VF1 funnel time group is where all concretes manufactured with iron slag are classified according to the EFNARC [²⁹].

Figure 5
V Funnel values of SCC..

3.2. Tests using hardened concrete

3.2.1. Compressive strength

After being cured in water for 28 days, the samples’ compressive strengths are displayed in Figure 6. Comparing concrete samples to other mixtures, the results show that adding iron slag up to 20% increases the samples’ compressive strength. Compared to natural sand, steel slag, which has a rough surface and high angularity, shows better cohesive and mechanical bite forces. Higher bonding strength results from its improved bond formation with cement paste. It is evident that mixes SCC50 and SCC60 had lower compressive strengths when compared with control samples. The growth of a calcite layer on the aggregate surface is one reason for the decreased compressive strength in concrete mixes with a high proportion of steel slag particles. This layer interferes with the paste-aggregate connection, which is essential to the concrete’s characteristics. A weak interface between the aggregate and coating occurs when less binding separates the granular surface from its protective layer than the coating layer between the paste. Forster explains that this weak contact hurts concrete mixtures’ mechanical and durability qualities. Moreover, the less water slag grains absorb, the free water there is in the concrete, increasing the cement-to-water ratio, as indicated in the slump flow section. Stated differently, the concrete samples included in coarse aggregate iron slag have greater free water levels. Because slag contains more free water than other coarse materials, it has been shown in several investigations to decrease the compressive strength of concrete. In concrete with high slag content, water tends to migrate towards the surface [³³]. This causes the cement paste to become less intense due to capillaries, fine cracks, and the formation of voids, especially in the ITZs (interfacial transition zones).

Figure 6
Compressive strength values of SCC..

3.2.2. Flexural strength

When concrete samples with different proportions of iron slag as coarse aggregate were cured in water for 28 days, the results of a flexural strength test were recorded, as shown in Figure 7. Figure 7 shows improved flexural strength from incorporating iron slag in SCC (Self-Compacting Concrete). All specimens’ flexural strength values were between 3.74 and 4.81 MPa. The results indicate that SCC60 had the highest flexural strength, and Mix SCC0 had the lowest. Comparing the flexural strength of the iron slag percentages (10%, 20%, 30%, 40%, 50%, and 60%) applied as coarse aggregate to the control sample, the increases were around 6.1, 9.2, 17.6, 22.5, 27.8, and 29.2%, as well. Specimens with higher concentrations of iron slag in their coarse aggregate showed faster rates of flexural strength improvement. This is because the iron slag aggregates’ angular shape helped create a more vital link with the cement paste, which increased the bonding strength. Furthermore, the slag granules’ extreme toughness is a significant factor in increasing flexural strength. Put another way, a fracture must go through the vicinity of the tough slag grains and will take a twisting route when it does so. These phenomena bring about improvements in flexural strength and resistance to fracture propagation.

Figure 7
Flexural strength values of SCC..

3.2.3. Split tensile strength

The control mix and SCC concrete with partial replacement of iron slag with coarse aggregates show an extraordinary rise in split tensile test values, shown in Figure 8. The split tensile strength rise by 2.18, 67.14, 9.72, 12.27, 16.91, and 17.13 percent when iron slag (%) of 10%, 20%, 30%, 40%, 50%, and 60% was utilized as coarse aggregate as opposed to the control mix. This may be associated with iron slag, which, in contrast to ordinary natural sand, has a higher cohesive and mechanical biting force, high angularity, and a rough surface, its defining features. Consequently, it creates a more robust connection with cement paste, increasing bonding strength. Previous research on replacing natural aggregates with slag has reported greater split strength to slag concentration. Studies have shown that substituting slag for 60% of natural aggregates is the ideal amount to utilize. On the other hand, in contrast to the control mix design, additional research has shown that the tensile strength of concrete is improved when 100% slag is used as an aggregate.

Figure 8
Split tensile strength values of SCC..

3.2.4. Water absorption

The surface water absorption results for the iron slag sample are displayed in Figure 9. Generally speaking, all combinations, including those with iron slag aggregates, absorbed less water than the control mix. All samples at various ages had surface water absorption levels ranging from 0.09% to 2.28% overall. The mix with the least amount of surface water absorption contained 40% slag. All types of concrete, including those with 10–60% iron slag, showed a decrease in surface water absorption values of 2.21–3.72%, 4.52–34.11%, 3.89–29.32%, and 2.92–27.18%, respectively, at one hour, one day, seven days, and twenty-eight days in comparison to the control mixes. The iron slag particles’ sharp angular form and the improved hydration process brought about by the increased surplus water in the concrete filled in the gaps and interrupted the capillary channels, reducing the absorption of surface water by the concrete. If all-natural particles are replaced by slag, there is relatively little increase in the surface water absorption of the concrete [³⁴]. The surface water absorption of concrete, including 60% slag, is reduced compared to the management of samples after one hour, seven days, and twenty-eight days [³⁵].

Figure 9
Water absorption of SCC..

3.2.5. Capillary water absorption

Samples having between 0 and 60% iron slag are shown in Figure 10 at three different times: 0.5, 1, 5, and 24 hours later. Concrete with iron slag particles has less sorptivity and ability to absorb water than concrete made with natural aggregates. Up to 30% replacement at 0.5 hours has been noted in the decreasing trend of water absorption. Nevertheless, decreased water absorption was seen up to 40% replacement at 1, 5, and 24 hours. The 50 and 60 percent substitution percentages have increased somewhat; however, the specimens’ water absorption remains less than the control mix showed. The decrease in water adsorption, relative to the control specimens, is 12.56–36.68%, 6.25–38.19%, 22.01–54.11%, and 19.21–79.46%, at 0.5, 1, 5, and 24 hours of testing. When the testing period was increased from 0.5 to 24 hours, the water absorption values for the concretes containing 0, 10, 20, 30, 40, 50, and 60% iron slag dropped by 81.27, 82.56, 84.13, 85.52, 81.71, 88.23, and 79.4%, respectively. Iron slag dramatically lowers the amount of water absorbed by concrete capillaries when used as a coarse aggregate, as seen in Figure 10. It should be mentioned that slag reduces water absorption by filling the gaps and capillaries and improving the hydration process. Slag particles with sharp edges also cause capillaries to break, creating a convoluted channel that lowers water absorption. Add more cementation additives, including silica fume, to concretes with more significant slag percentages to mitigate the partial increase in water absorption. In this instance, hydration chemicals like C-S-H fill the capillary gaps in the concrete, enhancing its porous structure and dramatically slowing down the rate at which water is absorbed [³⁶].

Figure 10
Capillary water absorption of SCC..

3.2.6. Resistance to electricity

Figure 11 displays the samples’ electrical resistance containing iron slag particles. Compared to control concrete, concrete mixtures with 10, 20, and 30% slag exhibit higher electrical resistance. On the other hand, compared to control concrete, concrete mixtures containing 40–60% slag show a notable reduction in electrical resistance. Electrical resistance is most excellent in the mix containing 20% slag (48.3% greater than in the control sample). On the other hand, compared to the control sample, the electrical resistance of the concrete containing 60% slag is reduced by 65.5%. Less linked pores and a denser structure are indicated by increased electrical resistance. When the amount of water in a mix exceeds 30, the structure becomes more porous and electrical resistance decreases.

Figure 11
Electrical resistance of SCC..

3.2.7. Acid resistance

Table 7 displays weight loss and strength decrease results for concrete samples built with 0–60% iron slag. The weight loss values are 1.71%, 0.81%, 0.57%, 1.01%, 1.38%, 1.81%, and 2.27% for concrete mixes including 0, 10, 20, 30, 40, 50 and 60% iron slag. As can be seen, samples with 50% and 60% slag lose more weight than concrete without slag. The amount of surface degradation in combination with 10% and 20% slag was minimal and barely perceptible. The appearance of these samples typically showed isolated patches of corrosion. When samples were soaked in acidic environments as opposed to being cured in water, the compressive strength of the materials often decreased. At 7.09, concrete containing 60% slag has the most significant drop in strength, while at 1.15%, concrete containing 20% slag has the lowest. Note that the pH value drops, and more calcium are released when the samples are submerged in an acidic environment. This has an impact on the composition and structure of the C-S-H segments. Muscle weakness and weight loss follow when the pH level lowers, causing the C-S-H assembly to develop unevenly and with more lime release. Slag replaces natural aggregates in increasing amounts; however, the replacement results in lower strength in acidic [³⁷]. A concrete sample is displayed in Figure 12 after exposure to an acidic environment.

Table 7
Acid resistance test values of SCC concrete mix.

TYPE OF MIX	WEIGHT OF THE MIX		LOSS OF MASS
	BEFORE ACID CURING	AFTER ACID CURING
SCC 0	2271	2237	−1.71
SCC 10	2291	2271	−0.81
SCC 20	2301	2286	−0.57
SCC 30	2322	2296	−1.01
SCC 40	2341	2317	−1.38
SCC 50	2354	2335	−1.81
SCC 60	2304	2315	−2.27
TYPE OF MIX	COMPRESSIVE STRENGTH OF THE MIX		REDUCTION IN STRENGTH
	BEFORE ACID CURING	AFTER ACID CURING
SCC 0	30.18	27.92	−4.12
SCC 10	31.27	30.51	−1.48
SCC 20	34.59	34.26	−1.12
SCC 30	32.54	32.08	−2.04
SCC 40	31.58	30.55	−3.21
SCC 50	28.47	27.42	−4.51
SCC 60	27.19	26.51	−7.18

Figure 12
Sample concrete cubes after acid exposure..

3.2.8. Ultrasonic pulse velocity (UPV)

After 28 days of water curing, the ultrasonic pulse velocity (UPV) values of the concrete specimens are displayed in Figure 13. When compared to the other specimens, 20% of iron slag replaced concrete mix showed the maximum UPV values, and 60% of iron slag replaced coarse aggregate concrete showed the minimum amount of UPV values. The findings show that the mixes’ UPV values, which were 6.8% and 11.1%, respectively, were lower than those of the control samples for SCC50 and SCC60. Similar trends were found in the compressive strength values. Also, the slump flow of the concrete mix was improved by substituting additional iron slag for natural coarse aggregate. Even the iron slag aggregates used more water than was available in the concrete specimens. Several studies also reported that the iron slag aggregates consume more water from the concrete mix and reduce the strength. Put another way, samples of concrete with higher free water content have lower compressive strength and more significant porosity, which lowers the material’s internal sound wave transmission velocity [³⁸, ³⁹].

Figure 13
UPV values of SCC..

3.2.9. SEM

This work microscopically examined concrete specimens with and without iron slag using SEM pictures. Variations in the mix SCC0’s strength and durability can be attributed to voids and porous structures, as seen in Figure 14. Comparing the SCC20 design (Fig. 14) to the control sample, an incredibly homogenous and solid concrete surface is shown.” The higher hydration products, particularly C-S-H gel, block openings and obstruct capillary channel routes, are responsible for these outcomes. The quantity of voids and porosity also rises in the SCC60 design, reducing the concrete specimen’s strength and durability. Another observation in other areas is the laminar structure of hydration products, which is not anticipated to endure pressure or carry weight. These observations may have caused section 3.2.1’s results on compressive strength. According to Brand and Roesler, slag-containing concrete has lower porosity. Compared to concrete containing natural aggregates, there is a more consistent concentration of calcium hydroxide in the ITZ (Interfacial Transition zone). Concrete with more significant percentages of slag has a much higher volume of free water due to its smooth surface and poor water absorption. The construction of many fractures and capillary channels follows due to the creation of microlending conditions and an increase in how thick the ITZ is surrounding the aggregates [⁴⁰].

Figure 14
SEM images of (a) SCC 0, (b) SCC 20 and (c) SCC 60 mixes..

4. CONCLUSION

The results of samples that used iron slag in place of coarse aggregate were examined in this study. The compressive strengths of the SCC-20 and SCC-60 mixtures are the highest and lowest, respectively. After being cured in water for 28 days, the specimens’ compressive strength varies between 27.36 and 35.78 MPa. The flexural strength values of all concrete specimens ranged from 3.74 to 4.81 MPa. Flexural strength was lowest for Mix SCC0 and most excellent for SCC60. Up to 30% replenishment at 0.5 hours has been noted as a declining trend in water absorption. Nonetheless, decreased water absorption up to 40% replacement was seen at 1, 5, and 24 hours. For concrete mixtures that contain iron slag in amounts of 0%, 10%, 20%, 30%, 40%, 50%, and 60%, the weight loss values are 1.73%, 0.83%, 0.59%, 1.05%, 1.41%, 1.88%, and 2.31%, in that order. SEM pictures revealed that the mix SCC0 had gaps and porous structures, which may impact the material’s strength and durability. In contrast to the control sample, a very cohesive and homogeneous concrete surface is shown in the SCC20 design. Additionally, the SCC60 design has more voids and porosity, reducing the concrete specimen’s strength and longevity.

5. BIBLIOGRAPHY

• ^[1]
  IBRAHIM, M., RAHMAN, M.K., NAJAMUDDIN, S.K., et al, “A review on utilization of industrial by-products in the production of controlled low strength materials and factors influencing the properties”, Construction & Building Materials, v. 325, pp. 126704, 2022. doi: http://doi.org/10.1016/j.conbuildmat.2022.126704.
  » https://doi.org/10.1016/j.conbuildmat.2022.126704
• ^[2]
  SRIVASTAVA, R.R., RAJAK, D.K., ILYAS, S., et al, “Challenges, regulations, and case studies on sustainable management of industrial waste”, Minerals (Basel), v. 13, n. 1, pp. 51, 2022. doi: http://doi.org/10.3390/min13010051.
  » https://doi.org/10.3390/min13010051
• ^[3]
  OCCHICONE, A., VUKČEVIĆ, M., BOSKOVIĆ, I., et al, “Red mud-blast furnace slag-based alkali-activated materials”, Sustainability (Basel), v. 13, n. 20, pp. 11298, 2021. doi: http://doi.org/10.3390/su132011298.
  » https://doi.org/10.3390/su132011298
• ^[4]
  WEI, Z., JIA, Y., WANG, S., et al, “Utilization of iron ore tailing as an alternative mineral filler in asphalt mastic: high-temperature performance and environmental aspects”, Journal of Cleaner Production, v. 335, pp. 130318, 2022. doi: http://doi.org/10.1016/j.jclepro.2021.130318.
  » https://doi.org/10.1016/j.jclepro.2021.130318
• ^[5]
  VALIZADEH, A., ASLANI, F., ASIF, Z., et al, “Development of heavyweight self-compacting concrete and ambient-cured heavyweight geopolymer concrete using magnetite aggregates”, Materials (Basel), v. 12, n. 7, pp. 1035, 2019. doi: http://doi.org/10.3390/ma12071035. PubMed PMID: 30925817.
  » https://doi.org/10.3390/ma12071035» https://doi.org/30925817
• ^[6]
  AHMAD, J., ZHOU, Z., DEIFALLA, A.F., “Self-compacting concrete with partially substitution of waste marble: a review”, International Journal of Concrete Structures and Materials, v. 17, n. 1, pp. 25, 2023. doi: http://doi.org/10.1186/s40069-023-00585-5.
  » https://doi.org/10.1186/s40069-023-00585-5
• ^[7]
  DUTT SHARMA, R., SINGH, N., “Optimizing the compressive strength behavior of iron slag and recycled aggregate concretes”, Materials Today: Proceedings, 2023. doi: http://doi.org/10.1016/j.matpr.2023.04.093.
  » https://doi.org/10.1016/j.matpr.2023.04.093
• ^[8]
  RESHMA, T.V., KUMAR PATNAIKUNI, C., TANU, H.M., et al, “Evaluation of strength, durability, and microstructure characteristics of slag-sand-induced concrete”, Cleaner Materials, v. 10, pp. 100212, 2023. doi: http://doi.org/10.1016/j.clema.2023.100212.
  » https://doi.org/10.1016/j.clema.2023.100212
• ^[9]
  IBRAHIM, A.M., MOHAMED, A.R., EL-KHATIB, A.M., et al, “Effect of hematite and iron slag as aggregate replacement on thermal, mechanical, and gamma-radiation shielding properties of concrete”, Construction & Building Materials, v. 310, pp. 125225, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2021.125225.
  » https://doi.org/10.1016/j.conbuildmat.2021.125225
• ^[10]
  BAALAMURUGAN, J., GANESH KUMAR, V., CHANDRASEKARAN, S., et al, “Recycling of steel slag aggregates for the development of high-density concrete: alternative & environment-friendly radiation shielding composite”, Composites. Part B, Engineering, v. 216, pp. 108885, 2021. doi: http://doi.org/10.1016/j.compositesb.2021.108885.
  » https://doi.org/10.1016/j.compositesb.2021.108885
• ^[11]
  TEYMOURI, E., WONG, K.S., MOHD PAUZI, N.N., “Iron slag pervious concrete for reducing urban runoff contamination”, Journal of Building Engineering, v. 70, pp. 106221, 2023. doi: http://doi.org/10.1016/j.jobe.2023.106221.
  » https://doi.org/10.1016/j.jobe.2023.106221
• ^[12]
  JABAR, A.B., T, P., “ANN-PSO modelling for predicting buckling of self-compacting concrete column containing RHA properties”, Matéria (Rio de Janeiro), v. 28, n. 2, pp. e20230102, 2023. doi: http://doi.org/10.1590/1517-7076-rmat-2023-0102.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0102
• ^[13]
  PERIYASAMY, M., KANAGARAJ, R., “Fiber reinforced self compacting concrete workability properties prediction and optimization of mix using machine learning modeling”, Matéria (Rio de Janeiro), v. 29, n. 1, pp. e20230309, 2024. doi: http://doi.org/10.1590/1517-7076-rmat-2023-0309.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0309
• ^[14]
  SINGH, G., SIDDIQUE, R., “Effect of iron slag as partial replacement of fine aggregates on the durability characteristics of self-compacting concrete”, Construction & Building Materials, v. 128, pp. 88–95, 2016. doi: http://doi.org/10.1016/j.conbuildmat.2016.10.074.
  » https://doi.org/10.1016/j.conbuildmat.2016.10.074
• ^[15]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C150/C150M-16e1 Standard Specification for Portland Cement, West Conshohocken, PA, USA, ASTM International, 2016. doi: http://doi.org/10.1520/C0150_C0150M-16E01
  » https://doi.org/10.1520/C0150_C0150M-16E01
• ^[16]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C128-07 Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate, West Conshohocken, PA, USA, ASTM International, 2007. doi: http://doi.org/10.1520/C0128-07
  » https://doi.org/10.1520/C0128-07
• ^[17]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C29/C29M-09 Standard test method for bulk density (“Unit Weight”) and voids in aggregate, West Conshohocken, PA, USA, ASTM International, 2009. doi: http://doi.org/10.1520/C0029_C0029M-23
  » https://doi.org/10.1520/C0029_C0029M-23
• ^[18]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C127-07 Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Coarse Aggregate, West Conshohocken, PA, USA, ASTM International, 2007. doi: http://doi.org/10.1520/C0127-07
  » https://doi.org/10.1520/C0127-07
• ^[19]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, C494/C494M-05 Standard Specification for Chemical Ad- mixtures for Concrete, West Conshohocken, PA, USA, ASTM International, 2005. doi: http://doi.org/10.1520/C0494_C0494M-05
  » https://doi.org/10.1520/C0494_C0494M-05
• ^[20]
  THE EUROPEAN FEDERATION OF CONCRETE ADMIXTURE ASSOCIATIONS , European Guidelines for Self-Compacting Concrete: Specification, Production and Use: Rep. SCC 028, Surrey, UK, 2005.
• ^[21]
  BRITISH STANDARD INSTITUTION, Testing Concrete: Method for Determination of Compressive Strength of Concrete Cubes, London, UK, British Standard Institution, 1983.
• ^[22]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C496/C496M-04 Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens, West Conshohocken, PA, USA, ASTM International, 2004. doi: http://doi.org/10.1520/C0496_C0496M-04.
  » https://doi.org/10.1520/C0496_C0496M-04
• ^[23]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C78-02 Standard Test Method for Flexural Strength of Concrete (Using Simple - Beam with Third -Point Loading), West Conshohocken, PA, USA, ASTM International, 2004. doi: http://doi.org/10.1520/C0078-02.
  » https://doi.org/10.1520/C0078-02
• ^[24]
  BRITISH STANDARD INSTITUTION, Method for determination of water absorption, London, UK, British Standard Institution, 1983.
• ^[25]
  AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C597-09 Standard test method for pulse velocity through concrete”, West Conshohocken, PA, USA, ASTM International, 2009. doi: http://doi.org/10.1520/C0597-09
  » https://doi.org/10.1520/C0597-09
• ^[26]
  HE, X., ZENG, X., DONG, R., et al, “Analysis of the effect of capillary water absorption on the resistivity of cementitious materials”, Applied Sciences (Basel, Switzerland), v. 13, n. 6, pp. 3562, 2023. doi: http://doi.org/10.3390/app13063562.
  » https://doi.org/10.3390/app13063562
• ^[27]
  DONG, L.I., SHI, L.I.U., HAIQING, L.I.U., “Effect of capillary water absorption on electrical resistivity of concrete with coal gangue ceramsite as coarse aggregates”, Advances in Civil Engineering, v. 2021, n. 1, pp. 6623808, 2021. doi: http://doi.org/10.1155/2021/6623808.
  » https://doi.org/10.1155/2021/6623808
• ^[28]
  THE EUROPEAN FEDERATION OF CONCRETE ADMIXTURE ASSOCIATIONS, Specification and Guidelines for Self-Compacting Concrete, Surrey, UK, 2002.
• ^[29]
  WEI, Z., JIA, Y., WANG, S., et al, “Influence of iron tailing filler on rheological behavior of asphalt mastic”, Construction & Building Materials, v. 3v, n. 52, pp. 129047, 2022. doi: http://doi.org/10.1016/j.conbuildmat.2022.129047.
  » https://doi.org/10.1016/j.conbuildmat.2022.129047
• ^[30]
  PRITHIVIRAJ, C., SWAMINATHAN, P., KUMAR, D.R., et al, “Fresh and hardened properties of self-compacting concrete comprising a copper slag”, Buildings, v. 12, n. 7, pp. 965, 2022. doi: http://doi.org/10.3390/buildings12070965.
  » https://doi.org/10.3390/buildings12070965
• ^[31]
  REN, Z., LI, D., “Application of steel slag as an aggregate in concrete production: a Review”, Materials (Basel), v. 16, n. 17, pp. 5841, 2023. doi: http://doi.org/10.3390/ma16175841. PubMed PMID: 37687534.
  » https://doi.org/10.3390/ma16175841» https://doi.org/37687534
• ^[32]
  ABDALLA, T.A., ALAHMARI, T.S., “Mechanical strength and microstructure properties of concrete incorporating copper slag as fine aggregate: a state-of-the-art review”, Advances in Civil Engineering, v. 2024, n. 1, pp. 4389616, 2024. doi: http://doi.org/10.1155/2024/4389616.
  » https://doi.org/10.1155/2024/4389616
• ^[33]
  ZAGO, S.C., VERNILLI, F., CASCUDO, O., “The reuse of basic oxygen furnace slag as concrete aggregate to achieve sustainable development: characteristics and limitations”, Buildings, v. 13, n. 5, pp. 1193, 2023. doi: http://doi.org/10.3390/buildings13051193.
  » https://doi.org/10.3390/buildings13051193
• ^[34]
  MORS, R., JONKERS, H., “Effect on concrete surface water absorption upon addition of lactate derived agent”, Coatings, v. 7, n. 51, pp. 51, 2017. doi: http://doi.org/10.3390/coatings7040051.
  » https://doi.org/10.3390/coatings7040051
• ^[35]
  ZAMORA-CASTRO, S.A., SALGADO-ESTRADA, R., SANDOVAL-HERAZO, L.C., et al, “Sustainable development of concrete through aggregates, and innovative materials: a review”, Applied Sciences (Basel, Switzerland), v. 11, n. 2, pp. 629, 2021. doi: http://doi.org/10.3390/app11020629.
  » https://doi.org/10.3390/app11020629
• ^[36]
  KUMAR, A., SINGH, N., “Mechanical performance of steel and iron slag concretes: a brief review”, Materials Today: Proceedings, v. 93, n. 3, pp. 62–70, 2023. doi: http://doi.org/10.1016/j.matpr.2023.06.463.
  » https://doi.org/10.1016/j.matpr.2023.06.463
• ^[37]
  PIEMONTI, A., CONFORTI, A., COMINOLI, L., et al, “Use of iron and steel slags in concrete: state of the art and future perspectives”, Sustainability (Basel), v. 13, n. 2, pp. 556, 2021. doi: http://doi.org/10.3390/su13020556.
  » https://doi.org/10.3390/su13020556
• ^[38]
  PERUMAL, P., GOURIOU, C., ADESANYA, E., et al, “Sustainable application of industrial side streams as alternative fine aggregates for cement mortar”, Innovative Infrastructure Solutions, v. 9, n. 29, pp. 29, 2024. doi: http://doi.org/10.1007/s41062-023-01334-z.
  » https://doi.org/10.1007/s41062-023-01334-z
• ^[39]
  JIN, Q., CHEN, L., “A review of the influence of copper slag on the properties of cement-based materials”, Materials (Basel), v. 15, n. 23, pp. 8594, 2022. doi: http://doi.org/10.3390/ma15238594. PubMed PMID: 36500090.
  » https://doi.org/10.3390/ma15238594» https://doi.org/36500090
• ^[40]
  FAN, D., ZHANG, C., XIN LU, J., et al, “Recycling of steel slag powder in green ultra-high strength concrete (UHSC) mortar at various curing conditions”, Journal of Building Engineering, v. 70, pp. 106361, 2023. doi: http://doi.org/10.1016/j.jobe.2023.106361.
  » https://doi.org/10.1016/j.jobe.2023.106361

Publication Dates

• Publication in this collection
  21 Oct 2024
• Date of issue
  2024

History

• Received
  03 July 2024
• Accepted
  21 Aug 2024