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8th International Masonry Conference 2010 in Dresden

8th International Masonry Conference Dresden 2010 1

Increment of thermal insulation capability of ceramic bricksmasonry

FRANZOY, MARIA1; GORDO, JUAN2; CITRONI, JORGE3; AVENDAÑO, MARCELO4;MARCIPAR, ALFREDO5; GRETHER, RUBÉN6

ABSTRACT: In Argentina, the application of ceramic brick masonry of 0.15 m thickness as exterior walls in housing is a widespread technique, but it is insufficient to achieve suitable thermal insulation for housing.

In order to solve this problem, lightweight ceramic bricks were developed by means of the incorporation of macroscopic pores in the mass of the brick produced by solid wastes that are consumed during the baking. Consequently, density diminishes, increasing the thermal insulation capability without significant reductions of compressive strength.

According to Argentine regulations, compressive strength of traditional and lightweight ceramic bricks and bearing capacity of masonry made with those bricks were evaluated. Also, thermal transmittance and the risk of both superficial and intermediate condensation were analyzed.

Obtained results demonstrate suitable mechanical and insulating behaviour for lightweight bricks,indicating that it is possible to build exterior walls of 0.15 m of thickness and still achieve the regulation requirements. Also, energy consumption can be diminished both in the production process and air conditioning in housing when the lightweight bricks are used.

Keywords: ceramic, wastes, recycling, density, thermal insulation.

NOTATION

S compression strength;S o strength at porosity zero;P porosity;K constant.

1 INTRODUCTION

According to IRAM Standard 11,605/96 [1], four environmental zones are distinguished in Argentina.The city of Santa Fe, where our study is based, is in zone II-B, for which the maximum values of wallthermal insulation which establishes levels of hydrothermal comfort in summer are: A(recommended), B (intermediate) and C (minimum).

1) Researcher scholar, Universidad Tecnológica Nacional F.R. Santa Fe, CECOVI-Materiales, [email protected] 2) Researcher scholar, Universidad Tecnológica Nacional F.R. Santa Fe, CECOVI-Materiales, [email protected] 3) Architect, Universidad Tecnológica Nacional F.R. Santa Fe, CECOVI-Dirección, [email protected] 4) Civil Engineer, Universidad Tecnológica Nacional F.R. Santa Fe, CECOVI-Transferencias, [email protected] 5) Construction Technician, Universidad Tecnológina Nacional F.R. Santa Fe, CECOVI-Gestión, [email protected] 6) Architect, Universidad Tecnológica Nacional F.R. Santa Fe, Departamento Obras, [email protected]

mailto:[email protected]















Franzoy, María; Gordo, Juan


In the Argentine Littoral zone, common ceramic bricks are used widely for the construction ofmasonry of housing. In most cases the exterior walls are 0.15 m wide, obtaining a thermal insulationof 2.03 W/m2 K, thus exceeding the top value tolerated, 1.80 W/m2 K. The breach of these minimalconditions propitiates the formation of microorganisms (mildew, fungi, others), some harmful to thehealth.

In order to find a solution to this problem, it is necessary to increase brick thermal capacity, byreducing their density and increasing their porosity. In the case of ceramic bricks, porosity can beraised by incorporating materials that are consumed during the burning process. In this respect, ananalysis of appropriate forms of domestic or industrial waste must be considered, bearing in mind notonly the technical characteristics but their availability, cost, environmental impact and energy use.

2 EXPERIMENTAL

The present development consists of including, within the mixture of mud and liga 7, a residue capableof disintegration during the burning process, generating macropores in the interior of the brick.Different dosages were tested in order to establish the ideal proportions, having in mind therequirements of this project: to increase the capacity of thermal insulation without significant

reductions in compression strength or excessive cost increases, and to reduce the quantity of naturalsoil and fuel used in the manufacture of bricks, but still applying the conventional technologies ofmanufacture.

After analyzing several possibilities, cinder and crushed expanded-polystyrene (EPS) wereselected, taking into account not only the technical characteristics but the factors mentioned above.

Cinder constitutes the waste of charcoal production that is sifted or shaken out at brick factories inorder to separate the coal fraction used as a fuel. This separation is carried out by a metallic meshwith an approximate opening of 13 mm. The possibility of incorporating cinder (a cheap residueavailable in abundant quantities) arose from the observation of the oven assembly technology, sincecinder is used between the rows of adobes8 for achieving a uniform temperature. This residue doesnot produce toxic emanations during the burning process and due to its high heating power itproduces beneficial effects, such as the utilization of energy. Hence, cinder was added in proportionsof 1:0.50, 1:0.60, 1:0.67 and 1:0.70 (ratio ‘sweep:cinder’, by volume).

The expanded-polystyrene (EPS) is a derivative of hydrocarbons, composed of 95% of polystyreneand 5% of gas, which forms bubbles that lead to a reduction in the material density. It is used indifferent ways such as, for example, the manufacture of packages, packing, as thermal insulator, oras a generator of energy from its calcination. Although it is a 100% recyclable material, in bothmechanical and chemical form, no suitable such treatment is carried out nowadays in Argentina, EPSbeing disposed of in sanitary. Besides, though EPS is an innocuous material -i.e. it does not generateleached liquids or toxic products in its decomposition process- it does need a long period for itsdisintegration.

To incorporate this residue inside brick, no cleaning processes are necessary. Besides, accordingto theoretical studies, its calcination helps to distribute the heat inside the piece, with a resultant lowerconsumption of fuel. An abundant source of EPS, and of interest to this project lies in the possibility ofcrushing the residues from the commercial and domestic sectors.

In this work, mixtures of crushed expanded-polystyrene recovered from the solid urban residues in

proportions of 1:0.50, 1:0.65, 1:0.8, 1:0.95, 1:1.1, 1:1.25, 1:1.4, 1:1.55 (ratio ‘sweep:EPS’, by volume)were evaluated. The incorporation of higher volumes of the residue was not possible due to smallcohesion of the mixtures. As the research work progressed, a great variation of the total brick porositywas detected, leading to mixtures with and without the incorporation of liga, that is, using expanded-polystyrene as a liga, as well.

7) The liga (‘joint’) is a material used to increase the cohesion and consistency of the adobes during their elaboration.8) An adobe is a piece composed of a mixture of soil, liga and water, which becomes a ceramic brick after the burning process.



Increment of thermal insulation capability of ceramic brick masonry


According to the traditional technologies of production, the mold process of the adobes is carriedout manually, with clayey soil. The burning is done in ovens assembled with the same adobes, andfed with fuelwood, at temperatures between 800 and 1000 °C.

Figure 1 shows the adobe mold process in a schematic way, with EPS incorporation. It also showsthe burning process, developed in pyramid-shape ovens made with the same adobes, with a few

openings named 'mouthpieces' in the lower part, where the fuelwood is placed.To evaluate the residue incorporated with the different proportions used, physical and mechanicaltests were performed on the bricks, such as compression [2], apparent dry density, porosity,absorption by dipping in cold water [3] and thermal conductivity, by the method of Less and Chorlton.Total porosity was determined by the difference between the unit and the quotient between apparentdensity and absolute density (IRAM Standard 1624/05).

With the purpose of obtaining information on the morphology of the macropores produced by bothtypes of residues, the resultant material was subjected to microscopy analysis. For this determinationa trinocular Olympus polarizing microscope with a high resolution camera was used.

After defining the type of residue and the dosage that provided the best results, the compressionstrength tests of light brick and normal brick masonry were carried out, according to the IRAMStandard 12,737 [4].

3 RESULTS AND DISCUSSIONSS

Table 1 summarizes the average results obtained for each dosage. These results were veryencouraging since a 23 % decrease in density was achieved, from 1.50 g/cm3 for normal bricks to1.15 g/cm3 for bricks with the incorporation of the expanded-polystyrene.

The reduction in compression strength of the light ceramic bricks as a consequence of the inclusionscan be explained by the relation between porosity and compression strength. The variation of strengthwith porosity [5] is represented by a curve based on equation (1). It has been shown for different

Figure 1. Molding and burning of adobes with EPS. (Source: Maria Franzoy, Santa Fe)

S = So.e -kP (1)





materials that strength depends principally on the porosity. In this way, when compared to porosity,the relation S/So presents a similar pattern for the materials tested (Figure 2).

For all the percentages of residue incorporation, cinder inclusded into bricks tends to produce a lowercompression strength than those that contain equal proportion of crushed expanded-polystyrene. If itis taken into account that the counterfoil (sweep of pisadero ) is the same for both types of bricks, itcan be inferred that the most significant reason for the strength reduction is the type of pores

Table 1. Brick properties

Dosage (byvolume)

ResidueIncorporated

[%]

ApparentDensity[g/cm

3]

TypicalCompressive

Strength[MPa]

ThermalConductivity[Kcal/hmºC]

ThermalTransmittance (0.15 m-wide)

[W/m2K]

TotalPorosity [%]

Pattern 0 1.53 10.4 0.568 2.03 40.9

Bricks with cinder

1:0.50 33 1.10 3.5 0.358 1.54 57.0

1:0.60 37 1.03 2.0 0.355 1.53 59.7

1:0.70 41 0.92 2.0 0.411 1.68 63.9

Bricks with incorporated EPS (with liga )

1:0.50 33 1.23 4.0 0.501 1.89 52.0

1:0.65 39 1.15 3.8 0.420 1.71 54.1

1:0.80 44 1.09 3.4 0.454 1.79 57.7

1:0.95 49 1.09 3.8 0.469 1.82 58.2

1:1.10 52 0.98 2.4 0.366 1.56 62.6

1:1.25 55 0.96 2.1 0.429 1.73 64.0

1:1.40 58 0.94 2.5 0.419 1.70 62.5

1:1.55 61 0.92 1.7 0.331 1.46 64.9

Bricks with incorporated EPS (without liga )

1:0.65 39 1.24 5.1 0.476 1.84 51.6

1:0.80 44 1.20 5.3 0.505 1.90 53.2

1:0.88 47 1.15 5.0 0.455 1.79 55.1

1:0.95 49 1.09 3.3 0.468 1.82 57.5





produced by each residue. As noticed in Figure 3, resultant of the microscopy analyses, themacropores originated by cinder calcination present an angular form with fissures at their ends thatweaken the zone. These angular forms can result in an important concentration of tensions. In thecase of the macropores originated by the calcination of crushed expanded-polystyrene, the cells havea regular spherical form, with well-defined edges and without any crack like fissures.

IRAM Standard 12,566-1 [6] states that the typical compression strength for normal bricks must behigher than 4 MPa. On the other hand, the Argentine Regulation Project for Structures of Masonry -CIRSOC 501 [7], determines that the minimum compression strength of the walls must be 5 MPa.

As seen in Figure 4, the values obtained in our tests for light bricks with expanded-polystyrene (andwithout liga ) present a typical compression strength superior to the minimal values established by theregulation. Light bricks with expanded-polystyrene and liga do not reach the above mentioned limits

Figure 2. Compression strength (y-axis) vs. total porosity (x-axis).

Figure 3. Brick macropores originated by cinder calcination (left picture) and expanded-polystyrene(right picture). (Source: Maria Franzoy, Santa Fe)





for typical strength, though the average strength is near to the 4 MPa demanded by the IRAMStandard 12,566-1/05 [6].

On the other hand, the results of the thermal conductivity test (method of Less and Chorlton) showa decrease of this property as expanded-polystyrene is added, resulting in a higher capacity ofthermal insulation. This behaviour is related to a bigger content of pores, as is the case of the cellular

concretes [8], which owe their higher thermal insulation to the pores, which are full of air.As shown in Figure 5, thermal conductivity decreases as total porosity of the bricks is increased. Itis possible to conclude that the incorporation of expanded-polystyrene into the brick mass leads to a20% decrease in the thermal conductivity of the material.

Walls of 0.13 m thickness built with normal bricks do not achieve the minimum level of thermalcomfort (1.80 W/m2K), since their transmittance is 2.03 W/m2K. For bricks with cinder included theresults of thermal transmittance are between the minimum and average levels, with values of 1.53W/m2K for the walls of 0.13 m thickness, 1.35 for those of 0.17 m and 1.21 W/m2K for those of 0.20 m(Figure 6).

In the case of bricks lightened with crushed polystyrene and liga , only two dosages (33 and 49% ofEPS) reach values of thermal transmittance that do not reach the minimum level of hydrothermalcomfort. For lightened bricks with crushed polystyrene but without liga -with 47% of EPS- a value of1.79 W/m2K is reached. With these light bricks, three masonry ‘walls-for-test’ were made for thecompression strength test, following the proceedings of the IRAM Standard 12,737 [4] and the Projectof Regulation CIRSOC 501 [7]. In addition, three similar ‘walls-for-test’ were built, but using normalceramic bricks.

The dimensions of the ‘walls-for-test’ were established by considering the minimum height (350mm) and an average slenderness of 3.80. A mortar composed of mortar-for-masonry and sand, in aproportion of 1:4 (ratio ‘mortar:sand’), was used in this case.

Figure 4. Compression strength (left y-axis) and density (right y-axis) vs. percentage of expanded-polystyrene incorporated (x-axis).





The values of compression strength were calculated according to the procedure established in theregulation [4] (Table 2). These results indicate that the light bricks might be used for the constructionof portantes -walls9 since they meet the requirement of typical compression strength established in theproject of regulation for masonry materials.

9) A type of wall used in structures without reinforced-concrete columns. These columns are replaced with paredes portantes (portantes -wall), which can be used in structures up to 3-stories tall (10 meters).

Figure 5. Thermal conductivity of light bricks (y-axis) vs. percentage of expanded-polystyreneincorporated (x-axis).

Table 2. Results of the masonry compression strength calculation.

Walls-for-testTest Value

[MPa]Average

Strength [MPa]

Relative

Scattering[MPa]

SpecifiedStrength [MPa]

CorrectedStrength [MPa]

Normal brick walls-for-test

No 1 4.23

3.59 0.016 1.91 1.87No 2 3.43

No 3 3.11

Light brick walls-for-test

No 1 4.02

4.25 0.005 3.67 3.59No 2 4.40

No 3 4.32





4 ENVIROMENTAL SUSTAINABILITY

The incorporation of crushed expanded-polystyrene into the brick presents great advantages from theenvironmental point of view. For example, the characteristics of the residue structure do not demandthe previous conditioning of the residue since it does not modify either the physical properties of themixture in the early states or the characteristics of the final product. This implies that the cleaning andwashing processes, and hence the use of water or other chemical products, are not necessary.

Another beneficial aspect is that the combustibility of this residue contributes to the generation ofheat for the functioning of the oven, helping to keep constant the temperature inside the piece, whichimplies a saving of fuel material (generally fuelwood of plant origin). As a way of quantifying theenergy contribution of the residue, 3000 kg of fuelwood are needed to burn an oven of 20,000 bricks,which generates a heating power of 5.40 x 107kJ. Considering that the EPS amount to incorporateinto the bricks (for the same quantity of units) is 15 m3 (300 kg), a heat energy of 1.38 x 107 kJ wouldbe obtained, reducing the fuelwood consumed in approximately 26%.

This initiative, on the other hand, involves a reduction in the volume of natural soil used for themanufacture of ceramic bricks. If it is considered that 40 to 50% of EPS may be incorporated into themass of the bricks, it might be possible to save approximately 15 m3 or 22.5 t of soil in themanufacture of 20,000 bricks, i.e. twice the amount of bricks could be made with the quantity of soilused today to make 20,000 bricks.

As previously exposed, the feasibility of using EPS in ceramic bricks turns out to be promising,

both from the technological, social and environmental point of view. Nevertheless, still remains theevaluation of an important aspect in the project: the analysis of the oven combustion gases when EPSis incorporated to ensure that they are harmless both for the brick-making workers and for thesurrounding environment. In this respect, it is important to emphasize that the EPS does not containany gas of the family of the chlorofluorocarbons (CFCs).

5 CONCLUSIONS

Incorporating residues such as cinder and expanded-polystyrene into the ceramic brick leads to theconclusion that the light bricks with crushed EPS show a better behaviour to compression strength,

Figure 6. Results of calculus of thermal transmittance for 0.13 m-wide walls.





mainly due to the spherical form of the macropores formed in the brick and the lack of fissures on itsperimeter. That is, to obtain good results and be able to control the total porosity, the bricks must bemade with the only addition of EPS as a liga .

From the results of the tests and calculations, an optimal dosage that meets the requirements ofcompression strength, thermal conductivity and density is obtained: 1:0.88 (ratio ‘sweep:EPS’) is

established as the ideal proportion corresponding to an incorporation of 47% of EPS.Applying this ideal dosage, then, results in a typical compression strength ensuring not only thatthe light bricks could be used to construct walls, but an acceptable level of hydrothermal comfort for0.13 m wide walls, and a 12% decrease in the thermal transmittance as well.

6 FUTURE ACTIONS

The final stage of this project considers evaluating the possibility of transferring this technology ofceramic brick manufacturing to the industry and other sectors of the community. Consequently, it isessential to ensure that the residue burning does not produce harmful compounds.

As mentioned above, theoretical studies concerning the burning of expanded polystyrene haveconcluded that the combustion gases released during burning are similar to those produced by other

organic fuels (for example, their toxicity would be similar to or even lower than those of woodcombustion).It is necessary to take into account that fuelwood is used as a fuel in the process of ceramic brick

burning, thus generating pollutant gases which, when combined with those produced by EPS, mightbe harmful. This aspect affects to a great extent the feasibility of applying the project on an industrialscale.

For this reason, the measurement and evaluation of pollutant gases generated from the productionof ceramic bricks with EPS is proposed, focusing on the composition of the combustion gases. If thereare harmful compounds, either for the environment or the population in the surrounding areas of thebrick-making factories, their presence could then be determined.

The properties of expanded polystyrene will then deserve an in-depth investigation, consideringmainly its chemical composition and the components involved in the manufacturing process. Besides,since EPS comes from solid urban residues (RSU in Spanish), it is necessary to pay attention to the

potential pollution with other compounds.Only by confirming the innocuousness of the gases will it be possible to transfer the productiontechnology to the brick-making factories, thus favouring a great commercial and social activity of theregion. The successful transfer of technology will encourage enterprises to adopt processes of thekind, recycling and reusing wastes in order to decrease the environmental impact.

REFERENCES

[1] IRAM Standard 11,605/96: Acondicionamiento térmico de edificios . Instituto Argentino deNormalizacion: Buenos Aires Dec. 1996.

[2] IRAM Standard 12,586/04: Ceramic clay bricks and blocks for wall construction. Test method forcompressive strength. Instituto Argentino de Normalizacion: Buenos Aires Jun. 2004.

[3] IRAM Standard 12,588/80: Ceramic clay bricks and blocks for wall construction . Test method todetermine the absorption capacity of water by inmersion in cold water and boiling water.Instituto Argentino de Normalizacion: Buenos Aires Apr. 2006.

[4] IRAM Standard 12,737/05: Clay bricks and blocks masonry. Method to determine thecompressive strength of walls by test of masonry prisms. Instituto Argentino de Normalizacion:Buenos Aires Jun. 2006.

[5] Mindess, S. & Young, J.: Concrete , Prentice Hall-inc. Englewood-Cliffs: New Jersey 1981.[6] IRAM Standard 12,566-1/05: Ceramic clay bricks and blocks for walls and partitions

construction. Part 1: Solid. Instituto Argentino de Normalizacion: Buenos Aires Mar. 2005.





[7] CIRSOC Standard 501: Proyecto de Reglamento Argentino de Estructuras de Mampostería .INTI-CIRSOC: Buenos Aires Mar. 2005.

[8] Miretti, R.E. & Grether, R.O. & Carrasco, M.F.: Hormigones Especiales , XV Reunión Técnica de la Asociación Argentina de tecnología del Hormigón. AATH: Santa Fe Oct. 2004.

8imc 55 full paper

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