Courtney Collins. Jason Ideker. Gayle Willis. Jessica Hurst
Alkali-Silica Reaction: The Cancer of Concrete Slide 2 What is ASR
and why is it important? How does ASR work? How can ASR damage be
prevented? Outline Slide 3 Alkali Silica Reaction (ASR) Alkalis +
Reactive Silica + Moisture ASR Gel which expands Concrete cracking
What is ASR? Slide 4 Concrete failure due to ASR AASHTO Innovative
Highway Technologies Georgia Tech School of CEE - Courtney Collins
Slide 5 Concrete quality Loss of strength, stiffness,
impermeability Premature failure of concrete structures
Economic/Environmental impacts ASR lowers concrete lifetime Less
reactive aggregates often expensive or difficult to find Cement
production creates 7% of the worlds CO 2 emissions (a greenhouse
gas). Why is it important to study ASR? Slide 6 Hydroelectric dam
built in 1938 180 mm of arch deflection due to alkali silica gel
expansion Cracking and gel flow in concrete Case Study: Parker Dam,
California http://www.acres.com/aar/Alkali-Aggregate Reactions in
Hydroelectric Plants and Dams: Slide 7 Possible ASR damage on
concrete retaining wall - picture taken 1/2002 Case Study: I-85 -
Atlanta, Georgia Slide 8 What we know: What we dont know: Which
reactants involved and their sources How alkali-silica gel is
created ASR prevention can be achieved by using low alkali cement
and non-reactive aggregate Additives such as lithium compounds and
pozzolanic material help prevent ASR damage Mechanism of gel
expansion Lithium: its mechanism of inhibition, which compounds
work best, how much of each compound is needed to prevent expansion
How does ASR work? Slide 9 Creation of alkali-silica gel Slide 10
Reactants: alkalis, reactive silica, and water Alkalis Main
cations: Sodium (Na + ) Potassium (K + ) Common sources: Portland
cement Deicing agents Seawater Creation of alkali-silica gel Slide
11 Reactive Silica Silica tetrahedron: Amorphous Silica Crystalline
Silica Creation of alkali-silica gel Slide 12 Reactive Silica
Creation of alkali-silica gel Amorphous silica = most chemically
reactive Common reactive rocks: opal obsidian cristobalite
tridymite chelcedony cherts cryptocrystalline volcanic rocks
strained quartz Slide 13 Water Found in pore spaces in concrete
Sources: Addition of water to concrete mixture Moist
environment/permeable concrete Creation of alkali-silica gel Slide
14 1. Aggregate in solution, pre-ASR damage Creation of
alkali-silica gel Slide 15 2. Surface of aggregate is attacked by
OH - H 2 0 + Si-O-SiSi-OHOH-Si Creation of alkali-silica gel Slide
16 3. Silanol groups (Si-OH) on surface are broken down by OH -
into SiO - molecules Si-OH + OH - SiO - + H 2 0 Creation of
alkali-silica gel Slide 17 4. Released SiO - molecules attract
alkali cations in pore solution, forming a gel around the aggregate
Creation of alkali-silica gel Slide 18 5. Alkali-silica gel takes
in water, expanding and exerting a force against surrounding
concrete. Creation of alkali-silica gel Slide 19 6. When the
expansionary pressure exceeds the tensile strength of the concrete,
the concrete cracks Creation of alkali-silica gel Slide 20 7. When
cracks reach the surface of the structure, map cracking results
Creation of alkali-silica gel Slide 21 Images of ASR damage Slide
22 Slide 23 Slide 24 How to prevent ASR damage Slide 25 Avoid high
alkali content: use low alkali portland cement replace cement with
pozzolanic admixtures Avoid reactive aggregate (amorphous silica)
Control access to water Use lithium additives prior to placement of
concrete or as a treatment in already existing concrete Alkalis +
Reactive Silica + Moisture ASR Gel Slide 26 ANY QUESTIONS?
