Sustainability of New and Strengthened Buildings

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1 Sustainability of New and Strengthened Buildings CORNELIU BOB*, LIANA BOB** *Faculty of Constructions, University Politehnica of Timisoara Str. Traian Lalescu nr.2, Timisoara ** Research Institute ICECON, Timisoara Branch Str. Petre Ramneantu nr. 2, Timisoara ROMANIA Abstract: - The paper deals with some aspects on sustainability of the new buildings as well as of strengthened structures. The first part of the paper is devoted to the energy incorporated in main building materials and the importance of thermal insulation, air tightness and thermal mass of the building envelope. The second part presents the calculated components of sustainability, total cost of strengthening solution, the energy used with raw materials, consolidation time. Key-Words: - Sustainability, CO 2 emission, raw material, enclosed energy, strengthening solutions, CFRP lamellas, CFRP sheets, biocomposites, thermal insulation 1. Introduction Sustainable construction has recently been identified as one of lead markets for the near future of Europe because of its high innovation potential, its ability to respond to market needs, the strength of European industry and the necessity to support it through the implementation of public policy measures [11]. The main concept of sustainability is to design buildings with a long service life, low operating and maintenance costs and high energy efficiency [7]. The reduce emissions of CO 2, the main gas responsible for the greenhouse effect is a fundamental objective for the preservation of our planet [3] Buildings and infrastructure generate one third of total CO 2 emissions. In this respect, the construction industry can make a significant contribution by going beyond old, land consuming planning methods [5]. In order to reduce the total CO 2 emissions of a structure the phase of its use is going to take more and more importance in its global evaluation as it accounts for 80 to 90 % of the total energy consumed throughout its entire lifecycle [9]. To reduce the impact of primary raw materials and the amount of demolition waste put to landfill, the importance of the end-of-life phase is also growing (Fig. 1), [11]. The fundamental point of an environmental management system is to reduce negative impacts while enhancing the positive impacts on the environment of a company s operations products and services. At a producing site this involves the safe disposal of waste materials, ensuring that dust and noise levels are kept to a minimum and also that the material has been responsibly sourced [10]. With regard to environmental and climate protection, the construction industry plays a crucial role. The industry generates about half of the total amount of waste, including excavated material [6]. 17% 3% 80% energy used during the service life of the building (80%) energy used with row materials (17%) contribution to energy due to demolition (3%) Fig.1. Total energy consumed through building lifecycle Biocomposites are sustainable structural materials made from renewable resources that ISSN: ISBN:

2 biodegrade in an anaerobic environment after their useful service life, thus reducing construction related waste. The biocomposites studied have the potential to be used for scaffolding, formwork, flooring, walls and for many other applications within buildings and within the construction process [9]. According to the previous conclusions of different researches, the authors of this paper present the splitting of total energy consumed through building lifecycle (Fig. 1). In addition the sustainability is based on the environmental, economic and social components and includes criteria such as technical process and site quality. A global quantitative model for evaluating the sustainability is difficult to be produced but for each structural element or building it can be established. For instance at part 3 Sustainability of strengthening solutions, the calculated components of sustainability are: total cost of strengthening solution; the energy used with raw materials; consolidation time; in the part 2 of the paper the energy incorporated in main building materials is presented. 2. Sustainability of new buildings The energy used for heating and/or cooling, during the service life of a building is approximately 80% of the total energy consumed through building lifecycle (Fig.1). The major part of CO 2 emitted by buildings is provided from the energy used during the service life of the building. To achieve good energy performance there is necessary to use: thermal insulation, air tightness and thermal mass. For the calculation of the energy, there is the method of EN ISO Energy performance of buildings Calculation of energy use for space heating and cooling. Sandwich wall panels have been used as the standard solution for the facades of multistory residential buildings; the insulation should provide a wall with a low overall coefficient of heat transmission. By using thermal mass (sandwich wall systems), the energy use is significantly reduced compared to a lightweight structure with the same coefficient of heat transmission; a lightweight alternative would require almost double the insulation thickness [4]. For optimal energy performance, the wall should be as air-tight as possible. As it was pointed, sustainability of the raw materials can be appreciated by energy incorporated during the manufacturing process of the building materials. The total energy (in kwh/t or kwh/m 3 ) as fuels, electrical energy for different operations and lubricants, for main building materials, is presented in Table 1 and Fig.2 [1], the data were obtained from a study of INCERC Bucuresti (1985). Table 1. Energy enclosed in materials (fuels, electrical energy, lubricants) No. Material Enclosed ρ E * ρ energy E t/m 3 kwh/m 3 kwh/t (kwh/m 2 ) 1 Sand Gravel Expanded slag Fly ash Portland Cement Hydraulic lime Plaster Bricks Concrete C 40/ Reinforced concrete Mortar Cell concrete Hot-rolled profiles Reinforced steel Timber Chipboard CFRP Sheet (32)* Lam (100)** 18 GFRP Sheet (18)* 19 Polyvinyl chloride Expanded polystyrene Mineral wool Notes: 1kWh=0.123 kg CC * Thickness of CFRP and GFRP sheets 0.38 mm **Thickness of CFRP lamellas 1.2 mm ISSN: ISBN:

3 Some important conclusions from the data presented can be underlined: - the high energy enclosed in the steel hot-rolled profiles and reinforcing steel; - a low energy used for producing traditional building materials as timber, brick and cellular expanded concrete; - a higher energy enclosed in expanded polystyrene as compared with mineral wool; - the CFRP and GFRP are characterized by a high energy enclosed in Tones (t) or m 3, but a small energy for materials as lamellas or sheets, expressed in m 2. An important contribution to the reduction of energy incorporated in structural elements is obtained by using ultra-high performance concrete (UHPC): the energy enclosed by UHPC is approximately half of ordinary concrete. Fig.2 Total energy for main building material UHPC is well suited to the use in very filigree, sustainable and cost efficient structures and to entirely new assembly and design methods [8]. UHPC mainly results from its better workability (self-compacting concrete), very low w/c ratio (about 0.2), higher strength, increased acid resistance etc. Finally, the sustainability of new building, known by the term green building, should be achievable by: the thermal insulation, air tightness and thermal mass of the building envelope; building materials with minimum energy incorporated during manufacturing process; ultra-high performance materials (concrete); biocomposites as structural materials made from renewable resources; building structure and envelope with low cost; advanced technology as self compacting concrete. ISSN: ISBN:

4 3. Sustainability of strengthening solutions The sustainability of the strengthening solutions was very little discussed as compared with the sustainability of new buildings. Five strengthening solutions will be analyzed in the paper (Fig. 3). The consolidated element is an existing RC column with the length of 8 m and a cross section of 600x600 mm. The rehabilitation solutions are: The coating by reinforced concrete with 150 mm concrete depth and 3ø20 mm re bars on each side and stirrups ø8/150 mm; Steel bracing with four angle irons of 80x80x8 mm, connected by flange plates of 100x8 mm at 500 mm distance; Carbon fibre polymer composites (CFRP) as it is illustrated in Fig. 3 with two variants: - CFRP lamellas (strips) in longitudinal direction and CFRP sheets (wraps) in transversal direction; - CFRP sheets in both longitudinal and transversal directions. Lamellas are with the cross section of 100x1.2 mm (two lamellas on each side) and CFRP sheets, of 600x0.38 mm (one sheet on each side) [2]. The calculated characteristics of the five strengthening solutions were: the value of the increasing bending moment, M, due to strengthening [12]; the total cost of strengthening solution at the level of year 2008; the total energy or conventional fuel for each solution; consolidation time. The results of the analysis are presented in Table 2 and Fig 4. The main conclusions from this data are: - The more sustainable solution is the strengthening with CFRP sheets in both directions, because of the minimum cost of strengthening, energy enclosed and consolidation time. - The strengthening by CFRP (lamellas and sheets) is sustainable too, due to small energy enclosed and minimum consolidation time, but the cost is higher. - The strengthening by RC coating and steel bracing are not sustainable solutions due to high energy incorporated and big consolidation time at a cost comparable with the solution CFRP sheets. Fig.3 Strengthening solutions for a RC column Fig.4 Sustainability of strengthening solutions ISSN: ISBN:

5 Table 2. Main characteristics of strengthening solutions Strengthening by coating with: Calculated characteristics Carbon fibres Reinforced Steel concrete profiles Sheets Lamellas+ Sheets Increase of the bending moment due to strengthening, [knm] ΔM 220* 235* 194.5**/444.7* 147**/336* Total cost of strengthening solutions (at year 2008) [ ] Energy of Energy [kwh] strengthening Conventional solutions fuel [kg] Consolidation time [manhours] Notes: * Bending moment at ultimate stage (failure/yield of strengthening material) ** Bending moment at maximum strain of compressive concrete 16 man-hours for surface preparation before strengthening 4. Conclusions The main ideas which can be underlined are: a). The sustainability of new buildings are obtained by the best thermal insulation, air tightness and thermal mass of the building envelope. b). The use of building materials with minimum energy incorporated during manufacturing process as well as of biocomposites as structural materials made from renewable resources. c). To erect building structure and envelope with advanced technology and low cost. d). For strengthening of the existing structures the most sustainable solution is by using CFRP materials (sheets and/or lamellas). References: [1] Bob C. and Bob L., Green buildings made with sustainable materials (in Romanian), Analele Universităţii din Oradea, Ed. Univ. Oradea, vol. XI, 2008, pp [2] Dan S., Bob C., Gruin A., Badea C. and Iures L., Strengthening of Reinforced Concrete Framed Structures in Seismic Zones by Using CFRP, WSEAS International Conference on Engineering Mechanics, Structures, Engineering Geology (EMESEG, 08), Heraklion, Crete Island, Greece, July 2008, pp [3] Dehaudt S., Consequences of the evolution of raw materials on the manufacturing of precast concrete, 19. BIBM International Congress Vienna, May 2008, pp [4] Lindström G., Sandwich wall systems the wall system of the future, 19. BIBM International Congress Vienna, May 2008, pp [5] Lundquist G., Vertical Street the Kobben. 19. BIBM International Congress Vienna, May 2008, pp [6] Maydl P., Assessing sustainability of construction products: Current trends and alternatives. 19. BIBM International Congress Vienna, May 2008, pp [7] Nuβbaumer M., Sustainability, 53. Beton Tage, Proceedings Concrete Solutions, Neu-Ulm, Februar 2009, pp.3-4. [8] Schmidt M., Concrete of the future High tech and sustainable. 19. BIBM International Congress Vienna, May 2008, pp [9] Schrass Christian S. and Billington S., Mechanical properties of biocomposites for sustainable construction practices, 17. Congress of IABSE Creating and Renewing Urban Structures, REPORT Chicago, September 2008, pp [10] Watkins M., Sustainability and the concrete producer, 19. BIBM International Congress Vienna, May 2008, pp [11] Wolschner B. The precast concrete industry Part of the European Lead Markets Initiative. 19. BIBM International Congress Vienna, May 2008, pp [12] *** Externally bonded FRP reinforcement for RC structures, fib Bulletin 14,Technical Report, ISSN: ISBN: