Contribution to mechanical characterization of CDW materials

for low volume traffic roads purposes

Extended abstract

Rosa Maria Matos Pestana

Dissertation to obtain the Degree of Master in

Civil Engineering

September 2008

1

1 - Introduction

In Portugal a lot of aggregates are produced every

year, about 88,3 million tones according to data

from the Union Européenne des Producteurs de

Granulats (UEPG) of 2006 [Gonçalves, 2007], to

be used in the construction activity. The extraction

of large quantities of natural aggregates,

particularly in quarries, damages the environment

seriously, the opening of new places of extraction

being always problematic. Thus, the raw material

is being gradually depleted and the awareness of

the need to recycle materials in order to use them

as aggregates is becoming usual, if in accordance

with the requirements. The recycling of

Construction and Demolition Waste (CDW) is thus

a possible source of alternative aggregates, which

aims to recover the waste, by converting it back

into raw material. Besides that, the recycling of

CDW helps solve problems related to their

management, particularly with the reduction in the

amounts of materials to be placed into

embankments. From the total production of CDW,

about 300 kg per capita in Portugal, only 100 kg

have an appropriate final destination. The

construction of roads is one of the activities with

great ability to reuse these materials, because it

requires large quantities of aggregates, which can

be obtained from the recycling of CDW. So they

can be applied on unbound layers, particularly on

base and sub-base layers. It is then important to

study the CDW, with its chemical, physical and

mechanical characterization in order to obtain

characteristic values for that type of material

allowing the establishment of specifications that

make viable its implementation in road pavements.

The purpose of the study in this work comes from

the need to evaluate the use of CDW, not only

from the point of view of the main geometric,

physical and chemical properties, as already done

in previous works, but also from a mechanical

point of view through tests that can study the

behavior of these materials when applied to

structural layers of roads and exposed to cyclical

stress states due to the repeated traffic. The

physical and mechanical characterization of CDW

was done based on the European standards.

Laboratory tests and also Geogauge, Falling

Weight Deflectometer and Light Falling Weight

Deflectometer tests were made in the Department

of Transportation of LNEC.

The material used in this study resulted from the

crushing of concrete cubes. The choice of this

material is an extensive amount of construction

and demolition waste generated in civil

construction, as it represents the majority of

structural elements such as beams, slabs and

pillars. In this case the term "crushed concrete"

can be used [Woodside, 2007]. The breaking of

the concrete cubes was made by using a crusher

set to 31,5 mm. In order to put the concrete cubes

into the crusher easily it was necessary to reduce

its size manually. The crushing process is a

determining factor in most of the properties of the

aggregates obtained which may vary according to

the type of crusher used.

2 - Mechanical behavior of unbound granular

materials

Description of the mechanical behavior

By applying an axial load to the pavement, the

granular layers are subject to a stress state that

causes strains. When the load is removed, only a

part of the total strain in each direction is

recovered. The strain which is recovered is called

resilient or elastic strain )(rε and the one which

remains is called permanent or plastic strain )(p

ε .

These strains which correspond to deformation of

the granular structure result from resilient and

permanent deformations. The former are

influenced by the application of the load and the

elastic deformation of each particle. The latter are

influenced by the application of the load, the slide

and friction among particles and their crushing.

2

During the first applications of the load, to stresses

far from the collapse state, the permanent

deformation is increasing, resulting from the

accumulation of successive permanent

deformations of each cycle. The resilient

deformation decreases. During this loading period

the material stiffness increases. After a large

number of applications of the load the permanent

deformation tends to stabilize and the deformation

in each cycle is almost totally recovered and it can

be assumed that the material presents an elastic

behavior. This behavior of the granular materials is

characterized by the resilient modulus

r

d

RM

1εσ

=

where )(31

σσσ −=d

represents the deviator

stress and )(1

rε represents the resilient axial strain.

Previous studies refer that the resilient modulus

and the permanent accumulated deformation are

the factors that most influence the structural

response and performance of conventional flexible

pavements, which are typically determined in cyclic

triaxial tests [Kancherla, 2004]. The pavement

layers are exposed to a cyclical loading, due to the

traffic. On that account the resilient modulus is a

more representative property for the

characterization of materials than static properties.

Resistance to fragmentation by Los Angeles

method

The fragmentation test by the method of Los

Angeles characterizes the resistance of the

aggregate to fragmentation, by measuring the

mass loss recorded during the test, and it is

applied to thick aggregates. The test is conducted

according to standard NP EN 1097-2 (2002). The

aggregate specimen of 15 kg, in the particle size

fraction from 10 mm to 14 mm is reduced to 5 kg

and is moved round inside a drum, together with

steel spheres. When submitting the drum to 500

rotations at a constant speed between 31 and 33

rotations per minute, the material is being worn out

and fragmented. The material that passes through

the 1,6 mm sieve, at the end of the test, is

considered worn out. The coefficient of Los

Angeles is expressed as a percentage of the initial

mass of the specimen that goes through the 1,6

mm sieve, after the conclusion of the test, so

50

5000 mLA

−=

where m represents the mass retained in the 1,6

mm sieve, in grams.

Wear resistance of micro-Deval

The micro-Deval wear test is intended to evaluate

the wear resistance of an aggregate specimen,

being described in Portuguese standard NP EN

1097-1 (2002). Its application is appropriate for

natural or artificial aggregates for civil engineering

purposes. An aggregate specimen of 2 kg, in the

particle size fraction from 10 mm to 14 mm is

reduced to two samples of 500 g and each one is

subject to friction with steel spheres inside four

cylinders, together with or without water. The test

ends after 120 minutes of rotations. The material

that passes through the 1,6 mm sieve, at the end

of the test, is considered worn out. Thus, the

micro-Deval coefficient is the percentage of the

original specimen reduced to a size less than 1,6

mm after the conclusion of the test, so

5

500 mM

DE

−=

where m is the mass retained in the 1,6 mm sieve,

in grams.

Cyclical triaxial test

The cyclic triaxial test is a laboratory test for

mechanical characterization of unbound granular

materials, where the load imposed by the traffic

and the pressures caused by the upper layers of

pavement are simulated on a cylindrical sample

previously prepared in the laboratory. As many

3

authors relate, though not totally reproduce the

complex stress state that occurs in situ, it is

considered that it can reflect the real conditions.

Then the resilient and permanent behavior of the

sample is determined and can be used to classify

the performance of the material and calculate the

structural response of the pavement. All the testing

procedures are specified in European standard EN

13286-7. The loading consists in applying an axial

load and a constant or variable confining pressure.

The resilient deformation test consists of two

phases: one of pre-conditioning of the sample

through a several cyclical loadings and another for

the characterization of the resilient behavior. The

former is necessary to secure the stabilization of

permanent deformations and the latter consists in

applying several stress paths during a series of

cycles each. In the permanent deformation test the

pre-conditioning is not necessary. Here the sample

is subject to a large number of cycles of loading for

a unique stress combination.

Load test with Falling Weight Deflectometer

The Falling Weight Deflectometer (FWD) is used in

the evaluation of the bearing capacity of road and

airport pavements, measuring the response of the

pavement to an impact load. It is also a non-

destructive and a fast test, with a good output. In

order to simulate the traffic at a speed of 60 to 80

km/h [Antunes, 1993] the mass is placed at a

certain height and dropped on a rigid plate that

transmits a force to the pavement. That force is

measured by a load cell placed near the plate and

in this central point the maximum deflection is

measured. To a certain distance from the center of

the plate are placed the accelerometers that

measure the vertical displacement of the surface

(deflections) in those points. The diameter of the

plate, the fall height of the mass, the number of

sensors used and the distance between them may

vary. These variations occur according to the aims

set for the test and the characteristics of the

pavement in study [Alves, 2007]. The data

acquisition is done on a computer which is set in

the towed vehicle. The impact loads applied can

reach 300 kN depending on the FWD type.

Load test with Light Falling Weight Deflectometer

The Light Falling Weight Deflectometer (LFWD) is

a portable version of the falling weight

deflectometer, which has the advantage of being

able to be used in areas of difficult access. It gives

immediate information in situ for a quick evaluation

of pavement characteristics. It is based on the

ASTM E2583-07. This device allows the deformed

surface to be determined by measuring the

deflections originated by the application of the

load, in a non-destructive way. A mobile mass is

lifted manually to a certain height (maximum of

0,80 m) and dropped on a set of shock-absorbers,

providing an impulse to the load plate and the

ground. The force applied to the ground by this

impulse is measured by a load cell and the

resulting deflection measured by a central

geofone, and more geofones can be used placed

sideways. The deflections and measured forces

are transmitted to the control system (laptop or

PDA), which through a software can use them to

calculate the modulus of deformability by

c

LFWDdEδσ

75,0=

where σ is the stress applied (kPa), d the

diameter of the plate (m) and cδ the central

deflection (m) [Fortunato, 2005].

Geogauge test

The Geogauge, also known as Soil Stiffness

Gauge (SSG) is an electro-mechanical portable

apparatus, easy handling and low cost of use,

which allows quickly measuring of the stiffness in

situ, without disturbing the ground. It is applied to

compacted layers of soils or aggregates. The

apparatus applies a sinusoidal load on the ground

4

surface and measures the resulting displacement

[HUMBOLDT, 2008], simulating the real conditions

of use. From the ratio between the force applied

(F ) and the displacement suffered (δ ) follows the

ground stiffness ( δFk = ) and with this it is

possible to calculate the modulus of deformability.

With these properties, and evaluating its variability,

it is possible to control the compaction process in a

fast, cheap, safe and precise way, instead of using

the density of the soil as a compaction measure

[Fiedler et al., 1998]. According to the

recommendations of HUMBOLDT (2008), the

contact between the base of the apparatus and the

ground must be at least 60%. This area of contact

is achieved in compacted layers finished with a

regular and leveled surface, requiring little or no

preparation. However, on rough surfaces where

the minimum contact is not assured, it is

recommended to place a thin layer of wet sand.

The elastic stiffness modulus is given by

RHE

SGG77,1

)1(2ν−

=

where SG

H is the reading of the Geogauge

stiffness in MN / m [Nazzal, 2003].

Behavior models for the determination of resilient

and permanent deformation

The Boyce model is one of the most used behavior

models for the determination of resilient

deformation. It is considered a realistic model,

which is characterized by expressions that allow

the calculation of the resilient volumetric strain and

of the resilient distortional strain of crushed

materials, based on cyclic triaxial tests with

variable confining pressure. It can also be

expressed in terms of volumetric compression

modulus and of distortion modulus. In its original

form, the resilient volumetric strain )( νε and

resilient distortional strain )(qε , related to the

average normal stress )(p and the deviator stress

)(q , are given by the following terms:

−=

2

1

11

p

qp

K

n βεν and

=

p

qp

G

n

q

13

1ε

where

1

1

6)1(G

Kn−=β ;

3

231

σσ +=p ;

31σσ −=q ;

and 1K ,

1G and n are constant parameters of the

material, determined in cyclical triaxial tests with

variable confining pressure. The fact of using only

three parameters is the main advantage of this

model.

As Fortunato (2005) refers, the Boyce model can

also be expressed in terms of volumetric

compression modulus )(K and of distortion

modulus )(G , through the expressions:

−

=−

2

1

1

1p

q

pKK

n

β

and npGG −= 1

1.

One of the behavior models for the determination

of permanent deformation with more emphasis is

the Paute et al. model (1994). This model is based

on triaxial tests with variable confining pressure

and it allows the estimation of permanent axial

deformation, depending on the number of load

cycles and on the stress level applied. Besides it is

based on the assumption that the accumulated

permanent deformation increases asymptotically,

being represented by the following expression

[Fortunato, 2005]:

)()100()( *

111NN ppp εεε +=

with

−=−B

p NAN

1001)(

1

*

1ε

where N is the number of load applications;

)(1Npε is the permanent axial strain accumulated

after N cycles; )100(1

pε is the permanent axial

strain accumulated after 100 cycles; )(*1N

pε is the

5

additional permanent axial strain for N > 100 and

1A and B are parameters obtained from the tests.

3 - Description of experimental case study

The identification and characterization of the

laboratory specimen of CDW was based on

particle size distribution, shape index, flakiness

index, Los Angeles fragmentation, micro-Deval

wear, crushed and broken surfaces, sand

equivalent, methylene blue and compaction test.

the results of the tests were compared with the

requirements exposed in the specifications of ex-

JAE currently in force and with the values usually

obtained for this type of material, including the

requirements of the specification LNEC E 473-

2008.

Recycled aggregate characterization, particularly

the structural behavior when placed on unbound

pavement layers, was done through tests on a

sample built in a test pit (Figure 1). This method

allows an adequate control of the building of the

layer and a good approach of the compaction

conditions, to those that are usually found in

pavements. The test pit was built in order to allow

tests on five different points. The dimensions

33,00,20,2 m×× were then admitted and five test

points for Geogauge and LFWD tests and four

points where it was checked the compacted state

and moisture content. Before the construction of

the unbound granular layer the underlying layer

that already existed was characterized. This

characterization was done with surface moisture-

density gauge (Troxler), LFWD and Geogauge, in

order to characterize the existing structure which

will serve as support to the granular layers.

The layer was built with material similar to that

used in laboratory tests referred previously and in

two stages, corresponding to the construction of

two layers, one of about 0,10 m and another

around 0,20 m. For both layers the evolution was

followed along the time, both the equivalent

modulus of deformability, and the moisture content

and density, through the execution of all the tests

on the compaction day and afterwards, until there

is a stabilization of values. The material was mixed

with the quantity of water desired and placed into

the test pit. The compaction of the first layer was

performed using a rammer and the second layer

was compacted with a vibrating roller compactor

(Figure 1). Each layer was built to have a moisture

content 2% under the optimum moisture content

obtained in the compaction laboratory test, 8,8%

and a dry density (DD) with a value of 95% of the

maximum dry density also obtained in the

compaction test, 1,66 g/cm3. The control of these

values was carried out using the Troxler. FWD was

also performed on the layer in order to

complement the CDW mechanical

characterization.

Figure 1 - Test pit (left) and compaction of unbound granular layer (right).

4 - Properties of CDW material

The results of the laboratory tests can be seen on

the Table 1.

Table 1 - Results of the laboratory tests.

Test Result

Particle size distribution

maximum dimension of particles 31,5 mm

fines content 3,8%

material retained on 19 mm sieve 30%

Shape index 19%

Flakiness index 14%

Los Angeles fragmentation 44%

Micro-Deval wear 48%

Crushed and broken surfaces

crushed and broken surfaces 97,8%

totaly crushed and broken surfaces 90,5%

rolled surfaces 2,2%

totaly rolled surfaces 0,5%

Sand equivalent 83%

Methylene blue 0,7 g/kg

Compaction test

optimum moisture content 10,8%

maximum dry density 1,75 g/cm3

The particle size distribution curve (Figure 2)

shows a continuous distribution, however a bit

badly graded what concerns fines particles. It has

6

a higher percentage of material in size between 20

mm and 31,5 mm. As far as the requirements of

the specification of ex-JAE for base and sub-base

layers are concerned, the distribution curve

obtained is outside the limits indicated for natural

materials. It should be noted, however, that this

comparison is made between requirements for

natural materials and the results for the crushed

concrete used.

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

40

37,5

31,520

19,016

14

12,510

9,58

6,3

4,754

2,001

0,5

0,425

0,25

0,180

0,125

0,075

0,063

Sieve (mm)

Cumulative percentage passed (%)

lower limit upper limit distribution curve

Figure 2 - Distribution curve and required limits.

The value obtained in shape index test is slightly

higher than the values usually obtained for natural

aggregates. It can be concluded that the recycled

aggregate, after crushing, has more angular

particles than desirable. The value obtained in

flakiness index test is higher than the value usually

obtained for natural aggregates. However it is

similar to the values usually obtained for CDW. It

should be noted that the flakiness particles are

more fragile particles which can be easily broken,

resulting in a change of the material, which may

not be desirable.

The result of the Los Angeles fragmentation test is

similar to the values usually obtained for this type

of material. The fact it is a higher coefficient

indicates that the material is not very resistant and

it can be worn. This may cause a change of

particles size and the amount of fine particles.

The results obtained in the crushed or broken

surfaces test shows a very low amount of particles

with totally rolled surfaces, included in a small

percentage of rolled surfaces particles. Observing

the crushed or broken particles it can be concluded

that they are all nearly totally crushed or broken.

The value obtained in the sand equivalent test

indicates a clean material, with very little amount of

clay. The value of methylene blue test indicates

the presence of a material with some sensitivity to

water, present in the aggregate. It is considered

that the methylene blue test is more reliable than

the sand equivalent test.

From the results obtained on the compaction test

and the consequent drawing of the distribution

curve it can be concluded that the optimum

moisture content is lower than it is usually obtained

with this type of material.

5 - In situ tests

After layer compaction it is necessary, as refers

Fortunato (2005), to do the tests for quality control

of layers, especially with the Geogauge and

LFWD, immediately after its construction, since the

moisture content tend to fall significantly. It is also

important to take measures with the Troxler every

time, since the modulus of deformability of the

material depends both on the applied load and on

the state of compactness and the moisture

content.

The surface moisture-density gauge Troxler, model

3440, measures, among other parameters, the

percentage of compaction and moisture content of

the aggregate, in a quick easy way. Therefore, it is

an effective method to control the compaction

granular layers. The control made with the Troxler

was done in four points: T1, T2, T3 and T4 (Figure

3). At each point in the first layer, were done tests

at depths 15 cm, 10 cm and at the surface. In the

second layer, the depths was 20 cm, 10 cm and on

the surface. For each depth there were three tests.

The results obtained on the second layer are in

Table 2.

7

Table 2 - Results of the surface moisture-density gauge tests on the second layer.

Tests conducted using Geogauge H-4140 (Figure

3) allow the measurement of stiffness of the

granular layer built and therefore calculate the

equivalent modulus of deformability. This

apparatus reaches a depth of influence of about

0,30 m. Although the surface layer is almost

regular and smooth, a thin layer of wet sand was

placed at the test points, where the surface was

less regular, to ensure the minimum contact

required of 60%. On the sand layer was placed the

apparatus, exerting a slight pressure with rotation.

The test points were P1, P2, P3, P4 and P5. At

each point there were three measurements with a

rotation of the apparatus in between. The results

obtained on the second layer are in Table 3.

Figure 3 - Surface moisture-density gauge test (left) and Geogauge test (right)

Table 3 - Results of Geogauge tests on the second layer.

For the load tests with LFWD was used the model

Prima 100 LFWD. A weight of 15 kg was used and

dropped at a 0,80 m high, on a plate with 300 mm

diameter. The deflections were measured at the

center of the plate through the central geofone.

The surface of the layer, as in the Geogauge test,

must be smooth and regular. At each point, P1,

P2, P3, P4 and P5, were made about ten tests

(Figure 4). The load applied was about 16 kN. The

results obtained on the second layer are in the

Table 4.

Table 4 - Results of LFWD tests on the second layer.

There were load tests with LNEC FWD, model PRI

2100 FWD from Grontmij | Carl Bro. The test was

done on the whole layer, with 30 cm high (Figure

4). A load plate with 300 mm diameter was used,

in order to be equal to the tests performed with the

LFWD. The readings were significant in the center

of the plate and in the first three accelerometers,

with distances of 30 cm, 45 cm and 60 cm from the

center of the plate. The plate is placed in the

center of the built layer (point P3). There were nine

tests, with 25, 30, 40, 50, 60, 70, 80, 90 and 100

cm fall heights. For each of these tests the

deflectometer records two measurements, but only

the second one will be analyzed. These results are

presented in Table 5.

Figure 4 - LFWD test (left) and FWD test (right).

Point test

compaction day

2 days after 5 days after 8 days after

DD (g/cm

3)

w (%)

DD (g/cm

3)

w (%)

DD (g/cm

3)

w (%)

DD (g/cm

3)

w (%)

T1 1,67 8,3 1,71 7,7 1,73 6,9 1,72 6,5

T2 1,68 8,3 1,68 7,7 1,67 7,0 1,67 6,5

T3 1,69 8,1 1,70 7,2 1,69 6,9 1,69 6,3

T4 1,63 8,2 1,65 7,5 1,65 7,2 1,70 6,7

Average values

1,67 8,2 1,68 7,5 1,68 7,0 1,70 6,5

Point test

Average value of the equivalent modulus of deformability (MPa)

compaction day

2 days after 5 days after 8 days after

P1 53,9 111,5 106,3 108,5

P2 56,8 114,0 116,4 94,0

P3 56,2 124,0 126,3 109,3

P4 57,1 105,8 123,6 102,9

P5 56,9 109,4 113,2 114,4

Average values

56,2 112,9 117,2 105,8

Point test

Average value of the equivalent modulus of deformability (MPa)

compaction day

2 days after

5 days after

8 days after

P1 99,0 105,9 136,1 157,8

P2 85,7 114,5 122,6 151,8

P3 81,7 100,8 110,7 125,8

P4 93,2 105,1 133,2 143,0

P5 121,1 169,9 201,4 249,5

Average values

96,1 119,2 140,8 165,6

8

Table 5 - Deflections measured on FDW test.

Fall height (cm)

Load (kN)

D0 (µm)

D30 (µm)

D45 (µm)

D60 (µm)

25 31,42 708 85 36 17

30 37,17 797 114 51 27

40 44,47 909 149 72 38

50 50,16 1007 176 84 44

60 54,77 1085 186 93 51

70 58,7 1168 199 97 54

80 62,31 1263 210 103 68

90 65,05 1346 211 102 57

100 67,52 1422 208 94 55

6 - Results analysis

Surface moisture-density gauge test

Analyzing test results with Troxler, for the second

layer, it can be checked that this has been

compacted with a similar value (8,2%) to the

desired moisture content. However the degree of

compaction desired was reached, with an average

value of 95%. There was a decrease in the

moisture content, as noted in Figure 5. The most

significant decrease takes place on the first day.

Assuming a linear evolution between the days, the

average change in the first two days was -0,35%

per day, followed by -0,17% per day in the three

following days and -0,18% per day until the eighth

day.

6,5

7,5

7,0

8,2

5,0

5,5

6,0

6,5

7,0

7,5

8,0

8,5

9,0

0 2 5 8

Time (days)

Average value of moisture content (%)

Figure 5 - Evolution of the moisture content.

Eight days after the compaction an average value

of moisture content of 6,5% was achieved,

representing a change of -1,7%. A similar

development has been observed in the first layer.

From the results obtained it can be concluded that

the second layer is relatively homogeneous. There

is very little change of the moisture content in the

different test points, related to the average value.

For the change of moisture content with the depth

it seems that the layer should be more uniform. It

seems that it can be concluded that the layer

becomes more uniform with depth as time goes

on.

Geogauge test

The measurement of the modulus of deformability

with Geogauge apparatus in the built layers was

extremely simple, fast and with significant results.

Considering all the values obtained a good

repeatability of the apparatus was reached.

Immediately after the compaction the second layer

presents an average equivalent modulus of

deformability of 56,2 MPa (Figure 6).

117,2

56,2

112,9

105,8

40

50

60

70

80

90

100

110

120

130

140

0 2 5 8

Time (days)

Average value of E GEO (MPa)

Figure 6 - Evolution of the equivalent modulus of deformability measured with Geogauge.

There was an increase of 61 MPa until the fifth

day. From here there was an average daily

decrease of -3,8 MPa. After eight days of

compacting, the equivalent modulus of

deformability measured with the Geogauge is

105,8 MPa, resulting in an increase of 49,6 MPa.

However the value of the equivalent modulus of

deformability does not seem to be stabilized after

those eight days. It follows that it would be

important to follow the remaining evolution of

modulus of deformability. The layer appears to be

relatively homogeneous in terms of equivalent

modulus of deformability. It was also found that the

correlation between the modulus and the moisture

content is high, with a correlation coefficient of

99,2%.

Load test with LFWD

The second layer presented an equivalent

modulus of deformability, after compaction, of 96,1

9

MPa, much higher than the value measured with

the Geogauge. The average trend of development

is observed in all test places, with the equivalent

modulus of deformability increasing more and

more. As shown in Figure 7 it is not possible to

state that the modulus value has stabilized. Indeed

the stabilization of the moisture content was not

previously checked. Until the second day there is

an increase of 23,1 MPa and from then on the

increase is smaller, 7,2 MPa per day to the fifth

day and 8,3 MPa per day to the eighth day. After

the eighth day, the average value of the modulus

of deformability is 165,6 MPa, representing a

change of 69,5 MPa. This layer presents some

variability as it regards the modulus of

deformability measured with the LFWD. The

relationship with the moisture content is total, with

a correlation coefficient of 100%.

96,1

165,6

119,2

140,8

60

100

140

180

220

260

0 2 5 8Time (days)

Average value of E LFWD (MPa)

Figure 7 - Evolution of the equivalent modulus of deformability measured with LFWD.

Load test with FWD

With the deflections obtained on FWD tests it was

possible to estimate the deformability modulus of

the layer. For this purpose an automatic calculation

program (BISAR) was used. The results are

presented in Table 6. It was observed that

deflections measured with the FWD increase with

the intensity of the force applied. The modulus of

deformability increases to the load level of 60 kN

(Figure 8). Knowing the loads with which the

LFWD operate it was possible to represent the

average value of the modulus measured on the

last day of the tests.

Table 6 - Deformations measured in FWD tests and moduli of deformability estimated with BISAR.

Load (kN) D0mes (µm)

D0calc (µm)

E (MPa)

30 676 676 195

40 838 837 220

50 1004 1006 235

60 1205 1207 235

65 1345 1342 225

70 1474 1465 220

It follows that the modulus measured with the

LFWD has a strong relationship with the estimated

modulus by FWD. Geogauge seems to have a

relationship but it is important to refer that this

apparatus operates with principles different from

the two other apparatus.

220

195

220

235225

235

LFWD

166

100

120

140

160

180

200

220

240

0 20 40 60 80

Load (kN)

EFWD (MPa)

Figure 8 - Moduli of deformability measured with FWD and related to LFWD.

7 - Conclusions and recommendations

The results obtained in the present study let

conclude that:

� the compaction of the first layer was made with

an average moisture content value of 8,4% and

an average dry density value of 1,71 g/cm3,

which corresponds to a degree of compaction of

98%;

� the compaction of the second layer was made

with an average moisture content value of 8,2%

and an average dry density value of 1,67 g/cm3,

which corresponds to a degree of compaction of

95%;

� were obtained equivalent deformability moduli

in the order of 100 to 170 MPa, on Geogauge

and LFWD tests;

10

� were obtained moduli of deformability in the

order of 195 to 235 MPa that were estimated

from FWD tests;

� the equivalent moduli of deformability obtained

are generally lower than those which occur in

granular layers built with natural aggregates;

� the values obtained from FWD tests are similar

to the values usually obtained in granular layers

built with natural aggregates;

� the values of equivalent modulus of

deformability may have been influenced by the

foundation structure, especially those measured by

the LFWD due to its wider scope;

� the equivalent modulus of deformability tends

to increase with the decrease of the moisture

content, which may be due to the effect of self-

cementing of the particles with the drying of the

layer;

� the measurements with the Geogauge are

more homogeneous in several test points than

those made with the LFWD;

� the equivalent moduli of deformability obtained

with the Geogauge are lower than those obtained

with the LFWD;

� the two methods of measurement used show a

strong correlation;

� in both methods a correlation with the moisture

content is obtained;

� the results obtained with FWD show that the

modulus of deformability increases to the load

level of 60 kN;

� comparing the results of the different methods

it can be concluded that the LFWD and the FWD

exhibit an evident relationship.

The study developed allowed to conclude that the

methods used, the Geogauge and LFWD, are very

useful in determining the equivalent modulus of

deformability in situ and being extremely simple to

use. The Troxler is also very easy to use and very

practical to control the compaction of granular

layers. These methods were chiefly characterized

by: they are non-destructive, they are easily

transported, they are easily placed on the surface

layer, they are easily operated by only one

operator, they have a high output, they let obtain

results in real time that make it easier to take

decisions at that moment and they allow the

repetition of the test in the same place. The test pit

showed itself as a valuable testing equipment for

such studies. With the results obtained it is

possible to come to some conclusions, namely that

the second layer does not appear to have reached

the stability on the eighth day being therefore

important to follow the evolution of the layer at

least until the fifteenth day. It should be referred it

is very important to do tests every day so that the

analysis can be more realistic, with minimum error.

Thus the evolution of the equivalent modulus of

deformability and the moisture content would be

better followed. It should be stressed that it is

important to build the layer correctly, with good

constructive practices, above all concerning the

homogenization when the water is added and

concerning the compaction, because only then can

consistent results be obtained.

It is considered that this study contributed to a

better understanding of the characteristics and

performance of CDW composed by crushed

concrete, when applied in road pavement layers,

enabling its application in such structures.

Regarding work to be developed it would be

important, as well as follow the progress every

day, to check whether the material was changed

after compaction, with regard to particle size

distribution.

The importance of going on with this study should

be referred, particularly with cyclic triaxial tests,

besides those already mentioned, which would

allow to draw more conclusions on the mechanical

behavior of recycled aggregate. Furthermore it is

important that more studies on this type of material

should be done, particularly with materials from

different origins and with different compositions

11

too. Only then will it be possible to encourage the

increased use of these materials, as an alternative

to the natural ones.

As a conclusion of this study it is considered that

these materials have a good performance, allowing

their application in unbound layers of low traffic

roads.

References

� Alves, T. (2007) - Metodologias de

Auscultação de Pavimentos Rodoviários -

Aplicação Prática do Radar de Prospecção e

do Deflectómetro de Impacto. Dissertação

para obtenção do grau de Mestre em

Engenharia Civil. Instituto Superior Técnico,

Lisboa.

� Antunes, M. L. (1993) - Avaliação da

Capacidade de Carga de Pavimentos

Utilizando Ensaios Dinâmicos. Tese de

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� EN 13286-7 (2004): Unbound and hydraulically

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� E 473-2006 (2006): Guia para a utilização de

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� Fiedler, S., Nelson, C., Berkman, E. F., Al

DiMillino (1998) - Soil Stiffness Gauge for Soil

Compaction Control. Public Roads.

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� Gonçalves, P. C. M. (2007) - Betão com

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� HUMBOLDT, H4140 (2008) - GeoGauge,

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� JAE (2002) - Caderno de Encargos Tipo -

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� Kancherla, B. S. (2004) - Resilient Modulus

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� Nazzal, M. D. (2003) - Field Evaluation of In-

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Construction of Pavement Layers and

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Agricultural and Mechanical College, Birzeit

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� NP EN 1097-2 (2002): Ensaios das

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propriedades mecânicas e físicas dos

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discussion).

12

� Woodside, A. R., Woodward, W. D. H.,

Farmer, D., Collins, R. J. (1997) - The use of

recycled concrete in highway pavement

construction. Thin Pavements, Surface

Treatments, and Unbound Roads: low cost,

low volume... high tech! geotrans - UNB

Natural Resources Geotechnique and

Transportation Engineering.