Extended fddfdAbstract José Saraiva Lima

8/11/2019 Extended fddfdAbstract Jos Saraiva Lima

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Fire behaviour of concrete produced with selected plastic

waste aggregates

Jos Guilherme Colao Alegre Saraiva Lima

Extended Abstract

Supervisor: Professor Doutor Joo Pedro Rama Ribeiro Correia (IST)

Co-Supervisor: Professor Doutor Jorge Manuel Calio Lopes de Brito (IST)

November 2012


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Extended abstract

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1. Introduction

The production of plastic waste has been increasing considerably, and is mostly sent to

dumping grounds. The interest in recycling it, both ecologic and economic, is not only due to its ag-

gressiveness towards the environment but also to its high volume in dumping grounds and high re-

sistance to atmospheric and biological agents, making this solution unsustainable.

Several studies related to its reuse have been carried out, in which the use of plastic waste

aggregates (PWA) as a partial substitute of natural aggregates (NA) in the production of structural

concrete is one of the goals (e.g., Ferreira, 2011; Silva, 2011; Saikia and Brito, 2011). This turns out to

be a very interesting medium term solution for disposing of plastic waste since, in addition to allow-

ing the flow of a high volume of waste which otherwise would be landfilled, its incorporation in con-

crete is an alternative to the extraction of natural aggregates from quarries. The weak bond between

the aggregates and the cementitious matrix results in an increase of the porosity of concrete. There-

fore, the substitution of NA by PWA results in a decay of the mechanical performance (Saiki and

Brito, 2011) and of the durability-related properties (Silva, 2011) of concrete. Such performancereduction increases with the replacement ratio.

Although concrete is a fire-resistant material, due to its incombustibility and low thermal con-

ductivity coefficient (compared to steel), its exposure to high temperatures induces a series of physic-

chemical reactions causing a degradation of its mechanical properties. The exposure of concrete to

high temperatures, associated to the thermal incompatibility of its constituents, results in the accumu-

lation of local stresses and, subsequently, in the formation of micro-cracks, depending its extension on

the temperature of exposure and the materials nature, namely the aggregates and the binder.

Above 100 C, the free water retained by capillarity inside concrete begins to evaporate. This

process ends at between 200 C and 300 C without any noticeable major changes in concrete. Dehy-

dration of the cementitious matrix occurs between 300 C and 400 C, which leads to major strength

loss and to the appearance of superficial cracks. At higher temperatures (between 400 C and 800 C),

the different thermal expansion of concretes components causes inner stresses and subsequent crack-

ing. Thermal expansion of limestone aggregates is clearly lower than for other types of aggregates, and

they even suffer a volume decrease between 600 C and 800 C due to their de-carbonation, a highly

endothermic reaction which is associated to a significant loss of mass and mechanical strength (Brito

and Neves, 1997). According to Chan et al. (1999), the major degradation of the mechanical strength of

concrete occurs at this stage. Between 950 and 1200 C, concrete becomes a calcinated material.

The fire behaviour of concrete is strongly influenced by its water content. Its evaporation re-

sults in an increase of its volume which, due to being confined to concrete pores, causes internalpressures that can lead to cracking and to spalling of the surface layer of concrete.

PWA are considerably more sensitive to high temperatures than the remaining constituents of

concrete, due to their combustibility. For the use of concrete containing PWA to become possible in the

building sector, it is necessary to know its properties, in particular its fire behaviour, including its me-

chanical strength degradation and fire reaction properties. It is essential to quantify fire both behavioural

aspects and, based on the corresponding performance, to conclude whether this material can withstand

high temperatures without collapsing or endangering human lives. It is also important to assess its resid-

ual mechanical performance, regarding its use after exposure to high temperatures. This dissertation

aims to fulfil the lack of information on the topic.

Three types of plastic waste aggregates, including coarse and fine particles, and two replace-ment ratios (7.5% and 15%) were studied. The residual properties were determined for two thermal


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Fire behaviour of concrete produced with selected plastic waste aggregates

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exposures (heating according to ISO 834 up to 600 C and 800 C, temperatures that were then main-

tained for 1 hour). The concrete specimens were characterized before and after the thermal exposure

by their compressive strength, splitting tensile strength, modulus of elasticity, ultrasonic pulse velocity

(UPV), surface hardness (Schmidt hammer) and water absorption (by immersion). Fire reaction proper-

ties were tested in a cone calorimeter for three heat fluxes (25 kW/m2, 50 kW/m2and 75 kW/m2).

2. Experimental programme

2.1Materials

In this investigation, crushed limestone and river sand were used as natural coarse and fine

aggregates, respectively. Three types of poly (ethylene terephthalate), PET, waste aggregates were

analysed: coarse / flakes (Pc) and fines (Pf), resulting from shredded PET waste, and pellets (Pp),

consisting of nearly-spherical shaped granules obtained from a post-heat treatment of PET waste. All

concrete specimens were produced with CEM II A-L 42.5 R cement and tap water. The aggregates

were characterized through the tests listed in Table 1, in accordance with the standards indicated.

Table 1 - Aggregate tests.

These tests allowed quantifying the differences between natural aggregates (NA) and plasticwaste aggregates (PWA) in terms of density, shape and size. The results are shown in Table 2.

Table 2 - Aggregate tests results.

Type of aggregateCoarse

gravel

Fine

gravelGranule Coarse sand Fine sand Pc Pp Pf

Particle dry density [kg/m3] 2671 2665 2732 2717 2647 1302 1303 1280

Water absorption [%] 0.55 0.92 0.31 0.05 0.15 0.75 0.39 0.11

Loose bulk density [kg/m3] 1394 1420 1469 1461 1462 261 739 438

Los Angeles coefficient [%] 32.0 29.3 - - - - - -

Shape index [%] 11.0 16.2 - - - - - -

2.2Sample preparation and compositions

The grading curve of concrete was determined using the Faurys method and the Si-

kacomp2.5 software, considering a maximum size aggregate of 22.4 mm. The reference concrete

(RC) was formulated for the target strength class C30/37 with an Abrams cone slump value of

125 10 mm, which was obtained using a cement content of 350 kg/m3and a water / cement ratio

(w/c) of 0.54. No admixtures or additional constituents were used.

Two replacement ratios of natural aggregates NA by PWA were evaluated for each type of

plastic aggregate, 7.5% and 15%. Due to the relevant mechanical performance decrease verified in the

investigation of Saikia and Brito (2011) for higher replacement ratios, only 7.5% was studied for Pc,

resulting in six different mixes: reference concrete (RC); Pc 7.5; Pp 7.5 and Pp 15; Pf 7.5 and Pf 15.

Tests Standard

Size grading analysis NP EN 933-1 and NP EN 933-2

Particle density and water absorption NP EN 1097-6

Loose bulk density NP EN 1097-3

Los Angeles abrasion LNEC E 237

Shape index NP EN 933-4


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Extended abstract

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The Abrams cone slump value of all mixes was set equal to 125 10 mm, in order to allow a

valid comparison between the results of each mix. The different influence of each type of PWA in the

workability of fresh concrete, associated to its replacement ratio, imposed an adjustment of the w/c

of each mix. The replacement of NA by flaky PWA (Pc and Pf) caused a reduction of slump values, the

more pronounced the greater the incorporation ratio, resulting in a w/c increase. On the other hand,

the more spherical shape of Pp in comparison to the NA allowed a reduction of the w/c.

The composition of all mixes is shown in Table 3.

Table 3 - Composition of concrete mixes.

Mix code RC Pc 7.5 Pf 7.5 Pf 15 Pp 7.5 Pp 15

w/c 0.54 0.61 0.56 0.60 0.53 0.51

ComponentParticle size

[mm]Quantities [kg/m

3]

Natural

coarse ag-gregate

16 - 22.4 323.0 311.3 319.6 313.0 324.6 328.0

11.2 - 16 321.2 309.6 317.8 311.2 322.8 326.1

8 - 11.2 122.8 113.2 121.5 119.0 123.4 124.75.6 - 8 125.5 60.9 124.2 121.6 126.1 127.4

4 - 5.6 110.7 60.0 109.6 107.3 111.3 112.4

Natural fine

aggregate

2 - 4 204.8 176.1 127.4 51.0 102.9 0.0

1 - 2 164.0 158.0 105.2 47.2 131.3 98.9

0.5 - 1 102.5 98.8 101.4 99.3 103.0 104.1

0.25 - 0.5 257.0 247.7 254.4 249.1 258.3 261.0

0.125 - 0.25 72.4 69.8 71.7 70.2 72.8 73.5

Pc

8 - 11.2 0 2.5 0 0 0 0

5.6 - 8 0 27.6 0 0 0 0

4 - 5.6 0 21.5 0 0 0 0

2 - 4 0 9.8 0 0 0 0

Pf2 - 4 0 0 35.3 69.1 0 0

1 - 2 0 0 28.9 56.6 0 0

Pp2 - 4 0 0 0 0 49.5 100.0

1 - 2 0 0 0 0 17.4 35.1

Cement 350 350 350 350 350 350

Water 189 214 186 179 196 210

For each mix / test conditions (28 days, T20, T600 and T800) five cubic samples (150 mm)

and five cylindrical samples (150 x 300 mm) were produced. Three additional cubic specimens

(150 mm) were made for water absorption (by immersion) test for both fire exposures (T600 e T800)

and reference temperature (T20). Cubic samples (100 mm) were cut with a diamond saw blade in

order to obtain fire reaction test specimens (100 x 100 x 15 mm), three for each mix / heat flux.

The samples were demoulded 24 hours after casting and placed in a wet curing chamber (T =

20 C and RH = 100%) until 28 days. The specimens used for fire behaviour characterization were

then transferred to a dry chamber (T = 20 2 C and RH = 50 5 %) until their testing. T20, T600 and

T800 samples remained there until 49 days. The time elapsed between casting of the samples and

the fire reaction tests was at least about 17 weeks.


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2.3Tests on fresh concrete

The fresh concrete was characterized in what concerns consistency (by means of the Abrams cone

test, NP EN 12350-2, 2002) and density (NP EN 12350-6, 2002).

2.4Thermal exposure

The degradation of the residual (post-fire) mechanical properties of concrete containing PWA

was evaluated for two thermal exposures, T600 and T800, corresponding respectively to a maximum

exposure temperature of 600 C and 800 C for 60 minutes. Heating was carried out in an oven fired by

gas burners according to the ISO 834 standard curve, defined by the following expression,

where g is the temperature inside the oven (in C) and tis the time in minutes. The samples were

cooled inside the oven.

Registered time / temperature (inside the oven) curves are shown in Figures 1.a and 1.b, for the

thermal exposures T600 and T800, respectively. The standard fire curve ISO 834 for each peak tempera-

ture (600 C and 800 C) and the cooling curve defined in EN 1992 - part 1.2 are also represented.

a) b)

Figure 1 - Registered time / temperature curves for each thermal exposure and standard curve ISO 834:

a) T600; b) T800.

In order to evaluate the evolution of temperature inside the concrete specimens, three type-

K thermocouples were introduced into a sample of each composition / thermal exposure at different

depth levels (10 mm, 37.5 mm and 75 mm from the sample base).

2.5Tests on hardened concrete

Each type of concrete was characterized regarding its compressive strength, splitting tensile

strength and modulus of elasticity. The ultrasonic pulse velocity (UPV), the surface hardness (Schmidt

hammer) and the water absorption (by immersion) were also measured before and after fire exposure in

order to evaluate the residual strength of concrete containing PWA by expeditious and non-destructive

methods. The tests on hardened concrete were carried out according to the standards shown in Table 4.


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Table 4 - Tests on hardened concrete.

Test Standard

Compressive strength NP EN 12390-3

Splitting tensile strength NP EN 12390-6

Modulus of elasticity LNEC E 397

Ultrasonic pulse velocity (UPV) EN 12504-4Surface hardness (Schmidt hammer) EN 12504-2

Water absorption (by immersion) LNEC E-394

2.6Fire reaction experiments

The fire reaction properties were determined through cone calorimeter tests (Figure 2), ac-

cording to ASTM E1354 and ISO 5660 standards. Concrete specimens with 15 x 100 x 100 mm3were

exposed to heat fluxes of 25 kW/m2, 50 kW/m2and 75 kW/m2 (corresponding to average tempera-

tures at the cone surface of 605 C, 782 C and 902 C, respectively) for 30 minutes. Two specimens

were tested for each composition and heat flux.

Figure 2 - Cone calorimeter.

The following fire reaction properties were studied: heat release rate (HRR), time to ignition,

remaining mass, effective heat of combustion (EHC), specific extinction area (SEA) and release rate of

carbon monoxide (CO) and carbon dioxide (CO2). Based on the fire reaction tests results, it is possible

to estimate the fire reaction class of each composition, which reflects the combustibility and the re-

lease of toxic gases during its combustion.

3. Results and discussion

3.1Properties of fresh concrete

The results obtained for slump test (Abrams cone) and fresh density are shown in Table 5 and Figure

3, respectively.


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Table 5 - Slump tests results (Abrams cone).

Slump [cm]

Mix 28 days T20 T600 T800

RC 12.2 12.9 12.6 13.2

Pc 7.5 11.3 11.8 11.7 11.6

Pp 7.5 12.0 13.3 12.8 14.0

Pp 15 12.2 13.5 11.4 13.5

Pf 7.5 12.8 13.0 12.1 13.4

Pf 15 12.3 12.0 11.7 13.7

Figure 3- Density of fresh concrete as a function of the replacement ratio for different types of aggregates.

The values for each mix fulfilled the established range (125 15 mm), allowing a valid com-

parison of results of the various mixes. In order to achieve the target workability, it was necessary to

adjust the w/c of each mix. The incorporation of flaky shaped PWA (Pc e Pf) led to an increase of the

w/c, while the substitution of NA by Pp allowed a decrease of the w/c.

The lower particle density of plastic aggregates in comparison to NA resulted in a nearly lin-

ear decrease of the concretes fresh density with the replacement ratio. For mixes Pc 7.5, Pp 15 and

Pf 15, the incorporation of WPA resulted in a density reduction between 100 kg/m3and 200 kg/m3.

Differences between each type of PWA may be explained by the different w/c of each mix.

3.2Tests on hardened concreteThe mechanical properties of the different types of concrete at 28 days are shown in Table 6.

The values presented for each mix correspond to the average result (fcm.28), the corresponding coef-

ficient of variation (cv) and relative variation in comparison to RC ().

Table 6 - Mechanical properties at 28 days.

Mix fcm. 28[MPa] c fctm. 28[MPa] c Ecm. 28[GPa] c

RC 44.0 3% - 2.8 8% - 34.8 8% -

Pc 7.5 29.3 2% -34% 2.3 5% -19% 26.8 2% -23%

Pp 7.5 38.6 5% -12% 2.5 12% -11% 31.8 3% -9%

Pp 15 36.3 3% -18% 2.0 8% -28% 28.8 2% -17%

Pf 7.5 34.7 1% -21% 2.3 6% -19% 29.8 1% -14%Pf 15 27.5 3% -37% 1.8 16% -37% 21.9 4% -37%


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As expected, the replacement of NA by PWA resulted in a decrease of the concretes me-

chanical performance (compressive strength, splitting tensile strength and modulus of elasticity), the

more pronounced the greater the incorporation ratio.

The deterioration of the mechanical strength of concrete is related to the significantly lower

stiffness of plastic aggregates in comparison with other constituents of concrete and weak bonding

between them and the cementitious matrix, which result in a poor contribution of PWA to the

strength of concrete. Apart from its smooth surface, which results in a weak macroscopic bonding,

the low porosity of PWA does not allow the impregnation and subsequent crystallization of the

binder therein.

The weak bond, associated with the less continuous aggregates grading curve of concrete

with PWA than the one for the reference concrete, results in an increase of the former concretes

porosity, affecting its mechanical strength.

The deterioration related to each type of PWA was not constant, which can be explained by

their different shape and size and the corresponding influence in the workability of concrete. In or-der to maintain the established workability, the w/c of each mix was adjusted. The higher w/c of

mixes containing Pc and Pf resulted in a decrease of the mechanical performance of concrete due to

the associated increase of the porosity, while the deterioration related to the replacement of NA by

Pp was attenuated by the lower w/c.

The splitting tensile strength proved to be more susceptible to the substitution of NA by

PWA, in comparison to compressive strength. This can be explained by the greater susceptibility of

this property to the quality of the bonding between the aggregate and the cementitious matrix.

Although plastic aggregates have a significantly higher tensile strength than other constitu-

ents of concrete, rupture occurs at the interface between the PWA and the cementitious matrix due

to their weak bond. Despite the highest w/c ratio, Pc 7.5 obtained similar results to Pp 7.5 and Pf 7.5,

which can be explained by a significant contribution of Pc aggregates to splitting tensile strength,

only possible due to their larger size in comparison to other types of PWA.

Besides the increase of the porosity associated to the replacement of NA by PWA, the reduc-

tion of modulus of elasticity due to the incorporation of PWA is related to their lower modulus of

elasticity in comparison with the remaining constituents of concrete.

The registered peak temperatures inside the concrete specimens for each composition /

thermal exposure are shown in Table 7. Some thermocouples did not provide valid measurements,

and, therefore, the corresponding values are not listed.

Table 7 - Maximum internal temperatures reached for each mix / thermal exposure.

Maximum internal temperature [C]

T600 T800

Depth [cm] 10 37.5 75 10 37.5 75

RC 151 148 146 485 453 438

Pc 7,5 407 332 323 625 572 564

Pp 7,5 - 224 220 - 509 505

Pp 15 334 331 322 606 568 568

Pf 7,5 264 247 237 565 - 562

Pf 15 327 327 319 588 - 581

As expected, the maximum temperatures within concrete were higher near the surface ofthe specimen, without ever reaching the thermal exposure temperature. The incorporation of PWA


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in concrete resulted in an increase of the temperatures inside the specimens. The increase of the

porosity of concrete, due to the replacement of NA by PWA and to the thermal decomposition of

plastic aggregates, seems to have facilitated the propagation of heat inside the concrete specimens.

Temperatures registered in the reference concrete for exposure T600 were lower than expected.

In similar experiments, Marques (2010) and Vieira (2010) registered temperatures between 200 C and

300 C inside current concrete submitted to an equivalent thermal exposure. This difference seems to

have been caused by an incident that occurred in the test of RC specimen for T600 exposure: in fact, this

specimen fell from the pile in which it was placed and the thermocouples may have stopped providing

reliable measurements.

The results of the residual mechanical performance (compressive strength, tensile strength

and modulus of elasticity) of concrete exposed to high temperatures are shown in Tables 8 to 10.

The values correspond to the average value of the property obtained for each composition, the coef-

ficient of variation (cv) and the residual value relative to the reference temperature (T20%). The in-

fluence of temperature on the residual mechanical properties is illustrated in Figures 4 to 6.

Table 8 - Residual compressive strength.

T20 T600 T800

Mix fcm[MPa] c fcm[MPa] c %T20 fcm[MPa] c %T20

RC 48.7 2% 36.6 8% 75% 15.5 19% 32%

Pc 7.5 33.7 3% 19.6 23% 58% 7.7 19% 23%

Pp 7.5 43.8 7% 20.6 16% 47% 12.7 42% 29%

Pp 15 42.3 2% 18.6 16% 44% 12.9 32% 30%

Pf 7.5 41.7 3% 22.3 11% 54% 8.6 39% 21%

Pf 15 32.4 2% 15.8 32% 49% 5.8 26% 18%

Figure 4 - Influence of temperature in residual compressive strength.

Results indicate an increase of the degradation of the compressive strength with the re-

placement of NA by PWA, the more pronounced the higher the exposure temperature.

The thermal decomposition of plastic aggregates results in an increase of the porosity of

concrete, reducing its compressive strength. Moreover, the subsequent higher porosity decreases

the resistance of concrete to the propagation of high temperatures, an effect which was confirmed

by the temperatures registered within the samples. This fact, in addition to the combustibility of

plastics aggregates, aggravates the thermal exposure.

The replacement rate increase of 7.5% to 15% does not seem to have a considerable effect

on the post-fire compressive strength of concrete. It is likely that the deterioration of the compres-

sive strength due to the higher porosity owing to the thermal decomposition of PWA is attenuated


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by the better accommodation of thermal expansions provided by the voids created. Furthermore,

such higher porosity also allows confined gases to escape, reducing the accumulation of internal

stresses and, thereby, concrete cracking. The attenuation of the effects of replacing NA by PWA in

the degradation of compressive strength are more evident for exposure T800, for which the thermal

decomposition of the PWA and thermal expansion of the constituents of the concrete are consid-

erably more pronounced than for T600 exposure.

Table 9 - Residual splitting tensile strength.

T20 T600 T800

Mix fctm[MPa] c fctm[MPa] c %T20 fctm[MPa] c %T20

RC 3.62 21.1% 2.04 4% 56% 0.66 18% 18%

Pc 7.5 2.29 10.8% 1.35 16% 59% 0.54 41% 24%

Pp 7.5 2.72 8.6% 1.61 23% 59% 0.84 30% 31%

Pp 15 2.24 11.0% 1.19 23% 53% 0.54 20% 24%

Pf 7.5 2.59 15.9% 1.54 26% 60% 0.39 59% 15%

Pf 15 2.26 6.1% 1.08 29% 48% 0.36 28% 16%

Figure 5 - Influence of temperature in residual splitting tensile strength.

The deterioration of the splitting tensile strength of concrete containing PWA was roughly similar

to that of compressive strength. The incorporation of PWA has not resulted in an increase of the degra-

dation of residual splitting tensile strength, yielding, in general, better results for the most severe thermal

exposure. This may be explained by the fact that the higher porosity related to the incorporation of PWA

attenuates the accumulation of internal stresses due to the thermal incompatibility of the constituents of

concrete and allows the dispersion of gases confined in its pores, thereby reducing its cracking.

Table 10 - Residual modulus of elasticity.

T20 T600 T800

Mix Ecm[GPa] c Ecm[GPa] c %T20 Ecm[GPa] c %T20

RC 37.0 2% 20.2 6% 54% 6.4 18% 17%

Pc 7.5 25.5 4% 12.2 14% 48% 4.4 14% 17%

Pp 7.5 34.3 1% 17.6 7% 51% 4.5 20% 13%

Pp 15 29.4 1% 12.6 7% 43% 3.8 16% 13%

Pf 7.5 32.2 3% 13.7 16% 43% 3.7 12% 11%

Pf 15 24.8 5% 9.5 22% 38% 2.8 12% 11%


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Figure 6 - Influence of temperature in the residual modulus of elasticity.

The modulus of elasticity of all compositions tested was, in general, more susceptible to the

thermal exposure than compressive strength and splitting tensile strength. The greater reduction in

this property is associated to its higher susceptibility to concrete cracking, which is intensified with

increasing thermal exposure.The results obtained for the non-destructive testing: ultrasonic pulse velocity (UPV), surface

hardness (rebound number - RN) and water absorption by immersion (WA) are shown in Tables 11

to 13. The results presented correspond to the average obtained for each composition, correspond-

ing coefficient of variation (cv), percentile variation from values of the reference concrete () and the

residual value relative to the reference temperature (T20%). The influence of temperature on the

residual values of these properties may be observed in Figures 7, 9 and 11.

Table 11 - Residual ultrasonic pulse-velocity (UPV).

T20 T600 T800

Mix UPV [m/s] c UPV [m/s] c %T20 UPV [m/s] c %T20

RC 4966 0% - 3537 17% 71% 1562 29% 31%

Pc 7,5 4561 1% -8% 2736 13% 55% 1172 30% 24%

Pp 7,5 4945 1% 0% 2659 26% 54% 923 60% 19%

Pp 15 4771 1% -4% 2747 9% 55% 916 38% 18%

Pf 7,5 4515 2% -9% 3179 8% 64% 956 28% 19%

Pf 15 4150 1% -16% 2328 24% 47% 780 17% 16%

Figure 7 - Influence of temperature in residual ultrasonic pulse velocity (UPV).

As expected, UPV results for the reference temperature (T20) indicate a decrease of the UPV

with increasing replacement ratio. This can be explained by the higher porosity of concrete resulting from

the substitution of NA per PWA, not only due to the weak bonding between the plastic aggregates and

the cementitious matrix, but also to the lesser continuous grading curve in comparison to the reference

concrete. This decrease of UPV is more pronounced by the higher w/c ratio of concrete produced with

flaky shaped PWA (Pc and Pf) and less pronounced for the compositions produced with Pp.


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Concerning the residual UPV of concrete exposed to high temperatures, the incorporation of

PWA resulted in increased degradation, the more so the greater the replacement ratio. This is explained

by the higher porosity of concrete due to the decomposition of PWA. There is no clear common pattern

for each type of PWA, and the influence of each one on the residual UPV degradation is not evident. The

relationship between residual UPV and compressive strength is nearly linear (Figure 8), which confirms

the suitability of measuring the UPV as an expeditious and non-destructive test to measure the residual

compressive strength of concrete containing PWA exposed to fire. As found for the mechanical perform-

ance properties, increasing the incorporation ratio of PWA from 7.5% to 15% did not increase the degra-

dation of the residual UPV, which can be explained by the same reasons.

Figure 8 - Relationship between UPV and compressive strength.

Table 12 - Residual rebound number (RN).

T20 T600 T800Mix RN [-] c RN [-] c %T20 RN [-] c %T20

RC 34 7% - 32 10% 94% 21 16% 64%

Pc 7,5 32 3% -5% 27 11% 85% 18 10% 57%

Pp 7,5 34 2% 1% 31 7% 91% 23 19% 67%

Pp 15 36 3% 6% 31 10% 87% 23 13% 66%

Pf 7,5 31 2% -7% 26 2% 84% 19 18% 61%

Pf 15 31 3% -7% 22 18% 70% 16 9% 51%

Figure 9 - Influence of temperature in the residual rebound number.


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Regarding the surface hardness, it was not possible to conclude about the influence of substi-

tuting NA for PWA, as the rebound number (RN) proved to vary linearly as a function of w/c. This oc-

curred because the surface hardness is directly related with the strength of the cementitious matrix.

However, one expected the replacement of NA by PWA to cause a reduction of the RN due to the sub-

sequent higher porosity of the paste and this was not clearly observed from the results obtained.

The results of the residual RN indicate a worsening of its deterioration with the increasing of

PWA content, except for concretes containing Pp, which does not seem to be influenced by its in-

corporation ratio. According to Savva et al. (2005), the reduction of the RN is justified by the chemi-

cal decomposition and cracking of the surface layer of concrete caused by the thermal exposure. The

combustion of PWA increases the porosity, weakening the surface layer of concrete.

Figure 10 shows that the relationship between the rebound number and compressive

strength is nearly linear. The relevant variability of the results does not allow the RN to be used as

quantitative indicator of post-fire compressive strength. However, the surface hardness is a useful

non-destructive and expeditious test in the detection of heterogeneities in concrete, elements ex-

posed to high temperatures and, thus, the areas most affected by the fire.

Figure 10 - Relation between the rebound number and the compressive strength.

As expected, the water absorption by immersion (WA) (Table 13 and Figure 11) increased

with the w/c and the replacement ratio, the first parameter having been more influent. According to

Silva (2011), besides the greater porosity due to the higher w/c, the higher WA values obtained for

concrete produced with flaky PWA, Pc and Pf, are most likely caused by the accumulation of air bub-

bles in its interface with the cement matrix

Table 13 - Residual water absorption by immersion (WA).

T20 T600 T800

Mix WA [%] c WA [%] c %T20 WA [%] c %T20

RC 13,9 3% - 15,5 30% 112% 19,3 9% 139%

Pc 7,5 15,3 9% +10% 17,6 8% 115% 22,4 10% 146%

Pp 7,5 13,8 11% -0% 14,7 1% 107% 21,6 3% 156%

Pp 15 12,6 1% -10% 13,6 0% 108% 22,3 1% 177%

Pf 7,5 15,3 11% +10% 15,3 3% 100% 22,9 5% 150%

Pf 15 15,6 3% +13% 16,4 4% 105% 27,0 3% 173%


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Figure 11 - Influence of temperature in water absorption by immersion.

The replacement of NA by PWA only resulted in a significant increase of the water absorption

(by immersion) for exposure T800. This can be explained by the almost complete combustion of the

plastic aggregates, resulting in a significant increase in the porosity of the concrete. Moreover, for ex-

posure T600, only the plastic aggregates located in the surface layer of concrete specimens suffered

some decomposition. Results associated to different types of PWA are quite similar. There is a possibil-

ity that the values concerning the exposure T600 may be lower than the actual ones, since the cover of

molten plastic may have partially water-tightened the surface layer of the samples.

Figure 12 shows the relationship between average values of compressive strength and water

absorption by immersion. As expected, concrete mixes which have suffered a higher thermal degrada-

tion and, thereby, have a lower post-fire compressive strength correspond to higher water absorption.

Figure 12 - Relationship between the water absorption (by immersion) and post-fire compressive

strength.

3.3Fire reaction experiments

As an example, Figure 13 illustrates the time dependent results registered for a Pp 15 speci-

men for each incident heat flux. Table 14 lists the maximum value (Max), the average value over 30

minutes (Avgoverall) and the average value over a period of 180 s after reaching the peak HRR (Avg180)

for Pp 7.5 and Pp 15. Due to a problem in the acquisition of EHC values (whose maximum values

were limited to 75 MJ/kg), the corresponding statistical parameters are not presented.


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14

Figure 13 - Fire reaction properties of Pp 15.


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Extended abstract

15

Table 14 - Average values of each fire reaction property for each mix / incident heat flux.

Mix Pp 7,5 Pp 15

Heat flux [kW/m] 25 50 75 25 50 75

Time to ignition [s] 1289 449 220 1249 348 178

HRR [kW/m]

Max 72,4 68,0 39,4 182,0 114,0 116,2

Avgoverall 4,5 9,0 16,6 8,0 19,5 32,0Avg180 20,5 18,1 13,1 41,6 64,4 75,0

SEA [m/kg]

Max 1739,2 1587,4 410,3 3065,7 4289,5 384,5

Avgoverall 370,8 513,4 70,9 669,2 495,9 89,9

Avg180 649,3 402,5 30,7 748,0 256,3 153,1

CO [kg/kg]

Max 0,0240 0,0190 0,0177 0,0309 0,1932 0,0252

Avgoverall 0,0062 0,0057 0,0068 0,0071 0,0163 0,0085

Avg180 0,0063 0,0022 0,0046 0,0094 0,0025 0,0018

CO [kg/kg]

Max 1,25 0,79 0,44 1,76 1,60 1,00

Avgoverall 0,096 0,069 0,086 0,136 0,259 0,288

Avg180 0,325 0,125 0,091 0,596 0,658 0,723

Remaining mass 95,7% 94,0% 92,4% 94,7% 90,9% 89,9%

Ignition occurs when the concentration of volatiles from the thermal decomposition of plastic

aggregates is enough for them to react with the sparker and ignite. As expected, the time to ignition (TTI)

decreased with the increase of both incident heat flux and ratio of plastic aggregates incorporation.

In the initial period, for all mixes and heat fluxes, no HRR was detected. After ignition of vol-

atiles from the thermal decomposition of plastic aggregates, HRR greatly increased. After reaching

the peak value, HRR fell gradually due to the decreasing amount of combustible material. For

75 kW/m2, more than one peak was observed, which can be explained by the inflammation of plastic

aggregates located deeper in the specimen.

Mass loss, which results mostly from the combustion of plastic aggregates, increased with both

heat flux and combustible material content. The ignition coincided with a noticeable mass drop.

The EHC is obtained numerically from the relationship between released heat and the corre-

sponding mass loss, and it reflects the energy efficiency of the combustion of plastic aggregates.

Higher EHC values would be expected for higher heat fluxes, since increased temperatures result in a

more complete and, therefore, more efficient combustion. Due to the already mentioned anomalies

related with EHC data acquisition, it was not possible to conclude about its relationship with the

incident heat flux.

SEA reflects the release of smoke from the combustion of plastic aggregates. SEA values were

lower for higher heat fluxes, which can be explained by the more complete combustion of plastic aggre-

gates for higher temperatures. Although the release of smoke results from the combustion of plastic

aggregates, increasing the replacement ratio from 7.5% to 15% did not result in higher smoke release.

The yield of CO2curves followed a close trend to the corresponding HRR ones, which is due

to the fact that both parameters are directly related to the combustion of plastic aggregates. After

ignition, the release rate of CO2greatly increased, reaching its peak value nearly at the same time as

the HRR. The yield of CO2 increased with the ratio of plastic aggregates incorporation, though no

clear relationship was identified between the CO2released and the incident heat flux.

The decreasing oxygen content due to its consumption in the combustion of plastic aggre-

gates resulted in a progressive decrease of the CO2 yield and an increase of the CO yield, which can

be explained by the fact that combustion gradually becomes more incomplete. The higher values


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16

were obtained after flames became extinct. Unlike what would be expectable, the ratio of plastic

aggregates incorporation and the incident heat flux did not seem to affect the yield of CO.

Results obtained for all types of WPA were relatively similar, since they consist on the same

material and, consequently, have the same combustible potential. As expected, increasing the incor-

poration ratio of plastic aggregates in concrete from 7.5% to 15% resulted in a worsening of several

fire reaction properties, namely the HHR, the mass drop and the yield of CO2.

The European fire reaction classification of building products is based on the single burning

item (SBI) test, a more complex experiment than the cone calorimeter test. Van Hees et al. (2002)

developed software (ConeTools) which, based on the HRR data for 50 kW/m2 and ignition times,

provides (i) a simulation of the fire growth rate index (FIGRA) obtained in the SBI test and (ii) the

corresponding fire reaction class according to the European standard.

Based on the FIGRA estimated by ConeTools, (Figure 14) all mixes correspond to Euroclasses

A2 to B (noncombustible to non-flammable).

(i) HRR (ii) FIGRA

Figure 14 - FIGRA curve determined byConeToolsfor Pp 15.

The Portuguese regulation for the fire safety in residential houses defines a set of require-

ments and restrictions for use of construction materials in several components and locations de-

pending on their fire reaction classification. According to the Portuguese regulation, none of the

analysed mixes can be used as structural concrete in roofs, stairs, ventilation ducts and garbage dis-

posal compartments. Regarding non-structural applications, the legislation bars their use as coating

material on evacuation routes, fire-proof enclosures and walls/ceilings of locations that pose high

risks of fire outbreak and development. In all other components and locations there are no re-

strictions for concrete made of PWA with the incorporation rates analysed in the present study.

4. Conclusions

This dissertation aimed at studying the fire performance of concrete produced with selected

waste plastics aggregates (PWA). The analysis of concrete with varying incorporation of PWA was done

based on the residual mechanical properties after exposure to high temperatures and the fire reaction

properties, i.e., released ratios of heat, smoke, carbon monoxide (CO) and carbon dioxide (CO2).

The results show a degradation of the residual mechanical properties with the replacementof natural aggregates (NA) by PWA. The thermal decomposition of plastic aggregates results in an


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Documents

Extended fddfdAbstract José Saraiva Lima