Durability of Mortar Incorporating Ferronickel Slag Aggregate and Supplementary Cementitious Materials Subjected to Wet–Dry Cycles
International Journal of Concrete Structures and Materials
Durability of Mortar Incorporating Ferronickel Slag Aggregate and Supplementary Cementitious Materials Subjected to Wet-Dry Cycles
Ashish Kumer Saha 0
Prabir Kumar Sarker 0
0 Department of Civil Engineering, Curtin University , Perth, WA 6845 , Australia
This paper presents the strength and durability of cement mortars using 0-100% ferronickel slag (FNS) as replacement of natural sand and 30% fly ash or ground granulated blast furnace slag (GGBFS) as cement replacement. The maximum mortar compressive strength was achieved with 50% sand replacement by FNS. Durability was evaluated by the changes in compressive strength and mass of mortar specimens after 28 cycles of alternate wetting at 23 C and drying at 110 C. Strength loss increased by the increase of FNS content with marginal increases in the mass loss. Though a maximum strength loss of up to 26% was observed, the values were only 3-9% for 25-100% FNS contents in the mixtures containing 30% fly ash. The XRD data showed that the pozzolanic reaction of fly ash helped to reduce the strength loss caused by wet-dry cycles. Overall, the volume of permeable voids (VPV) and performance in wet-dry cycles for 50% FNS and 30% fly ash were better than those for 100% OPC and natural sand.
ferronickel slag; fly ash; blast furnace slag; compressive strength; wet-dry cycle; porosity
Substantial amounts of industrial by-products are currently
used worldwide as construction materials. Nevertheless, it is
important to increase recycling of the unused by-products in
order to reduce the volume of waste causing environmental
pollution, to save the huge area of land occupied by them
and to reduce the depletion of natural resources. Concrete is
the most widely used construction material in the world and
it has a significant contribution to the greenhouse gas
emissions. Thus, utilisation of the currently available
industrial by-products in manufacture of concrete can
significantly improve sustainability of the construction sector.
Different types of granulated slags are produced as
byproducts in processing of minerals. A considerable amount
of research is available in literature on the utilisation of these
granulated slags as replacement of natural aggregate and
ground slag as replacement of cement. The most common
type of commercially available ground slag is GGBFS
(Hooton 2000; Shafigh et al. 2013; Yang et al. 2017)
Durability improvement of concrete by the use of GGBFS as
an SCM has been well documented by many works in
(Siddique and Khan 2011; Safiuddin et al. 2010; Kim
et al. 2016)
. While ground slags can be used as partial
replacement of cement, the binder usually occupies only
15–20% volume of concrete, and slags cannot be used as full
replacement of cement (Roychand et al. 2016). Since
aggregates occupy a much larger volume fraction in concrete
or mortar, the use of granulated slag as aggregate can
substantially increase its usage. In addition, use of granulated
slags as aggregate do not require grinding that can save cost
and energy. Furthermore, the demand of natural sand as fine
aggregate is increasing fast in many countries. Since river
sand is the most common fine aggregate, uncontrolled river
dredging is occurring in different parts of the world
et al. 2012; Davis et al. 2000)
. Extensive sand mining from
river bed can cause severe disruption of the aquatic
ecosystem (Padmalal et al. 2008). Therefore, the use of
granulated slag by-products can be considered as a cost-effective
and environmentally friendly alternative to natural sand for
Among different types of slag aggregates, coal bottom ash
(CBA), steel slag, copper slag and FNS are the most
frequently studied materials because they are produced in
considerable quantities. Aggregate plays a vital role on all
concrete properties such as workability, strength and
durability. The use of coal bottom ash as fine aggregate was
found to reduce compressive and tensile strengths of
concrete after the initial curing period. However, strength is
usually increased at the later ages by pozzolanic reaction of
(Yu¨ksel et al. 2011)
. Durability properties of CBA
concrete such as drying shrinkage and freeze–thaw
resistance were reported to improve as compared to the control
specimens (Bai et al. 2005). However, the resistance to wet–
dry cycle of CBA concrete was poor due to high porosity of
(Aggarwal et al. 2007; Ghafoori and Bucholc 1996)
use of steel slag or electric arc furnace (EAF) slag in
concrete was found to significantly reduce workability
(Etxeberria et al. 2010; Manso et al. 2004)
. Mechanical properties
of concrete such as compressive strength, splitting tensile
strength, flexural strength and modulus of elasticity were
reported to improve by the use of EAF slag
and Al-Zaid 1997; Qasrawi et al. 2009)
. The improvement of
mechanical properties is attributed to the higher angularity
and roughness of aggregate particles that can improve
bonding between cement paste and aggregate (Maslehuddin
et al. 2003). However, strength losses of concrete in
accelerated ageing and freeze–thaw exposures were higher for
steel slag aggregate as compared to natural aggregate. Over
25% loss of compressive strength was observed in steel slag
aggregate concrete by the exposure to wet–dry cycles. The
poor performance of EAF slag was attributed to the presence
of pernicious free lime and periclase in the slag
(Manso et al.
2006; Pellegrino and Gaddo 2009)
. Improvements of the
hardened properties of concrete such as compressive
strength, tensile strength and abrasion resistance by partial
replacement of fine aggregate with the copper slag have been
reported in the literature
(Al-Jabri et al. 2011; Wu et al.
2010; Brindha and Nagan 2011)
. Durability properties such
as sulphate resistance and carbonation resistance of concrete
with copper slag aggregate were reported to be identical to
those of the control specimens (Ayano and Sakata 2000).
However, the freeze–thaw resistance of copper slag concrete
was poor due to excessive bleeding that caused internal
defects in the samples
(Shoya et al. 1997)
Production of ferronickel alloys produces a large quantity
of FNS as by-product
(Saha and Sarker 2016)
limited quantities of this FNS is utilised in local construction
works. Figure 1 shows an example of the utilisation of FNS
aggregate as 30% replacement of natural sand in concrete
breakwaters in New Caledonia
(Saha and Sarker 2017a)
Although the nickel producers supply FNS locally for using
as fine aggregate, the properties of FNS aggregate concrete
is scarce in literature. Moreover, the physical and chemical
properties of FNS can vary significantly with the type of
source ore, smelting temperature and cooling method.
Fig. 1 Breakwaters of concrete with 30% ferronickel slag
aggregate in marine exposure for 20 years.
Laterite, garnierite and pentlandite ores are some primary
sources of nickel. The ore is usually smelted at a high
temperature that produces the molten slag as by-product.
The molten slag can be granulated by air or water (JSCE
Committee 1994). Very limited studies available in literature
show that FNS can be used as an alternative fine aggregate in
(Sakoi et al. 2013)
. It was shown that workability
decreased and bleeding increased by the use of FNS
aggregate in concrete due to its high unit weight
1991; Shoya et al. 1999; Sato et al. 2011)
. The hardened
concrete properties such as compressive strength, modulus
of elasticity and tensile strength were improved by the partial
replacement of sand with FNS. Improvement of these
mechanical properties was attributed to the physical
properties of FNS such as high unit weight, well-grading and
angularity of the particle, which improved bonding between
paste and aggregates
(Sakoi et al. 2013; Shoya et al. 1999)
Among the limited literature available on durability
properties of FNS aggregate concrete, Shoya et al. (1999)
showed that 50% replacement of natural aggregate by FNS
resulted in better freeze–thaw resistance as compared to the
control specimens. On the other hand,
Shoya et al. (2003)
reported better frost resistance of concrete containing FNS
Tomosawa et al. (1997)
alkali–silica reaction associated with FNS aggregates and
suggested the use of fly ash or blast furnace slag as partial
replacement of cement as a mitigation. The above studies
used FNS aggregates collected from the slow cooling pits.
This paper evaluates the strength and durability of cement
mortar using FNS fine aggregate produced by smelting of
garnierite ore at a temperature between 1500 and 1600 C
(Rahman et al. 2017)
. The molten slag is granulated by rapid
cooling using seawater. The FNS is characterised by
relatively high magnesium content as compared to the FNS
utilised in the previous studies
(Wang et al. 2011; Kang et al.
2014; Choi and Choi 2015)
. Thus, the source ore and
granulation method of this FNS are different from those used
in the studies available in literature. About 12–14 tonnes of
FNS is produced as by-product in the production process of
one tonne of ferronickel alloy. The annual FNS production
of the smelter is estimated as 1.7 million tonnes. The current
deposit of FNS in the premises of the smelter is about 25
million tonnes despite its various uses by the local
construction industries. The potential alkali–silica reaction
(ASR) of the FNS and the effectiveness of SCMs such as fly
ash and GGBFS as ASR mitigating measure was studied in
our ongoing work
(Saha and Sarker 2016)
. This paper
presents the strength development of mortars containing
different percentages of FNS with or without fly ash and
GGBFS as cement replacement. Further to the strength
development in normal environmental condition, it is also
important to have knowledge on the durability of a
construction material when exposed to seasonal variations and
aggressive environments. Thus, the long-term durability of
mortar specimens was evaluated in terms of volume of
permeable voids and the changes in mass and strength after
exposure to an accelerated weathering condition represented
by alternate cycles of wetting and drying at 110 C. The
mineralogical phases of the specimens after the wet–dry
cycles were studied in order to understand the effects of FNS
2. Experimental Work
Commercial ordinary Portland cement (OPC) was used as
the main binder in this study. A class F fly ash and GGBFS
were used as supplementary cementitious materials. FNS
was used as a replacement of natural sand in the form as it
was received from the smelter without any processing.
Table 1 shows the chemical compositions of these materials
as determined by X-Ray Fluorescence (XRF) test. It can be
seen that majority of the FNS constituents are Silicon,
Magnesium and Iron. The Calcium contents of OPC and
GGBFS are much higher than that of the fly ash (0.27%). On
the other hand, the main constituents of fly ash were silica
(76.34%) and alumina (14.72%). Table 2 presents the
physical properties of the binders.
Figure 2 shows the physical appearance of FNS fine
aggregate and natural sand used in this study. It can be seen
that FNS is angular in shape with much more coarser
particles as compared to natural sand.
The grading curves of fine aggregates combining different
percentages of FNS and natural sand are shown in Fig. 3.
The upper and lower limits of fine aggregates recommended
by the Australian Standard AS 2758.1 (1998) are also shown
in the figure. It can be seen that while most of the
combinations are within the limits of the Standard, the grading
curve of 100% FNS is slightly below the lower limit because
of the lack of fine particles in FNS. Thus, the size
distribution of fine aggregate was improved by combining FNS
with natural sand. It can be seen that the mix of 50% FNS
and 50% natural sand has resulted in a well-graded
combination, which includes particles of different sizes and shapes.
As given in Table 3, the fineness modulus of FNS was
4.07 and that of natural sand was 1.95. The unit weights of
FNS and natural sand were 2780 and 2160 kg/m3,
respectively. The water absorptions of FNS and sand were 0.42 and
2.2 Mixture Proportions and Test Methods
The mixture proportions of mortars used in this study are
given in Table 4. FNS aggregate was used to replace natural
sand by 0, 25, 50, 75 and 100% in the mortar mixtures.
Previous studies showed that FNS aggregates may
potentially cause alkali–silica reaction (ASR). Therefore, fly ash
and GGBFS were used as 30% replacement of cement. This
measure was found to substantially reduce the expansion due
to ASR in our ongoing study
(Saha and Sarker 2016)
. A total
of 15 mixtures in three series of the binder compositions
were investigated: 100% OPC, 30% cement replacement by
fly ash and 30% cement replacement by GGBFS. In Table 4,
the designation of a mixture starts with PC for 100% OPC,
FA for 30% fly ash or BFS for 30% GGBFS. The number at
Specific surface area (m2/kg)
the end of a mix designation represents the percentage of
FNS in fine aggregate.
Cube specimens of 50 mm sides were cast using freshly
mixed mortar. The specimens were demolded at 24 h after
casting and then cured in lime saturated water up to 28 days.
Compressive strength tests were conducted at 3, 7, 28, and
56 days of age. Three specimens were tested at each age and
an average value of the compressive strength is reported.
The tests were conducted at a loading rate of 0.333 MPa/s.
In order to determine porosity of the samples, volume of
permeable voids (VPV) test was conducted on the 50 mm
mortar cubes in accordance with the ASTM C 642 (2006)
standard. The test consists of measurements of masses of the
sample in oven-dry condition, saturated surface dry
condition, immersed in water and after subjecting to boiling
condition. At first, the samples were dried in an oven at
110 C for 24 h and then cooled down to room temperature
for 3 h to record the dry mass. The samples were then
submerged in water for 48 h and the immersed mass was
recorded. The saturated surface dry mass was measured after
moving the samples out from the water. The samples were
then boiled in water for 5 h, cooled down and the boiled
mass was recorded. Volume of the permeable voids was
calculated using the values of these masses.
The specimens were exposed to cycles of alternate drying
at 110 C and wetting at 23 C in order to evaluate their
resistance to an accelerated weathering condition. This
exposure condition is considered to accelerate the possible
degradation of mortar by seasonal variations of wetting–
drying and heating–cooling by surrounding environment
over the age. The specimens were cured in water at 23 C
for 28 days before beginning of the alternate wet–dry cycles.
One cycle of the exposure consisted of drying the specimen
at 110 C in an oven for 8 h, cooling at room temperature for
one hour and then wetting under water at 23 C for 15 h.
After completion of 28 cycles of alternate wetting and
drying, the changes in mass and compressive strengths of the
specimens were determined. A similar exposure condition
was used in previous studies to determine the durability of
concrete incorporating industrial waste aggregates such as
blast furnace slag and coal bottom ash
(Yu¨ksel et al. 2007;
Manso et al. 2006; Aggarwal 1995)
. An X-ray diffraction
(XRD) analysis was conducted on powdered samples in
order to understand the effects of alternate cycles of
hightemperature drying and wetting on the mineralogical phases.
The samples were tested on powder diffractometer D8
Advance, with a copper K-alpha radiation source 40 kV and
40 mA with a Lynx Eye detector. The scan parameter was 2h
ranging from 7.5 to 90 with a step size of 0.015 . A
Water absorption (%)
qualitative phase determination was carried out by
comparing the peak positions and relative intensity with the
database of known crystal structure.
3. Results and Discussion
3.1 Compressive Strength Development in Normal Curing Condition
The compressive strength results at the ages of 3, 7, 28 and
56 days are presented in Fig. 4. It can be seen that
compressive strength increased with increase of the percentage
of FNS up to 50% in all three series of mortars and then
declined with further increase of FNS. In the mortar series of
100% OPC as binder, the 28-day compressive strength
gradually increased from 39 MPa for 0% FNS to 57 MPa for
50% FNS and then gradually decreased to 44 MPa for 100%
FNS. While strength declined for the FNS contents beyond
50%, the compressive strength for 100% FNS was still
higher than that for 100% natural sand. The trends of
compressive strength variation with increase of FNS are
similar at the ages of 3, 7, 28, and 56 days. Thus, the
strength increase for 50% FNS and 100% FNS were 46%
and 12%, respectively, as compared to the strength of the
Fine aggregate (kg/m3)
mortar with 100% natural sand. The increase of compressive
strength by the inclusion of FNS is attributed to its high
density and angular shape as compared to the round shape of
natural sand. The increase of FNS content improved particle
packing as well as density of the samples. The improved
packing and interlocking by the high density FNS particles
have contributed to the increase of compressive strength.
Compressive strength then declined with further increase in
the FNS percentage. Therefore, 50% FNS showed the effect
of maximising the strength development of mortar. This is
attributed to the well-graded combination of fine aggregates,
as shown in Fig. 3. The decline of compressive strength for
FNS contents beyond 50% is considered to be because of
reduced fine particles in the aggregate combination, as
shown by the grading curves for 75 and 100% FNS
and Sarker 2017b, c)
The effect of FNS on strength development of the mortar
series containing 30% fly ash or 30% GGBFS is seen to be
similar to that of the series containing 100% OPC as binder.
The 28-day compressive strengths of the fly ash mortar with
0, 50 and 100% FNS were 30, 35 and 30 MPa respectively.
Thus, strength of the mortar with 100% FNS was same as
that of the mortar with 100% natural sand, whereas strength
of the mortar with 50% FNS was 16% higher than that of the
mortar with 100% natural sand. In the mortar series
containing 30% GGBFS, the 28-day compressive strengths were
32, 50, and 41 MPa for 0, 50 and 100% FNS, respectively.
Thus, compressive strength increased by 56 and 28% by
replacing 50 and 100% natural sand, respectively.
When the strength developments of mortars in three series
are compared, as expected, the highest strengths were
observed in the series of 100% OPC as binder and the lowest
strengths were observed in the series with 30% cement
replacement by fly ash. In addition, the mortars in the series
of 30% GGBFS as exhibited higher strengths than the
mortars with 30% fly ash. This is attributed to the higher
CaO content of GGBFS than fly ash. It can be seen from
Fig. 4 that the lowest 3-day strength occurred in the mortar
series containing 30% fly ash. However, the rate of strength
development at later ages was higher in this series than the
mortars of other two series, in particular between the ages of
28 and 56 days. The percentages of strength increase
between 28 and 56 days in the mortars containing 50% FNS
were 8, 20 and 8% for the binder series of 100% OPC, 30%
fly ash and 30% GGBFS, respectively. The higher late-age
strength gain of the fly ash mortar is because of the
continued pozzolanic reaction of fly ash. It should be noted that
though fly ash and GGBFS reduced the compressive
strength, it is important to use these supplementary binders
as a cement replacement in order to reduce the potential ASR
expansion of FNS aggregate. The effectiveness of
supplementary cementitious materials to reduce the potential ASR
expansion of FNS aggregate was demonstrated by
accelerated mortar bar test (AMBT) results. It was found that
lowcalcium fly ash was more effective to reduce the potential
ASR expansion of FNS than using GGBFS. Also, it can be
seen from Fig. 4 that continued pozzolanic reaction of fly
ash is further demonstrated at 56 days since the compressive
strength of mortars with 30% fly ash and 50% FNS reached
the same level of compressive strength as mortars with 100%
OPC and 100% natural sand. Therefore, the strength
developments of three series of mortars presented in Fig. 4
can be used in the selection of binder and aggregate
combination when using this FNS fine aggregate.
3.2 Volume of Permeable Voids (VPV)
The porosity of mortar specimens was evaluated by
measuring the volume of permeable voids (VPV). The
interconnected void space such as capillary pores, gel pores,
air voids and microcracks can be measured by this test
. This test provides an indication
of the ease of water penetration in concrete. The test results
are plotted in Fig. 5. It can be seen that porosity of the
samples increased with the increase of FNS content for all
three binder groups. The highest values of VPV were
observed in the mortar series of 100% cement as binder
(PCFNS series). The values of VPV were 15, 17, 18, 19 and
19% for 0, 25, 50, 75 and 100% FNS, respectively. Thus,
VPV increased by about 18% by the use of 50% FNS. This
increase of VPV is attributed to the increase of pores in the
mortar by larger and angular FNS particles. It can be seen
from Fig. 5 that the inclusion of fly ash and GGBFS in the
binder has reduced the VPV values of mortar specimens. In
the mortar series with 30% GGBFS (BFS-FNS series), VPV
increased from 14 to 17% with the increment of FNS
aggregates. Similarly, in the mortar series of 30% fly ash
(FA-FNS series), VPV increased from 12 to 15% due to the
use of FNS aggregates. The reduced VPV by fly ash and
GGBFS is attributed to the higher fineness and pozzolanic
reactions of the SCMs. The reduction of permeability of
paste by inclusion of SCMs is well documented in literature
(Osborne 1999; Bijen 1996; Shehata et al. 1999)
the results of Fig. 5 show that fly ash was more effective
than GGBFS in reducing VPV of the mortar specimens. The
greater effectiveness of fly ash over GGBFS is attributed to
its higher silica content. As shown in Table 1, silica content
of the fly ash used in this study was 76% as compared to
32% in GGBFS. The higher silica content of fly ash can
produce more C–S–H gel as a result of pozzolanic reaction
and reduce porosity. Therefore, the fly ash mortar specimens
exhibited lower VPV as compared to the GGBFS specimens.
Also, with 50% sand replacement by FNS, mortars using
30% fly ash or GGBFS either improved VPV or kept it at the
same level as it was with 100% OPC mortars with natural
3.3 Effect of Wet–Dry Cycles
3.3.1 Strength and Mass Changes by the Wet–Dry
The specimens were exposed to 28 cycles of 15 h of
wetting in water following by 8 h of oven drying at 110 C.
Typical images of the specimens of PC-FNS series
containing 100% FNS aggregate before and after the wet–dry
cycles are shown in Fig. 6. No visible signs of cracking or
damage were found in any of the specimens after the wet–
dry cycles. However, some thin whitish deposit was
observed on the surface after the wet–dry cycles. This thin
deposit on the surface is believed to be caused by leaching
out of some hydrated product from inside of the specimens.
The compressive strengths after 28 cycles of alternate
wetting and drying are shown in Fig. 7. The 56-day
compressive strengths of the specimens in normal condition are also
plotted in these figures for comparison. The effects of
FNS content (%)
Fig. 6 (a) PC-FNS100 before wet–dry cycles and (b)
PCFNS100 after wet–dry cycles.
Fig. 8 Relative strength loss after wet–dry cycles for different
Compressive strength before test Compressive strength after test
possible damages in the specimens by cycles of thermal
expansions and contractions, as well as the cycles of
moisture movement and shrinkage are considered to reflect in the
Figure 8 shows the percentage changes of compressive
strength after completion of the wet–dry cycles for various
proportions of FNS aggregate. It can be seen that the control
specimen with no SCM and 100% natural sand (PC-FNS0)
had a strength loss of 12% after the wet–dry cycles. The
strength losses of the other mortar specimens with no SCM
were 16, 20, 22 and 24% for 25, 50, 75 and 100% FNS
aggregate, respectively. Thus, strength loss of the specimens
with no SCM increased from 12 to 24% due to complete
replacement of natural sand by FNS aggregate. Similar
reductions of strength by wet–dry cycles were also observed
by other researchers using different types of manufactured
fine aggregates. A previous study by
Manso et al. (2006)
reported 30–50% strength loss of concrete containing EAF
slag aggregate after exposure to wet–dry cycles. Another
Yu¨ksel et al. (2007)
reported 20–40% strength loss
by 25 cycles of alternate wetting and drying using blast
furnace slag and bottom ash as fine aggregates. Therefore, it
can be said that the FNS aggregates used in this study
showed better performance than EAF, blast furnace slag and
bottom ash fine aggregates in the exposures of wet–dry
cycles. The increased volume of permeable voids by FNS
aggregate, as shown in Fig. 5, can increase the penetration of
water into the specimens. The higher water penetration can
cause higher vapour pressure in the specimen and result in
higher strength loss, as shown in Fig. 8.
The observed strength loss by wet–dry cycles is attributed
to three primary reasons. Firstly, thermal expansion and
contraction by alternate heating and cooling cycles may
develop internal micro-cracks. Secondly, the vapour pressure
in the drying period may cause some internal damages.
Thirdly, leaching out of some hydrated product by alternate
wet–dry cycles, as shown by the thin surface deposit in
Fig. 6, may weaken the bond between binder matrix and
aggregate. The combination of these effects is considered to
cause the observed strength loss of specimens after the wet–
As shown in Figs. 6 and 7, the trend of strength loss in the
mortar series with 30% GGBFS were similar to those of the
specimens with no SCM. The values of strength loss in the
specimens of this series varied from 9% for no FNS to 24%
for 100% FNS. On the other hand, the mortar mixes with
30% fly ash showed less strength loss after the wet–dry
cycles. In fact, there was an increase of strength by 3.38% in
the specimens containing 100% natural sand and no FNS
aggregate. The strength losses were 2.67, 6.13, 8.38, and
9.26% for the specimens containing 25, 50, 75 and 100%
FNS fine aggregate, respectively. The increase of
compressive strength for the specimens without FNS aggregate was
because of the pozzolanic reaction of fly ash during the
cycles of wetting and drying. The availability of moisture
and high-temperature (110 C) during the exposure period
accelerated the pozzolanic reaction of fly ash causing less
strength loss in the specimens containing FNS aggregate. In
addition, the strength loss due to wet–dry cycle is also
related to the porosity and water absorption of the samples.
The samples with lower porosity and water absorption
exhibited less strength loss due to wet–dry cycles. The
volume of permeable voids was reduced by fly ash, as shown
in Fig. 5. This resulted in less strength loss after wet–dry
cycles of the specimens with fly ash as compared to the
specimens of other two binder series. With 50% sand
replacement by FNS, mortars using 30% of GGBFS showed
strength loss of the same order as it was for the 100% OPC
mortars with natural sand. On the other hand, mortars using
30% fly ash showed a large improvement of strength loss as
compared to the 100% OPC mortars with natural sand.
The mass loss values during the wet–dry cycle are
presented in Fig. 9. It can be seen that mass loss increased
almost linearly with the increase of FNS content for all three
binder series. The mass loss varied from 4% to 6.2% and the
trends were similar to those of strength loss. An increase of
mass loss by about 30% was observed in a binder series for
40 50 60
FNS content (%)
the use of 100% FNS aggregate as compared to that with
100% natural sand.
3.3.2 XRD Phases After the Wet–Dry Cycles
The mineralogical phases of mortar specimens were
determined by XRD analysis after the wet–dry cycles. The
XRD pattern of the mortar with no SCM and no FNS
(PCFNS0) is presented in Fig. 10a. It can be seen that the
specimens of PC-FNS0 had a high amount of crystalline
minerals and the majority of them was quartz (SiO2). In
addition, small amounts of portlandite (Ca(OH)2), zeolite
(NaAlSi2O6Br (H2O)2) and biotite
(K(MgFe)3AlSi3O10 (OH)2) were observed in the phase analysis. Quartz
mineral is known for its chemical inertness and high
resistance to mechanical weathering. For this reason, the
specimens containing 100% natural sand had comparatively less
strength and mass losses after the wet–dry cycles as
compared to the specimens containing different percentages of
Figure 10b presents the XRD pattern of a specimen
containing 100% FNS aggregate and no SCM (PC-FNS100). It
can be seen that this specimen contained a significant
amount of amorphous minerals. Furthermore, there was a
significant decrease in the intensity of quartz phase as
compared to the specimens with 100% natural sand.
Moreover, a considerable number of peaks containing forsterite
(Mg2SiO4), forsterite hydrous (Mg2SiO3 OH), forsterite
ferroan (MgFeSiO4), forsterite hydrous ferron
(MgFeSiO3 OH) and andradite (Ca3Fe2Si3O12) can be observed.
These phases were originated from FNS. The forsterite
ferroan has an affinity to attract hydroxyl ion and form
forsterite hydrous and forsterite hydrous ferroan. Thus, during
the wetting cycles, the FNS mortar samples absorbed a
higher amount of water that increased vapour pressure in the
drying cycle. As a consequence, strength loss of the
specimens increased by the addition of FNS aggregate, as shown
in Fig. 8.
1. Forsterite = f
2. Andradite = a
3. Portlandite = p
4. Forsterite ferroan = ff
5. Forsterite hydrous = fh
6. Forsterite hydrous ferroan = fhf
7. Quartz = q
1. Forsterite = f
2. Portlandite = p
3. Calcium silicate = Cs
4. Calcite = c
5. Quartz = q
6. Forsterite ferroan = ff
7. Forsterite hydrous = fh
8. Forsterite hydrous ferroan = fhf
The XRD plot of a specimen with 30% GGBFS and 100%
natural sand (BFS-FNS0) is shown in Fig. 10c. It can be
seen that the main minerals of these samples are quartz,
portlandite, zeolite and biotite, which are similar to those of
the PC-FNS0 samples. There were prominent peaks of
portlandite analogous to the samples of PC-FNS series.
These high peaks of portlandite is an indicator of relatively
less pozzolanic reaction of GGBFS than fly ash, as shown by
the strengths in Fig. 6.
The XRD plot of the specimen with 30% GGBFS and 100%
FNS (BFS-FNS100) is presented in Fig. 10d. It can be seen
that the samples were composed of forsterite, forsterite
ferroan, forsterite hydrous, forsterite hydrous ferroan, andradite,
portlandite, and quartz. As expected, the majority of the peaks
consisted of forsterite from FNS aggregates. Again, the high
portlandite peaks indicate relatively less pozzolanic reaction
of GGBFS. As a result, the strength loss of these specimens
was similar to the samples with 100% OPC.
Figure 10e shows the XRD pattern of the specimen with
30% fly ash as SCM and 100% natural sand (FA-FNS0). A
significant reduction in the intensity of portlandite peaks can
be seen in this XRD pattern as compared to that of the
specimen with 100% OPC shown in Fig. 10a. Besides,
formation of calcite (CaCO3) and calcium silicate (Ca2O4Si)
is also noticeable in the XRD data. The formation calcium
silicate indicates the considerable pozzolanic reaction of fly
ash. The calcium silicate absorbs moisture and generated
amorphous calcium silicate hydrate (C–S–H). The reaction
can be generalised as Eqs. 1 and 2.
CaðOHÞ2 þ H4SiO4 !
CaH2SiO4 þ 2H2O
CaH2SiO4 þ 2H2O ! CaH2SiO4 2H2O
The formation of calcium silicate hydrate
(CaH2SiO4 2H2O) as a product of the pozzolanic reaction is known
to increase compressive strength. Which is the primary
reason for strength improvement of the specimen FA-FNS0,
as shown in Fig. 7.
The XRD results of a sample with 30% fly ash and 100%
FNS as aggregate (FA-FNS100) is presented in Fig. 10f. The
phases of forsterite, forsterite ferroan, forsterite hydrous,
forsterite hydrous ferroan, andradite, portlandite, calcium
silicate and calcite can be seen in the XRD. The majority of
minerals are forsterite due to 100% FNS aggregate of the
specimen. Again, the XRD plot shows the formation of C–
S–H, which is an indicator of the pozzolanic reaction of fly
ash. As a consequence, less strength loss as compared to
other two binder series was observed, as shown in Fig. 8.
In summary, the cycles of alternate wetting and drying at a
high temperature (110 C) favoured pozzolanic reaction of
fly ash that resulted in strength improvement of specimens,
as shown in Fig. 7. However, the use of FNS aggregate
caused internal damages of specimens subjected to alternate
wetting and drying.
By-product FNS was used as 25–100% replacement of
natural sand with 30% fly ash or GGBFS as SCM. The
strength and mass changes of mortar specimens subjected to
an accelerated weathering condition was studied as an
indicator of the long-term durability. The accelerated
condition consisted of 28 cycles of alternate drying at 110 C for
8 h and wetting under water at 23 C for 15 h. The
following conclusions are drawn from the study:
1. The maximum 28-day compressive strength was
achieved for mortar using 50% FNS as replacement of
2. The volume of permeable voids varied from 12 to 19%
showing an increasing trend with the increase of FNS
content. However, VPV decreased with the use of SCM.
3. The alternate wet–dry cycles reduced strength of all the
specimens except an increase for the mortar containing
100% natural sand and 30% fly ash. The mass loss
varied from 4% to 6% showing a similar trend of the
4. The losses of strength and mass are considered to be
mainly because of alternate thermal expansions and
contractions, shrinkage and swelling and internal vapour
5. As evidenced by XRD, use of fly ash compensated some
losses of strength by improving the volume of
permeable voids through pozzolanic reaction.
6. Therefore, the use of FNS as a partial replacement of
natural sand together with an SCM can be considered as
a potential application of this by-product in cement
The authors acknowledge the contribution and support of
SLN through its research department.
This article is distributed under the terms of the Creative
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