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Role of Cement & Concrete in

Kimberly Kurtis

School of Civil & Environmental Engineering

Sustainable Development

School of Civil & Environmental Engineering, Georgia Institute of Technology

Engineers for a Sustainable WorldNovember 15, 2012

Outline

Context– Why do we care about cement and concrete, in particular?

Case Study– Assessment and Utilization of Recycled Aggregate

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What are cement & concrete?Some common mineral cements: – portland (calcium silicate-based)– calcium aluminate

d t l d b t

– gypsum (plaster of paris)– calcium sulfoaluminate

l i ili t

Cement paste = +

M t

– some dental and bone cements – aluminosilicate

Mortar = + +

Concrete = + + +

Impacts of Infrastructure on EnvironmentAt the global level, the built environment in each country is estimated to account for:

25-40% of the energy consumption 30-40% of the material resource consumption 30-40% of the waste production 30-40% of the greenhouse gas (GHG) release

70% of raw materials consumed are used in

construction

Materials manufacture (cement, plastics, metals) currently accounts for 20-25% of

Source: http://www.ntnu.no/sustainability/crucial

Each year, 200M tons of construction wastes are discarded in landfills

worldwide energy consumption

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Why do we care about cement & concrete?The ubiquity of concrete construction presents an incredible opportunity for impact through development of innovative green technologies

With >20Bt placed each year, concrete is most widely used construction material

Ashby, 2009

Concrete ProductionEmbodied energy associated with concrete production

PCA, SN3001

~ ¼ barrel oil per yard or ~ 2 tons of concrete

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Cement Manufacture: ReviewTraditional cement manufacture:

Utilizes virgin materials: 1.5 t raw material is required for 1 t cementEnergy intensive: 6-8% worldwide fuel consumption

CaCO3 (limestone)2SiO2•Al2O3 (clay, shale)Fe2O3 (iron oxide)SiO2 (silica sand)

Kiln

Fossil fuel intensive Liberates CO2: CaCO3 –heat-> CaO + CO2 ( )

3CaO•SiO22CaO•SiO23CaO•Al2O34CaO•Al2O3•Fe2O3Clinker

intergroundFinishedcement

Gypsum +

CaO•SO3•2H2O

Kiln

CaCO3 60%

Fuel 40%

CO2 Emissions

WRI, 2005

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Cement ManufactureTremendous (40%) improvements in energy efficiency Alternatives to fossil fuel combustion would decrease CO2emissions associated with energy use– Waste fuels – Hydro (regional, enviro concerns)

N l ( i ) S l (i ffi i t)– Nuclear (enviro concerns) – Solar (inefficient)

Carbon capture??? Wet process (pre-1970’s)

Dry process (modern)

CementWater

AirFine Aggregate

65-75% of volume

Role of Aggregates? Recycled waste/by-product materials– recycled concrete

recycled tires

Coarse Aggregate

is stone & sand– recycled tires– slag…

Potential for CO2capture/sequestration– reaction with hydrated cement

in recycled concrete aggregates

– overcoming crushing energy critical for this application

Pervious concrete– control runoff– filtration

pervious concrete layer

open-graded gravel basesources: PCA; Offenburg, Conc. Int., 2005.

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Outline

Context– Why do we care about cement and concrete, in particular?

Case Study– Assessment and Utilization of Recycled Aggregate

Recycled Aggregate ConcreteAggregate extraction can contribute to: – Particulate matter generation/ release

N i ll ti

Each year, 200M tons of construction wastes are discarded in landfills;

100M tons are concrete– Noise pollution– Energy consumption (<10% of

concrete EE) – GHG emissions (<< cement)

Aggregate is a high bulk, low value commodityRecycled concrete aggregate (RCA) is primarily used low-value applications; in road base and as fill, with more limited usage in structural concrete

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Why would we want to use this as a case study? y“Scientists warned… (the earth) has not created a significant number of new rocks since the earth cooled some 3.5B years ago.Moreover, … (this supply has) been very slowlyhas) been very slowly depleting… due to growing demand for fireplace mantels, rock gardens, gravel and paperweights.”

Source: The Onion

Recycled Aggregate ConcreteRecycling concrete as aggregate makes most economic and ecological sense in regions that are:– Space constrained

Resource constrained– Resource constrained– Other (e.g., economic incentives,

abundance of recyclable material)

Increasing rates of aggregate recycling have largely stemmed from increased taxation on both mineral extraction and waste landfilling.

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Recycling Aggregate in CaribbeanThe 2010 Haiti earthquake resulted in ~20 million cubic yards of debris, enough to fill the Louisiana Superdome five times over .It is estimated that debris removal could take 20 years or more to accomplish at current removal rates. Two years following the earthquake in Haiti, reconstruction progresses slowly.

What to do with debris?In Haiti, as in other Caribbean islands:– Population density is high; landfilling debris is not a viable option– Environmental issues likely prevent use as fill or in artificial reefs– Limited natural resources for new constructionLimited natural resources for new construction

Finding a way to safely reuse the debris can have a huge positive impact on rebuilding efforts, while simultaneously minimizing the impact on the environment, and ultimately is a key to accelerating reconstruction.

Lessons learned canLessons learned can be applied in other countries and after other types of events

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Research Plan

Objective: To determine if Haitian concrete debris could be combined with other local materials to produce good quality concrete.quality concrete.Steps:– Obtain Haitian concrete and local fine aggregate; assess their

quality– Crush concrete to produce aggregate– Characterize recycled aggregate and local virgin aggregates to

obtain properties needed for mix design– Design, produce, and test concrete mixes – Assess long-term performance

Haitian Concrete QualityProportioning often done by eyeMixing performed often by hand

fcave= 1300psi

56-day strength results for cylinders batched and cast in Haiti

Low strength of debris is a significant challenge for reuse in structural concrete

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Concrete Aggregate Concrete

Concrete Strength Results

fcave= 1300psiHow can a concrete strength be greater than the strength of the

Concrete used as Aggregate

fcave= 3100psi

aggregate from which it is produced?

Recycled Aggregate Concrete

ave p

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Further Testing/Implementation

Variation with RCA source– Define limits on properties– Develop specificationsDevelop specifications

Long-term performance– Shrinkage, creep– Durability– Seismic behavior of RCA concrete

Environmental impacts– LCI/LCA– LCI/LCA– Dynamic assessment needed during reconstruction

Based upon these results Systematic recycling efforts can be developedhttp://www.statesman.com/blogs/content/shared-gen/blogs/austin/charity/entries/2011/01/10/haiti_one_year_later.html

Assessment of seismic performance of code-based and underreinforced beam-column connections, containing virgin and recycled concrete aggregate.

Further Testing/Implementation

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Questions?