FERROCEMENT CONSTRUCTION

FERROCEMENT

• The concept of the use of fibres to reinforce brittle materials dates back to back ancient constructions built in India using mud mud walls reinforced with woven bamboo mats and reeds.

• The ferrocement results in a composite material obtained by reinforcing the cement mortar with steel fibres in the form of a wire mesh.

Typical Section Of Ferrocement

• Ferrocement may be considered as a special form of reinforced concrete construction with more closely layered wire meshes than a material of construction.

• However,it exhibits a very different behaviour from reinforced concrete especially under moderate levels of stress.Because of the distribution of a small diameter wire mesh reinforcement over the entire surface,and sometimes over the entire volume of the matrix,a very high resistance to cracking.

Ferrocement improves……

• Toughness• Fatigue resistance• Strength• Impermeability• Durability

The Ferrocement Composition

• The ferrocement composite is a rich cement –mortar of 10 to 60 mm thickness with a volume reinforcement of 4 to 8 per cent in the form of one or more layers of very thin wire mesh and a skelton reinforcement consisting of either welded mesh or mild steel bars

• The matrix is typically rich in mortar.• Cement-sand ratio of 1:1.5 or 1:2 is used.The use

of 1:3 cement-mortar has also been reported.

• Port land cement with or with out pozzolana,is generally used for ferrocement.

• Plasticizers and other admixtures may also be added to improve the workability.

• Chromium trioxide can be added to prevent galvanic corrosion in steel in ferrocement.

• The water content which governs the strength and workability of mortar,primarily depends upon maximum grain size,fineness modulas and grading of sand.

The reinforcement used in the ferrocement constructions is of two types…….

Skelton steel & Wire mesh

Skelton Steel

• The skelton steel frame is made conforming exactly to the geometry and shape of structure and is used for holding the wire meshes in position and shape of structure.

• It comprises relatively of large diameter (about 3 to 8 mm ) steel rods spaced typically at 70 to 100 mm.

• It may be tied reinforcement or welded wire fabric.

Welded Steel Mesh before bending

Welded Steel mesh after bending

Wire Mesh

• The wire mesh consisting of galvanized wire of diameter 0.5 to 1.5 mm spaced at 6 to 20 mm centre- to-centre ,formed by welding ,twisting or weaving.

• Specific mesh types include woven or inter locking mesh,woven cloth,welded mesh in a rectangular pattern with or without diagonals.

• The hexagonal wire mesh is cheaper but less efficient.

• The required number of layers of wire mesh are fixed on both sides of the skelton frame.First,the external mesh layers are fixed and tied to the frame bars.The meshes should be fixed by staggering the hold positions in such a manner that the effective hole size is reduced.

• A spacing of at least 1 to 3 mm is left between two mesh layers.Wherever two pieces of the mesh are joined ,a minimum overlap of 80 mm should be provided and tied at a close interval of 80 to 100 mm centre to-centre.

Impregnation of meshes with matrix

• The placing of the mortar is termed the impregnation of meshes with matrix.

• This is the most critical operation in ferrocement casting.

• If the mortar impregnation is not proper ,the structure is bound to fail in its performance.

• Sufficient quantity of mortar is impregnated through mesh layers so that the mortar reaches the other side and there are no voids left in the surface.

Properties of Ferrocement

• Load carrying capacity of ferrocement is correlated with specific surface area of reinforcement.

• Consequently ,ferrocement has about 10 times as much specific surface area as the conventional reinforcement has and tensile strength as high as its compressive strength,ie 27 N/mm2

• Width of cracks are very smalleven at failure(about 0.05 mm).

• Ferrocement structures can be designed to watertight at service loads.

• The compressive strength of ferrocement is found to be contributed by strength of mortar.

• Impact tests on ferrocement slabs show that damage due to impact reduces with increasing specific surface and ultimate strength of mesh

• Fatigue test on ferrocement beams show poor resistance of ferrocement under cyclic loading.

• Due to the very high percentage of well distributed and continuously running steel reinforcement,the ferrocement behaves as steel plates.

• Ferrocement combines easy mouldability of concrete to any desired shape,and lightness,tenacity and toughness of steel plates

Applications

• Water tank• Silos and Bins• Boat hulls• Bio gas holders• Floor units• Pipes• Service units wind tunnel• Rain water harvesting etc…

Details and dimensions of a typical ferrocement tank

Heavy duty ferrocement tank

Ferro Cement Jars• Ferrocement consists of a thin sheet of cement mortar

which is reinforced with a cage made of wire mesh and steel bars. Because ferrocement is structurally more effectient than masonry, the thickness of the walls of the container are as low as 10 to 15 mm.

• Ferrocement components can be casted in any shape using suitable moulds. The technology is extremely simple to implement, and even semi-skilled workpersons can learn it with ease.

• Ferrocement requires only a few easily available materials - cement, sand, galvanized iron (GI) wire mesh, and mild steel (MS) bars - in small amounts compared to masonry and RCC.

Ferrocement Tank using Skeletal Cage:

• Phases of construction

i Selection of siteii Marking for circular foundation:Choose the diameter of foundation (Df) for required storage capacity from the table

• Capacity of storage tank (litres)• 5,000 and 6,000• 7,000 and 8,000• 9,000 and 10,000• Df• 2.40 m• 2.70 m• 3.00 m

The ferro-cement jar

• This design is already well known. The technology involves using chicken wire sandwiched between layers of cement mortar. A shaped mould is made from sacks and filled with sawdust. The mould is then plastered with sand/cement paste in a ratio of 3:1. This is then covered with 1/2" chicken wire and given a second coat of mortar. A tap and overflow are fitted and a plastic basin used to form the opening at the top – a filter is fitted here to remove large particles from the water. The jar is raised above the ground so that jerry cans can be filled easily from the tap.

Heavy-duty ferrocement tank (section)

Partially rendered skelton tank

Formwork

• The 2m high formwork is made from 16 sheets of standard galvanised roofing iron, 0.6mm thick with 7.5cm corrugations rolled into a cylinder with a radius of 1.25m. Steel angle iron (40 x 40 x 5mm) is bolted vertically on the inside face at the ends of each set of 4 sheets – this allows the sheets to be bolted together to form a circle. Between the edge of each section is placed a wedge which is pulled out to allow the formwork to be dismantled (see Figure 1).

Assembling the formwork

Typical domestic RWH systems

• A typical domestic RWH consists of a collection surface, gutters and a storage container. In addition, there are options for diverting first-flush water and filtration.

Ferrocement water tank shaped like a boulder

Advantages of Ferrocement

• Thin and light ,reduction in self weight.• Less foundation cost.• Suitable for precast units,can be easily

transported.• The simple construction technique and hence

doesnot require highly skilled labour.• Partial or complete elimination of form work

is possible ,

THANK ‘U’