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Multi-sustainable Ferrocement Concrete Technology

J.A. Desai, CEO, J A Desai Ferrocements Pvt. Ltd., Mumbai

Reinforced Cement Concrete is the material of construction used today alongwith steel construction. Inspite of its wide-spread use, the lacuna is the requirement of waterproofing and repairs after every few years has been persisting. Due to this drawback of reinforced cement concrete crores of rupees are spent to maintain its sustainability. This cannot be removed since reinforced cement concrete is heterogeneous material and the basic design is a cracked section. Cracks are expected to remain all the time with reason to open more and reach the reinforcement. With the advent of Ferrocement Technology construction, these two lacunae have been eliminated. Ferrocement is a durable waterproof no repairs crack resistance material. At the same time ferrocement is better earthquake resistant and wind resistant and resistant to all disasters. Ferrocement requires much less quantity of cement and steel giving better performance thus environment friendly. Therefore ferrocement is a multi-sustainable material with cost benefit as well as saving of lives against earthquake with high Richter scale of 8 and perhaps above. Ferrocement shall contribute to savings of crores of Rupees.

Introduction

The construction of structures with concrete started around the beginning of last century. The concrete in the form of reinforced cement concrete has sustained handicaps uptill now, updating the understanding of concrete with due remedial measures. The performance of concrete was improved stage by stage right from its inception as regards water-proof quality, cracking, spalling, deterioration due to corrosion of steel reinforcement, porosity, carbonation due to atmospheric gases etc. After about 20 to 30 years of construction experience, the water cement ratio was better understood and reduced to a great extent particularly with the use of plasticizers. The heterogeneous quality of concrete has certain drawbacks which can be improved only marginally. There was further improvement in its performance by methods such as concrete mix design and improvements in analysis of structures etc. Since about two and half decades deterioration of structures has been noticed. The intervals of repairs of RCC structures have increased because of improvement and latest method of repairs with advent of chemicals. Still the deterioration generally persists. Due to heterogeneous nature of concrete it will not be possible to improve its waterproof quality and sustainability against Repairs and rehabilitation.

Ferrocement for sustainability against Waterproofing and Repairs

The sustainability of concrete is improved totally by use of ferrocement plates around reinforced concrete sections. The phenomena of water-proofing is improved totally. At the same time there shall not be any spalling, deterioration, attack of atmospheric gases, carbonation and corrosion of reinforcement. The ferrocement plating around RCC shall be the shield against all these negative aspects of reinforced cement concrete. As such the durability shall be increased to a great extent and it will not be necessary to carry out Repairs rehabilitation as well as waterproofing treatment of RCC structures during its life time.

Ferrocement Construction
Ferrocement plated R.C.C. beams in process of construction for horizontal extension of a bungalow. The U- verticals of beams are not cast to enable the beams to be handled manually. However the bottom with all reinforcements such as flexure, shear of beams is cast on machinery set-up

Features and Advantages of Ferrocement Construction

Ferrocement construction eliminates use of formwork since surfaces of beams and columns act to contain concrete in the core. Since there is no formwork stripping operation the building activity of flooring, walls doors and windows fixing etc. can start in couple of days. The reinforcement required for construction is incorporated in the formwork itself at the time of its manufacture at factory premises. There is no activity of reinforcement placing at site. Ferrocement surfaces do not require plaster. There is no delamination in due course of time. As such no ceiling plaster falling phenomena and injury to occupants below. The cost of plaster and operation of plaster application is eliminated. Ferrocement construction saves time by about 20% and cost by about 15%. Ferrocement structures are very much efficient as compared to RCC. Ferrocement high rise structures can swing by a few cms and shall be back in original position, even under Earthquake of Richter scale 7.5 to 8. Similarly ferrocement is a very good material to resist disasters such as winds, fires, floods etc.

What is Ferrocement

Ferrocement is a thin section material, has features to arrest crack formation, is of high strength with large bonding forces on wiremesh reinforcement. Crack formation is prevented to the width of microns with uniform spread of wiremesh reinforcement in the body of ferrocement. The water cement ratio being very low, around 0.35 the carbonation phenomena is not possible. Structurally ferrocement is isotopic material upto about 40% of yield. The strength being of high value, ferrocement structures are designed near to yield value. The heterogeneous nature of ferrocement is minimal upto yield. Crack formation of ferrocement being about 20 to 30 microns, autogenous healing is efficient, fast and durable. Behaviour of Ferrocement from isotropic point to yield has enabled it to be highly ductile i.e. energy absorbing material.

The Ferrocement is most durable material lasting for many decades
Ferrocement Construction Ferrocement Construction
This Ferro-cement boat constructed in 1887 was observed to be serviceable in 1967. At present it is in the lounge of a Cement Industry, Amsterdam (Courtesy Prof. Antoine E. Naaman, Michigan University) A large barge constructed decades before in China (Courtesy Prof. Antoine E. Naaman, Michigan University)

Ferrocement plated RCC structures is much ductile and shall efficiently resist earthquake with capacity to bend upto substantial swing of few centimeters. After this swings, it is back to its original position without any damage when the earthquake is over. This will be upto about Richter scale 8.00 or so. It was experienced in Mexico that ferrocement structures vibrated like jelly and were untouched, that is not damaged at all during earthquake of Richter scale 7.2 and 7.4. Whereas all other RCC structures collapsed. Ferrocement plated RCC structures shall have very much low damage during fire since there is least water content in ferrocement to cause spurting of cement matrix as well better performance it being isotropic.

The crack formation in Ferrocement is of very minute width and depth
Ferrocement Construction
The graph shows crack width of very low value in a Ferrocement water storage tank.(Courtesy Prof. Antoine E. Naaman, Michigan University). University)

Ferrocement Construction
The graph shows Ferrocement is isotopic upto about 40% yield. It shows no collapse for large strains and very small crack width perhaps to trap water by surface tension. (Courtesy Prof. Antoine E. Naaman, Michigan University)
Ferrocement plated RCC structure is systematically reinforced with fibers in the form of wiremesh on its surfaces. This is better than random fiber reinforcement. Thus the structure is fiber reinforced saving/elimination of fibers in the core body of concrete. Ferrocement plated RCC slabs do not have plaster. As such there is no delamination in due course of time and injury to the occupants below.

Ferrocement is efficient against earthquake Richter scale around 8
Ferrocement Construction
A Ferrocement Auditorium of capacity 250 constructed around 1997 in Oascaco Mexico having dia. 24 mtrs. and ht. 12 mtrs. resisted earthquake of Richter scale 7.2 and 7.4, 1998 and remain untouched (Courtesy Prof. Antoine E. Naaman, Michigan University)

Ferrocement Plating around concrete section

Ferrocement is efficient Fire Resistant material
Ferrocement Construction
Qualitative test by UNIDO (United Nations Industrial Development Organisation) in about 1972 showed that the damage due to fire on a Ferrocement boat was negligible.
With these excellent structural and physical features, ferrocement plated RCC structures are constructed. Ferrocement plating is provided along the surfaces of columns, beams and soffit of slab. Shear and flexured reinforcement of beams, certain reinforcement of columns, and reinforcement of slabs are provided in ferrocement plates. Ferrocement plates in the form of 'U' for beams, boxes for columns and plates for slabs are manufactured on machinery set up under controlled conditions. The column boxes are erected in position and duly vibrated concrete poured in the boxes. After this 'U' incorporated with flexure, shear torsion reinforcement for beam, is placed on columns and duly connected by welding and joint finished. After this the plain cement concrete is poured in the hollow. Thus formwork is eliminated. Props to the beams may or may not be required. Ferrocement plate of the size of room incorporated with reinforcement for the slab, manufactured on machinery set up is placed with the help of crane on four beams duly connected and with provision of few props if at all. Concrete for balance thickness of slab is placed duly vibrated. Within three - four days' time further activity of construction can be started below the slab as well as above. Thus with ferrocement plated RCC structures the formwork is totally eliminated. There is no stripping operation. Ferrocement plate forms the part of the structure. There will be heavy saving in wood and steel for formwork.

Ferrocement is a corrosion-resistant material
Ferrocement Construction Ferrocement Construction
Most hard skin of the roof panel cast in the year 2000, could not be removed by chiseling. Had to be removed by Cutting wheel carefully not to damage the wiremesh. Most superficial line mapping on pouring of water on the surface- disappearing within a minute or so. Closer view wiremesh reinforcement showing no corrosion of wires but nominal brown colouration – indicating no corrosion for future.

Corrosion phenomena in R.C.C.
Ferrocement Construction Ferrocement Construction
Initial corrosion of reinforcement in RCC takes place due to reaction with residue water used for mixing concrete for placing. This is not due to any water or moisture from outside. In due course of time, crack formation takes place in the cover and travels to the surface. Water, moisture, gases etc. enter into cracks, and reach the reinforcement and corrodes steel more and travel along the reinforcement and deterioration starts. If column is treated with ferrocement wrapping then such cracks and deterioration stops. With any conventional method like polymers, cracks reappear and corrosion phenomena is resumed.

Corrosion Resistance–II
Ferrocement Construction Ferrocement Construction
Corroded metal roofs, Detroit, USA Such corrosion is not possible with Ferrocement

Multi-sustainability

The concrete construction shall become multi-sustainable with the use of ferrocement plated RCC structures as below:-
  • With ferrocement plating around concrete sections of RCC structures, the waterproofing lacuna is eliminated.
  • The ferrocement having crack-arrest mechanism and efficient autogenous healing of micro cracks, the repairs and rehabilitation aspects every few years shall not be required.
  • Ferrocement being relatively a strong material, consisting of less quantity of concrete, there will be reduction in requirement of cement and steel, both to the tune of about 10 to 15%.
  • Due to high ductile nature of ferrocement, ferrocement plated structures shall swing by few centimeters during earthquake and be back in its original position with no damage, Richter scale 8.00.
  • Similar is the case with cyclones.
  • The fire resistance of ferrocement structures shall be much better as compared to normal RCC, damage being negligible and duly repairable.
  • The resistance to carbonation by ferrocement is a factor to eliminate the spalling and disintegration lacuna of RCC.
  • The formwork for beams, columns, slabs shall not be required for construction of ferrocement plated RCC structures enabling the speed and convenience of construction.
  • The precasting, handling and erection of ferrocement formwork for columns, beams and slabs shall be most convenient easy and time saving in view of self-load being comparatively low.

Saving of Materials and Power

In view of above, there will be saving of substantial amount of materials as below:-

The cement requirement shall reduce by about 10 to 15%.

The steel requirement shall reduce by about 10 to 15%.

Requirement of cement and steel being low, there will be saving in Power required to manufacture these.

The minerals required from Mother Earth for production of cement and steel shall be reduced accordingly. This will arrest the depletion of natural resources. It is reported that the iron ore deposits shall last about 20 years only with the present rate of consumption for manufacture of steel.

Since the formwork is totally eliminated for the construction of ferrocement plated RCC structures, there will be huge saving of wood in the form of props, planks, scantlings as well as steel in the form of steel plates and structurals. Thus there will be huge environmental benefits.

The corrosion of reinforcement shall not take place since there will be no access of moisture, atmospheric gases to the concrete through ferrocement plating.

Financial Benefits

The financial benefits due to above shall be enormous as below:-

The saving in expenditure on waterproofing of RCC structures shall be very high running into crores of Rupees.

The saving in expenditure on account of elimination of repairs and rehabilitation on structures shall run into crores of rupees.

The power requirement to produce cement and steel shall be reduced considerably.

There construction after earthquakes of collapsed structures such as houses, buildings, bridges and other important structures shall not be necessary in view of very high resistance capacity of ferrocement structures during earthquake to the tune of Richter scale 8 and perhaps may be more.

Similar is in the case of cyclones.

This will save billions of crores of rupees. Also the time required to reconstruct the structures to their original uses shall not be saved.

The most important aspect of contribution of ferrocement structures against earthquake shall be saving of thousands of human lives. This is most invaluable.

Conclusion-Philosophy of Sustainability

Sustainability is a continuous process and is applicable to almost every walk of life. There will be perishment if there is non-sustainability For example the Dinosaurs and other animals, millions of years before could not sustain certain adverse conditions and therefore they became extinct. It is our recent experience that with the advent of Computers and Printers, the manual as well as Electronic Typewriters and carbon papers have become non-sustainable and therefore disappeared. Further the traveling by ships over the ocean to distant places became sustainable and redundant with the invention of aeroplanes. It was realized that it will save considerable time which is most important aspect in the present day life. Therefore we Engineers, have to be very vigilant to maintain the technologies sustainable by modifying materials, methodology, systems etc. With the advent of new technology, the sustainability may change totally. The form of Technology may change as it has happened in the case of Ferrocement Technology.

The imminent change to save the resources is developmentof Geopolymer concrete which will not require use of cement at all and shall be making profuse use of fly ash, blast furnace slag, copper slag etc. At the same time it will be much superior with many features than the present day concrete. This will also apply to Ferrocement Technology.

NBMCW June 2011



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