10-04-2017, 09:35 PM
Compressed Stabilised Earth Blocks
Compressed Earth Block often referred to simply as CEB, is a type of manufactured construction material formed in a mechanical press that forms a compressed block out of an appropriate mix of fairly dry inorganic soil, non-expansive clay, aggregate, and sometimes a small amount of cement. Typically, around 3000 psi is applied in compression, and the original soil volume is reduced by about half. The compression strength of properly made CEB can meet or exceed that of typical cement or adobe brick. Building standards have been developed for CEB.Creating CEBs differs from rammed earth in that the latter uses a larger formwork into which earth is poured and tamped down, creating larger forms such as a whole wall or more at one time.CEB blocks are assembled onto walls using standard bricklaying and masonry techniques. The "mortar" may be a simple slurry made of the same soil/clay mix without aggregate, spread or brushed very thinly between the blocks for bonding. Cement mortar may also be used for high strength, or when construction during freeze-thaw cycles causes stability issues.
INTRODUCTION
The history of civilization is synonymous to the history of masonry. Man s first civilization, which started about 6000 years ago, was evident from the remains of the Mesopotamians masonry heritage. During those days, masonry buildings were constructed from any available material at hand. The Mesopotamians used bricks, made from alluvial deposits of the nearby River Euphrates and Tigris to build their cities beside two rivers. Where civilization existed in the vicinity of mountains or rocky outcrops, stone was used. The Egyptian pyramids that existed along the rocky borders of the Nile valley were examples of such stone masonry. In the Eastern civilization, remains of historical masonry are the reputed Great Wall of China, which is considered as one of the seven construction wonders in the world.
The prevision of good quality housing is recognized as an important responsibility for welfare of people in any country. For this, building materials based on natural resources are often used. Some examples are the use of clay for making bricks, and river sand for making cement sand blocks. The commercial exploitation of these resources often leads to various environmental problems. If clay mines are not properly filled up, they can collec twater and allow mosquitoes to breed. Extensive sand mining can lower the river- beds and allow salt-water intrusion inland. Therefore, the development of many alternative walling materials as possible will be of immense benefit to minimize the impact on the environment. Earth can be used for construction of walls in many ways. However, there are few undesirable properties such as loss of strength when saturated with water, erosion due to wind or driving rain and poor dimensional stability. These draw backs can be eliminated signifycantly by stabilizing the soil with a chemical agent such as cement. Cement stabilized soil is generally used as individual blocks compacted either with manual hydraulically operated machines. Significant research data are available for these applications either as block strength or wall strength (Perera and Jayasingh, 2003; Reddy and Jagadish, 1989).
The early forms of masonry application in Malaysia dated back about 350 years ago with the construction of the Stadthuys in Malacca, built by the Dutch in 1650. The British colonized the Malaysia Peninsula initiated a more modern form of masonry construction. Brickwork buildings were at that time built specially for government offices, quarters and residential homes. The administrative block, Sultan Abdul Samad building built in 1894 and given a face-lift during the Fourth Malaysia Plan (1981- 1985) is an example of a masonry heritage, which stands as a remarkable landmark of Kuala Lumpur. During the Production of earth materials
Clay bricks
Brick is a ceramic material mainly used in construction industry. Its production process involves forming of clay into rectangular blocks of standard size, followed by firing to temperature ranging from 900 - 1200 C1. It is made of clay or shale and when given desired shape is dried and fired into a durable ceramic product. Brick is one of the most important building materials. Energy consumption and pollution are the two important environmental and cost concerns related to the brick industry. A report, in 1993, indicated that more than 3000 brick kilns in operation in the country with an annual growth of 3% (Egbert, 1993). Old rubber, low quality coal, wood and used-oil were reported as fuel in most brick kilns.
Consumption of these fuels, combined with inefficient combustion process produces large quantity of hazardous gases that threaten the environment as walls as those working in brick kilns. Since long, in fact, the brick-industry in the country has remained mostly traditional with no importance to enhancement or standardization of physical properties of the final product at all. Among the problems faced by the industry, the first and probably the most important is the supply of reasonably priced fuel in the form of fuel wood as walls as coal. A second major problem is that the industry is not walls organized and technically ill prepared with very little know-how about it and few engineers and scientists having taken interest in this industry (Egbert, 1993).
The history of brick industry is very old and can be traced back to about 5000 years old. Understanding of the brick, micro structure as influenced by the range of temperature during firing cycle has been enhanced by the experimental work in this area. For example, Convile et al. (2005) investigated the micro-structural evolution of various clays using XRD and TEM. They observed that,the pseudo-hexagonal morphology of the kaolinite changed to pseudo-hexagonal meta-kaolin at around 550 C with meta-kaolin broken down at temperatures > 900 C to -alumina-type spinal and a silica-rich phase.
The spinal type phase started to transform into mullite at > 1000 C. At 1300 C, mullite increased in size to 1 m and in some regions, cristobalite formed from the silica rich matrix (Convile et al., 2005; Lee et al., 1999). XRD, TGA/DTA and EF-TEM studies of clay have revealed that meta-kaolin partially transforms to -alumina at 920 C (Peters and Iberg, 1978) Figure 1. On further increase in the firing temperature to > 940 C, the crystallization of Al2O3-rich mullite began and excess amorphous silica was discarded into the matrix (Peters and Iberg, 1978).
Mullite begins to crystallise at 1050 C and its crystal size increases with increase in firing temperature (Convile et al., 2005). A number of phases are usually present in fired bricks. Quartz is observed in all samples, usually less abundant in the brick than in the raw material.Hematite is also present in all samples, which impart the red colour to bricks. Even in yellow bricks, the presence of Hematite is observed though in smaller amounts (Amjad, 2000).
Clay brick strength
Compressive strength of brick is important as an indicator of masonry strength and as a result brick strength has become an important requirement in brickwork design. A considerable amount of past research and studies on masonry indicated that stronger bricks contribute to greater brickwork strength (Hendry, 1990; Lenczer, 1972; Sahlin, 1971).
In Singapore, Standard SS 103 (1974), compressive strengths are classified as First, Second and Third Grade with minimum compressive strength of 35, 20 and 5.2 N/mm2
, respectively. Figure 2 shows the relationship between strength of brick and strength of wall. The British standard (BS, 3921, 1985) categorized compressive strength into classes of engineering A and B presented in Table 1. These classifications of bricks commonly used
Clay brick density
Raw materials and manufacturing process affect bricks density, which could vary between 1300 - 2200 kg/m3.The density of bricks influences the weight of walls and the variations in weight have implications on structural, acoustical and thermal design of the wall. Incorrect assumptions on wall weight can result in inaccurate dead loads and seismic loads, reduced factor of safety in shear walls and overestimate of acoustical transmission loss (Grimm, 1996).
Stabilized compressed earth blocks
The new technology focuses on stabilized earth masonry brick development incorporating an industrial by-product material, which is vital for the future of construction. The stabilized earth masonry brick technology relies on the use of an activated industrial by-product (Ground Granulated Blast-furnace Slag GGBS) and natural earth. Due to the use of a by-product material in the formulation, it is anticipated that the final pricing of the stabilized earth masonry building brick will be reduced.The added environmental advantage of utilizing industrial by-products available in the country will further improve the sustainability profile of masonry brick production. The use of a cement replacement material (GGBS) with a lower environmental burden offers opportunities for significant reductions in energy use and carbon dioxide emissions. One of the most effective alternatives to Portland cement is GGBS, which has the potential to typically replace up to 80% of the Portland cement (Oti et al., 2008a). GGBS has extremely low energy usage and CO2 emission when compared with PC. The energy usage of 1 ton of GGBS is 1300 MJ, with a corresponding CO2 emission of just 0.07 ton Higgins (2007), while the equivalent energy usage of 1 ton of PC is about 5000 MJ Higgins (2007), with at least 1 ton of CO2 emitted to the atmospheres (Wild, 2003).