Extended Abstract

MECHANICAL BEHAVIOUR OF CONCRETE WITH IN-

CORPORATION OF RECYCLED CERAMIC FINE AG-

GREGATES

André Filipe Corrêa dos Santos Vaz Alves

ABSTRACT

This research aims at evaluating the effect of the incorporation of recycled ceramic fine aggre-

gates, particularly aggregates from crushed bricks and crushed sanitary ware, on the mechanical

properties of concrete. The effect of such incorporation in properties such as the compressive

strength, the splitting tensile strength, the elasticity modulus and the abrasion resistance were

investigated and discussed in detail.

Cylindrical and cubic specimens were cast to test the aforementioned hardened properties of the

concrete, with seven different concrete mixes: a conventional reference concrete and six concrete

mixes with replacement rates of 20%, 50% and 100% of natural fine aggregates by fine recycled

brick aggregates and fine recycled sanitary ware aggregates. All mixes were prepared with the

same workability and the same grading curve to allow for a valid comparison of results. Results

obtained show that concrete with recycled crushed bricks exhibits adequate structural perfor-

mance. In opposition, concrete with recycled sanitary ware suffered considerable performance

reduction compared to the reference concrete.

KEYWORDS:

Construction and demolition waste; Concrete; Fine recycled brick aggregates; Fine recycled

sanitary ware aggregates; Mechanical behaviour

March 2013

Structural concrete with incorporated recycled ceramic fine aggregates

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1 INTRODUCTION

1.1 PRELIMINARY REMARKS

The use of recycled aggregates (RA) in concrete opens a whole new range of possibilities in

reusing and recycling construction and demolition waste. Reuse of ceramic waste as RA in new

concrete is beneficial from the viewpoint of environmental protection and preservation of re-

sources. This could be an important breakthrough for society in its endeavour towards sustain-

able development.

Preceding studies mainly focused on the mechanical properties and durability aspects. Brito

(2005) reviewed some of the studies on the mechanical behaviour of recycled aggregate con-

crete (RAC). This review shows that, in fact, none of those works indicated that RAC is unsuita-

ble for structural applications.

Recent investigations on the performance of concrete made with recycled ceramic fine aggre-

gates (Khatib, 2004; Debieb and Kenai, 2007; López et al., 2007) and recycled ceramic coarse

aggregates (Gomes, 2007; Pereira, 2005; Guerra et al., 2008; Medina et al., 2011), as well as

on the influence of the pre-saturation of recycled aggregates (Ferreira, 2007), have given posi-

tive results, which further support and encourage the odds of applying recycled ceramic aggre-

gate concrete (RCAC) in civil engineering structures.

1.2 SCOPE AND METHODOLOGY OF THE INVESTIGATION

The literature review showed that there is a lack of information regarding the influence of the

incorporation of recycled ceramic fine aggregates on the mechanical behaviour of concrete,

mainly fine sanitary ware aggregates. As such, this dissertation aims at assessing the influence

of such incorporation on the mechanical properties of recycled ceramic fine aggregate concrete

(RCFAC). The following mechanical properties were investigated: compressive strength, split-

ting tensile strength, elasticity modulus and abrasion resistance.

The primary stage of this investigation consisted of performing a literature review of internation-

al and national experimental studies on this topic. The information collected constituted a repos-

itory that refers the most important properties of the aggregates, the experimental test results,

and the conclusions of each campaign. A common trend to all the studies on this matter is that

they show a generalized worsening of the mechanical properties of the RAC, with the increase

of the substitution rate of natural aggregates (NA) by RA, when compared with natural aggre-

gate concrete (NAC) (concrete produced only with NA).

After this stage, the experimental program was planned and executed. The recycled ceramic

fine aggregates (RCFA) and NA (fine and coarse) were analysed. Seven concrete mixes were

produced. All concrete mixes were produced with the same workability and grading curves, in

order to allow a valid comparison between them. After curing, the hardened concrete tests were

performed.

Subsequently, the experimental results were analysed and discussed in detail. Correlations

were established between the properties of the RCFAC and the density and water absorption of

the aggregates and the substitution rate of natural fine aggregate (NFA) by RFCA.


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2 EXPERIMENTAL PROGRAM

2.1 MATERIALS

The following materials were used in the experimental campaign:

Recycled ceramic fine aggregates (RCFA): recycled fine brick aggregates (RFBA)

were provided by Grupo Tábuas e Leite & C.a, LDA and recycled fine sanitary ware

aggregates (RFSA) were provided by Grupo ROCA;

Natural aggregates (NA): the coarse NA (limestone) and fine NA (river sand) were

provided by Grupo Soarvamil;

Cement: ordinary CEM II A-L 42.5 R Portland cement was used;

Water: tap water was used in all mixes.

2.2 MIX DESIGN

The following seven concrete mixes were produced: a conventional reference concrete (NAC)

and six recycled concrete mixes with substitution rates of 20%, 50% and 100% of NFA by RCFA

(three types of concrete for each type of RCFA). As already mentioned, the concrete mixes

were prepared with the same workability (slump of 125 ± 10 mm) and the same aggregates„

grading curve. The proportions of the materials were determined on the basis of absolute vol-

ume of the constituents. The details of NAC‟s mix proportions are given in Table 1. The charac-

teristics of the reference concrete are as follows:

Concrete class: C 25/30;

Slump class: S3;

Exposure class: XC3;

Binder: cement CEM II A-L 42.5 R Portland;

Aggregates’ maximum size: Dmax = 22.4 mm;

Chemical and mineral admixtures: none.

Table 1 - Mix proportions of natural aggregate concrete (NAC)

Constituent Size (mm) Volume (m3/m

3)

Fine

0 to 0.063 0.0000

0.063 to 0.125 0.0142

0.125 to 0.25 0.0430

0.25 to 0.5 0.0493

0.5 to 1 0.0567

1 to 2 0.0651

2 to 4 0.0748

Aggregate Volume (m3/m

3)

Coarse

“Rice grain” 0.0570

Gravel 1 0.0223

Gravel 2 0.2923

Volume (m3/m

3)

Cement 0.1150

Water 0.1930

2.3 CURING CONDITIONS

The test specimens were subjected to curing in a wet chamber for 28 days.


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2.4 TESTING OF AGGREGATES

The particle size distribution was determined in accordance with EN 933-1 (1997) and EN 933-2

(1995) specifications. The particle density and water absorption were measured following EN

1097-6 (2000). The bulk density was determined in accordance with EN 1097-3 (1998). The

aggregates‟ resistance to abrasion was measured by the Los Angeles loss test following LNEC

E-237 (1970). The water content was determined in accordance with EN 1097-5 (2008). The

shape index was measured following EN 933-4 (2008).

2.5 TESTING OF FRESH CONCRETE

The fresh concrete was produced using a revolving drum concrete mixer. Immediately after

mixing, concrete was tested for slump and density. The slump was determined according to

Abrams‟ slump test following EN 12350-2 (1999). The concrete‟s fresh density was measured

according to EN 12350-6 (1999).

2.6 TESTING OF HARDENED CONCRETE

The 7, 28 and 56-day compressive strength of the concrete was determined in accordance with

EN 12390-3 (2001). The 28-day tensile splitting strength was measured following EN 12390-6

(2000). The elasticity modulus in compression was measured following LNEC E-397 (1993).

The abrasion resistance was determined by Böhme‟s grinding wheel wear test, in accordance

with DIN 52108 (2002).

3 RESULTS AND DISCUSSION

3.1 PROPERTIES OF AGGREGATES

Table 2 shows the results of the tests carried out on the aggregates.

Property Gravel 2 Gravel 1 "Rice Grain"

Coarse river sand

Fine river sand

RFSA RFBA

Bulk density (kg/m3)

2512.1 2545.7 2568.7 2554.3 2529.1 2968.5 1948.4

Water absorption (%)

1.7 1.7 1.6 0.6 0.3 0.2 12.2

Apparent bulk density (kg/m3)

1449.8 1437.6 1416.3 1578.8 1555.6 1318.9 1031.8

Los Angeles abra-sion resistance

(%) 28.4 25.8 22.7 - - - -

Shape index (%) 14.8 17.0 17.8 - - - -

3.2 WORKABILITY

Table 3 presents, for all rates of substitution of NFA by RCFA, the results of the Abrams cone

slump test (h) and the apparent and effective water / cement ratios. In this table, RBCi is the

concrete with incorporated RFBA with a substitution rate of i and RSCi is the concrete with in-

corporated RFSA with a substitution rate of i.


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Table 3 - Results of the Abrams cone slump test and apparent and effective water / cement ratio

Composition h (mm) Apparent water / cement ratio Effective water / cement ratio

NAC 123.0 ± 2.0 0.53 0.53

RBC20 123.0 ± 0.0 0.56 0.53

RBC50 133.5 ± 0.5 0.61 0.53

RBC100 115.5 ± 0.5 0.64 0.53

RSC20 119.5 ± 0.5 0.76 0.76

RSC50 116.0 ± 0.0 0.78 0.78

RSC100 116.0 ± 1.0 0.86 0.86

Table 3 shows that although recycled ceramic aggregates negatively affect the workability of the

concrete in which they are incorporated, changing the water / cement ratio is an effective pro-

cedure to overcome this problem. In fact, all concretes produced had a slump within the target

interval (125 ± 10 mm). The water / cement ratio had to be increased with the percentage of

aggregate substitution.

For all mixes incorporating RFBA, the increase of the apparent water / cement ratio is due to the

higher water absorption of those aggregates. In the case of mixes incorporating RFSA, despite

the lower water absorption of those aggregates, an increase of water was needed to obtain the

target slump. This is probably due to the glazed surface together with the referred low water

absorption of those aggregates. These two properties were probably responsible for the accu-

mulation of some water on the interface between the RFSA and NCA (natural coarse aggre-

gates) due to liquid bridges between them; therefore, higher water content was needed to ob-

tain the target slump.

In order to further contribute to the analysis of the viability of the use of fine sanitary ware ag-

gregates in concrete, additional specimens of RSC100 (not presented in Table 3) were pro-

duced with superplasticizer, aiming at avoiding this problem. When a superplasticizer content of

1% of cement mass was used together with the same water / cement ratio of the NAC mix, the

slump was kept within the target interval.

3.3 FRESH DENSITY

Figures 1 and 2 present the results of the fresh density test for all concretes produced.

Figure 1 - Fresh density of the mixes with

incorporated RFBA

Figure 2 - Fresh density of the mixes with

incorporated RFSA


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For mixes incorporating RFBA, due to the lower bulk density of these aggregates relatively to

the natural ones, fresh density decreases with the increase of the replacement ratio (Figure 1).

For mixes incorporating RFSA, despite the higher bulk density of these aggregates, when com-

pared to NFA, fresh density decreases with the increase of the replacement ratio (Figure 2).

This is due to the much higher water content of mixes incorporating RFSA.

3.4 COMPRESSIVE STRENGTH

The development of compressive strength with age is illustrated in Figure 3. The test results at

7, 28 and 56 days are presented in Figure 4. Detailed results are listed in Table 4, in which is

the relative difference compared with NAC

Table 4 - Compressive strength at 7, 28 and 56-days (average ± standard deviation)

Composition fcm 7 (MPa) Δ (%) fcm 28 (MPa) Δ (%) fcm 56 (MPa) Δ (%)

NAC 39.0 ± 2.1 - 46.2 ± 0.9 - 47.6 ± 1.5 -

RBC20 33.4 ± 0.3 -14.5 42.9 ± 0.4 -7.0 46.8 ± 0.4 -1.7

RBC50 29.3 ± 0.9 -24.9 41.8 ± 0.6 -9.5 45.5 ± 1.0 -4.4

RBC100 30.2 ± 2.1 -22.5 41.7 ± 2.0 -9.6 44.2 ± 2.4 -7.1

RSC20 25.1 ± 1.2 -35.7 31.2 ± 1.1 -32.5 34.0 ± 0.4 -28.5

RSC50 23.6 ± 0.7 -39.6 30.7 ± 0.3 -33.5 33.5 ± 1.5 -29.7

RSC100 19.6 ± 0.9 -49.8 26.6 ± 1.5 -42.5 31.0 ± 1.5 -34.9

Figure 3 - Compressive strength evolution with age

Figure 4 - Compressive strength versus ratio of NCA substitution by RCFA


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The results show that the compressive strength has a decreasing trend with the increase of the

replacement ratio. Another conclusion from Figures 3 and 4 is that, for any age and replace-

ment ratio, mixes incorporating RFBA have a higher resistance than those incorporating RFSA.

This is due to a significant difference in the water / cement ratio of these two types of concrete.

Analysing only the RBC compositions, at 28 days of age the maximum loss of resistance rela-

tively to NAC was 10% for RBC100. With the increase of age of these compositions, the differ-

ence between their strength and that of NAC decreases. This is probably due to some pozolanic

activity of the fine brick aggregates or due to the additional water added to the mix, which may

have contributed to a later cement hydration.

Analysing only RSC compositions, at 28 days of age, the maximum loss of resistance relatively

to NAC was 43% for RCS100. For these compositions, no decrease was observed in the differ-

ence of strength relatively to NAC.

The RSC100 composition with superplasticizer presented, at 28 days of age, a strength 28%

higher than that of NAC. This result indicates a high potential of this type of recycled ceramic

aggregates to produce structural concrete, provided that superplasticizer is used.

3.5 SPLITTING TENSILE STRENGTH

The results for the 28-day splitting tensile strength of concrete are presented in Figure 5 and

listed in detail in Table 5.

Table 5 - Splitting tensile strength

Composition fctm (MPa) Δ (%)

NAC 3.60 ± 0.2 -

RBC20 3.53 ± 0.1 -2.0

RBC50 3.40 ± 0.0 -5.7

RBC100 3.42 ± 0.4 -5.2

RSC20 2.71 ± 0.2 -24.8

RSC50 2.60 ± 0.3 -27.7

RSC100 2.38 ± 0.4 -33.8

Figure 5 - Splitting tensile strength versus ratio of NAC substitution by RCFA

Results show that the splitting tensile strength decreases with the replacement ratio for both

types of RCFA. Another conclusion from Figure 5 is that, for any replacement ratio, mixes incor-


8

porating RFBA have a higher resistance than mixes incorporating RFSA. This is due to a signif-

icant difference in the water / cement content of these two types of concrete.

Analysing only RBC compositions, at 28 days of age, the maximum loss of strength relatively to

NAC was 6% for RBC50. For RSC compositions, the maximum loss was 34%, for RSC100.

The RSC100 composition with superplasticizer presented a strength at 28 days of age that was

17% higher than that of NAC. This result indicates a high potential of this type of recycled ce-

ramic aggregates to produce structural concrete, provided that superplasticizer is used.

3.6 ELASTICITY MODULUS

The results for the elasticity modulus in compression of concrete are presented in Figure 6 and

listed, in detail, in Table 6.

The modulus of elasticity decreases with the increase in the incorporation of RFBA and RFSA.

For increasing incorporation ratios, it varied from 38.3 GPa to 27.2 GPa for RFBA and from 38.3

GPa to 28.3 GPa for RFSA.

Table 6 - Elasticity modulus

Composition Ecm (GPa) Δ (%)

NAC 38.3 ± 1.1 -

RBC20 32.4 ± 0.3 -15.4

RBC50 31.6 ± 0.3 -17.5

RBC100 27.2 ± 0.5 -29.0

RSC20 31.3 ± 0.1 -18.2

RSC50 31.0 ± 0.4 -19.1

RSC100 28.3 ± 0.6 -26.0

Figure 6 - Elasticity modulus versus ratio of NAC substitution by RCFA

The reduction observed in RBC compositions is mainly due to the increase of the water / ce-

ment ratio with the replacement ratio and to the lower elasticity modulus of the RFBA, relatively

to the NFA. For RSC compositions, despite the probably higher elasticity modulus of RFSA

when compared to the natural aggregates, the increase of the water / cement ratio with the re-

placement ratio prevails, contributing to the overall reduction of concrete stiffness. In fact, for a

replacement ratio of 100%, concrete incorporating RFSA has a higher elasticity modulus than

concrete with RFBA, despite the higher water content.


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3.7 ABRASION RESISTANCE

The results for the abrasion resistance of concrete are listed in Table7 and presented in Figure

7, where Δl is the loss of thickness of the specimen.

Since curing conditions strongly affect concrete‟s surface layer, the test specimens (71x71x50

mm3) were obtained by sawing larger concrete cubes (100 mm edge) after curing. This was

done in order to prevent the concrete‟s surface finishing from being a variable in the test. Thus,

the test surface is the cutting surface itself, i.e., an internal plane of the concrete element com-

posed by aggregates and binder mix, and not an outer surface.

Table 7 - Abrasion resistance

Composition Δlm (mm) Δ (%)

NAC 4.02 ± 0.1 -

RBC20 4.38 ± 0.2 9.0

RBC50 4.65 ± 0.3 15.8

RBC100 5.28 ± 0.3 31.4

RSC20 5.67 ± 0.3 41.0

RSC50 5.68 ± 0.2 41.4

RSC100 6.02 ± 0.3 49.8

Figure 7 - Abrasion resistance versus ratio of NAC substitution by RCFA

Figure 7 shows that the abrasion resistance decreases with the incorporation of fine ceramic

aggregates.

Analysing only RBC compositions, the maximum loss of depth relatively to NAC was 31% for

RBC100. Despite the fact that RFBA can obtain a better link to the cement than NFA (due to

their shape and porosity), the increase in the water content with the replacement ratio prevails,

thereby reducing the resistance of the concrete to abrasion.

Analysing only RSC compositions, the maximum loss of depth relatively to NAC was 50% for

RSC100. Similarly to mixes incorporating RFBA, the increase in the water / cement ratio of the-

se mixes is the cause of this resistance loss.

4 CONCLUSIONS

The use of RAC should always take into consideration that they have, in most cases, a lower

performance when compared to conventional concrete. Nevertheless, concrete incorporating

RFBA can exhibit adequate quality as structural concrete, unlike concrete with RFSA, which


10

does not seem to be adequate for structural purposes, at least without superplasticizeres. The

following conclusions can be drawn based on the experimental results obtained in this study:

(1) Compressive strength and splitting tensile strength do not seem to be highly affected by

RFBA incorporation, when compared with conventional concrete, but these two properties

considerably decrease with incorporation of RFSA;

(2) Elasticity modulus decreases with the increase of the replacement ratio of both RFBA and

RFSA;

(3) Abrasion resistance is negatively affected by RFBA and RFSA incorporation;

(4) Future studies analysing the influence of superplasticizeres on the mechanical behaviour of

mixes incorporating RCFA, especially RFSA, should be performed, in order to continue the

preliminary analysis undertaken within this study. The results presented herein suggest a

high potential of recycled ceramic aggregates (even RFSA) to produce structural concrete,

provided that superplasticizer is used.

5 REFERENCES

De Brito, J. (2005) - Recycled aggregates and their influence on concrete‟s properties (in Por-

tuguese). Public lecture within the full professorship in Civil Engineering pre-admission exami-

nation, Instituto Superior Técnico, Lisbon.

De Brito, J.; Pereira, A. S.; Correia, J. R. (2005) - Mechanical behaviour of non-structural

concrete made with recycled ceramic aggregates, Cement and Concrete Composites, Vol. 27,

nº 4, pp. 429 - 433.

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

wheel according to Böhme.

EN 1097-3 (1998) - Tests for mechanical and physical properties of aggregates. Part 3: Deter-

mination of loose bulk density and voids.


mination of the water content by drying in a ventilated oven.


mination of particle density and water absorption.

EN 12350-2 (1999) - Testing fresh concrete. Part 2: Slump test.

EN 12350-6 (1999) - Testing fresh concrete. Part 6: Density.

EN 12390-3 (2001) - Testing hardened concrete. Part 3: Compressive strength of test speci-

mens.

EN 12390-6 (2000) - Testing hardened concrete. Part 6: Tensile splitting strength of test speci-

mens.

EN 933-1 (1997) - Tests for geometrical properties of aggregates. Part 1: Determination of par-

ticle size distribution. Sieving method.


ticle size distribution. Test sieves, nominal size of apertures.


ticle shape. Shape index.


11

Ferreira, L. (2007) - Structural concrete with incorporation of coarse recycled concrete aggre-

gates: Influence of the pre-saturation (in Portuguese). MSc Dissertation in Civil Engineering,

Instituto Superior Técnico, Lisbon.

Gomes, M. (2007) - Structural concrete with incorporation of concrete, ceramic and mortar re-

cycled aggregates (in Portuguese). MSc Dissertation in Construction, Instituto Superior Técnico,

Lisbon.

Kenai, S.; Debieb, F. (2007) - The use of coarse and fine crushed bricks as aggregate in con-

crete, Construction and Building Materials, Vol. 22, nº 5, pp. 886 - 893.

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Concrete Research, Vol. 35, nº 4, pp. 763 - 769.

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LNEC E-397 (1993) - Concrete: Determination of elastic modulus in compression.

López, V.; Llamas, B.; Juan, A.; Morán, J. M.; Guerra, I. (2008) - Eco-efficient concretes:

Impact of the use of white ceramic powder on the mechanical properties of concrete, Biosys-

tems Engineering, Vol. 96, nº 4, pp. 559 - 564.

Medina, C.; Rojas, M. I. S.; Frías, M. (2011) - Reuse of sanitary ceramic wastes as coarse

aggregate in eco-efficient concretes, Cement and Concrete Composites, Vol. 34, nº 1, pp. 48 -

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Extended Abstract