LECTURE - 1

LIGHT WEIGHT CONSTRUCTION MATERIALSThe Northcap University, Gurgaon1UNIT-1LECTURE - 6Brig. S.K. Sharma (Retd.) Pro Vice Chancellor and Professor Department of Civil Engineering, The Northcap University, Gurgaon

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INDEXWASTE MATERIAL BASED CONCRETEORGANIC WASTESINORGANIC WASTES

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WASTE MATERIAL-BASED CONCRETERecent investigations have made it possible to make concrete using agro, urban and industrial waste materials. Successful utilization of a waste material depends on its use being economically competitive with the alternate natural materials. These costs are primarily made up of handling, processing and transportation. The stability and durability of products made of concrete using waste materials over the expected life span is of utmost importance, particularly in relation to building and structural applications. The forms in which they are used are wide and varied: they may be used as a binder material, as partial replacement of conventional Portland cements or directly as aggregates in their natural or processed states.

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For discussion waste materials may be classified as Organic wastes (agro-wastes), Inorganic wastes (urban wastes) and Industrial wastes.

A. ORGANIC WASTESThe waste materials included in this category are of plant origin, namely sawdust, coconut pith, rice husk, wheat husk, groundnut husk, etc. It must be appreciated that development of concrete using such aggregates is still in early stages and published data are limited. Before using organic wastes on a large scale as constituents in concrete, careful investigations regarding their structural properties and durability need be carried out.

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Uses Of Natural Organic Waste MaterialsThey are used for making lighweight concrete. However, they often contain substances (cement poisons) which retard the hydration and hardening of cement which need be neutralized appropriately. Moreover, it is difficult to obtain a waste material which is not a mixture of several species. Consequently, there is a considerable variation in results from batch to batch. The lightweight concrete produced using organic wastes have comparatively high moisture movement and show relatively higher percentage of volume changes. 5The Northcap University, Gurgaon

RICE HUSKHuge quantities of rice husk are generated in rice mills. Each tonne of paddy produces about 200 kg of husk. Because of its very low density, rice husk requires large space for storage and hauling. In India, it is disposed of by burning, thus reducing the bulky waste to manageable volumes of ash of less than 50 per cent of its initial volume but open burning creates severe pollution problems. Rick husk contains only very small quantities of water-soluble cement poisons as compared to saw dust. It has a low bulk density of only 100 to 150 kg/m3. The light weight concrete of bulk density 600 kg/m3, produced using rice husk as an aggregate is suitable mainly for making precast blocks and slabs for walls and partitions. 6The Northcap University, Gurgaon

Central building Research Institute, Roorkee has developed a cheap cementing material from rice husk and waste lime sludge available from the sugar and paper industries. The dried cakes of mixture of sludge and rice husk are burnt, and the burnt material on grinding yields a fast-setting gray-colored cementing material which can be used in place of cement or lime in mortars for brick masonry work, plastering and foundation concreting. 7The Northcap University, Gurgaon

RICE-HUSK ASH CEMENT CONCRETE: The compressive strengths of concretes made with rice-husk ash cement using siliceous gravel and crushed limestone are given in the Table below. The 28-day compressive strength using crushed limestone aggregate is about 23 per cent higher than that obtained using gravel aggregate, probably due to the formation of a stronger interfacial bond between the cement paste and aggregate. Because of black color of rice-husk cements, these cements can be used to make permanent black concrete for glare-free pavements and architectural applications. These concretes show better long-term color stability than that obtained by using coloring pigments.

Aggregate typeCompressive strength, MPa3 days7 days28 daysCrushed aggregate293947Gravel aggregate243338

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Rice-husk ash when mixed with sand and lime in suitable proportions with an appropriate quantity of water can be used to cast bricks. These require air curing followed by wet curing before being used. The rice-husk ash bricks have a density of 1400-1600 kg/m3 and compressive strength of 5-6 Mpa. The water absorption is 15-20 per cent.9The Northcap University, Gurgaon

B. INORGANIC WASTEThe inorganic wastes which are hard, particularly, the demolition waste such as broken concrete, broken bricks and crushed glass can be used to produce concretes of requisite strength and durability. BROKEN OR RECYCLED CONCRETE: Huge quantities of building rubble become available each year by the way of demolition of old structures to make way for new and modern ones due to rapid urbanization. The quantities increase tremendously during massive reconstruction after devastating earthquakes. Disposal of such materials is difficult in view of the scarcity of suitable dumping grounds, and meeting the environmental requirements. Hence, the broken concrete is increasingly being recycled. Recycled concrete is simply the old concrete that has been removed from buildings, foundations, pavements and other structures and crushed to the specified size.10The Northcap University, Gurgaon

The basic requirements for recycled aggregates for concrete construction is that the original concrete shall be sound, hard, normal concrete. As a rule, recycled concrete aggregate of distinctly different qualities shall be used separately. The cement mortar attached to the recycled aggregate primarily determines the performance of recycled concrete.Finishing materials, reinforcing bars and other embedded material, if any, in the original concrete shall be removed in the best possible way.Recycled aggregates shall not contain excessive amounts of dirt, plaster of Paris or gypsum and other injurious foreign matter like wood and asphalt which may adversely affect recycled aggregate concrete and steel used therein.

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PRODUCTION: The basic method of the recycling concrete is one of crushing the debris to produce a granular product of given particle size and then reprocessing and screening, the degree of which depends on the level of contamination and the application for which recycled aggregate is produced. Recycled aggregates normally have more angular shape and more coarser surface and exhibit more or less similar particle size distribution as that for natural aggregate. 12The Northcap University, Gurgaon

PROPERTIES OF RECYCLED AGGREGATE CONCRETE: The concrete produced with recycled aggregate loses its workability more rapidly than the conventional concrete, because recycled aggregate is more porous than natural aggregate. Thus concrete with recycled concrete aggregate may require 5 to 10 per cent more mixing water to achieve the same workability as the gravel concrete. If both fine and coarse aggregates are recycled aggregates, around 15 per cent more free water is required.

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APPLICATIONS: Utilization of recycled concrete in the form of aggregate is widely accepted for pavements, base and sub-base courses and to some extent for foundation purposes. The lean concretes produced using recycled aggregate are called econo cretes and have resulted in a saving in the cost of construction of order of 30 percent.

BROKEN-BRICK AGGREGATE CONCRETE: Broken brick is a waste product obtained as rejected overburnt or damaged bricks in brick work and at construction sites. Broken-brick aggregate is obtained by crushing waste bricks and has a density varying between 1600-2000 kg/m3. It is used in concrete for foundation in light buildings, flooring and walkways. Broken-brick aggregate may also be used in lightweight reinforced concrete floors. Broken-brick concrete can be designed to obtain the compressive strength between 15 MPa to 35 Mpa generally required in practice and such a concrete possesses satisfactory structural properties. 14The Northcap University, Gurgaon

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