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