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Rangaraju, P.R. & Harish K.V. Clemson Univ.
Vempati, R. ChK Group, Inc.
Romain, J.C. Holcim Cements
Performance of Carbon-Neutral Rice Hull Ash as a Supplementary CementitiousMaterial In Portland Cement Concrete
College Park, MarylandJune 23 – 25, 2009
Acknowledgements
o NSF SBIR Program
o Anheuser-Busch Companies
Overviewo Portland cement
o Production & Hydration Reactions
o Rice Hull Asho Composition & propertieso Pozzolanic reactiono Use as supplementary cementing material
o Implications for RHA as a sustainable construction material
Portland Cemento Portland cement was patented by a
British Mason, Joseph Aspdin, in 1824.o Portland cement is a mixture of:
o Calcium Silicateso Calcium Aluminateso Calcium Sulfate (Gypsum)
o The principal raw material used in production of Portland cement is limestone (CaCO3) and Clay.
Manufacture of Portland Cemento Limestone and Clay are heated in a rotary
kiln to temperatures between 1400 - 1500 degrees Celsius.
o CaCO3 CaO + CO2(upon heating)
o CO2 is a principal greenhouse gas.
o 1 ton of Cement produces 1 ton of CO2 gas.
Facts about cement usage
o The United States used more than 122 million metric tons of Portland cement in 2006, and China used about 800 million metric tons.
7
Volume Proportions in Concrete
8
Concrete Construction
Bridges Buildings Dams
9
Concrete ConstructionPlatforms Runways
Highways
Facts about concrete usageo Besides water, concrete is the most
used material by humans.
o Annually, 7 billion cubic yards of concrete is used worldwide (2006 –2007).
o 1 cu. yd of concrete per person per yr.
Hydration Reactions of Cement
o Calcium Silicates + Water Ca-Si-H Gel + Ca(OH)2
o Ca-Si-H Gel contributes to strength and long-term durability
o Ca(OH)2 does not contribute to the strength and can potentially lead to reduced strength and lowered durability
Rice Hullo Rice Husk is the outside shell of a Rice
Grain
Rice Hull Ash (RHA)o RHA is produced by controlled combustion of rice
husks.
o RHA has a high silica content (85% -95%)
o The degree of combustion affects whether the silica produced is amorphous or crystalline
o Amorphous silica is essential for reaction with cement
o Uncontrolled combustion process can result in significant unburnt carbon content in the ash.
Chemical Composition of RHA
% % %CaO 0.55 0.6 -SiO2 87.2 89.1 94.8Al2O3 0.15 0.1 0.52Fe2O3 0.16 0.04 0.13MgO 0.35 0.5 -
Na2O eq 3.54 0.86 2.92Carbon 5.91 5.1 0.24P2O5 0.5 0.9 1.09
Vempati [2008]Oxides
Zhang et al [1996]
Nehdi et al [2003]
Physical Properties of RHAo Average particle size of unground ash is in
the range of 70 to 100 microns.
o Specific gravity of RHA is 2.1
o Color of RHA is off-white, due to its low carbon content.
o High internal porosity and high specific surface area (~30,000 m2 per kg – BET method)
Microstructure of RHA
Microstructure of RHA
Pozzolanic Reactivity of RHA
SiO2 + Ca(OH)2 Ca-Si-H Gel
o Additional Ca-Si-H gel produced by RHA helps improve properties of portland cement concrete
Experimental Programo Mortars and concrete specimens containing RHA as
a cement replacement material were prepared.
o RHA was used at 0%, 5%, 10%, 15% and 20% replacement levels.
o Different properties were evaluated:o Pozzolanic reactivity (Ca(OH)2 content), o Compressive and flexural strength, o Workability, o Setting time, o Chloride permeability o Other properties
Pozzolanic Reactivity of RHA
Compressive strength of mortar
Corrosion of Steel in Bridges
Chloride Ion Permeability in Concrete
Workabilityo RHA being a vesicular material with
very high specific surface area, reduces the workability of concrete.
o However, workability can be regained by addition of superplasticizers.
Role of RHA as a Supplementary Cement
o Portland cement can be partially replaced by RHA to impart beneficial properties.
o RHA can be used to replace as much as 10% to 20% by mass of cement.
o 1 ton of Cement produces 1 ton of CO2gas.
Conclusionso Increased strength and durability of
concrete leads to longer-lasting concrete infrastructure.
o Reduced use of Portland cement leads to conserving natural resources
o Reduced carbon-foot print of concrete improves environment.
Thank you!
Rice Hull Productiono Current world production of rice grain:
o ~600 million tons/year
o ~1/5 of the rice grain weight is that of rice hull
o ~1 ton of rice husk produces about 200 kg of Rice Husk Ash
o RHA is a carbon-neutral material
o Use of RHA can make concrete more environmentally friendly and sustainable.
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