designing, specifying & constructing with modern concrete
DESCRIPTION
Concrete is everywhere. In pavements, building structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and bases for gates, fences poles and many more. Concrete is used more than any other man-made material on the planet. It has been said that instead of naming our era "the nuclear age" it should be named "the concrete age" as almost all of our modern lifestyle and constructions depend on this material. This course deals with concrete, it’s manufacturing, designing and maintaining. It includes the details about ingredients, its quality, quantity and effect on the final product of concrete. Concrete designing, its specifications, standards, codes are the parts of this course and the concrete mix design is discussed in detail. On field manufacturing of concrete, various procedures, precautions are also covered. The defects, investigations and the remedial measures, repairs are covered in detail. The modern concepts like ready mix concrete, precast and prestressed concrete and their applications are covered in this course. The admixtures used to get a specific quality concrete, special purpose concrete etc is also discussed in detail. http://www.idc-online.com/content/designing-specifying-and-constructing-modern-concrete-28TRANSCRIPT
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Understanding Concrete
• PORTLAND CEMENT + H2O + ROCK = HARD CONCRETE + ENERGY (HEAT)
• Cement only a component of concrete and concrete is structural material
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Objectives • What is concrete and how it work? • Basic chemistry of concrete • Analyze the strengths and weaknesses of
concrete• Basic concrete design • Extreme weather concreting • Analyze development and prevention of
cracks in concrete• Precautions while working with concrete
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Concrete as a Structural Material
Advantages of concrete over other construction materials
Economical
Long life
Low maintenance
Unlikely to rot, corrode, or decay
Fire-safe and able withstand high temperatures
High fire resistance
Useful for storm shelters
Resistant to wind, water, rodents, and insects
Ability to be molded or cast into almost any desired shape
Molds and casting can occur on the work-site which reduces costs
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Aggregates • Plays an important role in determining properties of concrete
• Occupies 75% of the volume of concrete
• Chemically inert, solid bodies held together by the cement
• Come in various shapes, sizes
• Materials ranging from fine particles of sand to large, coarse rocks
• Keep the cost of the concrete low
• Two basic types:–Corse: crushed rock, gravel or screenings–Fine: fine and coarse sands and crusher fines
• Selection depends upon required characteristics of concrete
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Special Aggregates• Classified by specific gravities : • Lightweight - High internal porosity. Most of these materials are synthetic. Clays, shale,
or slates will bloat at high temperatures resulting in an expansion in volume. Lightweight aggregates have high absorption capacity associated with their high porosity. Some materials have a coating resulting from the fusion process. May get damaged during handling resulting in an abrupt increase in absorption
• Normal-weight• Heavy-weight - A material with a high specific gravity. Mostly used for radiation
shielding and application where a high mass-to-volume ratio required
Source: http://home.howstuffworks.com/home-improvement/remodeling/concrete-countertop4.htm
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Aggregates With Specific Properties:
• Abrasion and Skid-Resistant Aggregates - Hard, dense aggregates used in heavy-industry applications where high resistance to abrasion is required. The strength of the cement paste and the cement-aggregate bond are more important than the aggregate hardness
• Marginal Aggregates - Require more care and thought in design, and generally more costly. Four areas of interest:
Concrete properties
Weaknesses of aggregate
Beneficiation
Use of protective measures
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EN 197: Classification of Cement
Type Name Properties
I Portland cementComprising Portland cement and up to 5% of minor additional constituents
IIPortland-composite cement
Portland cement and up to 35% of other single constituents
III Blastfurnace cementPortland cement and higher percentages of blastfurnace slag
IV Pozzolanic cementComprising Portland cement and higher percentages of pozzolana
V Composite cementComprising Portland cement and higher percentages of blastfurnace slag and pozzolana or fly ash
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Cement Manufacturing Process
Common raw material used : • common sources of calcium in cement:
– Limestone, marl, and chalk
• Common sources of silicon: – Clay, sand, and shale, certain waste products, such as fly ash
• Iron, aluminum recycled metals can also be used • About 5% of cement by weight is gypsum, a common
calcium- and sulfur-based mineral
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Cement Manufacturing Process Continued…
Cement Compound
Weight Percentage
Chemical Formula
Tricalcium silicate 50 % Ca3SiO5 or 3CaO.SiO2
Dicalcium silicate 25 % Ca2SiO4 or 2CaO.SiO2
Tricalcium aluminate
10 % Ca3Al2O6 or 3CaO .Al2O3
Tetracalcium aluminoferrite
10 % Ca4Al2Fe10 or 4CaO.Al2O3
.Fe2O3
Gypsum 5 % CaSO4.2H2O
• Composition of Portland cement :
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Cement Manufacturing Clinker
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Cement Manufacturing Process Continued…
PRODUCTION OF PORTLAND CEMENT
1. LIMESTONE 2. CLAY/SHALE
CRUSHED LIMESTONE + CLAY/SHALE
MIXTURE IS HEATED IN A KILN
GYPSUM IS ADDED AND THE MIXTURE IS
PORTLAND CEMENT
Raw materials
QUARRYING PROCESS
CRUSHING PROCESS
CLINKER
ARE MIXED AND GROUND TOGETHER
GROUND TO A POWDER RESULTING IN
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Heat of Hydration
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Concrete Proportioning
• For strong, durable concrete rests in careful proportioning and mixing of ingredients
Ingredient Proportion
Cement 10-15%
Sand & Aggregates 60-75%
Water 15-20%
Air 5-7%
Admixtures <1 -3% (varies with requirement)
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Permeability
• Should be controlled in order to prevent corrosion of reinforced steel bars
•Porosity
Expressed in terms of percentage by volume of concrete
Matrix pore structure that ultimately affects its permeability, sorptivity, and diffusivity
Size, distribution, interconnectivity, shape, and tortuosity of pores are all determining factors in overall permeability of a concrete matrix
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Reinforced Cement Concrete
Low tensile strength
High compressive strength
Normal concrete has:• HIGH compressive strength• VERY LOW tensile strength• VERY LOW shear strength
Reinforced Concrete has:• VERY HIGH compressive strength• VERY HIGH tensile strength• VERY HIGH shear strength
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Cracking in Concrete • Types of Cracks
Pre-setting cracks that happen before concrete hardens, while it is still workable
Hardened Cracking Cracks which happen after concrete hardens
• Types of pre-setting cracks :
• Formwork Movement
Form during placing, compaction and finishing caused by movement of concrete before it is dry
Develop cracks from sudden contraction
• Thermal Shock
Presetting Cracks
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