quantification of the properties of enzyme treated and untreated incinerator bottom ash waste used...
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Quantification of the properties of enzyme treated anduntreated incinerator bottom ash waste used as roadfoundationAbdelkader Ahmed a & Hussain A. Khalid ba Engineering School , University of Liverpool , Room 614, Brodie Tower, Brownlow Street,Liverpool, L69 3GQ, UKb Engineering School , University of Liverpool , Room 610, Brodie Tower, Brownlow Street,Liverpool, L69 3GQ, UKPublished online: 04 Jan 2011.
To cite this article: Abdelkader Ahmed & Hussain A. Khalid (2011) Quantification of the properties of enzyme treated anduntreated incinerator bottom ash waste used as road foundation, International Journal of Pavement Engineering, 12:03,253-261, DOI: 10.1080/10298436.2010.535537
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Quantification of the properties of enzyme treated and untreated incinerator bottom ash wasteused as road foundation
Abdelkader Ahmeda1 and Hussain A. Khalidb*aEngineering School, University of Liverpool, Room 614, Brodie Tower, Brownlow Street, Liverpool L69 3GQ, UK; bEngineering
School, University of Liverpool, Room 610, Brodie Tower, Brownlow Street, Liverpool L69 3GQ, UK
(Received 29 December 2008; final version received 20 September 2010)
A substantial amount of incinerator bottom ash (IBA) waste is generated annually from burning municipal solid waste. IBAis similar to aggregate consisting of ferric metals, non-ferrous metals, brick and tile fragments, ceramic, glass, stone, dirt,etc. In this work, IBA waste was mixed with conventional limestone aggregate in an attempt to achieve a blend withacceptable mechanical properties and minimum environmental risks for use in road foundation layers. Enzyme treatmentwas applied in order to improve the behaviour of IBA–limestone blends. A series of laboratory tests, such as cyclic triaxialcompression tests, pH monitoring and scanning electron microscope, were adopted to determine the materials’ mechanisticbehaviour and microstructure characteristics. Emphasis was on examining the effect of various parameters, such as IBAcontent, enzyme content, moisture content and curing time. Results of this study showed that IBA blends gave a favourableperformance as road foundation layers in comparison with the control limestone blend. Microstructure and chemicalanalysis results showed that the addition of plant-based enzyme improved the mechanical properties of the control limestoneblend; however, it did not have any noticeable effect on the IBA blends.
Keywords: incinerator bottom ash; enzyme; triaxial test; scanning electron microscope; chemical analysis
Introduction
Incinerator bottom ash (IBA) is a residual by-product
material produced by incinerating municipal solid waste
(MSW). In the past, IBA presented a widespread waste
disposal problem; however, various reuse and recycling
approaches have been adopted in recent years to mitigate
this problem, as well as to provide a useful alternative to
using primary aggregate resources. The engineering
properties of IBA as aggregate in road construction were
investigated in a number of research studies. Demars et al.
(1994) stated that bottom ash can be utilised as structural
fill, embankment materials and in pavement surface and
base courses. Pandeline et al. (1997) concluded that the
unconfined compressive strength of compacted bottom ash
was similar to strengths exhibited by compacted fine-
grained soils, and allowing compacted bottom ash to age
increased the compressive strength. Arm (2003) reported
that MSW bottom ash can replace not only sand but also
natural pavement gravel in unbound layers, if the content
of organic matter is kept low.
Stabilisation of subgrade and road foundation layers,
i.e. subbase and capping, is a common process to improve
the materials’ properties in anticipation of severe weather
and service conditions. Additives, e.g. cement and lime, are
adopted to modify and improve strength and durability
properties of road foundation materials; however, only a
few studies have been conducted where liquid enzymes
were used to stabilise the properties of subgrade and
unbound granular materials used in road pavement
foundation. Velasquez et al. (2006) concluded that
the enzyme adopted in their study improved the chemical
bonding that helps to fuse the soil particles together,
creating a permanent structure that is more resistant to
weathering, wear and water penetration. Velasquez et al.
(2006) also observed that the type of soil, per cent of fines
and chemical composition are properties that affect the
stabilisation mechanism. In addition, Wright-Fox et al.
(1993) reported that enzymes may increase soil shear
strength and that soil stabilised with enzymes should be
considered but only on a case-by-case basis. Scholen (1992)
indicated that failures encountered in enzyme-stabilised
subgradeswere due to application to thewrong soil type and
gradation. This suggests that it may still be unclear as to
how and under what conditions this and other enzyme
products work with soils. The surveyed literature revealed
that the use of enzyme stabilisation has not been subjected
to a considerable amount of research and is, thus, still in
need of further investigation and development.
This work focuses on the characterisation of the
behaviour of IBA blends for road foundations and the use
of a liquid enzyme treatment to improve their mechanical
properties. The study also considers some of the important
factors that affect the mechanical performance of these
ISSN 1029-8436 print/ISSN 1477-268X online
q 2011 Taylor & Francis
DOI: 10.1080/10298436.2010.535537
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*Corresponding author. Email: [email protected]
International Journal of Pavement Engineering
Vol. 12, No. 3, June 2011, 253–261
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blends. Cyclic triaxial tests (CTTs) were adopted to
determine the blends’ resilient modulus, which is an
essential parameter for mechanistically based pavement
design methods.
Additive technology often considers the microstruc-
ture characteristics of blends in order to elucidate the
interactions between components that lead to property
change. Chang (1995) used microscopic analysis to study
the stabilisation of granular soil modified with fly ash and
he concluded that the microstructure study confirmed the
existence of significant beneficial reactions, which
explained the improvement in strength and resilient
modulus due to the stabilisation process. Bhuiyan et al.
(1995) investigated the strength increase due to carbonate
cementation for base course materials stabilised with lime
using X-ray diffraction analysis. They indicated that X-ray
results showed the absence of clay minerals, which
affected the pozzolanic reaction between lime and
aggregate. In this study, scanning electron microscope
(SEM) and energy-dispersive X-ray spectrometry (EDXS)
were adopted to examine the physical and chemical
features of the enzyme stabilisation of IBA blends.
Materials
Four materials were used in this study: IBA, limestone,
enzyme solution and NaOH buffer. IBA was supplied in two
sizes: 20–10 and 10 mm to dust. Limestone was chosen as
the control aggregate in the mixtures. It was supplied in six
sizes: 20, 14, 10, 6 and 4 mm – dust and filler. The ‘as-
received’ enzyme solution is a thick white liquid containing
plant-based proteins in three different concentrations,
namely, 0.1, 0.3 and 0.5 g/l with 0.005 g/l potassium sorbets
as preservative. The enzyme solution was diluted prior to
application as 1 cc of enzyme per 500 cc of tap water. Then,
these new diluted solutions were mixed with blends
according to their optimum water contents. The chemical
composition of the diluted enzyme solution is presented in
Table 1, under ‘Chemical analysis results’ section. The
NaOH buffer consisted of 0.5 unit of sodium hydroxide with
one unit of water. The buffer was mixed with enzyme in two
concentrations: one unit of enzyme to one unit of buffer and
one unit of enzyme to five units of buffer. The samples were
divided into four groups, coded as A, B, C and D. Group A
was the control blend of limestone only, group B had 30%
bottom ash and 70% limestone, group C had 50% of each of
IBA and limestone and group D had 80% IBA. The particle
size distribution of the blends is presented in Figure 1.
Mechanical properties
Cyclic triaxial test
The CTT was conducted to study the resilient modulus of
the four blends. It was performed on cylindrical specimens,
placed in a cell, under a confining pressure, s3, and a
Table 1. Chemical analysis of the blends.
Element
Diluted enzymesolution of 0.5 g/l
(mg/l)Blend A(mg/kg)
Blend B(mg/kg)
Blend C(mg/kg)
Blend D(mg/kg)
Arsenic 0.01 1.7 1.9 2.6 3.1Calcium 16 290,000 200,000 160,000 71,000Cadmium 0.001 28 20 14 6.0Chromium 0.05 3.3 11 23 26Copper 0.02 7.3 630 930 930Potassium 3 18 240 310 490Magnesium 2 21 130 190 250Sodium 9 87 1900 2800 2900Nickel 0.05 4.9 15 42 53Lead 0.05 32 920 250 260Zinc 0.10 400 790 1600 1300Aluminium 0.10 580 9700 1900 20,000Sulphur (free) 1 100 100 100 100Total sulphate as SO4 24 0.08 0.36 0.41 0.57Silicon – 510 4400 6200 6900Water soluble chloride 10 0.01 0.06 0.09 0.14
Figure 1. Particle size distribution of the blends.
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vertical stress, s1. The type of cyclic loading applied was
constant confining pressure, where the axial stress was
cycled. In order to study the resilient behaviour, cured
specimens were tested according to the AASHTO TP46
protocol (FHWA 1996) for base/sub-base materials in which
a constant stress ratio was maintained by increasing both the
principal stresses simultaneously. The procedure consisted
of applying cyclic conditioning to the sample followed by a
series of cyclic loadings along different stress paths. The
objective of the conditioningwas to eliminate the permanent
deformations occurring during the initial load cycles of the
test, and to obtain stable resilient behaviour independent of
the number of cycles. Test results represent the average of
three identical samples.
Sample preparation
Cylindrical specimens of 100 mm diameter and 200 mm
height were prepared in a split-steel mould. Aggregates
were placed in the mould in three layers and compacted for
30 s each using a 30-kg vibrating hammer with a tamping
foot attachment that had a diameter equal to the internal
diameter of the compaction mould. The surface of each
layer was manually roughened before adding the next
layer on top; in this way, a good layer interlock and a
homogeneous sample was obtained. Specimens were kept
in the steel mould for 24 h within a plastic sheet to seal
them. Meanwhile, a membrane was placed on a stretcher
to which vacuum was applied. The membrane was then
carefully placed on the specimen. The stretcher was
removed from the membrane by switching off the vacuum.
After placing the rubber membrane around the specimen,
the specimen was kept in a humid environment at 208C for
7 days to allow for uniform distribution of water within the
specimen and for any pozzolanic reactions as well. After
7 days, the specimen was attached to the top and bottom
platens with rubber rings and was then installed in the
triaxial cell. Specimens were kept under the same curing
conditions and further tests were conducted after 14 and
28 days from the time of manufacture.
Mechanical test results
The resilient modulus is defined as the ratio of deviator
stress to recoverable strain under repeated loading. It is
generally considered as an appropriate measure of the
elastic property and stiffness of soil and unbound materials
(Seed et al. 1962).
K-u model
The effect of different blend properties was studied using a
well-known curve-fitting tool named the K-u model. It is a
non linear, stress-dependent power function model
described by Seed et al. (1962). The model is given as
follows:
MR ¼ K1uK2 ; ð1Þ
where MR is the resilient modulus, K1 and K2 are the
regression constants, and u ¼ bulk stress ¼ s1 þ s2 þ
s3. The model fits the experimental results well, with
coefficient of determination, R 2, values ranging from 0.86
to 0.99. Here, the model has been adopted to demonstrate
the influence of various parameters on the material’s
resilient modulus, as is shown in the following sections.
Effect of IBA content
Figure 2 shows resilient modulus results as a function of
bulk stress for blends with different IBA contents at
optimum moisture content (OMC). It is shown in Figure 1
that the particle size distribution of blends A, B and C is
quite close, thus enabling direct comparison of the impact of
the relative proportions of IBA and limestone on the
resilient modulus. It can be clearly seen from Figure 2 that
blends B and C have higher resilient moduli than the
limestone blend. This means that adding up to 50% IBA
improves the blend’s deformation characteristics, probably
because IBA improves interlock between particles and
initiates a pozzolanic reaction as well. Blend D with 80%
IBA, on the other hand, had a somewhat coarser particle size
distribution than the other three blends, thus, it would seem
difficult to attribute any observed differences in modulus
values purely to material type. It would be reasonable to
conceptualise that the relatively weaker IBA particles
coupled with coarser grading would lead to a reduction in
the blend’s modulus value, whereas any pozzolanic
reactions coupled with improved interlock would help
increase this value by comparison with that of the control
limestone blend. Blend D exhibited nearly the same resilient
behaviour as the control blend A as seen in Figure 2,
indicating a neutral net impact of the aforementioned
factors.
Figure 2. Effect of IBA content at OMC.
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Effect of moisture content
To investigate the effect of water content, three levels
were used, namely OMC, 2% less than OMC and 2%
higher than OMC. From Figure 3, it is observed that the
average resilient modulus increases with a decrease in
water content for all the blends in general, although with
relatively less clarity for blends C and D at 50 and 80%
IBA. This inverse trend is in line with results in the
published literature, which reported that an increase in
water content above the optimum in unbound granular
materials in the laboratory and in the field had led to a
decrease in resilient modulus (Hicks and Monismith
1971). The combination of a high degree of saturation and
low permeability, due to poor drainage, leads to high pore
pressure and low effective stress and, consequently, low
stiffness, low resistance to permanent deformation and
high-resilient deformation (Dawson et al. 1996).
Effect of enzyme addition
Figure 4 shows that the addition of enzyme at Day 7
increased the average resilient modulus of blend A and of
limestone only by 40%. From Figure 5, it can be seen that
the addition of the enzyme had a pronounced effect on the
resilient modulus of blend A during the first 14 days of
curing, where the average resilient modulus increased
significantly from 7 to 14 days by 51%. However, the
increase was very small from 14 to 28 days. With regard to
blends B, C and D, i.e. 30, 50 and 80% IBA, respectively,
enzyme addition led to a small increase in resilient
modulus after 14 days. Figure 6 shows the effect of curing
time on resilient modulus for blend C. Blends B and D,
although not shown here, exhibited similar trends. When
compared to Figure 5, it can be seen that the blend type and
IBA content significantly affected the impact of the
treatment. Velasquez et al. (2006) concluded that the type
of soil, per cent of fines and the chemical composition are
properties that affect the stabilisation mechanism. There-
fore, special attention should be paid to select the proper
treatment to be used for different soils.
To examine the enzyme content effect, three levels
were used, namely 0.1, 0.3 and 0.5 g/l. Figure 7 shows that,
for blend A, the enzyme effect increases with an increase
in enzyme content. However, Figure 8 shows that the
resilient modulus of blend B was either unaffected or
decreased with an increase in enzyme content. Blends C
and D exhibited similar behaviour to blend B, although the
results are not shown here for brevity and to avoid
repetitiveness.
Figure 3. Effect of water content.
Figure 4. Effect of enzyme addition at Day 7 for blend A.
Figure 5. Effect of adding 0.5 g/l enzyme on blend A atdifferent curing times.
Figure 6. Effect of adding 0.5 g/l enzyme on blend C atdifferent curing times.
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Effect of enzyme application rate
To examine the effect of enzyme application rate, two
markedly different enzyme rates of the solution with 0.5 g/l
enzyme concentration were used. The first is one unit of
enzyme solution to 500 units of water based on
recommended values in the surveyed literature. Several
studies have recommended an enzyme application rate of
1–2 cc in 1 l water solution, which implies application rates
of 1:1000 and 1:500, respectively (Tolleson et al. 2003;
Marasteanu et al. 2005; Velasquez et al. 2006). Both
application rates were tried but only one set of results is
presented here, i.e. that for 1:500, because they were similar.
The second enzyme solution is one unit of enzyme solution
to one unit of water. The reason for using such a widely
different rate was mainly to investigate the effect of very
high enzyme concentration values to establish credence of
the recommended application rates in the literature.
For blend A, Figures 9 and 10 show that, while the
modulus continued to increase with curing period from 7 to
28 days, the enzyme effect decreased with an increase in its
concentration in water. It seems that higher dosages of
enzyme might actually be harmful, i.e. results in a reduction
in the resilient modulus below that of the 1:500
concentration and even below the levels observed for
untreated samples. It was noticed that the use of the
recommended application rate for the enzyme adopted in
this study, i.e. 1:500, improved the effectiveness of the
stabilisation process with the limestone blend more than the
higher application rate. This tendency is probably due to the
fact that enzyme activity is quite sensitive to pH value and
the enzyme concentration, whereby an increase of the
enzyme molecules in the solution changes its pH and also
stops the enzyme’s catalytic reaction (Worthington 2009).
For IBA blends, neither of the enzyme application
rates had led to a positive impact on MR, as seen in Figure
11 for blend D, with the more negative result being for the
lower enzyme concentration; no feasible explanation can
be provided for the different impact between the two
application rates. The negative enzyme effect may be
because the IBA material works as an inhibitor of the
enzyme’s activity, or it has insufficient substrate molecules
to accelerate the binding reaction. In addition, studies by
Wright-Fox et al. (1993) and Worthington (2009) asserted
that some enzymes speed up the reaction and others slow it
down, which may indicate that this type of enzyme is
inappropriate to interact with the IBA materials.
Effect of using NaOH buffer with enzyme
The concept of ‘buffering’ refers to the improved
resistance to pH changes of partially neutralised solutions
of weak acids or bases on the addition of small amounts of
Figure 7. Effect of enzyme content at Day 14 curing time forblend A.
Figure 8. Effect of enzyme content at Day 14 curing time forblend B.
Figure 9. Effect of enzyme application rate at Day 7 curingtime for blend A.
Figure 10. Effect of enzyme application rate at Day 28 curingtime for blend A.
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strong acid or base. Buffers consist of an acid and its
conjugate base, such as carbonate and bicarbonate, or
acetate and acetic acid. The quality of a buffer is dependent
on its buffering capacity, i.e. resistance to change in pH by
the addition of strong acid or base, and ability to maintain a
stable pH upon the dilution or addition of neutral salts.
In this study, the impact of NaOH buffer addition to the
enzyme at 0.5 g/l concentration was investigated in an
attempt to improve the enzyme’s effect on the IBA blends
by providing and keeping a high alkalinity environment
for the enzyme. Thus, buffer addition to the enzyme was
applied only to blend D as the worst-case scenario of all
the IBA blends.
Figure 12 shows that after 7 days, the resilient modulus
of blend D was not sensitive to the addition of the enzyme
and also, in the case of adding the NaOH buffer to the
enzyme, the blend’s resilient modulus decreased. Further-
more, Figure 13 confirms that the use of the enzyme with
and without the buffer, after 28 days, still led to a decrease
in the resilient modulus of blend D.
Chemical properties
pH monitoring
To explore the extent of enzyme interaction with
aggregates, pH monitoring was adopted for limestone
and IBA materials mixed with the enzyme. From Figure 14,
the pH values after 1 and 24 h for limestone and IBA were
about 12 and 10, respectively, indicating very little change
in the alkalinity value due to incomplete reaction. It is clear
that, initially, limestone is more alkaline than IBA due to
the presence of calcium. After 28 days, as the enzyme
reacts with limestone, depleting the free calcium; results
showed a drop in the limestone alkalinity but in contrast,
there is no significant change for IBA. This indicates that
IBA acts in a similar manner to a strong buffer, as it keeps
the solution at an approximately constant pH value. In a
trial to provide an appropriate environment for the enzyme
to work successfully with IBA, NaOH was added at
different levels to the enzyme and blend D, with 80% IBA,
to increase the blend’s alkalinity. Figure 15 shows that
mixing IBA with the enzyme increased its solution’s pH
value from 8 to 8.5. Similar pH values were obtained
irrespective of NaOH; thus, increasing the solution’s
alkalinity did not change the reactivity.
Chemical analysis results
The chemical composition of IBA blends was monitored
twice, firstly by the chemical analysis for the dry blends,
Figure 11. Effect of enzyme application rate at Day 28 curingtime for blend D.
Figure 12. Effect of enzyme and NaOH buffer at Day 7 on theresilient modulus of blend D.
Figure 13. Effect of enzyme and NaOH buffer at Day 28 on theresilient modulus of blend D.
12
141 hour24 hours28 days
10
8
6
pH
4
2
0Water Enzyme W+Enz Ls+W
+Enz
Materials
IBA+W+Enz
Figure 14. pH monitoring.
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before adding the water and enzyme solution, and then by
the EDXS analysis to show the chemical change resulting
from the addition of water and the enzyme solution. EDXS
results are described in a later section.
Table 1 shows results of the bulk chemical analyses for
the added water, necessary for blend compaction and
curing, after incorporating the treatment enzyme. Results
are also presented in Table 1 for dry blends A–D before
adding the solution of enzyme in water. The materials’
chemical compositions indicated that, for example, blend
A had high calcium content and the IBA blends had high
contents of aluminium and silicon. Therefore, these
elements are important for the enzyme to be effective and
for the pozzolanic activity of the blends, as will be
explained in the microscopic analysis.
Mineralogical properties
Microscopic analysis
SEM and EDXS tests were adopted to study the physical
features of IBA blends and identify the nature of the
materials and any secondary reaction elements, especially
after mixing with water, with and without enzyme.
Sample preparation
Due to the particle size restriction for SEM examination,
special samples were prepared by crushing the materials
and sieving them through 2.36 mm sieve. This size range
was small enough to allow whole particles to be seen at the
lowest SEM magnification available, but was also much
larger than the size of individual mineralogical features
within the particles. The materials were mixed with water
with or without enzyme and the mixture was placed into a
5-cm diameter and 1-cm high stainless steel mould and
then kept in a humidity chamber for curing at 208C and
99% humidity for 28 days. Before SEM examination,
samples were subjected to vacuum to remove the free
water and coated with gold. The metal coating was used to
increase the conductivity of the materials to improve the
SEM examination quality.
SEM examination
Figure 16 shows the SEM photographs of untreated and
treated blends A and D, where it is evident that the
enzyme-treated limestone blend A has tightly cross-linked
interfaces in spite of their prominence and a denser surface
microstructure than the untreated blend. From Figure
16(c),(d), it can be seen that the untreated 80% IBA blend
exhibited a good external appearance in terms of its
microstructure surface, which is denser than the treated
blend. It was also found that the untreated blend had fibre-
shaped minerals, shown by a circle in Figure 16(c) and in a
large magnification in Figure 16(e), which are a likely
indication of pozzolanic activity (Bhuiyan et al. 1995).
This may also provide possible evidence regarding the
negative enzyme effect on the IBA blends as these fibres
could not be seen in the treated blends.
EDXS examination
EDXS is a non-destructive analytical technique used for
the elemental analysis or chemical characterisation of
materials. As a type of spectroscopy, it relies on the
investigation of a sample through interactions between
electromagnetic radiation and matter. SEM and EDXS
have been recently adopted as powerful analysis methods
to study the effect of stabilisation on the materials’
properties in a number of research studies (Bhuiyan et al.
1995, Chang 1995, Krzanowski et al. 1998). In this study,
the EDXS technique was adopted to examine the chemical
effect of the enzyme on IBA blends. Figures 17 and 18
show the X-ray microanalysis results for treated and
untreated blends A and D. Results show that treated and
untreated limestone blend A had higher Calcium content
than blend D, with 80% IBA. Calcium is most important
for enzyme activity because it has been reported to work
well with organic, e.g. plant based, enzymes. This
probably explains why the enzyme had a positive effect
on blend A and a negative effect on blend D. In addition,
the analysis showed that untreated blend D revealed three
primary elements, Ca, Si and Al, suggesting an aluminium
silicate compound. Krzanowski et al. (1998) confirmed
that the composition analysis of bottom ash particles
revealed the presence of metal oxides, Fe and Al silicates.
Si and Al when combined with water, especially in the
presence of Ca from limestone, hydrate to form the
cementing compounds of calcium–silicate–hydrate and
calcium–aluminates–hydrate. These compounds are
14
127 days28 days
10
8
pH
6
4
2
0Enz D+Enz Enz+N 0.2
Materials
D+Enz+N 0.2
Enz+N1 D+Enz+N1
Figure 15. Effect of NaOH addition. W, water; Enz, enzyme;Ls, limestone; D, blend D; N 0.2 and N 1, NaOH concentration.
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Figure 16. (a) Untreated limestone blend. (b) Treated limestone blend. (c) Untreated 80% IBA blend. (d) Treated 80% IBA blend. (e)Magnification for the part under the circle in (c).
Figure 17. EDXS result for blend A. Figure 18. EDXS result for blend D.
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responsible for the pozzolanic reaction which is perceived
to occur in IBA materials (Becquart et al. 2009).
Conclusions
From the results obtained in this study, the following
conclusions can be made:
. IBA blends gave a favourable performance as road
foundation layers in comparison with the control
limestone blend in respect of their resilient moduli.
On the basis of these results, IBA is recommended
for use in the construction of road foundation layers
as an alternative to natural limestone aggregates.. The K-umodel results showed that IBA behaves like
a conventional aggregate.. From CTTs, blends with 30 and 50% IBA had
higher resilient modulus values than the limestone
control blend. However, the 80% IBA blend
exhibited nearly the same resilient behaviour as
the limestone blend.. The plant-based enzyme improved the mechanical
properties of the limestone only, but it had no
noticeable effect in the case of IBA blends. This
behaviour may be because the IBA material works
as an inhibitor of the enzyme’s activity or it has
insufficient substrate molecules to accelerate the
binding reaction.. Microstructure and chemical analyses indicated that
the addition of enzyme to IBA blends has an
insignificant effect on the bond strength between
particles.
Acknowledgements
The authors are indebted to Aggregate Industries for thetechnical and financial support of this study. The authors alsoextend their gratitude to the technical staff in Material Science,School of Engineering, for their assistance with the SEM andEDXS work. The award of a study scholarship by the Egyptiangovernment to pursue this research programme is gratefullyacknowledged.
Note
1. Email: [email protected]
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