This is a series published in the 1980s by Volunteers in Technical Assistance to provide an introduction to specific state-of-the-art technologies of interest to people in developing countries. The papers are intended to be used as guidelines to help people choose technologies that are suitable to their situations. They are not intended to provide construction or implementation details. People are urged to contact a knowledgeable organization for further information and technical assistance if they find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated almost entirely by VITA Volunteer technical experts on a purely voluntary basis. Some 500 volunteers were involved in the production of the first 100 titles issued, contributing approximately 5,000 hours of their time. VITA staff included Leslie Gottschalk and Maria Giannuzzi as editors, Julie Berman handling typesetting and layout, and Margaret Crouch as project manager.
Permission has been granted by the current holder of Intellectual Property Rights for VITA content, Relief International, to publish the VITA library on ECHOcommunity.
Please note that re-release of these documents is a work in progress where we are recovering images and tables from archival documents.
128 ฉบับสำหรับการตีพิมพ์ครั้งนี้ (แสดงปัญหา 237 - 228)
People discovered bow to use clay over 20,000 years ago. The basic principles of shaping, drying, and firing clay are still the same today as they were then. The only significant changes since the discovery of clay have been the identification of additional clay materials and improvements in the methods of making clay products.
Every age has left behind objects made of clay. Before the introduction of plastics and sheet tin, most containers for food--whether in solid or liquid form--were made of clay or glass. Clay was also used for architectural decoration as well as structural material, for it was plentiful and long lasting.
Although the introduction of new materials and techniques has reduced the use of clay in many areas, clay still plays an important role. It is a versatile material that can be used at all levels of technology. It is common in most parts of the world, and it is possible to collect and use it for some types of products without large capital outlays. Yet, in many developing countries, it is an underutilized resource.
Clay occurs naturally almost everywhere in the world and is formed by the action of weathering on several kinds of rocks. This process takes many thousands of years, but it happens wherever the rocks are exposed to the natural forces of wind, water, frost, etc. The rocks change very slowly in both physical and chemical ways. Physically, they break down into smaller and smaller bits; chemically, elements are added and taken away. After a long, long time, some of the rock changes to clay. The longer the geological period of time, the more clay is formed. There are several different kinds of clay minerals and most clay deposits contain more than one kind. "Clay" is the general term that is used for all the clay minerals. Some of these clay minerals or clays are of greater use to the potter than others. It takes difficult laboratory tests to determine just which clay minerals are present in a particular clay. As practical potters, however, we are more concerned with how the clay works in use, rather than exactly what is in it.
Concrete is a strong and inexpensive construction material when it is properly prepared and used. This introduction explains the importance of a good mixture and describes the materials used in the mixture. Following this are entries on:
- Calculating amounts of materials for concrete
- Mixing concrete by machine or by hand
- Testing concrete mixtures
- Making forms for concrete
- Placing concrete in forms
- Curing concrete
- Making quick-setting concrete
- Useful sources of information on concrete
The investment and labor force required for this plant are very small. The objects are decorated with the application of ceramic colors, engobes, and stains, all of which can be purchased initially in the United States, England, France, or Germany, and later fabricated by the potter. The local market in less developed areas will be limited because of the low average income of the people. The market among tourists will depend to a large extent on the degree to which the products have preserved their native characteristics in the process of factory production. If a distinctive style is preserved and an export market established through direct shipments abroad (not only through tourist trade), factory production may be economically feasible.
Bridges are a part of the transportation system of a region. They are used to span an obstacle like a stream or chasm. Bridges make the system more efficient either by saving travel distance or by enabling vehicles or pedestrians to reach places that were previously inaccessible.
There are four basic types of free-standing bridges: beam, arch, truss, and suspension. In addition, pontoon bridges, which actually float on the surface of the water, are used in some situations. While all bridges are built from the basic structural units of bending, tension, and compression members, the design of suspension and pontoon bridges is highly specialized and their construction is usually too costly for small-scale applications. This paper, then, limits its discussion to beam, arch, and truss bridges.
Bamboo is one of the oldest materials people have used to increase their comfort and well-being. In today's world of plastics and steel, besides continuing to make its traditional contributions, bamboo is growing in importance. Outstanding varieties of bamboo from throughout the world are being tested to find out how they can contribute to local economies.
Every low-cost housing project seeks to build the most durable house at the lowest cost possible. Emphasis is always given to the maximum use of locally available materials, such as adobe. Common adobe, as it has been known for centuries, is simply a soil mixture with a clay content of at least 40 percent. It becomes a sticky mud when mixed with water. This soil is used to make building blocks using simple wooden molds. ()
Traditional adobe can be an acceptable alternative to wood, masonry, cement, or steel housing. If the adobe blocks are thoroughly dried before use, the walls should not shrink or crack. Adobe attracts moisture, which erodes its cohesiveness. An annual application of a firm coat of mud plaster will prevent block erosion. One coat is usually sufficient in regions that do not receive large amounts of rainfall; in rainier, more humid areas, two coats are needed. Stabilizing adobe will also prevent moisture degradation.
This paper suggests an approach for improving traditional adobe as a building material. It focuses on soil selection and the proper methods for controlling the moisture content of the material. These two factors influence the performance of the unstabilized adobe, and determine the success or failure of the stabilization process. Stabilizers that are known to be efficient when used with adobe (e.g., straws, cement, asphalt emulsion, and lime) will be discussed.
The Product. To make Portland cement, a crushed mixture of limestone and clay is heated to form "clinker," which is mixed with gypsum and ground to a fine, dehydrated powder. Quality control is essential during manufacture. The cement is shipped in moisture-resistant bags or other containers, or in bulk.
When mixed with sand, gravel, and water in proportions that depend upon the application, it sets to a dense, rock-like material, called concrete or mortar. Additives may accelerate or retard the set, increase strength, or make it resistant to acid, sulphate, shrinkage, or freeze-thaw cracking.
The Facility. This Profile describes a small plant producing 35,000 metric tons of cement a year.
In many parts of the world, the primary source of energy for such vital activities as cooking and space heating is burning wood and other agricultural products. An increasing population using a dwindling resource of combustible biomass materials will eventually result in a shortage of those materials unless steps are taken to reverse the trend.
One means of making more efficient use of existing resources is through the use of briquetting. Briquetting involves collecting combustible materials that are not usable due to a lack of density, and compressing them into a solid fuel of a convenient shape that can be burned like wood or charcoal. Materials such as sawdust, wood bark, rice husks, and straw have been successfully briquetted.
During the first and second World Wars, households in several European countries employed a simple lever-operated briquetting press that used soaked waste paper and other combustible domestic waste as a feed stock. Today's industrial briquetting machines, although much larger and more complex, operate on the same general principles.
Although briquetting has been widely used in the metallurgical industry to recover metal filings, shavings, and scraps that would otherwise be of little value, this paper is concerned solely with the briquetting of combustible materials for fuel. The focus is on simple technologies that can be employed on a small to intermediate scale.
The purpose of this manual is to outline, in as simple a manner as possible, the details of making and burning clay brick suitable for domestic building. The scope of the manual is confined to "cottage industries"; it does not cover large commercial production such as is known in the United States. The author has had personal contact with such brickmaking plants in both Central Mexico and Honduras. It is hoped that by publishing some of the observations and experiences made at these two locations, I can help community development leaders to offer advice and assistance in developing areas where brickmaking plants are needed.