International Journal of Architectural Heritage Conservation, Analysis, and Restoration
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Potential Use of Foamed Mortar (FM) for Thermal Upgrading of Chinese Traditional Hui-Style Residences Wei She, M. R. Jones, Yunsheng Zhang & Xing Shi To cite this article: Wei She, M. R. Jones, Yunsheng Zhang & Xing Shi (2015) Potential Use of Foamed Mortar (FM) for Thermal Upgrading of Chinese Traditional HuiStyle Residences, International Journal of Architectural Heritage, 9:7, 775-793, DOI: 10.1080/15583058.2013.855839 To link to this article: http://dx.doi.org/10.1080/15583058.2013.855839
Accepted author version posted online: 09 Sep 2014.
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Date: 21 November 2015, At: 20:38
International Journal of Architectural Heritage, 9: 775–793, 2015 Copyright © Taylor & Francis Group, LLC ISSN: 1558-3058 print / 1558-3066 online DOI: 10.1080/15583058.2013.855839
Potential Use of Foamed Mortar (FM) for Thermal Upgrading of Chinese Traditional Hui-Style Residences Wei She,1,2,3 M. R. Jones,3 Yunsheng Zhang,2 and Xing Shi4,5 1
Jiangsu Institute of Building Science Co., Ltd., Nanjing, People’s Republic of China Jiangsu Key Laboratory for Construction Materials, Southeast University, Nanjing, People’s Republic of China 3 Concrete Technology Unit, Division of Civil Engineering, University of Dundee, Dundee, Scotland, United Kingdom 4 Key Laboratory of Urban and Architectural Heritage Conservation, Ministry of Education, Beijing, People’s Republic of China 5 School of Architecture, Southeast University, Nanjing, People’s Republic of China
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1. INTRODUCTION The Hui-style residence is an important architectural heritage of China. The hollow wall structures are widely used to build its exterior wall system. However, the thermal performance of the hollow wall is no longer able to meet the new energy-saving and environmental requirement. This article describes a laboratory study of the development of foamed mortar (FM), with the potential for use in thermal upgrading of the Hui-style hollow wall system without dramatically changing its traditional structure. The key early age, physical, mechanical and thermal properties were systematically measured. Two extended models were respectively developed to calculate compressive strength and thermal conductivity, as a function of porosity. Environment chamber test was also employed to investigate the effectiveness of this novel thermal upgrading approach and the results show that filling the voids with FM can effectively improve the overall thermal resistance of the hollow wall system by 44%, which is almost equal to the overall thermal resistance when using the more expensive commercial inorganic stucco system. In addition, the combination of these two methods yielded an overall thermal resistance of 0.701 m2 ·K/W, which is even higher than 0.67 m2 ·K/W for the code required in the hot summer/cold winter climate zone. Keywords Hui-style residences, architectural heritage, thermal upgrading, foamed mortar (FM), strength model, thermal conductive model, environment chamber test
Received February 4, 2013; accepted October 11, 2013. Address correspondence to Wei She, Jiangsu Institute of Building Science Co., Ltd, 118 Liquan Street, Nanjing 210008, P. R. China. E-mail:
[email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uarc.
1.1. Hui-Style Traditional Residences and Hui-Zhou Region China is a country with a vast territory, complex topography, diverse climates, different cultures and ethnic groups. All these factors, combined with its long history, have resulted in a range of vernacular architectures. Hui-style architecture is one of the most famous architectural styles among them and has been successfully selected into the World Heritage List as representative of rural architecture. As many other vernacular residences in China, Hui-style residences (Figure 1) have distinct characteristic of regionalism, which built with black tiles and white walls, surrounded by high walls shaped like horse heads (for fireproofing), and harmonized with refined and elegant colors, bring us a strong sense of beauty and even has a profound influence on the architectural styles in other regions in China (Lu 2004). Hui-style ancient residence locates in old Hui-zhou region, which encompasses the southern part of Anhui Province and the northeastern part of Jiangxi Province. The Hui-zhou region belongs to the hot summer/cold winter region, according to the building energy efficiency design standard GB50176-1993 (Ministry of Construction of China 1993). In this climate zone, the weather is hot and humid in summer, and it can be cold to below freezing point in winter. The Hui-zhou region is mountainous, and fertile land has been in short supply throughout the history. Therefore, the ancient Hui-style villages are gathered to save the cultivated land. 1.2. “Hollow Wall” Structure and Building Materials in Hui-Style Residences The traditional residences in Hui-zhou have distinct architectural characteristics, with their exterior walls deemed
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FIG. 1. Image of Hui-style vernacular dwelling.
the most celebrated. The most common exterior wall system in Hui-style ancient residence is the so called hollow wall. Figure 2 shows a three-dimensional (3D) view of the hollow wall structure. Generally speaking, this wall system has two layers of clay brick, inner wythe and outer wythe, respectively. Between the two layers, some bricks, usually called through-the-wall brick, are vertically inserted through the wall to act as diaphragm. Therefore, the actual thickness of the wall is nearly half the width of a clay brick. The term hollow wall is derived from the fact that many voids formed inside the wall. In the past, these voids were filled with mud for multiple purposes, including increasing the integrity of the wall, and filling cracks and small holes in the wall. In newly built Hui-style residences, mud is not used anymore for the purpose of construction speed improvement as well as land protection. Various locally available construction materials were widely used in the exterior wall, considering that these local materials are natural and hence they remarkably reduce the cost of transporting building materials to the mountainous Hui-zhou region. Among various wall materials, a fired-clay brick with a dark greenish color was widely used to construct the base and the wall system (Figure 3a). A local natural granite stone (Figure 3b) was also commonly used for foundation of the wall. Small pebbles (Figure 3c) were another convenient material found in many local rivers. According to their sizes, small pebbles are chosen together with natural sand to fill the holes in the wall. Mixed with lime and water, the local mud or soil was widely used for gluing bricks, natural stones, and pebbles together, offering better bearing capacity. The wall systems built with these materials have undergone the test of time, there are more than 240 Hui-style ancient residences still structurally firm more than 950 years old. However, in newly built Hui-style
FIG. 2. A three-dimensional (3D) view of the hollow wall structure in Huistyle residence.
residences, traditional fired clay bricks are replaced by modern bricks (Figure 3d), which are made of aggregates, cement, and water, and cured in natural environment. The aggregates involve various materials, including industrial wastes such as cinders and fine tailings. This type of brick is relatively cheap and, thus commonly used by Hui-zhou’s local residents to build their houses. 1.3. Thermal Performance of Traditional and Newly Built Hui-Style Residences As discussed previously, the Hui-zhou region is located in the hot summer/cold winter climate region. Therefore, both
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(a)
(b)
(c)
(d)
FIG. 3. Common used building materials in Hui-style residences: (a) clay brick, (b) natural granite stone, (c) pebble, and (d) modern brick.
heating and cooling methods are needed to maintain a comfortable indoor thermal environment. In the old days when modern building heating and cooling technology was unavailable, the Hui-style residences depended on natural cooling in summer by adopting passive design techniques, such as shading, water cooling, and landscaping (Lu 2004). While in winter, local residents usually used fire basin to create warm indoor environment. At present, as unit air-conditioning system becomes common, many Hui-zhou residents buy and install them in their dwellings. Therefore, the thermal performance of the exterior wall system becomes a key factor in maintaining indoor thermal comfort and reducing the energy consumption. According to the building energy efficiency design code applicable to the hot summer/cold winter region (Ministry of Construction of China 2001), the overall heat transfer coefficient of the exterior wall system shall not exceed 1.5 W/m2 ·K, in other words, the overall thermal resistance shall be more than 0.67 K·m2 /W. However, according with previous field test conducted by the authors (Zhou 2011), the average heat transfer coefficient of the newly built hollow exterior walls was 2.8 W/m2 ·K. The results suggested the traditional hollow wall system no longer meet the new energy-saving and environmental requirements. The aim of this article is to discuss a method to improve the thermal performance of the exterior wall system in the Hui-style residences without dramatically changing the traditional hollow wall structure.
1.4. Foamed Mortar Foamed mortar (FM) is classified as lightweight building material, consisting of Portland cement paste or cement filler
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matrix (mortar) without coarse aggregate, in which a homogeneous pore structure is created by introducing suitable air suitable foaming agent (Ramamurthy, Kunhanandan Nambiar, and Indu Siva Ranjani 2009; Wei et al. 2013). It possesses self-compacting, lightweight, and excellent thermal insulation properties. By proper control in dosage of foam, a wide range of densities (400–1600 kg/m3 ) (Jones and McCarthy 2005b; Panyakapo and Panyakapo 2008) of FM can be obtained for application to partition, insulation and filling grades. Although the material was first patented in 1923, its construction applications as lightweight and semi-structural material are increasing in the last few years, with the technical development of synthetic foaming agents and utilization of effective foam generator machines(Jones and McCarthy 2005a). There also has been renewed interest in its potential for large scale utilization of wastes such as fly ash, incinerator bottom ash, recycled glass and foundry sand (Jones and McCarthy 2005a; 2005b; Panyakapo and Panyakapo 2008; Kearsley and Wainwright 2001). In the present study, FM was selected as a filling material for the voids in the Hui-style hollow wall to upgrade its thermal performance. Meanwhile fly ash was largely used in the preparation of FM and how it affected the key early age, physical, mechanical, and thermal properties were systematically analyzed. In order to increase the construction speed, a patented calcium sulfoaluminate based accelerator was also used for reducing the setting time and to improve the early strength of FM.
2. MATERIALS, MIX CONSTITUENT PROPORTIONS AND FOAMED MORTAR PRODUCTION 2.1. Raw Materials Combinations of the following constituent materials were used to produce the FM mixes: • Portland cement (PC) with the compressive strength of 64.5 MPa at 28 days, conforming to BSEN 197-1 type I cement (British Standards Institution 2000a). • “Fine” fly ash (FA) with a median particle size of 35 um, loss on ignition (LOI) of 5.0% and conforming to BS EN 450 (British Standards Institution 1995). It was used to replace PC at 20, 40 and 60% by mass fraction. • Polycarboxylic type of superplasticizer (SP) conforming to BS EN 934-2 (British Standards Institution 2001). The dosage was kept at 0.1% wt, of the total binders. • Surfactant (a commercial, protein based foaming agent), used in a 5% aqueous solution and foamed to a density of 55kg/m3 (of note, this approach is typical of industry practice) by a kind of air-compressed foam generator.
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TABLE 1 Chemical composition and physical properties of raw materials Physical properties Raw materials
Density (kg/m3 )
Blaine surface area (m2 /kg)
CaO
SiO2
Al2 O3
Fe2 O3
Na2 O
K2 O
MgO
SO3
Cement Fly ash
3150 2400
350.5 361.8
64.8 6.09
21 49.96
6.16 34.02
4.01 4.52
0.1 0.66
0.4 0.98
1.94 1.17
1 0.62
Percentage passing (%)
100
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Chemical composition (%)
Target wet density, D = b + W,
PC FA
80
where b = c + f Free water content, W = (W/b) × (c + f )
60 40 20 0
(1)
0.1
1
10
100
Particle diameter, µm
1000
FIG. 4. Particle size distribution of cement and fly ash.
• Accelerator (a patented, calcium sulfoaluminate based accelerating agent), used at 0.25% to 1% by mass fraction of total binders. The properties of cement and fly ash used in this study are presented in Table 1 and corresponding size distribution is shown in Figure 4.
2.2. Mix Proportions Although there are no standard methods for proportioning FM (Kearsley 1996), considering the w/c ratio, free water and fly ash content and maintaining a unit volume, the specified target wet density becomes a prime design criterion (Jones, McCarthy, and McCarthy 2003). However, it should be noted that it is difficult to design FMs according to their dry density, as FM will desorp between 50 and 150 kg/m3 of the total mix water, depending on the concrete wet density, early curing and subsequent exposure conditions. The mix proportioning method used in the study was that developed at University of Dundee in Dundee, Scotland, and thoroughly described in following text (Jones and McCarthy 2005b). Assuming a given target plastic density (D, kg/m3 ), water/ binder ratio (W/b) and fly ash/binder ratio (f/b), the total mix water (W, kg/m3 ), cement content (c, kg/m3 ), fly ash content (f , kg/m3 ) and foam volume (V foam , m3 ) were calculated as:
Foam volume, Vfoam = 1 − c/3150 kg/m3 − f /2400 kg/m3 − W/1000 kg/m3 Where 3150 kg/m3 , 2400 kg/m3 and 1000 kg/m3 are the densities of cement, fly ash and water, respectively. Thirteen mixtures proportions were designed for investigating the influence of wet density, fly ash and accelerator content on early age, mechanical and thermal performances of FM, as shown in Table 2. The water to binder ratio (w/b) of all mixtures was 0.35. Mixtures number FM300 to FM800 were specifically designed to investigate the effect of wet density, which presents the mixtures with wet density of 300 kg/m3 , 500 kg/m3 and 800 kg/m3 , respectively. Mixtures FM300-20 to FM800-60 were used to study the effect of fly ash content. Fly ash was added as a partial replacement of cement at levels of 20%, 40% and 60% by weight of total cementitious material in FM mixtures with wet density of 300 kg/m3 and 800 kg/m3 , respectively. Mixtures FM300-40-1 to FM30040-4 were chosen to evaluate the effect of accelerator content. The accelerator was added at levels of 0.25%, 0.5%, 0.75%, and 1% by weight of total cementitious material in the mixtures with the wet density of 300 kg/m3 and 40% fly ash. 2.3. Specimen Preparation According to mixture proportions in Table 2, the Portland cement and fly ash were firstly dry-mixed for 1 min in a vertical mixer. The total quantity of water was then added (along with the superplasticizer and accelerator) and mixed with the dry materials until a homogeneous mortar with no lumps of undispersed cement was obtained. The foam generator then produced the foam and the approximate quantity (calculated by the mix proportions) was added to the mix, immediately after preparation. This was combined with the mortar for at least 2 minutes, until all foam was uniformly distributed in the mix. The plastic density of the mix is then measured in accordance with BS EN 12350-6 (British Standards Institution 2000b) by weighing a
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TABLE 2 Mix constituent proportions of foamed concrete Composition of mixture (per m3 )
Mix No.
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Wet density FM300 FM500 FM800 Fly ash content FM300-20 FM300-40 FM300-60 FM800-20 FM800-40 FM800-60 Accelerator content FM300-40-1 FM300-40-2 FM300-40-3 FM300-40-4
Target wet density (kg/m3 )
Fly ash replacement ratio (%)
w/b
PC (kg)
FA (kg)
Water (kg)
Foam (m3 )
Accelerator (%)
300 500 800
— — —
0.35 0.35 0.35
222 370 593
— — —
78 130 207
0.854 0.755 0.608
— — —
300
20 40 60 20 40 60
0.35 0.35 0.35 0.35 0.35 0.35
178 133 89 474 356 237
44 89 133 119 237 356
78 78 78 207 207 207
0.848 0.844 0.839 0.594 0.584 0.571
— — — — — —
40 40 40 40
0.35 0.35 0.35 0.35
133 133 133 133
89 89 89 89
78 78 78 78
0.844 0.844 0.844 0.844
0.25 0.5 0.75 1
800
300
Note: w/b = water to binder ratio.
FM sample in pre-weighed container of a known volume. A tolerance on wet density was set at ±50 kg/m3 of the target value, which is typical of industry practice for FM production. If the density was higher, additional foam was added incrementally until the target value is achieved, followed by further mixing. Mixes with densities lower than the range of acceptable values were rejected.
3. EARLY AGE PROPERTIES 3.1. Consistence Consistence measurements comprise assessment of spreadability according to the Brewer test for controlled low-strength material (CLSM [Brewer 1996]) and ASTM C230 standard flow cone test (ASTM 1998) obtaining only the average spread without raising and dropping of the flow table in order to avoid the segregation of bubbles from the mix. The results are shown in Table 3, while the relationship between two methods above is examined in Figure 5. As seen in Table 3, the spread values ranged between 145 and 290 mm and between 242 and 420 mm according to the Brewer and flow cone methodologies, respectively. The performance ranking of all mixtures with different densities and fly ash contents remain constant in two spread measurements, with the minimum and maximum values observed on the FM300 and FM800-60, respectively.
Given that the volume of air in the 300 kg/m3 density FMs can account for up to 85% of the total unit volume, it would be expected to have a significant effect on its fresh properties. From Table 3 it is clearly to note that there were greater spreads at higher densities. A possible reason for these is that at lower densities there will be more foam, which will lead to the reduced self-weight and greater adhesion between the bubbles and solid particles in the mixture (Karl and Wörner 1994). For a given wet density, the spreads increased with an increase in fly ash replacement level. The enhanced consistence of fly ash FMs is attributed to a combination of factors. For one thing, it can be clearly seen from Table 2 that fly ash FMs contain smaller volume of foam (resulting in decreased cohesion) due to the lower specific gravity compared with cement. For the other, due to the “ball-bearing effect” of FA particles (Agulló et al. 1999), the packing of the solid phase will be improved and the absorption of mix water on to the FA particles will reduce inter-particle friction (Giannakou and Jones 2002). As regards the latter, an increase in the mix water will reduce the yield stress value of concrete (Marrs and Bartos 1996), and, in turn, improve spread. The relationship between Brewer test and standard flow cone test on results obtained on the FMs was also examined, as shown in Figure 5. Regression analysis of the data proved that good correlation (R2 = 0.977) existed between all spread values, and thus, the standard flow cone spread can be predicted accurately from the Brewer spread measurement using Equation (2):
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TABLE 3 Summary of consistence for foamed mortar (FM) Mixture Wet density (kg/m3 )
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300 500 800 300 300 300 800 800 800
Spread (mm)
Bingham model test
FA (%)
Brewer Test
Flow Cone Test
Yield stress (N/m2 )
Plastic viscosity (Ns/m2 )
— — — 20% 40% 60% 20% 40% 60%
145 185 245 175 210 225 265 280 290
242 263 325 270 295 320 357 385 420
48 22.1 9 36.4 28.2 20.7 6.1 3.2 1.6
0.09 0.2 0.31 0.1 0.07 0.17 0.35 0.28 0.37
FIG. 5. Relationship between Flow cone spread and Brewer spread methods.
Flow cone spread = 10.52e0.01×Brewer spread + 198.66, mm (2) In addition, it was found that the 200 mm spread requirement for flowing concrete according to the Brewer test method corresponds to minimum spread of 280 mm for standard flow cone test method. 3.2. Rheology The rheological behaviors of FMs were assessed with a Brookfield viscometer connecting a T-bar spindle and a Helipath stand. This equipment enabled measurement of torque on fresh material each time. Readings on the torque dial were taken after the spindle had rotated for a given time at each speed increment. Using the best fit line drawn through all the corresponding shear stress values (torque) against rate of shear values, values of plastic viscosity (slope angle) and yield stress
(intercept x-axis) can be obtained (Tattersall 1991, p. 262; Domone, Yongmo, and Banfill 1999). As expected from the literature (Jones and McCarthy 2005b; Banfill 1991, FM is demonstrated to be thixotropic from the shape of the rotational speed-torque curve during increasing and decreasing speed increments. Considering three wet densities (300, 500, and 800 kg/m3 ), the relationship between rotational speed and viscometer (torque) readings, obtained with the same T-spindle during decreasing rotational speed increments is given in Figure 6. The rotational speed at 0 rpm is indicative of the apparent yield value, which reflects the minimum force required to initiate mortar movement. The apparent plastic viscosity is a function of the reciprocal of the slope of the rheology curve, which for thixotropic materials approximates a line (Domone, Yongmo, and Banfill 1999). The apparent yield value and apparent plastic viscosity obtained from rheology curves for all FMs are also summarized in Table 3. As can be seen in Figure 6 and Table 3, the apparent yield value increased with a decrease in FM density, which matched the spread results discussed previously. For example, the FM 300 mix, which shows the highest apparent yield stress, while was measured the smallest spread, conforming the link between spreadability and yield stress of concrete (Tattersall 1991; Roussel 2006). The greater resistance to initial flow on lower densities can also be attributed to the reduced self-weight of the material and higher foam content resulting in increased cohesion. Considering the effect of fly ash content on rheology of FM, the relationship between apparent yield value and fly ash replacement level of 300 and 800 kg/m3 mixes are also shown in Table 3. For a given density, the apparent yield stress value decreases with an increase in fly ash replacement ratio. In the FM with higher fly ash content, the reduced force required to initiation of flow is also likely attributed to the “ball-bearing effect” of fly ash particles (Agulló et al. 1999) and less cohesion
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FIG. 6. Relationship between rotational speed and viscometer (torque) readings.
resulting from lower foam content due to the fly ash’s lower specific gravity compared with cement. Plastic viscosity is the measure of internal resistance of fluid to flow. Table 3 shows that the apparent plastic viscosity slightly increased as the wet density increased, thereby indicating that, at higher densities, the internal resistance for the fluid to flow is higher compared to that found at lower densities. This result agrees with previous work by Jones and McCarthy (2005b). However, since the differences of apparent plastic viscosity between the mixtures with fly ash are small, no clear trend can be observed. It should be noted that the graphical method of rheological data analysis enabled comparison of apparent yield values and apparent plastic viscosities between FMs, the T-bar spindles with the Helipath stand do not have directly definable shear rate and shear stress values (Brookfield Engineering Laboratories 1995) and hence the actual yield values (τ0 ) and plastic viscosities (η) could not be established. 3.3. Setting Time The initial and final setting times are very important for the practical application. Knowing the setting times of the FM during hardening is the tool to determine the moment of formwork removal and initial load bearing capacity. However there is no standard method for testing the setting time of FM. In this paper, the Vicat-Needle tests (VNT) were conducted in accordance with Chinese standard GB/T1346-2001 (similar to BS EN 1963 [British Standards Institution 2005]) to measure the setting time of the FM. The needle is on a 300 g moveable rod and has a diameter of 1 mm ± 0.05 mm. A specimen of fresh FM paste was prepared and placed in a frustum 40 mm in height. Initial setting time is considered in this paper as the time when the
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needle penetration is 39 mm ± 0.5 mm. The final setting time corresponds to less than 0.5 mm penetration. In this study, penetration tests were performed at regular time intervals (10 min) until the foamed concrete paste was finally set. As shown in Table 4, the setting time for the three wet densities (300, 500 and 800 kg/m3 ) ranged from 6.5 to 12 h and 10 to 17 h for initial and finial setting time, respectively. In both cases, the setting time decreased with an increase in wet density, indicating that the amount of foam incorporated into the mix delay the setting of FM. This phenomenon corresponds well with the results obtained by Jones (2000) when investigating the stiffening time of FM. This delay effect of foam is mainly attributed to the surfactant molecules in foam agent altering the crystal growth of the hydrate cement (Young, Berger, and Lawrence 1973; Jolicoeur and Simard 1998). These molecules become absorbed on to the rapidly forming membrane of hydrated cement and slow down the production of calcium hydroxide nuclei. The overall result is a reduction in the hydration rate of cement. Table 4 also shows the effect of using a partial (20 to 60%) replacement of PC with fly ash on setting times. As can be seen from Table 4, initial and final setting times increased with increasing fly ash replacement level. For example, when 60% fly ash was incorporated into FM with density of 300 kg/m3 , compared with FM300 group, the corresponding initial and final setting time increased by 68% and 65% (from 12 h to 20.2 and from 17 h to 28 h) respectively. The delay effect of fly ash on hardening process is due to the reduction in the cement content, resulting in an increase in the water to cement ratio (Lam, Wong, and Poon 2000; He, Scheetz, and Roy 1984). According to the aforementioned analysis, the setting time of FM is much longer than ordinary dense concrete, which maybe will have an impact on construction progress. Furthermore, if hardening is delayed too long the cell structure may become unstable and show a marked decrease in volume. Therefore, in order to prevent the potential risk of instability of FM and improve the construction speed, an accelerator was used in this study. The results of setting time are shown in Table 4. It can be seen that a stepwise increase of the accelerator dosage from 0% to 0.5% resulted in dramatically decreasing values for the initial and final setting time. Specifically, the initial and final setting time for FM300-40 without accelerator were 16.4 h and 23 h, when 0.5% accelerator was added, the corresponding setting time were shortened to 2 h and 3 h, respectively. Finally, the initial and final setting time decreased to 0.6 h and 1h respectively when the accelerator replacement was 1%. In addition, Regarding the practical use of fast setting FM, it can also be seen from Table 4 that, when 0.5% accelerator was incorporated into FM 300-40 mixture, the corresponding initial setting time meet the engineering requirement (between 2 h and 4 h) suggested by Turner for fast set FM for ‘same day reinstatement’ of openings in highways (Turner 2001).
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TABLE 4 Summary of setting time and compressive strength for foamed mortar (FM) Mixture
Setting time (h)
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Wet density (kg/m3 ) FM300 FM500 FM800 FM300-20 FM300-40 FM300-60 FM800-20 FM800-40 FM800-60 FM300-40-1 FM300-40-2 FM300-40-3 FM300-40-4
Compressive strength (MPa)
FA (%)
Initial setting
Final setting
3 days
7 days
28 days
56 days
90 days
— — — 20% 40% 60% 20% 40% 60% 40% 40% 40% 40%
12 8 6.5 14 16.4 20.2 8 9.2 12 10.2 2 0.8 0.6
17 13 10 19 23 28 11 13.5 18 15.6 3 1.5 1
0.1 0.4 2.2 0.12 0.08 0.06 2 1.4 1 — — — —
0.2 0.8 4.2 0.15 0.17 0.1 4.8 3.6 3 — — — —
0.5 2 8 0.42 0.4 0.25 7.5 6.8 4.8 — — — —
0.58 2.4 8.8 0.57 0.55 0.43 8.5 8 5.6 — — — —
0.7 3 9.6 0.75 0.68 0.5 10 9 6.6 — — — —
TABLE 5 Physical parameters for FM: density, porosity and average pore size Density (kg/m3 )
Mixture
Pore parameters
Wet density (kg/m3 )
FA (%)
Actual casting density
Dry density
Porosity
Average pore size (mm)
FM300 FM500 FM800 FM300-20 FM300-40 FM300-60 FM800-20 FM800-40 FM800-60
— — — 20% 40% 60% 20% 40% 60%
341 491 840 318 320 319 800 834 814
285 414 809 280 256 260 751 765 756
86.1 80.5 61.1 86 85.5 85.2 60.4 61 60
0.96 0.73 0.26 0.92 0.90 0.93 0.25 0.21 0.23
4. PHYSICAL PROPERTIES 4.1. Density The dry densities as indicated in Table 5 were determined by oven drying a cube at 105◦ C until no further reduction in weight took place. Wet density is required for mix design and quality control purposes. The relationship between wet density and dry density of the above-mentioned mixtures is indicated in Figure 7. For casting densities between 300 and 800 kg/m3 there seems to be a linear relation between the wet and dry density and this relation can be explained by the following equation: ρdry = ρwet − 62.4, kg/m
3
(3)
This R2 value of the regression is 0.99. If FM with a specific dry density is required, the equation as indicated above can be conveniently used to determine what the wet density would need to be. The content of free water that will desorp in FM is related to many factors (e.g. mixture composition, curing condition microstructure and hydration degree). The equations (2 and 3) presented here are based on the experimental results of FM mixtures with the densities below 1000 kg/m3 and constant water to binder ratio at 0.35. Whether similar functions can be found in FM mixtures with higher densities or different water to binder ratios will be discussed in the future work. 4.2. Porosity The pore structure of FM, predetermined by its porosity, is a very significant characteristic as it influences the properties of
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FIG. 7. Relationship between wet density and dry density of the all foamed mortar (FM) mixtures.
the material such as strength, thermal resistance and durability. Most traditional methods for characterization of microstructure, such as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), can only give information about the overall porosity and threshold pore size, and some two-dimensional (2D) images, however, neither 3D real size nor spatial distribution. Additionally, samples must be dried and exposed to high vacuum, which can produce irreversible changes in the microstructure (Rattanasak and Kendall 2005; Gallucci et al. 2007). This section illustrates the suitability of 3D-XCT to quantitatively study micro-structural parameters concerning both solid phases and the pore structure. Data collection and processing was done with the aid of XCT VG Studio MAX software. More details on the working principles of 3D-XCT and data acquisition can be found in other studies (Stock et al. 2002; Naik et al. 2004). It should be noted that the measurements were directly conducted on 4 cm cubes after 28 days under sealed curing without any prior drying preparation. In order to reduce the computing time and to avoid edge effects, the study was limited to a region of interest (ROI) of 64 cm3 (cube with an edge of 4 cm) taken in the center of the slices where the structure is the most homogeneous. To check that this volume was statistically representative, the standard deviation of the considered features in a series of volumes of progressively large sizes was measured (e.g., porosity of FM300, as shown in Figure 8). The result indicates that the ROI chosen was well above the size at which the fluctuation between different chosen volumes becomes steady. Figure 9 shows the reconstructed 3D-image of a FM300 sample as well as the corresponding segmented solid and pore fraction. From such images, the porosity and average pore size can be easily extracted and the corresponding results are shown in Table 5. As shown in Table 5, porosity and average pore
FIG. 8. Stabilization of the standard deviation of the porosity mean in FM300 foamed mortar (FM) versus increasing volume of region of interest (ROI).
size increased as an increase in foam content to reduce the wet density. Specifically, the porosity of FM300, FM500 and FM800 was 86.1%, 80.5% and 61.1%, while the corresponding average pore size was 0.96, 0.71 and 0.26 mm, respectively. This is because at higher foam volume, the merging of bubbles results in larger void size. 4.3. Porosity–Density Relationship Porosity is proved to be an important parameter in modeling the mechanical and functional performance of FM (Roßler and Odler 1985; Luping 1986; Hoff 1972; Kearsley and Wainwright 2002). Unfortunately, porosity is not easily measured outside the laboratory, and therefore it is necessary to provide a model to obtain the porosity. The simplest method to calculate the porosity value was to relate it to FM density. Since the pores inside FM were created due to addition of foams, by knowing the solid density of cement paste (without foam), one can easily predict the porosity of FM of any other density using the following equation: ε =1−
ρdry ρsolid
(4)
where ε is the porosity, ρdry is the dry density of FM and ρsolid is the solid density of cementitious paste (without foam). The accuracy of Equation (4) was checked by comparing the porosity values calculated using Equation (4) and the measured porosity values using the 3D-XCT mentioned above for different FM mixtures, as showed in Figure 10. It should be noted that an average solid density of cementitious paste (ρsolid ) of 2100 kg/m3 was established through experiment. The agreement is excellent. Therefore, according to Equation (3) and Equation (4), it is possible to
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FIG. 9. Extraction and three-dimensional (3D)-visualization of pore structure in FM300 foamed mortar (FM): (a) a gray-scale image of the representative slice (4 × 4 cm2 ); (b) the volume of interest extracted from the center of representative slice.
FIG. 10. Comparison of predicted porosity with measured porosity as a function of density.
obtain an accurate assessment of the porosity by using the wet density, which can be easily measured, at the construction site. The equation can be explained by the following equation: ε =1−
ρwet − 62.4 ρsolid
(5)
5. MECHANICAL PROPERTIES 5.1. Compressive Strength According to classification given by RILEM/CEB (AbdelReheem, Imam, and Shihata 2003), lightweight concrete used for insulation purpose should provide strength at least 0.5 MPa and a density less than 1450 kg/m3 . The compressive strength of FM is studied in this section. The compressive strength of FM was determined from 100 mm cubes, which were cast in steel molds, demolded after 24 ± 2 h, wrapped in polythene and kept in a constant temperature room at 22 ± 2 ◦ C up to
the day of testing. The compressive strengths recorded are the average of three cubes. As the FM strengths were relatively low, these cubes were crushed on a more sensitive machine with a 20 MPa capacity and recorded to the nearest 0.01 MPa. Cubes were crushed after 3, 7, 28, 56, and 90 days. Table 4 also shows the strength development of three FMs with different wet density (300, 500, and 800 kg/m3 ). Apparently, the rates of strength development have a similartrend. Specifically, all the three FMs were able to develop more than 40% of their corresponding 28-day strength at 7 days and 80% of their corresponding 90-day strength at 28 days. In addition, when the wet density decreased, as expected (Ramamurthy, Kunhanandan Nambiar, and Indu Siva Ranjani. 2009; Jones and McCarthy 2005b; Kearsley and Wainwright 2001), the compressive strength of FM reduced. For example, the 28-day strength values for 300, 500, and 800 kg/m3 FM were 0.5, 2, and 8 MPa, respectively. The effect of fly ash content on compressive strength development for FMs with 300 and 800 kg/m3 wet density are also shown in Table 4. Similar trend in long-term strength gain was observed that fly ash contributes little to strength at early ages, but significantly enhanced strength at later ages. For example, in the mixtures with a wet density of 300 kg/m3 , the FM300 without fly ash developed 79% of its 90-day strength after 28 days, while the fly ash FMs (20%, 40% and 60% FA) developed only 56%, 59% and 50% respectively. This is due to the relatively slow nature of the pozzolanic activity of the fly ash (He, Scheetz, and Roy 1984; Langan, Weng, and Ward 2002; Sánchez de Rojas, and Frías 1996). After prolonged curing time (28–90 days), the pozzolanic reaction of fly ash produces more hydration products resulting in a denser microstructure, so the strength of fly ash FM will eventually be close to or even greater than PC FM. This is proved from the fact that the optimum fly ash content for the highest ultimate strength seemed to be 20% by mass of cement, which yielded an average compressive strength of 0.75 and 10 MPa for 300 and 800 kg/m3 mixtures respectively. Additionally, up to 40% fly ash incorporation yielded similar ultimate strength to PC FM indicating that the cost of FM mixtures could be reduced by replacing large volumes of cement with fly ash, without significantly affecting the
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long-term strength. However, higher percentages replacement (60% FA) resulted in dramatically reduced strength in all the curing ages. The results indicates that there is a optimum FA content, beyond which there will be no advantage to strength in increasing the content of fly ash, due to the insufficient Ca(OH)2 for further pozzolanic hydration (Neville 1996; Jones 1986).
5.2. Strength–Porosity Relationship Balshin (1949) has shown that compressive strength of porous materials can be closely related to their porosity by the Equation 6.
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σ = σ0 (1 − P)n
(6)
where σ is the compressive strength of the porous material; σ 0 is the compressive strength of the matrix at zero porosity; P is the porosity; and n is a constant. Figure 11 plots the recorded compressive strength-porosity relationship for different FMs after 28 days under sealed curing. Using Balshin’s strength-porosity relationship, the best correlation is obtained with n = 2.7, which was represented by the solid curve in Figure 11. A correlation coefficient of 0.97 indicates a good correlation between this model and the test results. Thus, the 28 days compressive strength of FM can be expressed as a function of porosity as: σ = 90(1 − ε)2.7
X-CT images in this study), and the shape and size of the pores and its distribution (Nambiar and Ramamurthy 2007). Additionally, similar studies were carried out by others for FM with different densities or with different composition. The results are summarized in Table 6 and compared with the results in this study. The n value of FM obtained in this study was in line with the results by Hoff (1972), but was different from other researchers. The σ 0 values (90 MPa) of this study are much lower than those (115–290 MPa) from cement paste in Hoff’s studies, indicating that the addition of fly ash decreases the 28days compressive strength of the matrix at zero porosity. This is also due to the relatively slow nature of the pozzolanic activity of the fly ash (Langan, Weng, and Ward 2002; Sánchez de Rojas and Frías 1996).
(7)
The exact form of the relation may be uncertain, as the strength of FM may be influenced not only by the entrained air from the preformed foam, but also by entrapped air, capillary pores, gel pores (Some pores are too small to be measured from
6. THERMAL PROPERTIES 6.1. Thermal Conductivity The thermal conductivity test was done using a rapid-K thermal conductivity instrument (R-K). Three representative samples of each mix were tested and a mean value was calculated. After 28 days’ sealed curing, the slabs (30 cm × 30 cm × 3 cm) were oven-dried at a temperature of 60 ◦ C until constant mass (approximately 4 days). This drying was done to eliminate any moisture retained in the slabs, as it would have had effect on the conductivity results (Mydin and Wang 2012). The reason why the chosen temperature of the oven was below boiling point is to avoid cracking in the sample (Wang, Wu, and Wang 2005). High speed of water evaporation and thermal mismatch between the compositions will create more connected path and crack for heat to flow through, making thermal testing unreliable. The sample was placed between the two plates of the instrument and upper and lower temperature limits were chosen at 40 ◦ C and 0 ◦ C respectively. (These temperatures were chosen as they could reasonably be expected to be maximum and minimum temperature range that would be experienced in the hot summer/cold winter region in China.) Heat was allowed to flow between the two plates until the system stabilized. The maximum time allowed for the samples to stabilize was about 3 hours. Then the thermal conductivity was calculated using the Fourier heat flow equation: λ=
FIG. 11. Relationship between compressive strength and porosity.
Q×D A × T
(8)
where λ is thermal conductivity of the tested sample. Q is the time rate of heat flow. A and T are cross-sectional area and temperature difference across the sample, respectively. As shown in Table 7, it is interesting to note that the thermal conductivity of FM decreased sharply with an increase in foam content to reduce the wet density. Specifically, the thermal conductivity varied from 0.053 to 0.058 W/m2 ·K when wet density is 300 kg/m3 , and the thermal conductivity increased to the values from 0.106 to 0.134 W/m2 ·K when wet density
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TABLE 6 Comparison of constants in strength-porosity models for different foamed mortar (FM) Constants Researchers Hoff (1972) Narayanan and Ramamurthy (2000) Kearsley and Wainwright (2002) Mydin and Wang (2012)
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Present work
Concrete type Foamed mortar Aerated concrete Foamed mortar Foamed mortar (20–600◦ C) Foamed mortar
Density range (kg/m3 )
Strength (28days)
σ 0 (MPa)
n
Cement paste Cement–sand
320–1000 650–1350
0.4–6 1–19
115–290 26.6
2.7–3.0 3.2
Cement–sand–fly ash Cement–sand
1000–1500
2–18
188
3.1
800–1400
1.5–15.3
19.5–39.2
2.4–2.6
300–800
0.5–8
90
2.7
Mix composition
Cement–fly ash
TABLE 7 Thermal conductivity of foamed mortar (FM) measured by the rapid-K thermal conductivity instrument (R-K) method Mixture Wet density (kg/m3 )
FA (%)
Thermal conductivity (W/(m2 ·K))
FM300 FM500 FM800 FM300-20 FM300-40 FM300-60 FM800-20 FM800-40 FM800-60
— — — 20% 40% 60% 20% 40% 60%
0.054 0.066 0.107 0.055 0.053 0.058 0.123 0.106 0.134
g
λcm = λscnd + λcnd + λrd + λcnv
(9)
Where, λcm is the overall thermal conductivity of the cellular material. λs cnd and λg cnd are respectively the thermal conductivities due to conduction through the solid and gas phases and λrd and λcnv the radiation and convection terms. Skochdopole (1961) conducted of a simple experiment by reversing the hot and cold plates of a modified guarded hot plate unit in order to maximize and minimize convection, and showed that heat transfer by convection does not exist for cell diameters smaller than 4 mm. Most FMs in this study have closed cells smaller than 4 mm (Table 5), and therefore, heat transfer due to convection is negligible. The contribution due to conduction through the solid matrix, λs cnd , can be expressed as (Glicksman 1994): λscnd =
1 λs (2 − fs )(1 − ε) 3
(10)
increased to 800 kg/m3 .The thermal conductivity of normal concrete is as high as 1.70 W/m2 ·K which is about 12 to 32 times of that of FMs prepared in this paper. Therefore, reducing the density of FM is an effective way to reduce its thermal conductivity and hence enhances the thermal insulation properties of FM. Additionally, from the obtained results the optimum fly ash content for the lowest thermal conductivity seems to be 40%, which yielded an average thermal conductivity of 0.053 and 0.106 W/m2 ·K for 300 and 800kg/m3 FM mixtures, respectively.
Where, λs is the thermal conductivity of solid matrix. The value of thermal conductivity of cement paste solid is taken as 0.5 W/m2 ·K by Mydin and Wang (2012). The parameter fs is the fraction of the solid in the cell struts. A strut is the material formed at the intersection of three cell walls. A value of 0.8 was used for fs by Collishaw and Evans (1994). According to Equation (4), (1-ε) is the volume fraction of the solid matrix, and can be calculated as:
6.2. Thermal Conductivity Model Generally speaking, the heat transfer in any cellular material is the result of a contribution of three different mechanisms, conduction, convection and radiation, and therefore the overall thermal conductivity can be described as the result of four additive terms:
Where ε is the porosity, ρdry is the dry density of FM and ρsolid is the solid density of cementitious paste (without foam). The term for conduction through the gas in the cell is calculated by the following equation (Yuan 2009):
1−ε =
ρdry ρsolid
λcnd = 4.815 × 10−4 T 0.717 ε g
(11)
(12)
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Where T is in K and λg cnd in W/(m2 ·K). The radiation term in thermal conductivity equation is calculated by: λrd =
8 de σ T 3 3
(13)
Where T is again in K, σ is Stefan-Boltzmann constant and de is the cell diameters, which are summarized in Table 5. Finally, according to the Equations (9 to 13), the overall thermal conductivity of FM can be calculated by the following equation:
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1 8 λFM = 4.815 × 10−4 T 0.717 ε + λs (2 − fs )(1 − ε) + de σ T 3 3 3 (14) The result of calculated effective thermal conductivities for all the FM mixtures using the above model with the parameters listed in Table 8, are compared with the experimental results in Figure 12. This graph shows that the predicted thermal conductivities provide a reasonable estimate for the corresponding actual values.
TABLE 8 Summary of parameters used in model calculation Property
Value
Reference
T
293 K
λs fs de
0.5 W/m2 ·K 0.8 0.21–0.96 mm
Measured (mean temperature of FM sample) Mydin and Wang (2012) Collishaw and Evans (1994) Measured (Table 5)
FIG. 13. Contribution of each heat transfer mechanism in the thermal conductivity for foamed mortars (FM).
In addition, the contribution of each heat transfer mechanism to the overall thermal conductivity in Equation (14) was studied. The results are shown in Figure 13. All three contributions played a significant role for relative densities below 0.15 (corresponding to 315 kg/m3 dry density), and the contribution of the radiation mechanism became significant below this density. For higher relative densities only conduction (both gas and solid contributions) should be considered because the expected contribution of radiation was below 5%. Taking into account these results it is reasonable to consider different models for relative densities below and above 0.15. For low densities, all the main mechanisms (except convection) have to be considered while for higher densities only conduction plays a significant role. 7. CLIMATE CHAMBER TEST
FIG. 12. Comparison of test and predicted thermal conductivity by Equation (14).
7.1. Test Set-Up To investigate the effectiveness of adding FM into the Huistyle hollow wall system for thermal performance upgrading, two tested walls were built in a large-scale environmental test chamber (ETC). The ETC is capable of dynamically simulating temperature, humidity, solar radiation and acid rain. The main working principle is illustrated in Figure 14. In this study, static weather model was imposed to measure the thermal resistance of the walls. The temperature of outdoor chamber was set at 25 ◦ C and the data collecting procedure are performed every 10 minutes. The two tested walls were constructed with local bricks described above. The wall is approximately 3 m high and 1.78 m wide. Figure 15 is a 3D view of the tested wall, illustrating the construction of the hollow wall. The bottom eight layers of bricks were laid tightly to form a section of solid wall as the base. The section above it was constructed using a hollow wall technique mentioned above, as well as one layer of
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FIG. 14. Main working principle of environmental test chamber.
FIG. 15. A three-dimensional (3D)view of the tested wall.
strengthening bricks for every three layers of hollow walls. This configuration reflects the traditional practice of building hollow walls in Hui-zhou. A row of bricks was laid inclined to fill the gap between the top of the wall and the roof of the climate chamber, as shown in Figure 16. Expanded polystyrene
boards were inserted to insulate the two test wall panels from each other and the climate chamber to ensure the heat flow conducting through and perpendicular to the wall. Figure 17 shows the insulation between the side of the wall and the side of the ETC. The thermal insulation between the two test walls and
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FIG. 16. Top of the test wall and the inclined row of bricks to fill the gap.
FIG. 17. Thermal insulation strategy to ensure a through-wall heat flow.
between the top of the test wall panel and the bottom of the ETC was installed in a similar way. By applying different thermal upgrading strategies, four walls were actually tested. Wall I was the hollow wall construction without any thermal upgrading. Thus, it was used as the control group. Wall II was the hollow wall filled with foam concrete. Wall III was the hollow wall with a 20 mm thick commercially available inorganic stucco system applied to interior wall to reduce the effects of thermal bridges introduced by through-wall-bricks and strengthening bricks. Wall IV used a double upgrading strategy (i.e., with both foam concrete filling the voids and inorganic stucco system applied). Figure 18 shows a photo of the pouring of FM into the voids of the tested wall, and another depicts end of FM placement.
7.2. FM Mixture Choosing According to classification given by RILEM/CEB (AbdelReheem, Imam, and Shihata 2003) lightweight concrete used for insulation purpose may provide strength as low as 0.5 MPa and a density less than 1450 kg/m3 . The following points should be considered when choosing FM mixture to fill the hollow wall system. • Good workability and self-compacting: Brewer spread test value ≥200 mm (Brewer 1996); • Applicable setting time and early age strength: initial setting time requirement between 2 h and 4 h (Turner 2001);
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FIG. 18. Pouring of foamed mortar (FM) into the voids of tested wall, and the end of FM placement.
position. The overall thermal resistance of the tested wall is the arithmetic average of the 14 thermal resistances calculated by Equation (15).
• Reasonable strength satisfying the requirement for non-load structure: compressive strength ≥0.5 MPa (Abdel-Reheem, Imam, and Shihata 2003); • Good thermal resistance properties, that is, lower thermal conductivity; • Wide use of fly ash for the purpose of economic and environmental protection. Finally, mixture FM300-40-2 was chosen as the optimum filling material for the hollow wall system in this study, and the corresponding properties of which are concluded in Table 9. 7.3. Instrumentation Heat flow gauges and thermal couples were employed to measure the heat flow and temperature respectively. As shown in Figure 19, 14 measuring points were set in both interior and exterior wall surfaces so that the temperature difference can be obtained. Figure 19 shows the positions of sensors on the room side surface of the test wall panel. It should be noted that another 14 thermal couples were installed at the same points on the exterior wall surface, whereas the heat flow gauges were installed on the interior wall surface only. Equation (15) was used to calculate the thermal resistance of the wall at each sensor position. Ri =
TIi − TEi qi
(15)
Where Ri represents the thermal resistance of the tested wall at the ith sensor position; TIi and TEi respectively represent the temperature on the interior and exterior wall surface at the ith sensor position; and qi represents the heat flow at the ith sensor
7.4. Overall thermal resistance of thermally upgraded wall system Table 10 shows that by filling the voids in the hollow wall with FM, the overall thermal resistance increased from 0.279 to 0.403 m2 ·K/W (a 44% increase). The overall thermal resistance of wall II (hollow wall filled with FM) is slightly lower than that of wall III (hollow wall with commercial insulating stucco system applied to interior surface). In fact, it is only 1% less, indicating that filling the voids with FM is an effective means to upgrade the thermal performance of Hui-style wall system. In addition, the combination of the methods of filling the voids with FM and applying a continuous layer of the commercial insulating stucco offers the best thermal insulation performance, as indicated by an overall thermal resistance of 0.701 m2 ·K/W found on the tested wall IV. This thermal resistance was even higher than 0.67 m2 ·K/W, which is the standard requirement in the hot summer/cold winter climate zone in China.
CONCLUSIONS Architectural heritage conservation is an important field in architectural research. The Hui-style residence is an important architectural heritage of China. Its hollow wall system, with horsehead-like upper corners, is a distinct architectural feature that is worth preserving. However, the thermal performance of the hollow wall is relatively poor by today’s standard.
TABLE 9 Summary of properties of FM300-40-2
Mix FM300-40-2
FA
Accelerator
Brewer spread (mm)
40%
0.5%
210
Initial setting time (h)
Strength (MPa)
Thermal conductivity W/(m2 ·K)
2.1
0.5
0.053
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FIG. 19. Sensors’ positions in the interior walls surface.
TABLE 10 Overall thermal resistances of the four tested walls Wall type Overall thermal resistance, (m2 ·K/W)
I
II
III
IV
0.279
0.403
0.407
0.701
Therefore, an appropriate thermal upgrading strategy needs to be developed. In this paper, FM was proved to be a suitable void filling material for thermally upgrading the Hui-style wall system from the facts that it offers a reasonably good thermal performance and industrial wastes (FA) can be widely used in foam concrete making it an environment-friendly material. Based on the above experimental results, the following conclusions can be drawn: 1. There are great spreads at higher densities, the decreasing consistence at lower densities is due to the reduced selfweight and greater cohesion resulting from the higher foam content. At a given density, the spreads increased with an increase in fly ash replacement level due to their spherical morphology and lower specific density compared with cement. 2. Wet density, fly ash and accelerator addition have great impact on setting time of FM. Setting time increased with
an increase in accelerator content, while the reverse phenomenon was observed when pre-foamed foam and fly ash are incorporated. Addition of accelerator in FM was an effective means to prevent the potential risk of instability of FM and improve the construction speed. 3. Reducing the density of FM reduced its compressive strength and up to 40% fly ash can be used to replace cement, without significantly affecting the long-term strength. However, higher percentages replacement (60%) resulted in dramatically reduced strength due to the insufficient Ca(OH)2 for further pozzolanic hydration. In addition, the Balshin equation shown in Equation (6) can be used to calculate compressive strength, as a function of porosity of FM. 4. The thermal conductivity of FM increased with an increase in density. An extended model, shown in Equation (14) form the Glicksman (1994) and Yuan’s model (2009) and can give good prediction of the thermal conductivity and porosity relationship of FM. 5. Mixture FM300-40-2 was chosen as the optimum filling material for the environment chamber test in this study. The result shows that filling the voids with foam concrete can effectively improve the overall thermal resistance of the hollow wall system by 44%, which is almost equal to the overall thermal resistance when using the more expensive commercial inorganic stucco system. In addition, the combination of the methods of filling the voids with FM and applying a continuous layer of the commercial insulating stucco yields
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an overall thermal resistance of 0.701 m2 ·K/W, which meets the standard required in the hot summer/cold winter climate zone. 6. The novel approach presented here can also be used in thermal upgrading of existing Chinese traditional Hui-style residences for the point of view of architectural heritage conservation. This approach was deemed cost effective, easy to learn, and capable of preserving the architectural integrity of the wall. In addition, it is possible to design the properties of FM to meet the construction requirement by varying material parameters such as cement paste composition, foam size and volume friction. ACKNOWLEDGEMENTS Thanks are due to the Concrete Technology Unit, University of Dundee for providing facilities and equipment. FUNDING Authors gratefully acknowledge the financial support from open projects from state key laboratory of high performance civil engineering materials (2010CEM002), China National Natural Science Fund of China (51178106, 51138002), Program for New Century Excellent Talents in University (NCET-08-0116), 973 Program (2009CB623200), Program sponsored for scientific innovation research of college graduate in Jiangsu province (CXLX_0105).
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