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Smart elements for sustainable building envelopes

Final Report Summary - SESBE (Smart elements for sustainable building envelopes)

Executive Summary:
Limited recourses and increasing population demands new ideas in sustainable development and growth. In particular in the energy sector and to be more specific, in energy conservation, there are still multiple options for technological advancement. In the building sector the advance of new technologies and materials help to show new perspectives to decentralize energy production, increase energy savings by smart facility installation and appliances as well as by increasing energy efficiency by new materials used for the building envelope. The latter is the focus of the SESBE project: Smart Elements for Sustainable Building Envelopes. SESBE develops new types of façade elements with integrated insulation for new buildings and the existing building stock. The main objectives are sustainability, safety and energy efficiency increase in conjunction with weight and thickness reduction of elements (Fig. 1).
A new type of concrete, Reactive Powder Concrete (RPC), allows reducing drastically the thickness of elements due to its high mechanical performance. Energy efficiency will be reached by a new type of insulation based on foam concrete with Quartzene® incorporation, an aerogel-like material. Functionalization of the materials by nanotechnology allows enlarging the performance of the elements with further properties, such as self cleaning/easy-to-clean, heat reflectance, and humidity buffering. Furthermore, a new type of sealing tape for element joints and openings is being developed as well as a more effective intumescent coating for anchors and the metal substructure.
The project itself consists of 6 work packages (WP). WP2 to WP5 are of technical and scientific content. WP2 is dedicated to material development, WP3 to material functionalization and WPs 4 and 5 in façade element design, performance and production technologies.
Project Context and Objectives:
Overall and technical objectives
The overall objective of the project was to develop lightweight, energy efficient and fire-safe façade elements with multifunctional properties, using nanomaterials and nanotechnologies.
• Increasing energy efficiency by
- improving insulation/sealing materials by using aerogel. The used aerogel, called Quartzene®, by itself is not nanosized but the effect of aerogel is based on the nanostructured nature of the material (nanosized pores).
• Increasing fire resistance of materials by
- using mostly inorganic, non-combustible materials for the panel components (except for sealing tape);
- utilizing heat reflective coatings with transparent conductive oxides (TCO).
• Implementing surface functions of the façade elements by
- easy-to-clean properties by nanostructuring of concrete surfaces in conjunction with a bulk hydrophobic agent in the concrete;
- self-cleaning properties using a top coating of modified, super-oleophobic nanosized titanium dioxide.

Technical objectives
1. The weight of the sandwich elements shall be reduced by 50 to 60 % of existing sandwich panels of concrete. This will be realized by using FRRPC instead of standard reinforced concrete as layer material.

2. The thermal conductivity of the new insulation layer shall be lowered by 15 % in re-spect to EPS and by 25 % in respect to mineral wool. This will allow a reduction of thickness of the insulation layer by 20 %.

3. The total reduction in volume of concrete and insulation used shall be between 50 and 70 % with the new sandwich panels. This is due to the reduced thickness of the FRRPC and the insulation material.

4. The content of volatile organic compounds (VOC) will be drastically reduced by using inorganic components. There are only few organic components used in the fa-çade system. These concern essentially the sealing tape. The material will be used in low volumes and mostly applied in the exterior.

Project structure
The project itself consists of 6 work packages (WP). WP2 to WP5 are of technical and scientific content. WP2 is dedicated to material development, WP3 to material functionalization and WPs 4 and 5 in façade element design, performance and production technologies.
Project Results:
1 Material developments

The development of new façade systems was based the development of improved materials and methods for their functionalization. The development included three main materials for the actual façade elements and one coating for metal parts of the anchorage.

1.1 Textile fiber reinforced reactive powder concrete (FRRPC)

The concrete layers of traditional sandwich elements were replaced by FRRPC in order to make the panel thinner and lighter. Standard reinforced concrete layers have a thickness of minimum 80 mm. This derives from protection requirements for the steel reinforcement. Re-placing steel with an alternative non-corroding material, in our case carbon fiber textile grids, renders the thickness requirements unnecessary. At the same time the strength of these layers were drastically increased.
RPC is a material with high cement clinker content. In order to reduce the absolute clinker content supplementary cementitious materials (SCM) were employed. In total three different mixes were developed. The next figure shows the binder composition and the respective amounts of cement clinker replacement and the achieved compressive strength.

For upscaling of the development to the panel stage the mix design RPC-CBI1 was chosen since it performed best in mechanical, and early age properties. A name for this mix, Sesbonite®, was protected by a trademark. The main results of the FRRPC RPC1 are sum-marized in the following.
• Clinker replacement: 33 mass-%
• Compressive strength: 142 MPa
• E-modulus: 50 GPa
• Poison ratio: 0.216
• Can be mixed in large scale mixer with low energy (e.g. force action mixer)
• With textile reinforcement a high peak deformation can be achieved. In 4-point bending tests of 25 mm panels midspan deflections between 40 and 50 mm could be achieved be-fore failure.
• The costs for the developed RPC mix excluding the reinforcement is ca. 3 to 4 times more expensive as a standard concrete per cubic meter. However, reduction in material thick-ness reduces the total costs considerably.

1.2 Cellular lightweight concrete (CLC, foam concrete)

An inorganic lightweight insulation material was developed on the basis of CLC. The material has a density in the range of 120 to 150 kg/m3. For increased thermal performance the silica aerogel Quartzene® was incorporated into the mix. The material has the following properties:
• Density: 120 to 150 kg/m3
• Compressive strength: 100-300 kPa
• Increased post peak deformation due to the introduction of fibers
• Good handling properties
• Easy to produce
• Fire resistant since mostly consisting of non-flammable inorganic components
• Thermal performance without aerogel: 40 to 43 mW/(m·K)
• Thermal performance with aerogel: 29 to 32 mW/(m·K)
The latter value represents a ca. 15 % reduction in respect to EPS
• Costs without aerogel in the range of EPS
• Costs with aerogel ca. 10 times more expensive. This is also due to the fact that the aero-gel production is at the moment at a very small scale and more cost intensive. Increase of the production would also mean considerably lowering of the aerogel price and hence re-duction of the insulation costs.

1.3 Improved sealing tape

Expandable sealing tapes are used for door and window openings as well as for joints of elements. For the SESBE approach a layer composite was developed. The composite tape consisted of layers of material with Quartzene® aerogel and standard polymer material.
The thermal conductivity of this tape showed values between 34 and 39 mW/(m·K) after re-peated measurements compared to 48 mW/(m·K) in a standard sealing tape. The manufac-turing process is still under an optimization process and certain properties such as driving rain tightness and expandability needs to be fine adjusted.

1.4 Intumescent coating

An improved intumescent coating including Quartzene® aerogel was under development. However, Quartzene® proved not to be a suitable filler due to its high adsorption of solvent and the ensuing increase in viscosity of the coating. Subsequently different fillers were incor-porated. The best performance proved to be a graphite based filler system which improved the fire resistance by 10 %. This avenue needs to be studied further.

2 Functionalizing materials

Functionalization was achieved for the following scenarios:
• Self-cleaning concrete surfaces: Achieved with a functionalized photocatalytic TiO2 coating. The coating is not only self-cleaning in the classical photocatalytic sense but is also strongly hydrophilic and oleophobic. The latter causes in particular paint not to adhere too strongly to the concrete substrate, what is of advantage in case of graffiti. The following pictures show the effect of self-cleaning on a RPC panel, which was painted with a felt tip marker and exposed for 8 months outside.

• Easy to clean concrete surface: This was achieved by rendering the concrete surface super-hydrophobic. In principle dust and dirt washes off easier, if water in form of raindrops roll-off more easily. The rolling off was done by mimicking a lotus leaf effect. This was realized by imprinting a textile pattern into a hydrophobic concrete.

• Heat reflectivity: Heat reflective coatings can reduce the risks for causing fire due to heat transport. Heat reflective coatings were optimized for concrete applications. Heat absorp-tion could be reduced by more than 10 %, significantly decreasing the time for heating-up of façade elements and the risk of surface spalling. It was also explored insofar these coatings can reflect heat under ambient conditions inside or outside a building. Calculations showed, that around 5 % of the energy can be reflected by the coating, thus reducing costs for heating or cooling.

• Moisture buffering by polymer clay nanocomposite (PCN): In order to prevent con-densation within the cellular lightweight concrete (CLC) a polymer-clay nanocomposite (PCN) was developed. The PCN showed a high moisture absorption capacity above 90 % RH, thus capturing excess humidity. Additional beneficial properties are: When applied to a carbon fiber grid reinforcement it increases the adhesion of the grid within a reactive powder concrete.

3 Development of sandwich elements and half panels

3.1 Concepts, main data and production

The main components developed and their materials are shown in the following illustration.

Elements were produced by one industrial consortium partner in one facility in Sweden. Ele-ments consisted of sandwich and half panels for testing and for the mock-ups.
The general properties of sandwich panels are outlined as following:
• Total weight for a 200 mm thick panel: 140 kg/m2
• Total weight for a 250 mm thick panel: 146 kg/m2
• U-value for a 200 mm thick panel*: 0.19 W/(m2·K)
• U-value for a 250 mm thick panel*: 0.15 W/(m2·K)
• Mass reduction towards a standard concrete panel (non-load bearing): 65 % and 63 %
• Reduction in thickness towards a standard concrete panel: 46 % and 40 %
*Theoretical U-values of one panel without opening and joints.
Half panels have the following properties:
• Total weight for a 175 mm thick panel : 80 kg/m2
• Total weight for a 225 mm thick panel: 86 kg/m2
• U-values the same as for the sandwich elements for the two thicknesses.
Sandwich panels are casted layer by layer in a large form work system:
• Formwork is prepared according to the panel plans
• The first textile reinforcement layer is prepared and placed in the formwork
• The panel connectors are stitched into the reinforcement grid
• The first (outer) reactive powder concrete (RPC) layer is cast into the formwork on the reinforcement grid (25 mm)
• The cellular lightweight concrete (CLC) is mixed and casted on the first RPC layer
• The surface of the casted CLC is smoothed immediately after casting
• The second reinforcement grid is placed on the foam concrete layer and stitched into the panel connectors; anchors for the lifting of the panel are placed into cut-out recesses of the CLC
• The second (inner) RPC layer is mixed and casted on the foam concrete layer and the reinforcement grid
• After setting of the RPC its surface is ground smoothly
• After hardening the panel is lifted from the formwork (tilting table) and stored vertically for a couple of days
To connect the layers within the panels connectors were developed, which are based on glass fiber reinforced polymer (GFRP). The connectors can be used singular or in double configuration.
For both types of panels concepts for anchoring them to the load bearing frame of the build-ing (floor slabs) were developed. This included two anchorage alternatives for sandwich panels and one concept for half panels.

3.2 Testing data

The system was extensively tested concerning response towards different mechanical loads and fire safety. The panels were also tested against rain tightness and for temperature shock. The acoustic behaviour was tested on panels but also on the mock-up sets in Spain.
Numerical modelling approaches were implemented for mechanical and hygrothermal load-ing scenarios as well for the calculation of thermal performance of the façade of the hypo-thetical model house designed for the project. The latter include also openings and thermal bridges.
Mechanical loading scenarios were focussed on shear, flexural and wind loads with single and double GFRP connector configuration. Additionally the load capacity for anchors and connectors were tested. The following table gives a qualitative overview of the test program and results achieved.
The test on resistance against wind driven rain was performed according to EN 12865:2001 method B. It showed more ambivalent results. Due to minor shrinkage cracks, which were exacerbated during the horizontal transport of the panels, the results grade 2 leakages in form of several drops on the panel area.
A durability test was performed according to ETAG 004. Similar as to the driving rain test, the panel for the durability test showed many shrinkage cracks, probably due to the shrinkage reducer, which was not used for the test panels. Horizontal transport might have deepened the cracks in the panel. Due to the cracks, water was penetrating into the panels after a few cycles.
The large scale fire test showed a good performance of the panels. In the hottest zone RPC spalling occurred within the outer RPC layer but spalled pieces were small and only in the area where temperatures were ≥ 400 oC. All the effects of the fire observed were within the outer RPC layer. The CLC insulation was not affected at all. The GFRP connectors per-formed well within the RPC. GFRP connectors exposed within the hottest zone showed al-most no damage and there was never any risk of losing one or more of the sandwich layers. However, the test showed also possibilities for improvement, in particular concerning the carbon fiber grid, its coating and its mesh size.
The acoustic performance was tested according to EN 10140-2 by determining the Weighted Sound Reduction Index Rw. For the tests different material combinations were chosen: RPC only, RPC with 150 mm air gap, RPC with 150 mm CLC insulation (SESBE product), RPC with mineral wool (commercial), RPC with EPS insulation (commercial). The acoustic per-formance was best with the combinations of RPC with 150 mm CLC or RPC and 100 mm mineral wool (Rw = 55). Reduction in Rw was the result of thicker mineral wool layers (52 for 200 mm) or EPS (51 for 150 mm). In this sense CLC insulation seems to be better as EPS and at least similar to mineral wool insulation.
3.3 Modelling data

Modelling was done on mechanical, thermal and hygrothermal performance. The goal was to establish design parameters not only for plain sandwich elements and half panels but also of real scale panels including window and door openings.
For the finite element calculation on mechanical performance the models were calibrated on the experimental results. This was done for the shear transfer and the composite action as well as a verification of the wind load test. A detailed analysis of a façade element with open-ings was then based on these calibration data.
Structural loads and geometry of a sandwich element.
Displacement due to wind load (upper image) and crack probability (lower image).
The results of the finite element modelling helped to redefine the design of the panels con-cerning anchor points, number and placement of the GFRP connectors. The modelling was done on sandwich elements as well as on half elements.
The thermal modelling identified the influence of thermal bridges within a given building fa-çade. As a basis a multi block and multi storey residential/business building was designed and the calculation on thermal performance was based on the design (size/thickness/window openings) of the façade elements, the anchorage and the construction of standard window and door solutions.
Below is shown the floor plan with three apartments (interior walls not drawn) of one block and a rendering of several blocks with 6 floors.
Depending on the final panel window sizes thermal average thermal transmittance (U-) values of an entire façade can be realized in the range of 0.22 to 0.25 W/(m2·K) with an insulation thickness of 150 mm and an overall panel thickness of 200 mm. Those are typical values for facades with a 200 to 300 mm EPS insulation layer.
The hygrothermal modelling showed that an optimal performance of the sandwich element system is reached in extreme moist environmental scenarios (e.g. Bergen, Norway or Gothenburg, Sweden) when a functional water repellent surface is provided to the reactive powder concrete. For dryer climates a functional water repellent surface is not improving thermal performance.

3.4 Life cycle assessment data

LCA and LCC was used as a tool for identifying potential strength and weaknesses concern-ing the environmental impact of the new products and methods. The Life cycle cost estima-tion (LCC) was used to establish preliminary costs of the SESBE solutions in comparison to commercially available products. However, the latter needs to be considered as an indication only since the project’s goal was to develop new material and systems, which can then be further exploited within production chains optimized in technology and costs by the respective companies involved in the project. Costs related to production and materials are therefore inevitably higher in costs since they were not optimized within the project and materials and components were manufactured on a small scale.
The LCA was performed with SESBE materials and panels as well as three reference panels consisting of standard reinforced concrete (load bearing and non-load bearing panels NLB) and two types of commercial insulation materials (rock wool RW and EPS) for benchmarking. The following impact factors were considered for the LCA:

These factors were evaluated for all the single materials used for the panels (sandwich and half panels) and benchmarked towards the three reference panels. For the evaluation the results were grouped into impact categories as outlined below.
The results for sandwich elements are as follows (whole life cycle).
The results in the graph shows, that the SESBE solution is spiking in three categories: ODP, TRPE and TNRPE. In the other categories the SESBE solutions are similar (AP, EP) or lower (GWP, POCP, ADP). A closer analysis into the single components shows that the aerogel used in the CLC insulation is contributing most to the energy consumption and ozone deple-tion potential (80 to 95 %). It contributes also majorly to the other impact categories but with lesser impact (55 to 75 %). The carbon fiber grid, another material with high embodied ener-gy, is actually not contributing to such a high extend (ca. 5 to 15 % of a sandwich element). As a consequence, CLC insulation without aerogel has for example a ca. 40 % lower GWP during the production state. This shows that for the production of Quartzene®) there is still room for improving the process towards a reduction of the environmental impact categories. Many of these factors are controlled by the amount of aerogel produced and upscaling the production will lead to a decrease of the environmental factors.

4 Demonstration and monitoring

Mock-up buildings were constructed on two locations, one in Spain and one in Poland. The mock-ups consist of constructions of 2.5 x 2.5 x 2.5 m3. The mock-ups in Poland consisted of a reference building a muck-up with half panels and a mock-up with full panels. The struc-tures are based on a concrete platform and have an insulated roof.
A monitoring system was developed for the project and consisted of outside and in the walls embedded T-RH sensors, analog sensor nodes and BMS sensor nodes. The sensors register outside and inside changes in relative humidity and temperature as well as the same date from within the walls. The BMS node is transferring the data via internet to the responsible partner for data acquisition. The data will give some information about the thermal perfor-mance but more important about how long it will take for drying of the panels. Since both sandwich and half panels consist of cement based materials a certain moisture from produc-tion is remaining. The data from the in-built sensors will give an indication about the drying process. Monitoring is still ongoing. The data acquisition in Spain will last until April, the one in Poland until end of the year.

Potential Impact:

- Made aware new types of cement based multi functional cement based materials for facade applications: Thinner, lighter and a good thermal performance
- Developed new mineral based and highly effective insulation material
- Provided opportunities for participating industries to expand their knowledge and increase their marked competition
- Initiated material and component developments, which can be further developed to functional building products


Activities of the project can be found on the public website where all relevant results are combined. Besides the websites flyers and a poster were designed.
So far, the project has resulted in the following publications (including theses):
Stefanov, B., 2015. Photocatalytic TiO2 thin films for air cleaning. Effect of facet orientation, chemical functionalization, and reaction conditions. Uppsala University.
Williams Portal, N., 2015. Usability of Textile Reinforced Concrete: Structural Performance, Durability and Sustainability. Ph.D. thesis, Chalmers University of Technology.
Andersson, C., Mihajlovic, D., 2013. Development of innovative inorganic insulation material. Bachelor thesis, Högskolan i Borås. (in Swedish)
Nasiri, B., Oliva Rivera, A., 2015. Hydrophobic impregnation of concrete. Bachelor thesis, Högskolan i Borås. (in Swedish)
Williams Portal, N., Flansbjer, M., Tammo, K., Malaga, K., 2014. Alkali resistance of textile reinforce-ment for concrete façade panels, in: XII Nordic Concrete Research Symposia. Norsk Betong-förening, Reykjavik, Island, pp. 61–64.
Svensson, R., Försth, M., 2015. Low emissivity surfaces for improved fire performance, in: Fire and Materials 2015. Interscience Communications, San Francisco, USA, pp. 464–477.
Mueller, U., Williams Portal, N., Chozas, V., Flansbjer, M., Larraza, I., Malaga, K., da Silva, N., 2015. Reactive powder concrete for facade elements – A sustainable approach, in: VII International Congress on Architectural Envelopes. San Sebastian, Spain.
Flansbjer, M., Honfi, D., Mueller, U., Wlasak, L., Williams Portal, N.L. Edgar, J.-O. Larraza, I., 2015. Structural behavior of RPC sandwich façade elements with GFRP connectors, in: VII Interna-tional Congress on Architectural Envelopes. San Sebastian, Spain.
da Silva, N., Mueller, U., Malaga, K., Hallingberg, P., Cederquist, C., 2015. Foam concrete-aerogel composite for thermal insulation in lightweight sandwich facade elements, in: Concrete 2015. pp. 1355–1362.
Chozas, V., Larraza, I., Vera-Agullo, J., Williams Portal, N., Mueller, U., da Silva, N., Flansbjer, M., 2015. Synthesis and Characterization of Reactive Powder Concrete for its Application on Thermal Insulation Panels. IOP Conference Series: Materials Science and Engineering 96.
Flansbjer, M., Honfi, D., Vennetti, D., Williams Portal, N., Mueller, U., Własak, L., 2016. Structural concept of novel RPC sandwich façade elements with GFRP connectors, in: 19th IABSE Congress. Stockholm, Sweden (forthcoming).
Österlund, L., Topalian, Z., 2014. Photocatalytic oxide films in the built environment. Journal of Phys-ics: Conference Series 559, 1–9.
Mueller, U., Williams Portal, N., Chozas, V., Flansbjer, M., Larazza, I., da Silva, N., Malaga, K., 2016. Reactive powder concrete for façade elements – A sustainable approach. Journal of Facade Design and Engineering 4, 53–66.
Flansbjer, M., Honfi, D., Vennetti, D., Mueller, U., Williams Portal, N., Wlasak, L., 2016. Structural performance of GFRP connectors in composite sandwich facade elements. Journal of Facade Design and Engineering 4, 35–52.
Flansbjer, M., Williams Portal, N., Wlasak, L., Mueller, U., 2016. Structural Concept of Novel RPC Sandwich Façade Elements with GFRP Connectors. In: 19th IABSE Congress. Stockholm, Sweden.
Al-Ayish, N., Mueller, U., Malaga, K., Gudmundsson, K., 2017. Life cycle assessment of façade solu-tions made of durable reactive powder concrete. In: 14th International Conference on Durability of Building Materials and Components. Ghent, Belgium.
Mueller, U., Williams Portal, N., Flansbjer, M., Malaga, K., 2017. Textile Reinforced Reactive Powder Concrete and its Application for Facades. In: HPC-CIC Tromsö.

The products developed were grouped in key exploitable results and will be further exploited by the partners.

Besides numerous conferences and national events SESBE results were presented in a final SESBE workshop, located in Madrid, Spain in Nov. 2016.

List of Websites:
Urs Mueller,