1 Introduction

The challenges of ensuring flow of concrete in congested reinforcement, sloppy site and minimizing energy consumption in vibration, usually encountered during construction and placing of normal weight concrete, are well overcome with self-compacting concrete (SCC) technology. However, over reliance on the natural aggregate sources may affect SCC sustainability in near future. Cement concrete, a widely used construction material, requires good quality aggregates for its production in order to ensure its optimal performance. Aggregates, generally, are considered as volumetric material and occupying 65–75% of concrete volume, it plays a vital role, as it contributes more to the fresh and hardened stated properties of concrete [1,2,3,4]. However, studies [5,6,7] have reported that the increasing use of the natural aggregates could quicken the depletion of the sources. Thus, in order to preserve the natural aggregate sources, other alternative sources such as wastes are explored. Some of the wastes that have been considered over the years include those emanating from the construction and demolition activities, agricultural and industrial sectors [8,9,10,11,12].

Electric arc furnace oxidizing slag (EAFOS), one of the discarded materials from steel making plants, has been found to be useful for concrete production [13,14,15,16,17]. Apparently, the management of this waste can contribute to the effective management of the steel industry, as it can be used in ecofriendly way, owing to its physical structure. EAFOS is a recycled resource and a viable solution to the fast depletion of natural aggregates. The application of EAFOS as concrete aggregate has been considered for production of different types of concrete.

A study by Lee et al. [18] reported that normal weight concrete produced using EAFOS enhanced the ductile capacity of reinforced concrete columns. According to the authors, the slag provided a strong column development. González-Ortega et al. [19] studied the durability performance of concrete incorporating EAFOS aggregate, and it was established that EAFOS possess limited ability to enhance durability of concrete, as higher carbonation depths, water penetration and expansion were observed. Other studies [20,21,22,23] have utilized EAFOS as aggregate in concrete, with somewhat appreciate performance reported. In addition, studies have also reported about the use of different slags in self-compacting concrete (SCC). A few application involved the production of SCC using, stainless slag [24], granular steel slag [25], and granulated blast furnace slag [26,27,28,29].

Following the survey of literatures on the production and development of concrete using EAFOS, it can be seen that numerous applications of the material was more common in the aspect of normal weight concrete, than in SCC. While a number of investigations have been carried out using slags in SCC, however, not so much have been reported on the use of EAFOS for SCC production. Whereas, it is necessary to evaluate EAFOS application in SCC, because various slags certainly vary in properties according to their production condition. Therefore, in this study, the fresh properties of self-compacting concrete produced using electric arc furnace oxidizing slag as coarse aggregate is investigated. Various properties of the fresh SCC mixtures are considered for three grades of SCC, M20, M30 and M40. The study aims to provide useful data for concrete constructors in the built environment, thereby contributing to the sustainability process in the field.

2 Materials and methods

2.1 Materials

In this study, ordinary Portland cement (OPC) conforming to IS: 12269 [30] was utilised. The fineness and specific gravity of the cement was determined as 298 m2/kg and 3.14, respectively. The chemical composition of cement is shown in Table 1. Scanning electron microscopy (SEM) image and energy-dispersive X-ray spectroscopy (EDS) spectrum of cement are shown in Figs. 1 and 2, respectively. Finely ground low calcium fly ash (FA) obtained from Mettur (Tamil Nadu, India) thermal power plant was recycled as a secondary binder. The fineness and specific gravity of FA was determined as 294 m2/kg and 2.67, respectively. The chemical composition of FA is provided in Table 1. SEM image and EDS spectrum of FA are shown in Figs. 3 and 4, respectively. The obtained river sand was tested as per IS: 383 [31] and found as grade zone II. The specific gravity fineness modulus of river sand was 2.68 and 2.68, respectively. Crushed rock (granite) of 20 mm maximum size was utilized as coarse aggregate in normal strength concrete, and while 12 mm size was used for self-compacting concrete. The natural coarse aggregate (20 mm size) and crushed EAFOS (20 mm size) are presented in Figs. 5 and 6, respectively. The obtained coarse aggregate was tested as per British code [32], IS: 383 [31], IS: 2386 [33]. The relative density of the 20 mm size coarse aggregate is 2.75 and its fineness modulus is 7.08. The EAFOS used in the present investigation was obtained from Salem Steel Plant (SSP), India. The EAFOS was not used as concrete ingredient in its raw form, as it is known to swear overtime because it contains unrestricted calcium oxide (CaO) and silica (SiO2) contents [34]. The presence of the oxides causes the concrete to expand [35]. Thus, following the approach reported in a study [36], the slag was exposed to outdoor atmosphere for 24 months so as to reduce the concentration of CaO and SiO2 considerably. The aggregate crushing values for granite and EAFOS were 20 and 26, respectively. The surface of the slag is rough and hard (Fig. 6), which could largely contribute to the compactness of aggregate—paste interphase. Slag size less than 20 mm was selected in normal strength, and while 12 mm was used for self-compacting concrete. The specific gravity and water absorption values of EAFOS were 3.67 and 2.07%, respectively. The chemical properties of EAFOS is presented in Table 2. The particle size distribution curves of coarse aggregate used for normal weight concrete and EAFOS can be seen in Fig. 7.

Table 1 Cement and FA—chemical composition
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Fig. 1
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SEM image of cement particle

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Fig. 2
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EDS spectrum for cement particle

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Fig. 3
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SEM image of FA particle

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Fig. 4
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EDS spectrum for FA particle

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Fig. 5
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Coarse aggregate 20 mm size

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Fig. 6
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Crushed 20 mm EAFOS

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Table 2 EAFOS—chemical compositions
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Fig. 7
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Particle size distribution curves of coarse aggregate and EAFOS

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2.2 Experimental procedure

The study explored the fresh properties of SCC using slump-flow, time of spread of concrete to 500 mm diameter (T500), L-box, U-box test and V-funnel tests, following th procedures described in specification and guidelines for selfcompating concrete (EFNARC) [37].

Two series of concrete mixtures were considered. In Series-I, four mix combinations were considered, mix A consists of conventional concrete called normal concrete and mix B consists of 30% fly ash for making binary blended normal concrete with conventional granite aggregate. The concrete mixture proportions of control concrete were obtained as per the guidelines of BIS code IS: 10262 [38]. The mixture C and mixture D consist of 50% and 100% EAFOS aggregate, respectively in the binary blended concrete. The summery of concrete mix proportion for ordinary concrete prepared in this investigation is presented in Table 3. In series-II, the suitability of EAFOS in SCC was evaluated by comparing the results with ordinary concrete and SCC made with conventional granite aggregate. The aggregate and superplasticizer (polycarboxylate based) contents were slightly adjusted in order to maintain the required workability of the concrete. After several trials, the final mix proportion for SCC investigated in this study was developed as shown in Table 4.

Table 3 Mix proportioning of ordinary concrete
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Table 4 Mix proportioning of SCC
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3 Results and discussion

3.1 Effect of slag on slump value of normal concrete

The slump value for normal weight concrete is shown in Fig. 8. It was shown that the addition of FA caused marginal increase in slump value. However, there was insignificant reduction of slump value of concrete specimens with 50% and 100% EAFOS, which may be attributed to the rough textural characteristics of EAFOS. Also, wide surface area of the aggregate contributed to the workability. Generally, the required slump value (75–100 mm), according to British standard [39] and IS code [40], of all the mixtures was obtained by slightly modifying the superplastizer dosage level (Fig. 9).

Fig. 8
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Slump value of ordinary concrete

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Fig. 9
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V-funnel flow time (s)

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3.2 Effects of EAFOS on fresh SCC

3.2.1 Slump flow test

One of the important specification for SCC is its homogeneity and ability to flow under own weight, which is measured using flow test. In order to examine the flow of SCC with time after mixing, the flow value was determined after 30 min of mixing. Table 5 presents the results of slump flow. For the three grades of concretes produced M20, M30 and M40, the flow values of the mixtures fell with specified limits of 650–800 mm [37]. The same was the case, for slump flow measured at 0 min and that of 30 min. A significant drop in slump flow occurred as EAFOS content increased from 50 to 100%, which is attributable to the rough textural appearances of EAFOS.

Table 5 Slump-flow and T500 results of SCC
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The result of T500 are is also presented in Table 5. The T500 values for the concrete mixtures considered in the investigation satisfied the standard requirement for SCC [37].

3.2.2 V-funnel test

The flow time of the SCC mixtures through a V-funnel apparatus was calculated, so as to measure the passing ability of the mixture. The standard range of the V-funnel time is between 11 and 15 s [37]. The addition of EAFOS instead of natural aggregate caused reduction in the flow time of M20 grade SCC. A similar trend of reduction in flow time was observed in M30 and M40 grade SCC as well. Though there was reduction in flow time, overall, the mixtures satisfied the standard limits. From this results, it can be stated that the EAFOS is suitable for preparing SCC. A comparison between the T500 and V-flow time of the designated mixtures is presented graphically in Fig. 10. Thus, both the T500 and V-flow time were within the required limits, which suggests that the viscosity and segregation resistance of the mixtures is satisfactory.

Fig. 10
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V-funnel time versus T500

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3.2.3 U-box test

The U-box test was conducted according to EFNARC criteria [37], which requires that the difference of levels in two chambers (∆h) should be smaller than 30 mm. The average U-box result of M20 grade SCC without EAFOS was observed as 12 mm. The values of height difference (∆h) of the SCC were 15 mm and 17 mm for 50% and 100% EAFOS in M20 grade SCC, respectively. There was increase in the difference of levels (∆h) between the two chamber in an insignificant manner, especially where EAFOS was used instead of natural aggregate in the M20 grade SCC. A similar trend of reduction was found in U-box data for M30 and M40 grade of SCC. The decreased U-box results with EAFOS aggregate could be attributed to the surface properties of EAFOS. The relationship between V-flow time and difference in levels of U-box (∆h) for all the designated mixtures is shown in Fig. 11. The results of V-flow time and ∆h are within the target limit of 11 ≤ Tv ≤ 15 s and 0 ≤ ∆h ≤ 30 mm (26) which established that mixtures have acceptable filling ability. From the observations, it is evidence that the EAFOS can be suitable for preparing SCC.

Fig. 11
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Comparison between V-funnel flow and ∆h of U-box

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3.2.4 L-box test

The passing capacity of SCC between re-bars was examined using L-box, which is also known as blocking ratio. The L-box for the mixtures is shown in Fig. 12. The dashed line denotes the boundary of blocking ratio (H2/H1) and should be more than 0.8 [37]. The average ratio (H2/H1) of M20 grade SCC (BS20) without EAFOS was identified as 0.95. The values of blocking ratio of the SCC were 0.93 and 0.92 for 50% and 100% EAFOS based M20 grade SCC, respectively. A decrease in blocking ratio of concrete occurred when EAFOS was added to SCC in place of natural aggregate in M20 grade SCC. The same was also the case in L-box test result observed in M30 and M40 grade SCC. However, the L-box test results of all the designated SCC specimens considered in this investigation with EAFOS were within the self-flow zone as shown in Fig. 12, thus, it is evidence that the EAFOS can be suitable for preparing SCC.

Fig. 12
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Blocking ratio of SCC and EAFOS substitution level (%)

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4 Conclusions

In this study, the fresh properties of self-compacting concrete incorporating electric arc furnace oxidizing slag (EAFOS) as coarse aggregate was determined. The following conclusions were drawn from the study:

In the normal weight concrete, significant reduction in slump value occurred, which is attributable to the rough textural characteristics of the aggregate, which increased the total surface area of the aggregate. Slump value after 30 min was found to reduce from 15 to 20%, which was an indication that the workability of normal concrete was not affected by addition of EAFOS aggregate.

Also, the addition of EAFOS as partial replacement of natural aggregate caused decrease in slump flow value of the SCC. However, the flow values of EAFOS SCC mixture was between the limit (650–800 mm). The results of T500 of all the concrete mixtures considered in this investigation satisfied the requirements for SCC. The use of EAFOS as partial replacement of natural aggregate caused a reduction in the V-flow of SCC, but overall, the values were within the acceptable limits between of 11–15 s. Hence, this study shows that EAFOS can be suitable for production of SCC. The U-box results was smaller than the self flow zone value of 30 mm. A decrease in the blocking ratio of concrete was observed when EAFOS was utilized as a replacement of natural aggregate in SCC. Generally, this study has established the suitability of EAFOS for SCC mixtures based on fresh state properties, however, in the next phase of this research, both the mechanical properties in terms and strength thermal behavior, and durability properties in terms resistance to acid, chloride ingress and corrosion of steel will be reported.