- Email: [email protected]
Thermal conductivity of newspaper sandwiched aerated lightweight concrete panel
Energy and Buildings 42 (2010) 2452–2456
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Thermal conductivity of newspaper sandwiched aerated lightweight concrete panel Soon-Ching Ng ∗ , Kaw-Sai Low 1 Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, Setapak, 53300 Kuala Lumpur, Wilayah Persekutuan, Malaysia
a r t i c l e
i n f o
Article history: Received 8 April 2010 Received in revised form 23 August 2010 Accepted 25 August 2010 Keywords: Aerated lightweight concrete Thermal conductivity Energy efficient Newspaper sandwiched panel
a b s t r a c t Investigation on the thermal conductivity of newspaper sandwiched aerated lightweight concrete (ALC) panels is the main purpose of this study. Various densities of ALC panels ranging from 1700, 1400 and 1100 kg/m3 with three different aerial intensities of newspaper sandwiched were produced. Investigation was limited to the effect of aerial intensity of newspaper sandwiched and the effect of density of ALC on thermal conductivity. It is found that the thermal conductivity of newspaper sandwiched ALC panels reduced remarkably compared to control ALC panels. The reduction was recorded at 18.0%, 21.8% and 20.7% correspond to densities of 1700, 1400 and 1100 kg/m3 with just a mere 0.05 g/cm2 aerial intensity of newspaper sandwiched. Newspaper sandwiched has a significant impact on the performance of thermal conductivity of ALC panels based on regression analysis. © 2010 Elsevier B.V. All rights reserved.
1. Introduction With the rising energy costs and increasing awareness on the effects of global warming, the need for energy efficient design and construction has become increasingly urgent. In Malaysia, airconditioners are used in almost all commercial buildings to cool the space or room due to hot air outside the building and to absorb the heat produced by the people and electrical appliances from inside building [1]. This equipment is operated continuously all the time in tropical countries to provide comfortable working and dwelling environment. Hence, huge amount of money has been spent for electricity on each air-conditioner every year especially with the recent hike of fossil fuel’s price [2]. Moreover, the burning of fossil fuel for power generation releases green house gases and lead to global warming. Global warming is a phenomenon with wide reaching consequences. Reducing fossil fuel usage and recycling materials are the only two ways of reducing the devastating effects of global warming [3]. In construction industry, energy efficient building design needs to be adopted to reduce the quantities of fossil fuels consumption and thereby reduce the amount of green house gases discharge into the atmosphere [4]. Thus, disregards of increasing fossil fuels’ price or no, the burning of fossil fuels needs to be minimized [5]. Therefore, a proper insulation material with the objective of achieving acceptable comfort for building occupants and reducing the cooling load is imperative [1].
Thermal conductivity is the property of a material that plays a key role in all heat transfer calculations, may it be in the context of energy efficient building design or calculation of temperature profile [6]. The energy performance of a building highly depends on the thermal conductivity of the building materials which describes the ability of heat to flow across the material in the presence of a differential temperature [7]. Therefore, the use of low thermal conductivity building materials is crucial to reduce heat gain through the envelope into the building in hot climate country. Aerated lightweight concrete (ALC) has been recognized for its superior performance in thermal insulation and sound insulation characteristics due to its porous structure [8,9]. Apart from that, reduction in the dead weight of structural elements and size reduction of structural members [10,11] and reduce the risk of earthquake damages [12] are other advantages of lightweight concrete. This study investigates the effect of newspaper sandwiched and the effect of density on thermal conductivity performance of ALC panels. Newspaper was chosen to be embedded because it is believed that newspaper which originated from wood pulp possessed low thermal conductivity ranges from 0.12 to 0.16 W/mK [13]. Therefore, the newspaper sandwiched can act as a shield to reduce the rate of heat transfer. They are other advantages of using newspaper as sandwich material as it is available abundantly. 2. Experimental programme 2.1. Materials
∗ Corresponding author. Tel.: +60 12 4967886; fax: +60 34 1079803. E-mail addresses: [email protected] (S.-C. Ng), [email protected] (K.-S. Low). 1 Tel.: +60 12 3201678. 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.08.026
Newspaper sandwiched ALC panels were manufactured from Portland cement mortar paste with countless of pinhole size (0.3–0.8 mm diameter) air bubbles being entrained or entrapped
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
2453
to form a grid that holds the air bubbles or stable foams in place. The foaming agent was diluted with water at the ratio of 1:30. 2.1.5. Newspaper Tabloid newspaper with the dimension 580 mm × 395 mm was used in this study. 2.2. Aerated lightweight concrete compositions
Fig. 1. Particle size distribution of sand.
within its mortar matrix to give rise to its lightness. This was achieved using foaming agent where the entrapment was accomplished via a mechanical process. In general, the raw materials used are as follows. 2.1.1. Cement Ordinary Portland cement (OPC) obtained from YTL Cement (M) Sdn. Bhd. was used in this study. The OPC used complies with the Type I Portland cement as in ASTM C150 [14] and BS12 [15]. 2.1.2. Sand Mining sand which obtained sieve analysis result as shown in Fig. 1 was used as fine aggregates for all panels. The sand has uniformity coefficient (Cu ) of 4.57 and coefficient of curvature (Cc ) of 1.04 as well. These qualified the sand to be classified as well graded fine aggregates. 2.1.3. Water Through this experimental study tap water was used for the manufacture of the ALC panels. 2.1.4. Foaming agent A locally produced liquid synthetic foaming agent of LCM brand was used in conjunction with a foam generation machine. Preformed stable or closed-end foams were produced and mixed with the cementitious mixture. The thoroughly mixing process disperses the stable foams throughout the cement paste and sand particles
In the current investigation, ALC panels each measured 300 mm × 300 mm × 50 mm were made at three different densities namely 1100, 1400 and 1700 kg/m3 . The aerial intensity of newspaper sandwiched for each density varied from 0.05, 0.10 and 0.15 g/cm2 , respectively. Sand cement ratio was fixed at 1:1.5 while the water–cement ratio was fixed at 0.45 for all panels. Further details of the mix proportions and the panels’ densities are outlined in Table 1. 2.3. Specimen preparation The process of producing newspaper sandwiched ALC panels was to dry mix suitably weighed dry sand and cement in a drum mixer for about a minute before the required amount of water was added to it. Then wet mixing last for another minute will ensue before the predetermined quantity of stable foam was added to yield a mixture of required target density value. For instance, the ALC panel of 1100 kg/m3 density was produced by adding stable foams (37.4% of total mix volume) into mortar mixture (62.5% of total mix volume). The fresh ALC mixture so produced was cast into the steel moulds with dimension 300 mm × 300 mm. The fresh ALC panels were cured and hardened for approximately 24 h before they were demoulded and continued to be cured in a room with prevailing temperature of approximately 29 ◦ C. 2.4. Test method Thermal conductivity of the ALC panels was determined by means of guarded hot plate method as accordance to British Standard [16]. The thermal conductivity, k was calculated based on the following equation: d k = ˚ (T1 − T2 ) A where
Fig. 2. Effect of density on thermal conductivity for ALC panels.
(1)
2454
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
Table 1 Details of ALC panels. Panel description
Sand:cement
Water:cement
Stable form (%)
Mortar (%)
Aerial intensity of newspaper sandwiched (g/cm2 )
28-Day compression strength
Thermal conductivity, k (W/mK)
Ctr-1700 Ctr-1400 Ctr-1100 NP05-1700 NP05-1400 NP05-1100 NP10-1700 NP10-1400 NP10-1100 NP15-1700 NP15-1400 NP15-1100
1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
17.9 32.4 46.9 17.9 32.4 46.9 17.9 32.4 46.9 17.9 32.4 46.9
82.1 67.6 53.1 82.1 67.6 53.1 82.1 67.6 53.1 82.1 67.6 53.1
0 0 0 0.05 0.05 0.05 0.10 0.10 0.10 0.15 0.15 0.15
23.41 11.52 3.38 23.41 11.52 3.38 23.41 11.52 3.38 23.41 11.52 3.38
0.621 0.504 0.391 0.509 0.394 0.310 0.491 0.333 0.307 0.400 0.317 0.303
Fig. 3. Percent reduction of thermal conductivity based on density.
˚ = the average power supplied to the metering section of the heating unit. d = the average specimen thickness. A = is the metering area. T1 = the average temperature at the hot side of the specimen. T2 = the average temperature at the cool side of the specimen.
3. Results and discussions Thermal conductivity of all ALC panels is summarized in Table 1. Further discussions are categorized according to the effect of density and the effect of newspaper sandwiched on thermal conductivity.
Fig. 4. Effect of sandwiched newspaper intensity on thermal conductivity of ALC panels.
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
2455
Fig. 5. Percent reduction of thermal conductivity based on intensity of newspaper sandwiched.
3.1. Effect of density on thermal conductivity The results show that the thermal conductivity of all panels is positively proportionate with the density (Fig. 2). For instance, the thermal conductivity for control panels without newspaper sandwiched reduced from 0.621 to 0.504 W/mK and further reduced to 0.391 W/mK for corresponding densities of 1700, 1400 and 1100 kg/m3 , respectively. The percent of reduction was equivalent to 18.8% and 37.0% for densities 1400 and 1100 kg/m3 panels compared to density 1700 kg/m3 panel. The results have proven that lower density translates to lower thermal conductivity which is similar to the findings from other researchers [17–19]. The density of ALC panels is governed by the porosity or amount of air content. Lower density of ALC indicates greater porosity or greater amount of air contained. Therefore, thermal conductivity changes considerably with the porosity of ALC panel because air is the poorest conductor compared to solid and liquid due to its molecular structure. The results suggest that the trend of thermal conductivity reduction also applicable to newspaper sandwiched ALC panels. Fig. 3 shows the percent reduction on thermal conductivity of ALC panels compared to density 1700 kg/m3 ALC panels of similar aerial intensity of newspaper sandwiched. As shown in Fig. 3, the reduction of thermal conductivity is linear to the reduction of density for control panels. However, the reduction trend is not linear for newspaper sandwiched panels. 3.2. Effect of newspaper sandwiched on thermal conductivity Fig. 4 shows the thermal conductivity of ALC panels with different aerial intensities of newspaper sandwiched for three different densities namely 1700, 1400 and 1100 kg/m3 . The results indicate that newspaper sandwiched is effective in reducing the thermal conductivity of the panels. Generally, the thermal conductivity reduces as the aerial intensity of newspaper sandwiched increases. It is observed that a significant reduction on thermal conductivity portrayed by control ALC panels compared to all NP05 panels irrespective of density. For example, thermal conductivity reduction for control panels compared to NP05 panels were 0.112 W/mK or 18.0%, 0.110 W/mK or 21.8% and 0.081 W/mK or 20.7% correspond to densities 1700, 1400 and 1100 kg/m3 panels. The reduction of thermal conductivity is not linear to the increase of aerial intensity of newspaper sandwiched as shown in Fig. 5. Newspaper sandwiched of 0.05 g/cm2 aerial intensity was the most effective in reducing the thermal conductivity of ALC panels.
Thermal conductivity further reduced when the aerial intensity of newspaper sandwiched increased to 0.10 and 0.15 g/cm2 . However, the rate of percent reduction on thermal conductivity for 0.10 and 0.15 g/cm2 was lower than 0.05 g/cm2 aerial intensity newspaper sandwiched panels. 4. Development of regression model Regression analysis refers to technique used for modeling and analyzing several variables, where the focus is on the relationship between a dependent variable and one or more independent variables. More specifically, regression analysis helps to understand how the typical value of the dependent variable changes when any one of the independent variables is varied, while the other independent variables are held fixed. In this study, they were only two factors considered to influence the thermal conductivity of ALC panels namely density and aerial intensity of newspaper sandwiched. It is undoubtedly that they are many other factors influencing the thermal conductivity such as age, water–cement ratio, filler–cement ratio and temperature different [20]. However, the other factors were fixed in this investigation. Therefore, the factors influencing the thermal conductivity can be represented in Eq. (2). k = f (density, green shield)
(2)
The results of the regression analysis are summarized in Table 2. Both factors namely density and aerial intensity of newspaper sandwiched were statistically proven significant factors affecting the thermal conductivity of ALC panels at 95% confidence level as indicated by the sig. values in Table 2. From the regression analysis, it is found that density has a dominant effect on the thermal conductivity performance of ALC panels compared to aerial intensity of newspaper sandwiched based on standardized coefficient (Beta) or t value shown in Table 2 [21,22]. Table 2 Results generated from statistical analysis. Model
Constant Density Sandwiched Newspaper
Unstandardized coefficients
Standardized coefficients
B
Std. error
Beta
0.071 0.295 −1.044
0.044 0.030 0.133
– 0.731 −0.590
2456
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
The relationships between the thermal conductivity and two influencing factors are presented in Eq. (3) with coefficient of determination (R2 ) value of 0.88. This indicates that 88% of variation in thermal conductivity of ALC panels is due to density and newspaper sandwiched. Y = 0.295X1 − 1.044X2 + 0.071
(3)
where Y = k value of the panel. X1 = density of the panel in t/m3. X2 = aerial intensity of newspaper sandwiched in g/cm2 , either 0, 0.05, 0.10 or 0.15. 5. Conclusion Density and aerial intensity of newspaper sandwiched have an immense effect on thermal conductivity of ALC panels. The results indicate that newspaper sandwiched is effective in reducing the thermal conductivity of ALC panels. With a mere aerial intensity of 0.05 g/cm2 of newspaper sandwiched, the reduction on thermal conductivity was enormous ranging from 18.0% to 21.8% compared to control panels. The reduction of thermal conductivity was positively proportionate to the aerial intensity of newspaper sandwiched. The regression analysis suggested a relationship between thermal conductivity as a dependent variable while aerial intensity of newspaper sandwiched and density as independent variables. The equation developed from this study has high R2 value (0.88), this indicates that 88% on the variation of thermal conductivity was due to the density and aerial intensity of newspaper sandwiched. From the findings of this study, it has provided a potential solution to the construction industry. It has been a challenge all this while on producing porous and lighter concrete in order to enjoy the benefit of low thermal conductivity. However, lighter concrete normally has insufficient strength or non-compliance to various standards or code of practices on strength requirement. Thus, with the effectiveness of newspaper sandwiched in lowering the thermal conductivity of ALC panels, it allows the production of denser and stronger ALC yet having low thermal conductivity. Therefore, it is suitable to be used as wall envelope for energy efficient building construction. 6. Future research Further investigation should be conducted on the prototype scale of newspaper sandwiched ALC panels. The prototype panels should be exposed to the natural environment or transient condition to determine the effectiveness of newspaper sandwiched ALC panels in heat insulation as well as its constructability aspects.
References [1] T.M.I. Mahlia, B.N. Taufiq, H.H. Ismail, Masjuki, Correlation between thermal conductivity and the thickness of selected insulation materials for building wall, Energy and Buildings 39 (2) (2008) 182–187. [2] K.S. Al-Jabri, A.W. Hago, A.S. Al-Nuaimi, A.H. Al-Saidy, Concrete blocks for thermal insulation in hot climate, Cement and Concrete Research 35 (8) (2005) 1472–1479. [3] P. Sukontasukkul, Use of crumb rubber to improve thermal and sound properties of pre-cast concrete panel, Construction and Building Materials 23 (2) (2009) 1084–1092. [4] A.M. Papadopoulos, E. Giama, Environmental performance evaluation of thermal insulation materials and its impact on the building, Building and Environment 42 (5) (2007) 2178–2187. [5] R. Demirboga, Thermal conductivity and compressive strength of concrete incorporation with mineral admixtures, Building and Environment 42 (7) (2007) 2467–2471. [6] B. Battacherjee, S. Krishnamoorthy, Permeable porosity and thermal conductivity of construction materials, Journal of Materials in Civil Engineering 16 (4) (2004) 322–330. [7] I. Budaiwi, A. Abdou, M. Al-Homoud, Variations of thermal conductivity of insulation materials under different operating temperatures: impact on envelope-induced cooling load, Journal of Archaeological Engineering 8 (4) (2002) 125–132. [8] G.M. Glenn, G.M. Gray, W.J. Orts, D.W. Wood, Starch-based lightweight concrete: effect of starch source, processing method and aggregate geometry, Industrial Crops and Products 9 (2) (1999) 133–144. [9] A. Kılıc¸, C.D. Atis, E. Yas¸ar, Özcan, High-strength lightweight concrete made with scoria aggregate containing mineral admixtures, Cement Concrete Research 33 (10) (2003) 1595–1599. [10] J. Gao, W. Sun, K. Morino, Mechanical properties of steel fibre-reinforced highstrength, lightweight concrete, Cement Concrete Composites 19 (4) (1997) 307–313. [11] A.K. Suryavanshi, R.N. Swamy, Development of lightweight mixes using ceramic microspheres as filler, Cement Concrete Research 32 (11) (2002) 1783–1789. [12] E. Yasar, C.D. Atis, A. Kilic, H. Gulsen, Strength properties of lightweight concrete made with basaltic pumice and fly ash, Materials Letters 57 (15) (2003) 2267–2270. [13] F.P. Incropera, D.P. Dewitt, T.L. Bergman, A.S. Lavine, Introduction to heat transfer, fifth ed., John Wiley and Sons, Asia, 2007. [14] ASTM. C 150-02a, Standard Specification for Portland Cement, ASTM, West Conshohocken, PA, 2002. [15] BS 12 Specification for Portland Cement, London, 1991. [16] BSEN 12664, 2001. Thermal performance of building materials and products—Determination of thermal resistance by means of guarded hot plate and heat flow meter methods—Dry and moist products of medium and low thermal resistance. London. [17] N. Narayanan, K. Ramamurthy, Structure and properties of aerated concrete: a review, Cement Concrete Composites 22 (5) (2000) 321–329. [18] R. Demirboga, R. Gul, The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete, Cement Concrete Research 33 (10) (2003) 723–727. [19] J. Khedari, P. Watsanasathaporn, J. Hirunlabh, Development of fire-based soilcement block with low thermal conductivity, Cement Concrete Composites 27 (1) (2005) 111–116. [20] K.H. Kim, S.E. Jeon, J.K. Kim, S. Yang, An experimental study on thermal conductivity of concrete, Cement Concrete Research 33 (3) (2003) 363–371. [21] J.F. Hair, R.E. Anderson, R.L. Tatham, W.C. Black, Mulitvariate Data Analysis, fifth ed., Prentice Hall, 1998, pp. 141–156. [22] Y. Ma, B. Zhu, M. Tan, K. Wu, Effect of Y type polypropylene fiber on plastic shrinkage cracking of cement mortar, Materials and Structures 37 (2) (2004) 92–95.
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Thermal conductivity of newspaper sandwiched aerated lightweight concrete panel Soon-Ching Ng ∗ , Kaw-Sai Low 1 Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, Setapak, 53300 Kuala Lumpur, Wilayah Persekutuan, Malaysia
a r t i c l e
i n f o
Article history: Received 8 April 2010 Received in revised form 23 August 2010 Accepted 25 August 2010 Keywords: Aerated lightweight concrete Thermal conductivity Energy efficient Newspaper sandwiched panel
a b s t r a c t Investigation on the thermal conductivity of newspaper sandwiched aerated lightweight concrete (ALC) panels is the main purpose of this study. Various densities of ALC panels ranging from 1700, 1400 and 1100 kg/m3 with three different aerial intensities of newspaper sandwiched were produced. Investigation was limited to the effect of aerial intensity of newspaper sandwiched and the effect of density of ALC on thermal conductivity. It is found that the thermal conductivity of newspaper sandwiched ALC panels reduced remarkably compared to control ALC panels. The reduction was recorded at 18.0%, 21.8% and 20.7% correspond to densities of 1700, 1400 and 1100 kg/m3 with just a mere 0.05 g/cm2 aerial intensity of newspaper sandwiched. Newspaper sandwiched has a significant impact on the performance of thermal conductivity of ALC panels based on regression analysis. © 2010 Elsevier B.V. All rights reserved.
1. Introduction With the rising energy costs and increasing awareness on the effects of global warming, the need for energy efficient design and construction has become increasingly urgent. In Malaysia, airconditioners are used in almost all commercial buildings to cool the space or room due to hot air outside the building and to absorb the heat produced by the people and electrical appliances from inside building [1]. This equipment is operated continuously all the time in tropical countries to provide comfortable working and dwelling environment. Hence, huge amount of money has been spent for electricity on each air-conditioner every year especially with the recent hike of fossil fuel’s price [2]. Moreover, the burning of fossil fuel for power generation releases green house gases and lead to global warming. Global warming is a phenomenon with wide reaching consequences. Reducing fossil fuel usage and recycling materials are the only two ways of reducing the devastating effects of global warming [3]. In construction industry, energy efficient building design needs to be adopted to reduce the quantities of fossil fuels consumption and thereby reduce the amount of green house gases discharge into the atmosphere [4]. Thus, disregards of increasing fossil fuels’ price or no, the burning of fossil fuels needs to be minimized [5]. Therefore, a proper insulation material with the objective of achieving acceptable comfort for building occupants and reducing the cooling load is imperative [1].
Thermal conductivity is the property of a material that plays a key role in all heat transfer calculations, may it be in the context of energy efficient building design or calculation of temperature profile [6]. The energy performance of a building highly depends on the thermal conductivity of the building materials which describes the ability of heat to flow across the material in the presence of a differential temperature [7]. Therefore, the use of low thermal conductivity building materials is crucial to reduce heat gain through the envelope into the building in hot climate country. Aerated lightweight concrete (ALC) has been recognized for its superior performance in thermal insulation and sound insulation characteristics due to its porous structure [8,9]. Apart from that, reduction in the dead weight of structural elements and size reduction of structural members [10,11] and reduce the risk of earthquake damages [12] are other advantages of lightweight concrete. This study investigates the effect of newspaper sandwiched and the effect of density on thermal conductivity performance of ALC panels. Newspaper was chosen to be embedded because it is believed that newspaper which originated from wood pulp possessed low thermal conductivity ranges from 0.12 to 0.16 W/mK [13]. Therefore, the newspaper sandwiched can act as a shield to reduce the rate of heat transfer. They are other advantages of using newspaper as sandwich material as it is available abundantly. 2. Experimental programme 2.1. Materials
∗ Corresponding author. Tel.: +60 12 4967886; fax: +60 34 1079803. E-mail addresses: [email protected] (S.-C. Ng), [email protected] (K.-S. Low). 1 Tel.: +60 12 3201678. 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.08.026
Newspaper sandwiched ALC panels were manufactured from Portland cement mortar paste with countless of pinhole size (0.3–0.8 mm diameter) air bubbles being entrained or entrapped
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
2453
to form a grid that holds the air bubbles or stable foams in place. The foaming agent was diluted with water at the ratio of 1:30. 2.1.5. Newspaper Tabloid newspaper with the dimension 580 mm × 395 mm was used in this study. 2.2. Aerated lightweight concrete compositions
Fig. 1. Particle size distribution of sand.
within its mortar matrix to give rise to its lightness. This was achieved using foaming agent where the entrapment was accomplished via a mechanical process. In general, the raw materials used are as follows. 2.1.1. Cement Ordinary Portland cement (OPC) obtained from YTL Cement (M) Sdn. Bhd. was used in this study. The OPC used complies with the Type I Portland cement as in ASTM C150 [14] and BS12 [15]. 2.1.2. Sand Mining sand which obtained sieve analysis result as shown in Fig. 1 was used as fine aggregates for all panels. The sand has uniformity coefficient (Cu ) of 4.57 and coefficient of curvature (Cc ) of 1.04 as well. These qualified the sand to be classified as well graded fine aggregates. 2.1.3. Water Through this experimental study tap water was used for the manufacture of the ALC panels. 2.1.4. Foaming agent A locally produced liquid synthetic foaming agent of LCM brand was used in conjunction with a foam generation machine. Preformed stable or closed-end foams were produced and mixed with the cementitious mixture. The thoroughly mixing process disperses the stable foams throughout the cement paste and sand particles
In the current investigation, ALC panels each measured 300 mm × 300 mm × 50 mm were made at three different densities namely 1100, 1400 and 1700 kg/m3 . The aerial intensity of newspaper sandwiched for each density varied from 0.05, 0.10 and 0.15 g/cm2 , respectively. Sand cement ratio was fixed at 1:1.5 while the water–cement ratio was fixed at 0.45 for all panels. Further details of the mix proportions and the panels’ densities are outlined in Table 1. 2.3. Specimen preparation The process of producing newspaper sandwiched ALC panels was to dry mix suitably weighed dry sand and cement in a drum mixer for about a minute before the required amount of water was added to it. Then wet mixing last for another minute will ensue before the predetermined quantity of stable foam was added to yield a mixture of required target density value. For instance, the ALC panel of 1100 kg/m3 density was produced by adding stable foams (37.4% of total mix volume) into mortar mixture (62.5% of total mix volume). The fresh ALC mixture so produced was cast into the steel moulds with dimension 300 mm × 300 mm. The fresh ALC panels were cured and hardened for approximately 24 h before they were demoulded and continued to be cured in a room with prevailing temperature of approximately 29 ◦ C. 2.4. Test method Thermal conductivity of the ALC panels was determined by means of guarded hot plate method as accordance to British Standard [16]. The thermal conductivity, k was calculated based on the following equation: d k = ˚ (T1 − T2 ) A where
Fig. 2. Effect of density on thermal conductivity for ALC panels.
(1)
2454
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
Table 1 Details of ALC panels. Panel description
Sand:cement
Water:cement
Stable form (%)
Mortar (%)
Aerial intensity of newspaper sandwiched (g/cm2 )
28-Day compression strength
Thermal conductivity, k (W/mK)
Ctr-1700 Ctr-1400 Ctr-1100 NP05-1700 NP05-1400 NP05-1100 NP10-1700 NP10-1400 NP10-1100 NP15-1700 NP15-1400 NP15-1100
1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5 1:1.5
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
17.9 32.4 46.9 17.9 32.4 46.9 17.9 32.4 46.9 17.9 32.4 46.9
82.1 67.6 53.1 82.1 67.6 53.1 82.1 67.6 53.1 82.1 67.6 53.1
0 0 0 0.05 0.05 0.05 0.10 0.10 0.10 0.15 0.15 0.15
23.41 11.52 3.38 23.41 11.52 3.38 23.41 11.52 3.38 23.41 11.52 3.38
0.621 0.504 0.391 0.509 0.394 0.310 0.491 0.333 0.307 0.400 0.317 0.303
Fig. 3. Percent reduction of thermal conductivity based on density.
˚ = the average power supplied to the metering section of the heating unit. d = the average specimen thickness. A = is the metering area. T1 = the average temperature at the hot side of the specimen. T2 = the average temperature at the cool side of the specimen.
3. Results and discussions Thermal conductivity of all ALC panels is summarized in Table 1. Further discussions are categorized according to the effect of density and the effect of newspaper sandwiched on thermal conductivity.
Fig. 4. Effect of sandwiched newspaper intensity on thermal conductivity of ALC panels.
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
2455
Fig. 5. Percent reduction of thermal conductivity based on intensity of newspaper sandwiched.
3.1. Effect of density on thermal conductivity The results show that the thermal conductivity of all panels is positively proportionate with the density (Fig. 2). For instance, the thermal conductivity for control panels without newspaper sandwiched reduced from 0.621 to 0.504 W/mK and further reduced to 0.391 W/mK for corresponding densities of 1700, 1400 and 1100 kg/m3 , respectively. The percent of reduction was equivalent to 18.8% and 37.0% for densities 1400 and 1100 kg/m3 panels compared to density 1700 kg/m3 panel. The results have proven that lower density translates to lower thermal conductivity which is similar to the findings from other researchers [17–19]. The density of ALC panels is governed by the porosity or amount of air content. Lower density of ALC indicates greater porosity or greater amount of air contained. Therefore, thermal conductivity changes considerably with the porosity of ALC panel because air is the poorest conductor compared to solid and liquid due to its molecular structure. The results suggest that the trend of thermal conductivity reduction also applicable to newspaper sandwiched ALC panels. Fig. 3 shows the percent reduction on thermal conductivity of ALC panels compared to density 1700 kg/m3 ALC panels of similar aerial intensity of newspaper sandwiched. As shown in Fig. 3, the reduction of thermal conductivity is linear to the reduction of density for control panels. However, the reduction trend is not linear for newspaper sandwiched panels. 3.2. Effect of newspaper sandwiched on thermal conductivity Fig. 4 shows the thermal conductivity of ALC panels with different aerial intensities of newspaper sandwiched for three different densities namely 1700, 1400 and 1100 kg/m3 . The results indicate that newspaper sandwiched is effective in reducing the thermal conductivity of the panels. Generally, the thermal conductivity reduces as the aerial intensity of newspaper sandwiched increases. It is observed that a significant reduction on thermal conductivity portrayed by control ALC panels compared to all NP05 panels irrespective of density. For example, thermal conductivity reduction for control panels compared to NP05 panels were 0.112 W/mK or 18.0%, 0.110 W/mK or 21.8% and 0.081 W/mK or 20.7% correspond to densities 1700, 1400 and 1100 kg/m3 panels. The reduction of thermal conductivity is not linear to the increase of aerial intensity of newspaper sandwiched as shown in Fig. 5. Newspaper sandwiched of 0.05 g/cm2 aerial intensity was the most effective in reducing the thermal conductivity of ALC panels.
Thermal conductivity further reduced when the aerial intensity of newspaper sandwiched increased to 0.10 and 0.15 g/cm2 . However, the rate of percent reduction on thermal conductivity for 0.10 and 0.15 g/cm2 was lower than 0.05 g/cm2 aerial intensity newspaper sandwiched panels. 4. Development of regression model Regression analysis refers to technique used for modeling and analyzing several variables, where the focus is on the relationship between a dependent variable and one or more independent variables. More specifically, regression analysis helps to understand how the typical value of the dependent variable changes when any one of the independent variables is varied, while the other independent variables are held fixed. In this study, they were only two factors considered to influence the thermal conductivity of ALC panels namely density and aerial intensity of newspaper sandwiched. It is undoubtedly that they are many other factors influencing the thermal conductivity such as age, water–cement ratio, filler–cement ratio and temperature different [20]. However, the other factors were fixed in this investigation. Therefore, the factors influencing the thermal conductivity can be represented in Eq. (2). k = f (density, green shield)
(2)
The results of the regression analysis are summarized in Table 2. Both factors namely density and aerial intensity of newspaper sandwiched were statistically proven significant factors affecting the thermal conductivity of ALC panels at 95% confidence level as indicated by the sig. values in Table 2. From the regression analysis, it is found that density has a dominant effect on the thermal conductivity performance of ALC panels compared to aerial intensity of newspaper sandwiched based on standardized coefficient (Beta) or t value shown in Table 2 [21,22]. Table 2 Results generated from statistical analysis. Model
Constant Density Sandwiched Newspaper
Unstandardized coefficients
Standardized coefficients
B
Std. error
Beta
0.071 0.295 −1.044
0.044 0.030 0.133
– 0.731 −0.590
2456
S.-C. Ng, K.-S. Low / Energy and Buildings 42 (2010) 2452–2456
The relationships between the thermal conductivity and two influencing factors are presented in Eq. (3) with coefficient of determination (R2 ) value of 0.88. This indicates that 88% of variation in thermal conductivity of ALC panels is due to density and newspaper sandwiched. Y = 0.295X1 − 1.044X2 + 0.071
(3)
where Y = k value of the panel. X1 = density of the panel in t/m3. X2 = aerial intensity of newspaper sandwiched in g/cm2 , either 0, 0.05, 0.10 or 0.15. 5. Conclusion Density and aerial intensity of newspaper sandwiched have an immense effect on thermal conductivity of ALC panels. The results indicate that newspaper sandwiched is effective in reducing the thermal conductivity of ALC panels. With a mere aerial intensity of 0.05 g/cm2 of newspaper sandwiched, the reduction on thermal conductivity was enormous ranging from 18.0% to 21.8% compared to control panels. The reduction of thermal conductivity was positively proportionate to the aerial intensity of newspaper sandwiched. The regression analysis suggested a relationship between thermal conductivity as a dependent variable while aerial intensity of newspaper sandwiched and density as independent variables. The equation developed from this study has high R2 value (0.88), this indicates that 88% on the variation of thermal conductivity was due to the density and aerial intensity of newspaper sandwiched. From the findings of this study, it has provided a potential solution to the construction industry. It has been a challenge all this while on producing porous and lighter concrete in order to enjoy the benefit of low thermal conductivity. However, lighter concrete normally has insufficient strength or non-compliance to various standards or code of practices on strength requirement. Thus, with the effectiveness of newspaper sandwiched in lowering the thermal conductivity of ALC panels, it allows the production of denser and stronger ALC yet having low thermal conductivity. Therefore, it is suitable to be used as wall envelope for energy efficient building construction. 6. Future research Further investigation should be conducted on the prototype scale of newspaper sandwiched ALC panels. The prototype panels should be exposed to the natural environment or transient condition to determine the effectiveness of newspaper sandwiched ALC panels in heat insulation as well as its constructability aspects.
References [1] T.M.I. Mahlia, B.N. Taufiq, H.H. Ismail, Masjuki, Correlation between thermal conductivity and the thickness of selected insulation materials for building wall, Energy and Buildings 39 (2) (2008) 182–187. [2] K.S. Al-Jabri, A.W. Hago, A.S. Al-Nuaimi, A.H. Al-Saidy, Concrete blocks for thermal insulation in hot climate, Cement and Concrete Research 35 (8) (2005) 1472–1479. [3] P. Sukontasukkul, Use of crumb rubber to improve thermal and sound properties of pre-cast concrete panel, Construction and Building Materials 23 (2) (2009) 1084–1092. [4] A.M. Papadopoulos, E. Giama, Environmental performance evaluation of thermal insulation materials and its impact on the building, Building and Environment 42 (5) (2007) 2178–2187. [5] R. Demirboga, Thermal conductivity and compressive strength of concrete incorporation with mineral admixtures, Building and Environment 42 (7) (2007) 2467–2471. [6] B. Battacherjee, S. Krishnamoorthy, Permeable porosity and thermal conductivity of construction materials, Journal of Materials in Civil Engineering 16 (4) (2004) 322–330. [7] I. Budaiwi, A. Abdou, M. Al-Homoud, Variations of thermal conductivity of insulation materials under different operating temperatures: impact on envelope-induced cooling load, Journal of Archaeological Engineering 8 (4) (2002) 125–132. [8] G.M. Glenn, G.M. Gray, W.J. Orts, D.W. Wood, Starch-based lightweight concrete: effect of starch source, processing method and aggregate geometry, Industrial Crops and Products 9 (2) (1999) 133–144. [9] A. Kılıc¸, C.D. Atis, E. Yas¸ar, Özcan, High-strength lightweight concrete made with scoria aggregate containing mineral admixtures, Cement Concrete Research 33 (10) (2003) 1595–1599. [10] J. Gao, W. Sun, K. Morino, Mechanical properties of steel fibre-reinforced highstrength, lightweight concrete, Cement Concrete Composites 19 (4) (1997) 307–313. [11] A.K. Suryavanshi, R.N. Swamy, Development of lightweight mixes using ceramic microspheres as filler, Cement Concrete Research 32 (11) (2002) 1783–1789. [12] E. Yasar, C.D. Atis, A. Kilic, H. Gulsen, Strength properties of lightweight concrete made with basaltic pumice and fly ash, Materials Letters 57 (15) (2003) 2267–2270. [13] F.P. Incropera, D.P. Dewitt, T.L. Bergman, A.S. Lavine, Introduction to heat transfer, fifth ed., John Wiley and Sons, Asia, 2007. [14] ASTM. C 150-02a, Standard Specification for Portland Cement, ASTM, West Conshohocken, PA, 2002. [15] BS 12 Specification for Portland Cement, London, 1991. [16] BSEN 12664, 2001. Thermal performance of building materials and products—Determination of thermal resistance by means of guarded hot plate and heat flow meter methods—Dry and moist products of medium and low thermal resistance. London. [17] N. Narayanan, K. Ramamurthy, Structure and properties of aerated concrete: a review, Cement Concrete Composites 22 (5) (2000) 321–329. [18] R. Demirboga, R. Gul, The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete, Cement Concrete Research 33 (10) (2003) 723–727. [19] J. Khedari, P. Watsanasathaporn, J. Hirunlabh, Development of fire-based soilcement block with low thermal conductivity, Cement Concrete Composites 27 (1) (2005) 111–116. [20] K.H. Kim, S.E. Jeon, J.K. Kim, S. Yang, An experimental study on thermal conductivity of concrete, Cement Concrete Research 33 (3) (2003) 363–371. [21] J.F. Hair, R.E. Anderson, R.L. Tatham, W.C. Black, Mulitvariate Data Analysis, fifth ed., Prentice Hall, 1998, pp. 141–156. [22] Y. Ma, B. Zhu, M. Tan, K. Wu, Effect of Y type polypropylene fiber on plastic shrinkage cracking of cement mortar, Materials and Structures 37 (2) (2004) 92–95.