3
 Open Access. © 2020 Gostečnik M., Šinik P., Mladenovič A., Ščančar J., Milačič R., published by Sciendo. 
  This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. 
Received: Mar 11, 2020
Accepted: Mar 13, 2020
 DOI: 10.2478/rmzmag-2020-0002 
Original scientific paper 
Abstract
During carbon steel manufacturing, large amounts of 
electric arc furnace (EAF) slag are generated. EAF slag, 
if properly treated and processed into aggregate, is an 
alternative source of high-quality material, which can 
substitute the use of natural aggregates in most de-
manding applications in the construction sector , mostly 
for wearing asphalt courses. In this screening process 
of high-quality aggregates, a side material with grain 
size 0/32 mm is also produced, which can be used as an 
aggregate for unbound layers in road construction. In 
this study, the environmental impacts of slag aggregate 
(fraction 0/32 mm) were evaluated in mixed natural/
slag aggregates. Different mixtures of natural/slag ag-
gregates were prepared from aged (28 days) and fresh 
slag, and their environmental impacts were evaluated 
using leaching tests. It was shown that among the el-
ements, chromium (Cr) was leached from some mixed 
aggregates in quantities that exceeded the criterion for 
inert waste. The data from the present investigation 
revealed that mixed aggregates, prepared from aged 
slag (fraction 0/32 mm) and natural stone in the ratio 
10/90, are environmentally acceptable and can be safe-
ly used in unbound materials for road construction.
Keywords: electric arc furnace slag, natural aggrega-
te, mixed aggregates, environmental impacts, unbound 
materials for road construction.
Environmental Impacts of Mixed Aggregates 
for use in Unbound Layers in Road Construction
Okoljski vplivi mešanih agregatov za uporabo v nevezanih 
materialih v cestogradnji
Metka Gostečnik
1,2
, Predrag Šinik
1
, Ana Mladenovič
3
, Janez Ščančar
2,4
, Radmila Milačič
2,4,*
1
 Ekomineral d.o.o., Savinjska cesta 25, 3310 Žalec, Slovenia
2
 Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
3
 Department of Materials, Slovenian National Building and Civil Engineering Institute, Dimičeva 12, 1000 Ljubljana, Slovenia
4
 Department of Environmental Sciences, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
* radmila.milacic@ijs.si
Povzetek
Med proizvodnjo ogljičnega jekla v elektroobločnih pe-
čeh nastajajo velike količine žlindre. Pravilno obdelana 
in predelana žlindra je odličen material, ki lahko uspe-
šno nadomesti naravne agregate. Pred uporabo se žlin-
dra stara, drobi in separira v agregate različnih frakcij, 
ki se uporabljajo v gradbeništvu, predvsem kot visoko-
kakovosten agregat v obrabnih asfaltnih plasteh. Med 
separiranjem nastaja tudi agregat zrnavosti 0/32 mm, 
ki ni primeren za uporabo v asfaltnih plasteh, temveč 
se uporablja za nevezane nosilne plasti v cestogradnji. 
V našem delu smo preučili okoljske vplive mešanega 
agregata (frakcija 0/32 mm) žlindre in naravnega agre-
gata za njegovo uporabo v nevezanih materialih v ce-
stogradnji. Pripravili smo različne mešanice iz naravne-
ga agregata in agregata iz žlindre. Uporabili smo svežo 
in starano (28 dni) žlindro ter ocenili okoljske vplive 
pripravljenih mešanic z izlužitvenimi testi. Rezultati 
naše raziskave so pokazali, da se iz nekaterih pripra-
vljenih mešanic lahko izlužuje element krom (Cr) v ko-
ličinah, ki presegajo mejno vrednost za inertne odpad-
ke. Kot nevezane materiale v cestogradnji varno lahko 
uporabimo agregate, ki smo jih pripravili iz agregata iz 
starane žlindre (frakcija 0–32 mm) in naravnega agre-
gata v razmerju med 10/90.
Ključne besede: žlindra iz elektroobločne peči, narav-
ni agregat, mešani agregati, okoljski vplivi, nevezani 
materiali v cestogradnji.

Gostečnik M., Šinik P ., Mladenovič A., Ščančar J., Milačič R. RMZ – M&G | 2020 | Vol. 67 | pp. 003–012
4
Introduction
Industrial wastes or by-products are increas-
ingly being used as alternative materials that 
successfully substitute natural raw materials. 
Recycling and use of these materials lead to 
the preservation of natural resources, signif-
icant reduction of landfill load and protection 
of the environment [1]. Recycling of waste 
materials is in line with the main objectives 
of green building, i.e. application of processes 
that are environmentally responsible and re-
source efficient. The latter goals are strongly 
supported by the Directive 2018/851/ES on 
waste [2] and Construction Products Regula-
tion No. 305/2011 [3]. During steel manufac-
ture, huge amounts of waste materials, such 
as electric arc furnace (EAF) slag, ladle slag 
and EAF filter dust, are produced. In the Štore 
Steel plant, Slovenia, the annual steel produc-
tion is about 150,000 tonnes. Approximately 
20,000 tons of EAF slag, 2,000 tons of ladle slag 
and 2,500 tons of EAF dust are generated as 
waste per year [4].
During the production of steel in an EAF, scrap 
metal or metallised ore, or both, are melted 
along with lime in refractory lined vessels. 
Throughout the melting process, oxygen is in-
jected into the molten steel, which oxidises 
a part of metallic Fe and alloying components 
(e.g. Mn, Ni, Cr, Mo, V), as well as the impuri-
ties in steel scrap (e.g. Al, Si, Mn, P and C). 
The EAF steel slag is poured from the furnace in 
a molten state at the end of the process. About 
15–20% of EAF slag occurs per equivalent unit 
of steel. The principal components of EAF steel 
slag are calcium silicates and ferrites, together 
with oxides and compounds of iron, magne-
sium, manganese and alumina, which together 
make up 95% of the slag [5]. The main minerals 
in slag are wustite, dicalcium silicate, tricalcium 
silicate and brownmillerite; and the accessory 
minerals can be spinel, barite, CaO and MgO. 
Both of the latter components are unstable. In 
the presence of moisture, they transform into 
Mg(OH)
2
 and/or Ca(OH)
2
, which occupy a larg-
er volume than the primary components. The 
result is swelling of the composite into which 
the slag has been placed. The slag must there-
fore be “aged” long enough for the CaO and MgO 
to be transformed into stable forms. Slow, con-
trolled cooling also enables this material to de-
velop a microtexture, which ensures long-term 
toughness and roughness and is comparable 
with the porphyric texture of volcanic rocks.
EAF slag is highly durable and is, in terms of 
its physico-mechanical characteristics, compa-
rable to high-quality natural rocks. Due to its 
excellent physical and mechanical properties, it 
can be used as an alternative material that suc-
cessfully replaces natural aggregates. Hence, the 
greatest potential for recycling and use of steel 
slag is in the construction sector [6–9]. EAF slag 
aggregate is used in different types of concrete 
[9–13], in sub-base layer constructions [14, 15], 
and especially in asphalt mixes [6, 7, 16–18]. 
Other EAF slag applications include water and 
wastewater treatment [9], as well as usage in 
synthesis of alkali-activated materials [19].
The use of materials that contain industrial 
waste and/or by-products is possible when 
such materials possess appropriate technical 
characteristics [15, 20–23] and are environ-
mentally acceptable [20–24]. For evaluation 
of the environmental impacts of raw materi-
als and final products, the extent of leaching of 
contaminants is estimated by applying different 
leaching tests, e.g. the European test method for 
leaching of aggregates (Slovenian Institute for 
Standardisation [SIST] EN 1744-3) [25] and 
the compliance test for the leaching of granular 
waste materials and sludges (SIST EN 12457-4) 
[26]. In these leaching tests, shaking of the solid 
material with water (a liquid-to-solid ratio of 
10 L/kg) is performed over 24 h.
The EAF slag, which is generated during the met-
allurgical process of carbon steel production in 
Štore Steel (waste classification no.: 10 02 02), 
is first subjected to stabilisation by ageing. For 
this purpose, a process of slow cooling, wet-
ting with water and temporary storage for a 
period of 28 days (ageing) is carried out. Be-
fore final crushing and screening of the aggre-
gate, iron is extracted by magnetic separation. 
The 32/300 mm fraction is mostly used for un-
bound layers, the 32/63 mm fraction particles 
for railway ballast and the 2/4 mm, 4/8 mm 
and 8/11 mm fractions for asphalt mixes. 
During these screenings, an additional fraction 
(0/32 mm) is also formed, which is the mate-
rial for unbound layers in road construction. 
Therefore, the aim of the present study was to 

Environmental Impacts of Mixed Aggregates for use in Unbound Layers in Road Construction
5
evaluate the potential use of the mixed aggre-
gate (0/32 mm) from the EAF slag aggregate 
and natural aggregate as the unbound material 
for road construction from the environmental 
point of view. Different mixed aggregates were 
prepared and their environmental impacts 
were estimated by applying leaching tests.
Materials and Methods
Reagents
Merck (Darmstadt, Germany) suprapur acids 
and Milli-Q water (Direct-Q 5 Ultrapure wa-
ter system; Millipore, Watertown, MA, USA) 
were used for the preparation of samples and 
standard solutions. Certipur inductively cou-
pled plasma spectroscopy (ICP) multi-ele-
ment standard solution IV (1,000 ± 5 mg/L in 
5% HNO
3
) and single stock standard solution 
of Hg (1,000 ± 5 mg/L in 5% HCl), both pur-
chased from Merck, were used for the prepa-
ration of calibration curves in ICP–mass spec-
troscopy (MS) determinations. To control the 
stability of ICP–MS, Merck Ge, Rh, Sc and In 
(1,000 ± 2 mg/L in 5% HNO
3
) were used as in-
ternal standards. The reagents for spectropho-
tometry were obtained from Hach Lange GmbH 
(Düsseldorf, Germany). Cellulose nitrate mem-
brane filters (0.45 mm; Sartorius, Gottingen, 
Germany) were used for filtration. The certified 
reference material CRM 320R (trace elements 
in river sediment; Community Bureau of Ref-
erence, Geel, Belgium), the standard reference 
material SPS-SW1 (reference material for mea-
surement of elements in surface waters; ob-
tained from Spectrapure Standards, Oslo, Nor-
way) and reference material Anions – Whole 
Volume (purchased from Merck) were used to 
check the accuracy of the analytical procedures.
Apparatus
The concentrations of elements in the leach-
ates of natural aggregate, EAF slag aggregate 
and mixed aggregates were determined by 
ICP–MS on an Agilent 7700´ spectrometer (Ag-
ilent Technologies, Tokyo, Japan). The ICP–MS 
operating parameters are presented in Table 1.
Table 1. ICP–MS operating parameters for determination of element concentrations
Parameter Type/value Helium mode No gas mode
Sample introduction
Nebuliser Mira Mist
Spray chamber Scott
Skimmer and sampler Ni
Plasma conditions
Forward power 1,550 W
Plasma gas flow 15.0 L/min
Carrier gas flow 1.05 L/min 0.75 L/min
Dilution gas flow 0.10 L/min 0.45 L/min
He gas flow 4.5 mL/min
Quadrupole (QP) bias –15 V –3.6 V
Octapole (Oct) bias –18 V –8.0 V
Cell entrance –40 V –40 V
Cell exit –60 V –50 V
Deflect –2.2 V 13.4 V
Plate bias –60 V –40 V
Sample uptake rate 0.3 mL/min
Data acquisition 
parameters
Isotopes monitored 
52
Cr, 
60
Ni, 
63
Cu, 
66
Zn, 
75
As, 
78
Se,
 95
Mo
111
Cd, 
121
Sb, 
137
Ba,
201
Hg,
 208
Pb
Isotopes of internal 
standards
45
Sc, 
72
Ge,
 103
Rh, 
115
In
45
Sc, 
72
Ge,
 103
Rh, 
115
In

Gostečnik M., Šinik P ., Mladenovič A., Ščančar J., Milačič R. RMZ – M&G | 2020 | Vol. 67 | pp. 003–012
6
The contents of chlorides, sulphates and fluo-
rides were determined on the DR 3900 portable 
spectrophotometer (Hach, Manchester, Great 
Britain). The MARS 6 Microwave System (CEM 
Corporation; Matthews, NC, USA) was used for 
digestion of the slag samples. The WTW 330 pH 
meter (WTW, Weilheim, Germany) was used to 
determine the pH. The Mettler AE 163 (Mettler 
Toledo, Zürich, Switzerland) analytical balance 
was used for weighing.
Samples
The EAF slag samples from different batches 
were obtained from Štore Steel Company, Štore, 
Slovenia. After ageing of the slag and produc-
tion of aggregate fractions, the 0/32 mm frac-
tions from fresh and aged slags (time of ageing: 
28 days) were used in the present study. Nat-
ural aggregate (dolomite) was obtained from 
Andraž Quarry, Slovenia. Mixed aggregates of 
different natural-to-slag ratios were prepared 
from fresh and aged slags.
Sample preparation
To determine the total content of elements in 
the slag and aggregate samples, about 0.25 g of 
sample was subjected to microwave-assisted 
digestion, using a mixture of nitric, hydrochlo-
ric and hydrofluoric acids [27], and the concen-
trations of the elements in the digested samples 
were determined by ICP-MS.
The extent of leaching of selected elements and 
anions from bulk natural aggregates, bulk slag 
aggregates and bulk mixed aggregates of dif-
ferent ratios was evaluated by the preparation 
of aqueous leachates (a liquid-to-solid ratio of 
10 L/kg), following the SIST EN 1744-3 [25] 
test method for leaching of aggregates and the 
SIST EN 12457-4 [26] compliance test for the 
leaching of granular waste materials and slud-
ges. The concentrations of elements and anions 
in the aqueous leachates were determined by 
ICP-MS and spectrophotometry, respectively. 
The results are presented on a dry mass basis.
Results and Discussion
Quality control of the analytical data
The accuracy of determination of the total met-
al concentrations in the EAF slag aggregate was 
checked by analysis of CRM 320R, the total met-
al concentrations in the leachates were analysed 
by the SPS-SW1 quality control method and de-
termination of anions was done by analysing 
the reference material Anions – Whole Volume. 
The results are presented in Tables 2–4.
Table 2. Concentrations of elements in certified reference 
material CRM 320R (Trace Elements in River Sediment) 
determined by ICP-MS after microwave-assisted digestion
Element
Certified  
(mg/kg)
Determined  
(mg/kg)
Fe 25,700 ± 1,300 24,350 ± 700
Mn 910 ± 50 940 ± 30
Cr 59 ± 4 61 ± 2
Note: The results represent the mean concentration from two 
parallel samples.
Table 3. Concentrations of elements in standard reference 
material SPS-SW1 (reference material for measurements of 
elements in surface waters) determined by ICP-MS
Parameter
Certified 
concentration 
(mg/L)
Determined 
concentration 
(mg/L)
As 10.0 ± 0.1 10.4 ± 0.3
Ba 50 ± 1 52 ± 1
Cd 0.50 ± 0.01 0.48 ± 0.01
Total Cr 2.00 ± 0.02 1.97 ± 0.02
Cu 20 ± 1 19.6 ± 0.3
Mo 10.0 ± 0.1 9.8 ± 0.2
Ni 10.0 ± 0.1 10.2 ± 0.3
Pb 5.0 ± 0.1 4.91 ± 0.01
Se 2.00 ± 0.02 2.03 ± 0.02
Zn 20
a
21.0 ± 0.2
a
 Informative value.
Notes: The results represent the mean concentration from two 
parallel samples.
Table 4. Concentrations of chlorides, fluorides and sulphates 
in reference material Anions – Whole Volume determined by 
spectrophotometry
Parameter
Certified 
concentration 
(mg/L)
Determined 
concentration 
(mg/L)
Chlorides
95.0 ± 9.50 92.5 ± 5.0
Fluorides
1.17 ± 0.117 1.14 ± 0.06
Sulphates
44.3 ± 4.43 42.5 ± 2.0
Note: The results represent the mean concentration from two 
parallel samples.

Environmental Impacts of Mixed Aggregates for use in Unbound Layers in Road Construction
7
Data from Tables 2–4 show good agreement be-
tween the determined and certified values (the 
agreement between the results is better than 
±5%), which confirmed the accuracy of the ap-
plied analytical procedures for the determina-
tion of (a) elements in the EAF slag aggregate 
and (b) elements and anions in aqueous leach-
ate samples.
Chemical composition of the EAF slag
The chemical composition of the EAF slag ag-
gregate may differ according to the additives 
used in steel production. The concentration 
ranges of the main components in the EAF slag 
analysed are presented in Table 5. During EAF 
slag processing, elemental oxides are formed. 
Therefore, concentrations of the measured el-
ements in Table 5 are expressed in the form 
of their corresponding oxides. Results showed 
that the content of P
2
O
5
 and V
2
O
5
 was <1%, 
while oxides of other elements (Mo, Ba, Ni and 
Zn) were found in trace amounts.
As can be seen from the data of Table 5, the 
main components in the EAF slag are oxides of 
Fe, Ca, Si and Mg, whereas oxides of Al, Mn and 
Cr in general occur in concentrations <5%.
Environmental impacts of mixed aggregates 
from natural and EAF slag aggregates
In order to evaluate the environmental impacts 
of the mixed aggregates prepared from natural 
aggregate and EAF slag aggregate, leachates 
of bulk aggregates were prepared according 
to relevant test methods (a liquid-to-solid ra-
tio of 10 L/kg) [25, 26]. First, natural aggre-
gate from the Andraž Quarry, aged EAF slag 
aggregate (0/32 mm) and mixed aggregate 
containing aged slag aggregate (natural aggre-
gate-to-EAF slag aggregate ratio 30/70) were 
examined. Concentrations of elements and an-
ions in leachates were determined by ICP-MS 
and spectrophotometry, respectively. The mea-
sured parameters were selected based on the 
legislative requirements for inert waste [28]. 
Aggregates used in the unbound materials for 
road construction and earthwork structures 
are generally compacted at optimum moisture 
content in order to ensure maximum density 
and bearing capacity of the final product. In 
order to evaluate the environmental impacts of 
such aggregates, the worst-case scenario was 
considered. Therefore, the leaching procedure 
was not performed on the compacted aggregate 
sample but rather on the bulk sample without 
any pre-treatment. The results of these exper-
iments, along with the concentration limits for 
inert waste [28], are presented in Table 6.
As evident, the leaching of elements and anions 
from natural aggregate is below the instrumen-
tal limits of detection for all measured param-
eters. Due to the presence of soluble Ca(OH)
2
, 
which is formed after reaction of CaO with 
water, the pH values of EAF slag aggregate and 
mixed natural/EAF slag aggregate are high (pH 
12.5 and 12, respectively). As a consequence of 
the high pH, most of the elements in the aque-
ous leachates are precipitated. Hence, their 
concentrations in the leachates are very low, in 
general, far below the concentration limits for 
inert waste (Table 6). Attention should be paid 
to Cr, the concentration of which exceeded the 
concentration limit of 0.5 mg/kg for inert waste 
in EAF slag aggregate and in mixed natural/
EAF slag aggregates. Cr in EAF slag aggregate 
is present in the highly insoluble chromite min-
eral in its trivalent oxidation state. However, at 
high pH, traces of trivalent Cr are solubilised as 
the Cr(OH)
4
–
 complex. Although only a negligi-
ble amount, about 0.01% of the total Cr content 
in the EAF slag aggregate is leached with water; 
the solubilised Cr(III) is, under the highly alka-
line conditions, almost completely oxidised to 
hazardous Cr(VI) by the presence of dissolved 
oxygen. As an oxyanion, chromate (CrO
4
2–
), un-
der alkaline pH values, is a highly mobile and 
Table 5. Concentration ranges of elemental oxides in EAF slag 
aggregate samples (0–32 mm) determined by ICP-MS after 
microwave-assisted digestion
Parameter Concentration (%)
FeO and Fe
2
O
3
33–46
CaO 20–35
SiO
2
10–20
MgO 3–13
Al
2
O
3 
3–6
Mn
2
O
5 
3–5
Cr
2
O
3 
1–3
Notes: Measurement uncertainty is better than ±3%. Results 
represent concentration ranges obtained from five EAF slag 
samples.

Gostečnik M., Šinik P ., Mladenovič A., Ščančar J., Milačič R. RMZ – M&G | 2020 | Vol. 67 | pp. 003–012
8
highly stable species [23]. Similarly to Cr, Mo 
also forms the oxyanion molybdate (MoO
4
2–
), 
and thus, its leaching from slag aggregates is 
favourable at high pH values. Leaching of chlo-
rides, fluorides and sulphates from mixed ag-
gregates does not represent any environmental 
burden.
In the following experiments, mixed aggregates 
from stone and cured EAF slag of the same 
batch were prepared in different stone–to-EAF 
slag ratios. Based on the data from Table 6, only 
Cr and Mo were measured in the aqueous leach-
ates (Figure 1).
It can be seen that Cr and Mo concentrations 
in the leachates decrease with higher natural 
aggregate-to-slag aggregate ratio in the mixed 
aggregate. As expected, the pH also gradual-
ly decreased from pH 12 to pH 10. At natural 
aggregate-to-slag aggregate ratio 30/70 and 
90/10, about 0.25 and 0.05 mg/kg of Mo, re-
spectively is leached from the mixed aggre-
gate. These concentrations are lower than 
the legislative requirements for inert waste 
Table 6. Concentrations of As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se and Zn in aqueous leachates (a liquid-to-solid ratio of 
10 L/kg) of bulk natural aggregate, bulk aged EAF slag aggregate (0–32 mm) and bulk mixed aggregate from the aged EAF slag 
aggregate (natural aggregate-to-slag aggregate ratio 30/70) determined by ICP-MS and the content of chlorides, fluorides and 
sulphates determined by spectrophotometry
Parameter
Natural 
aggregate
EAF slag 
aggregate 
(0–30 mm)
Mixed aggregate (natural 
aggregate-to-slag 
aggregate ratio 30/70)
Concentration 
limits for 
inert waste
*
As (mg/kg) <0.001 <0.001 <0.001 0.5
Ba (mg/kg) <0.02 14 2.2 20
Cd (mg/kg) <0.002 <0.002 <0.002 0.04
Total Cr (mg/kg) <0.002 1.4 0.95 0.5
Cu (mg/kg) <0.001 <0.001 <0.001 2
Hg (mg/kg) <0.001 <0.001 <0.001 0.01
Mo (mg/kg) <0.002 0.26 0.24 0.5
Ni (mg/kg) <0.002 <0.002 <0.002 0.4
Pb (mg/kg) <0.005 0.45 0.15 0.5
Sb (mg/kg) <0.001 0.08 0.02 0.06
Se (mg/kg) <0.003 <0.003 <0.003 0.1
Zn (mg/kg) <0.005 1.95 0.2 4
Chlorides (mg/kg) <7 <7 <7 800
Fluorides (mg/kg) <1 4.59 <1 10
Sulphates (mg/kg) <10 19.5 <10 1000
pH 8.7 12.5 12.0 /
*
Decree on waste (2015): Official Gazette of Republic Slovenia RS, No. 37/15 and No. 69/15.
Notes: The results represent the mean concentration obtained from two parallel analyses of leachate. Measurement uncertainty 
for ICP-MS is better than ±3% and, for spectrophotometry, it is ±5%.
Figure 1. Concentrations of Cr and Mo in aqueous leachates 
(a liquid-to-solid ratio of 10 L/kg) of bulk mixed aggregates 
from aged EAF slag aggregate of the same batch, applying 
different natural aggregate-to-slag aggregate ratios. Notes: 
Bars represent mean Cr and Mo concentrations determined 
by ICP-MS, while the error bars indicate the minimum and 
maximum concentrations from two parallel determinations in 
the leachate by ICP-MS.

Environmental Impacts of Mixed Aggregates for use in Unbound Layers in Road Construction
9
(0.5 mg/kg Mo) [28]. Cr concentration in the 
leachate at natural aggregate-to-slag aggre-
gate ratio 30/70 is 0.95 mg/kg and gradually 
decreases with decrease in the amount of slag 
aggregate in the mixed aggregate. A concen-
tration that is below the limit for inert waste 
(0.5 mg/kg Cr) [28] is reached at ratio 85/15.
In order to evaluate the variability of Cr leach-
ing from mixed aggregates, aged slag aggregate 
from different batches was used for the prepa-
ration of mixed aggregates, applying natural 
aggregate-to-slag aggregate ratio 90/10. These 
results are presented in Figure 2.
The pH values of the leachates in the samples 
from Figure 2 were around 10. As evident from 
the data of Figure 2, the leaching of Cr from 13 
mixed aggregates ranged from 0.1 mg/kg up 
to 0.65 mg/kg. Only two samples exceeded the 
maximal legislative value set for inert waste. 
High variability in leached Cr concentrations in 
the aggregates prepared from aged EAF slag at 
the same natural aggregate-to-slag aggregate 
ratio (90/10), with constant pH (10), but from 
different slag aggregate batches, indicates the 
high variability of Cr content in the slag aggre-
gate samples from different batches. Cr content 
in the EAF slag aggregate is related to different 
compositions of Cr in steel.
Finally, the influence of EAF slag ageing on 
leaching of Cr from mixed aggregates was esti-
mated. For this purpose, mixed aggregates from 
four different batches were prepared from fresh 
and aged EAF slag aggregates, applying natural 
aggregate-to-slag aggregate ratio 90/10. The 
results of this experiment are shown in Fig-
ure 3.
The pH of the leachates investigated was around 
10. The data in Figure 3 demonstrate that, as a 
consequence of variable Cr content in different 
slag batches, leached Cr concentrations varied 
significantly. The ageing of EAF slag, which sta-
bilises its mineralogical phases, results in low-
er leachability of Cr. Leaching of Cr from mixed 
aggregates made of aged EAF slag aggregate 
is 30–60% lower than that of aggregates pre-
pared from fresh slag aggregate from the same 
batch. It is further evident that Cr leaching 
from mixed aggregates made of aged EAF slag 
aggregate (natural aggregate-to-slag aggregate 
ratio 90/10) from different EAF slag aggregate 
batches did not exceed 0.3 mg/kg.
Conclusions
The results from the present study revealed 
that in bulk mixed aggregates (0/32 mm), 
made of dolomite natural aggregate and EAF 
slag aggregate, only Cr, among all elements and 
anions investigated, may exceed the concentra-
tion limit for inert waste (0.5 mg/kg Cr). To find 
the conditions for safe use of mixed aggregates 
from natural aggregate and EAF slag aggregate, 
leaching of Cr from samples with different nat-
ural aggregate-to-EAF slag aggregate ratios was 
studied, applying fresh and aged (28 days) EAF 
Figure 2. Concentrations of Cr in aqueous leachates (a liquid-
to-solid ratio of 10 L/kg) of bulk mixed aggregates from aged 
EAF slag of different slag batches, applying natural aggregate-
to-slag aggregate ratio 90/10. Notes: Bars represent mean Cr 
concentrations determined by ICP-MS, while the error bars 
indicate the minimum and maximum concentrations from 
two parallel determinations in the leachate by ICP-MS.
Figure 3. Concentrations of Cr in aqueous leachates (a liquid-
to-solid ratio of 10 L/kg) of bulk mixed aggregates from fresh 
and aged EAF slags of different slag batches, applying natural 
aggregate-to-slag aggregate ratio 90/10. Notes: Bars represent 
mean Cr concentrations determined by ICP-MS, while the error 
bars indicate the minimum and maximum concentrations 
from two parallel determinations in the leachate by ICP-MS.

Gostečnik M., Šinik P ., Mladenovič A., Ščančar J., Milačič R. RMZ – M&G | 2020 | Vol. 67 | pp. 003–012
10
slag aggregate from different batches. High pH 
of mixed aggregates (pH 10–12) enabled the 
leaching of Cr in the form of oxyanion chromate. 
Due to variable Cr content in the EAF slag ag-
gregate from different batches, which is related 
to the composition of steel (different amounts 
of Cr added in the process to obtain the steel 
of desired properties), the extent of Cr leach-
ing from mixed aggregates varied significantly. 
Leaching of Cr from mixed aggregates made 
from aged EAF slag aggregate was 30–60% low-
er than that from fresh EAF slag aggregate. Data 
of the present investigation demonstrated that 
mixed aggregates prepared from natural aggre-
gate and EAF slag aggregate may be safely used 
in unbound materials for road construction if 
aged slag is used for preparation of mixed ag-
gregates at natural aggregate-to-EAF slag ag-
gregate ratio 90/10. The safe reuse of EAF slag 
leads to the protection of the environment and 
preservation of natural resources.
Acknowledgements
This work was supported by the Ministry of 
Education, Science and Sport, the Republic of 
Slovenia, by co-financing the doctoral studies 
of Metka Gostečnik at the Jožef Stefan Interna-
tional Postgraduate School (contract number 
C3330-16-500190). We also acknowledge the 
financial support received from the Slovenian 
Research Agency (ARRS) (programme groups 
P2-0273 and P1-0143).
References
[1] Banaitė, D., Tamošiūnienė, R. (2016): Sustainable 
development: the circular economy indicators’ 
selection model. Journal of Security and Sustain-
ability Issues, 6(2), http://dx.doi.org/10.9770/
jssi.2016.6.2(10).
[2] Regulation (EU) No 305/2011 of the European par-
liament and of the council, of 9 March 2011, Official 
Journal of the European Union, 4.4.2011.
[3] Official Journal of the European Union. (2011). Reg-
ulation (EU) No 305/2011 of the European parlia-
ment and of the council laying down harmonised 
conditions for the marketing of construction prod-
ucts and repealing Council Directive 89/106/EEC, 
88, pp. 5–43.
[4] ARSO annual report (2019): The type and quantity 
of waste generated in manufacturing and service ac-
tivities and the ways of managing (2018), https://
www.arso.gov.si/varstvo%20okolja/odpadki/po-
ro%c4%8dila%20in%20publikacije/. Last assessed 
march 2020.
[5] Yildirim, I., Prezzi, M. (2011): Chemical, miner-
alogical, and morphological properties of steel 
slag. Advances in Civil Engineering, pp. 1–13, 
doi:10.1155/2011/463638.
[6] Milačič, R., Zuliani, T ., Oblak, T ., Mladenovič, A., 
Ščančar, J. (2011): Environmental impacts of as-
phalt mixes with electric arc furnace steel slag. 
Journal of Environmental Quality, 40, pp. 115–1161, 
doi:10.2134/jeq2010.0516.
[7] Oblak, T ., Ščančar, J., Vahčič, M., Zuliani, T ., Mlade-
novič, A., Milačič, R. (2011): Environmental impacts 
of asphalt and cement composites with addition 
of EAF dust. RMZ - Materials and Geoenvironment, 
58(2), pp. 181–192.
[8] National Slag Association, Steel slag: A premier 
construction aggregate, Assessed on March 2020, 
from http://www.acobrasil.org.br/siderurgiaemfo-
co/CCABrasil/NSA%20Steel%20Furnace%20Bro-
chure.pdf. Last assessed March 2020.
[9] Lim, J.W., Chew, L.H., Choong, T .S.Y., Tezara, C., Yazdi, 
M.H. (2016): Overview of Steel Slag Application and 
Utilization, MATEC Web of Conferences 74, 00026, 
pp. 1–5, DOI: 10.1051/matecconf/20167400026.
[10] Arribas, I., Vegas, J., San-José, J., Manso, J.M. (2014): 
Durability studies on steelmaking slag concretes. 
Materials & Design, 63, pp. 168–176, https://doi.
org/10.1016/j.matdes.2014.06.002.
[11] Arribas, I., Santamaría, A., Ruiz, E., Ortega-López, 
Manso, J.M. (2015): Electric arc furnace slag and its 
use in hydraulic concrete. Construction and Building 
Materials, 15, pp. 68–79, https://doi.org/10.1016/j.
conbuildmat.2015.05.003.
[12] Roslan, N.H., Ismail, M., Abdul-Majid, Z., Ghoreishi-
amiri, S., Muhammad, B. (2016): Performance of 
steel slag and steel sludge in concrete. Construction 
and Building Materials, 104, pp. 1–24, https://doi.
org/10.1016/j.conbuildmat.2015.12.008.
[13] Penteado, C.S.G., Evangelista, B.L., dos Santos Fer-
reira, G.C., Borges, P .H.A., Lintz, R.C.C. (2019): Use of 
electric arc furnace slag for producing concrete pav-
ing blocks. Ambiente Construído, Porto Alegre, 19(2), 
pp. 21–32, http://dx.doi.org/10.1590/s1678-
86212019000200305.

Environmental Impacts of Mixed Aggregates for use in Unbound Layers in Road Construction
11
[14] Wang, G.C. (2016): 8 - Unbound slag aggregate use 
in construction. In: The Utilization of Slag in Civil 
Infrastructure Construction, Woodhead Publishing 
Series in Civil and Structural Engineering: Number 
68, Wang, G.C. (ed.). Elsevier Ltd., SPi Global: India, 
pp. 155–184, https://doi.org/10.1016/B978-0-08-
100381-7.00008-2.
[15] Gonawala, R.J., Kumar, R., Chauhan, K.A. (2019): Us-
age of Crushed EAF Slag in Granular Sub-base Layer 
Construction. In: Proceedings of ICIIF 2018, Spring-
er Nature, Singapore, Gateway East Singapore, 
pp. 257–266.
[16] Skaf, M., Manso, J.M., Aragón, Á., Fuente-Alonso, J.A., 
Ortega-López, V. (2017): EAF slag in asphalt mixes: 
A brief review of its possible re-use. Resources, Con-
servation and Recycling, 120, pp. 176–185. http://
dx.doi.org/10.1016/j.resconrec.2016.12.009.
[17] Maharaj, C., White, D., Maharaj, R., Morin, C. (2017): 
Reuse of steel slag as an aggregate to asphaltic road 
pavement surface. Cogent Engineering, 4(1), pp. 
1–12, doi.org/10.1080/23311916.2017.1416889.
[18] Vaiana, R., Balzano, F., Iuele, T ., Gallelli, V. (2019): 
Microtexture performance of EAF slags used as ag-
gregate in asphalt mixes: A comparative study with 
surface properties of natural stones. Applied Scienc-
es, 9(15), 3197, pp. 1–14, https://doi.org/10.3390/
app9153197.
[19] Češnovar, M., Traven, K., Horvat, B., Ducman, V. 
(2019): The Potential of Ladle Slag and Electric 
Arc Furnace Slag use in Synthesizing Alkali Activat-
ed Materials; the Influence of Curing on Mechan-
ical Properties. Materials, 12(7), 1173, pp. 1–18, 
doi:10.3390/ma12071173.
[20] Vahčič, M., Milačič, R., Mladenovič, A., Murko, S., 
Zuliani, T ., Zupančič, M., Ščančar, J. (2008): Leach-
ability of Cr(VI) and other metals from asphalt 
composites with addition of filter dust. Waste Man-
agement, 28, pp. 2667–2674, doi:10.1016/j.was-
man.2008.01.003.
[21] Šturm, T ., Milačič, R., Murko, S., Vahčič, M., Mlad-
enovič, A., Strupi Šuput, J., Ščančar, J. (2009): The 
use of EAF dust in cement composites: Assess-
ment of environmental impact. Journal of Hazard-
ous Materials, 166, pp. 277–283, doi:10.1016/j.
jhazmat.2008.11.015.
[22] Zalar Serjun, V., Mladenovič, A., Mirtič, B., Meden, 
A., Ščančar, J., Milačič, R. (2015): Recycling of ladle 
slag in cement composites: environmental impacts. 
Waste Management, 43, pp. 376–385, http://dx.doi.
org/10.1016/j.wasman.2015.05.006.
[23] Milačič, R., Zuliani, T ., Oblak, T ., Mladenovič, A., 
Ščančar, J. (2011): Environmental impacts of as-
phalt mixes with electric arc furnace steel slag. 
Journal of Environmental Quality, 40, pp. 115–1161, 
doi:10.2134/jeq2010.0516.
[24] Wang, G.C. (2016): 7 - Environmental aspects of 
slag utilization. In: The Utilization of Slag in Civil 
Infrastructure Construction, Woodhead Publishing 
Series in Civil and Structural Engineering: Number 
68, Wang, G.C. (ed.). Elsevier Ltd., SPi Global: India, 
pp. 131–153, https://doi.org/10.1016/B978-0-08-
100381-7.00007-0.
[25] SIST EN 1744-3 (2002). Tests for chemical properties 
of aggregates. Part 3, Preparation of eluents by leach-
ing of aggregates.
[26] SIST EN 12457-4 (2004). Characterisation of waste – 
Leaching – Compliance test for leaching of granular 
waste materials and sludges. Part 4, One stage batch 
test at a liquid to solid ratio of 10 L/kg for materials 
with particle size below 10 mm (without or with size 
reduction).
[27] Vidmar, J., Zuliani, T ., Novak, P ., Drinčić, A., Ščančar, J., 
Milačič, R. (2017): Elements in water, suspended 
particulate matter and sediments of the Sava River. 
Journal of Soils and Sediments, 17(7), pp. 1917–1927, 
doi 10.1007/s11368-016-1512-4.
[28] Decree on waste (2015): Official Gazette of Republic 
Slovenia RS, No. 37/15 and No. 69/15.