Ferrocement Applications in Developing Countries/Appendices

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Ferrocement Applications in Developing Countries

• Summary and Recommendations
• Background Information
• Ferrocement for Boatbuilding
• Ferrocement for Food-Storage Facilities
• Ferrocement for Food-Processing Equipment
• Ferrocement for Low-Cost Roofing
• Ferrocement Materials Technology
• Appendices

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The eight photographs herein of ferrocement boatbuilding in a commune in the People's Republic of China are the first such to be published in the West. They show a large boatbuilding program in which simple ferrocement craft are produced With unsophisticated techniques in a rural area of a developing country. The photographs were taken by Anne Keatley, of the National Academy of Sciences, who visited the People's Republic in June, 1971.

The following text includes a report by Robert Keatley, a journalist who observed the site in 1971, and an analysis by the NAS panel of a total of 26 photographs.

First, the journalist's account:

A drive from Shanghai through the nearby countryside quickly shows a visitor why small boat construction is an important activity there. The rich land is flat, nearly marshy; dry surface is so scarce that peasants use asphalt roads for drying their grain harvests-it may slow traffic, but the land itself remains too wet.

But such roads are scarce in coastal China, a land cries-crossed by rivers and canals. Thus, historically, the sampan has filled the transportation role occupied in northern China by the horse cart.

Horse Bridge People's Commune is probably more advanced economically than its neighbors; it is often singled out as a place to take foreign visitors. Yet it remains a poor place. Its 36,000 people [arm an area of only 8,000 acres, including a maze of canals and rivers, and the space alloted for buildings; and the 7 percent total given over to private plots. Its vehicle assets comprise little more than a few tractors and eight rubber-tired carts. The boat retains its importance as a means of moving goods within the commune, and outside it.

Horse Bridge Commune has more than so workers assigned to ferrocement boat construction, and they average more than one completion daily. The factory is a sideline for the commune; it produces boats according to a plan worked out by the county and sells its output to the county, which resells them to users elsewhere in the region.

The most common sizes are 12-meter boats with 6-ton cargo capacity, and 15-meter boats with 10-ton capacity. Construction began in 1964. Recently, the factory has produced a 60-ton capacity boat and plans to try installing a d*sel engine. The smaller ones are towed or poled along the still canals. Open cargo holds for carrying night soil are standard features of most, if not all, boats.

The commune sells its 6-ton boats for 750 yuan (us 5330) and charges 1,700 yuan (us ) for the 10-ton size. It claims to realize a 7 percent profit for the commune.

Workers cite "ten superiorities" over wooden sampans, including longer life and cheaper maintenance. They claim a wooden sampan will last 20-30 years with good care; they don't know yet how long a concrete boat will last. The amount of material needed is not great; a 6-ton capacity boat needs 800 kilos of concrete and has a total weight of something over 2 tons.

The main design change in converting wooden sampans to ferrocement boats was to make the bilge more rounded. The flat bottom and flat deck are retained, but there seems to be a slightly greater depth of hull to give more cargo space.

The boats are divided into six compartments, but only the three center compartments are used for cargo. The foremost compartment is used as living quarters for the crew of four men, who enter it through a deck hatch. The fifth and sixth compartments are living quarters for the owner and his family and are covered by an awning for shade and shelter. The vessels are propelled by sail and two yulohs (sculling oars). The stern yuloh (starboard side) is used in the conventional manner; the other, positioned over the forward bow (port side), is used also as a sweep.

Ferrocement is used to the fullest extent throughout, but wooden gunwales are used to absorb shock. The boats have a normal rudder attachment-a wooden gudgeon block bolt-fastened to the hull itself. The rudder is of a simple drop type that can be raised or lowered depending on the depth of water.

Before the Second World War, it was reported that suck vessels made approximately two trips per month, carrying night soil for fertilizer far into the countryside from the Shanghai area and often returning with vegetables for the local markets. Ferrocement boats are reported to cost only 50 percent as much as the wooden boats they replace and to have added stability and speed, apparently due to the improved hull shape allowed by the conversion from wood to ferrocement.

Although only one hull design is used (for the sake of economy), bulkheads are placed in any of several positions so that compartments can be constructed to hold different cargoes.

The pictures indicate an extremely interesting boatbuilding operation. In a modern building, the vessels are built upside down over a pit from which the inside of the hull can be plastered. Inside the building are several areas where bulkheads, afterdecks, and foredecks are assembled alone or in combination as subunits of the final boat. These subunits seem to be built in quantity and then used on any of several hulls.

When hull-building starts, high-tensile wires are positioned along what will become the turn of the bilge and the centerlines of the hull; they are held taut with a Spanish windlass and pass over temporary wooden spells (crosspieces which will hold in place bulkheads and frames of the hull to come). Next, the precast concrete (or welded steel) bulkheads and frames are positioned and attached to the high-tensile wires which hold them upright. The "new moon" shaped frames are spaced approximately 1 meter apart; they are approximately 1 inch thick, 2 inches wide at the ends (deck level), and 6 inches wide at the center (keel level). Once in place, the bulkheads and frames outline the hull and provide shape and support for mesh and mortar that, when added later, form the watertight skin of the hull.

Inside the precast-concrete bulkheads are reinforcing rods extending out beyond the concrete. The layers of wire mesh for the skin of the hull are maneuvered down over this protruding reinforcing until they are snug on the bulkhead itself. The bulkhead reinforcing rods are then bent over and laid alongside the hull's reinforcing, and the layers of mesh are firmly fastened to them both.

Three layers of wire mesh are used, and between the innermost layer and the outer two are placed reinforcing rods that run the length of the hull. Extra layers of mesh are placed at potential stress areas, e.g., along the curve of the bilge. The first layers are placed transversely across the hull; later ones are laid along the hull's length.

The photographs show women wiring together the layers of wire mesh. They work from the outside only and have no helper on the inside. Apparently, they use a hooking tool 5 or 6 inches long to maneuver the tie-wire in and out through the layers of mesh. This is an improved technique compared to methods used elsewhere. The wire in the hulls is stretched very tight; some parts are prewelded or precast, but there appears to be no welding during construction.

The wire mesh (square rather than hexagonal chicken wire) is irregular, with varying distances between the strands. Close inspection of the photographs indicates that the mesh itself is probably woven from single-strand wire in the commune (or at a nearby location). The ends of the mesh appear to have been looped and are not square, further suggesting that they are handwoven.

The longitudinal reinforcing rods appear to be about 1/4 inch in diameter, are spaced approximately 3 inches apart, and are securely fastened to the mesh. Apparently, there is no other longitudinal stiffening.

An analysis of 26 photographs suggests that 9 or probably 10 boats are being built and cured simultaneously. If the ferrocement is allowed to cure for 14 days, 2 boats could be built per day, yielding 18 to 20 boats per month. It is possible to shorten the curing time on land to 5 or 6 days if the remaining cure is done under water. Though the photographs show no positive evidence, it appears quite probable that this is done.

No pictures show the actual plastering operation; however, one freshly plastered hull and two being cured are visible. Curing is done by draping wetted fiber mats (hessian or burlap) over the hull. A sprinkler system may be used to cure the interior surfaces.

The boats are launched upside down, either to be rolled over in the water or to right themselves by their buoyancy, perhaps after final curing by immersion in the water. A crane with a boom about 10 meters long is used to launch the boats. The vessels are moved from the construction shed to the canal bank on a cradle that runs on tracks. The cradle is placed under the boats easily, without need for a crane, because it can be run under the hull and accurately placed by the people working in the pit over which the boats are built. Tracks run from each building bay through a set of railroad points to the canal bank next to the launching crane. The cradle consists of two dollies approximately 1.5 meters long, each having four wheels. The dollies are placed approximately one third of the vessel's length from either end. Once in place, the boat is rolled to the canal bank, apparently by manpower alone.

The mortar-mixing shed is roofed but has open sides and is located adjacent to the main construction building. Water is piped to a standard faucet, and there is a large area for premixing the concrete. A horizontal-type rotary concrete mixer is visible.

The building and organization are well engineered and produce what is probably a combination (with improvements) of different types of vessels previously built by individual families. An ever increasing demand to expand the fleet of small boats to cope with population increase may have made it mandatory to devise rapid boatbuilding techniques. Possibly, too, a natural depletion of good boatbuilding timber and the allocation of any available steel to other purposes led to the use of ferrocement.

The lesson to be learned from these photographs is that with proper engineering, mass production in ferrocement is not only feasible, but practical. Standardization of design appears important.

These methods of construction indicate a considerable amount of planning and engineering skill. Precasting sections of ferrocement hulls is a significant advance in construction techniques, one that makes mass production possible. It also suggests new design considerations and new lines for basic research into ferrocement science. In most parts of the world there is considerable controversy over the method to be used to provide support and shape for the layers of wire mesh. Temporary wooden and water-pipe supports are generally used, but both suffer drawbacks, particularly during their removal after the hull is mortared. The Chinese, in contrast, provide support and shape the mesh with precast concrete bulkheads or frames that end up as integral parts of the boats. Furthermore, these precast frames and bulkheads are the key to producing uniformly shaped vessels so that standardized sheets of mesh and fittings can be employed, with resulting economies from building boats of interchangeable parts on a "production line" basis.

Much can be learned, too, from the methods the Chinese use at their urban boatbuilding factories. Photographs of the Wusih ferrocement boat factory published some years ago show 20 hulls under construction inside a modern building.* They also show an even greater refinement in subassembly than in the commune, for all subassembly is done on one side of the building, and the overall construction and plastering on the other. Both steam and air curing operations take place in the same building.

The need for a large number of new hulls forced the Chinese to seek mass-production techniques. Ferrocement has allowed them to do this.

A family of cheap, airtight bins made of ferrocement, the Thai silos are sized to hold 4-10 tons of grain, other foodstuffs (e.g., peanuts, soybeans), salt, fertilizer, pesticide, cement, or 2,000-5,000 gallons of drinking water. The silos were developed over the past 4 years by a government corporation in Thailand* to fit requirements of the developing world. The designs are versatile; the storage units can be built on extremely adverse sites: where the water table is at the soil surface or in remote areas where even vehicular access is impossible. These bins require no maintenance, are easily padlocked against thieves, and protect against water, rodents, birds, insects, aerobic microorganisms, weather, and serious loss of seed germinability.

These properties are made possible by using the material and methods of ferrocement boatbuilding. This construction produces a high-quality product that can be built by local labor with minimal supervision.

The materials needed are cheap and readily available in developing countries: standard grades of cement, a wide range of wire meshes (e.g., chicken netting), and sand. (See Table B-1.)

TABLE B-1. Cost Record for first Experimental Thailo, Thailand, 1969

(a) Labor figures refer to initial experiment and can be drastically decreased in practice. Construction of several Thailos at the same time also reduces labor costs because time spent waiting for sections to cure can be used productively on adjacent bins.
(b) Used to date because of availability in Thailand but may not be necessary for adequate performance of completed Thailo.

Source: R.B.L. Smith, et. al., Thai. J. Agr. Sci. 4 (July 1971): 143-155

As previously noted, the ferrocement bins are watertight and airtight. Respiration of grain, or similar product, quickly removes oxygen from the atmosphere in the bin, so that any insect (adults, larvae, pupae, or eggs) or aerobic microorganisms present cannot survive to damage the stored product. Thus, no fumigation is needed.

Thailos are easy to use. They are filled through a hatch in the top and emptied through another at ground level. The sides are sloped for firm support of a ladder (Figure 11), and the fairly low height (7 feet, or a 5-step ladder) of the entrance hatch simplifies manual filling from sacks or buckets.

As with any type of silo, it is important to dry the grain before loading; otherwise molding may occur. Tests to investigate the feasibility of on-site drying, using a fan and small engine (designed by the Tropical Products Institute*) to force warm air through the product while it is in the Thailo have been conducted successfully in Thailand.

TECHNICAL DETAILS OF THAILO CONSTRUCTION (See Figures B-1-B-3.)

The base of the Thailo is saucer shaped and, where necessary, is built on an earth pile to raise it above the water table. This gives a strong, easily constructed structure that can resist foundation failure. It consists of two layers of 5-cm-thick concrete (1 cement: 1½ sand: 2 aggregate) with mesh reinforcement and an asphalt seal between as added protection at building sites subject to flooding. The base may be easily modified to suite different ground conditions.

The walls slope inward to a central entrance hatch at the top. This truncated cone shape gives a very rigid structure, both during and after construction, and it eliminates the need for a roof structure. The walls are reinforced with 2-m-long poles (water pipe or bamboo), reinforcing rods, and one layer of wire mesh on internal and external faces. The mortar is hand-mixed and is applied as a thick paste using trowels and fingers. No formwork is required to support the mortar. The wall mortar consists of 1 part of standard cement, 1.75 parts sand with the optional addition of a plasticizer to improve workability. Water/cement ratio is approximately 0.3, and with only enough water to hydrate the cement, no voids due to excess moisture are left in the ferrocement, which becomes impermeable.

The top may be cast on site or precast and erected before cementing the walls. It consists essentially of a ferrocement lid with circles of rubber to make airtight seals. An inner lid of aluminum (trashcan lid) with a polystrene lining to insulate against heat and to prevent moisture condensation can be also used.

Controlling the water content of the mix and curing for several days under moistened sacking to avoid direct exposure to the drying effects of sunlight and wind are paramount construction considerations. On completion, the bin may be tested by filling it with water for 1 week. This is an excellent quality-control test because water is considerably more heavy than products likely to be stored and any cracks or weak sections, caused by poor workmanship, can be readily seen as leaks.

In Harar Province, Ethiopia, underground pits are the traditional method of grain storage. It is estimated that 62 percent of the farmers use pit storage exclusively and a further 8 percent use pits in combination with other storage methods.** The basic shape of pit stores resembles that of a laboratory conical flask. The mouth of the pit is closed by strips of wood sealed with a mixture of mud and dung. The pits, if fairly well sealed and covered with a good depth of hard-packed soil, should provide a reasonably airtight storage chamber. In such a chamber any insects present in the stored grain should be killed as the oxygen is used up. However, unless the pit and grain are both dry, some mold growth is inevitable. In practice, few traditional pits are sufficiently airtight to eliminate insects, and mold damage is often considerable.

When the traditional pit is lined with ferrocement and provided with an improved airtight lid, a truly hermetic and waterproof storage chamber can be achieved.

Traditional pits in Harar Province hold from ½ to 20 tons of grain, but there are records of pits holding 50 to 70 tons. In theory, even the largest could be ferrocement lined, but to date the largest lined pit has a 7-ton capacity. This pit was approximately 3 meters deep and 4 meters at maximum width. Most lined pits hold ½-2 tons. A ½-ton pit is approximately 1 meter deep by 1 meter at the widest point; a 2-ton pit is correspondingly 1.75 meters by 2 meters.

Pit stores are built in all the major soil types of the province. Ferrocement linings have been shown to be satisfactory in even the wettest soil.

The ferrocement lining can be produced by any local laborers who are familiar with the use of cement in house building, but even local unskilled laborers can soon learn to do the work satisfactorily. After a 2-3 hour training period, unskilled laborers were able, without close supervision, to help other untrained workers with the techniques.

Although the materials needed are relatively cheap, they are sometimes beyond the reach of the small farmer. For these cases some assistance is likely to be forthcoming when the farmers' cooperatives, now in the early stages of development, become established. A factory in Dire Dawa, one of the two largest towns in the province, makes a standard grade of cement which is distributed throughout the province to even the smallest villages on a main highway or all-weather road. Wire mesh, in various grades, is available in all the major towns and in most villages served by an all-weather road. In most areas sand is available from dry riverbeds, but in some parts of the province graded and washed sand can be obtained.

Extension agents of the Imperial Ethiopian Government, Ministry of Agriculture, have been closely involved with the development of the improved pits and have received training in the use of ferrocement linings. Through this agency the general ideas of pit improvement are being disseminated to the local farming communities.

TABLE C-1. Costs on 1-Ton Ferrocement-Lined Storage Pit, 1972 (in US 0 (a)

(a) Based on average for all of Harar Province, Ethiopia. In remote areas, the price of materials is likely to be higher; in areas close to large towns, considerably lower.

TECHNICAL DETAILS OF FERROCEMENT PIT CONSTRUCTION (See Figures C-1- C-3.)

Before a pit is lined, a thorough cleaning operation is carried out: all rubbish is removed, and, when necessary, the walls are smoothed by scraping off loose soil. Evidence of termites is sought, and if found, the walls of the pit may be treated with an appropriate termiticide. A layer of hardcore is laid on the floor of the pit to a depth of about 10 cm, and a layer of concrete is laid on top. A layer of mortar 2.5-3 cm is applied by hand and trowel to the walls. The mortar consists of 1 part cement to 3 parts sand with as little water as possible. A chicken-wire mesh reinforcement is tacked onto the surface while it is still moist, and a second layer of mortar is applied on top. The lining is moist-cured for 5 to 7 days, after which a waterproofing coat is applied. The surface is prepared by brushing off loose material with a wire brush, and a priming coat of bitumen emulsion is diluted 1 volume of emulsion to 1 volume of water and applied with a stiff brush. The emulsion is scrubbed well into the cement layer. After the priming coat is dry, a bonding coat of neat emulsion is applied and allowed to dry. Finally, a cement/ emulsion mixture, using 1 volume of water to 1 volume cement to 10 volumes of emulsion is prepared and brushed over the whole surface of the lining.

Because this waterproofing method using bitumen emulsion is a relatively expensive and sophisticated treatment, a single layer of bitumen has been tested. This layer, applied between the two cement layers, has been found to be perfectly satisfactory. However, bitumen is available only in large drums and is rather difficult to apply to the sloping walls of a pit. No really easy way of applying it has yet been found.

The design of the mouth of the pit has been modified to incorporate a sloping lip, which will carry away any water that might penetrate the soil. Drain pipes can easily be included to carry the water even farther from the pit (Figure C-3).

The traditional wood-strip lid can be used with the lined pit; however, when a metal or concrete lid is used with a sealant such as bitumen, a truly airtight store can be obtained. Condensation on the inner surface of metal lids sometimes occurs, but can be avoided by use of a piece of old sacking as an inner liner.

Perhaps the greatest development in farm water storage in New Zealand has been the introduction of ferrocement tanks, which retain most of the advantages of earlier tanks with few of their limitations. The cost of smaller sizes is comparable to that of other tanks, but the storage cost per gallon drops off rapidly when larger sizes are used. Paralleling this consideration is the continuing economy offered by the indefinite life of the ferrocement tank.

In most parts of the country, ferrocement tanks are available as stock items in sizes ranging from 200 to 5,000 gallons, Thus, the factory can deliver a tank ready for pipe connections directly to the prepared base. If required, tanks larger than 5,000 gallons can be constructed on site by the same system used at the factory.

The widespread availability of ferrocement tanks and the versatility of the material provide the farmer with economic water-storage facilities involving only minimum site work. Permanent materials are used throughout, and, since all work can be controlled in the factory, most manufacturers confidently offer a 25-year guarantee on their products.

Factory-produced tanks are designed for convenient handling with simple equipment. Small tanks are loaded on the truck, and unloaded by a truck-mounted hoist. Usually, tanks over 1,000 gallons (4,500 litres) are winched onto the truck.

Site preparation is a simple matter, usually calling for no more than removal of vegetation and trimming the soil roughly level. If the tank is to be placed on rock, or if it is desirable to provide a concrete base, a layer of sand must be spread under the tank. This prevents point contact, which would generate high local stresses and probably result in cracking.

The tank is then ready for pipe connections. Generally, standard pipe fittings are built in during manufacture, but special items can be provided by arrangement. If necessary, additional items may be installed on site by chipping a hole and plastering the fitting in place.

Perhaps the most obvious adaptation from water-storage tanks is to tanks of other forms, such as sheep or cattle troughs and septic tanks. Septic tanks are constructed with earthenware fittings and are supplied ready for installation. They are manufactured in various forms, with the actual details determined somewhat by requirements of local governing bodies. (See Figure 5.)

Impermeability is an important characteristic of ferrocement in its use for water retention. Since impermeability promotes hygiene, this material is frequently used where hygiene is of prime importance. Most tank producers have a range of killing sheds, dairies, and freezing chambers-all constructed of ferrocement. (See Figure 4.)

By the simple process of placing a window or door frame against the inside former before plastering, the water tank is transformed into a tool shed, site office, pump room, small laboratory, or any similar structure. When required, plumbing and electrical circuits can be embedded in plaster.

Many manufacturers have developed additional features for special circumstances. Instead of using a circular former, as for tanks, the details may be modified slightly so that the office or pump room is square or rectangular. Freezing chambers are constructed of two layers of plaster separated by insulation and vapor barriers. Usually, the freezing equipment is mounted on the roof. Toilet rooms, shower rooms, and laundries are available with all plumbing fixtures in place, so that on site it is necessary to connect only the water supply and drains.

A further advantage of small ferrocement buildings is that relocation at a later date is no more of a problem than the initial delivery from the factory.

Tanks are constructed by applying two or three layers of plaster against an inside former until the required thickness has been built up. The reinforcing is placed at the stage appropriate to ensure correct location within the wall.

The water pressure in a loaded tank generates hoop stresses in the tank walls. The resulting tension is resisted by a continuous spiral of reinforcing wire, usually No. 8 s.w.g. The spacing of the wire is determined by the diameter and depth of the tank.

Some manufacturers prefer a woven mesh of No. 14 s.w.g. and I 1/2-in or 2-in mesh; others use a chain netting. In some instances a light welded-steel fabric is incorporated in the lower section of the walls to accommodate additional stresses that develop during handling.

The tank floor, which may range in thickness from 2 1/2 in (6.2 cm) for a small tank to 4 in (10 cm) for the largest, is reinforced with a welded grid of steel. A typical reinforcing is 3/8-in diameter rods welded into a grid at 8-in or 10-in centers (10 mm at 20-25 cm). Loops of light steel project into the wall section, and additional handling loops protrude from the edge of the floor for lifting or dragging the completed tank.

The manufacturing sequence varies from one factory to another. In some cases the floor is cast first; in others it is cast after the walls. Some manufacturers place 1/2 in (12 mm) of plaster against the former, position the steel, and then continue plastering up to a total thickness of 1 in to 1 1/4 (25 to 30 mm). At other plants the reinforcing is placed directly against the inside former, and the main body of plaster is applied. The final layer of plaster is applied from the inside after removing the form.

In all cases a strong concrete coving is provided between the wall and floor to seal and strengthen the joint.

The plaster may be applied either manually or pneumatically.

Most tanks are provided with a flat or conical roof 1 1/2 in to 2 in (38 to 50 mm) thick. The roof may incorporate a separate small header tank to provide constant pressure (Figure D-1). If a roof is not needed, the upper edge of the tank wall is thickened to give added strength.

Finally, the tank is given a cement wash inside and is painted outside with a cement-based paint or other suitable surface coating. A little water is placed in the tank, which is kept in the factory yard for some time before delivery to allow the humid atmosphere to cure the cement fully.