Sustainable building solutions with new generation autoclaved aerated concrete panel applications
Publish Time: 2020-10-14 Origin: Site
Abstract
Until now, autoclaved aerated concrete (AAC) was widely used in the construction industry mainly as a relatively simple (commodity) wall building material. The need and regulatory pressure for green, energy neutral buildings for residential housing and nonresidential constructions is becoming stronger every day. Consequently, we must challenge our construction designs and way of building to deal with increasing regulations, climatic and seismic conditions around world's geographical areas. This article presents new generation panel construction methods and a realized case study for a passive residential housing project designed with mid‐size modular AAC panels. The role and importance of this building method, applied with light‐ and heavy‐reinforcement panels, is also highlighted. The structural AAC panel design will be complemented and finished with autoclaved lightweight concrete (ALC) blocks, drywall sheets, and AAC partition panels. This partnership of building materials with installation integration at early stage of the construction process results in excellent insulation, efficient building, and supports HVAC.
Table of Content
Lego-Izing the construction: a new concept of modular building
Example 1. Fully energy neutral construction: A "Farm House" in the Netherlands
Example 2. Energy efficient construction: A "Residential House" in the Netherlands
Example 3. Energy efficient construction: A "Residential House" in the Netherlands
1 INTRODUCTION
The discussion topic of "Sustainable building solutions" or "Green building" is gaining more and more traction and importance in many countries through all layers of the society. It is not anymore a trend spoken of in developed building markets like Europe, USA, and Japan, but sustainable building has become a necessity on a global scale with countries like China, Argentina, Mexico, South Africa actively pursuing to build "greener" supported by regulatory changes to the local construction standards.
Why is sustainable building (green building) relevant and what does it bring us? Essentially, sustainable building is based on three key pillars: (1) environmental benefits, (2) economic benefits, (3) social benefits. Figure 1 illustrates these three areas of sustainability and their drivers.
Figure 1 Three pillars for sustainable building
1.1. But what exactly makes a building “green” or sustainable?
A sustainable building is a building that, in its design, construction, and operation, creates a positive impact on our climate and natural environment. Green buildings preserve precious natural resources and improve our quality of life. There are many features that can make a building "green." Some of the key features, among others, include efficient use of energy, water, and other resources.
Use of renewable energy, such as solar energy.
Pollution and waste reduction measures, and the enabling of reuse and recycling.
Good indoor environmental air quality.
Use of materials that are nontoxic, ethical, and sustainable.
Consideration of the environment in design, construction, and operation.
Consideration of the quality of life of occupants in design, construction, and operation.
A design that enables adaptation to a changing environment.
A design that makes a building future proof, short term and long term.
Taking into consideration the dynamics of the above features, one can conclude that green building requires a "Total Approach" that considers each component and element of a building, in relationship to the whole building picture, along with the impact on the environment, society, and economics around it. This "Total Approach" is rather complex, which requires architects, designers, engineers, suppliers, and, last but not least, product manufacturers to think creatively using systems integration throughout their product portfolio. Due to its key physical properties, autoclaved aerated concrete (AAC) is already in the frontline for adding value to the green building concept. Any building can be a green building, whether it is a residential house, factory, hotel, school, office, hospital, or any other type of structure, provided it includes features as listed above. Also in this perspective, more than several decades ago the "Passive House" or "Energy Neutral House" was born. Quick changing climate conditions and global warming force us to take responsibility for our planet and the children of the future. There are several technology toolkits and assessment methodologies that can help designers, suppliers, and builders with energy neutral building (PHPP, Passive House Planning Package, BREEAM, Design PH).
2 TRANSITIONS IN THE BUILDING MARKET
In the classic system, the client/stakeholder in the building industry specifies what he/she likes to have. Therefore, it is or was a capacity requirement in a capacity market. The contractors have to buy this capacity from distributors or product manufacturers. The main (principal) contractor is made responsible for the compliance of the specifications even if the building functionality is not good or wrong. Following this assumption, the main contractor is then subcontracting all or part of the work or disciplines to subcontractors. Subcontractors are responsible for their activities but not for the whole that sounds logical. Down in the chain, we see the material suppliers who supply to subcontractors or to the main contractor. Most of the AAC producers are acting in this area. Their responsibility goes up to the building site. Third parties do the control and inspections on the materials supplied.
Due to the increasing complexity, limited know‐how, and high risk for the client/stakeholder, you see that public clients, followed by private clients, withdraw from this construction model and tried to find a new model called "D&C" (Design and Contract). This means that the capacity market gets a transition to a process market. In such cases, the main contractor is responsible for the design and realization, sometimes supplemented with finance and maintenance for 10–30 years. Clients try to get their sureties by very extensive legal and costly conditions. In cases where deviations arise, high cost for legal procedures will arise and can take many years. In most cases, there are no winners and external parties, such as independent consultants and lawyers, create extra high cost for “bleeding” (cost bearing) parties.
This transition to a process market looks at the first instance defendable; however, everybody becomes afraid for everybody. Therefore, the innovation drive in building was and is often negatively affected. An additional circumstance was the crises with lower building activity and building materials demand. Most of the AAC suppliers are still in the lower area of the supply chain, offering commodity blocks.
In the last years, we could recognize a need for a new market transition to a Product Market. Several countries inside and outside the EU have problems with fulfilling their need for residential and nonresidential housing volume. Shortage of skilled people, building materials, and civil contractors is delaying projects severely. The houses we built 10 years ago are not the houses from today anymore and older housing has to be renovated drastically to comply with newer building and emissions regulations. The climate target has a deep‐rooted effect on the total world of building. Clients, in combination with users and consultants seeking solutions, start talking and cooperating with main suppliers, regulation makers, and suppliers in the building industry as in the car industry. The distance between users (clients) and products (manufacturers) is and will be reduced. Product manufacturers are experts of their products and can integrate quickly with other products and component suppliers. The product supplier will become a system supplier with a serious innovation power. He/she will manufacture the pieces in his/her plant and install on site with a high proven repetitive character. The pie slice for installation services and components has grown considerably up to 30–45% of the building cost over the past years. Therefore, you see a trend in several projects where installation companies take the role as the main supplier.
In this field of transition from Capacity Market to Product Market, we see an important role for the AAC industry. As a loadbearing material with several physical key properties with regard to green building, the chances and challenges are unlimited. Figure 2 illustrates the change in markets from Capacity to Product.
Figure 2 From a capacity market to a product market approach
3 ENERGY NEUTRAL BUILDING AND DESIGN
Different countries and regions have a wide variety of characteristics that determine the building culture such as specific climatic conditions; geological factors; culture and traditions; building types; and a wide‐ranging environmental, economic, and social priorities. All with an approach heading to the “Passive House” or energy neutral building.
Therefore, passive house building is the standard solution for our climate targets. It is an approach, a method rather than a building style, that is not the one and only solution. Specific solutions for a Passive House have to be adapted to the country's climate, functionality, and the program of wishes from developers or end users. Figure 3 illustrates the key areas to explore when assessing the “building design” and its operation for energy neutral building. We mention some of the areas: (1) energy efficiency and water management, (2) indoor air quality, (3) health and comfort, (4) safety, and (5) materials.
3.1. The most logical approach
The energy required to achieve an energy neutral house, heating/cooling is 15 kWh/m2 and for an average house, this sums to a total of 1500 kWh per year (150 m3 natural gas/150 liters of oil per year).
Regulations in the EU, and also in other continents, are quickly moving in this direction to fulfill our climate targets. An extra complication in the Netherlands is, for instance, to substitute the usage of local natural gas as soon as possible. Exploring gas in the north of the country is seriously leading to earth quakes and the Dutch government is facing a tremendous pressure from the society to find alternative solutions to reduce the consumption of natural gas. Therefore, new houses have to be refrained from local natural gas by 2020. The energy neutral building approach directly affects the whole chain of the building industry. This is not a matter of building material alone anymore and requires a total integrated approach between players in the supply chain.
Integration ( I) of energy ( E) and material performance ( M) of buildings:Part E of the equation stands for energy and focuses on all components for water, HVAC as well as installation services. The other part M is related to the material performance as well as assembly services. The importance of integrating the material components and installation services becomes suddenly much closer and a necessity with energy neutral building compared to building in the past. As mentioned before, this process has a significant influence on the eventual building material (component) supplier.
The application of a heat pump will neutralize most of the energy coming from the environment. The newest generation heat pumps can work very efficiently with a coefficient of performance (COP) higher than 5, which means that with only 2 kWh of external energy, we produce 10 kWh of heat to bring into our new generation houses and can be used for heating and warm/hot tap water consumption. To give a realistic impression, we show in Figure 4 three types of heat pump applications that can be used for nearly or complete energy neutral housing.
In a Passive House, the thermal comfort can be provided by post‐heating or post‐cooling of the fresh air flow that is required for good indoor air quality. This is a pure functional definition without any numerical values and is valid across all climates. Traditionally, ventilation is achieved by air leaks, air ventilator, or opening windows. However, in a Passive House, the ventilation heat recovery system provides sufficient fresh clean air to all habitable rooms while exhausted used stale air is brought outside.
The heat from the leaving stale inside air is taken out by a heat exchanger and brought to the new fresh incoming air. With an enthalpy changer, the latent energy from the stale air is brought back to the fresh ingoing air again. So, it becomes an energy recovery ventilation (ERV) system. This is another important energy saver that can go up to 90% of the ventilation heat loss.
Airtight housing structures prevent moist indoor air from leaking through the fabric (walls–roof–windows) of the building. An airtight building is therefore an essential factor in energy neutral housing. Airtight building in combination with a proper installation of heat pumps and energy recovery ventilation (ERV) brings passive building already into shape.
However, the most important part of an energy neutral house is the "shell" or, also called, "the building envelope." The heat resistance and thermal capacity from floors, walls, windows, and roofs determine the real value of sustainable building. Additional investments in PV panels (Solar), wind power, and or installing bigger heat pumps makes a building attractive by reducing or avoiding the use of fossil energy.
The shell of a building is the part that comes from the building material sector. AAC can play a very important role in this due to its unique properties. Furthermore, its user‐friendliness makes AAC a highly valued "partner" for the Passive Housing installation services branch. The ease and flexibility of the product to install plumbing, electricity, components, and installations is a big support to reduce time in construction. In order to use AAC as a building system for the envelope of the building, it is therefore of great importance to deeply understand the installation process and systems such that joint standardized solutions can be developed and delivered.
4 INTEGRATION OF BUILDING MATERIALS
It is clear that there is no single building material that has all the physical properties to meet today's and future design dynamics and building requirements. Although the design dynamics with AAC panels have come very far, houses will always consist of a composition of different materials. It is this combination of building materials that must ensure that a building meets the promised and expected quality. For this reason, materials in the construction process have to integrate with each other (Figure 5). Several building materials overlap each other in properties and can be used in the same area of applications. This is an interesting point. In such cases, it comes to choices of the client, architect, consultant, and sometimes even the contractor. Tradition, availability, relationship, experience, and price are the key decision drivers in this process. With the new way of green building, the playing field and decision‐making forces will be drastically changed. Now it comes to the party or supplier who offers the best solution or system to the market, which is a combination of sustainable design and materials together. The winners in this new playing field will be the ones offering an integrated product acceptance and positioning themselves as an innovative sustainable "system supplier" or "system integrator."
4.1 Prefabricated walls
AAC as a lightweight material, with excellent thermal, fire, and acoustic properties. It is a key material to take a leading role for cost effective and versatile new green building systems. Already for some years, suppliers of different materials tried to find market openings for ready walls, roofs, or even complete houses built in an industrial environment. These elements are built around structures from steel, concrete, timber, or carbon fibers in latest years. They bring it to site with heavy special transport and position, assemble it with big cranes in the building (Figure 6).
This system certainly works and is successful in most cases where new multiple houses in one or two levels are built. However, it is complicated for the cities and often not applicable in the renovation market. These manufacturers and suppliers are already integrating with other building materials to come to the desired, specified element‐based products. The large size and heavy weight of these elements, in combination with the high RC value requirement (between 6 and 10) have created a difficult hurdle. Transportation and installation are expensive and the "ready walls" decrease flexibility where changes/additional customer requirements are seriously disturbing the construction process. Until today, prefab masonry AAC walls play a modest role in most building markets. Although this application has already existed for over 25 years, it has varying success. The system is still going through trials and assembly improvements in different areas. Prefab AAC walls are still based on masonry blocks that are stacked together to preassemble walls in special frames (cassettes) in an industrial environment and thereafter brought to site. The air tightness and cold bridges are difficult areas to overcome. The solution is still far away from complete ready walls, prefabricated facades, and roofs in the line of green building.
4.2 Innovating the traditional AAC market with new system applications
We quote a well‐known saying from Prof. Klaus Schwab, Executive Chairman of the World Economic Forum, "In the new world, it is not the big fish which eats the small fish, it's the fast fish which eats the slow fish." Has the AAC industry already taken advantage of this building shift from supplier to system integrator to meet the new generation building requirements? In most European countries, the building method is still very traditional and based on a block stacking method with dry mortar. But to become competitive in the world of tomorrow, the industry needs to find rapid ways to turn architectural ideas into economically feasible, faster, and more cost effective than ever before. Fortunately, there are some innovative applications coming from new players to the market using an integrated combination of building materials such as wood framing, profiled steel sheet in combination with insulation products, and AAC panels. Steel offers the strength in a construction, and reinforcement in AAC panels will offer easy lightweight manageable strong elements. Insulation materials such as mineral wool, polyisocyanurate (PIR), EPS, or super lightweight AAC (SLAAC) will finish it to easy sizable wall, roof, floor, and partitioning thicknesses with the required properties.
Cold formed high strength steel, known as CFS, is a rapidly growing structural building material in several continents. It is cold formed from sheet metal strip on coil to precise lightweight construction profiles. When assembled, as a skeleton, it forms a strong stable light construction suitable for harsh weather conditions as hurricanes as well as for seismic zones (Figures 7 and 8). When combining CFS with AAC panels, we create a new innovative building system called “Frame‐Crete.” The Frame‐Crete system uses relatively thin reinforced (RIF) mid‐size AAC panels between 40 and 150 mm in combination with CFS that makes it a strong and stiff residential shell for buildings up to four levels. The very thin joints are filled with a sealant and a silicate paint. As a rule of thumb, the fire resistance of AAC cladding is 1 hr per 25 mm wall thickness, making the Frame‐Crete solution a much safer and sustainable building system than the drywall‐based cladding that is widely incorporated in the North American building culture. The ease of installation comes close to the wood installers. Fasteners like screws and clips are well accepted by AAC and the steel.
Mid‐size RIF AAC panels can also be perfectly used for exterior, interior, boundary, and partition walls. For roofing applications, the AAC panels are applied with a double RIF cage in various sizes from 75 to 150 mm.
5 LEGO‐IZING THE CONSTRUCTION: A NEW CONCEPT OF MODULAR BUILDING
Imagine that all relationships between the building elements were easy, manageable, and parametrically fixed in a digital model. Then it would be possible to mount and assemble it in every hull or shell for a building. Also, they would be dismountable and reusable. That is the future. You can compare it with termite mounds. They are sometimes called the perfect architects and builders of Mother Nature (Figures 9 and 10).
The termites build standard structures with standard elements and their saliva impressive mounds or buildings. It is an approach we can follow with building materials.
A construction site can be understood as a system. This system consists of elements that have a mutual relationship. The elements create due to its relationship a building construction. The relations between the elements give the construction a structure (Figure 11). A building construction brings all the elements back to a relatively high standardized product so that it together forms a system and a solution for sustainable building 2.
With such an approach, we can step into an evolutionary way of building, which means small innovative steps forward with a repetitive way of building. The experience is going from project to project; lower risks and limited learning curves are the results. Also, the installation services such as plumbing, electrics, HVAC, and data are important elements or components for sustainable housing and must have close relations in such a system. This means that element suppliers need to have full understanding of installation services and vice versa. In other words, it is necessary for an AAC supplier to understand the other elements and advise how to integrate or even supply its own elements. Some key elements for AAC are steel, timber, concrete, and fasteners, followed by insulation and installation services. An important precondition is that the dimensional sizes and weight are easily manageable with one or two people. Furthermore, the ease of working will offer an extra flexibility. In this way, the project‐based product individualization stops, and standardized products go to site and which can be quickly installed with the help of partners for steel, wood, insulation, and installation services. A realistic request from a client could be: “Can you design, deliver and install a complete building with detailed heating, cooling and ventilation plan for our building with your system?”
5.1 Building information modelling as a supporting tool
Architecture has been undergoing a radical transformation since we have computers and related software in 2D and nowadays in 3D. In the actual building industry, the purpose of a building information modelling (BIM) tool is to make the fragmented chain workable as an interconnected system. A 5D modeling system must secure that building materials will have a precise fit (3D), planning from activities and its requested timeline (4D) as well as cost sharing in quantities (5D). BIM is in its basics a simple idea and often compared with the car industry: A digital model of a building that everyone—architect, client, suppliers, builders, inspectors—can work on. The technology of BIM is more about the process of building than product or elements itself. The availability of digital information from all parties involved in this is the key. It allows for a full digital build before the actual construction is started. That brings the various phases of a project closer to each other, which will result in better designs and full clarity during construction and even maintenance (Figure 12). Furthermore, it enhances the learning curve of all parties involved. Repetitive and proven methods will speed up future design and construction processes considerably.
Connected to virtual reality designers, clients can enter their buildings before they even put one spade in the ground. This is a good thing as it brings promises and expectations closer to each other. It also limits any unwanted surprises later in the project.
BIM could bridge the gap between the designers and the real world of products, systems, and people who have to make it happen physically. On the other side, a digital build is inherently linked to the products and elements that are available on the market. You can only play with what you have. Therefore, it is essential to include all details of a supplier's portfolio into a BIM package, especially including "mid‐size" RIF panels in the AAC industry. Among others, this will show the versatile application of these panels as well as flexibility in design and a significant reduction in construction time.
5.2 Mid‐size AAC panels used as Lego‐ized construction
Mid‐size AAC panels offer a wide opportunity to the new generation of modular construction or Lego‐ized building. By combining AAC panels with other building elements, such as reinforcement steel, steel framing, timber framing, and concrete framing, it can cover a substantial part of the entire integrated system for residential, nonresidential, and high‐rise. In fact, this building system can be seen as a Lego box with highly standardized panel elements (Figure 13).
In Europe, we still see this modular AAC panel system as "new," as we often stick to our traditional building culture, with masonry in cavity and monolithic walls. The reality is that in several countries around the world, this modular panel building system is acquiring more market share successfully, for example, Japan, Australia, and even South East Asia and China are moving in the same direction of using AAC panels for modular applications. Mid‐size panels as a masonry system are used for partitioning and wall applications.
6 A DUTCH CASE STUDY OF SUSTAINABLE HOUSING DESIGNS
The following case study provides a grasp of the research program with the objective to examine the "as‐is" situation in the Netherlands in relation to green and sustainable building using AAC panels as the main building system. Figures 14-19 illustrate several fully energy neutral designs as per the revised building code and passive housing requirements by 2020. Although the outside appearance of these buildings has been adapted to the local regulations and culture, the underlying building system is mainly based on a modular application of AAC panels. Even though AAC panels are very much used in the Netherlands, the integrated application of the modular AAC panel system is still at the beginning of its development and likely to gain market share due to the shift in the building market as explained earlier in this article.
Example 1: Fully energy neutral construction: A “Farm House” in the Netherlands
Design specifications:Modular AAC panel system (combination of reinforced wall, floor, roof, and partition panels)
Supporting element relations: Steel frame, PIR insulation panels, ceramic brick outside, triple glass
Volume: 1.450 m3
Fully energy neutral construction as per the Dutch building code 2020 for passive housing
Airtight test qv 10 ≤ 0.15 l/s ⋅m2
Energy performance coefficient (EPC) value: 0.0
HVAC: Geothermal heating and active cooling applied (COP 5,3)
Ventilation system: Full heat recovery ventilation
Integrated solar system: 24 panels installed with a 300 Wp
Example 2: Energy efficient construction: A “Residential House” in the Netherlands
Design specifications:Combined integrated building system with steel frame, AAC reinforced panels, blocks, and wood
Supporting element relations: Steel frame, AAC floor panels, PIR insulation roof panels, ceramic brick outside, and HR++ glass
Volume: 750 m3
Energy efficient house (not fully neutral) as per the Dutch building code 2020 for passive housing
Airtightness test qv 10 ≤ 0.4 l/s⋅m2
EPC value: 0.4
HVAC: Gas fired low temperature heating/boiler
Ventilation: Mechanical ventilation (not full heat recovery system)
Integrated solar system: 12 panels installed with a 300 Wp
Example 3: Energy efficient construction: A “Residential House” in the Netherlands
Design specifications:Modular AAC building system (combination of thick monolithic blocks of 480 mm with λ = 0.08 for the walls and reinforced floor and roof panels)
Supporting element relations: Steel frame, PIR insulation panels, and triple glass
Energy efficient house (not fully neutral) as per the Dutch building code 2020 for passive housing
Volume: 700 m3
Airtightness test qv 10 ≤ 0.6 l/s⋅m2
EPC value: 0.4
HVAC: Geothermal heating and active cooling applied (COP 4.5)
Ventilation system: Full heat recovery ventilation
Integrated solar system: 72 panels installed with a 120 Wp
7 CONCLUSIONS
There is no doubt that the current climate changes will continue to have a strong impact on the future the way we build and the speed and requirement for "green" construction. In the EU, buildings account for the largest share of total final energy consumption (around 40%) and produce about 35% of all greenhouse emissions. Efficiency improvements for new and existing buildings and renovations have the highest priority. According to the EPBD, all new buildings shall be nearly zero‐energy buildings by December 31, 2020 and 2 years earlier for buildings occupied and owned by public authorities 3.
This, fortunately, drives the change in culture toward a more sustainable and energy efficient standard. The construction sector plays an important role in the delivery of the EU's goals for sustainable energy efficient buildings. It has a direct impact on construction products including the application with AAC. Large developers and contractors for both the public and private sector are strongly committed to find solutions to meet the close‐by future regulations. Consequently, the traditional triangle relation between customer, architect, and contractor as the playing field is changing away from the traditional capacity‐driven market. Building material producers and suppliers are now asked to provide integrated solutions, rather than a stand‐alone product. They can develop, create, and install the elements that are needed now and in the near future. These integrated material systems, offered by the new suppliers, generate the value to the end user and meet the new way of green and efficient building for the world of tomorrow.
There is no single building material that carries all characteristics to fulfill the requirements for sustainable building. The one who adopts quickly by integrating different material elements into a building system solution is the player who can add most value to the market requirements and therefore will achieve a large growth potential. In this model, suppliers will become system integrators and can offer full solutions, including installation and building services to the end customer.
AAC as a material has many valuable and powerful properties to be used as a key element for building systems of the future. In combination with steel frame, reinforcement, wood, and CFS (Frame‐Crete), one can build rapidly a shell or a building envelope according to the customer requirements. AAC panels are light and can be transported easily to building sites, realizing short delivery times. Installers can easily install up to 50 m2 per day. BIM will play a very important role to reduce cost upfront and increase efficiency in modular construction.
The case study and practical research on several green constructions in the Netherlands have shown us that local regulations are not fully in line yet with national or European laws on green and energy efficient buildings. Furthermore, we have seen that the combined building system of integrated AAC panel elements with steel frame can be very efficient and provides an excellent green performance to meet the new regulations for the future. Furthermore, this construction method is relatively easy and very fast, also making it a very economically attractive solution.
For the house in Example 1, the choice was made to build with RIF AAC (thin joint masonry) with reinforcement and extra insulation connected to a lightweight steel frame by means of fasteners. Dilations and thermal bridges were well taken into account in the design and fasteners were also conceived, made, and assembled beforehand. Airtight building was relatively simple and gave a better result than expected. The thermal capacity of the AAC roofs came out as indispensable and a must for comfort. Using of SUPER SMOOTH AAC panel elements, we significantly reduced the interior finishing cost of the houses by an average of 30%. Total building time for the envelope was considerably lower than expected.
Mid‐size AAC panels can be used as the key Lego piece in the integrated building material element. Due to its ease of use, speed, flexibility, and sustainability properties, it can have a fundamental role in the modular building systems of tomorrow.