Pozzolanic By-Products In Concrete Marcia C. Belcher, MSCE

Chloride Permeability of Concrete Corrosion of reinforcing steel Corrosion of reinforcing steel Internal stresses Internal stresses Cracking and spalling of concrete Cracking and spalling of concrete Loss of structural integrity and serviceability Loss of structural integrity and serviceability

Water Permeabilty and Freeze Thaw Resistance Concrete surfaces may be damaged by frost action either before or after the concrete has set. Concrete surfaces may be damaged by frost action either before or after the concrete has set. The expansion of water while freezing exerts a force sufficient to destroy the cohesion between particles. The expansion of water while freezing exerts a force sufficient to destroy the cohesion between particles. Pressures develop within the material as ice formation continues. Pressures develop within the material as ice formation continues. Spalling, scaling and cracking occur when the concrete cannot withstand the stress of the expansion and contraction associated with freeze/thaw. Spalling, scaling and cracking occur when the concrete cannot withstand the stress of the expansion and contraction associated with freeze/thaw.

Pozzolans in Concrete Pozzolans are cementitious in presence of moisture and calcium hydroxide (Portland cement) Pozzolans are cementitious in presence of moisture and calcium hydroxide (Portland cement) All of the pozzolans used today are by-products of other manufacturing processes. All of the pozzolans used today are by-products of other manufacturing processes. Use of them in concrete will: Use of them in concrete will:  Reduce exothermic reaction  Reduces thermal cracking  Produce finer microstructure  Reduce water permeability  Increases resistance to chloride penetration

Manufacture of Portland Cement Each ton of cement manufactured consumes approx. 6.5 million. Each ton of cement manufactured consumes approx. 6.5 million. Enough electricity to power the average American home for 24 days. Enough electricity to power the average American home for 24 days. Carbon dioxide emission equal to two months use of an automobile. Carbon dioxide emission equal to two months use of an automobile. It is estimated that cement production contributes to about 7 percent of carbon dioxide emissions from human sources It is estimated that cement production contributes to about 7 percent of carbon dioxide emissions from human sources

Some Pozzolans Used in Concrete Ground-granulated blast furnace slag (GGBFS) Ground-granulated blast furnace slag (GGBFS) Fly ash Fly ash Silica Fume Silica Fume

Fly Ash COAL COMBUSTION BY-PRODUCT COAL COMBUSTION BY-PRODUCT Fossil fuels are used in modern power plants to produce electric energy. Fossil fuels are used in modern power plants to produce electric energy. The inorganic residues that remains after pulverized coal is burned are known as ‘coal combustion by-product'. The inorganic residues that remains after pulverized coal is burned are known as ‘coal combustion by-product'. One of these by-products is “fly ash” One of these by-products is “fly ash” Captured in the exhaust of the boiler system. Captured in the exhaust of the boiler system.

Fly Ash Coal combustion by-products rapidly accumulate and cause enormous problems of disposal unless they can be utilized Coal combustion by-products rapidly accumulate and cause enormous problems of disposal unless they can be utilized In 2006, there were approx. 125 million tons of ash product produced in the US In 2006, there were approx. 125 million tons of ash product produced in the US Approx. 43% is recycled Approx. 43% is recycled Use of coal combustion products has increased more than 50% in the past decade Use of coal combustion products has increased more than 50% in the past decade

Fly Ash Fly Ash particles Fly Ash particles  250 micrometers in size  spheroidal

Fly Ash in Concrete Pozzolanic Pozzolanic Spherical particles increase workability Spherical particles increase workability Reduces heat of hydration Reduces heat of hydration Low early strength Low early strength

Silica Fume By-product from the production of metals in electric arc furnaces. By-product from the production of metals in electric arc furnaces. When added to concrete When added to concrete  Produces finer microstructures  Acts as a 'pozzolan,' reacting chemically to impart greater strength and durability to concrete

Silica Fume Very fine gray powder of spherical particles Very fine gray powder of spherical particles Particles average 0.1 to 0.3 microns in diameter Particles average 0.1 to 0.3 microns in diameter Glassy surface Glassy surface Surface area of 17 to 30 m 2 /g Surface area of 17 to 30 m 2 /g

Ground Blast Furnace Slag. In the production of iron, two products are obtained from the furnace: molten iron and slag. Slag comes from the furnace at 2700 F Resembles molten lava, cools and solidifies

Ground Blast Furnace Slag When ground and added to concrete: When ground and added to concrete:  pozzolanic  improves workability  improves chloride resistance  decreases water permeability  increases compressive strength

Test Method for Determining Chloride Ion Penetration Rapid Chloride Permeability Applied Voltage Cell

Typical Rapid Chloride Permeability Test Result Curve

Rapid Chloride Test Results for GGBFS Group 28-Day 90-Day Low Moderate High Very Low

Rapid Chloride Permeability Test Results for Fly Ash and Silica Fume Mixes Very Low Low Moderate High

28-Day Compressive Strength Data for GGBFS Group

28-Day Compressive Strength Data for Fly Ash and Silica Fume Group

Conclusions Benefits of pozzolans Benefits of pozzolans  Increased resistance to chloride penetration.  May increase compressive strength of concrete in appropriate proportions.