Research consultancy
CHAPTER TWO: LITERATURE REVIEW
2.1. Introduction
This chapter gives a breakdown on the concept of comparative analysis of rammed earth construction and traditional burned clay brick construction. From this Literature, the principles of a sustainable construction technique are highlighted and discussed. This Chapter also discusses earth construction and explains the advantages of rammed earth construction over traditional burned clay brick construction techniques. The properties of earth as a construction material are also discussed and the process of rammed earth construction is described in detail as to traditionally burned clay bricks.
In brief, this chapter gives an orientation to the research problem by referencing to previous theories and researches related to this particular area of study.
2.2. Theoretical Review
2.2.1.Traditionally Burned Clay Bricks
This research reports on a study that sought to evaluate people’s perceptions of the production and usage of fired Clay Bricks in construction in Uganda. The investigation was under a multi-partner research project on Energy and Low income Tropical Housing (ELITH) which was conceived as a concerted effort towards documenting low-income housing in the tropics and identifying possible areas of intervention to overcome the perceived challenges, especially pollution rooted in embodied energy and carbon. The Energy and Low-Income Tropical Housing Project ELITH is co-funded by the UK Department for International Development (DFID), the Engineering & Physical Science Research Council (EPSRC) and the Department for Energy & Climate Change (DECC), for the benefit of developing countries.
Clay brick masonry is one of the oldest and most durable construction techniques used by mankind. Masonry consists of manually built stable stacks of small elements, with or without mortar. It was a fundamental building material in the Mesopotamian, Egyptian and Roman periods. During the Roman period, the use of clay brick increased and became specialized in order to maximize its benefits. Clay brick masonry continued to be used during medieval and modern times. Despite several modifications of the clay brick uses, shape and manufacture along thousands of years of constant evolution, the simplicity that made its success remained. Numerous buildings built with clay bricks prevailed until the 21st century, which testifies to the strength of this material along centuries of rain storms, snow, thaw-freezing cycles, high temperatures and human induced deterioration. Moreover, brick could be easily, inexpensively and rapidly handled and produced with a simple manufacturing process. It is based on fired clay, a raw material available in large quantities all over the Earth. Its wide use proved that clay brick was an effective construction material that could provide both resistance to prevalent climatic conditions and insulation from cold and heat. It is known that the properties of ancient clay brick masonry rely essentially on the properties of the brick units, which depend on the quality of the raw materials used, together with the manufacturing process technology. The analysis of clay brick production and final properties are therefore fundamental. Generally, it is crucial to obtain information on the main physical, chemical and mechanical properties of clay bricks as well as the characteristics of the raw materials used and their manufacturing process
A large number of studies exist dealing with ancient structures and materials, fostered by the immense cultural and economic importance given to ancient monuments. Most of them have focused on the physical, chemical and mineralogical composition of ancient clay bricks (López-Arce et al. 2003; Cardiano et al. 2004; Pauriet al. 1994), durability and deterioration agents (Wijffels and Nijland 2004), neglecting the mechanical properties, which are more frequently retrieved in the case of the composite material (Binda et al. 2000). Despite the importance of mechanical properties and its relevance for the resistance and durability of masonry, only a few of the published studies focus on the mechanical properties of clay bricks (Papayianni and Stefanidou 2000; Baronio and Binda 1985). In fact, the compressive strength of clay bricks is usually related to other properties, such as porosity and firing temperature, which are key parameters for durability (Cultrone et al. 2000) but can markedly affect the mechanical resistance of bricks (Cultrone et al.2004).
As the properties of ancient bricks vary considerably in terms of raw materials, production methodology and period, attention here is paid to clay brick production and analysis of its properties in numerous examples recovered from a literature study and from samples of old bricks taken from six Portuguese monuments (Church of Outeiro, OU, Monastery of Pombeiro, PO, Monastery of Salzedas, SA, Monastery of São João de Tarouca, TA, Monastery of Tibães, TI and the Christ Cloister in Tomar, TO) dated to the period of 12th–18th centuries. The main physical, chemical and mechanical properties were determined. Instead of the laboratory testing of highly invasive uniaxial compressive strength, a new on site minor destructive technique to assess the drilling resistance of old clay bricks was tested.
2.2.2. Manufacturing Process
The manufacture of fired clay bricks can be divided into four stages according to basic principles followed during thousands of years. Firstly, the extraction and preparation of the raw clay takes place. As soon as the raw material is extracted, it is accumulated and moved to an open air storage area. During this period, the raw material is rummaged in order to reduce soluble salts to a minimum, leading to a more homogeneous material. The analysis of the constituents of historic bricks that have survived up until our day showed that they were not always produced using treated clays. In some cases, bad quality clays were used. Vitruvius (1960) stated, in the 1st century B.C., that the choice of the raw material was essential to improve the performance and durability of the bricks. Despite this fact, the selection of raw materials depended mostly on its availability at the construction location or nearby (Álvarez de Buergo and Limón 1994).After storage, clay is further crushed and mixed with water, in an operation designated as tempering.
In the early times, the mixing was carried out by hand, in a crude and often ineffective manner; but, later, horse driven heavy rollers or wheels in a ring pit were used. The amount of water used depends on the type of element being produced and, usually, smaller and thinner clay elements would require a greater amount of water. The resulting mix must be characterized by enough plasticity to facilitate the molding, but not “too plastic”, as it can lead to severe shrinkage during the drying phase, resulting in warping, twisting or cracking. In this case, plasticity of the clay can be reduced adding sand, for example. Early brick makers often used a mix of about 30% of sand and 70% of plastic clay (Weaver 1997; Chew, De Silva & Tan, 2004). The moulds in the past were bottomless wooden moulds placed down over the ground or over tables, which usually were protected with a thin film of sand in order to avoid letting the brick remain attached to the bottom base during the drying process.
The excess clay was removed with the aid of a rope, wooden ruler or with bare hands. The still crude clay elements were removed from the mould and dried in a covered space, which was generally a shelter made of scraps of wood and with a straw thatched roof: these shelters were known as hovels. Although inexpensive, this primitive method required a lot of open free space and was severely conditioned by climatic conditions. Generally, drying of clay bricks lasted for a week or more. In hot temperature regions, drying was faster but bricks had to be protected from direct sunlight since they could undergo warping and cracking. In colder regions, drying took more time due to the low temperatures and moisture conditions.The importance of the drying phase was mentioned by Vitruvius, who wrote that “bricks should be made in spring or autumn, so that they may dry uniformly”. Moreover, a too fast drying hardened the surface faster than the core, which remains crude for a longer time. Again, Vitruvius stated that bricks “made in summer are defective, because the fierce heat of the sun bakes their surface and makes the brick seem dry while inside it is not dry”.
Finally, the last stage was the hardening of the bricks in order to acquire additional resistance. Bricks were further sun dried, in the open air, or were put in a kiln or clamp with temperatures in the order of 1,000ºC, where they were fired, acquiring in this way much more resistance from both a mechanical and chemical point of view. Early kilns used wood or straw as combustibles and took several days to finish combustion. Coal was not commonly used until the last quarter of the 19th century. During this phase, complex chemical reactions took place, creating diverse ceramic products, according to the firing temperature and the quality of the clay. The firing conditions were crucial for the final properties of bricks, whose quality strongly affects the strength and durability of the masonry. According to Vitruvius, sun-dried clay bricks needed a minimum of two years to dry. To illustrate this statement, he gave the example of Utica, where the clay bricks used to build the walls had to be five years old. Here, attention is focused on fired clay bricks only.
2.2.3.Physical Properties of Fired Bricks
Clay bricks exhibit a set of properties that are important in the evaluation of strength and durability. The properties are closely related to the quality of the raw clay and directly associated with the conditions of manufacture. When working with old clay bricks, additional parameters related to weathering mechanisms, material ageing and long term effects must be considered, like cracking, peeling or efflorescence. These effects are usually increased by atmospheric agents such as wind and water. Thus, the properties exhibited today by old clay bricks do not necessarily represent their original properties. Nevertheless, the physical, mechanical, chemical and mineralogical parameters are relevant to the evaluation of the durability and resistance of old clay bricks.
- Porosity
Firing of clay bricks produces a series of mineralogical, textural and physical changes that depend on many factors that influence porosity. Porosity can be defined as the ratio between the volume of void spaces (pores and cracks) and the total volume of the specimen. Porosity is an important parameter concerning clay bricks due to its influence on properties such as chemical reactivity, mechanical strength, durability and the general quality of the brick. Old clay bricks exhibit high porosity values, ranging between 15 and 40 vol. % (Molina, 2011). The porosity of bricks from the Byzantine period was reported to be between 15 and 35 vol.%, while 70–80% of the pores had a diameter size of 70–250 μ m, independently of the type and origin of the clay (Papayianni and Stefanidou 2000 ). Livingston (1993 ) reported that the porosity of bricks in the Church of Hagia Sophia is in a range of 26–30 vol.% for the red coloured bricks and 40–55 vol.% for the beige ones; while Maierhofer et al. ( 2003 ) obtained porosity values between 21 and 35 vol.% in bricks from the 9th–10th and 13th centuries, respectively.
Fernandes (2006) reported the value of porosity of clay bricks from the 12th to 18th centuries as ranging from 12 to 43 vol. % with a mean value of 18 vol. %. In this case, around 80% of the samples exhibited a porosity larger than 25 vol. % and the vast majority between 25 and 35 vol. %, .The dimension and distribution of the pores is influenced by the quality of the raw clay, the presence of additives or impurities, the amount of water and the firing temperature. Prick, (1997). and Cultrone et al. (2004) observed that if the firing temperature increases, the proportion of large pores (3–15 μ m) increases and the connectivity between pores is reduced, whereas the amount of small pores diminishes. This has a strong impact on the durability of the bricks as it has been shown that large pores are less influenced by soluble salts and freeze/thaw cycles.
Further-more, several studies by Cultrone et al. ( 2004 ) and Elert et al. ( 2003 ) reported that the formation of small pores, with a diameter below 1 μ m, is promoted by carbonates in the raw clay (low quality material) and by a firing temperature between 800 and 1,000°C. Such pore sizes negatively influence the quality of the bricks, as their capacity to absorb and retain water increases. A similar conclusion was given by Winslow et al. (1988) for bricks with a pore size smaller to 1.5 μ m.
Ancient Clay Bricks: Manufacture and Properties
Figure 1:Distribution of porosity for the complete set of clay brick
Source 🙁 Fernandes, 2006)
- Apparent Density
Apparent density is described as the ratio between the dry brick weight and the volume of the clay brick, measuring the proportion of matter (clay) found in the volume. It is evident from this description that the higher this value is, the denser the brick is, and obviously, the better it’s mechanical and durability properties are. Typical values for the apparent density range from 1,200 to 1,900 g m
- Water Absorption
Pores constitute a large part of the brick’s volume, and when the bricks are exposed to rainfall or rising damp, water generally penetrates into the pores. Water absorption then determines the capacity of the fluid to be stored and to circulate within the brick, favouring deterioration and reduction of mechanical strength. In countries where temperatures fall below 0°C, the water inside the pores can freeze leading to surface delaminations, disintegration or cracking. Moreover, in the presence of soluble salts, water tends to react with them and to cause efflorescence. Though this is mostly an aesthetic deterioration of the surface of the brick, the volume increase caused by the crystallization of the salts can cause severe damage. The values found in the literature are significantly scattered, with a large quantity of bricks with higher than average water absorption rates. Binda et al. (2000b) reported different absorption rates with respect to the colour exhibited by 8th–13th century bricks from the bell tower of the Cathedral of Cremona, Italy. Brown and red bricks were found to have a water absorption of about 20.1 and 24.9 wt. %. In bricks from the 9th–10th centuries, values of water absorption between 18 and 19 wt. % were found, whereas values of 12 and 24% were attributed to bricks from the 13th century (Maierhofer et al. 1998). Moreover, clay bricks from the 12th to 18th centuries (Fernandes 2006) exhibited values between 6 and 32 wt. %,
Table 1:Typical Values of apparent density of old bricks
Source 🙁 Fernandes, 2006)
With an average value of 17 wt. %, and more than 90% of the values in the range 10–25 wt. %. Another relevant parameter is the velocity of water absorption, measured by suction rate. The water is sucked by the pores as a result of capillary tension along the walls of the pores. López-Arce et al. (2003) pointed out that tension is stronger in small pores than in large ones. Generally, old bricks exhibit absorption values between 0.5 and 3.5 kg m-2 min-1 which were further confirmed by Fernandes (2006), who reported values in the range 0.7–2.5 kg m −2 min −1
2.2.4. Moisture Expansion
The expansion or shrinkage observed in clay bricks can be partially or totally reversible due to wetting/drying, being not so relevant for old clay bricks. Moisture expansion in clay bricks is influenced by the contents of argillaceous minerals and by the presence of lime nodules. Typical values of 0.1–0.2% were indicated by Álvarez de Buergo and Limón (1994) and (Fernandes,2019).
2.2.5. Mechanical Properties
Masonry is a heterogeneous material, and therefore its compressive strength depends on the strength of the components: brick, mortar and brick-mortar interface. Nevertheless, experimental results indicate that masonry compressive strength is mostly influenced by the strength of the brick units. Therefore, brick mechanics is very relevant to the safety assessment of existing brick masonry structures. The mechanical properties of old bricks are frequently reported in the literature, so it is possible to gather a large amount of data.
In traditional masonry shapes, such as columns, walls, arches and vaults, bricks are mostly subjected to compressive stresses. The adopted structural shapes for these elements make full use of properties of clay bricks, namely reasonable strength in compression and low strength in tension.
2.2.6. Compressive Strength
Compressive strength is strongly influenced by the characteristics of the raw material and by the production process. It is known that the raw clay of old bricks were often of low quality and the manufacturing process was relatively primitive and inefficient. Other characteristics of existing old bricks can provide an indication about compressive strength, such as mineral composition, texture, crack pattern and porosity level, by revealing the conditions of drying and firing. On the other hand, the evaluation of the mechanical strength of bricks belonging to old buildings is often difficult due to the high variability in production and additional variability caused by deterioration from the weather or chemical agents such as soluble salts, freeze thawing cycles or load unload cycles. Moreover, clay bricks in a given structural element or building can belong to different construction periods or productions.
Finally, the experimental test set-up conditions (dimensions and moisture content of the sample, boundary conditions, temperature, etc.) can also influence the results. According to Pauri et al. (1994), the original properties of old clay bricks would only be obtained through the manufacture of bricks using traditional methodologies and raw materials recovered from indications in archives, which is impossible. The range of values found in the literature is quite wide (about1.5–32 MPa), meaning that in situ testing or destructive testing of samples must be carried out when the compressive strength of the brick is required. Even though they have been obtained using different testing equipment’s and procedures.
A wide range of compressive strengths was reported by Fernandes (2006) on clay bricks from six monasteries in Portugal that were built during the 12th–18th centuries period. The selection of the buildings was made according to the works being carried out by the University of Minho in these locations, and as a means to provide a broad knowledge on Portuguese clay bricks. It must be noted that most bricks were collected from vaults, buried remains, soil deposits and infill material, while clay bricks from two particular monasteries were obtained from building elements. Therefore, environmental actions and deterioration might have influenced the results obtained. The values range from 6.7 to 21.8 MPa and exhibit a very high coefficient of variation (up to 60%). Most studies indicate low values for compressive strength and a large dispersion of the values, with coefficients of variation ranging between 25 and 55%; but unusual strengths, higher than 50 MPa, were reported by Pauri et al. (1994).
The objective of the ongoing project is to reduce energy use and carbon emission in low and medium income households while improving the quality of interior environment and the quality of life for the residents. This specific study sought to respond to common perceptions about the fired bricks, run a comparative analysis for walling materials and then to propose viable alternative materials for wall construction the rural context. The envisaged option considered to replace fired brick wall, is a combination of revised earth technologies, which make use of locally available resources more favourably. This option is rooted in the fact that Earth technologies have been a reliable and consistent walling choice in Africa for centuries. Surprisingly, today Earth has taken a back seat since Cement blocks and fired clay bricks are regarded as symbols of modernity and progress even in the most remote communities (Perez, 2009).
Homeowners and their local artisans in Uganda often seek feasible opportunities to reduce construction cost. However, when unit cost remains the sole consideration, it is noticed that the fired clay brick emerges as the popular wall material choice. Fired brick, though considered a durable material; is environmentally harmful due to its low quality, very inefficient production processes and over dependence on local wood fuel in brick kilns, which contribute to deforestation and air pollution. According to the Second Volume of Inventory of Carbon, the embodied energy of “General Clay Bricks” in the UK is 3000 MJ/tonne (Hammond,2011). Here we should consider that kilns in the United Kingdom adhere to strict production regulations and restrictions. However, the average energy consumptions by artisans and small scale brick producers in third world countries are up to 5 times more than the average energy required for brick production in developed countries. Rural artisans rarely seek sustainable fuel sources like coffee husks or sawdust that have been adapted to fuel larger commercial kilns. Small scale producers by comparison target naturally occurring indigenous species in the absence of replacement and this disrupts flora and fauna patterns in the environment.
Further, artisans keep the firing period and temperature low to save on fuel (which is increasingly harder to come by), this in turn results in low quality bricks up to 45% of the entire production. Further, any variation is weather like unexpected gusts of wind or rains can severely diminish the output of a local kiln. Despite this low production efficiency, bricks are then recklessly handled during transportation, storage and construction. It is a common occurrence to notice, heaps of unused bricks strewn around building sites long after the construction process as shown in image 1.
Figure 2:heap of used bricks abandoned near a plantation.
This negligence is common place because the brunt of rural construction is relegated to unskilled homeowners or low skill level artisans since most rural developers cannot afford more competent contractors. In spite of their inclination to adhere to traditional construction methods, this study found that if given a cost saving alternative, local artisans and self-build homeowners in Uganda might quickly adopt a new strategy. Particularly one that further reduces labour costs, by accommodating the do it yourself strategy that is already prevalent in most rural construction. However, in either case an additional case needs to be made so that all construction stakeholders begin to deal with wastage and ecological footprints. This intervention is timely since according to Uganda Human Settlements Network (2014), materials made from clay are gradually becoming scarce in Uganda due to the limited availability of appropriate clay in the country coupled with high demand associated with an enhanced construction sector. It should be noted that new technologies such as interlocking stabilized soil blocks (ISSB) have not been integrated into the educational curricula of secondary vocational institutions and tertiary engineering and architectural institutions and thus their adoption remains slow.
Therefore, integrating these technologies into the educational system is another effective way to ensure their use in the fsuture. As such, this study shall culminate in the construction of an actual 105m2. DisplaySpace. The Display space construction seeks to engage local artisans and students to interrogate prevailing perceptual concerns like cost and durability of earth walling, create new job opportunities through skilled local artisan and empower social entrepreneurs. The finished building shall provide comparative data about the materials thermal performance against predicted estimates from software simulations. Further, the embodied energy and material saving analysis willfurther assess the meritsof this selected walling strategy.
The housing problems in Ethiopia is a very critical issue that not only its poor condition and level of affordability, but also its critical degradation of the environment. Because in the pastoral areas, villages as well as most of the towns are using wood for the construction of the houses, which lead to the environmental degradation and for high contribution to global warming. Ethiopia is like in many other developing countries; especially African countries have critical shortage and poor condition of the housing which have a significant effect on the environment. These problems can be solved through the application of engineering knowledge that the country need to stand for the whole development. Clay brick is the first man made artificial building material and one of the oldest building materials known. Its widespread use is mainly due to the availability of clay in most countries.
Due to inadequate resources in developing countries, cost reduction seems to be the best way forward, especially in housing for the economically weaker section. This can be achieved by innovating, manufacturing, and utilizing low cost, but durable construction materials from locally available resources. Traditional earth construction techniques such as compressed earth blocks are experiencing a new popularity, taking into account that they constitute green building materials, becoming economically competitive. The production process of Fired clay bricks in Jimma town consisted of preparing the clay materials from the quarry, tempering, and molding, drying and firing. Among these processes, firing is the most important for the hardening of the brick.
The firing process to locally produce fired clay bricks are by using heat from burning of woods. But this has an adverse impact on the environmental condition due to high deforestation of tress. Traditional brick requires a great deal of fuel during firing. This excess fuel consumption increases air pollution. If wood is used as a fuel, excess consumption often contributes to deforestation and associated environmental impacts.
Excessive energy waste during the production processes of fired burned bricks, with impacts such as deforestation; air pollution and other environmental issues are the major concern, which should be addressed. Owing to the general consensus that it is apparently the cheapest option, the fired clay brick has not left much room for consideration or evaluation of other possible alternatives. We acknowledge people’s taste and preference for the fired clay brick; however, suggest that this walling material has become a victim of its own success. Therefore, alternative-walling options that challenge this position would have a significant impact on construction attitudes and practices in general.
Preliminary field evidence shows that contractors, even on large scale projects, generally opt for rural artisan made fired clay bricks instead of the more sustainable Factory-manufactured options in a bid to save money. The danger associated with this decision is twofold: on one hand, the inefficient production process continues to strain local wood fuel sources, which contributes to deforestation, air pollution and environmental degradation. According to (NEMA 2002: 122), Uganda is experiencing rapid deforestation as up to 3% of forest cover is lost per year due to unsustainable harvesting. A look at fuel wood usage reveals that three quarters of households in Uganda use firewood for cooking while one in every five households, 21% use charcoal. Combined, biomass fuels constitute the main fuel for cooking for 96% of households (UBOS 2014). Of major concern is the source of the wood; according to UBOS (2014), 72% of households that used firewood for cooking got it from the Bush/Forest, and 16% got it from own plantations, while 13% bought from the market. The high percentage that that get firewood from the bush/forest has implications on environment protection. Worse still, excessive quantities of mortar as shown in the image below are used during brick construction due to rapid construction timelines, inconsistent brick sizes, negligence, and low mason skill levels. As a result, vast quantities of plaster are required to deliver a smooth finish to these uneven walls. Cement wastage in mortar and plaster cannot be ignored since cement production causes further pollution and accumulation of waste.
Figure 3:Excessive mortar joints contribute to waste associated with brick construction in Uganda.
This discussion does not claim to provide a comprehensive solution on material selection since as Sanya (2007) attests; the global discussion embodies the difficult to reconcile aims of safeguarding human wellbeing (including alleviation of poverty) and preservation of the environment. Our discussion here merely posits that there are actual viable alternatives to the brick wall. Often times, the argument against alternative construction methods has limited information on cost and performance as compared to conventional methods. Yet we, in the education for construction industry need to respond to the Sustainable Development Goals particularly; Ensure healthy lives and promote well-being for all at all ages, Make cities and human settlements inclusive, safe resilient and sustainable, as well as take urgent action to combat Climate change and its impacts.
Fortunately, when more practitioners get involved in this endeavour toward better buildings, irrefutable evidence of overall gains associated with alternative construction shall emerge. This evidence could then inform local communities to devise even more efficient site-specific alternatives and subsequently mitigate the latent cost impacts to our environment. It should be noted that fired brick production depletes the same wood fuel, which is the primary source for cooking energy in these rural communities. Brick masonry with EE at 580.2 GJ (Mishra & Usmani, 2013) consumes highest of the masonry options. Hollow concrete masonry at 508.8 GJ, consume less than brick masonry. Stabilised Soil Blocks consume a significantly lower 370.0GJ. This data is comparable to the following calculated Embodied Energy comparison for three walling types around the Nkozi village.
Taking sections through three walling options from around our local context, we used descriptive terms:- Old, Popular and Alternative. Embodied Energy for these options was compared to facilitate a discussion to propose future walling options. These samples were considered for an area of one square meter (1m2) of walling. The tables based in a given section indicate materials, layer thickness and levels that exist between the exterior and the interior. The tables presented for this discussion consider two basic wall types
This walling option does not record any Embodied Energy since raw materials are sourced locally from around the construction site with no transportation or manufacturing costs. It should be noted that human labour through expended during construction, values are not reflected for any of the walling options.
2.2.6. Popular Construction
Soil requires to be stabilized because the materials found in its natural state are not durable for long term use in buildings. By properly modifying the properties of soil, its long term performance can be significantly improved. Soil stabilization processes focus on altering its phase structure, namely the soil water air interface. The general goal is to reduce the volume of interstitial voids, fill empty voids and improve bonding between the soil grains. In this way, requires mechanical method to reduce porosity, limit dimensional changes, and enhance resistance to normal and sever exposure conditions can be achieved.
In addition to the environmental effect, firing by a traditional way also affects the quality of the produced fired clay bricks. When Clay soil reacts with water, it becomes plastic and can be moulded with different shapes. But for structural use of the produced product in addition of drying it should also be fired with a suitable temperature. The hardening process by firing of the bricks cannot be controlled by the traditional way of production of bricks. Therefore, this uncontrolled burning process results after burning or under burning of the bricks with lower qualities in both cases. This research study applied the concept of stabilizing the clay soil with cement and lime to provide the hardness of the bricks by chemical action as well as fired brick clay. Firing the bricks creates a ceramic bond in a specific temperature (900ºc -1200ºc) which increases the strength of brick making it water resistant. Using the right amount of fuel is very important not only for fuel and cost efficiency but also to provide the right temperature for bonding. Low temperature results in poor quality /bonding while high temperature would either slump or melt the bricks. (GSJ: Volume 5, Issue 12, December 2017)
Rammed earth is a form of unbaked construction used primarily to build walls. Other applications include floors, roofs and foundations. Recently it has also been used for furniture, garden ornaments and other features. Rammed earth is formed by compacting moist sub-soil inside temporary formwork. Loose moist soil is placed in layers 100-150mm deep and compacted .Traditionally, manual rammers have been used for compaction but nowadays pneumatically powered dynamic rammers are commonly used .Once the soil has been adequately compacted the formwork is removed, often immediately after compaction, leaving the finished wall to dry out .Walls are typically 300-450mm thick but this can vary widely according to design requirements.
Rammed earth walls often exhibit a distinctive layered appearance as a result of the construction process, corresponding to the successive layers of soil compacted within the formwork (peter walker, Rowland keable, Joe martin and vasilos maniatidis). In rammed earth construction organic matter content should be avoided, as this may lead to high shrinkage and possible biodeterioration as well as increasing susceptibility to insect attack. Organic material also interferes with action of stabilizers such as cement.
In order to increase the mechanical strength and weathering resistance of soil it is advantageous to minimize the voids ratio in order to increase the contact between soil particles. Theoretically soils with no voids can be achieved if the soil particles are entirely spherical and their distribution follows the Fuller Formula below:
………………………………………equation 2.1
Where: p is the proportion of grains of a given diameter, d is the diameter of grains for a given value of p,
D is the largest grain diameter,
n is the grading coefficient.
When the grains are entirely spherical then n is equal to 0.5. However, in earth construction a value of n between 0.20 and 0.25 is more appropriate depending on grain shape. In reality it is virtually impossible to find natural soils that match such an ideal distribution .There are four main particle types in sub-soil and these fragments range in size from coarse gravel through to fine gravel(sand), silt and finally to clay. The relative proportions of these constituents play an important role in the performance of the material. Gravel provides the inert skeleton or matrix and together with sand enhances the weather resistance of the exposed faces. Clays, which are quite different from the other constituents swell when wetted and shrink as they dry out.
The British Standard grading limits are:
| Material | Limits | ||
| Upper | lower | ||
| Gravel | 60mm | 2mm | |
| Sand | 2mm | 0.06mm | |
| Slit | 0.06mm | 0.02mm | |
| Clay | 0.02mm | – | |
Source: (…………….)
Figure 6: Structure of soil components for rammed earth application (top) and role in final product (bottom)
Source:………………….
A wide variety of sub-soils have been used for natural rammed earth buildings, with the exception of uniform coarse sands and gravels with no fines or cementing agents. Ideally the soil should have high sand/gravel content, with some silt. For unsterilized rammed earth, the clay content should be sufficient for compaction and to bind effectively together all other fractions without excessive shrinkage on drying. 8–15% clay fraction is usually suitable for most rammed earth soils.
According to Norton, any material coarser than 5-10mm should be sieved out. Previous experimental work indicates that increasing gravel size reduces the compressive strength of rammed earth; however more research is warranted to define grading for rammed earth, especially maximum gravel size and proportions. There is some agreement on the limits between the main soil elements. The minimum percentage of combined clay and silt should be between 20%-25% while the maximum between 30%-35%. Similarly, the minimum percentage of sand should be between 50%-55% while the maximum is between 70%-75%. In total, proposals tend to converge towards a 30% -70% balance between clay/silt and sand proportions. In the absence of suitable natural deposits, controlled engineered mixtures of gravel, sand, silt, and clay may be manufactured for rammed earth. The limestone aggregates in the soil were angular with an estimated crushing strength, based on parent material, between 20 and 30 N/mm2 (Ladan Taghiloha, 2013)
2.2.7. Cement Stabilized Rammed Earth
- Materials: soil type and binder
Stabilized rammed earth is a form of rammed earth that uses sub soils combined with stabilizing agents to improve the materials physical characteristics. Soils for cement stabilized rammed earth tend to have proportionally higher sand and gravel content and correspondingly lower fines content. For example, a soil suitable for Cement stabilization should have a significant sand content. The composition of soils in different parts of the world varies considerably due to the origin and the climatic conditions or due to our objectives in construction site and laboratory samples. For instance some studies indicates the uses of laterite soils and clayey soils for cement stabilized soil and here , some other materials that can be used for making stabilized rammed earth are described ,such as :limestone, artificial soil and recycled concrete aggregates(RCA).
- Artificial Soil
In the study realized by M. Yaqub, was decided to create an artificial soil so that the results can be repeated. Further advantages of using an artificial soil include the fact that the proportions of the soil constituents were known and could be controlled. The artificial soil was created using kaolin clay, silica flour, clean sand and 10mm blue aggregate. The mix proportions used are detailed in: clay 10%, sand 50%, silica flour 20%, gavel 20%.
- Binder
In rammed earth construction, Portland cement is the most common stabilizing agent used. Cement is typically proportioned to between 4% and 15% of the mixture, with the majority of mixes being between 6% and 10% cement stabilized.
There are various advantages when using cement as a stabilizer: The use of cement in rammed earth mixes has derived out of a need to improve wet strength and erosion resistance in very exposed walls. With the addition of cement wet compressive strength resistance improve significantly, so it could increase the overall factor of safety, resistance to water-borne deterioration and general durability and robustness. Soil samples gain strength from the formation of a cement gel matrix that binds together the soil particles. High levels of cement stabilization improve the surface coating and reduce erosion. Additionally, the presence of cement has a considerable influence in improving the resistance of soils vulnerable to frost attack. Cement stabilization increases the elastic modulus of the material from 1.89GPa for unsterilized soil to 2.51GPa for 10% cement stabilized soil.
In the western culture, we they are much oriented towards efficiency; it means that we are oriented towards quick results more than towards harmonious processes. Building in rammed earth is a process which has to adapt to many factors: weather, quality of the soil available, nature and dependability of tools, generosity of co-workers into effort etc. It is important to accept this challenge because this acceptance and spirit of adaptation will make the process more harmonious and more in tune with the environment, especially if simple means are implemented in order to make the process more accessible for people without or with reduced access to cash flow. It becomes a fascinating process when one opens to the quality of this harmony that cannot be experienced when one focuses only on quick results. Yet of course the purpose of building with rammed earth is also to erect a house where one can live.The process can even be experienced as a kind of meditation: the quality and mystery of a loose soil which can be transformed into walls, the gentleness of the process which sees almost exclusively work and creativity transformed into a house.
As such, rammed earth building is evidently a heavy and effortful process. Yet, when it is well organised and planned, it becomes easy, especially if the main effort (lifting) is supplied by simple machinery or tools: a simple crane with a simple pulley can change completely the ease and quality of the process. Yet many small problems appear regularly on the run and much patience is required for troubleshooting. These frequent problems impair the smooth development and take time. If the rammer needs repair, or if it starts raining heavily, it can take a few days until the work can go on. Once one has accepted this fact, there is no major hindrance for a harmonious development of this activity.
Figure 7: Formwork similar to ones used for concrete walls
Figure 2.5.
Source:………………………….
The construction method of the rammed earth walls is based on the setting up of double-wall formwork into which the earth is compacted and so creating a wall panel. The earthen material is compacted in layers between the formwork in vertical direction – wall construction and in horizontal direction – floors and slabs. After compaction, formwork can be removed immediately and will take a couple of hot and dry days to dry out the wall so it can gain the desired load-bearing strength.
The strength of rammed earth, similar to the strength of a concrete, in the process of maturation will continue to strengthen even after the start of using the building. Maturation of the wall can take up to two years, depending onthe thickness, climate, etc. When that hardening process is complete, the rammed earth wall has similar features as a masonry structure made of stone. Some builders add crushed glass bottle cullet in color or pieces of wood to get a more interesting appearance of the surface of rammed earth wall.
Figure 8: Placing and ramming in wall forms
Source: golubkaraman@gmail.com
The soil for the rammed earth construction which satisfies the required consistency limits is mixed with wet of OMC and an optimum amount of cement content in the studies done by Jayasinghe et aland Vasilioset al.The literature of Jayasingheet al also indicates the importance of moisture addition as it effects the stability during the construction. The construction method adopted for rammed earth wallet by Quocet al is by slip formwork in which the form work is raised after compaction of each layer which is being practiced in the site also. Generally a lift of 200mm is practiced in the site which is revealed in the studies done by Vasilioset al. Laboratory specimens prepared by manual compaction are kept for wet burlap curing for 28 days.
Material for rammed earth foundations and any walls below damp proof course level should be of masonry complying with the requirements of the applicable building by-laws or stabilized rammed earth if protected from dampness. Compressive strength and density should comply with Section 4 requirements.
Foundation strips in rammed earth should be at least as thick as the wall above, and otherwise have the dimensions. Foundation design for rammed earth buildings is very similar to that for low rise buildings. Concrete strip footings are the most common types of footings. The size of footings depends on the type of the supported structure and the soil bearing capacity underneath the foundation. It is important that foundation is of sufficient depth to avoid frost underneath and footings should be well protected from water infiltration. The ground immediately adjacent to the base of a rammed earth wall should be well drained. Also extended eaves and raised footings protect walls from rainfall.
Generally the installation of surface and underwater drains and damp-proof courses are considered essentials. We used bitumen sheets for water insulation.
Figure 9: bitumen sheets for water insulation.
Source:………………….
Formwork in rammed earth construction is used as a temporary support during soil compaction. Formwork can range from simple to complicated systems and you can use plywood or steel ones. Like concrete formwork it is required to have sufficient strength, stiffness and stability to resist pressures it is subjected to during assembly, pouring the soil mix, and dismantling. However, unlike concrete, rammed earth formwork can be removed after compaction, enabling much faster re-use efficient organization of formwork is essential to efficient rammed earth construction. Martin Rauch, has commented that typically 50% of his site time is spent erecting, aligning, checking, stripping, cleaning, moving and storing formwork (Boltshauser & Rauch, 2011).
Figure 10: Formwork in rammed earth construction
2.2.9. Ramming
The mixed moist soil was poured in the formwork creating a uniform level of almost 15 cm, which after ramming was compressed to 10 cm. As soon as the first layer was rammed properly another was poured to be rammed, and so on. Both electric and hand metal rammers were used to ram the soil. The metal were composed of a steel rod with a flat steel plate, the weight of the rammers and the size of the plates differs to suit the purpose for example to ram the corners. A layer was considered to be properly rammed as soon as an echoing sound was heard from the rammers, an indication of the compactness of that layer. The width of the formwork enabled users to stand inside it and ram, an advantage that ensured that all the corners and the edges were rammed properly. Mixing and blending
Soils should be well mixed prior to ramming, if:
- There is more than one source of soil to be rammed;
- Stabilizers are to be added;
- Additional water is required to achieve OMC.
Mixing by hand or by mechanical mixer should continue until there is uniform distribution of materials with uniform colour and consistency.
2.3. Stabilization
Stabilizing materials may be added to earth for rammed earth structures to improve strength, to improve resistance against water, or to achieve less shrinkage . Approved materials for stabilization are:
- a) Ordinary Portland cement – see EN 197-1;
- b) Lime or hydrated lime;
- c) Lime combined with pozzolanas such as pulverized fuel ash and ground granulated blast furnace slag;
When the soil, already mixed with a few percent’s of cement, arrives in the box, it is loose and it needs to be first spread with a shovel into the box in a regular layer and then compacted. Soil can be rammed by vibrations or by impacts. Our air compressor and rammer worked by impact; each impact moves the particles of soil that try to escape the pressure into the small niches they can find. The ramming effect creates a solid agglomerate of particles locked one into another, the finest finding some room between the bigger. It is interesting to understand that the locking process does not happen because of a high constant pressure but because the impact of the rammer chases the particles into a locking position from which they cannot return when the pressure has stopped because they remain entangled one with another.
The more they are pushed, the more they remain blocked. It is why it has no sense to use a too powerful rammer, that would put a very high pressure on the structure of the formwork and the building without achieving a better compacting of the soil,because the limit of compacting is easily obtained, even ramming by hand with a simple piece of wood. This description of the process of compacting explains why the layers that are poured into the formwork should not be too thick, because, when the top of the layer compacts under the impact of the rammer it creates a sort of locked assemblage that resists the impact of the rammer and does not transmit it to the lower part of the layer that remains therefore looser that the top part.
After undoing the formwork when the whole wall has been rammed, it is interesting to observe the structure of the wall and to notice how the different layers of successive ramming remain visible and how the bottom of each layer remains less compacted (see picture).
Figure 11: Stabilizing materials
Source Yves de
2.3.1. Shrinkage
Rammed earth as all earth building materials containing clay, swell on contact with water and shrink on drying. Only with tests you can predict the percentage of shrinkage. The range of acceptable shrinkage percentage differs from one building code to another and the range is from 0.05% till 3%. Regardless of any code requirements, the shrinkage characteristics of a soil should be examined and incorporated into the design to satisfy the serviceability requirement of the structure.
Colour lines ,every third or fourth layer you can add a colour line for decoration. One spoon of colour powder is added to the mix. Add the coloured layer in the edge of the wall then pour the normal mixture on top and ram.
Source:…….
2.4.Compressive Strength
For a load bearing structural element compressive strength is the most important strength parameter. Small scale experiments using cylindrical specimens have been reported for assessment of compressive strength and determination of elastic properties by measuring the axial and lateral deformations. BS 5628: Part 1 recommends tests on small panels to estimate wall strength when new masonry materials are used. Study of Jayasingheet al on the strength characteristics of cement stabilized rammed earth walls adopted wallets of height to thickness ratio about 4 and observed that failure is of compressive crushing nature. It is also suggested to have an overall factor of safety of at least 5 in estimating the design stress. IS 1905-1987 also recommends tests on prisms of h/t ratio not more than 5 and a factor of safety of 4 for and assessing the basic design compressive stress of masonry.
2.4.1The sample (resistance and aspect)
The best way to test your soil is to make a sample. Make a frame with wood and ram some soil into it, with the adequate humidity as in test. Let it dry for 1 day, unpack and test it. Expose it to rain and other external influences and see how it behaves. Do a few experiments with different percentages of cement: 2% or 5% or even more if it is necessary. It is best if you can make these tests pretty early in the process in order to give it time to dry, to shrink or crack eventually (too much clay). Test also the resistance to pressure and impact. Make a few different samples with different piles of soil. Let it weather outside, in the rain and in the sun. Make also a smaller sample to be able to transport it easily if you want to choose fitting colour for paint or other materials.
Figure 13: The sample (resistance and aspect)
For a load bearing structural element compressive strength is the most important strength parameter. Compressive strength test using cylindrical specimens gives small scale experimental results along with the determination of young’s modulus and the Poisson’s ratio by measuring the longitudinal and lateral deflections.(Department of CSE, MCA &CE, Mohandas College of Engineering and Technology, Thiruvananthapuram, Kerala, India)
The suitability of soil under test for rammed earth construction is determined using the following laboratory tests
- Particle size distribution analysis
To quantify the proportion of clay, silt and sand content hydrometer analysis was done on the soil, the proportion of clay, silt and sand obtained are 22, 17and 61% respectively. A soil suitable for cement stabilized rammed earth construction sand content should be greater than 50% and clay and silt content should be less than 30% as reported by in the review by Vasilios et.al based Australian earth building hand book. The result obtained from the particle size distribution analysis shows that the soil under test is suitable for cement stabilized rammed earth construction.
- Consistency limits
Determination of consistency or atterberg’s limits are important for classifying the soil and to find the suitability for rammed earth construction. The recommended values for these limits mentioned in review of Vasilioset al are LL to be below 35-40% and Plasticity index to be below 10-30%. In the studies done by Silva et al, it is said that shrinkage index should have a lower value as it affects the shrinkage/swelling characteristics of the soil.
Rammed earth is a material that can be found freely in nature, most often on the building site itself. The process of rammed earth building almost negates any consumption of energy for preparation, transport or building. Rammed earth is completely recyclable and sustainable? The process creates thick walls which protect the inner space from external fluctuations of temperature; the thermal mass flattens the extremes of temperature because of its thermal inertia, it means its slow reaction to change; before the hot sun has been able to heat up the considerable mass of the walls, evening has come with its usually cooling breeze. Similarly in winter the cold of the night has not enough impact to cool down the walls and the interior atmosphere remains warm enough until sun rise.
Thermal mass is different from insulation although it has a similar consequence in the way it prevents heat to be transferred easily through the walls. Insulation relies on many small vacuums in the insulating material that prevent the heat passing through the walls. Thermal mass allows the heat to go through but very slowly because material with thermal mass is usually a relatively bad heat conductor and most of the heat is used on the way through the wall to heat up the mass of the material. In summer the inner wall of a thermal mass will remain cool (it is nice to lean against it) and in winter it will remain warm (no cold radiation will emanate from it). Thermal mass works also to reduce the impact of the heat that penetrates inevitably through the doors and windows, which insulation cannot do. This combines with natural ventilation is very effective. Insulation is necessary in cold climates where the temperature remains low for many days.
Thermal mass is more appropriate for climates where the average temperature remains comfortable despite strong contrasts between day and nights, like generally in arid climates. Both are very different but combine well one with another, if insulation is on the exterior side of the wall and thermal mass on the inner side.Rammed earth is more appropriate for dry countries. Nevertheless many buildings in rammed earth exist in Europe. It is important in any case, in more humid climate, to protect the walls from heavy rains (large roof eves, render, and higher percentage of cement).
Source: Yves de Morsier
2.5. Thermal Performance
Current energy saving criteria require that materials of high thermal resistance (that is, a material’s ability to reduce heat flux) are used for construction, purportedly to reduce the amount of heat transferred through the boundary surfaces of a structure and so reduce its energy demand (Allinson and Hall, 2007). Thermal resistance can be increased either by reducing a material’s thermal conductivity or by increasing the distance through which the heat is passing; this latter option is unsuitable for most applications, however, due to the extra cost of providing the additional thickness. Rammed earth construction suffers as a consequence of this requirement, as the material has a very low thermal resistance (between 0.35 and 0.7 m2K/W, depending on wall thickness) as compared to more modern construction materials, for example insulated lightweight panels (1.51 m2K/W) (Maniatidis and Walker, 2003; Keeton, Owen, Montgomery, & Green, 1980).
However, rammed earth buildings around the world are renowned for their ability to provide comfortable living conditions for a range of climate types without the need for active HVAC control. This success therefore suggests that thermal resistance is not the material property responsible for ensuring comfortable living (Allinson and Hall, 2007; Faure and Le Roux, 2012).
Figure 15: rammed earth buildings
Source: Berge2009
Source: Yves de Morsier
2.6. Traditionally burned clay bricks
The materials used in this research are soils from MURTESA local brick production small and micro enterprise; Dangote Cement used in the stabilization process (42.5R ordinary Portland cement); and hydrated lime (Ca (OH) 2) from Dire Dawa cement and lime factory. While, the water used in this study was a potable tap water from MURTESA local brick production small and micro enterprise water supply system.
2.6.1. Preparation of Materials
Clay soil was excavated by using hand tools and collected on the plastic cover and air dried for one week. This was done to remove the moisture, and to make it easy for grinding. After air drying the grinding was undertaken using a shovel to break the lumps in the soil. Any coarser materials were grinded into fine by hands, and any vegetation roots and stones were removed. The AASHTO Classification of the soil was determined by using the properties of the soil, which represents the percent passing Sieve no. 200, liquid limit, plastic limit and plasticity index. Then the content of stabilization had been determined by the estimated amount of cement stabilization for different AASHTO class soils based on PCA. As indicated in the index properties of the soil the soil, it was A-7 clay soil with the stabilizing amount of cement 10%-14% by volume as per Portland Cement Association estimates. In this research, it was considered 10%, 12% and 14% contents of stabilizer.
Table 3: Standards to conduct index properties of the soil
2.6.2. Production of Clay Bricks
The fired clay bricks for the comparison of the compressive strength and other quality tests with stabilized clay bricks were purchased from MURTESA local brick production small scale enterprise‖. Production of fired clay bricks in Jimma Town is done, first by mudding the soil by foot and then molding by hand. Followed by the so-called green bricks, which is dried about one month if it is sunny season, or 2-3 months if it is rainy season. The final step is brick firing. The firing process takes place by building up a rectangular wall like structure with 40,000-50,000 dried green bricks. The bottom part has
Openings to facilitate the firing process which will last for up to 3 days. Generally, the local FCB production will need at least 35 days if there are 40,000-50,000 bricks can be molded per day which is not possible to obtain. The production of stabilized bricks in this research consisted of proportioning of materials, mixing, molding and curing. As indicated in the index properties of the soil, the clay belongs to A-7 clay soil with the stabilizing amount of cement 10%-14% by volume. The content of cement and lime were taken the same as the estimated cement content of 10%, 12% and 14%. This means, for the ratio of 10% stabilization, 90% parts was clay soil and the 10 parts was cement or lime. After mixing, it was manually compacted the moulded bricks, then curing of bricks followed by using water sprinkle for one week.
2.6.3. Compressive Strength Test on Bricks
Compressive strength test was carried-out to determine the compressive strength of both fired and stabilized bricks in accordance with ASTM C-67. In the laboratory, the materials capped with1: 2 Ratio (by weight) of cement, sand mortar and after 24hrs, the test conducted. Before the stabilized bricks attained the ages of curing for strength test of 7th day, 14th day, and 28th day, the samples brought from the curing area to the laboratory 3 days prior to the test to be conducted, for purpose of capping on its surface. The weight of each brick was recorded before being capped by 1:2 ratios (by weight) of cement sand mortar. Before the compressive strength test conducted, the capped bricks allowed to air dry for 24 hrs. The bricks were then crushed and the corresponding failure load recorded. The crushing force was divided by the sectional area of the bricks to arrive at the compressive strength. For each day of curing, five bricks from each content of stabilizers were taken. That is 5×6 (10% cement, 12% cement, 14% cement, and 10% lime, 12% lime and 14% lime).
The compressive strength test of cement stabilized bricks was conducted in JIT Construction materials laboratory at 7thday, 14th day and 28th day of curing period as per the test method on ASTM C-67. Five cement stabilized clay brick samples for each day of curing with cement content of 10%, 12% and 14% were undertaken(GSJ: Volume 5, Issue 12, December 2017)
The compressive strength of cement stabilized clay bricks (CSCB) is increased with increasing of the content of stabilizer on all days of curing period. The compressive strength results showed that the compressive strengths are increasing with the increment of the content of cement from 10% to 12% and to 14%. This indicated that as the content of cement in the mix increases, the bonding of the minerals in clay soil particles also increases that improved the compressive strength.
A building of the same surface area made of rammed earth construction, using light-clay, which is a combination of clay and straw, woodchips or some other lighter material with density of 900 kg/m3 to obtain a thermal conductivity of 0.3.Our earlier studies already showed that light-clay materials can have good mechanical characteristic.
Comparative analysis showed the variation in features between the rammed earth walls and sandwich wall with several layers of materials including a layer with enhanced thermal insulation characteristics. By comparing these results, it can be noticed that in this example rammed earth walls are only slightly more energy efficient. However, energy efficiency and sustainable development must not be observed only through the exploitation of the building, but rather throughout its whole life span, starting from raw material, incorporation of it into the structure of the building and finally by exploiting
Figure 16: Life span of the building
The energy consumption at each stage of this process, will affect the end result for the construction. By adding the energy consumption needed for demolition of the construction and recycling of the constituent materials, the total balance of energy efficiency can be obtained. It shows the full cost of the building.
Benefits of the rammed earth buildings can be also observed in the simplicity of the process. Raw material for construction is available at the construction site, preparation and construction itself is simple with low energy consumption and minimal mechanical or human labour. The use of traditional materials with new technology leads to energy efficient buildings, where operating costs are minimized with respect to sustainability.
2.6.4. Durability test
Durability test is done by spray test as recommended by IS: 1725-1982 on cubes of 150mmx150mm. One face of the block is exposed to a shower for 2 hours as shown in Fig.8 and then the exposed surfaces are examined for possible pitting. The limiting diameter of the pit formed is to be within 10 mm for passing this weathering as per IS 1725-1982
The pitting depth formed on the cube specimen after 2 hours exposure is 2 mm. Since the result is within the limit, the durability aspect is good for the investigated cement stabilized earth for rammed wall construction.
Figure 17: Spray test on cube specimen
Source:www.ijirset.com
Figure 18: Exposed face of the cube before and after the spray test
Source:
It is also interesting to describe the financial aspects of the work process although this can also vary considerably, given the wide variety of choices that can be made. The following example illustrates what we have spent in our case. It can be reduced to almost zero if one decides to work only with what is naturally available, providing therefore a much more important amount of physical work that has to be bartered in order not to necessitate cash. Although we had already the rammer and the cultivator, they are included in the following calculation as part of the investment. Although we used part of the joists of the building as whalers and did not have to buy so many whalers as described below, we include them in the following calculation as if we had to buy them as new whalers. Normal tools are not included as they are current ones most people have. Rounded figures below arein Australian dollars 2011.
Approximately 1 AUS$ = 1 US$ = 0.75 Euro.
Total surface of the rammed earth walls we built: 90m2 / 32 m3.In reality a first stage of the work has been executed with the help of a contractor to whom $6’000.- has been paid for this first stage (44 m2), work and machinery only, without material costs. Only the second stage has been executed as described above. The real cost of the first stage is also included in the calculation below so that the cost of the second stage can be compared with it.
2.7. Environmental sustainability of rammed earth
The economic and social benefits of rammed earth are not the only attractive features of this material. It has been recognised in different applications around the world that earthen techniques in general and rammed earth in particular have environmental and sustainable benefits. In a study conducted in France (Kouakou & Morel, 2009), the use of locally sourced materials in rammed earth construction demonstrated a significant reduction in the environmental impact when compared to a case in which the construction material is sourced far away and transported to the building site. The energy consumed in transportation can be reduced by 85% when comparing a rammed earth to a typical concrete house. In another project in India (Venkatarama Reddy and Jagadish, 2003), the use of soil and cement to create unfired masonry blocks resulted in a 62% reduction in embodied energy (which is the energy used to produce a material or a product) when compared with a reinforced concrete framed structure and a 45% reduction when compared with burnt clay brick masonry and reinforced concrete solid slab construction.
Table 2.3. Comparison between the total production energy per unit length of wall made of cement-stabilised rammed earth and steel framed.
Table 4: Comparison between the total production energy per unit length of wall made of cement-stabilised rammed earth and steel framed.
Source:………….
It is beyond the scope of this paper to give a proper definition of the word ‘sustainability’. In this work, ‘environmental sustainability’ is used as a term to indicate the environmental impact of the building materials analysed in this case study. The amount of embodied energy, or ‘emergy’, of a material is often used to give an indication of this type of impact (Boyle, 2005). Table 2.3.compares the production energy the energy required to produce the materials from which a building is constructed (Harris, 1999) of a 1 m long and 2.4 m high wall made of 10% cement-stabilised rammed earth and of steel framed panels. In the case of rammed earth, the thickness of the wall has been taken as 300 mm. In the case of the steel framed panels, an equivalent thickness of 5 mm has been calculated averaging the material used in a steel frame of 300 mm/m horizontal and 800/2.4 m vertical spacing, with a corrugated steel laminate on top of it. Assuming that the production energy of earth is negligible with respect to that of steel and cement (no mining or burning is required), the production energy for cement-stabilised rammed earth has been taken as equal to the energy of the cement used in the stabilisation. The numbers in Table 1 show that 10% cement-stabilised rammed earth has significantly lower production energy than steel.
Figure 19: Ram earth construction techniques
2.8. Literature Review Summary and Research Gaps
From previous studies, results and findings of the rammed earth material used is different from the material locally used in Gayaza Canaanite Estate.
