Construction and Building Materials 350 (2022) 128928

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Construction and Building Materials

journal homepage: www.elsevier.com/locate/conbuildmat

Performance of limestone-calcined clay cement mortar incorporating high

volume ferrochrome waste slag aggregate
H. Shoukry a, *, Priyadharshini Perumal b, Aref Abadel c, Hussam Alghamdi c,
Mohammed Alamri c, Hamdy A. Abdel-Gawwad d
a
Building Physics Institute (BPI), Housing and Building National Research Center (HBRC), 87 El-Tahrir St., Dokki, P.O. Box 1770, Cairo, Egypt
b
Fibre and Particle Engineering Research Unit, Faculty of Technology, Oulu, Finland
c
Department of Civil Engineering, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia
d
Raw Building Materials and Processing Technology Research Institute, Housing and Building National Research Center (HBRC), 87 El-Tahrir St., Dokki, P.O. Box 1770,
Cairo, Egypt

A R T I C L E I N F O A B S T R A C T

Keywords: This study set out to investigate the mechanical performance and physical properties of Limestone Calcined Clay
Limestone calcined clay cement Cement (LC3) – based mortar incorporating high dosage of ferrochrome (FeCr) slag aggregates. Green, sus­
Ferrochrome slag tainable and economical alternative binder has been prepared by replacing 60 wt% of the Ordinary Portland
Compressive strength
Cement (OPC) by a blend of limestone (LS) powder and metakaolin (MK) with LS: MK of 1:2 (wt%). The mortar
Tensile strength
Leaching
specimens were produced with FeCr slag aggregate as a substitute for natural sand with different replacement
Microstructure ratios ranging from 25 % to 100 % with a stride of 25 wt%. The mini-slump flow test was conducted to assess the
mortars behavior in the fresh state. Compressive and tensile strengths, capillary water absorption, leaching
behavior and microstructure were investigated for the hardened mortars at 28 days of hydration. With the in­
crease of FeCr replacement ratio, the water-binder ratio (w/b), compressive strength and tensile strength
increased. OPC and LC3 mortars incorporating 100 % FeCr attained enhancements by about 71 and 63 % for
compressive strength and 22 and 17 % for tensile strength respectively. The total replacement of sand with FeCr
aggregate has decreased the water absorption of LC3 mortars by 11 %. The chromium and heavy metals leaching
from LC3 mortar made with 100 % FeCr slag showed very low levels as a result of the improved microstructure in
terms of compactness and interfacial transition zone (ITZ) tightness. Recycling of FeCr waste with utilization of
green alternative binder in the production of mortar with improved mechanical performance is helpful in
reducing the carbon footprint in the construction industry.

sustainability goals and further steps should be taken to compensate

both the issues of natural resource management and waste valorisation.
1. Introduction One potential opportunity in this context is using industrial side streams
as secondary raw materials for construction materials to save the natural
Concrete is the most used construction material which is mainly resources and mitigate the environmental impact due to landfilling of
produced with the raw materials sourced from natural resources such as side streams. There are several research works trying to establish these
river sand, mountains, minerals reserves, and so on [1,2]. With the benefits in different applications. Among which, application as aggre­
growing infrastructure needs and urbanization around the world, gate in construction industry drawn attention in recent years [11–13].
depletion of natural reserves is accelerated for the need of raw materials. Main reason is the potential for high-volume consumption as large
On the other hand, industrialization also means the subsequent pro­ amount of aggregate are used in civil engineering applications every
duction and piling up of high volume of industrial side stream materials year [14]. Aggregate occupies 60 % – 75 % of the total volume of con­
which creates pressure to the society and environment [3]. Even, de­ crete. About 32 billion tons of concrete are produced annually, and the
molition of existing concrete structure, construction and mining activ­ number is expected to rise [15].
ities adds to the generation of such side streams [4–10]. In the current By-products or waste side streams such as slags [16,17], glass
situation, this needs high priority attention aligning to the UN

* Corresponding author.
E-mail address: hamadashoukry@yahoo.com (H. Shoukry).

https://doi.org/10.1016/j.conbuildmat.2022.128928
Received 26 June 2022; Received in revised form 24 July 2022; Accepted 17 August 2022
Available online 29 August 2022
0950-0618/© 2022 Elsevier Ltd. All rights reserved.
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

detected in FeCr in their oxide forms, such as, Cr2O3, Mn2O3, TiO2, and
Nomenclature SrO [38,41]. However, considering the application as aggregate, the
alternative side stream material should satisfy certain physical and
LC3 Limestone Calcined Clay Cement mechanical criteria, such as shape, density, size and water absorption.
OPC Ordinary Portland Cement FeCr shows higher density and specific gravity compared to the con­
LS Limestone ventional aggregates due to the presence of the metallic elements
MK Metakaolin [34,42,43]. Nevertheless, meets the general requirement to be used as
FeCr Ferrochrome fine aggregate in concrete, in spite of limited data available in this
ITZ Interfacial transition zone category [34].
USEPA United states environmental protection agency Use of FeCr in pavements is well explored in asphalt and concrete
w/b Water-binder ratio mixes and found to be beneficial due to its high strength and abrasion
DTA Differential thermal analysis resistance [41,44]. Workability was a concern with the use of FeCr as
SCM Supplementary cementitious material concrete aggregate owing to the rough surface and higher water ab­
XRD X-ray diffraction sorption due to its porous nature [42]. However, strength reports were
CH Calcium Hydroxide contradicting with some showing positive effect up to 40 % replacement
CSH Calcium silicate hydrate level and few other studies indicates a strength decline with increasing
CAH Calcium aluminate hydrate replacement percentages [38,42]. Variation in particle size distribution
CASH calcium aluminate silicate hydrate was expected to be the reason for such inconsistency in the results. Other
SEM Scanning electron microscopy than durability concerns, environmental impact was considered as an
EDAX Energy dispersive analytical X-ray interesting parameter to access FeCr as aggregate material. Presence of
high chromium content poses risk where oxidation of Cr (III) could
promote the leaching of toxic Cr (IV) based on the pH, temperature and
other external factors [45]. However, leaching of Cr from raw FeCr re­
[18–20], ceramic [21–23], plastic waste [24], crumb Rubber [25–27], ported to be within the allowable limits in various studies according to
marble [28], mine tailings [29], incinerated bottom ash [30–32] and US and European standards [34]. Moreover, when added to the
recycled concrete [33] are some of the potential aggregate materials cementitious matrix, it helps in immobilization of such hazardous ele­
studied elaborately in several research works [16–33]. Ferrochrome slag ments bring the leaching value further down [41,46]. Based on the
(FeCr) is emerging material in this category with huge potential due to studies about FeCr as aggregate for concrete production, it is evident
its desirable physical, chemical and mechanical properties [34]. There that there is no sufficient data to access the opportunities though the
are various possibilities for FeCr to be employed as aggregate, for potential is well established in other applications. Especially, there is
example, in base layers, bricks, bitumen and concrete mixes [35–38]. very few work about use of FeCr as fine aggregate or river sand
FeCr is formed as a fine-grained side-stream material while rapidly replacement material [34]. Hence, this issue is taken up in the present
cooled in the process of ferrochrome production. Approximately, 1.5 study to explore the influence of using high volume of FeCr as aggregate
tonnes of such FeCr are produced for every tonne of ferrochrome alloy in cement mortar properties. Furthermore, limestone calcined clay
processed and with an estimated global output of 11.7 million tonnes cement (LC3) is used as alternative to ordinary Portland cement (OPC)
every year [39,40]. FeCr is mainly composed of forsterite and spinal to increase the sustainability of the matrix.
mineralogical phases with the chemical composition dominated by SiO2, LC3 is a recent advancement in blended cement with three primary
MgO, and Al2O3 [34]. Residual heavy metal elements are typically components, cement clinker, calcined clay and limestone. It allows up to

Fig. 1. DTA pattern of raw clay.

2
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Table 1
Oxide compositions of OPC, MK, LS and FeCr-slag aggregate (mass, %).
Material SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2 O Cr2O3 SO3 TiO2 Cl- L.O.I.

Binder ingredients OPC 20.82 4.79 3.30 64.31 2.57 0.11 0.02 – 0.67 – – 3.4
MK 54.77 35.39 1.17 0.33 0.032 0.12 0.03 – 0.039 0.02 – 8.1
LS 0.12 0.06 0.03 55.69 0.11 0.09 – 0.04 – – 43.81
Aggregate FeCr 36.29 22.50 1.91 1.46 31.10 0.23 0.04 5.64 0.50 0.17 0.06 0.10

Fig. 2. XRD patterns of MK and LS.

40 % clinker replacement with 20 % energy saving and 40 % of CO2 2. Materials

emission, making this a sustainable and environmental friendly binder
[47,48]. Hence, present study revolves around two main motives, viz., 2.1. Binder constituents
exploring FeCr for fine aggregate replacement and its influence in the
performance of upcoming sustainable LC3 binder. Consequently, the 2.1.1. Ordinary Portland cement
study also emphasis the need to make wise choices in choosing the The cement used in this study was OPC (CEM I: 42.5 N) conforming
construction materials that results in lower strain to the environment by to ASTM C150. It was purchased from Helwan Cement Company (HCC),
means of production methods and carbon saving. The performance Egypt.
assessment of OPC-mortars incorporating FeCr slag as a substitute of
natural sand is reported in previous studies; however, The utilization of 2.1.2. Calcined clay (Metakaolin)
FeCr slag as an alternative aggregate along with LC3 alternative binder Kaolinite clay is one of the effective supplementary cementitious
wasn’t reported in literature yet, an effort is made to understand the materials (SCMs) adequately available all over the Middle East [49].
fresh and hardened properties of the LC3 based matrices with 25 to 100 Kaolinite clay can be activated/ calcined by relatively moderate thermal
% of FeCr aggregates and compared with the OPC mixes. Further, the treatment [50] to obtain amorphous/ highly reactive MK. The kaolinite
mortar properties were attempted to correlate with the properties of the clay used in this study was supplied from Middle East Mining In­
raw materials including their chemical and mineralogical characteris­ vestments Company (MEMCO), Egypt. It was thermally treated at 600 ◦ C
tics. Environmental impact analysis was made in the form of leaching for a period of 2 h according to the differential thermal analysis (DTA)
studies to understand the effect of the presence heavy metal on the final graph presented in Fig. 1.
products.
2.1.3. Limestone powder
The third component/ constituent of the binder is LS fine powder. LS
Table 2 is commercially available, it was supplied by MEMCO, Egypt. The
Physical properties of fine aggregates. chemical compositions of OPC, MK and LS are determined by XRF and
Property FeCr slag Natural sand presented in Table 1. The mineralogical composition of the binder ad­
Specific gravity 2.66 2.62 ditives MK and LS was determined by XRD as shown in Fig. 2.
Water absorption (%) 1.12 0.63
Fineness modulus 2.69 3.04

3
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 3. Gradation of sand and FeCr slag.

Fig. 4. XRD patterns of natural sand and FeCr-slag.

2.2. Aggregates FeCr slag aggregate has slightly higher specific gravity than fine sand.
The water absorption of FeCr fine aggregate is in the range of stan­
2.2.1. Fine sand dardized values [51].
The sand used in this study was natural siliceous sand passing The grain size distribution for sand and FeCr-slag aggregate (as
through a 2.36-mm sieve. The specific gravity, water absorption and received) along with the lower and upper acceptable limits of grading
Fineness modulus are illustrated in Table 2. according to ASTM C33 is presented in Fig. 3. It can be seen that, both
sand and FeCr grains are within the acceptable limits; i.e, well-graded.
2.2.2. FeCr slag The mineralogical phase compositions of used aggregates were
Ferrochrome (FeCr) slag is a by-product from the production of examined by X-ray diffractometer (XRD) as shown in Fig. 4. The XRD
ferrochrome, a main component in the stainless steel industry. FeCr slag pattern of the sand indicated its siliceous nature (i.e., quartz is the major
granules were collected from Gulf Mining plant of ferrochrome industry, phase); however, FeCr slag showed the presence of metallic phases like
situated in Sohar city, Oman. The chemical composition of FeCr is magnesiochromite (MgCr2O4) and chromoferride, and silicate phases
demonstrated in Table 1. like forsterite (Mg2SiO4), and fayalite (Fe2SiO4).
Some of the physical properties FeCr slag are summarized in Table 2. The particle morphology of FeCr slag in comparison to sand was

4
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 5. Particle morphology and elemental analysis of (a) Natural sand and (b) FeCr slag aggregates.

Table 3
Mix proportions of the investigated mortars [kg/m3].
Mix Code Binder Aggregates Water Flow spread w/b*
mm
OPC MK LS Fine sand FeCr-slag

FeCr0-OPC 551 0 0 1515.2 0 267.24 0.485

FeCr25-OPC 551 0 0 1136.4 378.8 278.1 23 0.54
FeCr50-OPC 551 0 0 757.6 757.6 298.7 21.6 0.58
FeCr75-OPC 551 0 0 378.8 1136.4 314.15 20.6 0.61
FeCr100-OPC 551 0 0 0 1515.2 329.6 19.6 0.64
19.2
FeCr0-LC3 220.4 220.4 110.2 1515.2 0 275.5 0.50
FeCr25-LC3 220.4 220.4 110.2 1136.4 378.8 308.56 22.6 0.56
FeCr50-LC3 220.4 220.4 110.2 757.6 757.6 336.11 21.4 0.61
FeCr75-LC3 220.4 220.4 110.2 378.8 1136.4 347.13 20.2 0.63
FeCr100-LC3 220.4 220.4 110.2 0 1515.2 369.17 19 0.67
*
w/b: water/binder ratio.

investigated by SEM as shown in Fig. 5. The sand grains are semi- as recommended by recent study [52]. The mortar samples were pre­
rounded and smooth-textured; while, FeCr grains are angular in shape pared using binder-sand ratio of 1:2.75 with w/b ratio of 0.485. Fine
and rough-textured. sand was replaced with FeCr-slag aggregates at the ratios of 0, 25, 50, 75
and 100 wt%; these mixtures were denoted as FeCr0, FeCr25, FeCr50,
FeCr75 and FeCr100 respectively. Two groups of samples (each group
2.3. Mix-proportions and samples preparation includes 45 cubes) were cast using different binders; a group made of
OPC and the other made of LC3. The blended mixtures were prepared
First, LC3 binder is produced by blending together 40 wt% of OPC with w/b ratios required to attain a constant degree of flowability as
with 40 wt% of MK in addition to 20 wt% of LS to a homogeneous blend

5
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 6. Test samples during (a) compressive strength and (b) indirect tensile strength tests.

illustrated in Table 3. test, in which a load is applied along the center of two opposite sides of a
5 cm cube by means of narrow steel strips as shown in Fig. 6.[55].
The tensile stress that is created in the plane between the line loads,
2.4. Testing and analysis which cause the splitting of the cube, is calculated from the following
formula [55]:
The flowability test was conducted to assess the mortar’s behavior in
the fresh state by using a mini-conical slump flow test method according Ts =
2P
to BS EN 1015–3 [53]. The used flow cone dimensions (60 mm in height, πL2
internal diameter was 100 mm at the base and 70 mm at the top). Where: Ts is the tensile strength (MPa), P is the load at failure (N) and
The fresh blended mixtures were poured in 50 × 05 × 05 mm cubes L is the edge length of the cube (mm).
to form the specimens for compressive strength, indirect tensile strength The capillary water absorption test was conducted in accordance
capillary water absorption and leaching tests. In order to attain a good with EN 1015–18 [56]. Prior to the test, the cube specimens were
packing, the moulds were vibrated on a vibratory table for 1 min, then removed from water, and oven dried at 70 ◦ C until a constant dry
the specimens were kept under the laboratory conditions for 24 h. the weight. Three samples were tested from every group and the average is
samples were then demoulded and kept under tape water for curing for a reported.
period up to 28 days before testing. Fig. 6 shows the photos during FeCr residue has more Cr2O3 (>5%) which is more harmful and toxic
casting and molding processes. [57]. As the potentiality of releasing hazardous compounds to the
At 28th day of curing, the test specimens were taken out from curing environment restricting their use and disposal, adequate leaching study
water and allowed to dry for 24 h before performing the mechanical has been performed to establish the environmental compatibility of the
strength tests. waste slag for utilization as fine aggregate material. Currently, potential
The Compressive strength test was carried out in accordance with the constituent release is evaluated based on single extraction leaching test
standard specification ASTM C109/C109M-20b [54] using RMU following Toxicity Characteristic Leaching Procedure (TCLP), using
57–2400 BERGAMO ITALY testing machine, at a loading rate of 0.9 kN/ acetic acid based on USEPA Test Method 1311 [58]. 20 h short tank
sec. Three specimens at each age were tested and the average value was leaching tests were performed on mortar cube samples containing 100 %
reported. FeCr slag as fine aggregate with TCLP extraction fluid of pH < 5.
The indirect tensile strength was determined through the splitting

Fig. 7. Variations of flow spread as a function of FeCr slag ratio.

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H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 8. Compressive strengths of mortars containing various amounts of FeCr aggregates made with OPC and LC3 binders at the age of 28 day of curing.

Leachate analysis has been performed by Flame Atomic Spectropho­ diameters than OPC mortars. The lowest flow diameters were obtained
tometry on PerkinElmer AA Analyst 300 & Perkin Elmer Graphite for the higher replacement ratio of 100 % FeCr slag, OPC and LC3
Furnace 850 Atomic Absorption. mortars possessed 19 and 23 % reduction in the spread respectively. The
The microstructure characteristics of freshly fractured pieces from reduced workability is attributed to the higher surface area of angular
the various mixtures were investigated by scanning electron microscope FeCr aggregates with rough texture, which requires more water for a
(Field Electron and Ion Company, FEI - Inspect S) equipped with energy standard workability than rounded sand [42]. As a result, with a view to
dispersive analtyical X-ray (EDAX) elemental analysis unit. achieve a constant degree of flowability among the various FeCr-
blended mortars, the w/b ratio for OPC mortars has been increased
3. Results and discussion gradually from 0.485 for FeCr0 to 0.54, 0.58, 0.61 and 0.64 for FeCr25,
FeCr50, FeCr75 and FeCr100 respectively. However, the w/b ratio for
3.1. Mini-slump LC3 mortars has been increased gradually from 0.50 for FeCr0 to 0.56,
0.61, 0.63, and 0.67 for FeCr25, FeCr50, FeCr75 and FeCr100 respec­
Fig. 7 shows the variation of flow spread (%) as a function of FeCr tively. These results are in agreement with the results of previous studies
slag replacement ratios. As it can be see, the inclusion of FeCr aggregate which reported that the use of FeCr fine aggregates into mortar led to a
has decreased the flow (spread) of both OPC and LC3 mortars, i.e., decrease in the workability [42].
reduced workability. The LC3 mortars possessed slightly lower flow

Fig. 9. Indirect tensile strengths of mortars containing various amounts of FeCr aggregates made with OPC and LC3 binders at the age of 28 day of curing.

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H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 10. Capillary water absorption for OPC and LC3-mortars made with fine sand and FeCr slag aggregates at 28 days of curing.

3.2. Compressive strength enhanced strength of LC3 binder even at a high cement replacement
level > 50 % is attributed to the formation of carboaluminate phase as a
The variations in compressive strength with FeCr aggregate result of the reaction of Aluminate phase (A) from calcined clay with
replacement ratios for OPC and LC3- based mortars at the age of 28 days Calcium Hydroxide (CH, liberated during cement hydration) and lime­
of curing is introduced in Fig. 8. As it is clear, both OPC and LC3 mortars stone (CC) [60] besides the formation of additional cementing phases
possessed the same trend of increasing compressive strength with like calcium silicate hydrate (CSH) and calcium aluminate hydrate
increasing the FeCr content; however, the LC3-mortars exhibited rela­ (CAH) by pozzolanic reaction of Silicate and Aluminate phases with CH
tively lesser enhancement ratios. The highest compressive strength [61]. Furthermore, FeCr slag aggregates are characterized by high
values were obtained for the mortars incorporating 100 % of FeCr slag toughness and surface roughness which positively contribute to me­
aggregate. Enhancements by about 71 and 63 % were attained by OPC chanical strength and interfacial bonding characteristics [34].Fig. 9.
and LC3-based mortars relative to the OPC standard mortar made with
natural sand fine aggregate respectively. These results are in agreement
3.3. Indirect tensile strength
with previous studies [42,59] reported a significant increase in the
compressive strength of concrete incorporating FeCr slag as a fine
Fig.9. clarifies the 28-day tensile strengths for the mortars incorpo­
aggregate. The compressive strength improvement of LC3 mortars
rating various percentages of FeCr slag aggregates prepared with OPC
incorporating FeCr aggregate point out the high quality and unique
and LC3 binders. The tensile strength increased with increasing FeCr
strength of LC3 binder and the good compatibility/ tight binding be­
replacement ratios. The OPC and LC3-blended mortars showed compa­
tween the LC3 host matrix and embedded FeCr aggregates. The
rable tensile strengths. The tensile strength of OPC mortar increased by
7, 13.8, 18 and 22.2 % and that of LC3 mortar increased by 6.8, 9.6, 13.7
Table 4 and 17.3 % upon replacing the sand with 25, 50, 75 and 100 % FeCr slag
Leaching test results of OPC and LC3 mortars with FeCr slag fine aggregates respectively. The enhancement in tensile strengths point out the unique
(Extraction with Acetic Acid). hardening characteristics of OPC and LC3 binders in addition to the
Element FeCr slag mortar Regulated Level improved interfacial bond strength with FeCr aggregates. The FeCr ag­
OPC LC3
USEPA [58] gregates exhibit relatively high surface roughness as compared to nat­
ural sand [42,61], it has been confirmed by Hong et al. 2014 [61] that
ppm ppm ppm
rough surfaces can achieve high bond strength. Furthermore, it was
Cadmium (Cd) n. d n. d 1.0 reported in previous studies that the utilization of high-strength aggre­
Lead (Pb) n. d n. d 5.0
gate with rough surface characteristics in concrete provides superior
Silver (Ag) n. d n. d 5.0
Nickel (Ni) n. d n. d
flexure performance [63]. The enhancement in tensile strength due to
Arsenic (As) 4.30 4.25 5.0 the replacement of fine sand with FeCr aggregate has been also
Copper (Cu) 0.04 0.01 confirmed by a recent study by Kopuri and Ramesh [59]. The mecha­
Chromium (Cr) 1 1.1 5.0 nism of increasing the interfacial bond strength is known as mechanical
Manganese(Mn) n. d 0.01
interlacing and can be explained as follows: the hydration products of
Zinc (Zn) 0.02 n. d
Iron (Fe) 0.2 n. d cement especially the gel-like CSH phase can penetrate the cavities or
Mercury (Hg) 0.21 0.18 0.2 fine wrinkles of the aggregate surface, providing several hooks binding
Strontium (Sr) 3.5 3.1 both matrix and aggregate, [62,63].
Vanadium (V) n. d n. d
Molybdenum (Mo) n. d n. d
Aluminum (Al) n. d 0.6 3.4. Capillary water absorption (Sorptivity)
Barium (Ba) 1.54 1.21 100.0
Selenium (Se) n. d n. d 1.0
The variations of the amount absorbed water with time in addition to

8
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 11. SEM micrographs and EDAX spectrum for selected area of OPC mortar made with (a) fine sand aggregate and (b) FeCr slag aggregate.

9
H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

Fig. 12. SEM micrographs and EDAX spectrum for selected area of LC3 mortar made with (a) fine sand aggregate and (b) FeCr slag aggregate.

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H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

the variation of capillary water absorption coefficients (Aw) with the resulted from the adequate grain size distribution of the used FeCr ag­
FeCr slag content for the mortars made with OPC and LC3 binders at 28 gregates. In addition, the EDAX pattern revealed high percentage of (Al)
days of curing are presented in Fig. 10. Although; the LC3 mortar which assigned to the calcium carboaluminate phase formed by the
showed slightly higher water absorption values as compared with the interaction of Aluminate phase from calcined clay with CH liberated
conventional OPC mortar, the total replacement of fine sand with FeCr during cement hydration and limestone powder. The carboaluminate
slag aggregate has decreased the water absorption coefficients for OPC positively contributes to strength [48]. This SEM analysis revealed the
and LC3 mortars by about 16 and 11 % respectively. The reduction in technical compatibility between the FeCr slag and the hydrated LC3 host
water absorption with the inclusion of FeCr aggregates match with the matrix and might explain the enhanced mechanical strength and the
enhanced mechanical strength results. This is assigned to the fact that, inferior leaching behaviors.
high strength cement-based structures have fewer voids and short micro
cracks than normal strength structures [59]. As the water ingress into 4. Conclusions
construction and building materials causes serious problems; hence,
reducing the water absorption helps in improving the durability The development of green and sustainable construction material via
characteristics. the use of the promising ternary blended cement (LC3) in lieu of OPC
and the reuse of FeCr waste slag as fine aggregate in the production of
3.5. Leaching characteristics mortar with enhanced mechanical performance has been examined in
this study. The following conclusions can be made:
Chromium is one of eight metals whose concentrations must be
checked in the leachate obtained in the TCLP test [58] to decide whether • The use of FeCr aggregate in lieu of natural sand led to a significant
the material is hazardous. Leaching test results of OPC and LC3 mortars improvement in mechanical performance of LC3-based mortar. As
with 100 % FeCr slag as fine aggregates are demonstrated in Table 4. All compared with the OPC standard mortar, Enhancements by about 63
detected values of chromium leaching fall within the USEPA safe/ and 17 % in compressive and tensile strengths have been attained
allowable regulatory limit for total chromium release of 5 ppm [64,65]. respectively.
In addition, the heavy noxious metals like As, Mn, V, Sr and Zn are below • The utilization of FeCr slag as fine aggregate helps in reducing the
the permissible limits. the Cr-leachability values agree with many water absorption coefficient of LC3 mortar. A reduction by about 11
studies that examined the chromium mobility from concrete containing % has been achieved by increasing FeCr aggregate replacement ratio
FeCr aggregate made with OPC [43,45]. The current study results point up to 100 %.
out the ability of LC3 matrix to immobilize the chromium physically and • Even at the highest replacement ratio of 100 % FeCr aggregate, LC3
chemically in FeCr slag aggregate. The immobilization of Cr through the based mortar demonstrated high efficiency for Cr-immobilization.
LC3 matrix confirms the adequate hardening and compact microstruc­ Cr-leachability values are well below US EPA allowable regulatory
ture of this alternative binder [35]. These outcomes could reflect the safe limits.
utilization of FeCr slag-blended LC3 composites in construction • As compared with the conventional OPC mortar, the LC3 mortar with
applications. 100 % FeCr aggregate revealed improved microstructure with
compact ITZ. The improvement in microstructure is attributed to the
3.6. Microstructure analysis unique hardening characteristics of LC3 binder and the rough texture
of FeCr aggregate.
The microstructure characteristics of both OPC and LC3 mortars • Due to the high limestone content, LC3 binder is favourable for
incorporating 0 and 100 wt% of FeCr slag aggregates at 28 days of curing normal concrete or concrete reinforced with polymer rebars. This
can be explored from SEM micrographs and EDAX spectra presented in can be considered as the limitation in the current study.
Figs. 11 and 12. Although; the microstructure of the OPC mortar made
with natural sand as fine aggregate showed compact hydrated cement Furthermore, future research should be performed to explore the
phases of CSH and CASH covering the sand grains, a very thin micro gap applications of the new composites including: resistance to fire/
has been observed at the interfacial transition zone (ITZ) between the elevated temperatures, corrosion characteristics (performance under
hydrated cement paste (hcp) and aggregate. ITZ is known to be the aggressive curing conditions) and durability.
weakest component of concrete; hence, its microstructure is the key
factor determining its mechanical performance, the micro gap of ITZ is CRediT authorship contribution statement
attributed to the higher concentration of calcium hydroxide (CH) near
ITZ compared to the cement matrix; i.e, the concentration of CSH gel is H. Shoukry: Conceptualization, Methodology, Writing – review &
lesser. As clear from Fig. 11a, the numbers of white deposits (identified editing, Supervision. Priyadharshini Perumal: Investigation, Writing –
as CH phase) are more visible [15]. Furthermore, few micro pores and original draft. Aref Abadel: Funding acquisition, Data curation. Hus­
micro cracks have been observed (see Fig. 11a). As it is clear; due to the sam Alghamdi: Project administration, Data curation. Mohammed
high surface roughness of FeCr aggregate, the SEM of OPC-mortar made Alamri: Project administration, Data curation. Hamdy A. Abdel-Gaw­
with FeCr slag (Fig. 11b) showed better binding at ITZ, this is confirmed wad: Conceptualization, Writing – review & editing.
also by previous studies [42,61]. Owing to the high number of tiny
protrusions of FeCr slag surface which act as nuclei for hydrates, gel-like Declaration of Competing Interest
hydration products (CSH and CSAH) grow on the surface of the aggre­
gate and cement matrix, overlap each other and effectively fill the gap The authors declare that they have no known competing financial
resulting in enhanced densification of the ITZ. In addition to the main interests or personal relationships that could have appeared to influence
constituents of cement hydrates of Calcium (Ca), Silicon (Si) and the work reported in this paper.
Aluminium (Al), the EDAX pattern revealed considerable amount of Mg
and low amount of Cr which are attributed to FeCr slag. As it is clear Data availability
from Fig. 12a, the microstructure of LC3 mortar resembles that of OPC
mortar. In the LC3 mortar made with FeCr aggregate, the same features No data was used for the research described in the article.
are obvious; as shown in Fig. 12b, the replacement of sand with FeCr led
to improved microstructure in terms of compactness and ITZ tightness.
The compact microstructure points to the improved packing which

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H. Shoukry et al. Construction and Building Materials 350 (2022) 128928

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