19cm Wall
Load bearing brick walls are usually constructed with the thickness of 35cm or 23cm.  The masonry is executed in various types of bond viz. English, Flemish etc.  A framed structure is built with columns and beams through which load from the floors (storeys) are transferred to the foundation.

Often the 23cm thick wall is replaced by 11.5 cm ones, to serve as infills.  The wall, still has to carry its own weight and needs to be constructed carefully so that load acts at the centre of the wall.  In practice, a small eccentricity in construction of masonry is unavoidable.  This may result in buckling thereby limiting the height of masonry to a value equal to 18 times the thickness of wall.  Thus, the allowable height of a 23 cm wall is 4.14 m and for a 11.5 cm is correspondingly 2.07m.  Normally in residential buildings, ceiling height is kept at 3.00-3.3m for which a 23cm wall is not cost effective.  Very recently a new bond has been developed.

The type of bond for 19cm wall is characterized by a unit of three courses.  This unit consists of three stretcher courses and two courses with brick on edge with a height of 11.25cm with a vertical joint distance of 5.7cm and horizontal joint distance of 3.8cm everywhere.  Mere repetition of these units gives rise to 19cm wall masonry.

Ferrocement
Various forms visualised by builders, architects and engineers have to be fabricated on site.  Reinforced cement concrete (R.C.C.) has been a versatile material used extensively for spherical domes, shells of typical curvature, doubly curved thin sheets, folded plates etc.  Though structurally sound, R.C.C. is expensive and fabrication requires formwork, often not reusable.  Tensile structures in R.C.C. are uneconomical as only the steel is effective in resisting tension.  For such structures, a material with better and proven field performance has emerged:  Ferrocement.

It is a homogenous mix formed by steel reinforcement in the form of weld mesh and wire mesh uniformly distributed through a rich cement matrix.  Ferrocement elements being slender, have resistance to bending, tension and impact, but shear has to be taken care of.  Its application include precast slab elements, roofing panels, cupboards, doors and windows, flooring tiles, toilet units, septic tanks, beams etc.

Many institutions like the Central Building Research Institute and the University of Roorkee, Structural Engineering Research Centre, the Auroville Building Centre are involved in innovative ferrocement applications.

Research work on ferrocement truss elements and rafters for sloped roofing systems is in progress at Development Alternatives.
V. Sriraman

Waste to Wealth
Building materials industry in India faces the daunting task of ensuring stable supplies in the wake of diminishing resources and spiralling costs of energy.  Further, the small scale sector is under pressure to improve its environmental performance due to devastation of natural resources and unabated pollution.  The annual requirement of 75 billion bricks for housing sector alone requires 200 million tonnes of top soil resulting in exploitation of 4000 hectares of fertile land.

The increased economic activity in the country has stimulated growth in power generation and the chemical sector.  These sectors contribute generously to generation of industrial wastes, flyash, press-mud, red-mud, fluorinated gypsum; collectively posing for the country major environmental threats.  The power sector alone generates 30 million tonnes of flyash.  In the absence of clear alternatives for mitigating such threats, the Department of Science and Technology has formulated a Technology Mission for “Flyash Disposal and Utilisation” to review current status and technologies.

The building materials industry will have to increasingly rely on industrial wastes rather than on virgin natural resources.  A new vision is needed to seize upon the opportunity arising out of environmental threats and develop technologies for waste utilisation.  “Wealth From Waste” incorporates concerns of environmental soundness, energy efficiency and economic affordability.  Several initiatives are underway for large scale utilisation of flyash, e.g. autoclaved cellular concrete blocks and Fal-G.

DA now runs a program for utilisation of industrial waste in collaboration with leading industries in India for evolving new building materials.  The approach is to study the intrinsic bonding characteristic of materials like flyash and press-mud and rely primarily on compaction to derive adequate compressive strength.  The admixtures through combining two wastes or minor additives will be used to impart properties of impact strength, abrasion resistance  and water proofing.  Energy input is eliminated as there is no requirement for sintering or auto-claving.

Dr. Arun Kumar