session 1 range of building materials properties of concrete clay and none clay building products

Session 1

Range of building materialsProperties of ConcreteClay and none clay building products

Introduction

Introduction

In this module you will learn about the characteristics and quality standards of building materials commonly used in residential scale buildings

There is a wide range of possible building materials available for our use and the performance of these materials has an impact on the cost, aesthetics and function of the building.

A well designed, economical building takes the following factors into account the properties and behaviour of building materials the initial and long-term costs the effects on the environment how the materials interact with each other.

Introduction

Well designed buildings take into account:

Properties and behavior of materials

Initial and long term costs

Effects of the environment

How building materials interact with each other

Introduction

Introduction

Learning outcomes

On completion of this unit, you should be able to:

Nominate the various factors that limit the life and durability of building materials.

Understand the various physical, chemical and biological factors that affect the performance of building materials in use

Understand the basic characteristics of different building materials.

Introduction

Introduction

Factors affecting the selection of building materials

The selection of materials is affected by a range of factors including:

Economic physical.

Let’s examine these factors in detail.

The Range of building materials

Factors affecting the selection of building materials

Economic factors

Energy content

Building materials are sometimes described as having a certain ’energy content’. This refers to the cost of their production. timber or sand are materials having a ’low energy content’, they do not require a primary manufacturing process.

By-products of other industrial processes (eg wood particles, blast furnace slag and pulverised ash) also have a low energy content.

Introduction

Energy content

Other materials require energy in their production, and therefore have a ’high energy content’. These include, glass, bricks, plastics, metals and cement. This adds to their cost, and if local supplies of the raw materials are exhausted or unavailable, then purchase and transport costs are also added to the overall cost.

Factors effecting the selection of building material


Labour and Materials costs

The cost ratio for housing is approximately:

55 per cent materials45 per cent labour

Labour and Materials

The choice of materials should not depend only on the purchase and installation cost, but also on the cost of repair, maintenance and replacement of short life-span products.

Less durable materials may be cheap to buy but repair or replacement costs are usually high.

Cheap materials usually lower the value of a building, whereas more durable materials, such as stone and brick, mellow with age and give the structure a more aesthetic appearance.


Conservation of resources

Most world resources of metals, rainforest timber, fossil fuel and limestone are non-renewable and limited.

It is important for us as consumers not only to be aware of those resources which are threatened or have bad effects on the environment, but also to use those which are, with management, safe both to our health and to the environment as a whole. Where possible we should use renewable resources, such as timber from re-planting programs.

It is also important that world fuel energy is not wasted by unnecessary processing and transportation. As well as being environmentally desirable, these savings mean cheaper materials.

Factors effecting the selection of buildingmaterial


Physical properties

Materials have different characteristics, or properties. These properties are affected by physical, chemical and biological factors.

Here we will be looking at the following properties:

Density and specific gravityStrengthElectrical conductivityThermal conductivity and capacityMoisture absorptionAcoustics.

Density and specific gravity

Different substances have different densities. Iron is much denser than aluminium which is why a piece of aluminium is much lighter than a piece of iron of the same size.

Ice floats in water because the ice is less dense than the water.

Density is measured by specific gravity.

Specific gravity is the ratio of the mass of a given volume of a liquid or solid to that of the same volume of water. The density of pure water is taken as 1 at 4°C.



Strength

A structure (eg a beam or a bridge) must be able to safely support its own weight plus the load it carries without distortion.

Distortion will reduce the efficiency of the structure or make it unstable or look unattractive.

A structure can be made much stronger without increasing its weight, by being made in a different shape.

Structures have different strength when used in different ways. See, for example, in Figure 1.1, where the steel beam A is much stronger than the steel beams B or C, even though they all contain the same amount of steel.


Figure 1.1: Different types of steel beams


Some materials strongly resist being squashed. They are said to have compressive strength. Concrete, stone and brick are such materials. Other materials, such as steel, are strong under tension and will resist being stretched.

The behaviour of concrete under pressure is illustrated in Figure 1.2. Concrete cracks easily when stretched. It has low tensile strength.


By using steel reinforcing in concrete, we combine the tensile strength of steel with the compressive strength of concrete, resulting in a product that is strong in tension as well as being strong in compression (see Figure 1.3)

Figure 1.3: The tensile (under tension) strength of steel is combined with the compressive strength of concrete when reinforcing mesh or bars are used in concrete


A piece of 25 mm wide galvanised steel strap, which is often used in bracing timber frames, is very difficult to stretch, but crumples easily when compressed lengthways. It has high tensile strength and low compressive strength.

Materials that are undergoing force are said to be stressed, and their change in shape is called strain. An elastic material is one which will recover its original shape when the stress is removed. A steel spring is elastic. A piece of chewing gum is not very elastic.

The response of materials to stress will depend on:how stress is applied to them whether the stress is continuous (eg a load-bearing arch)whether the material is compressed, stretched or twistedwhether it is affected by moisture or temperature.


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Electrical conductivity

Materials that easily carry electricity through them are said to be conductors. Materials that do not are non-conductors. For example, most metals are good conductors and most plastics are not. This is why electrical wiring is copper and the protective sheathing is plastic.


Thermal conductivity and capacity

The thermal properties of a material are concerned with how a material reacts to changes in temperature. The thermal properties include heat expansion or contraction, insulation, heat storing ability, cooling, and reaction to frost, snow and ice.

Thermal conductivity is a measure of how fast heat travels through materials. This rate may be affected by density, temperature, porosity and moisture content.


Moisture absorption

Some very porous materials will absorb moisture more readily than others. However, most materials may take up moisture from the air, from the ground (eg through poor dampcourses), from damaged roofs or gutters, or by condensation.

Condensation from moisture in the air will form on surfaces colder than the air.

Condensation often becomes trapped on the inner surface of water-tight materials (eg flat-roof coverings, metal and glass wall-cladding, foil insulation). This can be prevented by the correct use of vapour barriers (materials which are designed to prevent surface condensation by being placed on the warm side of walls or ceilings in such a way that there is no gap in them).


Acoustics

Insulation from noise can be achieved by the use of dense materials, by avoiding openings directly onto noise areas and by avoiding direct paths (eg a hall with a bend leading from a noisy machine shop to the workers’ tea room or a hall with lobbies or double doors would both reduce noise).

Some porous materials are used for modifying the acoustics in a room but sound can only be prevented from travelling from one space to another by the use of dense materials.On the inside of a building, double-glazed windows, heavy curtains, wall-hangings and carpet all help absorb noise. On the outside, walls, fences, hedges, trees and bushes may be used to reduce traffic or industrial noise.

Factors effecting the performance of building material Complete the check progress 2 questions in your Guide

Building materials undergo changes over time and the following factors affect their performance:

Movement caused by applied loadsMovement caused by temperatureMovement caused by moistureDurability of the materialsFire resistanceCompatibility of different materials.

Movements may be substantial and result in considerable stresses. If these stresses are greater than the strength of the material then, obviously, cracks or buckling will result.

Factors effecting the performance of building material

Movement caused by applied loads

These loads may occur by design or by accident. They may be caused by error in structural design or from overloading.

Movement caused by temperature

Most substances are affected by temperature changes, expanding when heated and contracting when cool, but some are affected more than others. This is called thermal movement. Figure 1.4 shows a comparison of the relative changes due to temperature in a number of materials.


Dark coloured materials set into light coloured ones

Dark coloured materials, when exposed to the sun, can heat up and expand greatly, causing cracks in the material in which they are set. Or else the dark materials may themselves crack or buckle. For this reason, roof surfaces (such as sheet metal) are best finished with a solar heat-reflecting surface or paint. Coloured glass in a sunny wall must be able to move freely, as it will expand and contract with temperature changes. If the glass is set between metal screws or beading that prevents this movement, it will crack. Putty or silicone caulk allows such movement.


Movement caused by moisture

A change in the moisture content of most materials will result in deformation: they will swell when wet and shrink when dry. These changes, called moisture movements, can result in warped, twisted, shrunk or cracked items.


Durability

Since all materials deteriorate over time to some extent, we should be able to anticipate these changes and take them into account when designing a structure, whether it is a house, a shed or a cupboard. We should foresee normal wear and tear, as well as the occasional very heavy stress caused by storms, fire, flood or burglary for example.

Durability will be different for different exposures. A coat of paint will last for many years inside a cupboard or less than a year in a sunny exposed position in a heavily polluted industrial area. We are all aware of the effect of salt spray on a car. Buildings are similarly affected, though it is not always so obvious.


Corrosion of metals

The effects of metal deterioration on surrounding materials can be significant, and will be looked at in the context of these materials when they are dealt with in later units.

Sunlight

Sunlight causes drying and cracking of timbers. It also fades colours and pigments and its heating of dark coloured materials can greatly speed up their breakdown.Ultraviolet radiation causes breakdown of clear finishes, stains, paints, rubber, some plastics and polythenes, tars and bitumen, fabrics and canvas.

Metals, bricks and stones are largely unaffected by sunlight.


Biological agencies

Certain bacteria in the soil break down sulphur chemicals which cause corrosion of metals such as iron, steel and lead.Burrowing animals or birds making nests can tunnel foundations, undermining footings; they can also excavate loose unsound material allowing rain in or weakening supports.

Tree roots and vines growing in cracks exert a very strong and destructive force, expanding and extending cracks in masonry, pipes, concrete or timber. They also hold moisture, encouraging the growth of moulds and fungi, and the uneven drying of brickwork (which causes uneven movements within the wall).


Water and frost

Care should be taken in the selection of materials for use in damp areas since some building materials react less well in such situations than others. For instance, limestone and marble slowly dissolve in water. Timber, chipboards, hardboards and other similar wood products lose some of their strength, and many flooring materials are less hard-wearing when wet.

Water can encourage fungal attack and certain destructive chemical reactions. Repeated wetting and drying causes surface crazing and cracking of timbers. Water also often carries destructive acids, salts and other soluble chemicals.

Factors effecting the performance of building materialSalt crystallisation

Salts that are dissolved in water can come from the sea, the ground and from some building materials. As moisture evaporates from a surface, the salts are left behind in the form of powder or crystals, called efflorescence. Sometimes this is just an unattractive coating, usually white, but sometimes yellow, green or brown. However, it can be destructive if allowed to persist for a long time.

Salts crystallising on the surface of a porous material can cause gradual erosion or flaking. This surface deterioration, called fretting or spalling, often occurs in soft sandstones, bricks (such as sandstocks) or in mortar layers in masonry. When moisture rises in the walls of a building these salts cause paint to bubble and peel. Fixing this problem can involve costly installation of dampcourses and removal of all affected plaster or render from the walls.


Chemical action

Cause swelling, shrinking, weakness or damaged appearance. Due to chemical changes within the material itself, or changes brought on by attack from outside chemicals. Heat and moisture aid most reactions.The presence of aggressive gases, in the air or in factories or dissolved in rainwater, can mean that some materials may need special protection, or that other more suitable materials should be used instead.


Groundwater, industrial wastes, soil, ash and wet clays are some of the substances that can produce soluble sulphates which attack cement products and metals.

Loss of volatilesVolatiles are liquids and gases. Plastics, paints, varnishes, finishes, mastic, rubber, tar and bitumen shrink and become brittle when their volatiles are lost.


Abrasion and impact

In situations of abnormal impact or abrasion, suitable materials and finishes need to be chosen. For example, a concrete path or floor that will take heavy traffic requires correct concreting techniques to be followed so as to produce a hard, durable surface.

VibrationVibration caused by proximity to machinery or heavy vehicular traffic can cause problems in light constructions and with brittle materials.

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Fire resistance

Fire is usually the fastest, most destructive and dangerous way in which a building can be damaged or destroyed. It is a very important consideration for both city and country dwellers.

Government bodies test materials and publish regulations and codes which are implemented by local councils concerned about fire hazards in public or private buildings.

Fire hazard indices (published by the Experimental Building Station as ’Notes on the Science of Building’, Nos 66, 98, 136, 137, 142) are lists based on extensive experiments on structures and materials.


Combustibility

Materials that ignite, that give off flammable gases or that show considerable self-heating when exposed to a set heat in a furnace, are called combustible.

Non-combustible materials, on the other hand, do not feed the fire, and flame does not spread over them. Non-combustibility does not mean fire resistance. Table 1.1 lists some combustible and non-combustible materials.

Non-combustible materials (such as steel) may expand and disturb attached structures, or lose strength and collapse. Other non-combustible materials may spall (flake) and shrink or crack. On the other hand, some combustible materials (such as timber) can often provide a useful degree of fire resistance.


Fire resistance

Fire is usually the fastest, most destructive and dangerous way in which a building can be damaged or destroyed. It is a very important consideration for both city and country dwellers.Government bodies test materials and publish regulations and codes which are implemented by local councils concerned about fire hazards in public or private buildings.

Fire hazard indices (published by the Experimental Building Station as ’Notes on the Science of Building’, Nos 66, 98, 136, 137, 142) are lists based on extensive experiments on structures and materials.


Fire Resistance

Fire resistance is expressed as the amount of time in hours and minutes a component survives a fire test of set temperature before it can no longer perform its function. It is considered to fail the test when any of the following occur:

It collapses.It forms holes or cracks through which flame can pass.It gets hot enough to ignite other combustible materials it is in contact with and which the fire hasn’t yet reached.


How certain materials behave in fire

Timber

Timber easily ignites at about 221–298°C. However, some timber (particularly large pieces, at least 100 by 75 mm in section or larger) are resistant to the fire once the surface has been charred. Many Australian hardwoods have this characteristic and, in fact, have proved to be more fire resistant in buildings than steel. However, all timbers do burn readily if temperatures stay high enough. Therefore, timber buildings are not classified as fire resistant.


How certain materials behave in fire

Timber

Timber has good thermal insulation, preventing materials not in contact with the fire from heating up to extreme temperatures. When hot, timber does not expand in length (unlike steel) and neither does it markedly lose strength.Laminated timber structures glued with synthetic resins have similar fire resistance to solid timber, although resistance will vary according to the type of timbers and glues.


Stone

Stone blocks and slabs are usually satisfactory in fires, but overhanging features and lintels are liable to fail. Free quartz (eg in granites) explodes suddenly at 575°C and should not be present in any stone that is required to be fire resistant. Sandstones behave better than granite, but in drying they may shrink and crack, with 30–50% loss of strength.

Plastics

Although many plastics are made in fire-retardant grades, all are combustible and some give off large quantities of toxic smoke. PVC (polyvinyl chloride) melts at fairly low temperatures, and most thermoplastics (plastics that can be heated and shaped) char above 400°C and burn at 700–900°C.


Clay products

Most clay products perform well in fires, having been made at kiln temperatures higher than most fires reach.Brickwork failure is often caused by expansion of enclosed or adjoining steel work.

Concrete

Ordinary Portland cement concrete disintegrates at 400–500°C. However, how the concrete performs depends very much on the presence of reinforcement and the type of aggregate it contains.


Metals

Metals used in building are non-combustible, but they lose strength when heated. Aluminium, lead and zinc melt in building fire temperatures. As previously mentioned, the expansion of the hot metal can cause problems. Also, the high thermal conductivity of metals means that the temperature of surfaces remote from a source of heat will approach the temperatures near the fire, causing fires to spread.

Steel

Mild steel behaves in an interesting way when heated. Up to 250°C, it gains strength, then gradually returns to normal strength by 400°C. After that, it rapidly weakens so that, at 550°C (referred to as the critical temperature), it begins to fail.Generally, structural steelwork must be protected with fire-resistant encasements, such as concrete or brickwork.


Glass

Although glass is non-combustible, it readily transmits heat and often shatters unpredictably at an early stage in a fire. Toughened glass is not fire-resistant.

Glass fibre and rockwool

Resin-bonded glass fibres are combustible. Glass fibres themselves melt at about 600°C.

Fibrous cement

This material tends to shatter when heated, sometimes explosively. It does not contribute to making a fire-resistant structure.


Paints

Generally, paint films are combustible and may help spread flame over surfaces. However, as they are thin, they only contribute a small amount to the fire load. When applied to combustible materials, certain paints can reduce the spread of flames. They delay but never prevent the spread of flame.

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Compatibility of materials

The large range of new materials on the market today, many of which are chemically based, plus widespread pollution, has led to new chemical and physical problems with materials. A material may break down many times faster than normal in the presence of another particular substance. Problems do not always show up until a product has been on the market for a number of years. Incompatibility of building

Materials can be grouped roughly under the following headings:

Corrosion of metalsStains and discolouring effectsProblems with surface finishesChemical reaction between materials.


Corrosion of metals

Galvanic reactions: These occur between metals that have different levels of electronegativity. This is often seen as corrosion of one metal or a deposition of metal scale on the other metal. Offcuts or filings of metals left around in moisture can cause rapid destruction of nearby metal building components. Some common galvanic reactions are listed below.

Lead used with zinc or aluminium promotes corrosion. Therefore, metal roof-flashings need to be carefully chosen.Steel screws or nails should not be used with aluminium or zinc roofing, unless they are zinc or cadmium coated.Copper should not touch or drain onto zinc, aluminium, zincalume or galvanised materials.

Factors effecting the performance of building materialCorrosion of metals

As heat speeds up corrosion, different metals should not be mixed in hot water systems.Copper and brass are permanently resistant to water.Aluminium: This becomes encrusted in coastal atmospheres. Mortar, cement or concrete pit the surface of aluminium if splashed on it.Industrial atmospheres: These are usually acidic and corrode all metals.

Stains and discolouring effects

Copper: Water dripping off copper causes green stains.Rust: Water running off exposed iron or steel will stain surrounding surfaces.Eucalypt timbers: When wet, many eucalypt timbers produce brown stains on masonry.


Problems with surface finishes

When finishes won’t stick to the surface they are applied to, it is usually due to the two being unsuitable for each other. The surface may either be too smooth or it may be powdery or flaky; or there might be a chemical incompatibility between the surface and the finish. Many silicone sealants will not accept paint.Acid-resisting grouts (for floor-tiles) cannot be satisfactorily cleaned from the tile surface.Primers, undercoats, finish paints, lacquers, varnishes and stains should all be used according to manufacturers’ instructions as many are incompatible with certain materials.

Factors effecting the performance of building materialTesting of materials

The testing of materials is carried out by the manufacturer or supplier before delivery (eg stress testing of timber). Upon delivery, an inspection should be carried out with respect to the quality and suitability for the construction situation it is intended.

Concrete is one material which is tested on site (the slump test), and later laboratory tested for compressive strength at 28 days. Materials such as paints, adhesives, glass and the like have been developed and trialled under strict laboratory controls and conform to Australian Standards.

Building The builder or supervisor of a project, needs to be informed of all the information relating to products being used. Details such as handling, storage, application, installation and warranties should be kept in a product file and updated to provide ready access to this information to avoid warranty problems associated with incorrect handling and installation.


Handling and storage

Planning for storage and handling of materials on site is an important job for building staff. Many materials are easily damaged if due care is not taken in handling, and some can deteriorate if exposed to moisture and direct sunlight.

Materials should be stored in accordance with manufacturers’ instructions; for example, stacked flat, off the ground, in a dry area or in a secure area for flammable or toxic materials.

Transportation to the site and unloading arrangements need to be given careful consideration and appropriate equipment must be organised.

When handling materials on site, safe working practices must be followed and all OHS regulations implemented.


Tolerances

All building work in Australia is covered by the Building Code of Australia and many Australian Standards. These standards have been developed for most building materials and detail tolerances, application, testing (if applicable) and method of installation. These tolerances should be followed and best industry practice adhered to.

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Properties of Concrete

Learning outcomes

On completion of this unit you should be able to:

• Identify the properties of concrete• Understand the nature and purpose of the materials which

make up concrete• Identify the procedures used in the transport and

placement of concrete• Understand the reason for and the methods of curing

concrete• list the uses of concrete in residential construction.


Cement

In Australia, all Portland cements are made to meet the requirements of AS3972–1991 ‘Portland and Blended Cements’.General purpose cements:

Type GP—general purpose Portland cementType GB— general purpose blended cement.Special purpose cements:Type HE— high early strength cementType LH— low heat cementType SR— sulphate resisting cement.


Special purpose cements

Type HE cement is used where high strength is required at an early stage; for example, where it is required to move forms as soon as possible or to put concrete into service as quickly as possible. It is also used in cold weather construction to reduce the required period of protection against low temperatures.

Type LH cement is intended for use in massive concrete structures such as dams. In such structures the temperature rise resulting from the heat generated during hardening of the concrete is likely to be a critical factor

Type SR—sulphate resisting cement has better resistance to attack by sulphates in ground water than other types because of its special chemical composition.


White and off-white cements

Off-white cement is in general use in cottage construction but white cement usually proves cost prohibitive.

High alumina cement

High alumina cement is not a Portland cement. If mixed with Portland cement it can give a rapid or ‘flash’ set. It is characterised by a very high rate of strength development accompanied by a high heat of hydration and by a greater resistance to sulphate and weak acid attack than Portland cements. Curing conditions require very close control for 24 hours after placement.

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Storage of cement

Cement will retain its quality indefinitely if it does not come in contact with moisture. If it is allowed to absorb appreciable moisture it will set more slowly and its strength will be reduced.

Therefore, storage of bagged cement requires storage facilities to be as airtight as possible, and the floor should be above ground level to protect against dampness.

The bags should be tightly packed to reduce air circulation, but they should not be stacked against outside walls. If they are to be held for a considerable period the stacks should be covered with tarpaulins or water-proof building paper.

Doors and windows should be kept closed. A ‘first-in-first-out’ rotation of bags should be maintained at all times.


Setting and hardening

Setting is the initial stiffening of the cement paste during the period in which the concrete loses its plasticity and before it gains much strength. This period is affected by the water content of the paste and the temperature. The more water in the paste the slower the set, the higher the temperature the faster the set.

Hardening is the gain in strength which takes place after the paste has set. It is affected by the type of cement used and the temperature. High temperatures cause more rapid hardening.


Water

Water suitable for drinking will generally be suitable for concrete making.

Aggregates

Aggregates used in concrete should consist of clean, hard, durable particles strong enough to withstand the loads to be imposed upon the concrete.

In general they should consist of either natural sands or gravels or crushed rocks, although some manufactured aggregates such as blast furnace slag and expanded shale and clays can be equally satisfactory.

Commonly used crushed rocks include basalt, granite, diorite, quartzite and the harder types


GradingBoth coarse and fine aggregates should contain a range of particle sizes. Graded aggregates produce more workable oncretes which are less prone to segregation and bleeding.Particle shape and surface textureThe particle shape and surface texture of aggregates affect the workability. For workability, particles should be smooth and rounded. On the other hand, angular materials result in greater strength, so that, in the final analysis, there is little or no difference in effectiveness. The ultimate decision is one of economics and availability.

Maximum size of aggregatesThe greatest economy is achieved when the largest maximum size aggregate is used. The factors limiting size are the availability, transporting and placing equipment to handle the larger sizes, and the clear spacing between reinforcing bars and the clear spacing between the reinforcement and the formwork.


Manufactured aggregates

Blast furnace slagIf sound and free from excessive quantities of ferrous iron, blast furnace slags are satisfactory concrete aggregates. Generally they are angular in shape and require a higher percentage of fines to produce workable concrete.

Lightweight aggregatesExpanded shale aggregates produce concrete having approximately two-thirds the density of those made with dense aggregates, but with comparable strengths. Lightweight aggregates may be smooth and rounded or harsh and angular, depending on the method of manufacture.


Testing of aggregates

Since aggregates comprise up to 75 per cent of the volume of concrete, their properties are obviously important. These properties include size and grading as well as cleanliness.

The testing of concrete aggregates is generally carried out to determine:Presence of organic or other deleterious material which may severely limit the strength of the concreteResistance to abrasion, which may limit the durability of the concretethe presence of any alkalis which may react with the cement and cause expansion of the aggregate.


Conclusion

Good concrete can be made from a wide variety of aggregates provided these are clean and free from harmful impurities. As the quality of concrete becomes higher, the quality of the

aggregate becomes more important and factors such as grading more critical. Good aggregates, although sometimes higher in initial cost, are generally more economical because of the higher quality and lower overall cost of the concrete they produce.


There are several properties of concrete which affect its quality.

These are:• Compressive strength• Tensile strength• Durability• Workability• Cohesiveness.• Let’s examine these properties in detail.


Compressive strength

Compressive strength remains the common criterion of concrete quality and will frequently form the basis of mix design. For fully compacted concrete made from sound clean aggregates the strength and other desirable properties under given job conditions are governed by the net quantity of mixing water used per bag of cement.

This relationship is known as the water/cement ratio, that is, the quantity of water in the mix to the amount of cement present.

Example: A concrete mix having a water/cement ratio of 0.5:1 would require 20 litres (20 kg) of water for each 40 kg bag of cement.The ultimate strength of concrete depends almost entirely on the water/cement ratio, for as the ratio increases the strength of the concrete decreases.


Tensile or flexural strength

This is the measure of the concrete’s ability to resist flexural or bending stresses.The tensile or flexural strength of concrete is dependent on the nature, shape and surface texture of the aggregate particles to a much greater degree than does the compressive strength.

Durability

Concrete may be subject to attack by weathering or chemical action. In either case the damage is caused largely by the penetration of water or chemical solutions into the concrete and is not confined to action on the surface. The resistance to attack may therefore be increased by improving the watertightness of the concrete. This is achieved by lowering the water/cement ratio, assuming the concrete is fully compacted.


Workability

The workability of concrete, or the effort required to handle and compact it, depends on several factors, as follows:

Water/cement ratio: The higher the water/cement ratio, the more workable concrete becomes. However, the water/cement ratio should be fixed by considerations other than workability (eg strength and durability), and should not be increased beyond the maximum dictated by these considerations.

Cement content: The cement paste in concrete acts as a lubricant, and at a fixed water/cement ratio, the higher the cement content, the more workable the concrete becomes. It follows then that any adjustments to increase workability should be made by increasing the cement and the water content at a constant water/cement ratio.

Grading of aggregates: Grading tends to produce more workable concrete.


Particle shape

Particle shape and size of aggregates:

Smooth, rounded aggregates will produce more workable concrete than rough, angular aggregates. Also, for a given water/cement ratio and cement content, workability increases as the maximum size of the aggregate increases.


Cohesiveness

The cohesiveness of concrete means the ability of plastic concrete to remain uniform, resisting segregation (separation into coarse and fine particles) and bleeding during placing and compaction.

Concrete in the plastic state should be cohesive to prevent ‘harshness’ of the mix during compaction, and to avoid segregation of the coarse and fine components during handling.

Segregation may occur during transporting over long distances, discharging down inclined chutes into a heap, dropping over the reinforcement or falling freely through a considerable height and placing in formwork which permits leakage of mortar.

Maximum cohesiveness usually occurs in a fairly dry mix, so as a rule the wetter the mix the more likely it is to segregate. Segregation can, however, occur in very dry mixes.


Testing of concrete

Concrete is tested on the site or in the laboratory to determine its strength and durability or to control its quality during construction.

These tests must be carried out carefully and in the correct manner or the results may be misleading and cause unnecessary delays while they are being checked. Worse still, faulty tests may result in either substandard concrete being accepted or even good concrete being rejected.

There are several ways in which testing can be carried out:by samplingby slump testingby compression testing.


Sampling

To make a composite sample from the discharge of a mixer or truck, three or more approximately equal portions should be taken from the discharge and then remixed on a non-absorbent board.

The sample portions should be taken at equal intervals during the discharge and none should be taken at the beginning or the end. The concrete at these points may not be truly representative of the whole mix.

When sampling freshly deposited concrete, a number or samples should be taken from different points and recombined to make a composite sample. Care should be exercised to make certain the sample is representative by avoiding places where obvious segregation has occurred or where excessive bleeding is occurring.


Slump testing

The slump test is a measure of the consistency or mobility of concrete and is the simplest way of ensuring that the concrete on the site is not varying.

It should be done often as an overall control on the various factors that can affect the result. Most important among these factors is the water content of the mix, variation of which can result in varying strengths of concrete.

A consistent slump means that the concrete is under control. If the results vary it means that something else has varied, usually the water, which can then be corrected.

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Compression testing

The strength of concrete is determined by making specimens, curing them, and then crushing them to ascertain their strength. The preparation of specimens is most important as a badly prepared specimen will nearly always give a low result.

Compressive test specimens are normally cylinders 150 mm in diameter and 300 mm high.

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Proportioning and mixing

Design strength

The designer of a concrete structure determines during the design stage, the concrete properties that are necessary to ensure that the structure performs in the desired manner. Since compressive strength is usually the most important property required and since most other desirable properties are directly related to it, it is usual for the designer to specify the minimum compressive strength required, usually at 28 days.

The ‘design strength’ is the minimum strength required by the designer.


Target strengthThe mix designer must design a mix which will produce concrete with a strength in excess of the design strength:

It is known that when a series of compressive tests are made from samples of concrete taken from time to time through the course of a job, the results will be scattered to either side of an average value.

This means that the concrete produced is never completely uniform in quality some weaker than the average strength and some stronger.

Since the designer has specified the minimum strength required, the mix designer must aim at an average strength, between the target strength and the design strength.

Generally, a target strength 33 per cent higher than the design strength meets the requirements of the building codes.


Specification of concrete

In writing the specification to ensure that the concrete has the properties required, the designer has two alternatives:specify the concrete by strength (the usual method)specify concrete by proportions.

Concrete specified by strengthThe designer specifies the minimum compressive strength required in the concrete and the age at which the concrete should have this strength, usually 28 days.


Batching

All materials, including water, should be accurately measured to ensure that concrete of uniform quality is produced.Batch proportions are often specified in relation to the bag of cement; for example, one 40 kg bag of cement to so many kilograms of coarse aggregate and so many kilograms of fine aggregate with perhaps 20 L or 20 kg of water.

One Litre of water has a mass of one kg and is not subject to variation.

With mass batching, there is no need to make allowance for the bulking of damp sand but allowance must be made for the non-absorbed water held by the aggregates as this moisture forms part of the mixing water.


Notes on mixing contained in your guide

Premixed concrete

Premixed concrete is used almost universally on residential building sites. The use of premixed concrete has advantages which include:Better quality control is possible at a large plant than under most site conditions.

Premixed concrete is controlled by AS1379–1991 Specification and Manufacture of Concrete, which should be referred to for information on methods of ordering, mixing and delivery.


Transporting concrete

Irrespective of the methods used to transport, place and compact the freshly mixed concrete, the following requirements are basic to good practice:The concrete must be transported, placed and compacted with as little delay as possible.The concrete must not be allowed to dry out before compaction.There must be no segregation of the materials.The concrete in the forms should be fully compacted.


Pumps and pipelines

Pumps and pipelines enable concrete to be transported across congested sites and where space is limited.

Concrete for pumping must be of medium workability with a slump of 70 mm to 120 mm and must be free from any tendency to segregate. The introduction of fly ash to the concrete improves pumpability and workability of the mix, and therefore adds appreciably to the distance concrete can be pumped.

More detailed information is contained in your guide


Placing concrete

Certain precautions must be taken when placing concrete, to ensure that:Formwork and reinforcement is not damaged or dislodgedThe concrete is free from segregationOther qualities of the concrete are not impaired.

Study the notes in your guide


Compacting

It is essential that concrete be properly compacted to ensure maximum density. Air holes must be eradicated, voids between aggregate particles must be filled and all aggregate particles must be coated with cement paste.

Thorough compaction results in:

Maximum strengthWatertight concreteSharp cornersGood bond to reinforcementProtective cover to reinforcementGood surface appearance.


Vibration

Concrete is usually vibrated to achieve good compaction. There are three types of vibrators:Immersion vibratorsForm vibratorsSurface or screed vibrators

The immersion vibrator is driven either electrically, mechanically or pneumatically and is probably the most efficient type of vibrator as it vibrates the concrete directly by immersion in the concrete. They are particularly suited to the compaction of large volumes of concrete.


Curing

Concrete increases in strength and other desirable properties with age, this is so only so long as drying is prevented.

The hydration of cement is a chemical reaction and this reaction will cease if the concrete is permitted to dry.

Evaporation of water from newly placed concrete not only stops the process of hydration, but also causes the concrete to shrink, thus creating tensile stresses at the drying surface; and if the concrete has not developed sufficient strength to resist these stresses, surface cracking may result.


Curing

As in many other chemical reactions, temperature affects the rate at which the reaction between the cement and water progresses; the rate is faster at high temperatures than at lower temperatures.

It follows then that concrete should be protected so that moisture is not lost during the early hardening period and should also be kept at a temperature that is favourable to hydration.


Curing methods

Curing methods can be classified as follows:

The supply of additional moisture to the concrete during the early hardening period.Sealing the surface to prevent loss of moisture from the concrete.

PondingSprinklingWet coveringsWaterproof paper, plasticsCuring compounds


Length of curing period

For most structural purposes, the curing time for concrete varies from a few days to two weeks according to conditions; for example, lean mixes require longer curing time than rich mixes and temperature affects the curing time as does the type of cement used.Since all the desirable properties of concrete are improved by curing, the curing period should be as long and as practicable in all cases.

Answer the questions in your guide


Reinforced concrete

Basic principles

Concrete, Is strong in compressive strength, and comparatively weak in tensile strength. To overcome this weakness in tension, concrete which is to be subjected to tensile stresses is reinforced with steel bars or mesh which is so placed that it will resist such stresses.

The designing and detailing of reinforcement is the job of the designing engineer and will not be dealt with in any great detail here, but it is important that those who supervise the fixing of reinforcement on the job have an appreciation of the basic principles of reinforced concrete.


Figure 3.5: Types of stress found in a structure


Reinforced concrete design combines the steel reinforcement with the concrete in such a manner that enough steel is included to resist the tensile stresses and excess shear stresses while the concrete is used to resist the compression stresses.

The bond between concrete and steel directly counteracts any tendency for the concrete to stretch and crack in a region subjected to tension

Concrete and steel expand and contract the same amount. If this were not so, the different expansion rates would break the bond between the two materials and so prevent the transfer of tensile stresses to the steel

Concrete has a high fire-resistance and protects the steel from the effects of fire.


Design of reinforced concrete

In order to be effective, the tensile reinforcement must be prevented from sliding in the concrete. The adhesion or bond between the concrete and the steel is related to the surface area of the steel embedded in the concrete.

Adequate anchorage is effected by extending the rods past the critical points (where no longer required to resist tensile and shear stresses) and by the use of:Standard hooksPlain rods extended into the supports (rarely used)Deformed bars (rolled with lugs or projections).

Study Figure 3.6 in your guide


Good formwork

The guiding principles for the production of good formwork are:QualitySafetyEconomy.


Quality

First quality formwork should be:

Accurate: True to the shapes, lines and dimensions required by the contract drawings.

Rigid: Forms must be sufficiently substantial so as to prevent any movement, bulging or sagging during the placing of the concrete.

Tight-jointed: If joints are not tight, they will leak mortar. This will leave blemishes in the shape of fins on the surface of the concrete and may result in honeycombing of the concrete close to the leaking joint.

Well-finished: The quality of the finish of the concrete is dependent on the finish of the forms. Nails, wires, screws and so on should not be allowed to mar the surface of the finished concrete.


Safety

Strength: For the safety of the workers and of the structure, the formwork must be strong enough to withstand not only the mass of the wet concrete but also the live loads of workers, materials and equipment. It is impossible to over emphasise how important this aspect of safety really is.

Soundness: Materials must be of good quality and durable enough for the job. The time will come, no doubt, when it will be essential to use for structural load-bearing members, only timber that has been tested with the mechanical stress grading process.


Economy

For economy, formwork should be:

Simple: Formwork should be designed for simplicity of erection and removal.

Easily handled: Shutters and units should be light enough to permit easy handling.

Standardised: Where standardisation of formwork is possible, the ease of assembly and the possibility of reuse serve to lower the formwork cost.

Reusable: Formwork should be designed for easy removal and in sections that are reusable. This will minimise the amount of waste material and thus decrease the cost of the formwork.


Supervision

Note:Study the notes in the guide carefully regarding supervision

Surface Treatments

There are many proprietary surface treatments available, some prevent adhesion to the formwork, others provide architectural finishes.


Stripping times

The time of the removal of forms is generally specified by the architect or engineer Forms can usually be safely stripped when the concrete has developed about two-thirds of its 28-day strength. However, the earliest possible removal of forms is desirable for the following reasons:

To allow the reuse of forms as planned.In hot weather, to permit curing to begin.To permit any surface repair work to be done while the concrete is still ‘green’ and favourable to good bonding.Vertical forms can generally be removed before the forms to the soffits of beams and slabs.


Table 3.1: Times for stripping formwork and supports

Study the chart in your guide


Concrete finishes

Many types of off form finishes:

SmoothWood grainArchitectural patternsTextured and patterned surfaces


Joints in concrete construction

If the concrete is allowed to stiffen to the extent that it cannot be worked, then a joint must be made. Other cases will occur when it is necessary, for structural reasons, to break the continuity of placing and to form a joint.

Joints can be of two general types:

Construction joints: Bond the new concrete to the hardened concrete in such a manner that the concrete appears to be monolithic and homogenous across the joint and allows for no relative movement of the concrete on either side of the joint.

Control joints: These allow for relative movement on either side of the joint, thus they can be either construction joints or expansion joints.


Construction joints

In practice, it is very difficult to obtain a perfect bond at a joint and a plane of weakness will always occur at a construction joint. For this reason, they should be avoided wherever possible.

While unscheduled interruptions are often unavoidable during placing, making an unplanned construction joint necessary, some breaks in the continuity of placing may be foreseen either in the design stage or just before commencement of construction, thus allowing the position of many joints to be planned.

Good planning will aim to interrupt placing in a position suitable for a control joint and so eliminate the need for a construction joint.


Location of construction joints

Where construction joints are necessary in structural members they should be made where the shear forces are at a minimum. The joint should be at right angles to the axis of the member so that axial forces act normally to the joint and do not tend to cause sliding along a weakened plane.

Concrete for columns should be poured continuously to just below the soffit of the beam, drop panel or capital, and the concrete left for at least two hours to settle before fresh concrete is placed.

The whole floor system around the head of the column should then be cast in one operation after suitable preparation of the joint.


Construction joints in beams should be made in the middle third of the span and on no account should they be made at or near the supports or over any other beam, column or wall since shearing stresses are usually very high at these positions.When a construction joint is required in a floor slab it should be made near the middle of the span.


Making vertical construction joints

When making a construction joint in a beam or slab, the concrete must not be allowed to assume its natural angle of repose, but should be taken up to a suitable stop board so as to form a vertical joint. To assist the transfer of load across the joint, either dowels or a keyway to aid mechanical bonding may be used at about mid-depth of the beam or slab. This is recommended in sections over 150 mm deep. Reinforcement must not be cut at a construction joint but must be left continuous in the member.


Making vertical construction joints


Watertight construction joints

A correctly made horizontal construction joint in a wall should not require sealing, but if the joint is to be in contact with water and particularly if subjected to hydraulic pressure, effective sealing will be necessary because of the tendency of the joint to open up as the concrete shrinks.

This can best be carried out by using a water stop. PVC water stop membranes extending into the concrete equally each side of the joint and welded or glued together at the ends to form a continuous diaphragm are commonly used.


Contraction joints

A contraction joint is a concrete joint made so that the concrete is free to shrink away from the joint while all other relative movement across the joint face is prevented.

As concrete sets, hardens and dries out, it shrinks. If no provision is made to relieve the drying-shrinkage tensile stresses within the concrete, cracking will occur when these stresses exceed the tensile strength of the concrete. If the concrete is completely unrestrained, cracking will not occur, but very few structures are completely unrestrained.

Contraction joints are most needed in unreinforced concrete structures because reinforcement considerably increases the tensile strength of concrete, restrains overall shrinkage movement and prevents the formation of large shrinkage cracks.


Location of joints

Contraction joints should be located where it can be expected that the severest concentration of tensile stresses will occur, such as:

Where abrupt changes in cross section occur.On irregularly shaped floors and slabs (eg T, H, L and U shapes), to divide them into rectangular shapes.Where structures are weakened by openings.In long structures such as walls and road pavements, which are not sufficiently reinforced to prevent the formation of shrinkage cracks.In large areas of pavement or slab on the ground.


Construction of joints

A vertical plane of weakness is purposely formed in the slab or wall. Vertical movement is controlled by forming a keyed joint or by using non-ferrous dowels with one end capped and coated so that they are free to slide. The bond between new and existing concrete at a contraction joint must be broken.


Dummy contraction joints

A dummy contraction joint is a plane of weakness built into a structure by means of a groove, either sawn or formed with a grooving tool.

This joint functions as a contraction joint by localising shrinkage cracks to beneath the groove. The irregularity of the crack serves to transfer loads across the joint and prevents relative movement in the plane of the joint.

Since this type of joint is an alternative to a full depth contraction joint, the location should be the same as for contraction joints.


Expansion joints

An expansion joint is formed by creating a gap between the two surfaces of the concrete to allow for expansion. The gap is usually filled with a compressible filler and all relative movement in the plane of the joint is prevented.

Expansion joints are generally provided in structures exceeding 30 m length, in unreinforced or lightly reinforced road pavements and as sliding joints between a roof slab and a supporting wall.

Answer the questions in your guide


Clay, Non-clay bricks,

blocks and Stone

Clay, Concrete & Stone

Clay has endured as a building material and even in early times its use was widespread (eg bricks, tiles, pipes and accessories). The shaping of plastic clay and then hardening it by drying and firing, was perhaps humanity’s earliest form of manufacturing but it was not until the late nineteenth century that machines became involved in the manufacturing process.

Learning outcomes

On completion of this unit, you should be able to:

• identify the uses of clay products in the building industry

• understand the role of brickwork in the building industry, and be familiar with the range of brick types and the different styles of bonding and tinting

• describe the desirable qualities of stone for specific applications

• discuss the uses and limitations of stone as a building material.

Clay

Clays are natural materials made up of very small crystalline mineral fragments. The shape, size and type of these fragments gives clays their plastic quality which allows them to be moulded and shaped when wet. These mineral fragments are also responsible for the hard, stony nature of clays after they are fired at high temperatures.

Clay products

When clay has been changed by heat (firing), the products are called ceramics. During firing, water is driven off, some recrystallisation of minerals takes place, and glass is formed from quartz sand present in the clay. The result is a hard, insoluble material. The higher the firing temperature, the more recrystallisation occurs and the more glass is formed, resulting in greater hardness and density.

The minerals present in the clay will determine its colour when fired. Ceramics are also coloured by having a specially prepared coating, or slip, applied before firing, which results in a glaze of the required colour or texture.

Different products require different firing temperatures, as shown in Table 4.1.

Table 4.1: Table of firing temperatures and uses of various ceramics

Uses of ceramics in building

There are five types of ceramics, apart from bricks, that are mainly used in building:

• terracotta

• fireclay

• stoneware

• vitreous china

• porcelain.

Table 4.2 shows how these different ceramics are made and used

Carry out activity 1 in your guide

Table 4.2: Features, firing temperatures and uses of ceramics used in building

Type of ceramic Features Firing temperature Uses

Terracotta Yellow to brownish red clays, which may be glazed or unglazed. Terracotta roofing tiles, although brittle, are stable in high climatic temperatures and do not contaminate run-off water

Fairly low temperature Main use is for floor and roofing tiles and air bricks (ventilators). Over the years, the most common pattern seen in Australia has been the French or Marseilles pattern (see Figure 4.1).

Fireclay Usually a creamish colour, it can withstand high temperatures over a period of time without cracking

Flue liners and firebricks in stoves, fireplaces, kilns and furnaces

Stoneware Harder, and less absorbent than fireclay. Contains more glass

Fired at a higher temperature than fireclay

Drainpipes and fittings.

Vitreous china High glass content. Even if its glaze should crack, it will not allow moisture to seep in

Very suitable for sanitary fittings such as toilet bowls, basins and sinks

Porcelain Similar to vitreous china but is purer.

Special uses, such as for electrical insulators

Bricks

Bricks used in construction are made from:

• clay or shale

• cement/concrete

• sand and lime (calcium silicate).

Methods of brick manufacture

Bricks are no longer made by hand but these are sometimes available second-hand from demolition sites. They are soft, porous, rather irregular in shape and, if protected from the weather, retain a pleasing warm appearance.

There are, now, two main methods of brick manufacture:

the dry pressed method the plastic or extruded process.

Dry pressed method

In this method, almost-dry clay powder is pressed into moulds and then fired. Most dry-pressed bricks have an indentation (called a frog) resulting from the shape of the mould (see Figure 4.2).

Plastic or extruded process

With the plastic or extruded process, a soft, moist mix is extruded through a die in the form of a long clay column which is then cut into brick-sized pieces by wires in a frame (see Figure 4.3). Extruded bricks have a much higher average compressive strength because the proportions between the raw materials are more accurate.

Brick classificationBricks are graded A, B or C, according to their compressive strength (with grade A being the strongest) and are classified according to type as shown below:

Clinkers overburnt and very hard but often distorted in shape; usually unsuitable for regular brickwork; often used for feature walling.

Callows underburnt, light in colour, soft, very absorbent; inferior for most structural purposes.

Commons general purpose bricks; hard in texture but often with flaws developed during manufacture.

Select commons best quality commons, with sharp arises and fairly uniform colour; suitable as a substitute for face bricks.

Face bricks good quality bricks, with smooth or texture faces in a variety of styles and colours.

Sandstock imitation (mechanically-made) or hand-made bricks.

Brickettes small-face bricks, with plain and textured faces; often used for fireplace facings and ornamental feature work.

Firebricks dry-pressed, usually cream in colour, available in a wide range of sizes and shapes; used in furnaces, stoves, fireplaces and areas of intense heat.

Brick classification

The different types of brick can best be illustrated by looking at appropriate product literature.

With modern methods of applying a surface coating to a compatible colour base, bricks are now available in many colour shades, from black, through reds and yellow to white.

There are also purpose-made bricks which are made in special shapes (eg bullnose or squint).

Brick quality and standards

The quality of good bricks is determined by their texture and hardness and their size and shape.

They should have an even, granular texture, be well-fired and free from flaws (eg face blisters or shrinkage cracks). Two bricks, when struck together, should give a clear ringing sound.

They should also have regular shaped faces and sharp arises (see Figures 4.2 and 4.3) and fall within a standard size range.

Brick sizes:

Metric modular brick 290 (90 ( 90 mm

Metric standard brick230 (110 (76 mm

The long face (called the stretcher) of a standard metric brick measures 230 (76 mm, and the short face (called the header) measures 100 (76 mm.

A closer (quarter brick) measures 50 (76 (110 mm (standard metric) and a queen closer (a standard metric brick split lengthways showing a closer face at each end) measures 50 (76 (230 mm (see Figure 4.4).

Laying bricks

Bonding is the way the bricks forming a structure are held together. Good bonding depends on the chemical bond between the bricks and mortar and on the mechanical bond resulting from how the bricks are laid.

The depth of mortar between bricks is usually 10 mm, providing a horizontal joint (called a bed joint) and a vertical joint (called a perpend).

Jointing is the term usually given to the surface finish of the mortar set between bricks. Such finishes vary according to trends. Tuck pointing used to be common about the turn of the century but has since faded from popularity. The most common forms of jointing in use at present are:

• ironed

• flush jointing

• raked jointing (see Figure 4.7).

Many different methods of laying bricks are used, some more effective than others. Bonding is provided by the way the bricks overlap each other and interlock, and it should:

distribute the load evenly throughout the mass of brickwork tie the mass of brickwork together as an integrated unit

provide a pleasing arrangement of bricks and joints.

Two types of bonding are illustrated in Figures 4.8 and 4.9. The stack bond (see Figure 4.8), for example, provides little mechanical bond between the bricks (because it creates a vertical downward thrust), whereas with stretcher bond (see Figure 4.9) the load is more evenly distributed throughout the brickwork.

Figure 4.8: Stack bond

Figure 4.9: Stretcher bond

Accessories for brickwork

There are a number of different accessories which are used with brickwork:

• wall ties

• damp proofing

• anti-termite caps

• ventilators

• lintels

• piers.

Let’s look at how they are used.

Wall ties Wall ties tie the two walls of a double brick wall together, so that they do not move apart from each other.

The most common type is 4 mm or 3.15 gauge galvanised wire bent to shape, with a kink (or drip) which should be positioned pointing down in the cavity between the two walls to prevent moisture passing along the inside wall (see Figure 4.11).

Wall ties should be spaced no more than 1 m apart and staggered every fourth course in height, with a minimum number of four ties per square metre. The ties should be at least 6 mm higher on the inner walls than on the outer walls. If the cavity width is greater than 75 mm, special length ties are used.

Figure 4.11: A wall ties

Damp-proof courses

Damp-proof courses are provided:

• horizontally in walls and on piers to prevent upward seepage of water from the ground or through concrete in contact with the ground

• vertically as vapour barriers to prevent penetration of moisture through a wall

• through walls and across cavities as flashing to control moisture from a roof or parapet or around windows, door heads and sills.

Anti-termite caps

Anti-termite caps made of galvanised iron are used on all piers under floor timbers.

Ventilators

Ventilators made of terracotta or concrete with wire mesh are set into brickwork to provide under-floor ventilation as close as possible to the underside of the floor, or ventilation into the cavity of double brick walls.

Reinforcement

Reinforcement should be placed in footings and walls where tension stress is likely to occur, because brickwork is weak in tensile strength. The types of reinforcement available are:

wire mesh welded wire fabric mesh expanded metal steel rods, generally used for vertical reinforcement

Figure 4.12: Reinforcement types

Lintels are steel bars, steel angles and so on, used over doors, windows, fireplaces or other openings to support the brickwork above (see Figure 4.13).

Lintels

Piers

Piers are brick columns which provide above-ground support for other structural members, usually floors. They are of two types, attached and isolated.

An attached (or engaged) pier is built attached or bonded to a wall. It may be used to stiffen or supply lateral support to the wall and carry a superimposed load by providing an additional bearing area.

An isolated (or sleeper) pier is free-standing and usually carries some structural load but it may also be purely decorative (ie non–load-bearing). In order to maintain stability, attention must be paid to the relationship between the height of the pier and the size of the base dimension. Tables can be obtained to provide guidance in this respect.

Figure 4.14: An isolated (sleeper) pier

Unfired clay or soil construction

Carry out the check progress 2 in your guide

Clay in mud and soil has a very long history as a building material. Wet or moist soil or clay is put into forms or moulds and allowed to sun-dry (cure). Mud brick (adobe), rammed earth (pisé), pressed blocks, wattle and daub, and cob are the five most common methods used.

Mud brick (adobe)

Mud brick walls are probably one of the oldest and most popular forms of earth housing. Wet mud is placed in boxes (forms) which are removed shortly after, and the blocks are allowed to cure for about a month before being used. The blocks are bonded with a mortar of the same mud that was used for making the blocks.

Rammed earth (pisé)

Moist soil is rammed into position between heavy wooden forms. The forms are moved along or up as work progresses. The ramming may be done by hand or with pneumatic tampers.

Machine-made (pressed earth) blocks

The method involves the use of a hand-operated machine to press the soil into bricks or blocks which are then allowed to sun-cure before being laid in courses like any other brick or block.

Wattle and daub

With this method, a wall of reeds or branches is woven over a timber frame and mud is plastered on the inside and outside of the weave. Although very cheap and fast to build, the mud often cracks and needs constant maintenance. White ants easily destroy the timber frame, and the buildings are not usually very durable.

Materials added to stabilised earth

Cement is often used in adobe, pisé, pressed block construction and in soil floors to improve inferior soils. The soil needs to be pulverised first. The cement (5–12% by weight) and water are then added and amounts made must be in smaller batches than for straight mud, since the concrete ‘goes off’.

Bitumen added to soil acts both as a binding and waterproofing agent.

Non-clay bricks and blocks

Concrete bricks and blocks

These are manufactured from graded sand, aggregate, Portland cement and water; fly ash is often used as a cementing agent. They are made in a variety of solid and hollow shapes but in standardised metric sizes, so that a block or half block, with the addition of 10 mm of mortar, measures whole units of 100 mm or 50 mm.

Brick type Length Height Width

Standard blocks 390 190 290, 190, 140, 90

Half-high blocks 390 90 190, 140, 90

Metric modular bricks 290 90 90

Standard bricks (same size as standard clay bricks)

230 76 110

Table 4.6: Concrete block and brick sizes

Concrete bricks, blocks and paving are very versatile with the advantage that they are not usually difficult for unskilled workers to use. They come in a variety of textures and colours.

Blocks are usually used hollow and unreinforced. They can easily be reinforced, if required, by using steel reinforcement and filling the central core with concrete.

Concrete blocks shrink and swell with temperature and humidity variations and this has to be allowed for, particularly in external work.

Paving blocks are available in new interlocking systems that make very hard-wearing, attractive roads or footways and which give good access to buried service piping.

Concrete roofing tiles are also available in a range of colours and shapes and are widely used.

Calcium silicate bricks

Calcium silicate or sand-lime bricks are also used, though not yet in the same quantities as clay bricks.

They are usually whitish or grey in colour, but their physical characteristics are different.

The main rock groups

Rocks, referred to in building as ‘stones’, can be divided into three groups, according to how they are formed in nature:

igneous rocks sedimentary rocks metamorphic rocks.

Igneous rocksIgneous rocks are all formed from molten rock which has cooled and hardened. For example, rocks such as basalts, volcanic glass and pumice (cooled glassy froth) are formed from volcanic lava. Rocks such as granite are formed from molten rock that has cooled and hardened underground.

Types of igneous rocks

Granite

Granites and granite-like rocks are hard rocks and are made up of a mosaic of fairly large crystals of various minerals easily visible to the naked eye.

Granites are usually light grey or pink in colour but can vary through to quite deep reds. The trade term ‘granite’ is also used to cover a number of darker rocks including gabbro, a black rock known as ‘black granite’.

Examples

• Moruya granite—pale grey (used for the Sydney Harbour Bridge pylons).

• Mudgee granite—deep reds.

• Bathurst granite—reds and pinks, various types from the area around Bathurst.

• Riverina grey—from the Tocumwal area; and pinks from Berrigan.

Trachyte

Trachyte has smaller grains than granite.

Examples:

Bowral trachyte—dark olive green or dark grey, occasionally streaked with beautiful veins of glassy crystals and quarried at ‘The Gib’. Bowral trachyte has been used on a number of Sydney buildings and for the piers of the old Hawkesbury bridge.

Canoblas trachyte—a very hard and durable stone, it polishes to a soft grey or buff base colour with small pink and black spots and is from Orange (held in great repute by local builders, it makes a good flagging stone and was used as such on the front of most of the older important buildings in Orange).

Basalt

Very dark to black, fine-grained igneous rock. Basalts are often called ‘bluestone’ or ‘blue metal’. They have been quarried from Orange, Kiama, Dundas, Stirling (near Inverell) and Uralla and used extensively in Melbourne (eg St Patrick’s Cathedral) and other parts of Victoria.

Dolerite

This is similar to basalt but coarser grained. It is used extensively as road metal, gravel and aggregate in concrete.

Sedimentary rocks

Sedimentary rocks are most often made up of bits of other rocks, usually as a result of erosion. For example, layers of mud and sand (the result of other rocks being worn down) become buried deep in the earth and are compressed and hardened to form shale and sandstone.

SandstoneFormed in nature by sand grains which are cemented together, sandstone is a popular building stone when available, as it is fairly easily worked, very attractive in appearance and not very heavy. Many sandstones, however, are too soft and crumbly to be useful.

Sandstones are porous, allowing dampness to soak through: so, when used as footings, they must have good damp-proof course. Inadequate or non-existent damp-proofing has resulted in rising damp problems in many old buildings with sandstone footings.

The predominant building stones used around Sydney have been the Sydney and Gosford sandstones. As these two stones are basically identical, descriptions of Sydney sandstone apply equally to Gosford sandstone.

Sydney sandstone is one of the finest building sandstones in Australia. Its colour is usually a pale yellowish or buff colour to pinkish or brownish tones, with colour variations within it. It is easily seen in many road cuttings around the Sydney area, such as the expressways north of Sydney, in the Blue Mountains, and approaches to the Harbour and Gladesville bridges.

Other areas in NSW where sandstone has been quarried include Marulan (used for St Saviour’s Anglican cathedral, Goulburn); Bundanoon, one of the best sandstones in NSW for large buildings, its colour varies from white to pink (used for the base of the soldier’s memorial and town hall in Goulburn and St Michael’s cathedral, Wagga Wagga); Yass; Canberra; Frogshole; Galong; Grong Grong; Milparinka; Mendooran; Newcastle (identical to Sydney sandstone); and Ravensfield.

Limestone

Limestones are sedimentary rocks formed from coral, sea shells and deposits of calcite (the mineral of which shells and coral are made).

Limestone as a building stone is worked and sold under the general name ‘marble’. However, limestone is also mined extensively for manufacturing lime and cement.

Metamorphic rocks

Metamorphic rocks are formed as a result of changes which have been usually brought about by heat and/or pressure in the earth’s crust. For example, when shale (a sedimentary rock) is compressed it becomes a metamorphic rock, slate; sandstone, when heated up, perhaps by volcanic lava, turns into quartzite; and limestone becomes marble under pressure.

SlateSlate is formed by immense pressure in the earth’s crust compressing and altering clay rocks such as shale. Slate splits easily in layers in one direction, like pages of a book. Some coloured shales are marketed for paving as ‘slate’, but a true slate is usually grey, greenish grey, bluish or purplish in colour.

Slate is fairly soft and easily scratched, but has a very pleasing appearance when well laid and cared for. Its softness is obvious when we see how the centre of the tread in the grey slate steps in old buildings are often worn away with use.

The high labour cost of cutting and laying slate roofs led to a decline, but its recent popularity for floors, wall facings and fireplace surrounds has renewed interest in it as a marketable product.

In the early days of the colony of NSW, slate was brought out from Britain as ship’s ballast. It was then used to roof many early Sydney buildings (some fine old slate roofs are still to be seen around NSW). Gradually Australian deposits were found and worked—at Chatsbury, Gundagai, Towrang, Black Mountain, Bathurst and Mudgee.

Marble

Limestone, acted on by heat and pressure in the earth’s crust, changes its structure and pattern of colour and becomes marble. Marble and limestone are both quarried for building stone as ‘marble’, so we will look at them together. Their colours vary from almost pure white through nearly every possible shade of greys, greens, yellows, reds and blues to black. They are used for making cement, for ornamental and monumental stones, statues and building stones.

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Stone classified for building purposes

In the building industry, special terms are used to describe different types of stone. These terms might indicate the quarry location, the colour, texture, pattern or use of the stone.

Trade terns

Some terms, such as the following, have a different meaning in the building industry to their geological meaning.

Granite any medium- or coarse-grained igneous rock used as dimension stone.

Sandstone sedimentary rock made of sand-size grains; sandstones with thin, even, regular bedding along which the rock is easily split are termed ‘natural flagstones’; in NSW sandstone which splits with equal ease in any direction is called ‘freestone’.

Marbleany limestone or marble which is able to take a polish and is used decoratively; also includes the metamorphic rock serpentine, termed ‘serpentine marble’.

Dimension stone

This term refers to natural rock used as ‘building stone’, ‘ornamental stone’ and ‘monumental stone’. It is generally quarried in blocks or slabs and marketed in a variety of sizes and finishes according to customers’ needs. The main varieties of dimension stone quarried and used in NSW are granite, marble, sandstone and slate.

Although most varieties of dimension stone are widespread in NSW, economically viable deposits are not common. Suitable sandstone deposits are available fairly close to Sydney, but the other stones are located in isolated areas a long way from major markets. These localities include: Wombeyan (marble); Yass (limestone); Mudgee (granite); Eugowra (granite); Bowral (trachyte); Bundanoon (sandstone); Tumut (marble); Mulyandry (granite); Middle Arm (slate).

Requirements of dimension stone

These may vary from one project to another but, in general, are as follows:

• It must be able to be extracted in large blocks free from joints and imperfections.

• It must be sound and durable.

• It should be uniform in colour and texture.

• It must have aesthetic appeal (difficult to describe, but such things as colour, pattern, texture and finish are important).

• Stones used for certain purposes must be capable of taking and keeping a polish. Only ‘granites’ and ‘serpentine marble’ keep a polish when exposed to weather.

• It must be available in quantity so that sufficient reserves exist of fairly uniform stone to meet large orders and future demands for maintenance or restoration work.

Economic outlook

Dimension stone is a moderate to high-cost material. It is often passed over for cheaper load-bearing materials such as steel and reinforced concrete.

Other dimension stones likely to be in demand include good quality purple and green slate for decorative purposes and good quality white marble, black marble, gabbro and granite.

Construction materials

Construction materials are low-cost minerals and rocks that are extracted in bulk. They require little processing and are used for construction purposes. Such materials include the following:

Coarse aggregate: Crushed and broken stone, prepared road base and gravel. Usually igneous rocks are used in NSW, though sedimentary sandstones have also been used successfully. The most important deposits are those situated near the larger cities. Much of the coarse aggregate is used in concrete.

Fine aggregate: Construction sand, which is usually dug from rivers, beaches or dunes and must be clean, with no soil or salt. It is used mostly for concrete, mortar, sand-lime bricks and fillers.

Unprocessed materials: These include weathered rock, gravel, soil and loam. They are used mainly for road-making and site-filling.

General properties of stone

Most natural stones are very good load-bearers and make good footings, walls and pylons.

The amount of thermal expansion is very low for marble and slightly greater for sandstone, slate and granite. However, allowance should be made for thermal movement.

Some stones, especially igneous rocks (such as granites, trachyte and basalt), are not all porous and therefore do not allow moisture penetration. Others, like sandstone, can be very porous.

Most natural stones are very durable—a property which can, however, be adversely affected by certain environmental factors.

Factors causing deterioration in stone

Atmospheric pollution

Sulphur chemicals in the air or soil dissolve in rainwater and form weak sulphuric acid which will slowly dissolve marble, limestone, calcareous sandstones and mortars.

Salt

Salts dissolved in water seep into rocks and dry out, forming crystals. These growing crystals cause pressure in porous rock or in mortar and, as they expand, can cause progressive decay.

Frost

Porous rocks in which water freezes will crack and disintegrate, often very quickly. However, frost action is not a problem in most parts of NSW

Factors causing deterioration in stoneSolubilityLimestone, marble and calcareous sandstone will slowly dissolve in water.

Wetting and dryingRepeated wetting and drying of porous rocks can cause slow surface crumbling and should be guarded against. (This also weakens mortars.)

Corrosion of metalsAs iron and steel rust, they swell. Where iron or steel rods, bolts or bars are fitted into or between pieces of masonry and allowed to rust, serious damage is caused in stone structures.Some metals also form salts as they corrode which can be destructive to surrounding stonework.

VegetationMost plants, including lichens and mosses, do little damage to stonework, but they do hold moisture, which may be a problem with mortars and porous rocks. Ivy, however, because of the way its roots penetrate cracks and cavities, can cause serious damage.

Finishes and maintenance of stonework

Surface finishesFigure 4.15 gives some idea of the range of tooling that can be done on stone with, usually, a mallet and various chisels. Today, with mechanisation, sawn and polished faces are used fairly frequently, especially with monumental work.

Rubble walling

Walls may be built either as:

• random rubble (uncoursed)• random rubble (coursed)• square rubble (uncoursed)• square rubble (built in courses).

Ashlar walling

Walls may be built either as:

• random ashlar

• ashlar (regular coursed)

• ashlar (irregular coursed).

Maintenance

Outside stonework should be cleaned regularly and defective joints raked out and refilled (reappointed) with a sand-lime mortar, not a cement mortar mix.

Methods of cleaning various stones are outlined in Table 4.7. Note that caustic soda and soda ash are very damaging and must never be used on any stone.

Stone Method Comments

All types Hydrofluoric acid (5% concentration)Sandblasting, dryMechanical abrasive tools

Risks damage to adjacent materials. Fast method, no staining, very dusty. Sand-blasting and abrasive tools produce a lot of dust

Limestone and marble

Clean water spray, mild detergent, dry and polish with soft cloth

Slow, not suitable for heavy encrustations

Granites Ammonium bifluoride Risks damage to adjacent materials

Preservation

Most stone is fairly durable, so fast decay usually occurs from wrong choice of stone, defects in design, or neglect. These errors should be corrected before attempting to ‘preserve’ the stone. For example, salts should not be sealed in, but should be removed by repeated sponging with water. Get qualified advice before using surface sealers as they can sometimes do more harm than good if not appropriate to the problem.

Alternative materials

Dimension stone faces considerable competition from cheaper materials, in particular exposed aggregate panels and other concrete-based products. Steel and concrete have virtually replaced dimension stone as a major load-bearing construction material.

Artificial stoneEconomic reasons, together with the greater range of architectural finishes available, have brought about a greater use of synthetic and artificial stones, such as the following.

Alternative materials

Cast synthetic stone Pure polyester resin or a mixture of polyester resin and acrylic is moulded into stone-like material which can be cast in single pieces. In situations where the use of stone would require a number of separate stone sections to be jointed together (eg in panels or columns) this method offers distinct advantages. It is also not as hard or as cold as stone and can be worked with wood tools. It can be produced in a variety of shapes and sizes and is usually used to imitate marble.

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Summary

In this unit you have learned about the uses of clay products, the role of brickwork in building, the range of brick types, bonding and tinting of bricks and about stone and its applications and limitations as a building material.

You will have come across many terms used to describe the processes and products linked with clay and stone. You may need to read back over this unit to refresh your memory of some of these. Carefully revise the meaning of those that you are unclear about.

You should be able to define all the materials we have looked at, know their qualities and how they are used.

In the next unit you will learn about the role of mortar in the building industry.

session 1 range of building materials properties of concrete clay and none clay building products

Documents

selection of materials

cent materials

cheap materials

durable materials

raw materials

choice of materials

building products

behavior of materials