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Ferrocement: Applications in Developing Countries - Part 1 of 3
By pinoyfarmer | July 30, 2007
The National Academy of Sciences, through its Board on Science and Technology for International Development (BOSTID), has been concerned for many years with the application of science and technology to international economic development. The activities of the board have been largely supported by the U.S. Agency for International Development (AID).
Recently, at the request of AID, the Board established an Advisory Committee on Technological Innovation (ACTI) to oversee a continuing, systematic search for, and assessment of, developments in fields of science and technology that may bear particular relevance to the solution of specific problems of developing countries.
An early inquiry referred to ACTI concerned the replacement of the fishing fleet destroyed in the November, 1970, cyclone in what was then East Pakistan. AID wished to obtain information on innovations in boat-building techniques that would accelerate the reconstruction of this desperately needed resource. Preliminary investigations showed that ferrocement held substantial promise for boatbuilding and, indeed, for many other applications. To explore the broad potential of this material for both water and land uses, the board convened the Ad Hoc Panel on the Utilization of Ferrocement in Developing Countries.
This report is the result of the panel’s deliberations during three 1-day meetings in Washington, D.C., and a 4-day session at Airlie House, Virginia, in the course of 1972.
During deliberations the panel often felt need of an analysis of the materials science and basic engineering of ferrocement. No such analysis exists, and the widespread fragmentation and scatter of data through the literature make conclusions and comparisons difficult. The panel recommends that a document on the materials science of ferrocement be prepared by a panel chosen for this purpose.
The panel’s efforts have been greatly assisted by Mignon Cabanilla, Administrative Secretary to the Advisory Committee on Technological Innovation, and by Jane Lecht, the BOSTID editor.
I. Summary and Recommendations
Ferrocement is a highly versatile form of reinforced concrete made of wire mesh, sand, water, and cement, which possesses unique qualities of strength and serviceability. It can be constructed with a minimum of skilled labor and utilizes readily available materials. Proven suitable for boatbuilding, it has many other tested or potential applications in agriculture, industry, and housing.
Ferrocement is particularly suited to developing countries for the following reasons:
· Its basic raw materials are available in most countries.
· It can be fabricated into almost any shape to meet the needs of the user; traditional designs can be reproduced and often improved. Properly fabricated, it is more durable than most woods and much cheaper than imported steel, and it can be used as a substitute for these materials in many applications.
· The skills for ferrocement construction are quickly acquired, and include many skills traditional in developing countries. Ferrocement construction does not need heavy plant or machinery; it is labor-intensive. Except for sophisticated and highly stressed designs, as those for deep-water vessels, a trained supervisor can achieve the requisite amount of quality control using fairly unskilled labor for the fabrication.
The following specific recommendations are based on documentation of the current state of the art and the ad hoc panel’s own evaluation of selected water and land applications of ferrocement, detailed later in this report.
Recommendation 1: Exploratory Research into the Full Range of Ferrocement Applications
The panel recommends that ferrocement be subjected to a wide-ranging program of research and development to explore all its potential uses. Such R & D is likely to produce many valuable applications for the developing world.
Some applications require laboratory analysis (e.g., interactions between stored food and mortar surfaces); some, structural testing; some, demonstration and pilot trials. Other are so speculative that only studies on paper are warranted at present. Research institutions, engineering laboratories, corporations with R & D capability, technical schools, universities, or innovative individuals can engage in this work. Exploration of these ferrocement applications is exceptionally well suited for work on location in the developing world, but a role for research in industrialized nations exists. Although this report stresses less sophisticated applications, ferrocement is adaptable to sophisticated technology, too. Factory-fabricated precision components made from ferrocement may ultimately be the main use of the material. One particularly promising area for more sophisticated R & D is in replacing ferrocement with chopped-wire concrete in which randomly placed short lengths of wire, mixed in with the mortar, take the place of wire mesh.
Following is a list of individual applications the panel felt were particularly worthy of detailed investigation. Some of these applications are specifically discussed in Recommendations 2-6. They are included here to convey a sense of the range of uses for ferrocement. (See also Figures 1-5.)
FIGURE 1: Water-conveying troughs, 20 mm thick, are mass-produced in precast ferrocement units in the USSR (Drawn from diagram in Kowalski, T.G. “Ferrocement in Hong Kong.” Far East Builder. July 1971, p.29.)
POTENTIAL APPLICATIONS OF FERROCEMENT
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Fishing and Cargo |
Boats Grain dryers |
Recommendation 2: Ferrocement for Indigenous Boats
The panel recommends ferrocement as a substitute for materials now used in the construction of traditionally shaped, indigenous boats. This application deserves widespread dissemination, a function that technical assistance agencies might well assume. The record of successful experiments confirms the technical feasibility, but field trials or demonstrations may be needed in some developing areas to overcome local resistance to innovation in boatbuilding.
The Food and Agriculture Organization of the United Nations (FAO) and the United Nations Industrial Development Organization (UNIDO) have taken the initiative in introducing ferrocement in developing countries and demonstrating its importance in a developing-country context. Thus far, however, these ferrocement-based technical assistance projects have been oriented toward larger, oceangoing trawlers with sophisticated western-style hulls, with the objective of increasing commercial fishing capability. Commercial fishing on this scale requires a considerable land-based organization to preserve, transport, and market the product, and the cost of large fishing boats represents an investment that subsistence-level fishermen cannot afford. In this report we are concerned with individual boatmen, whether commercial or subsistence, who would benefit from the low cost, long life, and easy repairs of small, familiarly shaped and familiarly propelled ferrocement boats.
Improving such craft will not initially have the same effect on economic development as introducing fishing trawlers. Yet, the ready acceptance of cheap, traditionally shaped boats could significantly affect economic development because of the much larger number of boats involved and the greatly increased life expectancy over their wooden counterparts.
Ferrocement’s unique characteristics-low cost of materials, strength, ease of maintenance and repair-recommend themselves particularly to the fabrication of small, “native” craft. The usual curved displacement hulls of indigenous craft are appropriate for this material. Small ferrocement workboats can be built on site, by local (but supervised) laborers who are usually available and low cost. Because these boats are mainly hull, and therefore without costly fittings, the builder’s savings are maximized. Never far from land and usually in fresh water, small workboats undergo less stress than deep-water vessels and require less stringent technology and quality control. Moreover, existing wooden craft are often so heavy that conversion to ferrocement sometimes yields boats equivalent or lighter in weight.
Since design improvements can be added incrementally, a traditionally shaped boat might, over the years, also be improved in design. In particular, the use of ferrocement allows all the complex curves of planked wooden boats, as well as the more complex curves that are not possible in wood but would improve the boat’s performance.
Ferrocement is free from attack by teredos (shipworms), wood rot, and other hazards of the tropics. Furthermore, ferrocement boats are inherently strong enough to be powered, some comparable wooden boats are not strong enough to take mechanical power.
Recommendation 3: Ferrocement for Food-Storage Facilities
The panel believes that the urgent need to preserve grain and other food crops in developing countries justifies extensive field trials in the use of ferrocement for silos and storage bins. The existence of successful prototypes suggests that little more research is needed, other than techno-economic and design studies for given localities.
In tropical regions, high temperatures and humidity promote the growth of mold and rot on foodstuffs, destroy moisture-sensitive materials such as bagged cement and fertilizer, and encourage thermal or ultraviolet degradation of many products. Insects, rodents, and birds also take an enormous toll. Perhaps 25 percent* of each year’s food crop in the developing world is rendered unfit or unavailable for consumption because of improper handling, storage methods, and facilities.
Hundreds of ferrocement boats floating on the world’s waterways demonstrate that this material is watertight, and other experience has shown that ferrocement does not readily corrode in the tropics.
Experience in Thailand and Ethiopia** has shown that ferrocement grain silos can be built on site very inexpensively, using only one supervisor and unskilled labor. A simplified version of known ferrocement boatbuilding materials and techniques was used to build the silos. Measurable losses in the prototype silos are less than 1 percent per annum. Rodents, birds, and insects cannot gain entrance. Since these ferrocement silos are airtight, the inside air is quickly deprived of oxygen by the respiring grain, and insects (eggs, larvae, pupae, or adults), as well as any other air-breathing organisms introduced with the grain. are destroyed.
This safe means of storing grains and other foods such as pulses and oilseeds could help farmers in the developing world to become more self-reliant, and could contribute significantly to a country’s economy and food reserves.
Recommendation 4: Ferrocement in Food Technology
In view of the properties, availability, ease of manufacture, and reliability of ferrocement, the panel recommends a serious, wide-ranging effort by research organizations to investigate the use of ferrocement to replace steel- particularly stainless steel-in manufacturing at least some units of basic food-processing equipment.
Many foods-highly perishable, irreversibly affected by temperature changes and biological and chemical contaminents-are lost to mankind because there are no rural processing plants to preserve, convey, or process food products soon after harvest. In many developing areas, high construction costs prohibit the use of even simple manufactured equipment. These costs are largely due to the traditional use of stainless steel, expensive on any account, but especially so in terms of foreign exchange when it has to be imported.
If ferrocement food-processing equipment (perhaps with an inert surface coating) can be developed, it may improve levels of nutrition and lend itself to labor-intensive, cottage-industry food processing in developing countries.
Some advantages of ferrocement for food-processing equipment are its (1) fabrication from mainly local materials; (2) structural strength and reliability, (3) ease, economy, and versatility of construction, (4) ease of maintenance and repair; and (5) easy-to-transport raw materials.
Extensive preliminary laboratory research is needed, particularly to investigate the sanitary properties of ferrocement structures and their ability to meet other specifications for food processing. Nevertheless, the panel believes that the effort is worthwhile in view of ferrocement’s apparent suitability for
· Processing of fruit and vegetables for preservation.
· Fermentation vats for fish sauces, soy sauce, beer, wine, etc.
· Storage vats or tanks for fruit juices, vegetable oil, whey, or drinking water.
· Many other purposes-spray driers for milk, driers for copra, cooking stoves or ovens, dairies, freezing chambers, and slaughterhouses.
Recommendation 5: Ferrocement for Low-Cost Roofing
The panel believes that ferrocement may prove a suitable material for low-cost roofing in developing countries. Applied-science laboratories in developing countries and technical assistance agencies should seriously consider this area for field trials and techno-economic studies.
Adequate shelter is an essential human need, and a roof is the basic element of shelter. But current materials are not meeting the need for roofs. The more-than-80 developing countries in the world suffer from housing shortages resulting from population growth, internal migration, and sometimes from war and natural disaster. For most dwellings in developing countries, a durable roof constitutes the major expense. Roofs made of cheap local materials, such as scrap metal, thatch, or earth products (sand, mud, rock), are usually unsafe and temporary. A secondary problem is the need for adequate and durable supporting structures. In some areas, scarce wooden supports are weakened by decay and insect attack.
Ferrocement represents a potential solution to roofing problems because of its relatively low cost, durability, weather-resistance, and particularly its versatility. Unlike most conventional materials, ferrocement can be easily shaped into domes, vaults, extruded type shapes, flat surfaces, or free-form areas. Because ferrocement is easily fabricated, even in rural areas, by supervised local labor using mainly indigenous materials, it seems an excellent medium for on-the-site manufacture of small or large tiles (shingles) or other roofing elements. Where wooden timbers are very expensive, ferrocement beams might be made on site to replace wooden structures used to support indigenous roof coverings. Its most economical use, however, appears to be for fairly large-span roofs.
Ferrocement is not commonly used for roofing because its promise has not generally been recognized. Its use, particularly in developing countries, must be preceded by more research and experimentation in design and production techniques suited to construction by unskilled labor.
Recommendation 6: Ferrocement in Disaster Relief
The panel recommends ferrocement for careful consideration by disaster-relief organizations. This recommendation combines all the potential applications in developing countries considered by the panel.
After fires, floods, droughts, and earthquakes, the needs for food, shelter, and public health facilities are urgent. Transportation is often disrupted by destruction of roads, bridges, boats, and airstrips. Supplies of bulky conventional building materials may be stranded outside the disaster area, whereas the basic ingredients of ferrocement may be available on the site or easily transported.
The versatility of ferrocement also reduces logistical supply problems: wire mesh, cement, sand, and water can be substituted for the metal used for roofing, woods or plastic for shelters and clinics, asphalt for helipads, steel for bridges, and so on. Moreover, most ferrocement structures, though built for an emergency, will last long after the emergency is over.
In the panel’s opinion, ferrocement could be used at a disaster site for many purposes:
· Transport facilities, from simple boats to barges, docks, marinas, helipads, and simple floating bridges or short footbridges-as well as road repairs.
· Food-storage facilities, quickly designed to local needs and quickly built, to preserve emergency food supplies.
· Emergency shelters such as, for example, the quonset type of roof, which is easy to erect and highly efficient.
· Public health facilities, such as latrines and clinics, built with ferrocement roofs and stucco-type walls of the same wire mesh and mortar.
To prepare for the use of ferrocement in disaster relief, demonstrations in simulated emergencies could be arranged for national and international relief agencies; and cadres of ferrocement workers could be trained in emergency applications and the supervision of local laborers at the disaster site.
Recommendation 7: A Coordinating Committee
The panel proposes that a multidisciplinary Committee for International Cooperation in the Research and Development of Ferrocement for Developing Nations be established, composed of experts from countries that have achieved high competence in using ferrocement, including the Soviet Union and the People’s Republic of China. The committee might be established under the auspices of such agencies as UNIDO and FAO, which already have similar groups concerned with other technologies.* No existing group is available to agencies in developing countries who seek competent advice; yet such an international committee of experts is required at least until adequate standards and safeguards for ferrocement construction** become available- particularly for deep-water uses. Such a committee could help to avoid repetition of several hapless ferrocement enterprises of the recent past.
The proposed committee should have, as a minimum, the following responsibilities:
1. To improve communication and cross-fertilization among all the areas of expertise involved (engineering, chemistry, architecture, agriculture, food science, construction, fisheries, boa/building);
2. To convene meetings that provide opportunities for communication among the experts and technicians; and
3. To provide direction and catalysis for the ferrocement training facilities described in Recommendation 8.
By these actions the committee could further the rational and effective introduction of ferrocement technology into developing countries and encourage research and development to move in an efficient and purposeful manner.
Recommendation 8: Ferrocement Training Facilities
The panel recommends that training facilities in ferrocement technology and application be established. Otherwise, the present serious shortage of trained staff to assist or advise in ferrocement construction projects may limit the establishment of high-quality programs.
The panel strongly believes that ferrocement’s potential justifies the location of such facilities in, or close to, the developing world.
Two existing programs in the South Pacific deserve attention and replication. In New Zealand, the government is funding a training school for ferrocement marine construction. UNIDO has a program in Fiji in which villagers travel to a central boatbuilding yard where they work together to build a “village” boat.
The ferrocement schools proposed by the panel should
1. Train personnel from developing countries to establish water and land ferrocement construction facilities and to supervise construction projects;
2. Prepare personnel to establish country- or local-level training schools; and
3. Produce audiovisual materials.
These ferrocement training schools could be grafted onto existing technical institutions or set up as separate establishments.
Recommendation 9: An International Ferrocement Information Service
Because of rising interest in ferrocement, the panel recommends the establishment of an international service to collect and disseminate information on ferrocement science. Such a service could prevent unnecessary duplication of research and development and ensure that an interested developing country is fully informed of relevant experience with ferrocement in other parts of the world.
This service should be particularly important for fabricators of specific products who wish to know how ferrocement will work for them. Because of the diversity of industries that are potential users of ferrocement and the tendency for individual industries to build up their knowledge independently, the availability of a centralized information service could help promote an efficient development of ferrocement technology.
The information service might well be set up at an academic or research institution already possessing competence and ongoing programs in ferrocement technology.
The information service should have at least the following functions:
1. To maintain an information bank and inquiry referral service on ferrocement;
2. To disseminate information on research and development efforts and on advances in ferrocement technology and experiences in applying it; and
3. To help developing countries identify experienced ferrocement companies and consultants, especially those with experience in developing countries.
Ferrocement is a term commonly used to describe a steel-and-mortar composite material. Essentially a form of reinforced concrete, it exhibits behavior so different from conventional reinforced concrete in performance, strength, and potential application that it must be classed as a completely separate material. It differs from conventional reinforced concrete in that its reinforcement consists of closely spaced, multiple layers of steel mesh completely impregnated with cement mortar. Ferrocement can be formed into sections less than 1 inch thick, with only a fraction of an inch of cover over the outermost mesh layer. Conventional concrete is cast into sections several inches thick with an inch or so of concrete cover over the outermost steel rods. Ferrocement reinforcing can be assembled over a light framework into the final desired shape and mortared directly in place, even upside down, with a thick mortar paste. Conventional concrete must be cast into forms.
These fairly simple differences lead to other, more remarkable differences. Thin panels of ferrocement can be designed to levels of strain or deformation, with complete structural integrity and water tightness, far beyond limits that render conventional concrete useless. Ease of fabrication makes it possible to form compound shapes with simple techniques; with inexpensive materials; and, if necessary, unskilled (but supervised) labor.
HISTORY OF FERROCEMENT
The most extensively used building medium in the world today is concrete and steel combined to make reinforced concrete; familiar uses are in high-rise buildings, highway bridges, and roadways. Yet, the first known example of reinforced concrete was a ferrocement boat. Joseph-Louis Lambot’s original French patents on wire-reinforced boats were issued in 1847 not long after the development of portland cement. (See Figures 6, 7.) This was the birth of reinforced concrete, but subsequent development differed from Lambot’s concept. The technology of the period could not accommodate the time and effort needed to make mesh of thousands of wires. Instead, large rods were used to make what is now called standard reinforced concrete, and the concept of ferrocement was almost forgotten for a hundred years. Reinforced concrete developed as the material familiar today in fairly massive structures for which formwork to hold the fresh concrete in the wide gaps between reinforcing rods and a fairly thick cover over the rods nearest the surface are required.
Reinforced concrete for boatbuilding reappeared briefly during the First World War, when a shortage of steel plates forced a search for other boatbuilding materials. The U.S. and U.K. governments, among others, commissioned shipbuilders to construct seagoing concrete ships and barges, some of which continued in use after the war. The same phenomenon occurred in the United States during the Second World War. However, the conventional use of large-diameter steel rods to reinforce the concrete required thick hulls, making the vessels less practical to operate than lighter wood or steel ships.
In the early 1940’s, Pier Luigi Nervi resurrected the original ferrocement concept when he observed that reinforcing concrete with layers of wire mesh produced a material possessing the mechanical characteristics of an approximately homogenous material and capable of resisting high impact. Thin slabs of concrete reinforced in this manner proved to be flexible, elastic, and exceptionally strong. After the Second World War, Nervi demonstrated the utility of ferrocement as a boatbuilding material. His firm built the 1 65-ton motor sailer Irene with a ferrocement hull 1.4 inches (3.6 ems) thick, weighing 5 percent less than a comparable wood hull, and costing 40 percent less. The Irene proved entirely seaworthy, surviving two serious accidents. Other than simple replastering necessitated by the accidents, the hull required little maintenance.
Despite this evidence that ferrocement was an adequate and economical boatbuilding material, it gained wide acceptance only in the early 1960’s in the United Kingdom, New Zealand, and Australia. In 1965, an American-owned ferrocement yacht built in New Zealand, the 53-foot Awahnee, circumnavigated the world without serious mishap, although it encountered 70-knot gales, collided with an iceberg, and was rammed by a steel-hulled yacht. Other ferrocement boats have shown similar practicality, and their number is steadily increasing.
Recent emphasis on ferrocement as a boatbuilding material has obscured Nervi’s noteworthy applications to buildings. He built a small storehouse of ferrocement in 1947 (Figure 15). Later he covered the swimming pool at the Italian Naval Academy with a 50-foot vault and then the famous Turin Exhibition Hall-a roof system spanning 300 feet. In both ferrocement is one of the structural components; the ribs and outer surface are reinforced concrete (as in Figure 8).
Nervi’s work and subsequent applications presage an application of ferrocement on land that may overshadow the fresh-water applications.
CHARACTERISTICS OF FERROCEMENT
Ferrocement is a high-quality structural material whose simple constituents and formation make it usable for many construction purposes in even the most underdeveloped societies. In no way an inferior product specifically for cheap uses, it is in some respects more sophisticated than prestressed concrete. Ferrocement usually uses a freestanding frame of wire mesh that is mortared in place on site. The wire mesh is formed into the desired shape (domes, simple curves, or compound curves). Supporting framework used to outline the shape can be wood, precast concrete, or a simple jig made from steel rods or pipes. These supports are usually very rudimentary and serve only to outline the shape for the layers of wire mesh to be added next. They can eventually be removed or left in place to become part of the final structure.
The economy of ferrocement construction, compared with steel, wood, or glass-fiber reinforced plastic (FRP), depends greatly on the product being built, but ferrocement is almost always competitive, particularly in tropical developing countries where steel is expensive, frequently drains foreign exchange reserves, and requires sophisticated facilities and skilled operators. FRP is much more costly, creates a fire hazard, requires advanced technology, sophisticated materials, and skilled labor; and its ingredients are sensitive to tropical temperatures. Wood is almost nonexistent in many arid or deltaic countries. Even heavily forested countries such as Indonesia, the Philippines, and Thailand foresee serious shortages due to growing demands of an increasing world population. Furthermore, in the tropics wood is subject to rot, insects, and teredos.
The relatively low unit cost of materials may be the greatest virtue of ferrocement. Worldwide, the costs of sand, cement, and wire mesh vary somewhat; but the greatest variable in construction costs is the unit cost of labor. In countries with high-cost labor, the economics of ferrocement often make it noncompetitive. But, according to UNIDO, experience has shown that where unskilled, low-cost labour is available and can be trained, and as long as a standard type of construction is adhered to, the efficiency of the labour will improve considerably, resulting in a reduced unit cost. Under these conditions, ferrocement compares more than favourably with other materials used in boatbuilding, such as timber, steel, aluminum or fibreglass, all of which have a higher unit material cost and require greater inputs of skilled labour.*
SUITABILITY TO DEVELOPING COUNTRIES
Although the increased interest in ferrocement for water and land use is fairly recent, successful examples of innovative applications, within a wide range of construction techniques and sophistication, already promise a major impact on developing countries for the following reasons:
1. Ferrocement may be fabricated into almost any conceivable form to meet the particular requirements of the user. This is particularly pertinent where acceptance of new materials may be dependent on their ability to reproduce traditional designs.
2. The basic raw materials for the construction of ferrocement-sand, cement, and reinforcing mesh-are readily available in most countries. Sand and cement are used in building and road construction, and mesh is used in agriculture (chicken netting) and housing construction (plastering lath).
3. Except for highly stressed or critical structures such as deep-water vessels, adequate ferrocement construction does not demand stringent specifications. A wide range of meshes can be used; both hexagonal and square meshes have produced successful structures. The cement is of standard quality used in building construction. Special grades are unnecessary.
4. Little new training is required for the laborers, providing a skilled supervisor is on hand. Cement construction techniques are widely known in developing countries, and indigenous construction workers often show a good aptitude for plastering. (See Figures 9, 10.)
5. Transportation, logistics, and materials-handling are serious problems in developing countries, and ferrocement construction simplifies each one. Sand and water can usually be obtained in the region of the building site; and the quantity of cement normally required can be easily transported. Only the wire mesh may require transportation from distant production centers. Under extremely difficult conditions (such as in the roadless highlands of Nepal), wire mesh may be handloomed on site from reels of straight wire, a technique apparently already in use in rural areas of the People’s Republic of China. (See Appendix A.) For simple, indigenous-type boat hulls and agricultural or construction uses, no well-developed or centralized building site is required (though it is an option for a builder). Construction can well be done on site at the riverbank, in the village, high in the mountains, or wherever needed.
6. Ferrocement withstands severe abuse. Authenticated reports tell of boat hulls wrecked on reefs and successfully surviving savage poundings. Afterwards, the ferrocement was easily and rapidly repaired on site. Only simple tools are needed to repair any damage to the mesh and only cement and sand to make a fresh mortar. Such repairs are usually good for the remaining life of most ferrocement products, though the more stringent requirements of deep-water boats may dictate that the repair be reworked by skilled labor.
This report explores these advantages in land and water uses, and summarizes the basic material properties of ferrocement. Appendices contain descriptions of specific applications.
III. Ferrocement for Boatbuilding
Ferrocement boats have been built and are now operating in, among other places, India, Ceylon, Uganda, Dahomey, New Guinea, Thailand, Samoa, New Caledonia, Fiji, Hong Kong, the Philippines, Cuba, Ecuador, the People’s Republic of China, South Vietnam, Iran, Egypt, Brazil, and the Bahamas. This steady growth in application in developing countries constantly adds to our understanding of ferrocement’s unusual properties and how this thin shell of highly reinforced cement can provide a surprisingly strong, yet simply fabricated boatbuilding material.
Boatbuilding applications of ferrocement can contribute to economic development and the general welfare of people in developing countries, particularly as quality timber suitable for boats becomes scarce because of housing and other demands from rapidly increasing populations. Moreover, quality timber often has a limited life: in tropical water teredos attack it, and in many coastal but arid regions (as the Red Sea region) the drying action of the sun seriously affects wooden craft pulled up on the beach. Accordingly, many boats last such a short time that owners are continually in debt-they cannot repay the initial loan before they need new loans to replace worn-out boats.
Of the two general types of ferrocement boatbuilding, one has been practiced in a good many countries around the world, and the other has found typical application in the People’s Republic of China. The first involves western-style craft with hulls built with state-of-the-art technology for deep-water fishing or recreation. Often as complicated as other boatbuilding methods, this type of construction requires some skilled labor, is relatively expensive, and in developing countries is mainly suited to equipped shipyards. Experience with this approach goes back a decade. Typical examples are FAO projects in Thailand* and Uganda, UNIDO projects in Fiji, and the commercial construction of fishing vessels in Hong Kong. The panel recommends that developing countries enter ferrocement programs for such oceangoing ferrocement boats only with expert supervision, with extreme emphasis on quality control, and in a well-equipped boatyard. Under these conditions, craft can be made that contribute significantly to deep-water fisheries development.
FERROCEMENT FOR CRAFT OF LOCAL DESIGN
The second type of ferrocement application is the construction of simple, indigenous hulls designed for smooth-water use, such as the ferrocement sampans built by the thousands in the People’s Republic of China. In Appendix A, these Chinese techniques are discussed, and photographs show clearly the unsophisticated conditions in which a rural commune produces fairly large and very satisfactory boats at a rate of about one per day. This experience demonstrates that unlike deep-water craft, these ferrocement boats can be built with confidence within the lesser standards attainable in rural areas of a nonindustrialized country.
Indigenous workboats (such as sampans, dugout canoes, chows, and the type of craft used on the Ganges, Nile, Zaire [Congo], and Mekong Rivers) with curved hulls 25-60 feet long are ideally suited to ferrocement’s unique characteristics and take best advantage of them. Ferrocement derives great strength in curved shapes. The lack of design specifications-a worry of naval architects now working on deep-water vessels-is relatively unimportant for these craft. They require less stringent technology and quality control because they undergo far less stress and danger than deep-water vessels.
Indigenous boats are mainly hull, which allows ferrocement’s cost savings to be maximized for the builder. (In a western-style boat internal fittings often account for a high percentage of costs; any saving on the hull is a small part of the total cost.) Indigenous-style boats are best built locally, by the usually available and low-cost labor supervised by a trained technician.
Indigenous craft are often unpowered, at least by an internal engine, so questions of adequate hull support for drive-shaft vibration (the lack of which caused one celebrated ferrocement failure in a developing country) are irrelevant. Yet, the boats can easily be powered externally, an important advantage where existing wooden boats are too frail to take power (as in the Ganges Delta).
Several panelists felt that the use of “long-tailed,” powerpole, outboard engines should be explored in development programs for simple ferrocement hulls. Such engines are used by the thousands in Thailand because of their simplicity, lightness, and versatility.
Ferrocement, with its adaptability to curves, may improve local designs by allowing the corners required by the current plank construction to be smoothed out.
Weight is not a major factor in the displacement-type hulls of indigenous-styled boats, although they are often already so heavy that conversion to ferrocement may yield craft equivalent or lighter in weight.
BUILDING A FERROCEMENT BOAT
In industrialized countries many ferrocement boats are built in backyards far from water, but in developing countries building sites will probably be at the water’s edge because of transportation difficulties. A waterfront location should be chosen with the size of craft, its draft, and its launching clearly in mind.
Although the site must be accessible for delivery of construction material, it can be located far from commercial harbors because needed equipment and tools are portable. Cement and wire mesh, as normally packed for shipping, seldom dictate choice of a site, but availability of sand may be important in areas where bulk transport is particularly difficult. Electricity may be desirable in some cases, but is not necessary. A shelter will be required to protect unused cement and improve working conditions in rainy areas. In river and coastal regions, where the need for boats may be very scattered, or in areas where flooding and terrain changes make a single building site less practical, the entire production facility could be located on a barge capable of moving to all sites, or of moving with fluctuating flood levels.
There are five fundamental steps in ferrocement boat construction:
1. The shape is outlined by a framing system.
2. Layers of wire mesh and reinforcing rod are laid over the framing system and tightly bound together.
3. The mortar is plastered into the layers of mesh and rod.
4. The structure is kept damp to cure.
5. The framing system is removed (though sometimes it is designed to remain as an internal support).
Where scaffolding equipment is not readily available, the hull may be built in an inverted, or upside-down, position, resting on a suitable base (see Appendix A). There are several ways to form the shape of a boat. One can build a rough wooden boat first, or use an existing, perhaps derelict, boat. In another method, pipes or steel rods frame the shape of the hull. A third way is exemplified by the construction of Chinese sampans (described in Appendix A): a series of frames (welded steel in this case) and bulkheads (precast in ferrocement) are erected to shape the hull. Layers of mesh are then firmly bound to the frames, which are left in place to give rigidity to the final hull.
Recent methods for outlining the hull’s shape include using thin strips of wood to which the mesh and rod are stapled and which remain inside the final concrete structure. Other innovations include plastering the outside of the hull first and finishing the inside a day or two later after the frames, or supports, have been removed.
BOAT SIZE
Ferrocement boats from 25 to 60 feet long have been built to operate successfully. Above and below this range, ferrocement has not yet been used long enough for the panel to class it markedly superior in all respects to alternative materials. Yet the need to build craft less than 25 feet long from cheaper and longer-lasting materials is great because many such small craft are used in developing countries. Most important for river use in certain countries, they often provide a major means of personal transport (in the Ganges Delta and Mekong Basin, for instance).
Some small craft have been built, and some U.S. university engineering schools have competed in ferrocement-canoe-building contests and races. These isolated examples suggest that further development work could make ferrocement boats in the less-than-25-foot range practical, as well as competitive with wood, fiberglass (FRP), and metal boats.
The panel believes that developing country laboratories interested in research into ferrocement application will find challenge in concentrating on methods to produce suitable small craft. Research is also needed at the other extreme, for hull lengths over 60 feet, but this job should not be tackled without adequate facilities.
QUALITY CONTROL
Ferrocement, like conventional boatbuilding materials such as steel, aluminum, or FRP, benefits by good specifications and quality control. At each step of assembly, careful inspection should ensure a product quality consistent with its expected use. Inspection procedures deal mainly with common-sense issues and are primarily visual.
In countries proposing to engage in significant ferrocement boatbuilding activities it would be desirable for appropriate laboratories to evaluate the basic raw materials at hand: cement, sand, and water-by district if necessary. Test panels should be made to determine their properties and to establish guidelines for appropriate mixes.
Ferrocement boatbuilding supervisors should maintain a continuing quality-control program. This vital factor is one potential source of weakness in the use of ferrocement for building deep-water vessels, since workmen in developing countries may have neither an understanding of, nor a concern for, specifications and quality control. It is to teach supervisors the principles of ferrocement quality control, among other things, that the training institutions suggested in Recommendation 8 are required.
When mortar is forced through the many layers of mesh used on a deep-water boat, it is difficult to ensure complete and uniform penetration. Some construction methods aggravate this difficulty more than others. Because of this problem, boats have been built with unsuspected air holes within the ferrocement; the resulting voids cause weak points in the hull, especially if water enters and corrodes the mesh. If necessary, hulls can be drilled to find voids and then grouted (filled with more mortar). Proper application technique and adequate quality control, however, will ensure that good mortar penetration takes place. A simple vibratory tool, such as an orbital sander, usually solves most of the problem. Corrosion seldom occurs if adequate mortar cover is maintained over the reinforcement.
However, as previously suggested, the degree to which these factors are important depends upon the expected use of the vessel.
CAUTIONS ON FERROCEMENT FOR DEEP-WATER CRAFT
The panel concentrated on simple craft for inland waterways of developing countries because in this situation current ferrocement technology can be utilized with confidence, despite the many differences of available skills, boat design, climate, etc., among countries. However, ferrocement boatbuilding in technically advanced countries has, so far, emphasized pleasure craft and trawlers designed for deep-water use, and the panel feels a responsibility to reiterate the warning to developing countries that more caution is needed when they consider ferrocement for these craft.
Ferrocement meets its ultimate test at sea: the stresses are large and unpredictable, and human lives are at stake. Boat design is not a precise science, and a pressing worldwide need exists for adequate structural-design information. This need applies to other materials, but ferrocement is less widely known or understood. Because its very nature requires combinations of constituent materials, quality control is important, but the development of ferrocement has been pushed forward largely by innovative amateurs who little understood the material and, sometimes, boat design. Only now is the engineering community beginning to investigate ferrocement as a boatbuilding material. Detailed specifications and standards are still at an early stage of formulation.
Successful ocean-going boats and marine structures can be built, and have been by the hundreds. Some ferrocement boats have survived extremely rough treatment, but there have also been striking failures. In developed countries, some commercial ferrocement boatbuilding ventures have been overpromoted and have gone into bankruptcy. The panel recommends that developing countries planning to construct ferrocement trawlers and other deep-water craft should exercise great care in selecting boat designs and ferrocement expertise at this time. They should carefully investigate any company proposing to establish local operations, inquiring into the number of boats it has built, and the professional background of the company’s staff (see Recommendation 9).
Ferrocement’s weakest feature, compared to wood or steel, in deep-water boats is its lessened resistance to penetration by a sharp object. This penetration is called “punching” to separate it from “impact” in which a broad surface area is struck and to which ferrocement is quite resistant. Small holes can be quickly repaired, but when punching is likely to be a serious problem, some sort of surface protection might be added, or the steel content of the ferrocement could be increased.
These cautions do not contradict earlier statements on the simplicity of ferrocement construction; they stress only that techniques of design and construction are new and that for deep-water boats they must meet very stringent requirements.
OTHER APPLICATIONS ON WATER
Ferrocement could be used in the construction of floating wharfs, which can be placed (or built) in any location, thus providing access to otherwise inaccessible coastal or river areas. Tugboats seem to be ideal craft for ferrocement construction because they are heavy and highly fendered. Barges are also important applications for ferrocement, particularly the ark-shaped lighters used widely in Southeast Asia, Africa, and Latin America. Flat-sided, flat-bottomed barges are less adaptable, but an apparently successful one is operating in Thailand, carrying cement on the Chao Phya River. Reinforced concrete barges (with reinforcing rods rather than mesh and with walls several inches thick) have been operating successfully for many years in Hawaii, the Philippines, and New Zealand.
Developing countries might also take advantage of their labor resources to construct high-quality, western-style, deep-water pleasure craft for export to North America and Europe.
Other structures on water are adaptable to ferrocement construction in developing countries. They are listed below to suggest the possibilities.
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Buoys |
Floating and submerged oil reservoirs |
Related Posts:
Ferrocement: Applications in Developing Countries - Part 2
Ferrocement: Applications in Developing Countries - Part 3
Source: Ferrocement: Applications in Developing Countries (BOSTID, 1973, 89 p.)
Topics: Technologies |
