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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: khalid@liverpool.ac.uk

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: a.t.ahmed@liv.ac.uk

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