José Maria Guedes Machado Lemos de Figueiredo Extended … · Slump NP EN12350-2 Fresh density NP EN12350-6 Hardened concrete tests Test standard Compressive strength NP EN 12390-3

MECHANICAL PERFORMANCE OF CONCRETE WITH RECYCLED LIGHT-

WEIGHT AGGREGATE FROM CRUSHED LIGHTWEIGHT CONCRETE

José Maria Guedes Machado Lemos de Figueiredo

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

April 2013

MECHANICAL PERFORMANCE OF CONCRETE WITH RECYCLED LIGHTWEIGHT AGGREGATE FROM CRUSHED LIGHTWEIGHT

CONCRETE

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1. INTRODUCTION

Construction is currently one of the economic sectors that generate the largest amounts of

waste, due to the nature of the materials involved.

According to Zordan (1997) the reuse of construction waste begins to be considered a good

alternative to using traditional raw materials.

Reusing solutions/waste recycling promotes sustainability of the construction sector. On the

other hand, for the implementation of this concept, besides multidisciplinary, cultural changes, envi-

ronmental education and a systemic view are also necessary [Brandon (1998); Angulo (1998); John

(2000); Zwan (1997)].

Concrete is nowadays one of the most employed materials in the construction industry. Its su-

premacy is justified by the countless advantages it presents in economic, versatility and mechanical

behaviour terms.

It is common to associate concrete to the concept of a heavy and cold material, a factor that

leads to the increasing need of solutions that seek to correct and enhance all the advantages it pre-

sents. Lightweight concrete with low-density aggregates (LWC), characterized by densities lower

than 2000 kg/m3 and thermal conductivity lower than conventional concrete, meets these require-

ments. Density reduction allows the design of lighter structures,, which is a huge advantage.

Silva et al. (2004) reported that the use of concrete with lightweight aggregates versus that of

conventional concrete presents a number of attractive features that lead to a cost reduction making

its use increasingly frequent in construction.

This kind of concrete (LWC) has been the subject of numerous studies concluding that the use

of some types of expanded clay aggregates can currently achieve lightweight concrete with similar

strength to conventional concrete with equivalent composition.

2. EXPERIMENTAL PROGRAM

2.1. Research significance

This research aims to associate recycling of lightweight concrete with its production, in order

to understand well what the performance, at the mechanical level, of concrete with aggregates from

crushed lightweight aggregates concrete. With that purpose a total of 12 concrete mixes were manu-

factured with compositions changing in term of the replacement rate (0%, 20%, 50% and 100%),

for two types of lightweight aggregates (Leca M and Leca HD) and two types of recycled light-

weight aggregates (RLHD and RLM), and subsequently the results were analyzed in terms of me-

chanical performance.


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Simultaneously another dissertation was carried out by João Miguel Quilhó Correia Cabaço

from Instituto Superior Técnico, which analyses the “Performance of lightweight aggregate con-

crete from shredding of lightweight concrete floors in terms of durability”.

In this study, specimens were tested in order to determine the main features of concrete be-

haviour. Table 1 presents the tests conducted during the experimental campaign, as well as the

standards used.

Table 1 - Description of performed tests and standards.

Aggregate tests Test standard

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 EN1097-5

Shape index NP EN933-4

Fresh concrete tests Test standard

Slump NP EN12350-2

Fresh density NP EN12350-6

Hardened concrete tests Test standard

Compressive strength NP EN 12390-3

Splitting tensile strength NP EN 12390-6

Modulus of elasticity LNEC E 397

Abrasion resistance DIN 52108 (2002)

2.2. Materials

During the investigation, expanded clay aggregates of two types were used, commercially

known as: Leca HD - aggregates for structural lightweight concrete; Leca M - aggregates for non-

structural lightweight concrete.

Figure 1 - Lightweight aggregate, Leca®.


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In this study it was decided to use two types of siliceous sand in order to obtain compact mix-

es. It was also used Portland cement CEM I 42.5 provided by SECIL, located in Outão, Setúbal.

Finally, the water used in the production of the lightweight concrete was tap water.

Table 2 summarizes the main features of the aggregates used in this experimental campaign,

namely their particle dry density, 24-hour water absorption, loose bulk density, crushing strength

and grading range (di/Di).

Table 2 - Properties of aggregates

Material bulk density

(kg/m3)

Water absorp-

tion (%)

Apparent bulk

density (kg/m3)

Crushing re-

sistance (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

Given the unavailability of recycled lightweight aggregates, they were produced in the Con-

struction Laboratory of the Department of Construction, Architecture and Georresources of IST,

Lisbon.

The production of recycled lightweight aggregates resulted from casting, curing and subse-

quent crushing of source concrete (BO), followed by the separation of crushed aggregates by size

fractions.

Regarding the experimental program of this research, two types of recycled aggregates,

RLHD and RLM, were used, from the production and subsequent grinding of structural and non-

structural lightweight concrete, respectively (Table 3).

The compositions of the origin concretes produced are presented in table 3.

Table 3 - Composition of the two original concrete mixes (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


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Crushing of the two types of source concrete blocks (Figures 2 and 3) was performed accord-

ing to a mechanical process, in a jaw crusher, in the Laboratory of Construction of the Department

of Construction and Architecture of IST, Lisbon (Figure 4). That was followed by particle size sep-

aration of the recycled lightweight aggregate generated using a vibrating sieving device (Figure 5).

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, Architecture and Georresources of IST, Lisbon

Figure 5 - Vibrating sieving device, Laboratory of

Construction in the Department of Construction,

Architecture and Georresources of IST, Lisbon

2.2.1. Properties of aggregates

The dry bulk density of lightweight aggregate revealed to be consistent with the values made

available by the supplier. An analysis of this property in the recycled lightweight concrete aggre-

gates showed an increase in the dry bulk density of 60% and 50% compared to structural and non-

structural lightweight aggregates, respectively. The recycled aggregates are made of a fraction of

original lightweight aggregates and another of mortar or paste. Since the bulk density of this frac-

tion is higher than that of the original lightweight aggregate, an increase of this property is ex-

pected.

As expected, the non-structural lightweight aggregate (Leca M) recorded higher absorption


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values than those of the structural lightweight aggregate (Leca HD). The non-structural lightweight

aggregate (Leca M) has lower density and greater inner porosity, which results in increased water

absorption. Concerning the RWLAC, similarly to the differences observed between the structural

and the non-structural lightweight aggregate, they also showed an increased absorption compared to

lightweight aggregates. This increase results from two factors: the highest content of broken parti-

cles; the mortar surrounding the lightweight aggregates.

The apparent bulk density had a remarkable increase in recycled aggregates, with a sharp in-

crease in those from structural lightweight concrete (RLHD). This was expected since this property

is directly affected by the particle size, shape and the compactness of the aggregate.

Regarding crushing strength, the results for lightweight aggregates were again in agreement

with those provided by the supplier. On the other hand, aggregates with higher density and higher

apparent bulk density (Leca HD) recorded higher values of crushing strength compared to non-

structural lightweight aggregate (Leca M).

In recycled aggregates, the amount of mortar stuck to the aggregate itself confers an increase

of the crushing strength. This is a very unique feature of recycled lightweight aggregates concrete,

since it does not happen with natural aggregates, given their greater strength against that of mortar.

Structural lightweight concrete recycled aggregate (RLHD) had higher shape index than non-

structural lightweight concrete recycled aggregate (RLM). This results from the most angular shape

found in RLHD particles. As several authors [Matias and de Brito (2005), Pereira (2010), Fonseca

(2009) and Amorim (2008)] found, this is a characteristic of recycled concrete aggregate.

Figure 6 shows the evolution of the water absorption of lightweight and recycled aggregates.

The aim of this test is to understand the evolution of the water absorption of lightweight ag-

gregates and recycled. Knowing this property allows assessing more accurately the amount of addi-

tional mixing water, since both lightweight aggregates and recycled aggregates have high porosity.

Figure 6 shows there was a rather high initial absorption for both lightweight aggregates used,

and a significant slowing-down after the first 30 minutes.

Figure 6 - Aggregates water absorption over time.

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


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2.3. Concrete design

In order to understand the mechanical performance of concrete with recycled lightweight ag-

gregate from crushed lightweight concrete, four families of concrete were produced, resulting from

the partial or total replacement of the original lightweight aggregates (Leca HD and Leca M) with

the recycled lightweight aggregates (RLHD and RLM). The substitution rates adopted were 0%,

20%, 50% and 100%, comprising 12 concrete mixes, which are referred to as:

BRHD - control lightweight concrete with structural expanded clay (Leca HD);

BRM - control lightweight concrete with non-structural expanded clay (Leca M);

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

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

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

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

B100RHD - lightweight concrete with 100% of RLHD;

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

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

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

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

B100RM - lightweight concrete with 100% of RLM;

In order to obtain a concrete similar to the one used in structural applications, it was decided

to produce the mixes with the following features:

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.

However, one must emphasize the functional difference between the two reference concrete

mixes. BRHD is a structural lightweight concrete while BRM has non-structural characteristics.

Table 4 shows the amounts adopted for the production of the two reference concrete mixess

(BRHD and BRM). Each concrete was designed for a total volume of 222.8 dm3.


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

Size grading BRHD BRM

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

3. Results and discussion

3.1. Fresh concrete properties

3.1.1. Workability

A range of 125 ± 10 mm in the slump test was stipulated for all compositions, corresponding

to a concrete consistency class S3.

Figure 7 shows the results of the slump test by Abram’s cone for all mixes produced.

Figure 7 - Slump test results.

Figure 7 allows concluding that all mixes complied with the stipulated range for slump, with

values within the interval set, with no need to correct the ratio w/c.

According to the project EuroLightCon R12 (2000), the absorption of lightweight aggregates

100

110

120

130

140

0 10 20 30 40 50 60 70 80 90 100

Slu

mp

(m

m)

Replacement rate of LWA with RLWAC (%)

BHD

BHD20RHD

BM20RHD

BHD50RHD

BM50RHD

B100RHD

BM

BHD20RM

BM20RM

BHD50RM

BM50RM

B100RM


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can lead to variations in the workability of concrete.

So, before producing the mixes, two tests were carried out (water content and water absorp-

tion at 30 minutes) to assess the amount of additional mixing water needed, to keep constant the

effective w/c. However, this is difficult to control and may result in variations in water quantity.

The largest slump obtained in BHD50RM (135 mm) can be associated with a variation of the water

absorption of the used aggregates, due to the difficulty of controlling the amount of mixing water.

3.1.2. Fresh concrete density

Figure 8 shows how the fresh concrete bulk density varies with the substitution rate of light-

weight aggregate (Leca HD and Leca M) with recycled lightweight aggregate (RLHD and RLM).

There is a clear growing trend of the fresh bulk density as recycled aggregates replace light-

weight aggregates. This result was expected, since the bulk density of recycled aggregates is higher

than that of lightweight aggregates. However, the replacement of lightweight aggregate Leca HD by

recycled aggregate RLM results in a decrease of this property, due to the greater density of light-

weight aggregate Leca HD, when compared to the recycled aggregate RLM.

Figure 8 - Fresh concrete density test results.

3.2. Hardened concrete properties

3.2.1. Compressive strength

This tests aims to evaluate the strength of the various concrete mixes produced when subject-

ed to an uniform compression stress. Thus, the mixes were exposed to an uniform growing com-

pression stress until collapse was reached.

Table 5 shows the average compressive strength values at 7, 28 and 90 days.

1700

1800

1900

2000

2100

2200

0 20 40 60 80 100

Den

sity

(k

g/m

3)

Replacement rate of LWA with RLWAC (%)

BHDRHD BMRHD BHDRM BMRM


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Table 5 - Compressive strength at 7, 28 and 90 days.

7 days 28 days 90 days

Concrete mix Replacement ratio

LWA-RLWAC (%)

ρdry

(kg/m3)

(fcm / ρdry) 28

days (103 m)

fcm (MPa) fcm (MPa) fcm (MPa)

BRHD 0 1628 23.6 32.8 38.4 39.3

BH20RHD 20 1672 24.1 33.9 40.4 41.3

BH50RHD 50 1739 24.8 34.4 43.1 46.8

B100RHD 100 1852 23.6 36.1 43.7 48.5

BHD20RM 20 1612 23.9 33.1 38.5 39.2

BH50RM 50 1590 22.8 32.2 36.3 38.7

BRM 0 1453 13.2 16.0 19.2 20.7

BM20RM 20 1473 17.0 21.6 25.1 26.5

BM50RM 50 1503 18.4 23.8 27.7 30.5

B100RM 100 1552 21.5 27.7 33.4 34.6

BM20RHD 20 1533 17.2 22.6 26.4 28.6

BM50RHD 50 1653 18.6 24.2 30.7 32.8

All mixes tended to increase its compressive strength with age. However, a less sharp devel-

opment occurred after 7 days, in particular in mixes with lower recycled aggregates’ content.

Figures 9 and 10 show the influence that the replacement rate has on the compressive strength

at 28 days of series BHD and BM, respectively.

Figure 9 - Effect of the replacement rate on the compressive

strength at 28 days of series BHD.

Figure 10 - Effect of the replacement rate on the compressive

strength at 28 days of series BM.

Figure 9 shows there is a greater influence on compressive strength of series BHD when recy-

cled lightweight aggregate RLM are incorporated, compared to RLHD. This has to do with the

composition of the source concrete, since it is a non-structural concrete (devoid of fine aggregate)

and the fact that was low-strength mortars, with w/c = 0.55, were used.

y = 0,1x + 39,199 R² = 0,84

y = -0,1x + 38,953 R² = 0,96

32,0

34,0

36,0

38,0

40,0

42,0

44,0

46,0

0 20 40 60 80 100

f cm

, 2

8 d

ias (M

Pa)

Replacement rate (%)

Série BHDRHD

Série BHDRM

y = 0,1x + 20,721 R² = 0,94

y = 0,2x + 20,028 R² = 0,98

15,0

20,0

25,0

30,0

35,0

40,0

45,0

0 20 40 60 80 100

f cm

, 28

dia

s (M

Pa)


Série BMRM

Série BMRHD


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Unlike with the replacement with RLHD, there was a decrease on compressive strength with

the replacement with RLM. This reduction results from the lower strength of recycled aggregate.

Nevertheless, the increase in compressive strength observed for mixes of series BHD with RLHD

results from the increase of mortar content and the higher strength of the recycled aggregate.

Unlikely series BHD, Figure 10 shows that for the BM series there is a greater influence of

the substitution of lightweight aggregate Leca HD with recycled lightweight aggregate RLM. This

results from the increase of mortar content that the use of this type of recycled lightweight aggre-

gate (RLHD) causes in the mix and the improvement of the characteristics of lightweight aggregate.

Nevertheless, the incorporation of RLM also caused a growing trend of compressive strength, due

again to the increase of mortar content and the greater strength of the recycled aggregate (resulting

from the effect of confinement of the light aggregate due to the paste).

3.2.2. Splitting tensile strength

This test consists of subjecting the cylindrical concrete specimens to a compressive force ap-

plied on a narrow area along their length, which generates orthogonal stresses to the plane of stress,

leading to the rupture of the specimen under tensile stress.

Table 6 shows the average values of splitting tensile strength for all the mixes, at 28 days.

Table 6 - Splitting tensile strength at 28days.

Splitting tensile strength

Concrete mix Replacement ratio LWA-RLWAC (%) fctm, SP (MPa)

BRHD 0 3.0

BHD20RHD 20 2.9

BHD50RHD 50 3.5

B100RHD 100 3.9

BHD20RM 20 3.0

BHD50RM 50 2.9

BRM 0 1.5

BM20RM 20 2.5

BM50RM 50 2.4

B100RM 100 2.7

BM20RHD 20 2.5

BM50RHD 50 2.8

Figures 11 and 12 show that the replacement of lightweight aggregate with recycled aggregate

improves the splitting tensile strength of mixes, at 28 days.


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Figure 11 - Effect of the replacement rate on splitting tensile

strength at 28 days of series BHD.

Figure 12 - Effect of the replacement rate on splitting tensile

strength at 28 days of series BM.

Figure 11 shows a clear evolution of the splitting tensile strength as the aggregate replacement

of lightweight aggregate Leca HD with recycled RLHD increases, suggesting that it has a big influ-

ence on this property. The variation of this property derives mainly from the texture of the aggre-

gate, its tensile strength and the quality of the aggregate-paste transition zone. So the use of recy-

cled aggregate RLHD promotes increased tensile strength, given the higher angular shape and ten-

sile stress of lightweight aggregate Leca HD. On the other hand, lightweight aggregate Leca HD

replacement with recycled aggregate RLM shows a decrease in splitting tensile strength. This re-

duction is again due to the shape of RLM, which is less angular than the RLHD’s and its strength,

which is lower than that of Leca HD. Regarding series BM, Figure 12 shows a significant im-

provement in splitting tensile strength, as the substitution of lightweight aggregate Leca M with

recycled aggregate RLHD increases. However, the main cause of this increase is the higher tensile

strength of the recycled lightweight aggregate. On the other hand, the use of recycled aggregate

RLM led to a growth of splitting tensile strength. This growth of tensile strength is not as signifi-

cant as when replacing with RLHD, because of the lower tensile strength displayed by the RLM.

Finally, all mixes of both series showed the same mode of rupture, with the rupture surface in-

tersecting the aggregates. So, it can be concluded that this property tends to be mainly conditioned

by the tensile strength of the aggregate.

3.2.3. Modulus of elasticity

The analysis of modulus of elasticity allows assessing the stiffness characteristics or deforma-

bility of concrete based on the relationship between stress and strain (σ - ε) under elastic defor-

y = 0,01x + 2,8673 R² = 0,91

y = -0,003x + 2,996 R² = 0,93

2,6

2,8

3,0

3,2

3,4

3,6

3,8

4,0

0 20 40 60 80 100

f ctm

, sp

, 28

dia

s (M

Pa)


BHDRHD

BHDRM

y = 0,01x + 1,9034 R² = 0,61

y = 0,02x + 1,7574 R² = 0,94

1,4

1,9

2,4

2,9

3,4

3,9

0 20 40 60 80 100

f ctm

, sp

, 28

dia

s (M

Pa)


BMRM

BMRHD


CONCRETE

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mations. Thus, the response of structures to imposed loads is intrinsically related to this parameter,

both in terms of deformation and the distribution of stresses.

Table 7 shows the average values of the modulus of elasticity for all mixes at 28 days.

The variation of the modulus of elasticity with the rate of replacement of light aggregate with

recycled aggregate is illustrated in Figures 13 and 14.

Table 7 - Modulus of elasticity at 28 days.

Modulus of elasticity

Concrete mix Replacement ratio LWA-RLWAC (%) E (GPa)

BRHD 0 20.75

BHD20RHD 20 20.74

BHD50RHD 50 23.41

B100RHD 100 25.37

BHD20RM 20 21.26

BHD50RM 50 21.19

BRM 0 12.77

BM20RM 20 19.11

BM50RM 50 19.82

B100RM 100 20.64

BM20RHD 20 18.40

BM50RHD 50 21.79

Figure 13 - Effect of the replacement rate on the modulus of

elasticity at 28 days of series BHD.

Figure 14 - Effect of the replacement rate on the modulus of

elasticity at 28 days of series BM.

Figure 13 shows a high influence on the modulus of elasticity of the replacement rate of

the lightweight aggregate Leca HD with recycled aggregate RLHD. The elasticity modulus de-

y = 0,05x + 20,426 R² = 0,95

y = -0,003x + 21,068 R² = 0,12

18,00

19,00

20,00

21,00

22,00

23,00

24,00

25,00

26,00

0 20 40 60 80 100

E (G

Pa)


BHDRHD

BHDRM

y = 0,06x + 15,363 R² = 0,60

y = 0,1x + 14,593 R² = 0,91

12,00

14,00

16,00

18,00

20,00

22,00

24,00

26,00

0 20 40 60 80 100

E (G

Pa)


BMRM

BMRHD


CONCRETE

13

pends mostly on the proportion and stiffness of its elements, particularly the cement and aggre-

gates. The replacement of lightweight aggregate with RLHD implies increased mortar content

in the mix, leading to an increase in the modulus of elasticity. On the other hand, there was a

slight improvement of the initial modulus of elasticity in the mixes of series BHD composed by

RLM, linked to the increased stiffness of the recycled lightweight aggregate RLM (effect of the

envelopment of mortar around the original lightweight aggregate Leca M). Nevertheless, the

increase in the replacement rate of lightweight aggregate with RLM shows a slight reducing

trend of this property, justified by the similarity of the stiffness of recycled aggregate RLM and

the original lightweight aggregate (Leca HD). This results from the similarity of bulk densities

of the lightweight aggregate (Leca HD) and recycled aggregate RLM. On the other hand, the

paste that surrounds the recycled aggregate RLM acts as a confinement of the latter, which con-

tributes to a further increase of its stiffness. So, even though the bulk density of the RLM is

slightly lower than that of the original lightweight aggregate (Leca HD), their stiffness tends to

be identical.

Figure 14 also proves there is a big influence on the modulus of elasticity of the replace-

ment rate of lightweight aggregate Leca M with recycled aggregate RLHD. This substitution led

to a significant growth of this property that is justified by the higher strength and stiffness of

the recycled lightweight aggregate RLHD, when compared to Leca M. All mixes of series BM

made with RLM also show an improvement of this property with the increase of the replace-

ment rate. The stiffness increase results, once again, from the incorporation of a recycled aggre-

gate (RLM) with higher stiffness than the original aggregate (Leca M), not only because it has

greater bulk density but also because of the envelopment of the paste, which confines the ag-

gregate itself.

3.2.4. Abrasion resistance

The precise characterization of the abrasion resistance is a factor of great importance in

structures where the concrete is subjected to exterior actions which cause the deployment of its

elements.

Table 8 shows the average abrasion resistance values recorded for all mixes at 91 days.

Figures 15 and 16 show the influence of the replacement rate on the average wear result-

ing from the characterization of the abrasion resistance of the specimens.

In lightweight concrete, abrasion resistance depends not only on the lightweight aggre-

gates, but also on the strength of the matrix and bond between the aggregates and the cement

paste.


CONCRETE

14

Table 8 - Abrasion resistance at 91 days.

Abrasion resistance

Concrete mix Replacement ratio LWA-RLWAC (%) Average wear (mm) Mass difference (g)

BRHD 0 4.55 9.3

BHD20RHD 20 4.22 9.0

BHD50RHD 50 4.12 8.5

B100RHD 100 4.46 9.4

BHD20RM 20 4.53 9.5

BHD50RM 50 4.17 8.5

BRM 0 5.78 12.2

BM20RM 20 4.69 9.9

BM50RM 50 3.59 7.5

B100RM 100 4.10 8.5

BM20RHD 20 4.88 10.0

BM50RHD 50 3.61 8.1

Figure 15 - Influence of the replacement rate on the average

wear at 91 days of series BHD.

Figure 16 - Influence of the replacement rate on the average

wear at 91 days of series BM.

Figure 15 shows that the replacement of lightweight aggregate Leca HD with RLHD pro-

motes a significant improvement of wear resistance as the replacement rate, increases except for the

B100RHD mix, whose result appears to be anomalous in view of the trend. This improvement re-

sults from the increase of mortar content conferred by RLHD. The result obtained for the B100RHD

mix can be partly justified by the variability associated to abrasion test.

On the other hand, the replacement of lightweight aggregate Leca HD with RLM led to signif-

icant improvements in abrasion resistance, i.e. a wear reduction with the increase of replacement

rate with RLM. This can be justified, once again, by the increase of mortar content in the mix, as

y = -0,0002x + 4,3478 R² = 0,002

y = -0,005x + 4,5779 R² = 0,86

4,0

4,1

4,2

4,3

4,4

4,5

4,6

4,7

4,8

4,9

5,0

0 20 40 60 80 100

We

ar a

vera

ge (

mm

)


BHDRHD

BHDRM

y = -0,016x + 5,2036 R² = 0,52

y = -0,01x + 5,2332 R² = 0,38

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

0 20 40 60 80 100

We

ar a

vera

ge (

mm

)

Replacemente rate (%)

BMRM

BMRHD


CONCRETE

15

well as by the fact that the original lightweight aggregate (Leca M) is benefited by a confinement

effect, which results in increasing its surface resistance, and therefore its wear resistance.

Regarding the replacement of lightweight aggregate Leca M with RLM, Figure 16 shows

again the increase of abrasion resistance for replacement rates up to 50%, primarily due to the

strength increase of the replaced aggregate that stems from the action of the paste that involves the

original lightweight aggregate Leca M and the increase of mortar content. However, for replace-

ment rates of 100% recycled aggregate (RLHD / RLM), there were, similarly to the BHD series,

anomalous values. In parallel, the replacement with RLHD showed a similar trend to that observed

for the replacement with RLM, even though leading to a higher degradation of abrasion resistance.

4. CONCLUSIONS

In this study, the mechanical performance of concrete with lightweight aggregates from

crushed lightweight concrete floors was analysed. Through the analysis of all the results, in the

course of this dissertation, it can be concluded that:

It is feasible to use recycled lightweight aggregate from crushed lightweight concrete, in the

production of recycled lightweight concrete (bulk density less than 2000 kg/m3);

In general, the incorporation of recycled lightweight aggregate promotes the increase of

compression strength, as well as structural efficiency. However, in mixes with structural

lightweight aggregate (Leca HD) the substitution of lightweight aggregate with non-

structural recycled lightweight aggregate (RLM) results in a decrease of this property;

Like compressive strength, splitting tensile strength showed very significant improvements

with the increase of the replacement rate of lightweight aggregate with recycled lightweight

aggregate, allowing confirming the correlation of this property with the rupture mode (the

surface rupture intersected the aggregates in both series), as well as with its tensile strength.

However, for mixes with structural lightweight aggregates (Leca HD),« the substitution with

recycled lightweight aggregates RLM led to a reduction of this property;

The modulus of elasticity showed a trend similar to that obtained in the characterization of

the splitting tensile and compressive strength, improving with the increase of the replace-

ment rate with recycled aggregate. With the exception of mixes composed by structural

lightweight aggregate (Leca HD) and recycled lightweight aggregate RLM, the results indi-

cate that there is a high relationship between the modulus of elasticity and the stiffness and

proportion of the elements of structural lightweight concrete;

Abrasion resistance also showed, in general, an improvement with the increase of the re-

placement rate. However, the variability associated to the abrasion test produced anomalous


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results (by comparison with the trend observed) for mixes composed only by lightweight

aggregate recycled (RLHD and MLR), i.e. with no original lightweight aggregates.

Generally, the replacement in concrete of lightweight aggregate with recycled lightweight ag-

gregate promotes the improvement of its mechanical properties. This is promoted by the increased

bulk density, which usually translates into a negligible variation of structural efficiency (except for

mixes of series BHD composed by RLM). Nevertheless, the incorporation of 20% recycled light-

weight aggregate RLM, in the production of lightweight concrete led to very significant improve-

ments at the level of its mechanical performance.

5. REFERENCES

Amorim, P. (2008) - “Influence of the curing conditions in the performance in terms of du-

rability of concretes with recycled concrete aggregates (in Portuguese)”, MSc Dissertation

in Civil Engineering, Instituto Superior Técnico, Lisbon;

Angulo, S. (1998) - “Production of concrete with recycled aggregates (in Portuguese)”,

MSc Dissertation in Civil Engineering, Universidade Estadual de Londrina, Brazil.

Brandon, P. S. (1998) - “Sustainability in management and organization: the key issues”,

CIB Building congress - Materials and technologies for sustainable construction, Switzer-

land, pp.1739-47;

DIN 52108 (2002) - Testing of inorganic non-metallic materials: wear test with the grinding

wheel according to Boehme;

EuroLightCon R12 (2000) - “Applicability of the particle-matrix model to LWAC”, Project

BE96-3942R12;

Fonseca, N. (2009) - “Structural concrete with incorporated recycled concrete coarse ag-

gregates - Influence of the curing conditions (in Portuguese)”, MSc Dissertation in Civil

Engineering, Instituto Superior Técnico, Lisbon;

John, V. M. (2000) - “Recycling of waste in construction: A contribution to the methodolo-

gy of research and development (in Portuguese)”, Escola Politécnica da Universidade de

São Paulo, Brazil;

LNEC E 397 (1993) – Concrete: Determination of modulus of elasticity in compression (in

Portuguese), LNEC, Lisbon;

Matias, D.; Brito, J. de (2005) - “Concrete with recycled coarse aggregate concrete and

the use of admixtures (in Portuguese)”, ICIST DTC nº. 3/05 Report, Instituto Superior

Técnico, Lisbon;


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NP EN 933-1 (2000) - Geometric property test for aggregates: Size grading analysis. Siev-

ing method (in Portuguese), IPQ, Lisbon;

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

tion. 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;.


Determination of water content by drying in a ventilated oven (in Portuguese), IPQ, Lisbon;


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

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

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

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

mens (in Portuguese), IPQ, Lisbon;

NP EN 12390-6 (2003) - Tests on hardened concrete: Splitting tensile strength of test spec-

imens (in Portuguese), IPQ, Lisbon;

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

minous mixtures and surface treatments and for unbound and bound applications (in Portu-

guese), IPQ, Lisbon;

Pereira, P. S. B. (2010) - “Influence of superplasticizers on the mechanical behavior (in

Portuguese)”, MSc Dissertation in Civil Engineering, Instituto Superior Técnico, Lisbon;

Zordan, S. (1997) - “The use of debris as an aggregate in the production of concrete (in

Portuguese)”, MSc Dissertation in Civil Engineering, Universidade Estadual de Campinas,

brazil;

Zwan, J. T. (1997) - “Application of waste materials - A success now, a success in the fu-

ture”, Waste materials in constructions: Putting theory into practice, Great Britain, pp. 869-

81.

Documents

José Maria Guedes Machado Lemos de Figueiredo Extended … · Slump NP EN12350-2 Fresh density NP EN12350-6 Hardened concrete tests Test standard Compressive strength NP EN 12390-3