cement & admixtures

Cement & AdmixturesA paper to refresh concrete knowledge

Contents

1 Concrete 11.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.1.1 Ancient Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.2 Modern additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Impact of modern concrete use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.1 Environmental and health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.2 Concrete recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Education and research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Composition of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.1 Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.2 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.3 Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.4 Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.4.5 Chemical admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.4.6 Mineral admixtures and blended cements . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.5 Concrete production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.5.1 Mixing concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5.2 Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5.3 Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.6 Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.7 Concrete degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.8 Microbial concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.9 Use of concrete in infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.9.1 Mass concrete structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.9.2 Prestressed concrete structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.9.3 Concrete textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.10 Building with concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10.1 Concrete Roads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10.2 Energy eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10.3 Pervious concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10.4 Nano concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10.5 Fire safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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1.10.6 Earthquake safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.10.7 Useful life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.11 World records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.12 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.13 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.13.1 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.13.2 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.14 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2 Cement 172.1 Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2 History of the origin of cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2.1 Cements before the 18th century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.2.2 Cements in the 18th, 19th, and 20th centuries . . . . . . . . . . . . . . . . . . . . . . . . 18

2.3 Modern cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.4 Types of modern cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.4.1 Portland cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.4.2 Energetically modied cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.4.3 Portland cement blends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.5 Curing (setting) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.6 Safety issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.7 Cement industry in the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.7.1 China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.7.2 Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.8 Environmental impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.8.1 CO2 emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.8.2 Heavy metal emissions in the air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.8.3 Heavy metals present in the clinker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.8.4 Use of alternative fuels and by-products materials . . . . . . . . . . . . . . . . . . . . . . 23

2.9 Green cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.10 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.12 Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.13 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3 Portland cement 273.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.2 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.2.1 Cement grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.3 Setting and hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.4 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.5 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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3.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.5.2 ASTM C150 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.5.3 EN 197 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.5.4 White Portland cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.6 Safety issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.7 Environmental eects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.8 Cement plants used for waste disposal or processing . . . . . . . . . . . . . . . . . . . . . . . . . 323.9 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.11 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4 Pozzolan 344.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.2 Pozzolanic materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.3 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.4 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5 Fly ash 375.1 Chemical composition and classication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.1.1 Class F y ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.1.2 Class C y ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.2 Disposal and market sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.3 Fly ash reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.3.1 Portland cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.3.2 Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.3.3 Soil stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.4 Flowable ll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.5 Asphalt concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.6 Geopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.7 Roller compacted concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.8 Bricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.9 Metal matrix composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.3.10 Waste treatment and stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.3.11 As a catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.4 Environmental problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.4.1 Present production rate of y ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.4.2 Groundwater contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.4.3 Spills of bulk storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.4.4 Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.5 Exposure concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.6 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

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5.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.8 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

6 Silica fume 456.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.2 Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.3 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

6.4.1 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.5 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.7 Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.8 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

7 Ground granulated blast-furnace slag 477.1 Production and composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477.3 How GGBS cement is used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.4 Architectural and engineering benets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

7.4.1 Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.4.2 Appearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.4.3 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.4.4 Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

7.5 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.6 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

8 Superplasticizer 508.1 Polycarboxylate ether superplasticizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

8.1.1 Chemical structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508.1.2 Working mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

8.2 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

9 Metakaolin 529.1 Kaolinite sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529.2 Forming metakaolin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529.3 High-reactivity metakaolin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529.4 Adsorption properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529.5 Concrete application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539.6 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539.7 Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

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9.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539.10 Text and image sources, contributors, and licenses . . . . . . . . . . . . . . . . . . . . . . . . . . 54

9.10.1 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549.10.2 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569.10.3 Content license . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Chapter 1

Concrete

This article is about the construction material. For otheruses, see Concrete (disambiguation).Not to be confused with cement.Concrete is a composite material composed mainly of

Outer view of the Roman Pantheon, still the largest unreinforcedsolid concrete dome.[1]

Inside the Pantheon dome, looking straight up. The concrete forthe coered dome was laid on moulds, probably mounted on tem-porary scaolding.

Opus caementicium exposed in a characteristic Roman arch. Incontrast to modern concrete structures, the concrete used in Ro-man buildings was usually covered with brick or stone.

water, aggregate, and cement. Often, additives and rein-forcements (such as rebar) are included in the mixture toachieve the desired physical properties of the nishedma-terial. When these ingredients are mixed together, theyform a uid mass that is easily molded into shape. Overtime, the cement forms a hard matrix which binds the restof the ingredients together into a durable stone-like ma-terial with many uses.[2]

Famous concrete structures include the Hoover Dam, thePanama Canal and the Roman Pantheon. The earliestlarge-scale users of concrete technology were the ancientRomans, and concrete was widely used in the RomanEmpire. The Colosseum in Rome was built largely of

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2 CHAPTER 1. CONCRETE

concrete, and the concrete dome of the Pantheon is theworlds largest unreinforced concrete dome.[3]

After the Roman Empire collapsed, use of concrete be-came rare until the technology was re-pioneered in themid-18th century. Today, concrete is the most widelyused man-made material (measured by tonnage).

1.1 HistoryThe word concrete comes from the Latin word "concre-tus" (meaning compact or condensed),[4] the perfect pas-sive participle of "concrescere", from "con-" (together)and "crescere" (to grow).Perhaps the earliest known occurrence of cement wastwelvemillion years ago. A deposit of cement was formedafter an occurrence of oil shale located adjacent to a bedof limestone burned due to natural causes. These ancientdeposits were investigated in the 1960s and 1970s.[5]

On a human time-scale, small usages of concrete go backfor thousands of years. The ancient Nabatea culture wasusing materials roughly analogous to concrete at leasteight thousand years ago, some structures of which sur-vive to this day.[6]

German archaeologist Heinrich Schliemann found con-crete oors, which were made of lime and pebbles, in theroyal palace of Tiryns, Greece, which dates roughly to1400-1200 BC.[7][8] Lime mortars were used in Greece,Crete, andCyprus in 800BC. TheAssyrian JerwanAque-duct (688 BC) made use of fully waterproof concrete.[9]Concrete was used for construction in many ancientstructures.[10]

The Romans used concrete extensively from 300 BC to476 AD, a span of more than seven hundred years.[5]During the Roman Empire, Roman concrete (or opuscaementicium) was made from quicklime, pozzolana andan aggregate of pumice. Its widespread use in manyRoman structures, a key event in the history of architec-ture termed the Roman Architectural Revolution, freedRoman construction from the restrictions of stone andbrick material and allowed for revolutionary new designsin terms of both structural complexity and dimension.[11]

Concrete, as the Romans knew it, was anew and revolutionary material. Laid in theshape of arches, vaults and domes, it quicklyhardened into a rigid mass, free from manyof the internal thrusts and strains that troubledthe builders of similar structures in stone orbrick.[12]

Modern tests show that opus caementicium had as muchcompressive strength as modern Portland-cement con-crete (ca. 200 kg/cm2).[13] However, due to the absenceof reinforcement, its tensile strength was far lower than

modern reinforced concrete, and its mode of applicationwas also dierent:[14]

Modern structural concrete diers fromRoman concrete in two important details.First, its mix consistency is uid and homo-geneous, allowing it to be poured into formsrather than requiring hand-layering togetherwith the placement of aggregate, which, in Ro-man practice, often consisted of rubble. Sec-ond, integral reinforcing steel gives modernconcrete assemblies great strength in tension,whereas Roman concrete could depend onlyupon the strength of the concrete bonding toresist tension.[15]

Eddystone Lighthouse

The widespread use of concrete in many Roman struc-tures ensured that many survive to the present day. TheBaths of Caracalla in Rome are just one example. ManyRoman aqueducts and bridges such as the magnicentPont du Gard have masonry cladding on a concrete core,as does the dome of the Pantheon.After the Roman Empire, the use of burned lime and poz-zolana was greatly reduced until the technique was all butforgotten between 500 AD and the 1300s. Between the1300s until the mid-1700s, the use of cement gradually

1.2. IMPACT OF MODERN CONCRETE USE 3

returned. The Canal du Midi was built using concrete in1670,[16] and there are concrete structures in Finland thatdate from the 16th century.Perhaps the greatest driver behind the modern usage ofconcrete was the third Eddystone Lighthouse in Devon,England. To create this structure, between 1756 and1793, British engineer John Smeaton pioneered the use ofhydraulic lime in concrete, using pebbles and powderedbrick as aggregate.[17]

A method for producing Portland cement was patentedby Joseph Aspdin on 1824.[18]

Reinforced concrete was invented in 1849 by JosephMonier.[19] In 1889 the rst concrete reinforced bridgewas built, and the rst large concrete dams were built in1936, Hoover Dam and Grand Coulee Dam.[20]

1.1.1 Ancient AdditivesConcrete like materials were used since 6500BC by theNabataea traders or Bedouins who occupied and con-trolled a series of oases and developed a small empirein the regions of southern Syria and northern Jordan.They discovered the advantages of hydraulic lime, withsome self-cementing properties by 700 BC. They builtkilns to supply mortar for the construction of rubble-wallhouses, concrete oors, and underground waterproof cis-terns. The cisterns were kept secret and were one of thereasons the Nabataea were able to thrive in the desert.[6]In both Roman and Egyptian times it was re-discoveredthat adding volcanic ash to the mix allowed it to set un-derwater. Similarly, the Romans knew that adding horsehair made concrete less liable to crack while it hardened,and adding blood made it more frost-resistant.[21]

1.1.2 Modern additivesIn modern times, researchers have experimented with theaddition of other materials to create concrete with im-proved properties, such as higher strength, electrical con-ductivity, or resistance to damages through spillage.[22]

1.2 Impact of modern concrete useConcrete is widely used for making architecturalstructures, foundations, brick/block walls, pavements,bridges/overpasses, highways, runways, parking struc-tures, dams, pools/reservoirs, pipes, footings for gates,fences and poles and even boats. Concrete is used in largequantities almost everywhere mankind has a need for in-frastructure.The amount of concrete used worldwide, ton for ton, istwice that of steel, wood, plastics, and aluminum com-bined. Concretes use in the modern world is exceededonly by that of naturally occurring water.[23]

Concrete mixing plant in Birmingham, Alabama in 1936

Concrete is also the basis of a large commercial indus-try. Globally, the ready-mix concrete industry, the largestsegment of the concrete market, is projected to exceed$100 billion in revenue by 2015.[24] In the United Statesalone, concrete production is a $30-billion-per-year in-dustry, considering only the value of the ready-mixedconcrete sold each year.[25] Given the size of the con-crete industry, and the fundamental way concrete is usedto shape the infrastructure of the modern world, it is dif-cult to overstate the role this material plays today.

1.2.1 Environmental and healthMain article: Environmental impact of concrete

The manufacture and use of concrete produce a widerange of environmental and social consequences. Someare harmful, some welcome, and some both, dependingon circumstances.A major component of concrete is cement, which simi-larly exerts environmental and social eects.[26]:142 Thecement industry is one of the three primary producersof carbon dioxide, a major greenhouse gas (the othertwo being the energy production and transportation in-dustries). As of 2001, the production of Portland cementcontributed 7% to global anthropogenic CO2 emissions,largely due to the sintering of limestone and clay at 1,500C (2,730 F).[27]

Concrete is used to create hard surfaces that contribute tosurface runo, which can cause heavy soil erosion, waterpollution, and ooding, but conversely can be used to di-


vert, dam, and control ooding.Concrete is a primary contributor to the urban heat islandeect, though less so than asphalt.Workers who cut, grind or polish concrete are at risk ofinhaling airborne silica, which can lead to silicosis.[28]Concrete dust released by building demolition and nat-ural disasters can be a major source of dangerous air pol-lution.The presence of some substances in concrete, includ-ing useful and unwanted additives, can cause health con-cerns due to toxicity and radioactivity. Wet concrete ishighly alkaline and must be handled with proper protec-tive equipment.

Recycled crushed concrete, to be reused as granular ll, is loadedinto a semi-dump truck.

1.2.2 Concrete recyclingMain article: Concrete recycling

Concrete recycling is an increasingly common method ofdisposing of concrete structures. Concrete debris wasonce routinely shipped to landlls for disposal, but recy-cling is increasing due to improved environmental aware-ness, governmental laws and economic benets.Concrete, which must be free of trash, wood, paper andother such materials, is collected from demolition sitesand put through a crushing machine, often along withasphalt, bricks and rocks.Reinforced concrete contains rebar and other metallic re-inforcements, which are removed with magnets and re-cycled elsewhere. The remaining aggregate chunks aresorted by size. Larger chunks may go through the crusheragain. Smaller pieces of concrete are used as gravel fornew construction projects. Aggregate base gravel is laiddown as the lowest layer in a road, with fresh concreteor asphalt placed over it. Crushed recycled concrete cansometimes be used as the dry aggregate for brand newconcrete if it is free of contaminants, though the use of re-

cycled concrete limits strength and is not allowed in manyjurisdictions. On 3 March 1983, a government-fundedresearch team (the VIRL research.codep) estimated thatalmost 17% ofworldwide landll was by-products of con-crete based waste.

1.3 Education and researchThe National BuildingMuseum inWashington, D.C. cre-ated an exhibition titled Liquid Stone: New Architecture inConcrete.[29] This exhibition, dedicated solely to the studyof concrete as a building material, was on view for thepublic from June 2004 - January 2006.

1.4 Composition of concreteThere are many types of concrete available, created byvarying the proportions of the main ingredients below.In this way or by substitution for the cementitious andaggregate phases, the nished product can be tailored toits application with varying strength, density, or chemicaland thermal resistance properties."Aggregate" consists of large chunks of material in a con-crete mix, generally a coarse gravel or crushed rocks suchas limestone, or granite, along with ner materials such assand."Cement", most commonly Portland cement is associatedwith the general term concrete. A range of materialscan be used as the cement in concrete. One of the mostfamiliar of these alternative cements is asphalt. Other ce-mentitious materials such as y ash and slag cement, aresometimes added to Portland cement and become a partof the binder for the aggregate.Water is then mixed with this dry composite, which pro-duces a semi-liquid that workers can shape (typically bypouring it into a form). The concrete solidies and hard-ens through a chemical process called hydration. The wa-ter reacts with the cement, which bonds the other com-ponents together, creating a robust stone-like material."Chemical admixtures" are added to achieve varied prop-erties. These ingredients may speed or slow down the rateat which the concrete hardens, and impart many otheruseful properties including increased tensile strength andwater resistance."Reinforcements" are often added to concrete. Concretecan be formulated with high compressive strength, but al-ways has lower tensile strength. For this reason it is usu-ally reinforced with materials that are strong in tension(often steel)."Mineral admixtures" are becoming more popular in re-cent decades. The use of recycled materials as con-crete ingredients has been gaining popularity because ofincreasingly stringent environmental legislation, and the

1.4. COMPOSITION OF CONCRETE 5

discovery that such materials often have complementaryand valuable properties. The most conspicuous of theseare y ash, a by-product of coal-red power plants, andsilica fume, a byproduct of industrial electric arc fur-naces. The use of these materials in concrete reduces theamount of resources required, as the ash and fume act asa cement replacement. This displaces some cement pro-duction, an energetically expensive and environmentallyproblematic process, while reducing the amount of indus-trial waste that must be disposed of.The mix design depends on the type of structure beingbuilt, how the concrete is mixed and delivered, and howit is placed to form the structure.

1.4.1 CementMain article: CementPortland cement is the most common type of cement

A few tons of bagged cement. This amount represents about twominutes of output from a 10,000 ton per day cement kiln.

in general usage. It is a basic ingredient of concrete,mortar and plaster. English masonry worker Joseph As-pdin patented Portland cement in 1824. It was named be-cause of the similarity of its color to Portland limestone,quarried from the English Isle of Portland and used ex-tensively in London architecture. It consists of a mixtureof oxides of calcium, silicon and aluminium. Portland ce-ment and similar materials are made by heating limestone(a source of calcium) with clay and grinding this product(called clinker) with a source of sulfate (most commonlygypsum).In modern cement kilns many advanced features are usedto lower the fuel consumption per ton of clinker pro-duced. Cement kilns are extremely large, complex, andinherently dusty industrial installations, and have emis-sions which must be controlled. Of the various ingredi-ents used in concrete the cement is the most energeticallyexpensive. Even complex and ecient kilns require 3.3to 3.6 gigajoules of energy to produce a ton of clinkerand then grind it into cement. Many kilns can be fueledwith dicult-to-dispose-of wastes, the most common be-

ing used tires. The extremely high temperatures and longperiods of time at those temperatures allows cement kilnsto eciently and completely burn even dicult-to-usefuels.[30]

1.4.2 Water

Combining water with a cementitious material forms acement paste by the process of hydration. The cementpaste glues the aggregate together, lls voids within it,and makes it ow more freely.[31]

A lower water-to-cement ratio yields a stronger, moredurable concrete, whereas more water gives a freer-owing concrete with a higher slump.[32] Impure waterused to make concrete can cause problems when settingor in causing premature failure of the structure.[33]

Hydration involves many dierent reactions, often occur-ring at the same time. As the reactions proceed, the prod-ucts of the cement hydration process gradually bond to-gether the individual sand and gravel particles and othercomponents of the concrete to form a solid mass.[34]

Reaction:[34]

Cement chemist notation: C3S + H C-S-H+ CHStandard notation: Ca3SiO5 + H2O (CaO)(SiO2)(H2O)(gel) + Ca(OH)2Balanced: 2Ca3SiO5 + 7H2O 3(CaO)2(SiO2)4(H2O)(gel) + 3Ca(OH)2

1.4.3 Aggregates

Crushed stone aggregate

Main article: Construction aggregate

Fine and coarse aggregates make up the bulk of a con-crete mixture. Sand, natural gravel, and crushed stone areused mainly for this purpose. Recycled aggregates (from


construction, demolition, and excavation waste) are in-creasingly used as partial replacements of natural aggre-gates, while a number of manufactured aggregates, in-cluding air-cooled blast furnace slag and bottom ash arealso permitted.The presence of aggregate greatly increases the durabilityof concrete above that of cement, which is a brittle ma-terial in its pure state. Thus concrete is a true compositematerial.[35]

Redistribution of aggregates after compaction often cre-ates inhomogeneity due to the inuence of vibration. Thiscan lead to strength gradients.[36]

Decorative stones such as quartzite, small river stones orcrushed glass are sometimes added to the surface of con-crete for a decorative exposed aggregate nish, popularamong landscape designers.In addition to being decorative, exposed aggregate addsrobustness to a concrete driveway.[37]

1.4.4 Reinforcement

Constructing a rebar cage. This cage will be permanently embed-ded in poured concrete to create a reinforced concrete structure.

Main article: reinforced concrete

Concrete is strong in compression, as the aggregate e-ciently carries the compression load. However, it is weakin tension as the cement holding the aggregate in placecan crack, allowing the structure to fail. Reinforced con-crete adds either steel reinforcing bars, steel bers, glass

bers, or plastic bers to carry tensile loads.

1.4.5 Chemical admixtures

Chemical admixtures are materials in the form of powderor uids that are added to the concrete to give it certaincharacteristics not obtainable with plain concrete mixes.In normal use, admixture dosages are less than 5% bymass of cement and are added to the concrete at the timeof batching/mixing.[38] (See the section on Concrete Pro-duction, below.)The common types of admixtures[39] areas follows.

Accelerators speed up the hydration (hardening) ofthe concrete. Typical materials used are CaCl2, Ca(NO3)2 and NaNO3. However, use of chlo-rides may cause corrosion in steel reinforcing and isprohibited in some countries, so that nitrates maybe favored. Accelerating admixtures are especiallyuseful for modifying the properties of concrete incold weather.

Retarders slow the hydration of concrete and areused in large or dicult pours where partial settingbefore the pour is complete is undesirable. Typi-cal polyol retarders are sugar, sucrose, sodium glu-conate, glucose, citric acid, and tartaric acid.

Air entrainments add and entrain tiny air bubbles inthe concrete, which reduces damage during freeze-thaw cycles, increasing durability. However, en-trained air entails a trade o with strength, as each1% of air may decrease compressive strength 5%. Iftoo much air becomes trapped in the concrete as aresult of the mixing process, Defoamers can be usedto encourage the air bubble to agglomerate, rise tothe surface of the wet concrete and then disperse.

Plasticizers increase the workability of plastic orfresh concrete, allowing it be placed more eas-ily, with less consolidating eort. A typical plas-ticizer is lignosulfonate. Plasticizers can be usedto reduce the water content of a concrete whilemaintaining workability and are sometimes calledwater-reducers due to this use. Such treatmentimproves its strength and durability characteris-tics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewerdeleterious eects and can be used to increase work-ability more than is practical with traditional plas-ticizers. Compounds used as superplasticizers in-clude sulfonated naphthalene formaldehyde conden-sate, sulfonated melamine formaldehyde conden-sate, acetone formaldehyde condensate and polycar-boxylate ethers.

Pigments can be used to change the color of con-crete, for aesthetics.

1.5. CONCRETE PRODUCTION 7

Corrosion inhibitors are used to minimize the cor-rosion of steel and steel bars in concrete.

Bonding agents are used to create a bond betweenold and new concrete (typically a type of polymer)with wide temperature tolerance and corrosion re-sistance.

Pumping aids improve pumpability, thicken thepaste and reduce separation and bleeding.

1.4.6 Mineral admixtures and blended ce-ments

Inorganic materials that have pozzolanic or latent hy-draulic properties, these very ne-grained materials areadded to the concrete mix to improve the properties ofconcrete (mineral admixtures),[38] or as a replacement forPortland cement (blended cements).[42] Products whichincorporate limestone, y ash, blast furnace slag, andother useful materials with pozzolanic properties into themix, are being tested and used. This development isdue to cement production being one of the largest pro-ducers (at about 5 to 10%) of global greenhouse gasemissions,[43] as well as lowering costs, improving con-crete properties, and recycling wastes.

Fly ash: A by-product of coal-red electric gener-ating plants, it is used to partially replace Portlandcement (by up to 60% by mass). The properties ofy ash depend on the type of coal burnt. In general,siliceous y ash is pozzolanic, while calcareous yash has latent hydraulic properties.[44]

Ground granulated blast furnace slag (GGBFS orGGBS): A by-product of steel production is used topartially replace Portland cement (by up to 80% bymass). It has latent hydraulic properties.[45]

Silica fume: A byproduct of the production of sil-icon and ferrosilicon alloys. Silica fume is similarto y ash, but has a particle size 100 times smaller.This results in a higher surface-to-volume ratio anda much faster pozzolanic reaction. Silica fume isused to increase strength and durability of concrete,but generally requires the use of superplasticizers forworkability.[46]

High reactivityMetakaolin (HRM):Metakaolin pro-duces concrete with strength and durability simi-lar to concrete made with silica fume. While silicafume is usually dark gray or black in color, high-reactivity metakaolin is usually bright white in color,making it the preferred choice for architectural con-crete where appearance is important.

Concrete plant facility showing a Concrete mixer being lledfrom the ingredient silos.

1.5 Concrete production

Concrete production is the process of mixing together thevarious ingredientswater, aggregate, cement, and anyadditivesto produce concrete. Concrete production istime-sensitive. Once the ingredients are mixed, workersmust put the concrete in place before it hardens. In mod-ern usage, most concrete production takes place in a largetype of industrial facility called a concrete plant, or oftena batch plant.In general usage, concrete plants come in two main types,ready mix plants and central mix plants. A ready mixplant mixes all the ingredients except water, while a cen-tral mix plant mixes all the ingredients including water. Acentral mix plant oers more accurate control of the con-crete quality through better measurements of the amountof water added, but must be placed closer to the work sitewhere the concrete will be used, since hydration begins atthe plant.A concrete plant consists of large storage hoppers for var-ious reactive ingredients like cement, storage for bulk in-gredients like aggregate and water, mechanisms for theaddition of various additives and amendments, machin-ery to accurately weigh, move, and mix some or all ofthose ingredients, and facilities to dispense the mixedconcrete, often to a concrete mixer truck.


Modern concrete is usually prepared as a viscous uid,so that it may be poured into forms, which are contain-ers erected in the eld to give the concrete its desiredshape. There are many dierent ways in which concreteformwork can be prepared, such as Slip forming and Steelplate construction. Alternatively, concrete can be mixedinto dryer, non-uid forms and used in factory settings tomanufacture Precast concrete products.There is a wide variety of equipment for processing con-crete, from hand tools to heavy industrial machinery.Whichever equipment builders use, however, the objec-tive is to produce the desired building material; ingredi-entsmust be properlymixed, placed, shaped, and retainedwithin time constraints. Once the mix is where it shouldbe, the curing process must be controlled to ensure thatthe concrete attains the desired attributes. During con-crete preparation, various technical details may aect thequality and nature of the product.When initially mixed, Portland cement and water rapidlyform a gel of tangled chains of interlocking crystals, andcomponents of the gel continue to react over time. Ini-tially the gel is uid, which improves workability and aidsin placement of the material, but as the concrete sets, thechains of crystals join into a rigid structure, counteract-ing the uidity of the gel and xing the particles of ag-gregate in place. During curing, the cement continues toreact with the residual water in a process of hydration.In properly formulated concrete, once this curing processhas terminated the product has the desired physical andchemical properties. Among the qualities typically de-sired, are mechanical strength, low moisture permeabil-ity, and chemical and volumetric stability.

1.5.1 Mixing concrete

See also: Volumetric concrete mixer and Concrete mixer

Thorough mixing is essential for the production of uni-form, high-quality concrete. For this reason equipmentand methods should be capable of eectively mixing con-crete materials containing the largest specied aggregateto produce uniform mixtures of the lowest slump practicalfor the work.Separate paste mixing has shown that the mixing of ce-ment and water into a paste before combining thesematerials with aggregates can increase the compressivestrength of the resulting concrete.[47] The paste is gen-erally mixed in a high-speed, shear-type mixer at aw/cm (water to cement ratio) of 0.30 to 0.45 by mass.The cement paste premix may include admixtures suchas accelerators or retarders, superplasticizers, pigments,or silica fume. The premixed paste is then blendedwith aggregates and any remaining batch water and -nal mixing is completed in conventional concrete mixingequipment.[48]

Decorative plate made of Nano concrete with High-Energy Mix-ing (HEM)

Nano concrete is created by High-energy mixing (HEM)of cement, sand and water using a specic consumedpower of 30 - 600 watt/kg for a net specic energy con-sumption of at least 5 kJ/kg of the mix.[49] A plasticizeror a superplasticizer is then added to the activated mix-ture which can later be mixed with aggregates in a con-ventional concrete mixer. In the HEM process sand pro-vides dissipation of energy and increases shear stresseson the surface of cement particles. The quasi-laminarow of the mixture characterized with Reynolds num-ber less than 800 [50] is necessary to provide more eec-tive energy absorption. This results in the increased vol-ume of water interacting with cement and acceleration ofCalcium Silicate Hydrate (C-S-H) colloid creation. Theinitial natural process of cement hydration with forma-tion of colloidal globules about 5 nm in diameter[51] af-ter 3-5 min of HEM spreads out over the entire volumeof cement water matrix. HEM is the bottom-up ap-proach in Nanotechnology of concrete. The liquid acti-vated mixture is used by itself for casting small architec-tural details and decorative items, or foamed (expanded)for lightweight concrete. HEM Nano concrete hardensin low and subzero temperature conditions and possessesan increased volume of gel, which drastically reducescapillarity in solid and porous materials.

1.5.2 Workability

Main article: Concrete slump test

Workability is the ability of a fresh (plastic) concretemix to ll the form/mold properly with the desired work(vibration) and without reducing the concretes quality.Workability depends on water content, aggregate (shapeand size distribution), cementitious content and age (levelof hydration) and can be modied by adding chemicaladmixtures, like superplasticizer. Raising the water con-tent or adding chemical admixtures increases concreteworkability. Excessive water leads to increased bleeding

1.5. CONCRETE PRODUCTION 9

Pouring and smoothing out concrete at Palisades Park in Wash-ington DC.

(surface water) and/or segregation of aggregates (whenthe cement and aggregates start to separate), with the re-sulting concrete having reduced quality. The use of anaggregate with an undesirable gradation can result in avery harsh mix design with a very low slump, which can-not readily be made more workable by addition of rea-sonable amounts of water.Workability can be measured by the concrete slump test,a simplistic measure of the plasticity of a fresh batchof concrete following the ASTM C 143 or EN 12350-2test standards. Slump is normally measured by lling an"Abrams cone" with a sample from a fresh batch of con-crete. The cone is placed with the wide end down onto alevel, non-absorptive surface. It is then lled in three lay-ers of equal volume, with each layer being tamped witha steel rod to consolidate the layer. When the cone iscarefully lifted o, the enclosed material slumps a cer-tain amount, owing to gravity. A relatively dry sampleslumps very little, having a slump value of one or twoinches (25 or 50 mm) out of one foot (305 mm). A rel-atively wet concrete sample may slump as much as eightinches. Workability can also be measured by the ow ta-ble test.Slump can be increased by addition of chemical ad-mixtures such as plasticizer or superplasticizer withoutchanging the water-cement ratio.[52] Some other admix-tures, especially air-entraining admixture, can increasethe slump of a mix.High-ow concrete, like self-consolidating concrete, istested by other ow-measuring methods. One of thesemethods includes placing the cone on the narrow end andobserving how the mix ows through the cone while it isgradually lifted.After mixing, concrete is a uid and can be pumped tothe location where needed.

A concrete slab ponded while curing.

1.5.3 CuringIn all but the least critical applications, care must betaken to properly cure concrete, to achieve best strengthand hardness. This happens after the concrete has beenplaced. Cement requires a moist, controlled environmentto gain strength and harden fully. The cement paste hard-ens over time, initially setting and becoming rigid thoughvery weak and gaining in strength in the weeks follow-ing. In around 4 weeks, typically over 90% of the nalstrength is reached, though strengthening may continuefor decades.[53] The conversion of calcium hydroxide inthe concrete into calcium carbonate from absorption ofCO2 over several decades further strengthens the con-crete and makes it more resistant to damage. However,this reaction, called carbonation, lowers the pH of the ce-ment pore solution and can cause the reinforcement barsto corrode.Hydration and hardening of concrete during the rst threedays is critical. Abnormally fast drying and shrinkage dueto factors such as evaporation from wind during place-ment may lead to increased tensile stresses at a timewhen it has not yet gained sucient strength, resultingin greater shrinkage cracking. The early strength of theconcrete can be increased if it is kept damp during thecuring process. Minimizing stress prior to curing mini-mizes cracking. High-early-strength concrete is designedto hydrate faster, often by increased use of cement thatincreases shrinkage and cracking. The strength of con-crete changes (increases) for up to three years. It dependson cross-section dimension of elements and conditions ofstructure exploitation.[54]

During this period concretemust be kept under controlledtemperature and humid atmosphere. In practice, thisis achieved by spraying or ponding the concrete surfacewith water, thereby protecting the concrete mass from illeects of ambient conditions. The picture to the rightshows one of many ways to achieve this, ponding sub-merging setting concrete in water and wrapping in plasticto contain the water in the mix. Additional common cur-ing methods include wet burlap and/or plastic sheeting


covering the fresh concrete, or by spraying on a water-impermeable temporary curing membrane.Properly curing concrete leads to increased strength andlower permeability and avoids cracking where the sur-face dries out prematurely. Care must also be taken toavoid freezing or overheating due to the exothermic set-ting of cement. Improper curing can cause scaling, re-duced strength, poor abrasion resistance and cracking.

1.6 Properties

Main article: Properties of concrete

Concrete has relatively high compressive strength, butmuch lower tensile strength. For this reason it is usuallyreinforced with materials that are strong in tension (of-ten steel). The elasticity of concrete is relatively constantat low stress levels but starts decreasing at higher stresslevels as matrix cracking develops. Concrete has a verylow coecient of thermal expansion and shrinks as it ma-tures. All concrete structures crack to some extent, dueto shrinkage and tension. Concrete that is subjected tolong-duration forces is prone to creep.Tests can be performed to ensure that the properties ofconcrete correspond to specications for the application.Dierent mixes of concrete ingredients produce dierentstrengths. Concrete strength values are usually speciedas the compressive strength of either a cylindrical or cu-bic specimen, where these values usually dier by around20% for the same concrete mix.Dierent strengths of concrete are used for dierent pur-poses. Very low-strength (14 MPa or less) concretemay be used when the concrete must be lightweight.[55]Lightweight concrete is often achieved by adding air,foams, or lightweight aggregates, with the side eect thatthe strength is reduced. For most routine uses, 20 to 32MPa concrete is often used. 40 MPa concrete is readilycommercially available as a more durable, although moreexpensive, option. Higher-strength concrete is often usedfor larger civil projects.[56] Strengths above 40 MPa areoften used for specic building elements. For exam-ple, the lower oor columns of high-rise concrete build-ings may use concrete of 80 MPa or more, to keep thesize of the columns small. Bridges may use long beamsof high-strength concrete to lower the number of spansrequired.[57][58] Occasionally, other structural needs mayrequire high-strength concrete. If a structure must bevery rigid, concrete of very high strength may be spec-ied, even much stronger than is required to bear the ser-vice loads. Strengths as high as 130 MPa have been usedcommercially for these reasons.[57]

Compression testing of a concrete cylinder

1.7 Concrete degradation

Concrete spalling caused by the corrosion of rebar

Main article: Concrete degradation

Concrete can be damaged by many processes, suchas the expansion of corrosion products of the steelreinforcement bars, freezing of trapped water, reor radiant heat, aggregate expansion, sea water ef-fects, bacterial corrosion, leaching, erosion by fast-owing water, physical damage and chemical damage(from carbonatation, chlorides, sulfates and distillatewater). The micro fungi Aspergillus Alternaria andCladosporium were able to grow on samples of concreteused as a radioactive waste barrier in the Chernobyl reac-tor; leaching aluminium, iron, calcium and silicon.[59]

1.9. USE OF CONCRETE IN INFRASTRUCTURE 11

1.8 Microbial concreteBacteria such as Bacillus pasteurii, Bacillus pseudormus,Bacillus cohnii, Sporosarcina pasteuri, and Arthrobactercrystallopoietes increase the compression strength ofconcrete through their biomass. Not all bacteria in-crease the strength of concrete signicantly with theirbiomass.[26]:143 Bacillus sp. CT-5. can reduce corro-sion of reinforcement in reinforced concrete by up to fourtimes. Sporosarcina pasteurii reduces water and chlo-ride permeability. B. pasteurii increases resistance toacid.[26]:146 Bacillus pasteurii and B. sphaericuscan inducecalcium carbonate precipitation in the surface of cracks,adding compression strength.[26]:147

1.9 Use of concrete in infrastruc-ture

Aerial photo of reconstruction at Taum Sauk (Missouri) pumpedstorage facility in late November, 2009. After the original reser-voir failed, the new reservoir was made of roller-compacted con-crete.

1.9.1 Mass concrete structures

Main article: Mass concrete

Large concrete structures such as dams, navigation locks,large mat foundations, and large breakwaters generateexcessive heat during cement hydration and associatedexpansion. To mitigate these eects post-cooling[60] iscommonly applied during construction. An early exam-ple at Hoover Dam, installed a network of pipes betweenvertical concrete placements to circulate cooling waterduring the curing process to avoid damaging overheating.Similar systems are still used; depending on volume ofthe pour, the concrete mix used, and ambient air temper-ature, the cooling process may last for many months afterthe concrete is placed. Various methods also are used topre-cool the concrete mix in mass concrete structures.[60]

Another approach to mass concrete structures that is be-coming more widespread is the use of roller-compactedconcrete, which uses much lower amounts of cement andwater than conventional concrete mixtures and is gener-ally not poured into place. Instead it is placed in thicklayers as a semi-dry material and compacted into a dense,strong mass with rolling compactors. Because it uses lesscementitious material, roller-compacted concrete has amuch lower cooling requirement than conventional con-crete.

1.9.2 Prestressed concrete structures

40-foot cacti decorate a sound/retaining wall in Scottsdale, Ari-zona

Main article: Prestressed concrete

Prestressed concrete is a form of reinforced concrete thatbuilds in compressive stresses during construction to op-pose those experienced in use. This can greatly reducethe weight of beams or slabs, by better distributing thestresses in the structure to make optimal use of the rein-forcement. For example, a horizontal beam tends to sag.Prestressed reinforcement along the bottom of the beamcounteracts this. In pre-tensioned concrete, the prestress-ing is achieved by using steel or polymer tendons or barsthat are subjected to a tensile force prior to casting, or forpost-tensioned concrete, after casting.

1.9.3 Concrete textures

When one thinks of concrete, the image of a dull, grayconcrete wall often comes to mind. With the use ofform liner, concrete can be cast and molded into dif-ferent textures and used for decorative concrete appli-cations. Sound/retaining walls, bridges, oce buildingsand more serve as the optimal canvases for concrete art.For example, the Pima Freeway/Loop 101 retaining andsound walls in Scottsdale, Arizona, feature desert oraand fauna, a 67-foot (20 m) lizard and 40-foot (12 m)


cacti along the 8-mile (13 km) stretch. The project, ti-tled The Path Most Traveled, is one example of howconcrete can be shaped using elastomeric form liner.

1.10 Building with concrete

The Bualo City Court Building in Bualo, NY.

Concrete is one of the most durable building materials. Itprovides superior re resistance compared with woodenconstruction and gains strength over time. Structuresmade of concrete can have a long service life. Concreteis used more than any other manmade material in theworld.[61] As of 2006, about 7.5 billion cubic meters ofconcrete are made each year, more than one cubic meterfor every person on Earth.[62]

More than 55,000 miles (89,000 km) of highways in theUnited States are paved with this material. Reinforcedconcrete, prestressed concrete and precast concrete arethe most widely used types of concrete functional exten-sions in modern days. See Brutalism.

1.10.1 Concrete RoadsConcrete roads are more fuel ecient to drive on,[63]more reective and last signicantly longer than otherpaving surfaces, yet have a much smaller market sharethan other paving solutions. Modern paving methods and

design practices have changed the economics of concretepaving, so that a well designed and placed concrete pave-ment will be less expensive on initial costs and signi-cantly less expensive over the life cycle.

1.10.2 Energy eciencyEnergy requirements for transportation of concrete arelow because it is produced locally from local resources,typically manufactured within 100 kilometers of the jobsite. Similarly, relatively little energy is used in producingand combining the raw materials (although large amountsof CO2 are produced by the chemical reactions in cementmanufacture). The overall embodied energy of concreteis therefore lower than for most structural materials otherthan wood.Once in place, concrete oers great energy eciencyover the lifetime of a building.[64] Concrete walls leakair far less than those made of wood frames. Air leak-age accounts for a large percentage of energy loss froma home. The thermal mass properties of concrete in-crease the eciency of both residential and commercialbuildings. By storing and releasing the energy needed forheating or cooling, concretes thermal mass delivers year-round benets by reducing temperature swings inside andminimizing heating and cooling costs.[65] While insula-tion reduces energy loss through the building envelope,thermal mass uses walls to store and release energy. Mod-ern concrete wall systems use both external insulation andthermal mass to create an energy-ecient building. Insu-lating concrete forms (ICFs) are hollow blocks or panelsmade of either insulating foam or rastra that are stackedto form the shape of the walls of a building and then lledwith reinforced concrete to create the structure.

1.10.3 Pervious concrete

Main article: Pervious concrete

Pervious concrete is a mix of specially graded coarse ag-gregate, cement, water and little-to-no ne aggregates.This concrete is also known as no-nes or porous con-crete. Mixing the ingredients in a carefully controlledprocess creates a paste that coats and bonds the aggregateparticles. The hardened concrete contains interconnectedair voids totalling approximately 15 to 25 percent. Wa-ter runs through the voids in the pavement to the soil un-derneath. Air entrainment admixtures are often used infreezethaw climates to minimize the possibility of frostdamage.

1.10.4 Nano concreteConcrete is the most widely manufactured constructionmaterial. The addition of carbon nanobres to concrete

1.10. BUILDING WITH CONCRETE 13

has many advantages in terms of mechanical and electri-cal properties (e.g. higher strength and higher Youngsmodulus) and self-monitoring behavior due to the hightensile strength and high conductivity. Mullapudi[66] usedthe pulse velocity method to characterize the propertiesof concrete containing carbon nanobres. The test re-sults indicate that the compressive strength and percent-age reduction in electrical resistance while loading con-crete containing carbon nanobres dier from those ofplain concrete. A reasonable concentration of carbonnanobres need to be determined for use in concrete,which not only enhances compressive strength, but alsoimproves the electrical properties required for strainmon-itoring, damage evaluation and self-health monitoring ofconcrete. See also: Mixing concrete

1.10.5 Fire safety

A modern building: Boston City Hall (completed 1968) is con-structed largely of concrete, both precast and poured in place. OfBrutalist architecture, it was voted TheWorlds Ugliest Buildingin 2008.

Concrete buildings are more resistant to re than thoseconstructed using steel frames, since concrete has lowerheat conductivity than steel and can thus last longer underthe same re conditions. Concrete is sometimes used asa re protection for steel frames, for the same eect asabove. Concrete as a re shield, for example Fondu fyre,can also be used in extreme environments like a missilelaunch pad.Options for non-combustible construction include oors,ceilings and roofs made of cast-in-place and hollow-coreprecast concrete. For walls, concrete masonry technol-ogy and Insulating Concrete Forms (ICFs) are additionaloptions. ICFs are hollow blocks or panels made of re-proof insulating foam that are stacked to form the shapeof the walls of a building and then lled with reinforcedconcrete to create the structure.Concrete also provides good resistance against externallyapplied forces such as high winds, hurricanes, and torna-does owing to its lateral stiness, which results in minimalhorizontal movement. However this stiness can workagainst certain types of concrete structures, particularly

where a relatively higher exing structure is require to re-sist more extreme forces.

1.10.6 Earthquake safetyAs discussed above, concrete is very strong in compres-sion, but weak in tension. Larger earthquakes can gen-erate very large shear loads on structures. These shearloads subject the structure to both tensile and compres-sional loads. Concrete structures without reinforcement,like other unreinforced masonry structures, can fail dur-ing severe earthquake shaking. Unreinforced masonrystructures constitute one of the largest earthquake risksglobally.[67] These risks can be reduced through seismicretrotting of at-risk buildings, (e.g. school buildings inIstanbul, Turkey[68]).

1.10.7 Useful life

The Tunkhannock Viaduct was begun in 1912 and is still in reg-ular service as of 2014.

Concrete can be viewed as a form of articial sedimen-tary rock. As a type of mineral, the compounds of whichit is composed are extremely stable.[69] Many concretestructures are built with an expected lifetime of approxi-mately 100 years,[70] but researchers have suggested thatadding silica fume could extend the useful life of bridgesand other concrete uses to as long as 16,000 years.[71]Coatings are also available to protect concrete from dam-age, and extend the useful life. Epoxy coatings may beapplied only to interior surfaces, though, as they wouldotherwise trap moisture in the concrete.[72]

A self-healing concrete has been developed that can alsolast longer than conventional concrete.[73]

Large dams, such as the Hoover Dam, and the ThreeGorges Dam are intended to last forever, a period thatis not quantied.[74]


1.11 World recordsThe world record for the largest concrete pour in a sin-gle project is the Three Gorges Dam in Hubei Province,China by the Three Gorges Corporation. The amount ofconcrete used in the construction of the dam is estimatedat 16 million cubic meters over 17 years. The previousrecord was 12.3 million cubic meters held by Itaipu hy-dropower station in Brazil.[75][76][76][77]

The world record for concrete pumping was set on 7August 2009 during the construction of the Parbati Hy-droelectric Project, near the village of Suind, HimachalPradesh, India, when the concrete mix was pumpedthrough a vertical height of 715 m (2,346 ft).[78][79]

The world record for the largest continuously poured con-crete raft was achieved in August 2007 in Abu Dhabi bycontracting rm Al Habtoor-CCC Joint Venture and theconcrete supplier is Unibeton ReadyMix.[80][81] The pour(a part of the foundation for the Abu Dhabis LandmarkTower) was 16,000 cubic meters of concrete pouredwithin a two-day period.[82] The previous record, 13,200cubic meters poured in 54 hours despite a severe tropi-cal storm requiring the site to be covered with tarpaulinsto allow work to continue, was achieved in 1992 byjoint Japanese and South Korean consortiums HazamaCorporation and the Samsung C&T Corporation for theconstruction of the Petronas Towers in Kuala Lumpur,Malaysia.[83]

The world record for largest continuously poured con-crete oor was completed 8 November 1997, inLouisville, Kentucky by design-build rm EXXCELProject Management. The monolithic placement con-sisted of 225,000 square feet (20,900 m2) of concreteplaced within a 30-hour period, nished to a atness tol-erance of FF 54.60 and a levelness tolerance of FL 43.83.This surpassed the previous record by 50% in total vol-ume and 7.5% in total area.[84][85]

The record for the largest continuously placed underwaterconcrete pour was completed 18 October 2010, in NewOrleans, Louisiana by contractor C. J. Mahan Construc-tion Company, LLC of Grove City, Ohio. The placementconsisted of 10,251 cubic yards of concrete placed in a58.5 hour period using two concrete pumps and two dedi-cated concrete batch plants. Upon curing, this placementallows the 50,180-square-foot (4,662 m2) coerdam tobe dewatered approximately 26 feet (7.9 m) below sealevel to allow the construction of the Inner Harbor Navi-gation Canal Sill & Monolith Project to be completed inthe dry.[86]

1.12 See also

1.13 References

1.13.1 Notes[1] The Roman Pantheon: The Triumph of Concrete. Ro-

manconcrete.com. Retrieved on 2013-02-19.

[2] Zongjin Li; Advanced concrete technology; 2011

[3] Moore, David (1999). The Pantheon. romancon-crete.com. Retrieved 26 September 2011.

[4] concretus. Latin Lookup. Retrieved 1 October 2012.

[5] The History of Concrete. Dept. of Materials Sci-ence and Engineering, University of Illinois, Urbana-Champaign. Retrieved 8 January 2013.

[6] FromThe History of Concrete - InterNACHI http://www.nachi.org/history-of-concrete.htm#ixzz31V47Zuuj

[7] Heinrich Schliemann with Wilhelm Drpfeld and FelixAdler, Tiryns: The Prehistoric Palace of the Kings ofTiryns, The Results of the Latest Excavations, (New York,New York: Charles Scribners Sons, 1885), pages 203-204, 215, and 190.

[8] Amelia Carolina Sparavigna, Ancient concrete works

[9] Jacobsen T and Lloyd S, (1935) Sennacheribs Aqueduct atJerwan, Oriental Institute Publications 24, Chicago Uni-versity Press

[10] Stella L. Marusin (1 January 1996). Ancient ConcreteStructures 18 (1). Concrete International. pp. 5658.

[11] Lancaster, Lynne (2005). Concrete Vaulted Constructionin Imperial Rome. Innovations in Context. CambridgeUniversity Press. ISBN 978-0-511-16068-4.

[12] D.S. Robertson: Greek and Roman Architecture, Cam-bridge, 1969, p. 233

[13] Henry Cowan: The Masterbuilders, New York 1977, p.56, ISBN 978-0-471-02740-9

[14] History of Concrete. Ce.memphis.edu. Retrieved on2013-02-19.

[15] Robert Mark, Paul Hutchinson: On the Structure of theRoman Pantheon, Art Bulletin, Vol. 68, No. 1 (1986), p.26, fn. 5

[16] The Politics of Rediscovery in the History of Science:Tacit Knowledge of Concrete before its Discovery atthe Wayback Machine (archived May 5, 2010). allaca-demic.com

[17] Nick Gromicko and Kenton Shepard. the History ofConcrete. The International Association of CertiedHome Inspectors (InterNACHI). Retrieved 8 January2013.

[18] Herring, Benjamin. The Secrets of Roman Concrete.Romanconcrete.com. Retrieved 1 October 2012.

[19] The History of Concrete and Cement. Inven-tors.about.com (2012-04-09). Retrieved on 2013-02-19.

[20] Historical Timeline of Concrete. Auburn.edu. Retrievedon 2013-02-19.

1.13. REFERENCES 15

[21] Brief history of concrete. Djc.com. Retrieved on 2013-02-19.

[22] Evaluation of Electrically Conductive Concrete Contain-ing Carbon Products for Deicing. ACIMaterials Journal.Retrieved 1 October 2012.

[23] What is the development impact of concrete?". CementTrust. Retrieved 10 January 2013.

[24] http://www.prweb.com/releases/ready_mix_concrete/cement/prweb3747364.htm

[25] ReadyMixedConcrete Production Statistics. NRMCA-National Ready Mixed Concrete Association. Retrieved10 January 2013.

[26] Navdeep Kaur Dhami; Sudhakara M. Reddy; AbhijitMukherjee (2012). Biolm and Microbial Applicationsin Biomineralized Concrete.

[27] Worrell, E.; Price, L.; Martin, N.; Hendriks, C.; OzawaMeida, L. (2001). Carbon dioxide emissions from theglobal cement industry. Annu. Rev. Energy Environ. 26:303329. Cited in[26]

[28] Shepherd and Woskie. Controlling Dust from ConcreteSaw Cutting. Journal of Occupational and Environmen-tal Hygiene. Retrieved 14 June 2013.

[29] http://www.nbm.org/exhibitions-collections/exhibitions/liquid-stone.html

[30] Evelien.Cochez and Wouter.Nijs; Giorgio.Simbolotti andGiancarlo Tosato. Cement Production. IEA ETSAP Technology Brief I03 June 2010: IEA ETSAP- EnergyTechnology Systems Analysis Programme. Retrieved 9January 2013.

[31] Gibbons, Jack. MeasuringWater in Concrete. ConcreteConstruction. Retrieved 1 October 2012.

[32] CHAPTER 9Designing and Proportioning Normal Con-crete Mixtures. PCA manual. Portland Concrete Asso-ciation. Retrieved 1 October 2012.

[33] Taha, Ramzi A. Use of Production and Brackish Waterin Concrete Mixtures. Int. J. of Sustainable Water andEnvironmental System. Retrieved 1 October 2012.

[34] Cement hydration. Understanding Cement. Retrieved1 October 2012.

[35] The Eect of Aggregate Properties on Concrete.Engr.psu.edu. Retrieved on 2013-02-19.

[36] Veretennykov, Vitaliy I.; Yugov, Anatoliy M.; Dolmatov,Andriy O.; Bulavytskyi, Maksym S.; Kukharev, DmytroI.; Bulavytskyi, Artem S. (2008). Concrete Inhomogene-ity of Vertical Cast-in-Place Elements in Skeleton-TypeBuildings. In Mohammed Ettouney. AEI 2008: BuildingIntegration Solutions. Reston, Virginia: American Societyof Civil Engineers. doi:10.1061/41002(328)17. ISBN978-0-7844-1002-8. Retrieved 25 December 2010.

[37] Exposed Aggregate. Uniquepaving.com.au. Retrieved on2013-02-19.

[38] U.S. Federal Highway Administration (14 June 1999).Admixtures. Retrieved 25 January 2007.

[39] Cement Admixture Association. Admixture Types.Retrieved 25 December 2010.

[40] Holland, Terence C. (2005). Silica Fume Users Man-ual. Silica Fume Association and United States Depart-ment of Transportation Federal Highway AdministrationTechnical Report FHWA-IF-05-016. Retrieved October31, 2014.

[41] Kosmatka, S.; Kerkho, B.; Panerese, W. (2002). De-sign and Control of Concrete Mixtures (14 ed.). PortlandCement Association, Skokie, Illinois.

[42] Kosmatka, S.H.; Panarese,W.C. (1988). Design and Con-trol of Concrete Mixtures. Skokie, IL, USA: Portland Ce-ment Association. pp. 17, 42, 70, 184. ISBN 978-0-89312-087-0.

[43] Paving the way to greenhouse gas reductions.Web.mit.edu (2011-08-28). Retrieved on 2013-02-19.

[44] U.S. Federal Highway Administration (14 June 1999).Fly Ash. Archived from the original on 9 July 2007.Retrieved 24 January 2007.

[45] U.S. Federal Highway Administration. Ground Granu-lated Blast-Furnace Slag. Retrieved 24 January 2007.

[46] U.S. Federal Highway Administration. Silica Fume.Retrieved 24 January 2007.

[47] Premixed cement paste. Concreteinternational.com(1989-11-01). Retrieved on 2013-02-19.

[48] Measuring, mixing, transporting and placing concrete.Concrete.org. Retrieved on 2013-02-19.

[49] US 5,443,313, Fridman, Vladen, Method for producingConstruction Mixture for concrete., issued August 22,1995

[50] 20130305963 A1 US Application 20130305963 A1,Fridman, Vladlen, Method of producing activated con-struction mixture, published November 21, 2013

[51] Raki, Laila; Beaudoin, James; Alizadeh, Rouhollah;Makar, Jon; Sato, Taijiro (2010). Cement and ConcreteNanoscience and Nanotechnology. Materials (NationalResearch Council Canada, Institute for Research in Con-struction) 3: 918942. doi:10.3390/ma3020918. ISSN1996-1944.

[52] Ferrari, L; Kaufmann, J; Winnefeld, F; Plank, J(2011). Multi-method approach to study inu-ence of superplasticizers on cement suspensions.Cement and Concrete Research 41 (10): 1058.doi:10.1016/j.cemconres.2011.06.010.

[53] Concrete Testing. Retrieved 10 November 2008.

[54] Resulting strength distribution in vertical elements re-searched and presented at the article Concrete inhomo-geneity of vertical cast-in-place elements in skeleton-typebuildings.


[55] Structural lightweight concrete. Concrete Construction.The Aberdeen Group. March 1981.

[56] Ordering Concrete by PSI. American Concrete. Re-trieved 10 January 2013.

[57] Henry G. Russel, PE. Why Use High Performance Con-crete?". Technical Talk. Retrieved 10 January 2013.

[58] Concrete in Practice: What, Why, and How?".NRMCA-National Ready Mixed Concrete Association.Retrieved 10 January 2013.

[59] Georey Michael Gadd (March 2010). Metals, miner-als and microbes: geomicrobiology and bioremediation.Microbiology 156. pp. 609643.

[60] Mass Concrete. (PDF) . Retrieved on 2013-02-19.

[61] Lomborg, Bjrn (2001). The Skeptical Environmentalist:Measuring the Real State of the World. p. 138. ISBN 978-0-521-80447-9.

[62] Minerals commodity summary cement 2007. USUnited States Geological Survey. 1 June 2007. Retrieved16 January 2008.

[63] Mapping of Excess Fuel Consumption.

[64] John Gajda (2001) Energy Use of Single Family Houseswith Various Exterior Walls, Construction TechnologyLaboratories Inc.

[65] Features and Usage of Foam Concrete.

[66] Mullapudi, T.R.S., Gao, D., and Ayoub, A.S., Non-destructive Evaluation of Carbon-Nanober Concrete,Magazine of Concrete Research, ICE, V. 65 (18), 2013,pp. 1081-1091.

[67] Unreinforced Masonry Buildings and Earthquakes: De-veloping Successful Risk Reduction Programs, FEMA P-774 / October 2009

[68] Seismic Retrot Design Of Historic Century-Old SchoolBuildings In Istanbul, Turkey, C.C. Simsir, A. Jain, G.C.Hart, and M.P. Levy, The 14th World Conference onEarthquake Engineering, 1217 October 2008, Beijing,China

[69] Sedimentary Rocks p. 7, msnucleus.org

[70] Sustainable Development of Concrete Technology. (PDF). Retrieved on 2013-02-19.

[71] Concrete Structures Could Last 16,000 Years. Eco-geek.org. Retrieved on 2013-02-19.

[72] Concrete Coating Considerations To Extend PerformanceLife. Facilitiesnet.com. Retrieved on 2013-02-19.

[73] Self-Healing Concrete: Research Yields Cost-EectiveSystem to Extend Life of Structures 25 May 2010

[74] How long are dams like Hoover Dam engineered to last?Whats the largest dam ever to fail?. Straightdope.com(2006-08-11). Retrieved on 2013-02-19.

[75] Itaipu Web-site. 2 January 2012. Retrieved 2 January2012.

[76] Chinas Three Gorges Dam By The Numbers. Probein-ternational.org. Retrieved on 2013-02-19.

[77] Concrete Pouring of Three Gorges Project Sets WorldRecord. Peoples Daily. 4 January 2001. Retrieved 24August 2009.

[78] Concrete Pumping to 715 m Vertical A New WorldRecord Parbati Hydroelectric Project Inclined PressureShaft Himachal Pradesh A case Study. The Master-builder. Retrieved 21 October 2010.

[79] SCHWING Stetter Launches New Truck mounted Con-crete Pump S-36. NBM&CW (New Building Materialsand Construction World). October 2009. Retrieved 21October 2010.

[80] Concrete Supplier for Landmark Tower.

[81] The world record Concrete Supplier for LandmarkTower Unibeton Ready Mix.

[82] Al Habtoor Engineering Abu Dhabi Landmark Towerhas a record-breaking pour September/October 2007,Page 7.

[83] National Geographic Channel International / CarolineAnstey (2005), Megastructures: Petronas Twin Towers

[84] Continuous cast: Exxcel Contract Management overseesrecord concrete pour. US Concrete Products. 1 March1998. Retrieved 25 August 2009.

[85] Exxcel Project Management Design Build, GeneralContractors. Exxcel.com. Retrieved on 2013-02-19.

[86] Contractors Prepare to Set Gates to Close New OrleansStorm Surge Barrier 12 May 2011

1.13.2 Bibliography Matthias Dupke: Textilbewehrter Beton als Kor-

rosionsschutz. Diplomica Verlag, Hamburg 2010,ISBN 978-3-8366-9405-6.

1.14 External links Chemistry of Concrete at The Periodic Table of

Videos (University of Nottingham)

Refractory Concrete Information related to heat re-sistant concrete; recipes, ingredients mixing ratio,work with and applications.

Chapter 2

Cement

For other uses, see Cement (disambiguation).Not to be confused with Concrete.A cement is a binder, a substance that sets and hard-

Cement is usually a grey powder before being mixed with othermaterials and water. Cement powder causes allergic reactionsat skin contact and is biohazardous to skin, eyes and lungs, sohandlers should wear a dust mask, goggles and protective gloves,unlike this man.[1][2][3]

ens and can bind other materials together. The word ce-ment traces to the Romans, who used the term opuscaementicium to describe masonry resembling modernconcrete that was made from crushed rock with burntlime as binder. The volcanic ash and pulverized bricksupplements that were added to the burnt lime, to obtaina hydraulic binder, were later referred to as cementum,cimentum, cment, and cement.

Cements used in construction can be characterized as be-ing either hydraulic or non-hydraulic, depending uponthe ability of the cement to be used in the presence ofwater (see hydraulic and non-hydraulic lime plaster).Non-hydraulic cement will not set in wet conditions orunderwater, rather it sets as it dries and reacts with carbondioxide in the air. It can be attacked by some aggressivechemicals after setting.Hydraulic cement is made by replacing some of thecement in a mix with activated aluminium silicates,pozzolanas, such as y ash. The chemical reaction re-sults in hydrates that are not very water-soluble and soare quite durable in water and safe from chemical attack.This allows setting in wet condition or underwater andfurther protects the hardened material from chemical at-tack (e.g., Portland cement).The chemical process for hydraulic cement found by an-cient Romans used volcanic ash (activated aluminium sil-icates). Presently cheaper than volcanic ash, y ash frompower stations, recovered as a pollution control measure,or other waste or by products are used as pozzolanas withplain cement to produce hydraulic cement. Pozzolanascan constitute up to 40% of Portland cement.The most important uses of cement are as a component inthe production of mortar in masonry, and of concrete, acombination of cement and an aggregate to form a strongbuilding material.

2.1 ChemistryNon-hydraulic cement, such as slaked lime (calcium hy-droxide mixed with water), hardens by carbonation in thepresence of carbon dioxide naturally present in the air.First calcium oxide is produced by lime calcination attemperatures above 825 C (1,517 F) for about 10 hoursat atmospheric pressure:

CaCO3 CaO + CO2

The calcium oxide is then spent (slaked) mixing it withwater to make slaked lime:

CaO + H2O Ca(OH)2

17

18 CHAPTER 2. CEMENT

Once the water in excess from the slaked lime is com-pletely evaporated (this process is technically called set-ting), the carbonation starts:

Ca(OH)2 + CO2 CaCO3 + H2O

This reaction takes a signicant amount of time becausethe partial pressure of carbon dioxide in the air is low.The carbonation reaction requires the dry cement to beexposed to air, for this reason the slaked lime is a non-hydraulic cement and cannot be used under water. Thiswhole process is called the lime cycle.Conversely, the chemistry ruling the action of the hy-draulic cement is hydration. Hydraulic cements (suchas Portland cement) are made of a mixture of silicatesand oxides, the four main components being:

Belite (2CaOSiO2);Alite (3CaOSiO2);Celite (3CaOAl2O3);Brownmillerite (4CaOAl2O3Fe2O3).

The silicates are responsible of the mechanical propertiesof the cement, the celite and the brownmillerite are essen-tial to allow the formation of the liquid phase during thekiln sintering (ring). The chemistry of the above listedreactions is not completely clear and is still the object ofresearch.[4]

2.2 History of the origin of cement

2.2.1 Cements before the 18th centuryAn early version of cement made with lime, sand, andgravel was used in Mesopotamia in the third millen-nium B.C. and later in Egypt. It is uncertain where itwas rst discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mix-ture (see also: Pozzolanic reaction), but concrete madefrom such mixtures was used by the Ancient Macedo-nians[5][6] and three centuries later on a large scale byRoman engineers.[7] They used both natural pozzolans(trass or pumice) and articial pozzolans (ground brickor pottery) in these concretes. The huge dome of thePantheon in Rome and the massive Baths of Caracallaare examples of ancient structures made from these con-cretes, many of which are still standing.[8] The vast sys-tem of Roman aqueducts also made extensive use ofhydraulic cement.[9] Although any preservation of thisknowledge in literary sources from the Middle Ages isunknown, medieval masons and some military engineersmaintained an active tradition of using hydraulic ce-ment in structures such as canals, fortresses, harbors, andshipbuilding facilities.[10][11] This technical knowledge ofmaking hydraulic cement was later formalized by Frenchand British engineers in the 18th century.[10]

2.2.2 Cements in the 18th, 19th, and 20thcenturies

John Smeaton made an important contribution to thedevelopment of cements while planning the construc-tion of the third Eddystone Lighthouse (175559) in theEnglish Channel now known as Smeatons Tower. Heneeded a hydraulic mortar that would set and developsome strength in the twelve hour period between succes-sive high tides. He performed experiments with combina-tions of dierent limestones and additives including trassand pozzolanas[12] and did exhaustive market researchon the available hydraulic limes, visiting their productionsites, and noted that the hydraulicity of the lime wasdirectly related to the clay content of the limestone fromwhich it was made. Smeaton was a civil engineer by pro-fession, and took the idea no further.In Britain particularly, good quality building stone be-came ever more expensive during a period of rapidgrowth, and it became a common practice to constructprestige buildings from the new industrial bricks, and tonish them with a stucco to imitate stone. Hydrauliclimes were favored for this, but the need for a fast set timeencouraged the development of new cements. Most fa-mous was Parkers "Roman cement".[13] This was devel-oped by James Parker in the 1780s, and nally patentedin 1796. It was, in fact, nothing like material used bythe Romans, but was a natural cement made by burn-ing septaria nodules that are found in certain clay de-posits, and that contain both clay minerals and calciumcarbonate. The burnt nodules were ground to a ne pow-der. This product, made into a mortar with sand, set in515 minutes. The success of Roman cement led othermanufacturers to develop rival products by burning arti-cial hydraulic lime cements of clay and chalk. Romancement quickly became popular but was largely replacedby Portland cement in the 1850s.[12]

In Russia, Egor Cheliev created a new binder by mix-ing lime and clay. His results were published in 1822 inhis book A Treatise on the Art to Prepare a Good Mortarpublished in St. Petersburg. A few years later in 1825,he published another book, which described the variousmethods of making cement and concrete, as well as thebenets of cement in the construction of buildings andembankments.[14][15]

Apparently unaware of Smeatons work, the same prin-ciple was identied by Frenchman Louis Vicat in therst decade of the nineteenth century. Vicat went onto devise a method of combining chalk and clay intoan intimate mixture, and, burning this, produced anarticial cement in 1817[16] considered the principalforerunner[12] of Portland cement and "...Edgar Dobbsof Southwark patented a cement of this kind in 1811.[12]

James Frost,[17] working in Britain, produced what hecalled British cement in a similar manner around thesame time, but did not obtain a patent until 1822. In

2.3. MODERN CEMENTS 19

1824, Joseph Aspdin patented a similar material, whichhe called Portland cement, because the render made fromit was in color similar to the prestigious Portland stone.However, Aspdins cement was nothing like modern Port-land cement but was a rst step in its development, calleda proto-Portland cement.[12] Joseph Aspdins son WilliamAspdin had left his fathers company and in his cementmanufacturing apparently accidentally produced calciumsilicates in the 1840s, a middle step in the development ofPortland cement. William Aspdins innovation was coun-terintuitive for manufacturers of articial cements, be-cause they required more lime in the mix (a problem forhis father), a much higher kiln temperature (and thereforemore fuel), and the resulting clinker was very hard andrapidly wore down the millstones, which were the onlyavailable grinding technology of the time. Manufacturingcosts were therefore considerably higher, but the prod-uct set reasonably slowly and developed strength quickly,thus opening up a market for use in concrete. The useof concrete in construction grew rapidly from 1850 on-ward, and was soon the dominant use for cements. ThusPortland cement began its predominant role.Isaac Charles Johnson further rened the production ofmeso-Portland cement (middle stage of development) andclaimed to be the real father of Portland cement.[18]

Setting time and early strength are important charac-teristics of cements. Hydraulic limes, natural cements,and articial cements all rely upon their belite con-tent for strength development. Belite develops strengthslowly. Because they were burned at temperatures below1,250 C (2,280 F), they contained no alite, which is re-sponsible for early strength in modern cements. The rstcement to consistently contain alite was made byWilliamAspdin in the early 1840s: This was what we call todaymodern Portland cement. Because of the air of mys-tery with which William Aspdin surrounded his prod-uct, others (e.g., Vicat and Johnson) have claimed prece-dence in this invention, but recent analysis[19] of bothhis concrete and raw cement have shown that WilliamAspdins product made at Northeet, Kent was a truealite-based cement. However, Aspdins methods wererule-of-thumb": Vicat is responsible for establishing thechemical basis of these cements, and Johnson establishedthe importance of sintering the mix in the kiln.Sorel cement was patented in 1867 by FrenchmanStanislas Sorel and was stronger than Portland cementbut its poor water restive and corrosive qualities limitedits use in building construction. The next developmentwith the manufacture of Portland cement was the intro-duction of the rotary kiln which allowed a stronger, morehomogeneous mixture and a continuous manufacturingprocess.[12]

Also, tabby, a wall building method using lime, sandand oyster shells to form a concrete, was introduced tothe Americas by the Spanish in the sixteenth century.[20]The lime may have been made from burned oyster shells

which were available in some coastal areas in the form ofshell middens. Calcium aluminate cements were patentedin 1908 in France by Jules Bied for better resistance tosulfates.

The National Cement Share Company of Ethiopia's new plant inDire Dawa.

In the US the rst large-scale use of cement wasRosendale cement, a natural cement mined from a mas-sive deposit of a large dolostone rock deposit discoveredin the early 19th century near Rosendale, New York.Rosendale cement was extremely popular for the founda-tion of buildings (e.g., Statue of Liberty, Capitol Build-ing, Brooklyn Bridge) and lining water pipes. But itslong curing time of at least a month made it unpopu-lar after World War One in the construction of high-ways and bridges and many states and construction rmsturned to the use of Portland cement. Because of theswitch to Portland cement, by the end of the 1920s ofthe 15 Rosendale cement companies, only one had sur-vived. But in the early 1930s it was discovered that,while Portland cement had a faster setting time it wasnot as durable, especially for highways, to the point thatsome states stopped building highways and roads withcement. Bertrain H. Wait, an engineer whose companyhad worked on the construction of the New York CitysCatskill Aqueduct, was impressed with the durability ofRosendale

cement & admixtures

Documents

use of concrete

composition of concrete

mixing concrete

concrete production71

concrete textures

concrete roads

concrete recycling41

concrete degradation