COST-EFFECTIVE MATERIALS

11.7.1 Fly ash

Fly ash is an industrial waste from thermal power stations using coal as boiler fuel. Disposal of fly ash poses an operational constraint and is an environmental hazard. Annual generation of fly ash is 30 million tonnes. Fly ash can be used:

1. As a replacement of cement by 20 per cent by weight in RCC works.
2. In lean concrete mixes and cement mortars.
3. To make good burnt bricks by mixing 15–20 per cent of it with clay.
4. To make stabilized bricks by mixing it with asphalt and sand in proper proportions. Some quantity of sulphur can be added for bonding.

11.7.2 Soil-cement blocks

These are a mixture of pulverized soil and measured amount of Portland cement and water compacted to high density. These reduce cement consumption in construction.

11.7.3 Stabilized mud blocks

Any material used for wall construction should possess adequate compressive strength and erosion resistance. These properties can be imparted to the mud blocks by stabilizing it by cementitious admixtures, such as cement and lime and by compaction.

Lime is relatively cheap compared to cement and locally available in many places. So pressed soil lime blocks are better for rural applications.

11.7.4 Stone blocks

Random rubble masonry walls are widely used where building stone is abundantly available and cheaper than local bricks. The new method developed uses pre-cast stone masonry blocks of 30 cm × 20 cm × 15 cm nominal size. The blocks have one face with stone texture and weigh 18 kg. Their use reduces wall thickness from 30 to 20 cm, saving material cost and increasing the usable floor area.

1. Their use avoids the requirement of skilled labour.
2. They require only 1.5 cm plastering thickness instead of 2.5 cm required for random rubble masonry and that too only on one side.

11.7.5 Lime-based stone masonry blocks

Stone masonry building blocks made with lime-based binders possess many advantageous properties including compressive strength sufficient for use in load-bearing walls of 3–5 storey heights.

Stone masonry building blocks have the following advantages:

1. Convenient to use
2. Economic
3. Speed up construction work
4. Require less amount of mortar
5. Compressive strength increases continuously for long periods, even after 28 and 60 days
6. Can be used for the construction of load-bearing walls
7. Show good resistance to rain penetration and are subject to hardly any volume change or cracks with ageing.

11.7.6 Uses of lime

1. Easy to handle
2. Does not require any further processing at site
3. Good workability, less shrinkage, good strength resistance to moisture and freedom from major cracks
4. Replaces the use of cement by 50 per cent
5. Reduces the overall cost of construction

11.7.7 Concrete hollow blocks

Concrete hollow blocks have the following cost-effective characteristics:

1. Material economy
2. Lightweight material
3. Fast rate of construction
4. Good heat tightness
5. Good heat and sound insulation

Their advantages over solid masonry are:

1. Increased size of individual units reduce the construction time
2. The above implies few joints and, thus, increased compressive strength and saving in cement mortar
3. It reduces the self-weight of masonry

11.7.8 Fibre reinforced concrete (FRC)

It has superior fatigue, crack and impact resistance. It has greater durability and is used in roads, pavements, air fields, etc.

11.7.9 Sand lime bricks

These are made from silicious sand and hydrated lime with just sufficient water to allow them to be moulded under pressure. The bricks are cured in an autoclave under saturated steam.

The advantages are as follows:

1. Economical as less energy is used in their manufacture, i.e., 1/3 of fuel is used compared to that for a brick.
2. No need of clay and the land used for brick manufacture can be used for agricultural purpose.
3. In some places removal of sand leaves a good cultivable land.

11.7.10 Ferrocement

Highly versatile form of RCC in which cement mortar is reinforced with layers of continuous and relatively small wire meshes. It is considered as a cheap construction material. It has a unique combination of stiffness, high strength and serviceability. It is a homogeneous material and cracks only at higher loads.

The advantages are:

1. Easy to make, maintain and repair
2. This technique improves the engineering properties of the material such as failure, tensile and flexure strength, toughness, fatigue resistance, etc.
3. Mouldable and is of one-piece construction

11.7.11 Fibre reinforced polymers (FRPs)

FRPs are typically organized in a laminate structure, such that each lamina (or flat layer) contains an arrangement of unidirectional fibres or woven fibre fabrics embedded within a thin layer of light polymer matrix material. The fibres, typically composed of carbon or glass, provide the strength and stiffness. The matrix, commonly made of polyester, epoxy or nylon, binds and protects the fibres from damage and transfers the stresses between fibres.

The strength properties of FRPs collectively make up one of the primary reasons for which civil engineers select them in the design of structures. A material’s strength is governed by its ability to sustain a load without excessive deformation or failure. The response of FRPs to axial compression is reliant on the relative proportion in volume of fibres, the properties of the fibre and resin and the interface bond strength. FRP composite compression failure occurs when the fibres exhibit extreme (often sudden and dramatic) lateral or sideways deflection called fibre buckling.

Among FRP’s high strength properties, the most relevant features include excellent durability and corrosion resistance. Furthermore, their high strength-to-weight ratio is of significant benefit; a member composed of FRP can support larger live loads since its deadweight does not contribute significantly to the loads that it must bear. Other features include ease of installation, versatility, anti-seismic behaviour, electromagnetic neutrality, excellent fatigue behaviour and fire resistance.

There are three broad divisions into which applications of FRP in civil engineering can be classified: applications for new construction, repair and rehabilitation applications and architectural applications. FRPs have been used widely by civil engineers in the design of new construction. Structures such as bridges and columns built completely out of FRP composites have demonstrated exceptional durability and effective resistance to effects of environmental exposure. Pre-stressing tendons, reinforcing bars, grid reinforcement and dowels are all examples of the many diverse applications of FRP in new structures. One of the most common uses for FRP involves the repair and rehabilitation of damaged or deteriorating structures. The many applications for which FRP can be used have also been discovered. These include structures such as siding/cladding, roofing, flooring and partitions.