1. INTRODUCTION
⌅In
recent years, Brazil has followed the global trend of modernization and
improvement in the construction industry, including in terms of thermal
performance. Through a new standardization to verify the performance of
residential buildings, the Brazilian construction industry enters a new
regulatory level that will require new technologies to optimize the
results of its products and services. In the European Union, the
regulations aim at the construction of energy efficient buildings to
improve people’s quality of life and generate additional benefits to the
economy and society (11.
European Union (2010). Directive 2010/31/EU of the European parliament
and of the council of 19 May 2010 on the energy performance of buildings
(EPBD recast). Off. J. Eur. Union 2010, 53. Retrieved from https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:153:0013:0035:EN:PDF
).
The interaction of the building with the
environment in which it is located is important to fully meet the needs
of users through the optimization of its functionalities. Accurate
knowledge of the properties and thermal behavior in building elements
under typical conditions is essential for innovative products and
techniques. It may optimize current projects and produce more accurate
data for the cost-benefit analysis for future projects (2-52.
Byrne, A.; Byrne, G.; Robinson, A. (2017) Compact facility for testing
steady and transient thermal performance of building walls. Energy Build. 152, 602-614. https://doi.org/10.1016/j.enbuild.2017.07.086.
3.
Geraldi, M.S.; Ghisi, E. (2020) Building-level and Stock-level in
contrast: a literature review of the energy performance of buildings
during the operational stage. Energy Build. 211, 109810. https://doi.org/10.1016/j.enbuild.2020.109810.
4. Marinakis, V. (2020) Big data for energy management and energy-efficient buildings. Energies. 13 [7], 1555. https://doi.org/10.3390/en13071555.
5.
Al-Naghi, A.A.A.; Rahman, M.K.; Al-Amoudi, O.S.B.; Al-Dulaijan, S.U.
(2020) Thermal performance evaluation of walls with aac blocks,
insulating plaster, and reflective coating. J. Energy Eng. 146, 04019040. https://doi.org/10.1061/(asce)ey.1943-7897.0000636.
).
Ascione et al. (66.
Ascione, F.; Bianco, N.; de Masi, R.F.; Mauro, G.M.; Vanoli, G.P.
(2015) Design of the Building Envelope: A novel multi-objective approach
for the optimization of energy performance and thermal comfort. Sustainability. 7 [8], 10809. https://doi.org/10.3390/su70810809.
)
highlight that the use and development of construction components
characterized by values of thermal transmittance, thermal capacity, and
radiative properties is a key strategy for reducing the need for energy
for microclimate control. The thermal behavior of a building has
intervening factors: the climate, thermal physiology of the users, and
even the processes of heat transmission, which are directly linked to
the building elements, especially floors, roofs, and facades (7-97.
Lamberts, R.; Duarte, V.C.P. (2016) Desempenho térmico de edificações,
Universidade Federal de Santa Catarina, Florianopolis, Brazil.
8.
Echarri, V.; Espinosa, A.; Rizo, C. (2017) Thermal transmission through
existing building enclosures: destructive monitoring in intermediate
layers versus non-destructive monitoring with sensors on surfaces. Sensors. 17 [12], 2848. https://doi.org/10.3390/s17122848.
9.
Economidou, M.; Todeschi, V.; Bertoldi, P.; Agostino, D.; Zangheri, P.;
Castellazzi, L. (2020) Review of 50 years of EU energy efficiency
policies for buildings. Energy Build. 225, 110322. https://doi.org/10.1016/j.enbuild.2020.110322.
).
According to Pereira (1010.
Pereira, B.M.S. (2014) A eficiência energética em edifícios: análise
comparativa da regulamentação aplicável na península Ibérica, Master’s
Thesis, Instituto Politécnico de Viana do Castelo, Viana do Castelo,
Brazil.
), the quality of a building is no longer
assessed by looking only at architectural, structural, or installation
projects. The comfort component of users is increasingly demanded both
by the users themselves and by councils and supervisory bodies,
especially through rules and regulations (1111.
Najjar, M.; Figueiredo, K.; Hammad, A.W.A.; Haddad, A. (2019)
Integrated optimization with building information modeling and life
cycle assessment for generating energy efficient buildings. Appl. Energy. 250, 1366-1382. https://doi.org/10.1016/j.apenergy.2019.05.101.
). According to Aguilera et al. (1212.
Aguilera, D.G.; Lagüelab, S.; Rodríguez-Gonzálveza, P.;
Hernández-López, D. (2013) Image-based thermographic modeling for
assessing energy efficiency of buildings façades. Energy Build. 65, 29-36. https://doi.org/10.1016/j.enbuild.2013.05.040.
),
the current century will be one of energy efficiency in buildings, as
shown by the appearance of many national and international guidelines in
recent years, such as the European 20/20/20 objectives, in which a 20%
reduction in the energy consumption in buildings is established for the
year 2020. In this sense, the European Commission in 2021, to promote
the energy efficiency of buildings, established a review of the Energy
Performance of Buildings Directive (EPBD), proposing a regulatory
framework. This improvement includes five general EPB standards: a) ISO
52000-1 (1313.
International Organization for Standardization - ISO (2017). ISO
52000-1:2017. Energy performance of buildings - Overarching EPB
assessment - Part 1: General framework and procedures. Geneva,
Switzerland.
), is the general framework of EPB evaluation; b) ISO 52003-1 (1414.
International Organization for Standardization - ISO (2017). ISO
52003-1:2017. Energy performance of buildings - Indicators,
requirements, ratings and certificates - Part 1: General aspects and
application to the overall energy performance. Geneva, Switzerland.
), information for processing the results of the EPB standards, resulting into general and partial indicators; c) ISO 52010-1 (1515.
International Organization for Standardization - ISO (2017). ISO
52010-1:2017 Energy performance of buildings - External climatic
conditions - Part 1: Conversion of climatic data for energy
calculations. Geneva, Switzerland.
), procedures for evaluation of climatic data; d) ISO 52016-1 (1616.
International Organization for Standardization - ISO (2017). ISO
52016-1:2017. Energy performance of buildings - Energy needs for heating
and cooling, internal temperatures and sensible and latent heat loads -
Part 1: Calculation procedures. Geneva, Switzerland.
), guidelines for calculating temperatures and energy needs, and e) ISO 52018-1 (1717.
International Organization for Standardization - ISO (2017). ISO
52018-1:2017. Energy performance of buildings - Indicators for partial
EPB requirements related to thermal energy balance and fabric features -
Part 1: Overview of options. Geneva, Switzerland.
), description of the indicators for specific EPB requirements.
Tubelo et al. (1818.
Tubelo, R.C.S.; Rodrigues, L.T.; Gillot, M.A. (2014) Comparative study
of the brazilian energy labelling system and the passivhaus standard for
housing. Buildings. 4 [2], 207-221. https://doi.org/10.3390/buildings4020207.
) as well as Bogo (1919.
Bogo, A.J. (2016) Reflexões críticas quanto as limitações do texto das
normas brasileiras de desempenho NBR 15220-3 e NBR 15575. Holos. 32, 290-298. https://doi.org/10.15628/holos.2016.4389.
)
affirm that the advances in norms, regulations, and patterns of energy
use have an important role to play in supporting the construction of
superior quality houses, which are more thermally comfortable and
economical power. The Brazilian mandatory legal standards NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
) and NBR 15575 (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
), and, in an informative way, the Technical Quality Regulation for the Energy Efficiency Level Residential Buildings (RTQ-R) (2222.
Instituto Nacional de Metrologia, Normalização e Qualidade Industrial
(2012) Regulamento técnico da qualidade para o nível de eficiência
energética edificações residenciais (RTQ-R), INMETRO, Rio de Janeiro,
Brasil, 2012.
), are the support legal instruments in Brazil.
Two normative procedures are established by NBR 15575 (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
):
the simplified and computer simulation method. The first consists of
calculating and observing parameters of the thermal behavior of the
systems and comparing them with the minimum allowable values. The second
procedure should be used if the building does not meet the requirements
of the simplified method (minimum performance) or if it is desired to
achieve intermediate and higher performance (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
, 2323.
Marques, T.H.T.; Chavatala, K.M.S. (2013) Review of the Brazilian NBR
15575 standard: applying the simulation and simplified methods for
evaluating a social house thermal performance. Proceedings of the
Symposium on Simulation for Architecture and Urban Design. San Diego:
SimAUD.
, 2424.
Dalbem, R.; Grala da Cunha, E.; Vicente, R.; Figueiredo, A.; Oliveira,
R.; Silva, A.C. (2019) Optimisation of a social housing for south of
Brazil: From basic performance standard to passive house concept. Energy. 167, 1278-1296. https://doi.org/10.1016/j.energy.2018.11.053.
).
In addition to these procedures, there is the experimental measurement
method where measurements are made on buildings or prototypes built.
Experimental
studies of construction elements, especially vertical sealing blocks,
have been carried out to evaluate their thermal properties (25-3325.
Silva, E.P.; Melo, A.B.; Queiroga, A.B.R.E. (2013) Desempenho térmico
de vedações: estudo comparativo com blocos de eva, tijolo cerâmico e
gesso acartonado. Proceedings of the Encontro Nacional de Conforto no
Ambiente Construído. Brasília (ENCAC).
26. Lakatos, A. (2017)
Investigation of the moisture induced degradation of the thermal
properties of aerogel blankets: Measurements, calculations, simulations. Energy Build. 139, 506-516. https://doi.org/10.1016/j.enbuild.2017.01.054.
27.
Souza, C.R.N. (2015) Estudo da condutividade térmica do gesso (CaSO4
0,5 H2O) em função de sua porosidade. Master’s Thesis, Universidade
Federal do Vale do São Francisco, Juazeiro, Brazil.
28. Specht, L.P.;
Borges P.A.P.; Rupp, R.F.; Varnier, R. (2010) Análise da transferência
de calor em paredes compostas por diferentes materiais. Amb. Constr. 10, 7-18. https://doi.org/10.1590/S1678-86212010000400002.
29.
Otteléa, M.; Perinib, K. (2017) Comparative experimental approach to
investigate the thermal behaviour of vertical greened façades of
buildings. Ecol. Eng. 108 [Part A], 152-161. https://doi.org/10.1016/j.ecoleng.2017.08.016.
30.
Silva, E.P.; Cahino, J.E.M.; Melo, A.B. (2012) Avaliação do desempenho
térmico de blocos EVA, Proceedings of the Encontro Nacional de
Tecnologia no Ambiente Construído, Juiz de Fora (ENTAC).
31. Allam, R.; Issaadi, N.; Belarbi, R.; El-Meligy, M.; Altahrany, A. (2018) Hygrothermal behavior for a clay brick wall. J. Heat Mass. 54, 1579-1591. https://doi.org/10.1007/s00231-017-2271-5.
32.
Danieslki, I.; Fröling, M. (2015) Diagnosis of buildings’ thermal
performance: a quantitative method using thermography under non-steady
state heat flow. Energy Procedia. 83, 320-329. https://doi.org/10.1016/j.egypro.2015.12.186.
33. Liu, C.; Zhang, Z. (2019) Thermal response of wall implanted with heat pipes: Experimental analysis. Renew. Energy. 143, 1687-1697. https://doi.org/10.1016/j.renene.2019.05.123.
).
The use of thermal chambers that simulate the environments in a thermal
gradient assesses the behavior of the components experimentally. It is a
practical method that has shown significant results, especially for the
comparison of components of different materials, such as ceramic and
concrete blocks with substitution of fine aggregates by residues of
Ethyl Vinyl Acetate from the shoe industry (3030.
Silva, E.P.; Cahino, J.E.M.; Melo, A.B. (2012) Avaliação do desempenho
térmico de blocos EVA, Proceedings of the Encontro Nacional de
Tecnologia no Ambiente Construído, Juiz de Fora (ENTAC).
). For clay bricks, Allam et al. (3131. Allam, R.; Issaadi, N.; Belarbi, R.; El-Meligy, M.; Altahrany, A. (2018) Hygrothermal behavior for a clay brick wall. J. Heat Mass. 54, 1579-1591. https://doi.org/10.1007/s00231-017-2271-5.
)
developed a thermal chamber and performed heat and humidity flow tests
based on the control and reproduction of various environmental
conditions. Specht et al. (2828.
Specht, L.P.; Borges P.A.P.; Rupp, R.F.; Varnier, R. (2010) Análise da
transferência de calor em paredes compostas por diferentes materiais. Amb. Constr. 10, 7-18. https://doi.org/10.1590/S1678-86212010000400002.
)
built a chamber to test prototypes of walls and perform, in parallel,
mathematical simulations to evaluate the experimental results on the
heat flow to walls of different materials.
Infrared thermography
is not yet an established method for assessing the performance and
thermal behavior of buildings and is not present in the relevant
Brazilian standards NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
) and NBR 15575 (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
). However, some studies verify the potential of the use of thermography (66.
Ascione, F.; Bianco, N.; de Masi, R.F.; Mauro, G.M.; Vanoli, G.P.
(2015) Design of the Building Envelope: A novel multi-objective approach
for the optimization of energy performance and thermal comfort. Sustainability. 7 [8], 10809. https://doi.org/10.3390/su70810809.
, 1010.
Pereira, B.M.S. (2014) A eficiência energética em edifícios: análise
comparativa da regulamentação aplicável na península Ibérica, Master’s
Thesis, Instituto Politécnico de Viana do Castelo, Viana do Castelo,
Brazil.
, 1212.
Aguilera, D.G.; Lagüelab, S.; Rodríguez-Gonzálveza, P.;
Hernández-López, D. (2013) Image-based thermographic modeling for
assessing energy efficiency of buildings façades. Energy Build. 65, 29-36. https://doi.org/10.1016/j.enbuild.2013.05.040.
, 2323.
Marques, T.H.T.; Chavatala, K.M.S. (2013) Review of the Brazilian NBR
15575 standard: applying the simulation and simplified methods for
evaluating a social house thermal performance. Proceedings of the
Symposium on Simulation for Architecture and Urban Design. San Diego:
SimAUD.
, 32-3932.
Danieslki, I.; Fröling, M. (2015) Diagnosis of buildings’ thermal
performance: a quantitative method using thermography under non-steady
state heat flow. Energy Procedia. 83, 320-329. https://doi.org/10.1016/j.egypro.2015.12.186.
33. Liu, C.; Zhang, Z. (2019) Thermal response of wall implanted with heat pipes: Experimental analysis. Renew. Energy. 143, 1687-1697. https://doi.org/10.1016/j.renene.2019.05.123.
34.
Bauer, E.; Leal, F.E. (2013) Condicionantes das medições termográficas
para avaliação da temperatura em fachadas. Proceedings of the X Simpósio
Brasileiro de Tecnologia das Argamassas. Porto Alegre (X SBTA).
35.
Ibañez Puy, M.; Viadurre-Arbizu, M.; Sacristán-Fernández, J.A.; Martín
Gómez, F.C. (2017) Opaque Ventilated Façades: Thermal and energy
performance review. Renew. Sust. Energ. Rev. 79, 180-191. https://doi.org/10.1016/j.rser.2017.05.059.
36.
Marques, D.F.P.C. (2014) Avaliação da qualidade térmica da envolvente
de edifícios - Estudo de caso através da análise numérica e por
termografia infravermelha. Master’s Thesis, Faculdade de Ciências e
Tecnologias da Universidade Nova de Lisboa, Porto, Portugal.
37.
Kylili, A.; Fokaides, P.A.; Christou, P.; Kalogirou, S.A. (2014)
Infrared thermography (IRT) applications for building diagnostics: A
review. Appl. Energy. 134, 531-549. https://doi.org/10.1016/j.apenergy.2014.08.005.
38.
Shariq, M.H.; Hughes, B.R. (2020) Revolutionising building inspection
techniques to meet large-scale energy demands: A review of the
state-of-the-art. Renew. Sust. Energ. Rev. 130, 109979. https://doi.org/10.1016/j.rser.2020.109979.
39.
François, A.; Ibos, L.; Feuillet, V.; Meulemans, J. (2021) In situ
measurement method for the quantification of the thermal transmittance
of a non-homogeneous wall or a thermal bridge using an inverse technique
and active infrared thermography. Energy Build. 233, 110633. https://doi.org/10.1016/j.enbuild.2020.110633.
),
both (a) for measuring parameters of thermal properties for the
elements and the building, and (b) to find problems related to thermal
bridges and the overall performance of the building.
A thermal
performance study is critical for construction sector, especially in
developing countries where more energy may be consumed than in developed
countries (4040.
Lamrani, M.; Laaroussi, N.; Khabbazi, A.; Khalfaoui, M.; Garoum, M.;
Feiz, A. (2017) Experimental study of thermal properties of a new
ecological building material based on peanut shells and plaster. Case Stud. Constr. Mater. 7, 294-304. https://doi.org/10.1016/j.cscm.2017.09.006.
).
However, a unique method to evaluate thermal performance in plaster
composite materials is unavailable. In this context, ways to measure and
estimate thermal properties in plaster composite materials have been
proposed by literature (41-4441.
Rahmanian, I.; Wang, Y.C. (2012) A combined experimental and numerical
method for extracting temperature-dependent thermal conductivity of
gypsum boards. Constr. Build. Mater. 26, 707-722. https://doi.org/10.1016/j.conbuildmat.2011.06.078.
42. Yu, J.; Yang, J.; Xiong, C. (2015) Study of dynamic thermal performance of hollow block ventilated wall. Renew. Energy. 84, 145-151. https://doi.org/10.1016/j.renene.2015.07.020.
43.
Iucolano, F.; Liguori, B.; Aprea, P.; Caputo, D. (2018)
Thermo-mechanical behaviour of hemp fibers-reinforced gypsum plasters. Constr. Build. Mater. 185, 256-263. https://doi.org/10.1016/j.conbuildmat.2018.07.036.
44.
Uriarte-Flores, J.; Xamán, J.; Chávez, Y.; Hernández-López, I.; Moraga,
N.O.; Aguilar, J.O. (2019) Thermal performance of walls with passive
cooling techniques using traditional materials available in the Mexican
market. Appl. Therm. Eng. 149, 1154-1169. https://doi.org/10.1016/j.applthermaleng.2018.12.045.
). Those studies have suggested using thermal chambers (4545.
Kheradmand, M.; Azenha, M.; de Aguiar, J.L.; Castro-Gomes, J. (2016)
Experimental and numerical studies of hybrid PCM embedded in plastering
mortar for enhanced thermal behaviour of buildings. Energy. 94, 250-261. https://doi.org/10.1016/j.energy.2015.10.131.
, 4646.
Pedreño-Rojas, M.A.; Morales-Conde, M.J.; Pérez-Gálvez, F.;
Rodríguez-Liñán, C. (2017) Eco-efficient acoustic and thermal
conditioning using false ceiling plates made from plaster and wood
waste. J. Clean. Prod. 166, 690-705. https://doi.org/10.1016/j.jclepro.2017.08.077.
), specific equipment (47-4947.
Toppi, T.; Mazzarella, L. (2013) Gypsum based composite materials with
micro-encapsulated PCM: Experimental correlations for thermal properties
estimation on the basis of the composition. Energy Build. 57, 227-236. https://doi.org/10.1016/j.enbuild.2012.11.009.
48.
Belayachi, N.; Hoxha, D.; Slaimia, M. (2016) Impact of accelerated
climatic aging on the behavior of gypsum plaster-straw material for
building thermal insulation. Constr. Build. Mater. 125, 912-918. https://doi.org/10.1016/j.conbuildmat.2016.08.120.
49.
Bicer, A.; Kar, F. (2017) Thermal and mechanical properties of gypsum
plaster mixed with expanded polystyrene and tragacanth. Therm. Sci. Eng. Prog. 1, 59-65. https://doi.org/10.1016/j.tsep.2017.02.008.
) and infrared thermography (5050.
Al-Naghi, A.A.A.; Rahman, M.K.; Al-Amoudi, O.S.B.; Al-Dulaijan, S.U.
(2020) Thermal performance evaluation of walls with AAC blocks,
insulating plaster, and reflective coating. J. Energy Eng. 146, 04019040. https://doi.org/10.1061/(asce)ey.1943-7897.0000636.
). As mentioned by Batista (5151.
Batista, P.I.B. (2019). Parâmetros de desempenho térmico de blocos de
gesso, Master’s Thesis. Escola Politécnica de Pernambuco, Universidade
de Pernambuco, Recife, Brazil.
), there is a small
amount of research that considers the plaster block for a vertical
sealing element and a smaller amount evaluating it in thermal behavior,
associated with the equally minimal mention of these elements in the
relevant Brazilian standards reflect the importance of greater research
in this sense (52-5652.
Delgado, J.M.P.Q.; Paula, P. (2018) Hygrothermal performance evaluation
of gypsum plaser houses in Brazil. In: J. Delgado, A. Barbosa de Lima
(Eds). Transport phenomena in multiphase systems, advanced structured
materials. 93, 1-53. United States: Springer. https://doi.org/10.1007/978-3-319-91062-8_1.
53.
Santos, A.N. (2017) Comportamento higrotérmico de paredes em gesso:
avaliação da adequabilidade a zonas climáticas do Brasil, PhD Thesis,
Faculdade de Engenharia, Universidade do Porto, Porto, Portugal.
55.
Neves, M.L.R. (2011) Método construtivo de vedação vertical interna com
blocos de gesso. Master’s Thesis. Escola Politécnica de Pernambuco,
Universidade de Pernambuco, Recife, Brazil.
56. Pires Sobrinho, C.W.
(2010) Divisórias internas de edifícios em alvenaria de blocos de gesso-
Vantagens técnicas, económicas e ambientais. Proceedings of the
Congresso Internacional de Tecnologia Aplicada para a Arquitetura &
Engenharia Sustentáveis. Recife.
).
This article aims to evaluate the main thermal properties of plaster blocks from theoretical calculations and using thermal chamber and infrared thermography as experimental methods, considering the technical and economic potential of these elements for the economy of the northeast region of Brazil. The experimental program included the development of a thermal chamber with sensors, a digital thermometer, a heat source with intensity control, in addition to having a compatible format for infrared thermography, the latter for capturing thermal images during tests. This combination allowed for a broad, original, and data-rich analysis for thermal performance in testing elements.
2. MATERIALS AND METHODS
⌅To
evaluate the thermal properties of plaster blocks, three analysis
fronts were performed: one theoretical, based on the simplified method;
one determined by test - both proposed by NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
);
and an experimental study from an instrumented thermal chamber
developed for this work. Methodology used for this research is detailed
in Figure 1.
2.1. Test elements
⌅From plaster blocks standardized by NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
),
eight test elements were produced, covering the different thicknesses
for the configurations available between hollow and compact in the
Brazilian market. The main characteristics are presented in Table 1.
Code | Type | Internal structure (all dimensions in mm) | Water/plaster ratio (w/p) | Flexural strength MPa | Apparent mass density range |
---|---|---|---|---|---|
GS 50 + | Standard | Compact |
0.72 | 1 | Average¹ |
GS 70 - | Standard | Hollow - conical |
0.70 | 1.2 | Average¹ |
GS 70 + | Standard | Compact |
0.70 | 1.2 | Average¹ |
GS 76 - | Standard | Hollow - conical |
0.68 | 1.4 | Average¹ |
GS 76 = | Standard | Hollow - cylindrical |
0.68 | 1.4 | Average¹ |
GS 100 - | Standard | Hollow - conical |
0.65 | 1.5 | Average¹ |
GS 100 + | Standard | Compact |
0.65 | 1.5 | Average¹ |
GH 100 + | Hydrofugated² | Compact |
0.65 | 1.5 | Average¹ |
¹Average density: ≥ 800.0 and <1100.0 kg / m³, according to NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
).² Hydrofugate: Hydrofugate blocks with water absorption ≤ 5.0%, according to NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
).
Both chemical and physical characteristics used in manufacturing plaster blocks are shown in Table 2.
Characteristics | Plaster | Requirement | Brazilian Standards |
---|---|---|---|
Calcium oxide - CaO (%) | 39.8 | >38.0 | NBR 13207 (5858. Associação Brasileira de Normas Técnicas (2017) NBR 13207: Gesso para construção civil - Requisitos. ABNT, Rio de Janeiro. ) |
Sulfuric anhydride - SO3 (%) | 55.1 | >55.0 | NBR 13207 (5858. Associação Brasileira de Normas Técnicas (2017) NBR 13207: Gesso para construção civil - Requisitos. ABNT, Rio de Janeiro. ) |
Crystallization water (%) | 5.97 | 4.2 - 6.2 | NBR 13207 (5858. Associação Brasileira de Normas Técnicas (2017) NBR 13207: Gesso para construção civil - Requisitos. ABNT, Rio de Janeiro. ) |
Fineness modulus | 0.18 | <1.1 | NBR 12127 (5959.
Associação Brasileira de Normas Técnicas (2019) NBR 12127: Gesso para
construção civil - Determinação das propriedades físicas do pó. ABNT,
Rio de Janeiro. ) |
Unit mass (kg/m3) | 610 | <700 | NBR 12127 (5959.
Associação Brasileira de Normas Técnicas (2019) NBR 12127: Gesso para
construção civil - Determinação das propriedades físicas do pó. ABNT,
Rio de Janeiro. ) |
Data provided by manufacturer
Every
plaster block was manufactured in an industrial manner, including
cubical metal molds (solid and hollow) with smooth surface and side
fits. Subsequently, plaster blocks were dismounted after 60 min and
taken to an oven at 40 ºC for 24 hours, according to NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
).
It is worth mentioning that test elements are from the plaster block
cuts provided by the industry. Therefore, their lateral dimensions were
changed to a 42 cm square on the side, inserting the identification
acronym and the Type K thermocouple temperature sensors in the central
part on both sides of the test elements (Figure 2).
Figure 3 presents the mechanical properties of the plaster specimens. The
flexural strength of the blocks meets the requirements of NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
). The compressive strength was determined by ABNT 12129 (6060.
Associação Brasileira de Normas Técnicas (2019) NBR 12129: Gesso para
construção civil - Determinação das propriedades mecânicas. ABNT, Rio de
Janeiro.
), using cubic specimens of 50 cm x 50 cm x 50 cm.
2.2. Thermal chamber
⌅In
order to carry out the thermal chamber behavior experiment, a thermal
chamber was developed and built to provide the test element with the
positioning between two environments with a temperature gradient between
them (2525.
Silva, E.P.; Melo, A.B.; Queiroga, A.B.R.E. (2013) Desempenho térmico
de vedações: estudo comparativo com blocos de eva, tijolo cerâmico e
gesso acartonado. Proceedings of the Encontro Nacional de Conforto no
Ambiente Construído. Brasília (ENCAC).
, 2828.
Specht, L.P.; Borges P.A.P.; Rupp, R.F.; Varnier, R. (2010) Análise da
transferência de calor em paredes compostas por diferentes materiais. Amb. Constr. 10, 7-18. https://doi.org/10.1590/S1678-86212010000400002.
, 3131. Allam, R.; Issaadi, N.; Belarbi, R.; El-Meligy, M.; Altahrany, A. (2018) Hygrothermal behavior for a clay brick wall. J. Heat Mass. 54, 1579-1591. https://doi.org/10.1007/s00231-017-2271-5.
).
The test apparatus was built of wood, with insulation on the heated
side and opening on the cold side (controlled room temperature). In
addition, temperature sensors were inserted on both sides with a display
on the control panel. A dimmer switch was also inserted to regulate the
heating provided by an infrared lamp present in the central part of the
hot side and the location for installing the digital thermometer with
integrated data logger (Figure 4). Although there is no official standard, a proposed thermal chamber was developed according to Standard ASTM C1363 (6161.
American Society for Testing and Materials (2005) ASTM C1363. Standard
test method for thermal performance of building materials and envelope
assemblies by means of a hot box apparatus. West Consohoken: ASTM.
) provisions and studies by Kheradmand et al. (4545.
Kheradmand, M.; Azenha, M.; de Aguiar, J.L.; Castro-Gomes, J. (2016)
Experimental and numerical studies of hybrid PCM embedded in plastering
mortar for enhanced thermal behaviour of buildings. Energy. 94, 250-261. https://doi.org/10.1016/j.energy.2015.10.131.
), Pedreño-Rojas et al. (4646.
Pedreño-Rojas, M.A.; Morales-Conde, M.J.; Pérez-Gálvez, F.;
Rodríguez-Liñán, C. (2017) Eco-efficient acoustic and thermal
conditioning using false ceiling plates made from plaster and wood
waste. J. Clean. Prod. 166, 690-705. https://doi.org/10.1016/j.jclepro.2017.08.077.
), and Ferrari and Zanotto (6262.
Ferrari, S.; Zanotto, V. (2013) The thermal performance of walls under
actual service conditions: Evaluating the results of climatic chamber
tests. Constr. Build. Mater. 43, 309-316. https://doi.org/10.1016/j.conbuildmat.2013.02.056.
).
The thermal chamber was used for temperature monitoring through thermal
sensors. Additionally, elements’ surface temperature distribution was
evaluated through infrared thermography.
The procedure of the experiment consists of controlling the temperature in the environment: 26 ± 1 °C, from an air conditioner. Then, the test elements are placed with the “outer face” turned to the inside the chamber. Strips of expanded polystyrene are placed on the edges the sensors are connected, the data logger is programmed, and heating is started. The heating lasts 360 minutes. Thermograms are recorded every 60 minutes on the cold side of the test elements and the temperatures are recorded every minute. After the warm-up period, the test elements cool for 120 minutes, with the same rate of temperature recording by the sensors. However, thermograms are made every 30 minutes and in various positions (cold side, hot side, lateral, and perspective) to observe the heat transition in the test element. The follow-up used the FLIR E-60 equipment, with main characteristics are shown in Table 3.
Model FLIR E-60 | |
---|---|
IR resolution | 320x240 pixels |
Thermal Sensitivity | ˂ 0.05ºC |
Temperature range | -20 and 650 °C |
Accuracy | ± 2ºC or ± 2% |
Video camera (no backlit) | 3.1 MP |
Source: FLIR (6363. FLIR (2014) User’s manual FLIR Exx Series, first ed. Wilsonville: FLIR.
).
The emissivity values of the analyzed surfaces were found using the black layer method. Interaction was performed between the emissivity value of the tape - known - and that of the neighboring surface (material, whose emissivity is unknown) until the temperatures coincide. Values between 0.93 and 0.95 were found for the plaster. The distance to the object was always between 1.0 and 1.5 m. The reflected temperature was the same as that of the environment, with no interference in the results (no interference from sunlight, variation in lighting, or considerable temperature in the controlled environment).
2.3. Heat flow meter
⌅The NBR 15220 standard (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
)
recommends the performance of tests to determine the thermal resistance
of elements. One of the methods mentioned is the flow meter; the test
is based on ISO 8301. For this research, the Netzsch heat flow meter -
HFM 436/6 was used, with main characteristics presented in Table 4. Tests were performed under the steady-state heat transfer, using the absolute technique, detailed by Zhao et al. (6464.
Zhao, D.; Qian, X.; Gu, X.; Jajja, S.A.; Yang, R. (2016) Measurement
techniques for thermal conductivity and interfacial thermal conductance
of bulk and thin film materials. J. Electron. Packag. 138 [4], 040802. http://doi.org/10.1115/1.4034605.
).
Model NETZSCH - HFM 436/6 | |
---|---|
Temperature range | -20 ~ 70 °C |
Cooling system | External cooler |
Specimen size | 600 x 600 x 10 ~ 200 mm |
Detectable area of the heat flow transducer | 25.4 cm x 25.4 cm |
Range for thermal resistance | 0.1 ~ 8.0 m²K/W |
Thermal conductivity range | 0.005 ~ 0.50 W/m.K |
Accuracy | ±1 ~ 3% |
Repeatability | 0.50% |
Source: NETZSCH (6565. NETZSCH (2010) Operating instructions of Heat Flow Meter HFM 436/6 Lambda, NETZSCH, Selb, Germany.
).
To
carry out this test, the wells of the hollow blocks were closed with
plaster paste, with the aid of a glass plate to prevent heat loss from
the sides. It is noteworthy that the size of the test elements (42 cm x
42 cm) is compatible and still have a margin in relation to the
detectable area of the heat flow transducer (25.4 cm x 25.4 cm) (Table 4). In addition to the tests on plaster blocks - all belonging to the medium density range as shown in Table 1 -, 3 plaster plates had the exact size of the equipment’s specimen (60
cm x 60 cm x 5 cm). The plates are D1 - 901.77 kg/m³, D2 - 1011.49 kg/m³
and D3 - 1165.93 kg/m³: two distant points but within the average range
(between 800 and 1100 kg/m³) and one point within the high-density
range (greater than 1100 kg/m³), according to NBR 16494 (5757.
Associação Brasileira de Normas Técnicas (2017) NBR 16494: Bloco de
gesso para vedação vertical - Requisitos. ABNT, Rio de Janeiro.
).
The plasterboards were tested to have a greater range of results,
considering that the plates were made specifically for the size of the
equipment (60 cm x 60 cm). In addition, the plasterboards are made of a
homogeneous material, which makes it possible to better infer thermal
conductivity, based on the relationship between thermal resistance and
the thickness of the test specimen.
The test was carried out according to the recommendations of the NBR 15520 standard (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
) and the manufacturer’s recommendations (6565. NETZSCH (2010) Operating instructions of Heat Flow Meter HFM 436/6 Lambda, NETZSCH, Selb, Germany.
).
For the test with the 8 plaster block test elements, two main
temperature values were used - Mean T of 24 and 40 °C - referring to a
temperature close to the environment in part of Brazil and a higher one
representing a peak during summer or artificial warming situations. On
the other hand, for the plasterboard, in addition to these main
temperatures, other two higher ones (50 and 60 °C) were added to expand
the analysis of plaster, considering thermal conductivity (λ) under
density conditions of apparent mass present in this work.
2.4. Characteristics of the heat flow meter
⌅To
obtain theoretical thermal properties for test elements, calculations
of several parameters were performed according to prescriptions and
tabulated input data values present in NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
).
Among the input data values collected, the following stand out for the
plaster: specific heat (c) of 0·84 kJ/kg·K, thermal conductivity (λ) of
0.35 W/m·K, and apparent mass density (ρ) of 875.0 kg/m³. The
calculations were performed with the aid of spreadsheets programmed in
the PTC Mathcad and MS Excel software. The calculated parameters were
thermal resistance (R) (Equation [1] and Equation [2]), thermal transmittance (U) (Equation [3]), thermal capacity (CT) (Equation [4]), and thermal delay (φ) (Equation [5]).
Here, e is the layer thickness (m); λ is the thermal conductivity (W/m·K); RT is the total thermal resistance m²·K/W; Rj is the thermal resistance of each component layer (m²·K/W); RSI is the internal surface thermal resistance (m²·K/W), and RSE is the external surface thermal resistance (m²·K/W).
Here, λj is the thermal conductivity of each component layer (W/m·K); Rj is the thermal resistance of each component layer (m²·K/W); cj is the material specific heat of each component layer (kJ/kg·K); ρj is the apparent mass density of each component layer (kg/m³), and ej is the layer thickness of each component layer (m).
Here, Rt is the surface to surface thermal resistance (m²·K/W); λ is the thermal conductivity of the material (W/m·K); c is the material specific heat (kJ/kg·K); ρ is the apparent mass density of the material (kg/m³), and REXT is the thermal resistance of the component’s outer layer (m²·K/W).
3. RESULTS AND DISCUSSION
⌅The discussion of the results is presented for each of the three analyzes carried out.
3.1. Thermal Resistance (R) and Thermal Conductivity (λ)
⌅Flow
meter measured the thermal resistance and based on the thickness of the
specimen, calculates the thermal conductivity (in case of homogeneous
material). The values found for thermal conductivity corroborate with
the value suggested in NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
), which is 0.35 W/m·K for a temperature of 27 °C (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
).
For densities D1, D2, and D3, the values for temperature 24 °C were
0.358 W/m·K, 0.354 W/m·K, and 0.364 W/m·K, respectively. The value
suggested in the standard, therefore, can be used if testing is not
available, according to the presented results. The values of R and λ for
each of the main temperatures are in Table 5.
Test element | Measured thickness1 | Calculated density | SP2 | Main temperature | Thermal conductivity (λ) |
---|---|---|---|---|---|
cm | kg/m³ | # | °C | W/m.K | |
Plate D1 | 5.20 | 901.77 | 1 | 25.31 | 0.358 |
2 | 39.84 | 0.403 | |||
3 | 49.64 | 0.409 | |||
4 | 59.43 | 0.405 | |||
Plate D2 | 5.21 | 1011.49 | 1 | 22.33 | 0.354 |
2 | 40.17 | 0.368 | |||
3 | 49.92 | 0.372 | |||
4 | 59.75 | 0.365 | |||
Plate D3 | 5.21 | 1165.92 | 1 | 22.38 | 0.364 |
2 | 40.17 | 0.368 | |||
3 | 49.85 | 0.361 | |||
4 | 59.60 | 0.356 |
1Thickness provided by the flow meter during the test.
2 Set point - Test data collection point.
It should be
noted that the variation in the conductivity value with temperature
occurs in a more sensitive way when this difference is high in most
materials (6666.
Incropera, F.P.; Dewitt, D.P. (2008) Fundamentos de transferência de
calor e de massa, sixth ed., Rio de Janeiro: Guanabara Koogan.
).
For the nominal main temperature of 24 °C (SP#1 in Table 5),
there is slight variation in conductivity in relation to the density of
the material. However, for higher temperatures, an increase in thermal
conductivity occurred with a decrease in the density of apparent mass.
This situation differs from the results pointed out by Souza (2727.
Souza, C.R.N. (2015) Estudo da condutividade térmica do gesso (CaSO4
0,5 H2O) em função de sua porosidade. Master’s Thesis, Universidade
Federal do Vale do São Francisco, Juazeiro, Brazil.
)
who concluded in his study that the increase in the porosity of plaster
specimens with the addition of sodium bicarbonate caused the decrease in
thermal conductivity. The author also states that heat transfer through
pores are slow processes and that the stagnant air, usually present
inside the pores, is a bad heat conductor (λ = 0.02 W/m·K); when
isolated, they make gas convection difficult (2727.
Souza, C.R.N. (2015) Estudo da condutividade térmica do gesso (CaSO4
0,5 H2O) em função de sua porosidade. Master’s Thesis, Universidade
Federal do Vale do São Francisco, Juazeiro, Brazil.
).
The
temperature affects the thermal conductivity of ceramic materials, the
increase in temperature (in this case up to 60 °C) can explain the
increase in thermal conductivity. On the other hand, porosity also has a
direct influence, the increase in volume and/or number of pores reduces
the thermal conductivity of ceramic materials (6767. Callister, W.; Rethwisch, D. (2018) Materials science and engineering: an introduction. New York: Wiley.
, 6868. Correia, C.; Souza, M. (2009) Mechanical strength and thermal conductivity of low-porosity gypsum plates. Mater. Res. 12 [1], 95-99. https://doi.org/10.1590/S1516-14392009000100012.
).
In this case, based on the results presented, the higher temperatures
of the test had more influence than the porosity on the thermal
conductivity; however, a detailed study about the phenomena involved
could better define this behavior.
Regarding the test elements from plaster blocks, Table 6 shows results and details for the apparent mass density, with specific
value for each tested element. Results confirmed the trend of less thick
blocks (GS 50 +, GS 70 + and GS 70 -) to have the lowest R values.
Among the blocks of 100 mm thick, those massive (GH 100 + and GS 100 +)
presented lower values than the hollow ones (GS 100-) and even lower
values than both 76 mm hollow blocks (GS 76 - and GS 76 =). It
highlights the significant contribution of the air layer (alveoli)
inside these blocks to the increase of thermal resistance, even with the
reduction of the total thickness. Similar results were reported when
thermal resistance for hollowed-block walls was evaluated (4444.
Uriarte-Flores, J.; Xamán, J.; Chávez, Y.; Hernández-López, I.; Moraga,
N.O.; Aguilar, J.O. (2019) Thermal performance of walls with passive
cooling techniques using traditional materials available in the Mexican
market. Appl. Therm. Eng. 149, 1154-1169. https://doi.org/10.1016/j.applthermaleng.2018.12.045.
, 6969.
Huelsz, G.; Barrios, G.; Rojas, J. (2016)
Equivalent-homogeneous-layers-set method for time-dependent heat
transfer through hollow-block walls. Appl. Therm. Eng. 102, 1019-1023. https://doi.org/10.1016/j.applthermaleng.2016.03.113.
).
The values of the standard 100 mm compact, water repellent compact, and
standard hollow blocks ranged between 0.25 and 0.30 m²·K/W, while both
76 mm blocks performed with R around 0.29 m²·K/W.
Test element | Measured thickness1 | Calculated density | SP2 | Main temperature | Thermal resistance (R) |
---|---|---|---|---|---|
cm | kg/m³ | # | °C | m².K/W | |
GS 50 + | 5.1999 | 871.2 | 1 | 25.06 | 0.163 |
2 | 39.66 | 0.168 | |||
GS 70 + | 7.0259 | 999.3 | 1 | 24.87 | 0.192 |
2 | 39.19 | 0.202 | |||
GS 100 + | 10.0802 | 978.6 | 1 | 24.76 | 0.260 |
2 | 38.54 | 0.270 | |||
GH 100 + | 9.9942 | 991.0 | 1 | 24.78 | 0.248 |
2 | 38.82 | 0.262 | |||
GS 70 - | 6.9812 | 812.8 | 1 | 23.98 | 0.219 |
2 | 40.23 | 0.229 | |||
GS 76 - | 7.5551 | 822.8 | 1 | 25.04 | 0.295 |
2 | 39.22 | 0.298 | |||
GS 76 = | 7.5567 | 867.2 | 1 | 25.28 | 0.287 |
2 | 39.89 | 0.283 | |||
GS 100 - | 10.1819 | 960.4 | 1 | 25.34 | 0.300 |
2 | 39.31 | 0.298 |
1Thickness provided by the flow meter during the test.
2 Set point - Test data collection point.
The values
of heat flow for the plaster block test elements are also graphically
presented in ascending order for the two main temperatures of 24 °C and
40 °C (Figure 5). Thermal resistance is not significantly modified by temperature (up to 40 °C). However, Mansour et al. (7070.
Mansour, M.B.; Soukaina, C.A.; Benhamou, B.; Jabrallah, S.B. (2013)
Thermal characterization of a Tunisian gypsum plaster as construction
material. Energy Procedia. 42, 680-688. https://doi.org/10.1016/j.egypro.2013.11.070.
) points out that higher temperatures (above 100 °C) may cause the plaster work as a firebreak.
3.2. Thermal performance parameters
⌅ Table 7 presents the results of the thermal performance parameters calculated as indicated in NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
) for the 8 plaster block test elements.
).
Test element | Thermal resistance (R) | Total thermal resistance (RT)1 | Thermal transmitance (U) | Thermal capacity (CT) | Thermal delay (φ) |
---|---|---|---|---|---|
m². K/W | m². K/W | W/m²K | kJ/m². K | h | |
GS 50 + | 0.143 | 0.313 | 3.19 | 37 | 1.7 |
GS 70 + | 0.200 | 0.370 | 2.70 | 59 | 2.5 |
GS 100 + | 0.286 | 0.456 | 2.19 | 82 | 3.5 |
GH 100 + | 0.286 | 0.456 | 2.19 | 83 | 3.5 |
GS 70 - | 0.228 | 0.398 | 2.51 | 41 | 1.9 |
GS 76 - | 0.248 | 0.418 | 2.39 | 37 | 1.8 |
GS 76 = | 0.240 | 0.410 | 2.44 | 28 | 1.5 |
GS 100 - | 0.294 | 0.464 | 2.15 | 51 | 2.3 |
1Considering the surface resistance plots (RSI + RSE = 0.170): value used to calculate U.
Analyzing the thermal resistance value, calculated from the presence of the alveoli in the plaster blocks, it is observed that this causes an increase in the thermal resistance value when compared to the compact ones (solid). An increase of 14% is observed between the 70 mm blocks while it’s only 3% for the 100 mm blocks. This difference in magnitude in the increase between the 70 and 100 blocks is due to the greater influence of the alveoli size in relation to their total thickness in the less thick block - since the alveoli have the same size. However, this behavior does not happen between elements with 76 mm plaster blocks, where there is a decrease in the resistance for the block with the largest alveolus (GS 76 =) - around 3% (Figure 6).
The
“removal” of solid material from the blocks proved to be an alternative
to increase the total resistance, as seen in the results of the flow
meter (Table 6 and Figure 5). Evidence shows less thick hollow blocks with results superior to other thicker blocks. As mentioned by Zhang et al. (7171.
Zhang, Y.; Du, K.; He, J.; Yang, L.; Li, Y.; Li, S. (2014). Impact
factors analysis on the thermal performance of hollow block wall. Energy Build. 75:330-341. https://doi.org/10.1016/j.enbuild.2014.02.037.
),
hollow blocks improve thermal insulation properties in walls (mainly
thermal resistance) and reduce energy consumption. This is caused by
thermal resistance of air contained in the block. However, the amount of
reduction in plaster thickness presented in the “popular block”,
material for the “GS 76 =” element, resulted in a decrease in thermal
resistance since the calculation considers a fixed value for the
resistance of the air layer: if it is increased, the only practical
effect is to reduce the thickness of the solid material and,
consequently, decrease its contribution to the element thermal
resistance.
Thermal transmittance (U) and thermal capacity (CT) are two criteria analyzed by the building performance standard NBR 15575 (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
)
for external vertical sealing systems. This work points out that
usually compartmentalization of environments, as to thermal aspects, is
needed. Therefore, it is important to understand the properties of the
blocks as one of the components in sealing systems, both external and
internal (the latter more common for plaster blocks). Figure 7 presents a joint graph of these parameters.
For the bioclimatic zone 8 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
) minimum values of CT are not required, while in the other zones (1 to 7) at least 130
kJ/m².K is imperative for minimum thermal performance, according to NBR
15575 (2121.
Associação Brasileira de Normas Técnicas (2013) NBR 15575: Edificações
habitacionais - Desempenho - Parte 1 -5. ABNT, Rio de Janeiro.
).
In addition, for U appreciation it is necessary to know the absorption
to solar radiation (α), which is related to the last outer layer of the
External Vertical Sealing System. Therefore, for the plaster block test
elements (without coating), this analysis, according to the normative
requirements, is not relevant. However, it is interesting to note that
the test elements in solid plaster blocks (GS 100 + and GH 100 +)
presented the best combination of results: low U values - around 2.2
W/m².K - and CT - about 82 kJ/m²·K. All test elements with
thicknesses from 76 mm show U values within the requirements of any of
the bioclimatic zones for walls (U≤ 2.5), even without coatings, which
significantly improve these values (blue line in Figure 7). The minimum CT value (130 kJ/m²·K) for zones 1 to 7 corresponds to the orange line (Figure 7).
Although the thermal transmittance (U) values are higher than those reported by Bianco et al. (7272.
Bianco, L.; Serra, V.; Fantucci, S.; Dutto, M.; Massolino, M. (2015)
Thermal insulating plaster as a solution for refurbishing historic
building envelopes: First experimental results. Energy Build. 95, 86-91. https://doi.org/10.1016/j.enbuild.2014.11.016.
) (0.56-0.8 W/m²·K) and Asdrubali et al. (7373.
Asdrubali, F.; D’Alessandro, F.; Baldinelli, G.; Bianchi, F. (2014)
Evaluating in situ thermal transmittance of green buildings masonries-A
case study. Case Stud. Constr. Mater. 1, 53-59. https://doi.org/10.1016/j.cscm.2014.04.004.
)
(0.23-0.33 W/m²·K) testing conditions and material settings were
different. In previous studies, tests were carried out in situ and
coating was included.
For thermal delay (φ), test elements with
greater thickness and less voids present, in general, the highest
values, as reported by Simões et al (7474. Simões, I.; Simões, N.; Tadeu, A. (2012) Thermal delay simulation in multilayer systems using analytical solutions. Energy Build. 49, 631-639. https://doi.org/10.1016/j.enbuild.2012.03.005.
) and Tadeu et al. (7575.
Tadeu, A.; Moreira, A.; António, J.; Simões, N.; Simões, I. (2014)
Thermal delay provided by floors containing layers that incorporate
expanded cork granule waste. Energy Build. 68, 611-619. https://doi.org/10.1016/j.enbuild.2013.10.007.
).
This statement is even clearer when observing the test elements of the
same thickness, with a difference only in the presence and size of the
alveoli. Among the test elements with 100 mm, there is a 44% reduction
between the massive one (3.5 h) and the hollow sample (2.3 h); for the
70 mm (GS 70 - and GS 70 +) blocks, there is 1.9 h for the hollow and
2.5 h for the similar compact. Finally, for the 76 mm elements, the
difference was only 0.3 h: 1.5 hrs for GS 76 = and 1.8 hrs for GS 76 -;
the 50 mm block had a thermal delay slightly higher than the GS 76 =,
with 1.7 h.
3.3. Thermal chamber
⌅The average temperature evolution of both the cold and warm environments in the thermal chamber is shown in Figure 8. Values were collected every 60 minutes through the display located on the controller board (Figure 4); the room temperature sensors were positioned close to the surface of the test elements on both sides.
Figure 8 shows that increasing temperature also causes an increase in standard deviation, resulting in greater variation, especially on the hot side of the chamber. Additionally, it was possible to compare the thermal behavior of the test elements in plaster block, since the variation occurred within an acceptable range, with a maximum value of 2.6 °C in the final minutes of heating. The graph for a 360-minute heating period for the 8 test elements is shown in Figure 9. In this graph, the control of the initial temperature is observed with values for all curves always within the range 26 ± 1 °C. The parameter most related to the thermal chamber behavior test is the thermal transmittance (U). To relate this parameter to the assay curves, Figure 10 presents a diagram where the test elements are on the sides in decreasing order for U value. In the central part, they are presented in the order of the curves for every 60 minutes.
However,
one of the test elements, the GS 70 - (purple), shows less congruence
in relation to the theoretical U value and its behavior during the test.
Near 240 minutes, it presents a curve with very reduced acceleration
and, therefore, almost no growth during the next 120 minutes (Figure 10).
GS 76 - showed similar behavior. That happened especially between 180
and 300 minutes, with a possible state of balance between the room
temperature on the cold side and the heat flow coming from the hot side.
This situation may have been, in both cases, due to a cooling of the
environment by the prolonged absence of operators, external climate, or
even by distortions of the air conditioner thermostat. These situations
were also indicated by Ferrari and Zanotto (6262.
Ferrari, S.; Zanotto, V. (2013) The thermal performance of walls under
actual service conditions: Evaluating the results of climatic chamber
tests. Constr. Build. Mater. 43, 309-316. https://doi.org/10.1016/j.conbuildmat.2013.02.056.
).
Considering a trend in the curves of these two elements before the
different points, in the final 60 minutes the relationship between U and
the temperature on the cold side would probably be even clearer.
Relevant behavior is shown by the set of 100 mm blocks. The curves of the test elements GS 100 -, GH 100 + and GS 100 + remain isolated from the others between 40 and 260 minutes, returning to find the other hollow blocks (GS 70 -, GS 76) and approach the GS 76 = around 300 minutes. Behavior in 76 mm test elements should also be highlighted. It is important to note here that the difference between them is only due to the thickness of the alveoli, which is about 25% greater in GS 76 =. Figure 10 shows the first 80 minutes of heating, both show a similar behavior; however, after that time, the curve of the block with the largest number of voids and the highest U value maintains the same acceleration, while the GS 76 - presents a deceleration over a period of 200 minutes. It will increase again only in the final stage, after 320 minutes. Both in the measured values of thermal resistance by the flowmetry method, as well as by the theoretical calculation, the thermal parameters of the GS 76 - proved to be superior to those of the GS 76 = and. In the test, such values were corroborated, despite the greater temperature difference between them: 2.5 °C for about 260 minutes of heating and at the end of the process, over 1 °C.
The GS 50 + showed little capacity to retain the heat passage during the test, in accordance with the theoretical values of its low thermal resistance, R = 0.143 and R = 0.163, calculated and measured, respectively. At the end of the process, there was almost 10 °C of temperature difference for the GS 100 +, which showed the best behavior, and 6 °C of difference for the second with the worst performance, the GS 70 +. The use of this block is restricted to decorations, cabinets, and small closings. It is rarely used for closing masonry. One possibility of use would be associated with a back layer to the ventilation layer in double walls, as it presents the characteristics common to plaster, such as flatness suitable for finishing, low density of apparent mass; it presents greater thickness and self-supporting capacity than plasterboard: drywall boards common thickness is 12.5 mm, and they need metal profiles for support.
Results obtained from the thermal chamber enable
understanding thermal dynamic behavior and verifying theoretical values
for tested plaster blocks. Previous studies have also established these
thermal chamber advantages for plaster compounds (4545.
Kheradmand, M.; Azenha, M.; de Aguiar, J.L.; Castro-Gomes, J. (2016)
Experimental and numerical studies of hybrid PCM embedded in plastering
mortar for enhanced thermal behaviour of buildings. Energy. 94, 250-261. https://doi.org/10.1016/j.energy.2015.10.131.
, 4646.
Pedreño-Rojas, M.A.; Morales-Conde, M.J.; Pérez-Gálvez, F.;
Rodríguez-Liñán, C. (2017) Eco-efficient acoustic and thermal
conditioning using false ceiling plates made from plaster and wood
waste. J. Clean. Prod. 166, 690-705. https://doi.org/10.1016/j.jclepro.2017.08.077.
).
To
complement the data collected by a digital thermometer, the thermograms
made it possible to observe the distribution of heat by the test
element during the heating period (Figures 11 and 12).
By the test element arrangement in the thermal chamber (bottom on the
base of the chamber and the upper part with a gap for the top), there is
a greater pre-disposition of heating in the upper part, aggravated by
the lightness of the hot air that rises (7676.
He, Z.; He, Z.; Zhang, X.; Li, Z. (2015) Study of hot air recirculation
and thermal management in data centers by using temperature rise
distribution. Build. Simul. 9, 541-55. https://doi.org/10.1007/s12273-016-0282-7.
).
The heat transfer to the base of the chamber by conduction promotes
this lower temperature at the base of the test element, as seen in Figures 11 and 12.
Although the expanded polystyrene strips have shown effectiveness in
reducing the exchange of air between the hot and cold parts through the
side and top cracks during the test, a possible improvement for the
insulation is to make it closer to all the edges of the test elements,
including the base.
The thermograms in Figures 11 and 12 corroborate the need to only use contact thermocouples in the central
part of the test element, when heated by a point source, as mentioned in
similar works (2828.
Specht, L.P.; Borges P.A.P.; Rupp, R.F.; Varnier, R. (2010) Análise da
transferência de calor em paredes compostas por diferentes materiais. Amb. Constr. 10, 7-18. https://doi.org/10.1590/S1678-86212010000400002.
, 3030.
Silva, E.P.; Cahino, J.E.M.; Melo, A.B. (2012) Avaliação do desempenho
térmico de blocos EVA, Proceedings of the Encontro Nacional de
Tecnologia no Ambiente Construído, Juiz de Fora (ENTAC).
).
Figures 11 and 12 also indicate that the presence of the vertical alveoli (Figure 11) causes a more vertical distribution of heat due to the transfer by convection that occurs within the air layer. On the other hand, in the solid element (Figure 12), a more radial distribution of the heat focus is clearly seen in the center due to the position of the heating lamp. Unlike the hollow element, where heat tends to rise between the alveoli, conduction allows the heating to be better distributed in the captured area, including the base (see part “6h” Figure 12). This situation can even explain the cause of the behavior of the GS 70 -; in the simulation it differs from the expected, when observing the values of its thermal parameters (Tables 6 and 7). Since the alveoli are open at the top through the gap between the test element and the roof of the thermal chamber, the exchange of hot air, even though it is hampered by the lateral closing and the use of polystyrene strips, occurred, and may have “part the heat flow” perpendicular to the face of the element for that point. Since the GS 70 - is the least thick hollow element, this circumstance affected its behavior more than the other hollow elements, as in Figure 10, and in the behavior scheme (Figure 9).
The possibility of visualizing the heat distribution and transmission by the thickness of the element over time was impossible due to the shape and opacity of the walls in the thermal chamber. In view of this, after the removal of the chamber, this visualization will become possible and allow relevant analyzes on the test.
The side view of the plaster block test element GS 100 + is shown in Figure 13 in digital image (upper left corner) and in thermal images during cooling. Four points were selected: 2 at the ends and 2 in the central part. It was possible to observe how the heat transfer occurs in the block by conduction and from it to the environment by convection, predominantly. When the test element was removed from the chamber, it was subjected to room temperature, around 26 °C - colder than any of the exposed faces. Besides, the test element itself had heat transfer still occurring, mostly by conduction. The flow occurs from the point of highest temperature to the lowest; therefore, heat transfer to the environment and between the thermally different points of the test element itself. In Figure 13, point SP1 is closest to the hot (heated) side and SP4 to the cold side.
Regarding
the thermogram of 0 min, a lighter stain appears, indicating a warmer
region. This is because this thermogram is made as soon as the test
element has been removed from the thermal chamber, right after the
influence of the heat source. In the following thermograms, it is
possible to see that this stain “moves” towards the side center of the
test element. Then, in the 90 min thermogram, a symmetrical temperature
balance occurs, with the most heated points in the center. With the heat
convection, the cooling tends to occur in a similar way in the two main
directions. As cooling time happens, the temperatures tend to present a
“normal” curve shape, considering, for this test, that room
temperatures on both main faces are equal (temperature of the same
environment). It is noteworthy that the cooling of the walls usually
occurs under different room temperature values. Consequently, the heat
flow tends to be different with greater temperature difference; it can
become balanced when the external and internal temperatures are equal.
Previous studies have also used infrared thermography to study plaster
thermal during heating and cooling cycles (7777.
de Freitas, S.S.; de Freitas, V.P.; Barreira, E. (2014) Detection of
façade plaster detachments using infrared thermography-A nondestructive
technique. Constr. Build. Mater. 70, 80-87. https://doi.org/10.1016/j.conbuildmat.2014.07.094.
, 7878.
Theodorakeas, P.; Avdelidis, N.P.; Cheilakou, E.; Koui, M. (2014)
Quantitative analysis of plastered mosaics by means of active infrared
thermography. Constr. Build. Mater. 73, 417-425. https://doi.org/10.1016/j.conbuildmat.2014.09.089.
).
Just like in these studies, infrared thermography allowing dynamic
thermal evaluation, and identification of thermic resistance to heat
fluxes were observed.
4. CONCLUSIONS
⌅This work investigated the thermal properties and behavior of plaster block components. An experimental study were carried out: through a thermal chamber, infrared thermography, and normative parameters. The results achieved aimed to advance the studies on the plaster block and contribute to the debate on materials and construction techniques with a focus on the thermal performance of buildings.
The use of the
flowmetry method to obtain the thermal conductivity of the plaster
allowed observing values for the high and medium density ranges of
plaster blocks. The medium density was around 0.356 W/(m·K), very close
to the 0.350 W/(m·K) value suggested by NBR 15520 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
).
In addition to thermal conductivity, this method allowed the
measurement of the thermal resistance for 8 types of solid and hollow
plaster blocks. The values were between 0.16 m²·K/W (50 mm solid block)
and 0.30 m²·K/W (100 mm hollow block).
The calculation of thermal parameters using NBR 15220 (2020.
Associação Brasileira de Normas Técnicas (2005) NBR 15220: Desempenho
térmico de edificações - Parte 1-5. ABNT, Rio de Janeiro.
)
showed the 100 mm hollow block as the one with the lowest thermal
transmittance value; however, it was only 2% smaller than the 100 mm
solid block, which in turn has higher values of thermal delay and
thermal capacity. Also, the latter showed better thermal behavior in the
tests, ending the heating with temperature on the opposite side to the
heat around 1.5 °C lower than the similar hollow block.
The thermal chamber developed for this work proved to be efficient for carrying out a heating experiment of test elements of vertical seals. The instrumentation used to control, measure, and record temperature through a dimmer, thermocouple, and digital thermometer with the data logger, respectively, allowed verifying and comparing the behavior of the components, without major failure. From the curves generated every minute during 360 minutes of heating, the different thermal behaviors between the 8 types of plaster blocks were observed. It was possible to conclude that the presence of small voids associated with great thicknesses tends to make these blocks the ones that show superior thermal behavior.
The calculations of the thermal parameters corroborated with the results of the thermal chamber test, with few variations in the order of performance of the blocks. The use of thermography during the tests proved to be relevant and pertinent since it was possible to visualize the temperature distribution superficially: it expandes the scope of the point analysis obtained by contact thermocouple and digital thermometer. The thermal behavior of the laying joints in the mini-wall test elements was noticed as well as the voids in the elements with the presence of septa or alveoli. Additionally, through thermography, it was possible to qualitatively analyze the distribution of heating from the heat source and the losses from small cracks in the experimental apparatus.