Role of Cement & Concrete in Sustainable Development

Transcription

1 Role of Cement & Concrete in Sustainable Development Kimberly Kurtis School of Civil & Environmental Engineering, Georgia Institute of Technology Engineers for a Sustainable World November 15, 2012 Outline Context Why do we care about cement and concrete, in particular? Case Study Assessment and Utilization of Recycled Aggregate 1

2 What are cement & concrete? Some common mineral cements: portland (calcium silicate-based) calcium aluminate gypsum (plaster of paris) calcium sulfoaluminate some dental and bone cements aluminosilicate ili Cement paste = + Mortar = + + Concrete = Impacts of Infrastructure on Environment At 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 Materials manufacture (cement, plastics, metals) currently accounts for 20-25% of worldwide energy consumption 70% of raw materials consumed are used in construction Source: Each year, 200M tons of construction wastes are discarded in landfills 2

3 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 Production Embodied energy associated with concrete production ~ ¼ barrel oil per yard or ~ 2 tons of concrete PCA, SN3001 3

4 Cement Manufacture: Review Traditional cement manufacture: Utilizes virgin materials: 1.5 t raw material is required for 1 t cement Energy intensive: 6-8% worldwide fuel consumption Fossil fuel intensive Liberates CO 2 : CaCO 3 heat-> CaO + CO 2 ( ) CaCO 3 (limestone) 2SiO 2 Al 2 O 3 (clay, shale) Fe 2 O 3 (iron oxide) SiO 2 (silica sand) CO 2 Emissions Kiln CaCO 3 60% Fuel 40% Finished cement CaO SO 3 2H 2 O Gypsum + Clinker interground 3CaO SiO 2 2CaO SiO 2 3CaO Al 2 O 3 4CaO Al 2 O 3 Fe 2 O 3 WRI,

5 Cement Manufacture Tremendous (40%) improvements in energy efficiency Alternatives to fossil fuel combustion would decrease CO 2 emissions associated with energy use Waste fuels Hydro (regional, enviro concerns) Nuclear (enviro concerns) Solar (inefficient) i Carbon capture??? Wet process (pre-1970 s) Dry process (modern) Role of Aggregates? Recycled waste/by-product materials recycled concrete recycled tires slag Potential for CO 2 capture/sequestration reaction with hydrated cement in recycled concrete aggregates overcoming crushing energy critical for this application Pervious concrete control runoff filtration sources: PCA; Offenburg, Conc. Int., Cement Water Air Fine Aggregate 65-75% of volume is stone & sand pervious concrete layer open-graded gravel base Coarse Aggregate 5

6 Outline Context Why do we care about cement and concrete, in particular? Case Study Assessment and Utilization of Recycled Aggregate Recycled Aggregate Concrete Aggregate extraction can contribute to: Particulate matter generation/ release Noise pollution Energy consumption (<10% of concrete EE) GHG emissions (<< cement) Each year, 200M tons of construction wastes are discarded in landfills; 100M tons are concrete Aggregate is a high bulk, low value commodity Recycled concrete aggregate (RCA) is primarily used lowvalue applications; in road base and as fill, with more limited usage in structural concrete 6

7 Why would we want to use this as a case study? 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 slowly depleting due to growing demand for fireplace mantels, rock gardens, gravel and paperweights. Source: The Onion Recycled Aggregate Concrete Recycling concrete as aggregate makes most economic and ecological sense in regions that are: Space 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. 7

8 Recycling Aggregate in Caribbean The 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 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 can Lessons learned can be applied in other countries and after other types of events 8

9 Research Plan Objective: To determine if Haitian concrete debris could be combined with other local materials to produce good 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 Quality Proportioning often done by eye Mixing performed often by hand fc ave = 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 9

10 Concrete Aggregate Concrete Concrete Strength Results Concrete used as Aggregate fc ave = 1300psi How can a concrete strength be greater than the strength of the aggregate from which it is produced? Recycled Aggregate Concrete fc ave = 3100psi ave 10

11 Further Testing/Implementation Variation with RCA source Define limits on properties Develop specifications Long-term performance Shrinkage, creep Durability Seismic behavior of RCA concrete Environmental impacts LCI/LCA Dynamic assessment needed during reconstruction Based upon these results Systematic recycling efforts can be developed ater.html Further Testing/Implementation Assessment of seismic performance of code-based and underreinforced beam-column connections, containing virgin and recycled concrete aggregate. 11

12 Questions? 12