Ferrocement in construction

Its economics in Current ranges of ferrocement composition and properties developed countries differ from those in Wire-mesh reinforcement developing countries Wire diameter 0.020 to 0.62 inches (0.5 to 1.5 millimeters) Type of mesh Chicken wire or square woven or welded wire galvanized mesh; expanded metal

1 Size of mesh openings ⁄4 to 1 inch (6 to 25 millimeters) BY S. P. SHAH PROFESSOR OF CIVIL ENGINEERING Number of mesh layers Up to 12 layers per inch of thickness AND GRADUATE DIRECTOR UNIVERSITY OF ILLINOIS (5 layers per 10 millimeters of thickness) AT CHICAGO CIRCLE Fraction volume of Up to 8 percent in both directions reinforcement corresponding to up to 40 pounds of steel per cubic foot of concrete (630 kilograms per cubic meter)

e r rocement can be consid- Specific surface of Up to 10 square inches per cubic e red a type of thin re i n f o rc e d reinforcement inch (400 square millimeters per c o n c rete construction in 100 cubic millimeters) in both directions Fwhich large amounts of small-diameter wire meshes are Intermediate skeletal reinforcement, if used used uniformly throughout the Type Wires; wire fabric, rods; strands c ross section instead of discre t e l y 1 3 placed re i n f o rcing bars and in Diameter ⁄8 to ⁄8 inch (3 to 10 millimeters) which portland cement mortar is Grid size 2 to 4 inches (50 to 100 millimeters) used instead of concrete. Metallic mesh is the most com- mon type of re i n f o rcement. Me s h e s Typical mortar composition made of alkali-resistant glass fibers, Portland cement Any type depending on application and woven fabric made of ve g e t a b l e Sand-to-cement ratio 1.0 to 2.5 by weight fibers such as jute-burlap and bam- b o o, have also been tried as re i n- Water-cement ratio 0.4 to 0.6 by weight f o rcement. This article deals pri- m a rily with steel wire meshes. The Recommendations Fine sand all passing U.S. sieve Number 8 commonly used composition and and having 5 percent by weight passing Number 100, with a continuous grading p ro p e r ties of ferrocement made curve in between with steel wire mesh re i n f o rc e m e n t a re summari zed in the table (see al- Composite properties so Re f e rences 1 and 2). Thickness 1/4 to 2 inches (6 to 50 millimeters) The development of the materi a l called ferrocement as defined above Steel cover 1/16 to 3/16 inch (1.5 to 5 millimeters) is generally credited to Pier Lu i g i Ne rvi in the years 1942-1943. It is in- Ultimate tensile strength Up to 5000 psi (34 megapascals) t e resting to note, howe ve r, that one Allowable tensile stress Up to 1500 psi (10 megapascals) of the first applications of re i n f o rc e d c o n c rete construction was the fer- Modulus of rupture Up to 8000 psi (55 megapascals) rocement rowboat built by Lambot in France in 1849. Lambot took out Compressive strength 4000 to 10,000 psi (28 to 69 megapascals) French and Belgian patents on what This is a model of the ferrocement boat that Lambot built in 1856. Here the model floats in a pond at the Fulmer Grange Training Centre in England. he termed “f e rc i m e n t” in 1856. One of his boats was still and joined by re i n f o rced concrete ribs cast in place in afloat 100 years later in 1949 and is currently on display the troughs and crests of the corru g a t i o n s. in a museum in Bri g n o l e s, France and re p o rtedly in good Despite these demonstrations of its usefulness, ferro- condition. In 1887 a similar boat was constructed in Ho l- cement did not gain wide acceptance until the early land. This vessel, now 81 years old, is still afloat on the Pelican Pond at Amsterdam Zo o. T h e re was ve r y little activity of true ferrocement con- s t ruction from 1888 until 1942 when Ne rvi began a seri e s of experiments on ferrocement. He observed that re i n- f o rcing concrete with layers of wire mesh produced a m a t e rial capable of resisting high impact. Thin slabs of c o n c rete re i n f o rced in this manner proved to be flexible, elastic and exceptionally strong. After the Second Wo r l d Wa r, Ne r vi demonstrated the utility of ferrocement as a boat building material by building the 165-ton1* motor 7 2 sailer Irene with a ferrocement hull 1 ⁄1 6 i n c h e s t h i c k . Ac c o rding to Ne r vi, the weight of the vessel was approx- imately 5 percent less than that of an equivalent wooden ship and its cost was 40 percent of that of a similar wood- en hull. Ne r vi also built ferrocement civil engineering stru c- t u re s. He constructed a small warehouse whose walls 3 3 and roof we re 1 ⁄1 6- i n c h - t h i c k c o r r ugated ferro c e m e n t . He used the concept of corrugation for the roofs of sev- e ral major stru c t u res including a roof system spanning 320 feet4 for the Tu rin Exhibition Hall. The ferro c e m e n t 9 5 c o r r ugated units, less than 1 ⁄1 6 i n c h thick, we re pre c a s t A ferrocement ceiling cast on dome pans—part of nervi’s Palazzo del Lavoro in Turin, Italy. Some of the pans have * Superscript numbers refer to metric equivalents listed with this article. been lowered onto the scaffolding. 1 9 6 0 s. In 1965, an Ameri c a n - owned ferrocement yacht s c r ibed in Re f e rence 4 for use in marine stru c t u res can built in New Zealand, the 56-foot6 Aw a n e e, circ u m n a v i- reduce the labor cost. Ex p e rience has shown that the gated the world without any serious mishap, although it quality and application of mortar are critical. Mo rtar can e n c o u n t e red gales of 70 knots,7 collided with an iceberg be applied by hand or by shotcreting. Since no form w o rk and was rammed by a steel-hull yacht. Since then there is re q u i red, ferrocement is especially suitable for stru c- has been increasing activity with ferrocement constru c- t u res with curved surfaces such as shells and fre e - f o r m tion through the world, including both developed and s h a p e s. d e veloping countri e s. In addition to boat hulls, applica- Fe r rocement has ve ry high tensile stre n g t h - t o - we i g h t tions of ferrocement construction include floating ma- ratio and a superior cracking behavior. Thus for boats, rine stru c t u re s, ro o f s, silos, pipes, water tanks and low - b a rg e s, mobile homes or other portable stru c t u re s cost housing. which must be light in weight, impact resistant and wa- t e r tight, ferrocement may be an attra c t i ve materi a l . Organized study Building components that are seldom moved place only In 1972 the U. S. National Academy of Sciences, a moderate premium on lightness in weight; and eve n t h rough its Bo a rd of Science and Technology for In t e r- though ferrocement is more efficient, pound for pound, national De velopment, established an ad hoc panel on it is cheaper to build heavy stru c t u res with conve n t i o n - the Utilization of Fe r rocement in De veloping Co u n t ri e s. ally re i n f o rced concre t e. This is especially true in deve l- The re p o rt of the panel is a good summary of the history oped countries where high material cost and the more and applications of ferrocement construction (Re f e r- labor intensive nature of ferrocement limit its use to spe- ence 3). In 1975, the American Co n c rete Institute form e d c i a l i zed applications. These include geodesic domes, Committee 549 to develop a body of knowledge on fer- wind tunnels, roof shells, mobile homes, modular hous- rocement. In 1976, The In t e r national Fe r rocement In- ing, tanks and swimming pools. Even for these applica- f o rmation Center was founded at the Asian Institute of t i o n s, in developed countri e s, the ready availability of Te c h n o l o g y, Box 2754, Bangkok, Thailand. The center, fi- mobile cranes and efficient systems for precasting, pre- nanced by the United States Agency for In t e rn a t i o n a l s t ressing and erecting re i n f o rced concrete stru c t u res of De velopment, the gove rnment of New Zealand and the any size makes widespread use of ferrocement unlikely. In t e rnational De velopment Re s e a rch Center of Ca n a d a , Fe r rocement can compete favo rably with fiberg l a s s s e rves as a clearing house for information on ferro c e- laminates or steel. Two recent feasibility studies have ment and publishes the Jo u rnal of Fe r rocement. In 1979, s h own ferrocement to be cheaper than steel for the con- RILEM (In t e rnational Union of Testing and Re s e a rc h s t r uction of wind tunnels (Re f e rence 5) and cheaper L a b o ra t o ries of Ma t e rials and St ru c t u res) established than either steel or fiberglass for construction of tanks Committee 48-FC to evaluate testing methods for ferro- for storing hot water (Re f e rence 6). c e m e n t . Conclusions Applications Fe r rocement has come into widespread use only in Fe r rocement construction has come into widespre a d the last two decades and the state of the art of ferro c e- use only in the last 20 years and application of this new ment is still in its infancy. Ne ve rt h e l e s s, sufficient de- c o n s t r uction material is still in its infancy. Not enough sign information is available and adequate field experi- l o n g - t e rm experience with ferrocement stru c t u r es has ence has been acquired to enable safe design and been accumulated and analyzed to assess the success of c o n s t ruction of many types of ferrocement stru c t u re s. the stru c t u res already built. The main applications that Whether ferrocement can economically compete with h a ve been made of ferrocement construction can be a l t e r nate materials depends on the type and location of classified in three categories: (1) boats, (2) silos and application. For industrially developing countries where tanks and (3) ro o f s. the cost of materials is re l a t i vely higher than the cost of Fe r rocement construction can be divided into four l a b o r, construction of boats, silos, tanks and roofs ap- p h a s e s : pears especially attra c t i ve. For industrially deve l o p e d c o u n t ri e s, ferrocement seems economical for medium- • fabricating the skeletal framing system s i ze storage tanks, some types of roof shell constru c t i o n , • applying rods and mesh boats and ships, and where ver the ease of forming com- • plasteri n g plicated shapes and the lighter weight of ferro c e m e n t can be safely exploited. • curi n g References Note that special skills are re q u i red for Phases 1 and 3 (1) Shah, S. P., “New Reinforcing Materials in Concrete Con- while Phase 2 is ve r y labor intensive, a possible short- struction,” Journal of the American Concrete Institute, May coming for industrially developing countries but an ad- 1974, pages 257-262. vantage for countries where unskilled labor is re l a t i ve l y (2) Shah, S. P., “Tentative Recommendations for the Con- abundant. Laminating techniques similar to those de- struction of Ferrocement Tanks,” Ferrocement—Materials and Applications, publication SP-61, American Concrete In- Metric equivalents stitute, Detroit, 1979, pages 103-113. (1) 150-megagram (2) 36 millimeters (3) Ferrocement: Applications in Developing Countries, Na- tional Academy of Sciences, Washington, D.C., February (3) 30-millimeter-thick 1973, 103 pages. (4) 98 meters (5) 40 millimeters (4) Martin, E. I. and Watson, L. L., Jr., U.S. Patent 3,652,755, (6) 17-meter issued March 28, 1972. (7) 130 kilometers per hour (5) “Study and Evaluation of Ferrocement for Use in Wind Tunnel Construction” Report JABE-ARC-07, Research Con- tract Number NA52-5889, NASA Ames Research Center, Moffett Field, California, July 1972, 88 pages.

(6) “An Integrated Solar Energy Heating and Cooling System for a New Physical Science Education Center in Richmond, Virginia,” Final report prepared for U.S. Energy Research P U B L I C AT I O N # C 8 1 0 2 6 9 and Development Administration, Division of Solar Energy, Copyright © 1981, The Aberdeen Gro u p Contract Number E-(40-1) 4899, 106 pages. All rights re s e r v e d