Performance of Carbon-Neutral Rice Hull Ash as a Supplementary Cementitious Material In Portland Cement Concrete

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1 Performance of Carbon-Neutral Rice Hull Ash as a Supplementary Cementitious Material In Portland Cement Concrete Rangaraju, P.R. & Harish K.V. Clemson Univ. Vempati, R. ChK Group, Inc. Romain, J.C. Holcim Cements College Park, Maryland June 23 25, 2009

2 Acknowledgements o NSF SBIR Program o Anheuser-Busch Companies

3 o Portland cement Overview o Production & Hydration Reactions o Rice Hull Ash o Composition & properties o Pozzolanic reaction o Use as supplementary cementing material o Implications for RHA as a sustainable construction material

4 Portland Cement o Portland cement was patented by a British Mason, Joseph Aspdin, in o Portland cement is a mixture of: o Calcium Silicates o Calcium Aluminates o Calcium Sulfate (Gypsum) o The principal raw material used in production of Portland cement is limestone (CaCO 3 ) and Clay.

5 Manufacture of Portland Cement o Limestone and Clay are heated in a rotary kiln to temperatures between degrees Celsius. o CaCO 3 CaO + CO 2 (upon heating) o CO 2 is a principal greenhouse gas. o 1 ton of Cement produces 1 ton of CO 2 gas.

6 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 7

8 Concrete Construction Bridges Buildings Dams 8

9 Concrete Construction Platforms Runways Highways 9

10 Facts about concrete usage o Besides water, concrete is the most used material by humans. o Annually, 7 billion cubic yards of concrete is used worldwide ( ). o 1 cu. yd of concrete per person per yr.

11 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

12 Rice Hull o Rice Husk is the outside shell of a Rice Grain

13 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.

14 Chemical Composition of RHA Oxides Zhang et al [1996] Nehdi et al [2003] Vempati [2008] % % % CaO SiO Al 2 O Fe 2 O MgO Na 2 O eq Carbon P 2 O

15 Physical Properties of RHA o 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 m 2 per kg BET method)

16 Microstructure of RHA

17 Microstructure of RHA

18 Pozzolanic Reactivity of RHA SiO 2 + Ca(OH) 2 Ca-Si-H Gel o Additional Ca-Si-H gel produced by RHA helps improve properties of portland cement concrete

19 Experimental Program o 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

20 Pozzolanic Reactivity of RHA

21 Compressive strength of mortar

22 Corrosion of Steel in Bridges

23 Chloride Ion Permeability in Concrete

24 Workability o 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.

25 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 CO 2 gas.

26 Conclusions o 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.

27 Thank you!

28 Rice Hull Production o 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.