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Joe Dralle4/19/10
Why Concrete?It’s common, it’s everywhere, it’s old
Most people don’t know its technical aspects
Concrete can be complexDifferent types and usesEngineering material with problems and
solutions
What is Concrete?Solid building material made from aggregate
and cement
Aggregate encompasses things like:Small stonesGravelSand
Cement is often Portland Cement, which is the “glue” that keeps concrete together
History~6000-3000 BC: used by ancient Babylonians,
Egyptians and Chinese in several primitive forms
128 AD: the Romans build the Pantheon with an unreinforced concrete dome
1756: John Smeaton of Britain discovered modern hydraulic cement and pioneered modern use
1824: Joseph Aspdin of Britain patented Portland Cement for his mixture of crushed limestone and clay
1892: Reinforced concrete patented in France and became an industry standard soon afterward
Types of Concrete Reinforced Concrete
Made with steel bars to provide tensile strength
Shotcrete Concrete delivered by pressure hoses onto vertical or overhanging
surfaces
Refractory Concrete (high temperature) Uses specialty cement to withstand high temperatures in masonry
ovens and production of metals
Cellular Concrete Aerated, lightweight concrete
Polymer Concrete Fast-setting concrete with polymers added as binding agent
Cement ClassificationHydraulic Non-hydraulic
Hardens when in contact with water
Hydration reactions occur in the cement as it hardens
Portland cement is hydraulic
Cannot set when in contact with water
Composed of non-hydraulic lime and other minerals
Not widely used today
Common Make-UpConcrete and cement composition Mix component Rolled gravel (silica+limestone) 5/15 mm
1093 kg/m3Sand 0/5 mm 734
kg/m3Portland cement: OPC HP (high performance) 358 kg/m3Water 179 kg/m3 Cement composition
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O
% Weight 21.4 6.0 2.3 63.0 1.4 3.0 0.5
Cement Production
Clinker
Properties of Concrete High compressive strength (6000 psi is common) and lower
tensile strength
Water/Cement ratio (W/C) determines strength High W/C = high workability, but lower strength Low W/C = less workability, but greater strength
Curing pertains to the period of hydration as the concrete absorbs moisture and becomes dry Steady curing rates result in the best structure
Cracks occur after repetitive expansion and shrinking, often due to temperature changes
Creeping may occur over longer periods of time as the concrete deforms from internal stresses
UsesBuildings, roads, pavement, bridgesDams/breakwatersColumns and other decorationsFences/wallsFoundationsTunnels and sewersRecreational surfaces
Worldwide Usage
CO2 Emissions
Asphalt ConcreteType of concrete held together by bitumen
Bitumen is a thick, sticky substance made from mostly polycyclic aromatic hydrocarbons (PAH)Naphthalene, Anthracene, Napthacene, Pyrene
PAH are most commonly found in oil, coal and tar deposits
AsphaltAsphalt is technically
synonymous with bitumen, but often asphalt is referred to as the concrete structure that we call “black-top”
Asphalt/bitumen is often considered a colloid with solids suspended within a viscous fluid
Modern Adjustments and Considerations
Decrease the amount of lime in cement to curb carbon emissions
Using recycled concrete and cement
Using additives and replacement materials to adjust cost and propertiesSilica fume (high surface area silica) is used to
make very high strength concreteBlast furnace cement uses slag as the primary
material in cement
Referenceshttp://petrolog.typepad.com/photos/blog_illustrations/
global_co2_emissionshttp://www.ashokaengineering.com/images/flow-charthttp://www.auburn.edu/academic/architecture/bsc/
classes/bsc314/timeline/timeline.htmlwww.ecocem.ie/img/chart01.pnghttp://www.howconcreteworks.com/
application_of_concrete.htmlhttp://www.sciencedirect.com.ezproxy.library.wisc.edu/
science?_ob=MImg&_imagekey=B6TWG-4PMYXPH-1-17&_cdi=5562&_user=443835&_pii=S0008884607001718&_orig=search&_coverDate=11%2F30%2F2007&_sk=999629988&view=c&wchp=dGLbVzb-zSkzk&md5=3edbf10071b6ad505ebf1095f005d8fa&ie=/sdarticle.pdf