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FACULTY OF EN GI N EERI N G UN I VERSI TY OF TECHNOLOGY, SYDNEY

48352: Construction Materials

LECTURE NOTES Module No. 2: Concrete Making Materials

P REPARED

BY

D R R S RI R AVINDRARAJAH F ACULTY U NIVERSITY

OF

OF

E NGINEERING ,

T ECHNOLOGY , S YDNEY

Page 2

TABLE OF CONTENTS 5.

6.

7.

8.

9.

Concrete as a Construction Material

3

Tutorial No. 5: Mix Compositions

14

Cement and other Binder Materials

15

Tutorial No. 6: Binder Materials

29

Aggregates for Concrete Mixes

30

Tutorial No. 7: Aggregates for Concrete Mixes

38

Water and its Significance in Concrete

39

Tutorial No. 8: Water

43

Admixtures for Concrete

44

Tutorial No. 9: Admixtures for concrete

48

Additional Notes, please refer to UTSonline for extra handouts.

OTHER MODULES FOR THIS SUBJECT Module No. 1: Materials and Metals Module No. 3: Concrete Production and Properties Module No. 4: Other Construction Materials Module No. 5: Construction Materials Testing

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CHAPTER 5: CONCRETE AS A CONSTRUCTION MATERIAL 1. Introduction Portland cement concrete is foremost among the construction materials used in civil engineering projects in Australia and overseas. The reasons for concrete's pre-eminence are varied, but among the more important are: • the economic and widespread availability of its constituents; • its versatility and adaptability, as evidenced by many types of construction in which it is used; and • the minimal maintenance requirements during service. As in the case with any other materials, it’s successful use depends upon an intelligent application of its properties in design, and the supply of a uniform, high quality product. Concrete is unique among major construction materials in that it is generally designed specifically for a particular project using locally available materials. Therefore, the project engineer has full control and responsibility over the final material used in construction. If concrete is not properly designed for the service conditions and is not properly handled and cured, it would result in sub-standard performance. It is thus essential that civil engineers acquire a thorough understanding of the properties of concrete and the procedures that are essential to providing concrete of the required quality and performance Concrete is a hardened product created by mixing a chemically inert, granular material, known as aggregate, with a matrix composed of a cement. When water is added, chemical reactions between the cement and water cause the cement paste, in which the aggregate is embedded, to set and harden with elapsed time, producing the familiar material known as concrete. The structural concrete, used for civil engineering construction contains expensive Portland cement as the binder material. The aggregates as the cheap filler materials are gravel or crushed stone and sand. In addition to the cement, supplementary cementing materials (SCM) are used in concrete mixes for economical and technical reasons. These materials are the by-products of other industries. The most commonly used such materials are fly ash (a residue of burnt coal in power station), ground granulated blast-furnace slag (a by-product of iron production), and silica fume (a by-product from ferro-silicon industry). Other examples for SCM are rice-husk ash and natural pozzolan (volcanic ash). Concrete is the most versatile construction material. There can be virtually no significant structure being built anywhere in the world that is not using concrete in one way or another. The use of concrete is immediately apparent in buildings, bridges, roads, runways, silos, waterretaining structures, and dams. Other uses may be less obvious. Steel framed structures stand on sound concrete foundations and frequently protected against fire by concrete. Clay bricks are bound together by cement-based mortar to build walls that may be rendered. Even timber buildings usually stand on concrete footings. So even buildings, that are not considered to be concrete, rely heavily upon the versatility of concrete for their very existence.

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2. Historical background Concrete has been used as a construction material for centuries because most of those parts of the world where early civilizations were established had natural cement deposits. In Mediterranean countries, there are many remains of Roman concrete construction. Concrete has been used by the Egyptians some 2,000 BC. The use of lime-based mortars for the floors of huts has been found in excavations dated as long ago as 5600 BC. The Egyptians used lime mortars and gypsum mortars in the building the Pyramids of Cheops and other structures, while Greeks seem to have used predominantly lime mortars. Probably the most substantial existing concrete building from antiquity is the Pantheon in Rome (27 BC). This has 50 m diameter unsupported roof that is comprised lightweight concrete segments. Volcanic pumice was used as aggregate and this is bound in a lime and pozzolana matrix. The whole roof was designed to be in compression, so that there is no need for tensile reinforcement. The survival of this roof for over 2,000 years clearly shows that concrete can be very durable. In 1759, John Smeaton built a new lighthouse on the Eddystone rock off Plymouth on a concrete foundation. This lighthouse stood for 126 years before it was replaced. Smeaton recognized that the ordinary lime mortar would not harden under water and would not be sufficiently durable to resist the wear from the waves of the sea. He found that the best mortar came from the limestone, which contained the greatest percentage of clay. On December 15, 1824, Joseph Aspdin (1779 to 1855), a brick-layer in England took out a patent for the manufacture of a new and improved cement which he called Portland cement because it resembled in colour the stone which came from the Isle of Portland. Portland cement was of more uniform quality than the natural cement and made more strong and durable concrete than lime.

3. Versatility of Concrete There are two specific characteristics that make concrete so generally useful. Firstly, concrete could be moulded into different shapes and sizes either on site or in precast concrete works at ambient temperatures above freezing. So long as concrete remains wet, it will harden and gain strength progressively. The second dominant virtue is the protection concrete can give to steel to inhibit rusting. All other benefits attribute to concrete are secondary to these with the possible exception of cost. The full versatility of concrete is much greater in that by selection of the constituents of concrete, the compressive strength may lie within the range of 5 MPa to well over 100 MPa and densities from a 500 to well over 3,000 kg/m3. The lowest density concretes are ideal for insulation purposes, whilst the heaviest can provide shielding against nuclear radiation. The density of normal weight concrete is about 2400 kg/m3 and the compressive strength of structural concrete varies from 20 to 100 MPa. Concrete is weak in tension and its tensile strength is about 10% of its compressive strength. Concrete is normally reinforced with high tensile steel bars to produce useful reinforced concrete structures. Very high-tensile steel tendons are used to produce pre-stressed concrete structures.

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It is also possible to use different types of fibers to raise the tensile strength of concrete by controlling the crack initiation and growth and to change the brittle nature of concrete to ductile. Asbestos, glass, steel and polypropylene fibres are some examples of fibres used in producing fibre-reinforced concrete. Each type of fibre contributes particular characteristics thereby adding to the total versatility of concrete and providing opportunities for new uses of concrete products in construction. Another way to expand the potential range of properties of concrete to satisfy the needs of the user is by the inclusion of polymer-based admixtures into concrete mixes to produce polymer concrete. Water-based emulsions of rubber latex or polymers or co-polymers like methyl methacrylate or styrene butadiene have been used. They often increase the failure strain of concrete and provide greater resistance to chemically aggressive environments. The development of chemical admixtures to modify the properties of concrete to enable them to be used in even wider ways has been very rapid. In particular, the fresh concrete properties such as flow and setting could be significantly modified. Concretes (self-compacting concrete) could be made to flow freely with only a minimum vibration to fill the formwork to a level surface. Moreover, such free flowing concrete can be achieved with low water to cement ratios and with minimum segregation and bleeding. Other chemical admixtures allow concretes to be pumped over long distances for placement at considerable heights in a structure or well away from the delivery point on site. Concrete could be made with proper selection of constituent materials and mix compositions to resist varying exposure conditions. Concrete structures showed successful performance in marine environment, underground environment, sewer environment, against radiation, under very low (cryogenic) temperatures to store liquefied gases, in very high furnace temperature conditions and in severe chemical environment. Home task: No. 1: Do Google search with the following key words: Fibre-reinforced concrete; Polymer concrete and Self-compacting concrete. Write short notes (300 words) on these types of concretes) Table 5.1: Advantages and Disadvantages of using Concrete A dvantages

D isadvantages

Ability to cast

Low tensile strength

Economical

Low ductility

Durable

Volume instability

Fire resistant

Low strength-to-weight ratio

Energy efficient On-site fabrication Aesthetic properties

4. Advantages an Limitations of Concrete As a construction material, concrete is exceeded in the use only by timber. However, a large amount of timber is used for construction of formwork and false work during the fabrication of concrete structures. The major advantages and disadvantages of concrete are summarized in Table 5.1. The ability of concrete to be cast to any desired shape and configuration is an 48352/Construction Materials/Dr. Ravi/UTS/Lecture Notes

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important characteristic that can offset other shortcomings. Concrete could be cast into arches and columns, complex hyperbolic shells, or into massive, monolithic sections used in dams, piers, and abutments. On-site construction means that local materials could be used to a large extent, thereby keeping the cost down. Concrete is brittle with very low tensile strength (2 to 5 MPa). Thus, in general concrete should not to be loaded in tension. Reinforcing steel could be used to carry tensile loads. Inadvertent tensile loading causes cracking in concrete structures. The low ductility of concrete also means that concrete lacks impact strength and toughness compared to metals. Even under compression, concrete has a relatively low strength-to-weight ratio (Chapter 1), and a high load carrying capacity requires comparatively large masses of concrete. Since the concrete is a low cost material, this is economically possible. Concrete undergoes considerable irreversible shrinkage due to moisture loss at ambient temperatures, and also creeps significantly under sustained load even under normal service conditions.

5. Competitiveness of concrete Cement competes with other materials such as masonry, steel, glass and timber in a variety of applications. Concrete had been successful in gaining new markets by displacing traditional materials. Australian examples include concrete replacing wooden railway sleepers, wooden light poles and asphalt roads. These developments can be attributed to the greater savings obtained from concrete construction. Concrete has become cost competitive in many new areas. This because of the following reasons: (a) It could utilize cost efficient construction techniques; (b) it has lower maintenance costs; and (c) alternative materials have increased in relative price. The competitiveness of concrete is also enhanced by the wide range of applications, such as for the construction of: dams, underground structures, tunnels, bomb shelters, water-retaining structures, runways, floating structures, sporting facilities, roads, buildings and bridges. Table 5.2: Strength based classification for concrete Classification

6.

Concrete strength (MPa)

Low strength concrete

below 20

Medium strength concrete High strength concrete

20 to 40 40 to 100

Ultra high strength concrete

above 100

Concrete as an environmentally friendly materials

Concrete is in tune with the environment. From homes to office buildings to highways, using concrete as a construction material actually helps protect our natural resources and affords unique benefits to consumers. From an environmental standpoint, concrete has a lot to offer. Concrete is environmentally friendly in a variety of ways. The ingredients of concrete (water, aggregate, and cement) are abundant in supply and take a lesser toll in their extraction than other construction materials. Quarries, the primary source of raw materials, can be easily reclaimed for recreational, residential, or commercial use. Or they can be restored to their natural state.

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As a nearly inert material, concrete is an ideal medium for recycling waste or industrial byproducts. Many materials that would end up in landfills can be used instead to make concrete. Blast furnace slag, recycled polystyrene, and fly ash are among materials that can be included in the recipe for concrete and further enhance its appeal. Waste products such as scrap tires and kiln dust are used to fuel the manufacture of cement. And even old concrete itself can be reborn as aggregate for new concrete mixtures. Another environmental plus for concrete is energy efficiency. From manufacture to transport to construction, concrete is modest in its energy needs and generous in its payback. The only energy intensive demand is in the manufacture of portland cement, typically a 10-15% component of concrete. Since the materials for concrete are so readily available, concrete products and ready-mixed concrete can be made from local resources and processed near a jobsite. Local shipping minimizes fuel requirements for handling and transportation. Once in place, concrete offers significant energy savings over the lifetime of a building or pavement. In homes and buildings concrete’s thermal mass, bolstered by insulating materials, affords high R-factors and moderates temperature swings by storing and releasing energy needed for heating and cooling. Rigid concrete pavement design means heavy trucks consume less fuel. And the light reflective nature of concrete makes it less costly to illuminate. Further commendable characteristics of concrete are waste minimization and long life. Whether cast-in-place or precast, concrete is used on an as-needed basis. Leftovers are easily reused or recycled. And concrete is a durable material that actually gains strength over time, conserving resources by reducing maintenance and the need for reconstruction. A reliable and versatile product for centuries, concrete paves the way toward an environmentally secure future for successive generations here on Earth. Home task No. 2: Visit the following web-sites: Environmentally friendly building materials: http://www.miconcrete.org/page.cfm/125 http://www.cement.ca/cement.nsf/0/C911DD7AE73D49D285256BE20048F41A?OpenDocument

6. Classification of concrete Concretes used for structural applications, are identified either by the nature of the aggregate or the cement, or by specific attributes or treatment. 6.1

Based on strength

The strength of concrete is normally expressed in terms of its compressive strength at 28 days. It is determined by testing standard cylinders, having height to diameter ratio of 2, (100 mm diameter by 200 mm high or 150 mm diameter by 300 mm high) as in Australia, New Zealand, India, Germany, and USA or testing standard cubes (100 mm or 150 mm) as in UK and some commonwealth countries. It is necessary to conduct the strength tests according to the accepted standards to obtain any meaningful results. Concrete is classified on the strength basis into several categories (low, medium, high and ultrahigh) as given in Table 5.2. In high rise buildings, the use of high-strength concrete for columns

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and core walls provide several advantages, such as improvement in stiffness, reduction in axial shortening of compression elements, early stripping of formwork and reduction in member size. In Australia, the first substantial use of high-strength concrete was made in 1970 for the construction of the University of Technology, Sydney which included 375m3 of concrete of 55MPa in major columns. The strongest commercially supplied high-strength concretes in Australia had been 100 MPa at 90 days for bankers' safe construction and 90 MPa at 56 days for a high-rise building in Melbourne. 6.2

Based on density

6.2.1

Lightweight concrete

Lightweight aggregate concrete having a weight substantially less than that of the ordinary concrete could be produced using lightweight aggregates. Natural materials such as pumice and heat-treated materials such as foamed blast-furnace slag, expanded clay or shale, sintered fly ash could be used as lightweight aggregates. Such aggregates produce concretes having the density between 320 and 1900 kg/m3. However, the reduction in density is generally reduces its strength. Such concretes have special properties - such as high thermal insulation - which is advantageous in the construction of walls and other building components. Modern techniques, however, make it possible to produce lightweight concretes having comparable strength to that of normal weight concrete. An obvious advantage of the lightweight is the reduced dead weight of the structure with consequent savings in cost, especially in regard to the foundation. Expanded polystyrene beads or granulates could be used to produce lightweight structural concrete, having a range of density. Home task No. 3: Study the technical paper from my homepage (http://www.eng.uts.edu.au/~ravir) under Publications on Lightweight Concrete by Sabaa, B. A., and Sri Ravindrarajah, R., Engineering properties of lightweight concrete contained crushed expanded polystyrene waste]

No-fines concrete, as the term implies, is concrete without having fine aggregate. This type of concrete consists of coarse aggregate, cement, water, and large void, which are uniformly distributed through the concrete. The main applications for no-fines concrete are in the construction of load-bearing walls for low and medium-rise housing. Other uses include the provision of drainage layers in civil engineering works and the paving of free-draining parking areas. Another form of lightweight concrete is cellular concrete, also known as aerated or gas concrete, in which metallic powder is mixed with sand, cement, and water. A chemical re...