sustainable building and alternative materials in …sustainable building and alternative materials...

SUSTAINABLE BUILDING AND ALTERNATIVE MATERIALS IN THE NEGEV DESERT

David PEARLMUTTER1 Constantin FREIDIN2

Nora HUBERMAN3

1 Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, Israel [email protected]

2 Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, Israel [email protected]

3 Albert Katz School for Desert Studies, Ben-Gurion University of the Negev, Sede-Boqer Campus, Israel [email protected]

Keywords: life-cycle analysis, embodied energy, energy efficiency

Abstract An energy-efficient residential building in the Negev region of Israel is used as a model for assessing architectural sustainability in desert areas. Designed with a number of climatically-responsive design strategies and conventional concrete-based materials, the building was found to be nearly energy-independent in terms of summer cooling and winter heating. As a second step to the assessment, the possible integration of alternative building components based on recycled waste and local raw materials in the building’s walls was considered through thermal simulation. The use of such sustainable materials can significantly reduce the burden of resource consumption in the construction process, and therefore contribute to the overall sustainability of the building. The alternative components included in the simulation are produced through a process which was developed to make use of fly-ash from oil-shale and coal burning power plants, as well as local crushed stone and sand. The effect of the main technological parameters (such as composition and molding pressure) on the compressive strength of the components was analyzed using laboratory specimens cured under environmental conditions. The open-air stability of the developed materials was also studied and found to be sufficient. Manufacturing recommendations based on laboratory data were confirmed by results of test production in a commercial block-manufacturing plant. It was established that high-quality building components could be produced using the developed technological procedure with standard manufacturing equipment. An experimental demonstration wall was constructed from plant-produced components and found to be stable over ten years under Negev desert conditions. The consumption of both embodied and operational energy was analyzed over the building’s useful lifespan, and this life-cycle analysis showed the clear advantage of integrating alternative materials in a sustainable desert building.

1. Life-cycle sustainability in desert buildings In most industrialized countries, the building sector accounts for between one third and one half of all energy consumption (Langston and Ding, 2001; Huberman and Pearlmutter, 2004). In order to ease this environmental burden, radical improvements are called for in building energy-efficiency, or the amount of energy required to maintain a given level of quality and comfort. Opportunities for increasing efficiency may be found by dividing the energy consumed by buildings into three phases:

Pre-use phase: Energy required for the production of a building and its components (embodied energy), which includes such activities as material extraction, production and transportation, and building construction itself. Use phase: Energy required for the use and maintenance of a building during its useful life

(operational energy), which is dominated by heating, cooling and lighting, and is affected by the thermal properties of materials. Post-use phase: Energy needed after the building’s useful life, which includes demolition and

disposal, or possible reuse or recycling.

The 2005 World Sustainable Building Conference,Tokyo, 27-29 September 2005 (SB05Tokyo)

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These phases are clearly manifested in the building industry in Israel, where rapid population growth has not only accelerated the pace of industrialized construction, but also increased pressure for the development of “peripheral” regions such as the Negev desert – where climatically extreme conditions usually require exorbitant amounts of energy to be expended on keeping dwellings thermally comfortable. When properly understood, however, these climatic forces – such as intense solar radiation on winter days, or cool winds on summer nights – can in fact be exploited to improve thermal comfort while reducing non-renewable energy consumption. The design options available for achieving this include the appropriate use of materials, for example as thermal mass or insulation in the building envelope. Strategies which reduce a building’s energy needs for thermal comfort, however, do not necessarily lower energy demand in the production phase. Manufactured building products, such as super-insulated aluminum windows or concrete panels, may contribute to the building’s operational energy efficiency but at the same time rely on raw materials which are energy-intensive in production. By substituting solar or human energy for non-renewable energy in the manufacturing process, low “embodied-energy” materials may likewise reduce environmental impacts – and further benefits accrue when such materials are reused or recycled, rather than discarded in the typical process of demolition and disposal. Environmental impacts associated with construction materials are thus related to the energy inputs and outputs required during all three building phases. Attempts at producing more energy-efficient buildings, however, have usually been limited to reducing energy consumption for the building’s operation, which are predominantly related to heating and cooling. This may be due, at least in part, to the common assumption that energy needed for the pre-use phase is relatively small compared with use-phase energy. Research has shown, however, that embodied energy may actually represent up to 50% of the total energy flows in a typical building (Langston and Ding, 2001), though the few publications which have addressed this trend have been limited to the analysis of the embodied energy of individual materials (Venkatarama Reddy and Jagadish, 2003). Overall, little may be gained if energy expenditure in each particular phase is considered in isolation. It is only recently that studies have taken a full-life-cycle approach to buildings - examining the relationship between embodied and operational energy, or the role of construction techniques on a building’s ultimate environmental impact (Suzuki and Oka, 1998). Life-Cycle Analysis (LCA) is such a process, whereby the component and overall energy flows in a system are quantified and evaluated (Huberman and Pearlmutter, 2004).

2. Alternative materials Concrete blocks are widely used as a wall material in desert housing. As a rule, they are manufactured using Portland cement or its modifications as a binder, together with sand and breakstone as fine and coarse aggregates. Research carried out in the Negev desert region of Israel has shown that cement, which is highly energy-intensive in its production, can be substituted by High Calcium Oil Shale Fly Ash (HCOSFA), an industrial waste material and potentially large-scale pollutant (Bentur et al., 1982; Freidin, 1999). HCOSFA is obtained as a by-product in the combustion of local oil shale at the PAMA (Developing Energy Resources, Ltd.) quarrying and processing plant in the Negev. Due to its composition, HCOSFA can participate in both pozzolanic and cementitious reactions and cure with water, without the need for an activator. In order to prevent or moderate weakening of the material in atmospheric air, it has been recommended by Freidin (1998) to partially substitute HCOSFA by Low Calcium Coal Fly Ash (LCCFA), which is obtained from a coal burning power plant on Israel’s Mediterranean Coastline. Here the main technological parameters (composition, compaction pressure and curing conditions) affecting the compressive strength of material specimens based on HCOSFA and LCCFA are discussed, along with manufacturing experimentation which was performed on full-size blocks. In laboratory experiments, different batches of pressed specimens were compared to determine the influence of varying levels of fly-ash and water content on the compressive strength of the material at a compaction pressure of 4 MPa, and specimens were subsequently compacted at increasing pressure intervals up to 28 MPa. The specimens were cured under 28-day conditions of moist air (20±3°C and R.H.>96%), atmospheric air (18-23°C and R.H. of 35-60%), and with 8-hour steam curing (temperatures of 60°C and 90°C). To determine the change in long-term compressive strength, specimens were crushed after 1-, 3-, 6-, 12-, 18-, 24-, 36-, 48- and 60-month periods of exposure to atmospheric air. The effect of fly-ash content on compressive strength is shown in Fig. 1 for specimens with 20 and 25% mix-water (MW). It may be seen that a maximum strength of 8.8 MPa is achieved for specimens made from 48% HCOSFA+12% LCCFA and 25% MW, and it is also clear from Fig. 1 that a higher water content


induces greater compressive strength. Similar patterns of strength development were observed in experiments with varying percentages of sand in the mixture.

Figure 1. 28-day compressive strength of moist cured specimens at various HCOSFA+LCCFA content. Specimen composition (by weight): HCOSFA+LCCFA mixture - 60%, Sand - 40%.

From Fig. 2, it is seen that compressive strength could be further increased with greater compaction pressure, reaching a peak of nearly 11 MPa at a pressure 28 MPa. The strength-development curves show diminishing improvement after 12 MPa, however, such that nearly full strength is achieved with considerably less than the maximum pressure tested.

Figure 2. Influence of compaction pressure on 28-day compressive strength of moist cured specimens composed from 60% (HCOSFA+LCCFA) and 40% sand.

As can be seen from Table 1, moist curing is preferable to air curing. Moist cured specimens turned out to have almost 1.5 times greater strength compared to specimens cured in atmospheric air. Steam conditions accelerate the curing process as well. After a short curing period of eight hours at temperatures of 60°C and 90°C, the compressive strength of specimens was 4.9 and 7.5 MPa accordingly.

Table 1 Compressive Strength of Specimens Cured in Various Conditions

Curing conditions Period Compressive Strength (MPa) Moist curing (t=20±3°C, RH≥96%) 28 days 6.0 Air curing (t=18-23°C, RH=35-60%) 28 days 4.1 Steam curing (t=60°C) 8 h 4.9 Steam curing (t=90°C) 8h 7.5

Fig. 3 presents the long-term pattern of change in compressive strength of specimens containing 36% HCOSFA, 24% LCCFA and 40% sand, the composition which was found to be optimal with respect to the material’s stability in atmospheric air. Three distinct sections are noticeable in the compressive strength curve. The first section shows evidence of the curing process and development of strength within the first month. The second section (from one to 6 months) shows an abrupt decrease in strength. In the third section,

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starting from the sixth month, strength declines at a slower rate and then stabilizes, such that from 24 months onward a level is maintained at about 50% of the initial one-month compressive strength of specimens in atmospheric air. Based on this level, it can be established that the material based on HCOSFA and LCCFA is sufficiently stable in atmospheric air.

Figure 3. Development of the compressive strength in atmospheric air

In addition to the testing of specimens, actual concrete-like hollow blocks with standard dimensions of 40x20x20 cm were manufactured in a block-making plant using conventional industrial machinery. Two types of blocks were produced: the first with crushed limestone and sand as an aggregate, and the second with only sand, while both types were made with locally produced fly-ash (mixture of HCOSFA and LCCFA). The blocks initially cured for 1-3 days in moist conditions, and thereafter in the open air. The blocks were tested in the Standards Institute of Israel, and both types were found to adhere to the requirements of the relevant national standard for shape, structure, finish, dimensions, spatial weight as well as compressive strength. The average strength of blocks with crushed limestone was 7.8 MPa, and blocks with sand as the only aggregate were tested at an average of 5.1 MPa. These levels are both clearly above the standard requirement for compressive strength, which calls for not less than 3.0 MPa. Also an experimental demonstration wall was constructed from manufactured blocks (Fig. 4), and found to be stable over ten years under Negev desert conditions.

Figure 4. Demonstration wall was constructed from manufactured fly-ash blocks.

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3. Case study The aim of this study is to quantify the energy consumption associated with selected building materials when used in a residential building in a desert environment, over the life-cycle of the building’s construction and use (the post-use phase is not considered here). Emphasis in the analysis is placed on comparing alternative materials developed for environmental sustainability with more commonly used industrial materials, and gauging their relative influence on life-cycle energy consumption. Also considered is the “payback” period for alternative materials, or the time required for an operational energy advantage (or disadvantage) to outweigh an initial investment (or savings) in embodied energy. The life-cycle analysis was performed by estimating the overall energy consumed in the production and operation of an existing building, and comparing the results with a hypothetical scenario in which the building’s material composition is modified. Serving as a model for this case-study is a single-family house built in the “Neve-Zin” desert solar neighborhood, which is located at the Midreshet Ben-Gurion community in the arid Negev Highlands of southern Israel (30.8°N latitude, 480 m above sea level). The climate of the Negev desert is characterized by wide daily and seasonal thermal fluctuations. In summer, daily temperatures range from well under 20°C to over 32°C and are accompanied by low daytime relative humidity, intense solar radiation and consistently strong winds from the northwest in the late afternoon and evening. In winter the climate is cold, with a total of over 1000 Heating Degree Days (based on the standard design temperature of 18.3°C used in Israel – Bitan and Rubin, 1991) The cold conditions are amplified by strong winds, though clear skies allow for abundant solar radiation in the daytime. The region is sparsely populated, with relatively small, isolated communities situated within a radius of approximately 50 km from the main city, Beer-Sheva. While the actual case study site is typical of the region in terms of its climate and its remoteness, it is atypical in other respects, which have implications for long-term sustainability (Pearlmutter, 2000). As part of a self-contained educational campus (in which Ben-Gurion University’s Institute for Desert Research and other environmentally-oriented facilities provide local employment to most of the population), the Neve-Zin neighborhood is also unique in terms of the overall approach to urban design embodied in its development plan. The plan was designed by the Institute's Desert Architecture and Urban Planning Unit, and incorporates innovative features that encourage bio-climatic building by guaranteeing access to direct sun in winter and cooling breezes in summer (Etzion, 1989). The 140 m2 house selected for the case study (see Fig. 5) is representative of this approach. Large south-facing openings take advantage of direct solar gain in winter, and every room is designed for summer night cooling by cross-ventilation. It is spatially organized around an internal patio, which facilitates these strategies in different parts of the building: by spacing the southern wing of the house, which contains the main living areas, apart from the northern two-story bedroom wing, both enjoy access to both low-angle winter sun and northwesterly summer breezes.

Figure 5. Case-study house: ground floor plan (left), and section (right) showing climatic response in summer

(top) and winter (bottom).


The entire building envelope was designed with a material cross-section containing internal thermal mass and exterior insulation, and glazed openings are protected by operable louver shutters which alternately provide shade on hot summer days, ventilation on cool summer nights, full exposure on sunny winter days and insulation on cold winter nights. The combination of these strategies in the house’s design makes summer air conditioning unnecessary, and backup heating needs are minimal (see Fig. 6) – with the actual energy consumption quantified in the first part of this study. At the same time, the house was built using conventional, high embodied-energy concrete-based materials, with reinforced concrete structural elements and hollow concrete block walls. Therefore as a second step to the assessment, these blocks were hypothetically “replaced” by alternative blocks based on fly-ash (as described in Section 2) in the building’s walls, as a means for reducing the embodied energy of the system.

Figure 6. Winter temperatures measured in the case-study house, showing typical period when heating energy is required to maintain the standard design comfort temperature of 18.3oC.

In order to establish the pre-use energy requirement of the building, in both its actual and alternative configurations, per-unit embodied-energy values were derived for individual building components (including major finish materials as well as bulk and insulation materials in the envelope) and then multiplied by their quantities within the building as designed. While ranges of such values were obtained for various materials from published studies using hybrid analysis (Alcorn and Baird, 1996; Baird et al., 1997; Chani et al., 2003; Lawson, 1996; Venkatarama Reddy and Jagadish, 2003;), the embodied energy of major components was calculated for the local situation by combining available data for raw material extraction and processing with actual transportation energy requirements according to resource locations within the region. Product manufacturing was assumed to take place in the city of Beer-Sheva, and the alternative blocks based on fly-ash were assumed to have energy embodied in their final manufacture and transportation only – since the two types of ash are produced as industrial by-products which would otherwise be disposed of as waste. Energy in construction of the building itself was estimated as a percentage of the overall material embodied energy according to the approach of Fay and Treloar (1998). As mentioned above, operational energy was accounted for by quantifying heating energy only, which for the house as-built was estimated from utility bills as well as from thermal simulations using QuickII software. For the hypothetical configuration, the building’s use-phase energy needs were predicted through thermal simulation only. The active steady-state heating simulation was based on the previously-mentioned standard design temperature of 18.3oC, and standard infiltration rates were assumed. Daily heating loads were multiplied by a statistical distribution factor expressing the length of the season in which mechanical heating is required, and by a performance factor representing the efficiency of mechanical equipment. Annual use-phase energy was taken cumulatively over an assumed 50-year lifespan, which when summed together with the initial embodied energy represents the life-cycle energy budget of the building.


4. Life-cycle energy results By calculating embodied energy according to published figures for cement production (Lawson, 1996; Chani et al., 2003) and regional transportation distances of raw and finished materials, a value of 1210 MJ/m3 was reached for the conventional concrete blocks used in the case-study house. This is close to the average of the range of values found in the literature, with the highest figure of approximately 1700 MJ/m3 (1.5 MJ/kg) from Australia (Lawson, 1996) and the lowest of about 700 MJ/m3 (11 MJ/block) from India (Chani et al., 2003). The alternative blocks based on fly-ash (which is considered to be a zero- production energy replacement for cement) were found to have a total embodied energy of 190 MJ/m3, or close to 85% less than the conventional concrete block. When taken within the entire building, the saving provided by alternative blocks appears considerably less: as seen in Fig. 7, this saving in embodied energy amounts to about 40 GJ, or a reduction of some 15%. In an operationally-efficient building, however, embodied energy accounts for a large proportion of overall lifetime consumption: with the annual requirement in the case-study house estimated at about 1.5 GJ, embodied energy contributes 270-310 GJ out of the total 50-year requirement of 340-380 GJ (or between 85-90%) for the configurations shown in Fig. 7. Therefore the given difference of 40 GJ (or 285 MJ per square meter of building) is equivalent to over 25 years of operational energy in either of the configurations (since the two types of block are nearly identical in their thermal properties), which represents over half the assumed lifespan of the building. Based on this finding, an additional comparison was made. Using the alternative wall material and at the same time taking advantage of the embodied energy “credit” it provides, the building’s thermal insulation was doubled in thickness. This results in an embodied energy increase approximately equal to the previously-mentioned saving of 40 GJ, but lowers the operational energy rate by about one-half. The return in this “investment” is only seen, however, after nearly the full 50-year period has elapsed, when the lines of trajectory for the two alternative configurations intersect (see Fig. 7). It is important to note that even when using a bulk wall material based on zero-energy industrial waste, the overall embodied energy of the entire building (including structural concrete, insulation and finish materials) is still substantial. Therefore, the potential exists for further savings if the fundamental concepts of building construction are reexamined, for instance by considering roof forms (vaults, domes, etc.) which, through their structural efficiency, can make use of alternative materials whose strength is insufficient for flat slabs.

Figure 7. Cumulative life-cycle energy consumption for the case-study house, as built (with conventional concrete block) and in hypothetical scenarios with alternative fly-ash block (with insulation as originally

designed, and of double thickness).


5. Conclusions This brief case study illustrates how sustainability in the built environment may be enhanced when energy-efficient materials are combined with energy-efficient building design. In summarizing the findings of the study, a number of conclusions may be proposed:

An alternative to conventional concrete blocks, which has been developed in Israel on the basis of two types of fly-ash that are produced as an industrial by-product, can feasibly be manufactured with acceptable compressive strength and long-term stability. Such a material is entirely free of energy-intensive cement, and makes productive use of a potentially large-scale pollutant. The embodied-energy savings generated through use of this alternative material, when quantified as

a hypothetical alternative in a climatically-responsive desert building, is equivalent to about 285 MJ/m2, or about 25 years of operational energy – fully half the assumed lifespan of the building. This relation highlights the fact that when a building is nearly passive in its operation, its pre-use

phase energy accounts for a large proportion of overall lifetime consumption (85-90%), regardless of the wall material. In such cases, it is especially important to pay attention to the possibility that thermal efficiency may be coming at a high expense in terms of embodied energy. The embodied energy of the entire building may potentially be reduced in many ways other than

improving the wall infill material. Since a prime candidate for such further improvement is the structure itself, it is suggested that energy-efficient structural forms could hold the key to future efforts in creating more sustainable buildings.

References Alcorn, J. A. and Baird, G. 1996, Embodied energy analysis of New Zealand building materials – methods and result. In Embodied Energy – the current state of play, Deakin University, pp. 61-71. Baird, G., Alcorn, A. and Haslam, P. 1997, The energy embodied in building materials - updated New Zealand coefficients and their significance, IPENZ Transactions, 24, pp. 46-54. Bentur, A. 1982, Application of oil shale ash as building material. Silicates Industrials, 7/8, pp. 163-168. Bitan, A. and Rubin, S. 1991, Climatic Atlas of Israel for Physical Planning and Design. Israel Meteorological Service and Ministry of Energy and Infrastructure. Chani, P.S. Najamuddin and Kaushik, S.K. 2003, Comparative Analysis of Embodied Energy Rates for Walling Elements in India, Architectural Engineering 84, pp. 47-50, The Institution of Engineers (India). Etzion, Y. 1989, A desert solar neighborhood in Sede-Boker Israel, Architectural Science Review, 33, pp. 103-109. Fay, R. and Treloar, G. 1998, Life-cycle energy analysis – a measure of the environmental impact of buildings, Environment Design Guide GEN 22, RAIA, Canberra. Freidin, C. 1998, Hydration and strength development of binder based on high-calcium oil shale fly ash. Cement and Concrete Research, 28, pp. 829-839. Freidin, C. 1999, Cementless buildings units based on oil shale and coal fly ash binder. Construction and Building Materials, 13, pp. 363-369. Huberman, N. and Pearlmutter, D. 2004, Life Cycle Energy Performance of Building Materials: Alternatives for a Desert Environment. In Built environments and environmental buildings: Proceedings of the 21st International PLEA Conference, Eindhoven, The Netherlands. Langston, C. A. and Ding, G. C. K. 2001, Sustainable practices in the built environment. Butterworth Heinemann. Lawson, B. 1996, Building materials, energy and the environment: Towards ecologically sustainable development, RAIA, Canberra. Pearlmutter, D. 2000, Patterns of sustainability in desert architecture. Arid Lands Newsletter, 47, http://ag.arizona.edu/OALS/ALN/aln47/pearlmutter.html. Suzuki, M. and Oka, T. 1998, Estimation of life cycle energy consumption and CO2 emission of office buildings in Japan. Energy and Buildings, 28, pp. 33-41. Venkatarama Reddy, B.V. and Jagadish, K. S. 2003, Embodied energy of common and alternative building materials and technologies. Energy and Buildings, 35, pp. 129-137.


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