Modern rammed earth construction in China
Abstract:
Although China has one of the longest rammed earth histories of any country in the world, the traditional building method has virtually died out and has even been made illegal. However, the explosion in construction combined with the lack of natural resources is creating renewed interest for rammed earth, in particular modern rammed earth. This chapter will explore the challenges and opportunities that face the growth of modern rammed earth construction in China. It will also touch on the selection and engineering of local earth, construction techniques and future trends. As the field begins to see renewed interest, it is turning away from its roots and looking abroad for technical know-how. Without a doubt, if the opportunities come to outweigh the challenges, China could well become the global source of innovation for rammed earth construction.
24.1 Introduction
From the famous communal Hakka round houses in Fujian to the desert portions of the Great Wall in Gansu province, passing by the hundreds of thousands of traditional structures that still dot the countryside, rammed earth construction needs no introduction in China (see Fig. 24.1). However, in its traditional form it is artisanal, largely unpredictable and more akin to cooking than building science, with mixes that usually contain egg whites, brown sugar and sticky rice. It is viewed as a technique of the past and consequently has been relegated to the annals of history, particularly as the country continues its giant shift to implementing science-based standards.
The latter has led China to favor reinforced concrete and structural steel. However, the ferocity and scale of development in China has placed enormous pressure on these natural resources globally, as well as local energy sources. With much development still needing to be done, China has begun to look into systems that use renewable, indigenous resources. The choices are few, and by far the most prominent and promising is inorganic earth.
24.2 Challenges for modern rammed earth construction in China
Virtually all of the traditional rammed earth that has survived the test of time is found in areas that are mountainous and/or dry. In other words, they are found in areas of low population density. For example, the Hakka houses are found in the isolated Wuyi mountains, which is entirely due to the quality of the soil in these areas. The Wuyi mountains are dominated by craton and punctuated by zones of granite (National Geological Archives of China, China Geological survey, 2002). Here, the relatively sharp and strong base soil allows for the creation of strong walls. In turn, the desert portions of the Great Wall are characterized by zones of granulite, greenschist and magmatic granite. Not as sharp or strong as in other locations, these soils have been adequate and the resulting walls have endured in large part due to the dryness of the areas they were built in.
By contrast, a geographic look at population density (World Trade Press, China Population, 2007) shows that China’s great cities are found in some of the most challenging areas to build with rammed earth: large alluvial basins with round, weak and highly segregated soil types. Without a doubt, the greatest challenge for China is to achieve strength from the soils that are local to the great urban centers.
The second biggest challenge is legal: the lack of a building code for modern rammed earth. Unlike other countries, China does not have a provision in the code for equivalencies. The code must first be written for a particular material at the national level before that material can be used. Not only is this a time-and cost-intensive process, it also requires that the government be willing to consider the particular material being submitted. In the interim it is at times possible – albeit very difficult – to work at a district level, which at the very least requires that the laboratory crush test reports are documented and that the structural drawings are stamped by a local design Institute. It should also be noted that if the owner of the building does not require a title deed, the building need not provide any of the above. This is often the case for buildings of low value, temporary nature and/or landscape walls. It is worth noting that with rammed earth gaining in popularity as an alternative construction method, the above-mentioned structures are becoming the source of local experimentation. Given the absence of a submittal process or the need to adhere to quality standards, these structures contribute to another significant challenge: layering a new understanding of rammed earth over a traditional one that is deeply rooted into China’s cultural history.
Everyone in China is familiar with rammed earth. This is both a blessing and a curse: whereas it takes very little time to introduce the concept to the average person, a lot of time is required to get beyond the traditional associations with rammed earth, particularly seeing as the strength and durability of its modern counterpart can be so radically different.
In the mind of the average Chinese person, traditional rammed earth washes away in the rain, can be eroded with one’s fingers, is uneven, impossible to clean, bug-ridden, limited to low-rise structures and is a method used by the poor in rural areas. Many Chinese still have memories of these structures, having grown up in them and being happy to have moved on. Typically the only positive quality that they remember is the ability of the walls to keep houses cool in summer and warm in winter. Their experience is obviously well founded: in virtually all cases the clay content is high (35% not being unusual, as per our own findings in crushing samples of local rammed earth from the Pearl River basin, the Yangtze River basin and the Moganshan area) and the walls often contain a large amount of organic material: from topsoil to bamboo and branches used as reinforcement, to eggs, brown sugar and glutinous rice thrown in as binders. Within this context, it is understandable that the initial reaction to building with rammed earth is not taken seriously or is viewed negatively. This reaction is further compounded by the government out-lawing traditional building techniques, including traditional rammed earth and traditional clay brick. The reasons for this are environmental: both methods contribute significantly to topsoil depletion as they require surface mining.
In terms of ‘earth’ content, most modern rammed earth methods avoid organic topsoil and are more similar to concrete than to traditional rammed earth. Hence, the above-mentioned laws do not apply. This is certainly true of the walls that we have been building, where the ‘earth’ is entirely inorganic and sourced from the same quarries as the aggregate used in concrete. However, lacking standards and a clear definition of modern rammed earth, and with the existence of modern projects that use traditional mixes and techniques, modern rammed earth will continue to be perceived as being illegal until standards are created and users are educated.
Soils can be carefully chosen, people can be educated, standards can be created and new laws can be passed, but one lasting challenge for China is that of air pollution. Although it affects all buildings – buildings that look 20–30 years old in China are often no older than 5–10 years old – it is a particularly significant problem with rammed earth.
Where acceptable limits are between 10 and 30 parts per million μg/m3, our own tests on micro-particulates have shown Shanghai to hover between 90 and 180 μg/m3, whereas Beijing often reaches and exceeds 250 μg/m3. These particulates are deposited onto buildings by wind and rain, resulting in gray, streaked walls within just a few months.
In areas of low air pollution, one of the key ecological advantages of modern rammed earth is that it is one of the few structural systems that does not require an outside finishing material such as tiles or paint. However, this feature is crippled by air pollution. The surface of modern rammed earth walls are porous and not easily cleaned, creating a need to consider adding an outside finish to the walls. So far, we have mitigated this issue by building large roof overhangs, however this is only a solution for low-rise structures.
The final great challenge is that of density. Globally, there is very little modern rammed earth construction that is higher than one or two storeys. As it currently undergoes the greatest urban migration in the history of humanity,11 China clearly has a need for high-density solutions. In other words, one-or two-storey structures are insignificant in this country, as are developments in low-strength, non-predictable, traditional rammed earth methods. Modern rammed earth can already attain strengths that make it suitable for mid-rise construction, but special forming and soil delivery techniques would need to be developed, while the energy used in moving so much mass vertically would have to be weighed against the benefits of modern rammed earth.
24.3 Opportunities for modern rammed earth construction in China
While the reality of diminishing natural resources is relatively new to most of the world, it is a reality that China has been bumping up against for hundreds of years. The country and its people have a long history of making marginal resources work for them. As we reach the limits of availability for energy and natural resources, and as their resulting costs continue to rise, it is simply a matter of time until the country turns its attention to modern rammed earth.
China is extremely cost conscious, and while this has been an almost insurmountable obstacle in the past, the stakes are beginning to even out. As the cost of conventional construction and operations continue to rise, the economics of higher performance systems are becoming more convincing, particularly when the added cost is marginal compared to other systems. This is particularly true for insulated rammed earth.
It is also significant to note that unlike North America and Europe, Chinese politicians emerge from science and engineering backgrounds, as opposed to law. Although this may seem trivial to the western reader, it is of significant importance as Chinese government officials are for more effective and proactive at recognizing the physical source of issues and evaluating the potential solutions. Their political structure also gives them the power to implement changes almost overnight. Moreover, if modern rammed earth is to make inroads in China it will have to be supported by an unshakeable scientific foundation: something that Chinese political leaders greatly value and prioritize.
In short, the combination of political structure, magnitude of construction that is left to take place and the double constraints of natural resources and energy, could set the stage for significant developments in China, which could then benefit the rest of the world. Examples include:
• The opportunity to develop competitive forming and delivery techniques for multi-storey buildings
• The opportunity to develop an economy for construction waste used to build rammed earth walls, eventually building walls with virtually no virgin material and yielding a Cradle-to-Cradle building system
• Leveraging the scale and speed of development to accelerate research in the field, from replacing cement in stabilized walls to additives for weather-proofing
• Developing high-performance hybrid systems designed to solve the challenges presented by modern high-performance buildings.
24.4 Approaches to material type and selection
As with most other areas in the world, the spread of traditional rammed earth and approaches to soil selection in China have been through trial and error. The term ‘Hakka’ derives from the word ‘guest’. The people who lent their name to the large multi-structures in the Fujian province serve as an example of how the system spread. As they moved from province to province they brought their earth building technique with them. In places where the soils couldn’t be formed or washed away in the rain after one season, the system never took root. In other areas where the soil was ‘just right’ the system endured for hundreds of years. Traditional rammed earth evolved as an art where soils with high clay contents were favored, particularly when they contained fragments of weathered gravel-sized rock. The old builders who still remember the traditional techniques also mention the preference for soils that contain sharp fragments rather than round ones.
For the most part, the new rammed earth projects in China have been inspired by Korean, Japanese, Australian and German techniques. While most forming techniques have been monolithic and modern in nature, the choice of soils has remained mostly traditional. In some cases, a percentage of cement was added as a stabilizer, but nonetheless, the selection of soils has been more of an art than a science. In most cases the walls are non-load-bearing. In all cases they are uninsulated. Our own interest in rammed earth was to create a system that used a scientific approach and hence could be predictable and quantifiable. It also needed to have high thermal performance not just in terms of the fly-wheel effect but also in terms of insulation. Without these qualities, modern rammed earth would not be possible to scale up in China and couldn’t have a significant impact. Further investigation led us to adopting the research and construction methodology developed by SIREWALL. SIREWALL is an insulated rammed earth system that has been developed with a strict scientific and quality control process that is critical to its application in China. It allowed us to begin adapting the process to China almost immediately, focusing on multi-storey construction and, most importantly, understanding local soils.
In simplified geographic terms, China consists of one large tilted plane sloping from the jagged Tibetan plateau in the west to the alluvial plains in the east. The historical center of the country, home to Xi’an and the terracotta warriors, lies on the world’s largest quaternary loess deposit. The Sichuan basin, home to Chengdu and Chongqing is alluvial and rests on unmetamorphosed strata, which is marginal for rammed earth construction due to its friable nature. The Sichuan basin is however surrounded by mountains while the unmetamorphosed strata lies on craton, which brings potential to the area. In the south, Guangzhou and Shenzhen fare somewhat better. Although they lie in the alluvial basin of the Pearl River, they border areas of greenschist and magmatic granite.
However, without a doubt, the most challenging area for rammed earth is in the east China alluvial plain, home to both the Yellow and Yangzi Rivers. Partially interrupted by the igneous Shandong peninsula, this zone spans the area from the south of Beijing all the way to Shanghai. Not only is it alluvial, it also consists of highly friable unmetamorphosed strata. In plain English, Shanghai is one of the most challenging areas in the world to build using rammed earth, and this is precisely where we have been doing most of our research.
In the words of the Chinese elders: there is no traditional rammed earth in Shanghai for a reason. However, we have come to realize that if we can build here, we can build anywhere. Working with alluvial soils leaves no room for error seeing as they make extremely poor material for rammed earth. Blending them with sharp aggregate can improve their strength, but only if the sharp aggregate is itself strong, which is not the case in the shanghai area.
Rivers are phenomenally effective at rounding off soil particles. After having been carried downstream for hundreds of kilometers the particles found in river deltas are almost perfectly spherical. One only need to imagine building a wall out of stacked marbles to understand that round particles do not make strong walls.
Rivers are also extremely effective at segregating particle sizes. Each particle size precipitates at the point at which it can no longer be carried by the speed of the water. Hence, river deltas are characterized by areas of pure sand, silt and clay. For example, at one of our sites 150 km upstream from the mouth of the Yangzi river, 85.8% of the river sand was 0.15 mm in diameter, as per our particle size distribution analyses, and was extremely well-rounded. On land, the strata immediately below the organic topsoil was composed of pure clay, 100% of which passed through the 0.075-mm sieve. In a world where sharp, well-graded soil is critical for creating strong walls, this was not good news. Furthermore, the local quarry produced a sedimentary stone that could be crushed between one’s fingers, and was consequently extremely high in fines. In a world where a wall can only be as strong as its weakest component, this was also not good news.
Engineering a wall in these conditions is extremely difficult. Blending soils to create a well-graded mix becomes absolutely critical and leaves no room for error. Relying on alluvial content only provides a narrow range of particles, typically 0.3 mm and below. Hence, one must rely mostly on quarried (crushed) content, supplemented by alluvial content where necessary. However, in an area of friable, unmetamorphosed strata, the science of grading soils becomes somewhat elusive as the ramming process partially pulverizes the soil and changes the percentage of particle sizes in the blend. For example, in another one of our projects (Moganshan, just outside of Hangzhou) we found a mix that contained 10% fines (clay and silt) became one that contained over 30% fines after ramming.
In the river conditions we found that a well-graded mix, compacted with a mechanical rammer could only achieve unconfined compressive strengths of about 1–2 MPa. No wonder the area had little to no history of rammed earth. Once stabilized with 10% cement, we still struggled to get the strength up to 11 MPa. Interestingly, the Moganshan area does have a history of rammed earth, being rammed sequentially upwards, block by block. Lime is added to the mix, with the final result being strong enough for a two-storey house, but weak enough to wear away with one’s fingers. The scientific approach to the local technique, which involved blending soils to optimize particle size distribution, using the sharpest particles available with fines limited to about 5% and 10% cement, ramming mechanically and having the samples properly cured (submerged in water), yielded samples of 15 MPa strength.
It has been enough of a struggle to obtain adequate strengths that if we were not building projects in different parts of the world, I would be led to believe that our approach is wrong. Particularly seeing as our SIREWALL counterparts in Canada and the US were obtaining strengths that rivaled and exceeded concrete with exactly the same technique. It is thus interesting to note that the exact same approach used in southern Sri Lanka yielded strengths of 28 MPa after only two weeks of curing. In this particular case, the parent rock was gneiss (mostly granitic), which is both very sharp and strong. Here, it is worth saying a few words about Sri Lanka. Almost the entire island consists of metamorphic rock, including gneisses, quartzite, granites and marbles (Cooray, 1984). Only the northern tip and north-western edge of the island are alluvial and lagoonal, consisting of clays, silts and sands. Furthermore, the Sri Lankan climate makes insulation virtually unnecessary. However, in the tropical plains area and coastal belt there is a definite need to protect walls from direct sunlight in order to avoid thermal gain and the resulting radiant heat that would be given off by the walls. In fact, the Sri Lankans refer to the necessity of ‘wetting’ traditional earth walls so that they may cool by evaporation. Albeit, they are mostly referring to earth walls consisting of wattle and daub techniques, or sun-baked clay bricks. Of course, wetting the walls is not something we would favor given the efflorescence that could occur.
Climactically, the area best suited for modern rammed earth is the Central Highlands, where daily temperatures swing from about 20°C during the day to 15°C at night (going as low as 5°C in some areas). Here, radiant heat given off by the walls at night would be very welcome. Truly, the combination of parent rock and climate make modern rammed earth the material of choice for this particular area.
At the time of writing, Sri Lanka has emerged from civil war and is entering a period of rapid growth, particularly in the field of hospitality and tourism. This will put a definite strain on natural resources and building materials. Although it is still too early to come to conclusions, Sri Lanka may well be ripe for rapid developments and innovation in the field of modern rammed earth.
Speaking broadly in terms of material selection, we have learned that a sharp, well-graded soil derived from a strong parent rock is key to achieving strength. Fines such as clay and silt should be kept below 10%, and preferably in the 5% range. The specification for water content has not changed in centuries, requiring just enough for a handful of earth to form a ball when compressed in one’s hand, and to shatter when dropped from waist height. Deviating from these five basic points creates mixes that rely increasingly on cement as the strengthening agent.
In this field, one of our primary goals is to eliminate the use of cement as a stabilizer from the blend. However, in areas such as the east China alluvial plain it is clear that using a binder is absolutely necessary. We have yet to find one that matches or exceeds the strength of cement while being benign for the environment.
Conversely, removing cement as a binder in an area like Sri Lanka should prove to be far more realistic. As mentioned above, the suitability of Sri Lankan soils and the resulting strength will allow us to obtain strengths of 10–12 MPa with far less cement. This opens the door of possibilities in terms of replacing cement with a lower strength binder.
Another key goal is to close the loop on the source of soil. Currently, the main source of inorganic soil comes from quarries, where rock is dynamited and crushed yielding coarse gravel, fine gravel and tailings. Rather than quarrying rock, waste concrete could be used as the source material, crushed to produce the same gravel-to-tailings soil gradient. In this way the ideal soil gradient could be directly produced as opposed to researched and blended, saving time, costs, transportation and enabling predictable results. However, for this to be possible, the supply chain would first need to be established.
The current state of demolition rubble is that it contains everything from plaster, brick, gypsum board and ceiling tiles, to pieces of cabinetry, posters and doll arms. In order to obtain clean material, the residual value of concrete rubble would have to be significant enough for demolition crews to first strip buildings down to the concrete structure and then demolish them. At the other end of the price spectrum, it is also obvious that the market price of concrete rubble could not exceed the price of local quarry material. Our preliminary research has shown that this could be possible on a per project basis, but is influenced heavily by local conditions such as the distance between the source material (be it quarry or rubble) and the construction site, the cost of the quarry material in the particular locality, etc. Of course, this presupposes that the quarry material is good. In areas such as shanghai, the price of concrete rubble could exceed that of quarry material on the basis of quality. Here, the market cap would be that of modern rammed earth vs. other structural solutions. The current cost of labor, cost of transportation and amount of construction currently taking place in China make sourcing waste rubble a potentially viable solution within the areas we have researched. This will be the subject of our next project. The initial demand will have to be generated on a per project basis, requiring us to locate demolition sites and negotiate prices for clean rubble. However, to serve as a long-term solution the obviousness of market direction should still be stated. In an expanding construction market such as China’s, the demand for waste material could outstrip the supply. In other words, in an expanding market, sourcing from waste material would not eliminate the need for quarrying.
The topic of sourcing waste material generates one more relevant thread: hybrid systems where modern rammed earth is but one of several components in a wall. Currently, modern rammed earth is still being used around the world in a very traditional assembly. While other structural materials such as steel, reinforced concrete, brick and wood have all evolved to become components of a total wall assembly, stabilized rammed earth (SRE) is still being used as a stand-alone material. This fact serves as a testimony to just how niche and new modern rammed earth is: unlike other materials, it has barely begun to include other system components in an effort to adapt to various climates and other constraints. Globally, SIREWALL is perhaps the only example of a modern rammed earth system that has begun to move along this path.
As modern rammed earth evolves to meet the needs of high-performance buildings around the world and as it enters the palette of more architects, developers and builders, it will evolve from being a stand-alone material to a system of components. It is just a matter of time before an architect in northern China specifies modern rammed earth as a structural material and interior finish, with 20–30 cm of insulation mounted to the outside, protected by external cladding.
One of the challenges of these new systems will be ensuring that they can be easily disassembled for recycling or reuse. For instance, the assembly mentioned above would require a modern rammed earth wall with a demountable substructure on the outside, insulation that can be easily stripped out and an exterior rain screen that can be unclipped. As modern rammed earth-related building systems begin to emerge, it will be critical that those who design these systems are thinking in reverse (in terms of disassembly) so that modern rammed earth does not follow the same path as brick, concrete, steel, stud frame, insulated masonry units, etc., which have evolved into hybrid systems that are almost impossible to disassemble cleanly.
24.5 Construction techniques and formwork
The traditional forming system in China consisted of sliding forms: essentially two wood side boards held together by through-pins and end panels. Earth was rammed into the resulting box, the panels taken down and reassembled alongside for the next block to be rammed in place. In this way, walls of any length and height could be rammed incrementally. Conversely, modern systems tend to be monolithic, with entire walls being formed at one time.
As mentioned above, our approach is founded on the Canadian SIREWALL system, where the formwork springs from the end-panels and is completely braced from the outside. In other words, long plywood side panels are horizontally supported by whalers spaced vertically every 300 mm. In turn, the horizontal whalers are supported by vertical end panels and vertical strong-backs if the distance between the end panels exceed 3 m. On the outside, the result is a forming system that also serves as scaffolding for the construction crew to climb up and down. On the inside, the result is a box that is unobstructed, which is ideal for running electrical conduits, rebar (steel reinforcement) and insulation (placed in the middle of the wall). The result is a monolithic wall with no vertical cold joints and, in many cases, no horizontal cold joints either. The monolithic system also creates a finer visual finish – an important consideration for a material if it is to become mainstream. As a side note on the quality of finish as related to form-ply, we have found that lower to mid-grade plywood produces a more consistent and nicer finish than high-grade laminated plywood. The ability of lower grade plywood to wick up a slight excess of moisture in the earth mix helps create a dry sandstone-like finish, as opposed to a smoother wet finish more akin to concrete.
Our challenge in China is that of forming multi-storey construction. These challenges include precision forming and bracing.
Precision forming is required because we use rammed earth as a final finish material, making the demands for forming more akin to fine finish structural concrete. Unlike regular structural concrete, which gets covered with a finish material, modern rammed earth leaves no room for error. Whereas these standards are fairly easy to attain at ground level, they become more difficult in multi-storey construction. This is mostly due to the external bracing.
In concrete multi-storey construction, formwork can be entirely braced from the inside. This is thanks to the horizontal ties that are used within the formwork. For our work we have opted not to use form ties for a number of reasons. One important reason is esthetics: a fine smooth surface appeals to a wider audience than one characterized by tie holes. Another reason is ease of assembly and workability: the use of form ties clutters up the space in the formwork and slows the ramming, particularly in combination with the central insulation plane.
However, our decision not to use form-ties does add constraints to the way we brace the formwork. Currently our forming and bracing techniques require one side of the formwork to be built up to full height, with the other side being raised as the layers of the wall get rammed into place. In a multi-storey building the ramming would happen from the inside, making the outside-facing portion of the formwork the full-height supporting one. Suddenly what is a simple proposition at ground level becomes a complex one several storeys up. On the one hand, climbing around the outside of a mid-or high-rise building to place, brace and remove formwork is a potentially dangerous and time-consuming proposition. On the other hand, the external formwork lacks a firm base to rest upon. It either requires supports that cantilever from the internal slab or requires an outside plinth to rest upon.
Without a doubt, multi-storey construction will require modular or pre-assembled form sections as well as external scaffolding. The impetus will be to do as much work as possible from the inside. Pre-assembled/modular forms where the actual spandrel panel, external horizontal and vertical bracing are monolithic would enable the outside facing formwork to be placed and cross-braced from the inside. However, this would not solve the greater issue of formwork removal. Once again, handling a heavy piece of formwork from the outside of a multi-storey building is a potentially dangerous proposition.
For this reason, scaffolding on the outside of the building will most likely be a necessity, either rising from the ground up or cantilevering from the finished floor slab. In China, both techniques are common for mid- and high-rise buildings.
A final proposition would be to mount and brace the outside facing formwork entirely from the inside, running it proud in all directions. This piece of formwork could be released and craned from above. This would potentially eliminate the need for scaffolding.
There are certainly other systems and methods that could be adapted from the world of reinforced concrete or that of SRE techniques that use form-ties. However, this research still remains to be done in China.
24.6 Case studies
This section is not meant to be an exhaustive study of cases built in China. Rather, it is intended to highlight the principal projects that have served as milestones in the introduction of modern rammed earth to China.
24.6.1 Split house, Commune by the Great Wall
This project, designed by Atelier Feichang Jianzhu (FCJZ) of Beijing, is the first project in China to use traditional rammed earth in modern architecture. Designed as part of the Commune by the Great Wall project and built in 2001, the architect’s motivation was to develop a modern building type that could return to the earth, thereby greatly reducing waste over the life of the entire building. The earth mix was traditional, for which the soil was sourced from the neighboring plot where another house was being built for the Commune. The earth mix was unstabilized and inspired mostly by a traditional Korean approach, which involved sieving the earth by shoveling it through a screen and then mixing it with lime. The walls were hand-tamped, 600 mm wide and reinforced laterally with raw linen laid between every few lifts. The project was unable to obtain code approval and have an engineer sign off on the earth as structure, so the final walls support only their own weight and serve as a rain-screen. The actual structure is composed of laminated wood beams and columns, crossed-braced by steel cables.
Overall, the project represents an important milestone towards China’s emerging interest in modern applications of the vernacular. At the time, the use of traditional techniques in a modern context was pioneering, and consequently the project enjoyed a significant amount of press. Unfortunately, this press was not successful in terms of creating a new market, or building acceptance for rammed earth. Its true success was in identifying the challenges that lay ahead of traditional rammed earth in terms of reaching modern requirements for performance, safety, quality control and scalability.
24.6.2 Cross waters eco-retreat, Huizhou
This project is better known for its use of structural bamboo than rammed earth. Similar to rammed earth, there is no section in the Chinese building code that allows for bamboo construction. Hence, without a doubt Australian architect Paul Pholeros must have faced significant challenges even in having his incredible bamboo structures implemented, let alone the rammed earth. Perhaps it is for this reason that the rammed earth walls in this project consist only of full-height, free-standing landscape walls that frame the entrance to the various houses within the retreat. In this setting, the architect did not need to obtain significant strengths nor did he need to pass the requirements of the code. Given that some of the locals were still familiar with traditional rammed earth, the approach in this case was simply to let the locals source the earth they normally would for this purpose and then stabilize it with a percentage of cement. Also, rather than building the walls incrementally with a sliding form, Australian forming techniques were introduced, thereby forming entire walls at a time. Although the scale is modest, it highlights a technique that is often used: that of a soil, which has been selected by trial and error and stabilized with cement. This represents something of a shot in the dark because, unless there is a particle size distribution analysis and the soil mix is well researched, the opportunity to optimize the strength of the walls, reduce the amount of cement and standardize quality cannot be attained. As neither code approval nor strength were of critical concern, the method used was evidently the simplest. However, in the interest of properly differentiating SRE from traditional rammed earth, the next evolutionary step would be to ensure that all walls, be they landscape or architectural, meet minimum standards for strength and durability.
24.6.3 River house eco-retreat, Zhangjiagang
This project evolved out of a client’s unusual and pioneering request: to build an experimental retreat that used the most environmentally responsible techniques. In order to achieve this, the client was willing to pay the cost of innovation for technologies that would be more expensive at the onset, as long as they had the possibility of being scalable and cost-effective thereafter. These requirements set the stage for stabilized and insulated rammed earth to enter China. Not only did the walls have to be built out of local non-toxic materials, they had to be extremely energy efficient, meet the compressive, shear and tensile strength requirements of modern structures, cost-competitive, equivalent to standard building methods in terms of construction time and ‘beautiful’. This was no small order, and getting there required a multi-step process, the first of which was bringing professionally developed SIREWALL techniques to China. At the time (2006), its main weakness was never having built multiple storeys of insulated rammed earth, nor having worked with alluvial soils – the challenges of which have already been discussed above.
A00 Architecture, the architects of the retreat, started by creating smaller opportunities to train their local builder: EMCC (from Einstein’s E = MC2, given the company’s particular interest in doing things no one else has). The first of these was Just Grapes, a wine bar located in downtown Shanghai and completed in 2006 (see Fig. 24.2). Although the walls for this project were non-load-bearing and used only as an interior finish, the learning curve was high. First off, the project was akin to building a ship in a bottle, given the very narrow and long proportions of the space, as well as the necessity to form entire walls at once. The local tampers had a side-mounted pressure valve that sprayed excess air and moisture, but also oil leaking from inside the shaft. This resulted in black oil stains on the interior of the formwork and subsequently on the walls. The crew also struggled with the appropriate water content, this being their first time. With a tendency for more water than less, many layers have a smoother, glossy look. On their first wall, the crew also struggled with the control of the surface finish, varying between very boney and perfectly distributed. This was the result of how they shoveled earth into the forms: if the earth was ‘thrown’ against the front side of the form work, the fines had a tendency to be projected out of the mix and against the finished side, while the larger pieces rolled out the back. This created a smooth finish. Conversely, if the earth was thrown against the back of the forms, the large particles rolled towards the finished side and the result was a boney finish. Also, attempting to achieve the smoothest possible finish, the plywood used for the formwork was faced with a black laminate, which heavily stained the earth walls. Finally, being the first project that used alluvial soil, about 15 different mixes needed to be calculated on paper, rammed and crushed in the lab before we achieved one that reached just over 6 MPa after two weeks – and this with the addition of 10% cement. Not great, but sufficient for our purposes.
The final project received awards and extensive press for beauty and design innovation. These were the first stabilized modern rammed earth walls in China.
A00 Architecture and EMCC went on to design and build [wi:]: a small free-standing test pavilion, which consisted of two parallel walls separated into six segments (see Fig. 24.3). Four of the segments were 6 m long, while two were 3 m long. All of them were 4 m tall and were used to test something slightly different.
The walls were all built using the same reusable formwork, including modular aluminum end panels into which whalers and spandrel panels could slot. The first wall served as the pilot, with a 9-MPa mix that included 10% cement. Part of the wall also included 0.2% crystalline admixture. Although the soil was mostly alluvial and almost identical to that of the wine store, the rounder mid-sized gravel that had been used previously was substituted for a quarried, sharper gravel. The first wall also used the same black forms as the wine store. At the time, the oil projected by the local tampers was believed to be solely responsible for staining the walls, and so the valve was covered with a gauze, acting as a filter. Finally, the 6-m length was only vertically braced at the ends and in the middle.
The wall took two days to form and ram. It was stripped on the third day. The wall was sprayed for curing and in order to accelerate efflorescence, simulating long-term exposure to rain, with the effect that the portion which contained the crystalline admixture fared marginally better. However, the efflorescence was very pronounced overall. Also, the black stains were still present on the wall meaning the tamper was not the culprit. It was only by the third wall that the plywood was identified as the problem. We formed half of the wall with the black plastic laminated plywood while the other half was formed with a cheaper and rougher unfaced plywood. The difference was astounding: the unfaced ply left the colors of the wall unaltered.
The third wall was also used to train the team on carving figures into the formwork, in this case a full scale Corbusian Modular man. The remaining walls tested variations on soil delivery and spacing of the whalers and strong-backs. In the end, the six walls were covered by a glass butterfly roof with recirculating water in an effort to control the inside temperature with the flow of water. With earth walls on either side and the water running overhead, the experiential effect was that of being at the bottom of a fast-moving river. Although many of the techniques that we tested had been taught to us by SIREWALL, it was critical to enact them all in the Chinese context with a different set of tools, materials and workers – the latter being the most important. Training a group of people who could properly understand the process, strengths and limits of the system was critical to the success of future projects. Completed in 2007, these six walls represented the first free-standing and load-bearing stabilized rammed earth walls in China. They were, however, still uninsulated.
After these two projects, the client, A00 and EMCC finally felt confident enough to undertake the sample house at the River house eco-retreat (see Fig. 24.4). It consisted of a single storey of insulated rammed earth and included some of the more structurally challenging elements of the future main house. One such example was developing a special hidden steel lintel detail that would allow us to span a 3-m-wide opening without the addition of a visible concrete beam and without creating thermal bridging through the insulation. This was achieved with two steel angles placed against the central insulation, with their flanges facing out so as to support the rammed earth and the vertical rebar that continued up into the wall. The final span was monitored for settlement for one month. Three years later, it still hasn’t moved.
Even though lessons are taught, it is clear that mistakes need to be made to understand the value of those lessons. Although the crew understood the importance of cross-bracing and how much lateral force the formwork was subject to during ramming, that lesson was learned once again on one particular wall. Being the tallest wall to date, the amount of cross-bracing was increased but the half-buried concrete blocks used to anchor the braces turned out to be insufficient. Two-thirds of the way up the wall, the force of ramming was enough to cause the bracing blocks to slip. Overall, the total slippage was about 0.9 cm spread over about seven lifts (about 105 cm).
A further lesson had to do with the challenges of ramming in extreme hot weather. Even though the crew understood the importance of keeping the base soil moist prior to mixing and ramming, a few days of extreme hot weather created additional challenges. At this heat, the soil mix dries incredibly fast and the quantities need to be kept as small as possible. Also, the side of the formwork facing the sun bakes the interior face of the rammed earth wall, causing the cement to dry before it cures. Consequently the surface of one of our walls ended up being ‘soft’ up to a depth of 1–2 mm. That is to say, a sharp metal object could normally only scratch the surface, but in this case it could scrape it off. Fortunately, this did not affect the overall strength of the wall.
However, perhaps the biggest lesson was the importance of designing according to the strengths of a material and avoiding its weaknesses: the main house had been designed before rammed earth had been chosen as a structural material, and included some very ambitious cantilevers. Therefore, the sample house was designed to include and test similar details. Here, two of the four walls contained an oversized puddled-earth cap that projected beyond the ends of the walls and joined to form a cantilevered corner, on top of which a steel column supported the roof. The complexity of this detail required the crew to stop ramming for the better part of a day as they installed the rebar necessary to achieve this detail. Of course, by the time the cap was ready to be poured, the rammed earth wall had time to dry and shrink just enough to pull back from the forms. EMCC knew this would happen, and tightened up the forms by hammering wood wedges between the whalers and the form-ply. Nonetheless, some of the mix from the puddled cap leached down the surface of the wall below. Here, the problem was not the skill of the crew but rather designing outside the limits of a given material.
Overall, the sample house was extremely successful. It allowed the crew to familiarize themselves with many new insulation details, in particular those related to connections with doors, windows and roofs. Completed in October of 2007, it took the further step of being the first stabilized and insulated rammed earth structure in China. However, the challenge of insulated multistorey structures still lay ahead.
At its tallest, the main house was three storeys in height (see Fig. 24.5). It also included a free-standing central space that went up to two storeys in height.
The first challenge came with the foundation. In the areas where the structure were to be back-filled, the engineer had insisted on using reinforced concrete. Whereas he had agreed to design many ambitious details for a material he had never worked with, he drew the line at the foundations. The result was stepped concrete foundation walls that rose over one storey in height. The rammed earth walls were started directly on top of these foundations, and singular hairline cracks developed in the rammed earth at many of the ‘steps’ in the concrete foundation.
Another lesson was with ramming in near 0°C temperatures. On one particular night the weather dropped below zero with the wind chill. The last lift that had been rammed that day suffered the most damage, up to a depth of 1 cm on the outside of the wall. Interestingly, the lift right below it suffered virtually no damage. A couple of extra hours of curing had made a significant difference. Fortunately, the walls for this house were over-sized, totaling 600 mm in width with a central insulation core of 100 mm.
The house design included many ambitious elements, such as cantilevered portions of rammed earth walls as well as terracing, which were challenging in terms of structural detailing and water-proofing, as well as creating a continuous insulation plane.
However, by far the greatest challenge was in bracing the formwork on the second and third storeys. At each level, the top of the wall was finished with a puddled cap. Within that cap, a wood strip was inserted to create a shadow joint and to hold anchor bolts. The anchor bolts served to strap on a brace to support the outside facing form-work. In turn, the inside facing formwork simply rested on the new floor slab. Once the wall was completed, the formwork was taken off and the anchor bolts cut back and patched within the space of the shadow joint, making them quite discreet. Although this approach worked quite well it was far too customized to be a cost-effective and scalable solution. The formwork system was developed to suit the design of the house and, to be effective, the order would have to be reversed: future houses would have to be designed according to the formwork.
Mixing of the soil was done with a concrete rotary drum and then turned onto the ground to be finished by hand with shovels. It was then sent up in wheelbarrows hoisted by cranes. Again, although this worked well for one project, scaling up to build larger scale projects would require volumetric mixers and faster delivery systems.
Still, further lessons were learned with this project. For instance, the crew developed a two-person system, where one rammed and the other continuously ‘sprinkled’ earth into the forms. The result was a continuous and monolithic wall without any visible lifts and with a constant maximum density. Although this method would almost certainly make for a stronger wall, we never cored and tested any samples. The resulting wall was not visually compelling and the technique was discontinued.
A particular ongoing challenge was also mentioned earlier in this chapter: that of air pollution and premature ageing of the walls. Although this can be largely prevented with deep roof overhangs on a single-storey structure, the overhang stops protecting the walls after a certain height. We have found no solution to this problem as of yet.
Despite being a modest three storeys, the River House is currently the first and only one of its kind in Asia, and possibly the world. It has opened the door for research into multi-storey, stabilized and insulated rammed earth structural systems.
24.6.4 Naked Stables Private Reserve
Nestled in a valley that lies at the foothills of Moganshan (near Hangzhou), naked stables is an ambitious resort that combines traditional rammed earth construction with curved, stabilized and insulated rammed earth walls. It is one of the few areas in the world where traditional and modern rammed earth were constructed at the same time. The traditional rammed earth is local to the area and is being used in the resort for structures such as the stables and the staff quarters. In stark contrast to this lie the stabilized and insulated rammed earth walls that make up the welcome center and clubhouse, as well as the 40 single-room chalets that dot the forest (see Fig. 24.6). The walls were designed by Delphine Yip and A00 Architecture, respectively, and were built by EMCC.
Although the original plan was to use site soil, it was tested as being too weak for the purposes of the modern walls. High in clay content, the parent rock was also extremely friable. Consequently all the soil came from local, neighboring quarries. However, the local site soil was used for the traditional walls, as it has been for decades.
The most significant part of this project was the repetitiveness of a single chalet type featuring a semi-circular SIREWALL, justifying the production of curved reusable steel forms. Being extremely hands-on, many new ideas were tested by the owner himself: Grant Horsfield. The original design of the foundation by the engineer called for a deep concrete foundation; however, Grant mixed traditional and modern techniques to minimize the need for reinforced concrete. The base of the foundation was built out of dry stone walls, laid according to a local technique that positions the stones diagonally, thereby forcing the walls to further interlock after they are loaded. On top of these walls a 20-cm half-ring beam was poured in order to support the vertical rebar for the rammed earth wall that was to be built on top of the beam. At the time of writing, all of the walls were complete and the stone foundations had not shown any movement, with the oldest being almost 2 years old.
More than anything though, naked Stables is a perfect case study for the single most important challenge that lies ahead of rammed earth in terms of becoming a mainstream building material: protection of the final product. The key issue is that rammed earth is not only a structural material, but also a finish material. These two qualities are diametrically opposed in terms of when they should be appearing on site. The finished nature of the walls require that they be carefully protected until the very end of construction.
This particular project was an excellent example of how many factors can complicate the issue of wall protection, from damage done by the elements to that done by the rest of the construction process. The latter is especially challenging when multiple teams are used and when the order of ‘required attention to detail’ is reversed. In this case, not only were the teams for the rammed earth walls and for the roof structure different, but the latter had no culture of attention to detail. Structural teams – especially in China – tend to be extremely rough as most of their work gets covered up. Changing this entire culture represents a titanic task. For instance, the protective covering on the walls was stripped back and left to fall apart no matter how many times the project managers followed up. Habit and inertia are more powerful than common sense. From rust paint drippings to sloppy welding burn marks, many walls were irreparably damaged in numerous ways. In order to make the thermal barrier continuous, the rammed earth crew had intentionally left the insulation plane coming from the center of the wall exposed. Unprotected, this left a path for the rain to enter the center of the wall, flow back out through the rammed earth and cause rapid efflorescence. What’s more, a black stain in the form of a film and streaks began to appear on the walls. The origin of the black staining is still not completely understood and is probably from multiple sources. Judging by our experience on the River House project, we think a significant portion comes from particulates in the rain as well as from the rust-proof paint. Most of the streaks run from the top ledge of the wall downwards, particularly in the areas where the steel rafters meet the wall. Finally, a portion might be coming from the impurities that are commonly found in Chinese cement, although this would have been minimized by the fact that white cement was used. Still, the black stains seem to be coming from within the walls, as though pushed out by water. Moreover, they only appear on the walls that were rammed in winter. White cement is certainly not perfectly free of impurities and it is possible that it did not fully hydrate given the colder weather, allowing residual impurities to be pushed to the surface of the wall by water. More research is required to arrive at a full conclusion.
Three of the 40 walls were more heavily affected than the others. They were the first to be completed and were wrapped prior to leaving for a three-week national holiday. In the first few days of the holiday the wrapping failed or was removed, leaving the walls exposed to direct rain for several weeks and causing heavy efflorescence. Moreover, these three walls were rammed in near-freezing weather, which we believe made the walls even more prone to efflorescence. Having built 40 identical walls where the progressive increase in temperature (from about 0°C to 30°C) was the only variable, and where all walls were exposed to rain, it is highly probable that walls rammed in cold weather are indeed more prone to efflorescence. As mentioned above, our only theory is that the colder weather prevents the cement from fully hydrating. This leaves many of the finer particles in the walls ‘free’ to be pushed out by water moving through the pores.
Many cleaning techniques were used on the affected walls, from water to muriatic acid with soft to hard brushes, from sponging to using a belt sander. The muriatic acid was generally successful at removing efflorescence, although it did also end up spreading the salts around and muting the walls. However, only the belt sander was able to remove the black stains. Still, none of the solutions were effective in bringing back the original beauty of the particularly affected walls. The ‘old’ rule stays the same: touch the walls as little as possible. That being said, the walls are still stunning, particularly when they are experienced as whole: all 40 of them nestled into the flank of a hill and weaving in and out of the forest.
24.6.5 Vidal Sassoon Academy, Shanghai
This project most likely marks the first instance in the world where a large multinational company (Procter and Gamble) has adopted modern rammed earth as a feature element for one of its major brands. In many ways, this signals a coming of age for modern rammed earth.
Located in Shanghai, designed by A00 Architecture and built by EMCC, the Vidal Sassoon Academy is similar in size and scope to Just Grapes: the walls are used as an interior finish and are non-load-bearing. Sassoon chose rammed earth as the feature of its flagship Academy in order to signal its commitment to ecological responsibility and innovation, and because it was an evocative representation of two key concepts that are shared by the fields of hairstyling and architecture: layering and shear (see Fig. 24.7). To this end, the team experimented with the control of color in the layering as well as representing shear through angled rammed earth walls. In terms of the latter, the tip of the main wall was tilted forward by 11°, while one of the side walls was tilted laterally by 11°. The team created these two conditions to experiment with ramming tilted walls. In order to account for the added vertical pressure from the mechanical rammers, the formwork was built stronger and the walls came out beautifully. However, despite its modest size, the true significance of this project is the introduction of modern rammed earth to a high-profile and mainstream market segment.
24.7 Future trends
China is a place of extremes and tends to be all or nothing. This is certainly true of the potential that stabilized and insulated rammed earth has in this country. China’s current code system does not welcome new materials, and so the introduction of the technique begins with a significant uphill battle. Of course, once the country decides to adopt a certain practice an uphill battle can become one that is won overnight. Over the next couple of years, modern rammed earth will have to continue creating precedents and accumulating science-based data. It will also have to demonstrate how it is scalable. Armed with the proof of results and within our context of growing environmental challenges, modern rammed earth could be well positioned to have the code written in its favor. If this happens, we will see the development of multi-storey rammed earth structures, the adoption of insulation in rammed earth construction, the development of walls made almost entirely of waste material and, finally, the development of hybrid structures that leverage the structural and thermal mass properties of rammed earth. Beyond this, two great challenges will remain.
I am confident that we can deepen our knowledge of soil types and the science of blending, and thereby increase the strength of rammed earth walls. Following this, I am confident that we will be able to significantly reduce – if not eliminate – the use of cement in stabilized rammed earth. I am also confident that we will soon be able to build insulated multistorey structures cost-effectively. These are all technical issues that mostly require time and research. I am less confident about the time it will take for China to clean up its skies, and hence resolve the problem of the premature ageing of the walls. I am also less confident in the ability of people to properly protect the walls during the rest of construction. Although this is not an issue with a small, dedicated team working on specialty projects, it will most certainly become an issue with large-scale projects that employ hundreds of workers and see the regular turnover of project managers. Maintaining quality will require steel-fisted project managers, or cultures with a universal sense of personal pride and respect.
Without a doubt, if the opportunities come to outweigh the challenges and China chooses to invest itself, it could well become the global source of innovation for rammed earth construction.
24.8 References
China Geological Survey. A series of small scale geological maps of China, Beijing, 2002. http://old.cgs.gov.cn/ev/gs/Geomap.htm [Available from].
Cooray, P.G. An Introduction to the Geology of Sri Lanka (Ceylon), 2nd revised edition. Colombo: National Museums Department; 1984.
World Trade Press, China population, Petaluma, Cal., World Trade Press. 2007 www.worldtradepress.com
United Nations/Department of Economic and Social Affairs/Population Division. World Urbanization Prospects: The 2007 Revision. New York: United Nations Publications; 2008.
1In 2007, 42.2% of the Chinese population lived in urban centers. This percentage is estimated to increase to 56.9% in 2025 and 72.9% in 2050, representing 260,958,000 people moving to urban centers between 2007 and 2025, and 205,085,000 more people between 2025 and 2050 (United Nations, Department of Economic and Social Affairs, Population Division, 2008).