João Miguel Quilhó Correia Cabaço Extended Abstract · Slump NP EN12350-2 Fresh density NP...

DURABILITY OF CONCRETE WITH RECYCLED LIGHTWEIGHT

AGGREGATE FROM CRUSHED LIGHTWEIGHT CONCRETE

João Miguel Quilhó Correia Cabaço

Extended Abstract

Masters in Civil Engineering

Supervisor: Prof. Dr. Jorge Manuel Caliço Lopes de Brito

Co-supervisor: Prof. Dr. José Alexandre de Brito Aleixo Bogas

May 2013

DURABILITY OF CONCRETE WITH RECYCLED LIGHTWEIGHT AGGREGATE FROM CRUSHED LIGHTWEIGHT CONCRETE

1

1. INTRODUCTION

In a world that constantly tries to find an answer to environmental problems, including the level

of pollution and the excessive consumption of resources, it is essential that construction industry worries

about its sustainability. According to Ortiz et al. (2007), a project, in order to be sustainable, has to be:

ecologically friendly; economically viable and culturally acceptable. This topic has been one of the

biggest issues debated in civil engineering. As well, Zordan (1997) mentions that construction waste must

be seen as a good alternative raw material for concrete production.

Nowadays, concrete is one of the most used materials in the construction industry. However,

there is concern to find new variants of concrete which can provide more advantages.

The weight of the concrete structures can affect the global cost of the construction. So, if the density

of the concrete could be decreased, it would be possible to reduce the global cost of the project. This issue is

one reason for the appearance of lightweight concrete which can be characterized by a dry density lower than

2000 kg/m3 (NP EN 206-1; EN 13055-1). The use of such concrete is highly useful, as it allows slender

construction solutions, lower stresses in vertical elements and better alternatives for rehabilitation solutions.

Due to scientific progress, this new material is increasingly developed. It is possible, nowadays,

to use lightweight aggregates in all kind of constructions, such as bridges, buildings or oil rigs. However,

for economic reasons, the most common use of lightweight concrete involves non-structural applications,

for example, in the rehabilitation of existing structures, mainly in floors and walls, due to its

characteristics of lightness and thermal and acoustic insulation (Silva, 2007) (Bogas, 2010).

This study aims to contribute to the development of the existing research in the field of

management and reuse of construction waste, in order to support the reduction of their environmental

impact.

2. EXPERIMENTAL PROGRAM

2.1. Research significance

This work is aimed at evaluating the possibility of reusing waste from building demolition as

aggregate for lightweight concrete. For this purpose, lightweight concrete mixes with recycled

lightweight aggregate concrete (RLWAC) were tested in terms of durability, varying the proportion of

concrete waste, by replacing a fraction of the same amount (in volume) of expanded clay by two types of

lightweight concrete waste at the substitution percentages of 20%, 50% and 100% of the total volume of

aggregates. The results were compared with two control concrete mixes, without recycled aggregates.

Therefore, it was possible to evaluate the influence of RLWCA in concrete production.

Along with this dissertation, another one was performed on the "Mechanical performance of

concrete with recycled lightweight aggregates from crushed lightweight concrete", by José Maria Guedes,

from Instituto Superior Técnico, Lisbon.

.


2

In this investigation, tests were performed, in order to evaluate the influence of RLWCA on

concrete. Table 1 lists the tests performed within the experimental campaign, as well as the test

specifications.

Table 1 - Description of performed tests and specifications.

Aggregate tests Test specification

Sieve analysis NP EN933-1/ NP EN933-2

Particle density and water absorption NP EN1097-6

Apparent bulk density NP EN1097-3

Crushing strength NP EN13055-2

Water content NP 956

Shape index NP EN933-4

Fresh concrete tests Test specification

Slump NP EN12350-2

Fresh density NP EN12350-6

Hardened concrete tests Test specification

Drying shrinkage LNEC E398

Water absorption by immersion LNEC E394/LNEC E395

Water absorption by capillarity LNEC E393

Carbonation resistamce LNEC E391

Chloride penetration resistance Nordtest NT Build 492

2.2. Materials

Two types of Portuguese expanded clay lightweight aggregates, commercially known as Leca M

and Leca HD, were selected. Their particle dry density, 24hours water absorption, loose bulk density,

crushing strength and grading range (di/Di) are listed in Table 2. Two types of silicious sand with different

granulometries were used in order to obtain better mixture compacities. Their main characteristics are

listed in Table 2. Portland cement CEM I 42,5R, from the SECIL cement plant in Outão, Setúbal, was

also used. Water came from the public main supply.

Figure 1 – Lightweight aggregate, Leca®.

Since there was no opportunity of receiving recycled lightweight aggregate concrete from a

demolition site, it was decided to produce lightweight concrete (LWC). Therefore, two types of recycled

LWC were obtained by crushing blocks from two different primary lightweight concrete mixes, one with

structural expanded clay (BOHD) and the other with non-structural expand clay (BOM). The

compositions of the mixes are presented in Table 3.BOM is an insulated no-fines concrete, i.e., without

fine aggregate.


3

Table 2 – Properties of aggregates

Material bulk density

(kg/m3)

Water

absorption

(%)

Apparent bulk

density

(kg/m3)

Crushing

resistance

(MPa)

Shape index

(%)

Fine sand 2604 0,20 1494 - -

Coarse sand 2610 0,22 1493 - -

Leca HD 1092 12,61 681 5,71 -

Leca M 595 23,22 339 1,20 -

RLHD 1735 15,72 1000 7,55 23.9

RLM 878 29,41 463 1,95 8.8

Table 3 - Composition of the two original concretemixes (l/m3 of concrete).

Materials BOHD BOM

Sand (l/m3) 313,25 -

Leca HD (l/m3) 350 -

Leca M (l/m3) - 630

Cement (kg/m3) 350 150

Water (l/m3) 192,5 90

fcm 7 days (MPa) 34,2 0,7

fcm 28 days (MPa) 37,2 0,7

After 28 days the two original concrete mixes were crushed, resulting in two RLWAC; RLHD

from crushed blocks of BOHD (Figure 2) and RLM from crushed blocks of BOM (Figure 3). The

grinding is made through a mechanical process, using a jaw crusher, in the Laboratory of Construction in

the Department of Construction and Architecture of IST, Lisbon (Figure 4). After obtaining the crushed

material, the recycle aggregates were separated by sieve fractions, in order to get the same amount of

material, corresponding to the expanded clay. This separation was obtained using a vibrating sieving

device.

Figure 2 - Structural lightweight concrete blocks Figure 3 - Non-structural lightweight concrete blocks

Figure 4 - Jaw crusher, Laboratory of Construction in the Department of Construction and Architecture of IST,

Lisbon


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2.2.1. Properties of aggregates

As expected, the structural lightweight expanded clay (Leca HD) has higher density than the

non-structural expanded clay, whose values are within the ones provided by the supplier. However, it was

possible to notice an increase on the density of the recycled lightweight aggregates. This effect can be

explained by the bonded mortar on the RLWCA, which, besides increasing the open porosity of the

aggregate, has higher density than the primary LWA, causing a significant increase in the density of the

recycled aggregate. Kralj (2009) documented similar conclusions.

Table 2 also shows the increase on water absorption by the RLWCA. This increase was 3.11%

for RLHD and 6.19% for RLM, when compared with the primary lightweight aggregates. The bonded

mortar and the exposure of the internal porosity of the LWA, due to the amount of broken particles, are

the main reasons for this phenomenon.

On the other hand, the adhered mortar provides higher strength to the recycled aggregate, which

is confirmed through the increase of the crushing strength by the RLWCA. Also, as Table 2 shows, this

property is related to the density of the aggregate.

Lightweight aggregates of expand clay are characterized by having a spherical shape. For this

reason the shape index test was not performed for the LWA. However, the recycled aggregates are often

known for having longer and angular forms, due to their production process. The results of the shape

index test demonstrate that most of the RLWCA particles are both elongated and angular, which can

affect the mechanical and durability properties of the produced concretes.

Water absorption was also tested. Figure 5 shows the evolution of water absorption over 24

hours.

Figure 5 - Aggregates water absorption over time.

This test has major importance since it allows quantifying the water absorbed by LWA and

RLWCA during mixing, evaluating in advance the total of water required for the concrete production. As

0

5

10

15

20

25

30

0 250 500 750 1000 1250 1500

Wa

ter a

bso

rpti

on

(%

)

Time (minutes)

Leca HD Leca M RLHD RLM


5

Figure 5 reveals, the absorption curve shows a very high initial absorption. After this period, the

absorption is rather slow and less meaningful.

2.3. Concrete Design

For this study, 12 concrete mixes were produced with different substitution ratios of the two

primary expanded clay aggregates (Leca HD and Leca M) by two different RLWCA, RLHD from

crushed blocks of structural lightweight concrete and RLM from crushed blocks of non-structural

lightweight concrete.

The 12 concrete mixes are referred to as:

BHD - control lightweight concrete with structural expanded clay (leca HD);

BM - control lightweight concrete with non-structural expanded clay (leca M);

BHD20RHD - lightweight concrete with leca HD replaced by 20% of RLHD;

BHD50RHD - lightweight concrete with leca HD replaced by 50% of RLHD;

BM20RHD - lightweight concrete with leca M replaced by 20% of RLHD;

BM50RHD - lightweight concrete with leca M replaced by 50% of RLHD;

B100RHD - lightweight concrete with 100% of RLHD;

BHD20RM - lightweight concrete with leca HD replaced by 20% of RLM;

BHD50RM - lightweight concrete with leca HD replaced by 50% of RLM;

BM20RM - lightweight concrete with leca M replaced by 20% of RLM;

BM50RM - lightweight concrete with leca M replaced by 50% of RLM;

B100RM - lightweight concrete with 100% of RLM;

In order to achieve a set of concrete families that are compatible with a significant number of current

structural applications, the produced concrete mixes complied with the following characteristics:

Strength class: LC35/38;

Consistency class: S3 (100 a 150 mm) - Target: 125 ± 10 mm;

Water/cement ratio: 0.55;

Binder: CEM II A-L 42.5 R cement from Secil, Outão, Setúbal;

Mixing water: tap water, from the public supply network;

Maximum aggregate size: 11.2 mm.

The BM control concrete was produced with a non-structural lightweight aggregate (Leca M)

which is not appropriate for structural applications. However, since this material is more often used in

existing buildings, its production was considered relevant.

Table 4 shows the proportions of the materials used in the production of the control concrete

mixes. Each concrete mix was dimensioned to a total volume of 222.8 dm3.


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Table 4 - Composition of the two control concretes (kg/m3 of concrete).

Size grading BHD BM

Lightweight

aggregate

12,5 - 14 4,8 2,6

11,2 - 12,5 19,5 10,6

8 - 11,2 76,6 41,7

Coarse aggregate 6,3 - 8 77,2 42,1

5,6 - 6,3 46,3 25,2

4 - 5,6 133,5 72,8

2 - 4 22,8 12,4

Fine aggregate Sand Coarse sand 565,0 565,0

Fine sand 260,3 260,3

cement 350,0 350,0

water 192,5 192,5

2.4. Concrete mixing and curing

The mix process followed by Bogas (2011) in his research was adopted, in order to minimize the

effect of high water absorption of the lightweight aggregates.

Table 5 - Curing procedures used for each test

This process started off by mixing coarse aggregates and 60% of water, with the concrete mill

running, for about 30 seconds. After this period, the equipment remained at rest for a another 30 seconds,

by this way, it can be assured that, in the end of mix process, the LWA and the RLWCA absorbs about

Test Specimen form Number of

specimens

Specimen

dimension

(cm)

Curing procedure

Drying shrinkage Prisms 2 15 x 15 x 60

Cure at dry chamber

with temperature at 22

± 2 ° C and relative

humidity of 50 ± 5%

Water absorption by

capillarity Cylinder 1 15 x 30

Cure for 14 days at

humid chamber with

relative humidity of

95% and the remaining

days at 50 ° C

Water absorption by

immersion Cube 3 10 x 10 x 10

Cure at humid

chamber with relative

humidity of 95%

Carbonation

resistance Cylinder 2 10 x 20

Cure for 7 days at

humid chamber with

relative humidity of

95% and the remaining

days at dry chamber

with temperature at 22

± 2 ° C and relative

humidity of 50 ± 5%

Chloride

penetration

resistance

Cylinder 2 10 x 20

Cure at humid

chamber with relative

humidity of 95%


7

90% of its full water absorption capacity. Then, with the concrete mill running, the fine aggregates were

placed in the mixer and left at mix for 120 seconds. This process ended by mixing the cement and,

gradually, the remaining 40% of water. This final part of the process lasted for at least 240 seconds, until

homogeneous mixture was obtained.

Due to the specificity of each test, not all specimens were under the same curing conditions. The

curing procedures used for each test are presented in Table 5.

3. RESULTS AND DISCUSSION

3.1. Fresh concrete properties

3.1.1. Workability

Figure 6 shows the results of the slump test by Abrams’s cone for all of the manufactured mixes.

In order to ensure the trustworthiness of the comparison between the various properties of the produced

concretes mixes, it was guaranteed that all of the compositions presented a similar workability. Therefore,

all of the results are ranged between 125 ± 10 mm.

Figure 6 - Slump test results.

Figure 6 shows that all concrete mixes registered a slump within the range defined without any

corrections of w/c ratio. Despite the control tests performed (water absorption at 30 min and water content

of the aggregates), it is difficult to accurately predict, the amount of total water, so as not to affect the

effective w/c ratio. This might be the main reason for the slump registered for BHD50RM composition.

Actually, it is recognized that the workability of lightweight concrete is highly influenced by the

water absorption of the LWA (EuroLightCon R12, 2000).

100

110

120

130

140

0 10 20 30 40 50 60 70 80 90 100

Wo

rka

bil

ity

(m

m)

Replacement rate of LWA by RLWAC (%)

BHD

BHD20RHD

BM20RHD

BHD50RHD

BM50RHD

B100RHD

BM

BHD20RM

BM20RM

BHD50RM

BM50RM

B100RM


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3..1.2. Fresh concrete density

Figure 7 exhibits the fresh concrete density results of the produced mixes. The results show that

the density of concrete increases with the replacement rate of LWA by RLWCA. This is an expected

behavior since the density of the produced concrete is influenced by the density of the aggregates in it.

Figure 7 - Fresh concrete density test results.

Although the density of concrete increases with the replacement rate of LWA by RLWCA, when

considering the BHDRM compositions, Figure 7 shows that, in this particular mix, the incorporation of

RLM tends to decrease the density of concrete. In fact, RLM has lower bulk density than primary LWA

(Leca HD), which leads to a decrease of the concrete density.

3.2. Hardened concrete properties

3.2.1. Compressive strength after 28 days

The compressive strength test was performed as stipulated by the NP EN 12390-3 (2003)

standard and the specimens were subjected to a uniform compression stress. As such, the results obtained

by José Maria Guedes in a parallel research work were analyzed and the average compressive strength

values at 28 days from five specimens are presented in Table 6.

As shown in Table 6, in general, as replacement ratio increases so does the average compressive

strength at 28 days, except in the BHDRM compositions. In lightweight concrete mixes, concrete’s

strength is highly influenced by the aggregate’s strength. Since the RLHD is the aggregate with the

highest strength, it is easy to understand why the compressive strength increases with the replacement rate

of LWA by this aggregate.

When considering the BHDRM compositions, there is a decrease of the compressive strength as

the replacement ratio increases. In fact, the RLM has lower strength than Leca HD, which leads to a

decrease of the concrete compressive strength.

1700

1800

1900

2000

2100

2200

0 10 20 30 40 50 60 70 80 90 100

Den

sity

(k

g/m

3)

Replacement rate of LWA by RLWAC (%)

BHDRHD BMRHD BHDRM BMRM


9

Table 6 - Compressive strength at 28 days of age results.

Concrete mix Compressive strength at 28 days

(MPa)

Replacement ratio

LWA-RLWAC (%)

BHD 38,4 0

BHD20RHD 40,4 20

BHD50RHD 43,1 50

B100RHD 43,7 100

BM 19,2 0

BM20RHD 26,4 20

BM50RHD 30,7 50

B100RHD 43,7 100

BHD 38,4 0

BHD20RM 38,5 20

BHD50RM 36,3 50

B100RM 33,4 100

BM 19,2 0

BM20RM 25,1 20

BM50RM 27,7 50

B100RM 33,4 100

3.2.2. Drying shrinkage

This property is one the most relevant characteristics of concrete, and, according to several

authors, is one of the most influenced by the incorporation of recycled aggregates. Figure 8 presents the

test results at 91 days.

Figure 8 shows that the replacement of LWA by RLWCA leads to an increase of concrete shrinkage.

The amount of mortar bonded to the primary aggregate contributes to the increase of the deformation.

The mixes with structural expanded clay are more influenced by RLWCA than the control

concrete, with variations between 90% and 130%. On the one hand, despite the higher strength of RLHD,

compared to Leca HD, the amount of mortar added to the recycled aggregate causes an increase of the

paste volume in the BHDRHD compositions, which contributes to higher deformations . On the other

hand, considering the BHDRM compositions, RLM has lower stifness than Leca HD, which, along with

the mortar added to the recycled aggregate, are the main reasons for the higher shrinkage observed in

these concrete mixes.

Although the recycled aggregates cause an increase on concrete shrinkage, the higher water

absorption capacity by the RLWCA contributes to reduce the initial shrinkage, because in the early ages

the water retained in the recycled aggregates can compensate the evaporated water by internal curing.


10

Figure 8 - Drying shrinkage tests results at the age of 91 days.

3.2.3. Water absorption through capillarity

Through this test it is possible to evaluate the concrete’s capacity to absorb liquid through its

capillary vessels. Figure 9 presents the results for the water absorption by capillarity at the end of the test.

Figure 9 - Water absorption through capillarity tests results at 72 hours.

For reasons that could not be identified, the results analysis suggests that values of the control

concrete BM are somehow anomalous. Setting these values aside, it can be seen that the incorporation of

RLWCA on concrete increases the capacity of water absorption. Structural concrete is the most affected

by the incorporation of RLWCA. However, the incorporation of RLHD showed worse results than that of

RLM. The bonded mortar on the recycled aggregate has an important role in this property, as it increases

the capacity of water absorption by capillarity. The RLHD presents a larger amount of mortar than the

6,00E-04

8,00E-04

1,00E-03

1,20E-03

1,40E-03

1,60E-03

0 10 20 30 40 50 60 70 80 90 100

Sh

rin

ka

ge

(m/m

)

Replacement rate of LWA by RLWCA


2,0

2,5

3,0

3,5

4,0

4,5

5,0

0 20 40 60 80 100

Wa

ter a

bso

rpti

on

by

ca

pil

lari

ty

(10

-3g

/mm

2)

Replacement rate of LWA by RLWCA



11

RLM, which might be the main reason to explain why the mixes with recycled non-structural aggregates

showed better performances than the ones with recycled structural aggregates.

In this way, the obtained results show a higher importance of the mortar adhered to the primary

aggregates than the overall porosity of the recycled aggregates, in water absorption by capillarity.

Figures 10 to 13 present the results of the absorption coefficient for the tested compositions. An

absorption coefficient was defined corresponding to the value of the slope of the absorption regression

line between 1 hour and 24 hours of testing, measured as a function of √ t. A similar procedeure was

adopted by (Bogas, 2011).

Considering Figures 10 and 11, it is observed that the absorption coefficient tends to increase

with the replacement rate. However, the introduction of the RLHD in concrete causes similar absorption

coefficients in the two concrete families, which can prove that this property is more related to the increase

of the volume of paste than with the low porosity of the aggregate.

Figures 12 and 13 show that the absorption in concrete with RLM is identical in the two

compositions. Therefore, it is possible to show the importance of the adhered mortar in this property.

Finally, comparing compositions B100RHD and B100RM, there is a higher value for B100RHD

evidencing that the absorption coefficient is more dependent on the paste volume than on the porosity of

the aggregate. In fact, the larger capillaries in aggregates will cut the absorption action from the narrower

capillaries of the mortar in their vicinity.

Figures 10 - Coefficient of water absorption through capillarity, compositions with RLHD.

0.19

0.41 0.42

0.49

0

0,1

0,2

0,3

0,4

0,5

0,6

Ab

sorp

tio

n c

oef

fici

ent

(10

-3 g

/(m

m2x

min

0,5

)

0,37 0,39 0,42

0,49

0

0,1

0,2

0,3

0,4

0,5

0,6

Ap

sorp

tio

n c

oef

fici

ent

(10

-3 g

/(m

m2x

min

0,5

)


12

Figures 11 - Coefficient of water absorption through capillarity, compositions with RLM.

3.2.4. Water absorption by immersion

This test allows an estimation of the concrete’s open porosity after 28 days. Figure 14 shows the

results of the performed tests.

Except for the BMRHD compositions, the results analysis reveals that concrete’s water

absorption by immersion increases along with the RLWCA’s incorporation ratio, just as predicted, as

expected.

Figure 14 shows that the mixes with RLM incorporation are the ones most influenced by the

replacement of LWA by RLWCA. The BHDRM composition (with 100% of RLM) has a water

absorption increment of 95%, when compared to the control concrete BHD. This effect is mostly

explained by the higher porosity of the RLWCA, which leads to higher levels of water absorption, due to

the increase of concrete’s porosity. However, when considering the BMRHD compositions, the concrete

shows better performances along with the replacement ratio. In fact, RLHD has lower water absorption

than Leca M; therefore, as expected, the incorporation of RLHD on non-structural mixes causes a

decrease of the water absorption by immersion.

Figure 12 - Water absorption by immersion tests results.

0.19

0.36 0.41

0.46

0

0,1

0,2

0,3

0,4

0,5

Ab

sorp

tio

n c

oef

fici

ent

(10

-3 g

/(m

m2x

min

0,5

) 0,37 0,35

0,42 0,46

0

0,1

0,2

0,3

0,4

0,5

Ab

sorp

tio

n c

oef

fici

ent

(10

-3 g

/(m

m2x

min

0,5

)

10

12

14

16

18

20

22

24

26

0 10 20 30 40 50 60 70 80 90 100Wa

ter a

bso

rpti

on

by

im

mer

sio

n (

%)

Replacement rate of LWA by RLWCA (%)



13

3.2.5. Carbonation resistance

This test allows evaluating the carbonation resistance. Figure 15 shows the carbonation depth

with different replacement rates of LWA by RLWCA.

Figure 13 - Carbonation depth at the age of 120 days.

The depth of carbonation tends to increase when replacing the Leca HD by RLWCA. In fact, the

higher porosity of the RLWCA accelerates the diffusion of gases in the concrete. So, as well as the water

absorption by immersion, the incorporation of RLWCA causes worse performances in the concrete,

which was expected since the two properties are related to the open porosity of concrete.

On the other hand, the incorporation of RLWCA on Leca M’s mixes leads to a decrease of the

carbonation depth. For the BMRHD compositions, this phenomenon was expected and can be explained

by the lower porosity of the RLHD aggregate, when compared to Leca M, reducing the diffusion of gases

inside concrete. The performance of the BMRM compositions was less expected, for the reason that RLM

aggregate has higher porosity than Leca M. However, the adhered mortar, along with the high amount of

unbroken particles of this aggregate, seems to protect the aggregate, reducing the CO2 diffusion through

concrete.

3.6. Chloride penetration resistance

This test allows evaluating the concrete’s resistance to the chloride ions migration. Figures 16 to

19 present the results of the performed tests at two different ages, 28 and 91 days.

The tests results obtained for the chloride penetration resistance show that the incorporation of

RLWCA increases the chloride diffusion , despite some anomalous results. In conventional concrete, this

property is mostly related to mortar quality, since the aggregates do not allow the diffusion of chlorides.

However, in lightweight concrete, due to the porosity of the LWA, the diffusion through them cannot be

ignored, especially in saturated conditions, such as in the tests performed, where the samples were

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100

Ca

rbo

na

tio

n d

epth

(m

m)

Replacement rate of LWA by RLWCA (%)



14

saturated in sodium hydroxide. Therefore, it is possible that the aggregates have an active role in the

diffusion of chlorides which, along with the increased porosity by RLWCA, will cause a decrease of the

chloride penetration resistance of concrete.

Finally, the diffusion levels obtained at 91 days were lower than the ones obtained at 28 days.

This fact can be partly explained by the hydration evolution of the cement paste.

Figures 14 - Coefficient of ion chloride diffusion ate the age of 28 and 91 days, compositions with RLHD.

Figures 15 - Coefficient of ion chloride diffusion ate the age of 28 and 91 days, compositions with RLM.

4. CONCLUSIONS

In this study, the durability performance of structural concrete containing recycled lightweight

aggregates from crushed lightweight concretes was analyzed. After a comprehensive experimental study,

the following conclusions can be drawn:

It is possible to crush lightweight aggregate concrete so that it can be reused as lightweight

aggregate (RLWCA). However, as expected, the recycled aggregate has higher density than the

primary lightweight aggregate (LWA);

Concrete density reflects the density of each of its components and all the recycled concrete

mixes had a dry density lower than 2000 kg/m3. So it is possible to produce lightweight concrete

with RLWCA;

0

2

4

6

8

10

12

14

16

18

Ch

lori

de

dif

fusi

on

co

effi

cien

t

(10

-2m

2/s

)

0

2

4

6

8

10

12

14

16

18

20

Ch

lori

de

dif

fusi

on

co

effi

cien

te

(1

0-2

m2/s

)

0

2

4

6

8

10

12

14

16

18

Ch

lori

de

dif

fusi

on

co

effi

cien

t

(10

-2m

2/s

)

0

2

4

6

8

10

12

14

16

18

20

Ch

lori

de

dif

fusi

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co

effi

cien

t

(1

0-2

m2/s

)


15

The compressive strength is affected by the RLWCA’s incorporation. In general, the

compressive strength increased along with the replacement rate of LWA by RLWCA. The only

exception was the BHDRM family, where the non-structural characteristic of the RLM caused a

decrease of the compressive strength, but followed by a decrease of the concrete density;

The shrinkage of recycled lightweight concrete mixes with RLWCA is higher than that of the

control lightweight mixes. The adhered mortar on the primary LWA is the main reason for this

phenomenon. However, it was confirmed that the higher water absorption capacity of RLWCA

contributes to reduce the shrinkage in concrete’s early ages, where the water retained in the

recycled aggregates compensates the evaporated water;

The incorporation of RLWCA in concrete results in higher water absorption by capillarity. It was

also confirmed that the absorption by capillarity increases along with the amount of adhered

mortar in the recycled aggregate;

In general, the water absorption by immersion was also higher in mixes with RLWCA. Though

the BMRHD compositions presented lower water absorption as the substitution ratio increased,

this fact can be explained by the lower porosity of the RLHD against the Leca M. Therefore, it

was shown that the water absorption by immersion is highly influenced by concrete’s porosity;

The incorporation of RLWCA in concrete caused similar levels of carbonation depth on

structural concrete mixes. However, when incorporated in a non-structural concrete, it results in

better performances. The BMRM performance was somewhat unexpected. The bonded mortar,

along with the high amount of unbroken particles, seemed to protect the recycled aggregate,

reducing the CO2 diffusion through concrete;

In general, the incorporation of RLWCA increased the diffusion of Cl- . Since these tests were

made in saturated conditions, and aggregates only allow chloride diffusion if they are saturated,

the lightweight aggregates can have an active role in the chloride diffusion, due to their porosity

and high water absorption. These effects along with the increased porosity of RLWCA are the

reasons for their lower performance in recycled concrete.

Overall, the results allow concluding that the RLHD (lightweight aggregate from recycled

structural lightweight concrete) incorporation decreases the concrete’s performance in terms of

durability, despite ensuring mechanical efficiency, especially in compositions with structural Leca.

However, for concrete mixe with Leca HD (structural LWA) and 20% of RLHD the concrete’s

performance is relatively similar to that of the control concrete BHD.

On the other hand, the reuse of non-structural concrete as aggregate, also, reduces the concrete’s

performance. However, this aggregate might be considered as an advantage in the production of non-

structural concrete.


16

5. REFERENCES

ACI213R (2003) - “Guide for structural Lightweight-Aggregate Concrete”, Concrete Institute;

Bogas, J. (2011) - “Characterization of structural lightweight aggregate concrete expanded clay”,

PhD Thesis in Civil Engineering, Instituto Superior Técnico, Lisbon (in Portuguese);

Brito, J. (2005) - “Recycled aggregate and its influence on the properties of concrete”, Lesson

Summary of Aggregation in Civil Engineering, Instituto Superior Técnico, Lisbon (in Portuguese);

Chandra, S.; Berntsson, L. (2003) - “Lightweight concrete. Science, Technology and

applications”, Noyes publications-Wiliam Andrew Publishing, USA;

Coutinho, A.; Gonçalves, A. (1997) - “Production and properties of concrete”, Volume I, II e III,

LNEC, Lisbon (in Portuguese);

EuroLightCon R18 (2000) - “Durability of LWAC made with natural lightweight aggregates”,

Project BE96-3942R18;

EuroLightCon R26 (2000) - “Recycling lightweight aggregate concrete”, Project BE96-3942R26;

Kralj, D. (2009) - “Experimental study of recycling lightweight concrete with aggregates

containing expanded glass”, Process Safety and Environmental Protection, Vol. 87, pp 267-273;

Leite, M. (2001) - “Evaluation of mechanical properties of concrete made with recycled aggregates

from construction and demolition waste”, PhD Thesis in Civil Engineering, Universidade Federal do

Rio Grande Sul, Porto Alegre (in Portuguese);

Liu, X.; Chia K.; Zhang M. (2011) - “Water absorption, permeability, and resistance to chloride-

ion penetration of lightweight aggregate concrete”, Construction and building Materials, Vol. 25,

pp 335-343;

LNEC E 391 (1993) - Concrete: Calculation of carbonation resistance (in Portuguese), LNEC,

Lisbon;.

LNEC E 393 (1993) - Concrete: Calculation of water absorption by capillary action (in

Portuguese), LNEC, Lisbon;.

LNEC E 394 (1993) - Concrete: Calculation of water absorption by immersion. Atmospheric

pressure test (in Portuguese), LNEC, Lisbon;.

LNEC E 395 (1993) - Concrete: Calculation of water absorption by immersion. Vacuum test (in

Portuguese), LNEC, Lisbon;.

LNEC E 398 (1993) - Concrete: calculation of drying shrinkage and expansion (in Portuguese),

LNEC, Lisbon;.

Nordest NT Build 492 (1999) - Concrete, mortar and cement-based repair materials: Chloride

migration coefficient from non-steady-state migration experiments, Nordtest, Finland;

NP 956 (1973) - Aggregates for mortar and concrete. Calculation of water content (in Portuguese),

IPQ, Lisbon;.

NP EN 206-1 (2007) - Concrete. Part 1: Specification, performance, production and conformity (in

Portuguese), IPQ, Lisboa;

NP EN 933-1 (2000) - Geometric property test for aggregates: Granulometric analysis. Sieving


17

method (in Poruguese), IPQ, Lisbon;

NP EN 933-4 (2002) - Geometric property tests for aggregates: Particle shape determination.

Shape index (in Portuguese), IPQ, Lisbon;.

NP EN 1097-3 (2002) - Tests to find the mechanical and physical properties of aggregates: Method

to determine density and voids (in Portuguese), IPQ, Lisbon;.

NP EN 1097-6 (2003) - Tests to find the mechanical and physical properties of aggregates:

Determination of density and water absorption (in Portuguese), IPQ, Lisbon;

NP EN 13055-1 (2005) - Lightweight aggregates. Part 1: Lightweight aggregates for concrete,

mortar and grout (in Portuguese), IPQ, Lisbon;

NP EN 13055-2 (2005) - Lightweight aggregates. Part 2: Lightweight aggregates for bituminous

mixtures and surface treatments and for unbound and bound applications (in Portuguese), IPQ,

Lisbon;

NP EN 12350-2 (2009) - Tests on fresh concrete: Slump test (in Portuguese), IPQ, Lisbon;

NP EN 12390-3 (2003) - Tests on hardened concrete: Compressive strength of test specimens (in

Portuguese), IPQ, Lisbon;

NP EN 12350-6 (2009) - Tests on fresh concrete: Density (in Portuguese), IPQ, Lisbon;

Reinhardt, H. e Kummel, J. (1999) - “Some tests on creep an shrinkage of recycled lightweight

concrete”, Otto-Graf journal, Vol. 10

Zordan, S. (1997) - “The use of waste as aggregate in concrete production”, Master degree in Civil

Engineering, Universidade Estadual de Campinas, São Paulo (in Portuguese).

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