Mitigating Alkali Silicate Reaction using Fly Ash ACI Spring 2008 Convention Los Angeles, CA by Dr. David L. Gress Recycled Materials Resource Center Department of Civil Engineering University of New Hampshire

Acknowledgements RMRC FHWA

ASR, what is it? Reactive Aggregates Alkali High pH Calcium ASR gel

ASR Background 1922 - Buck Hydroelectric Plant (New River, Virginia) ASR distress within 10 years Thomas E. Stanton 1938, PCC Failure (California) 1st Published Article on ASR (ASCE)

ASR Gel Forms in concrete pore system Swells with water absorption Tensile stresses cause concrete to fail

Materials and Mitigation Strategies Low Alkali Cement ( 0.3 Na2Oeq) Class F Fly Ash (15 to 25% Substitution) Ground Granulated Blast Furnace Slag (GGBFS) (25 to 55% Substitution) Lithium Nitrate (70 to 150% Dosage) Silica Fume Blended Cement (7 to 12% Substitution) Metakaolin (10 % Substitution) Class C Fly Ash (>>35%)

Class F Fly Ash Burning Pulverized Bituminous Coal Low Calcium Content Pozzolan + H2O + Ca(OH)2 = CSH Consumes Calcium Ties up Alkali in CSH pH lowers and ASR stops Supplements the Portland Cement Improved Density and Permeability

Class C Fly Ash Burning Pulverized Sub-bituminous Coal High Calcium Content Higher Alkali content Higher Alkali Solubility Requires Higher Dose to be Effective Pozzolan + H2O + Ca(OH)2 = CSH Ties up Alkali but also contributes Alkali and Calcium Supplements the Portland Cement Improved Density and Permeability

Accepted Testing Procedures ASTM C1260 (Mortar –Bar Method) ASTM C1293 (Standard Prism Beam)

ASTM C 1260 1 x 1 x 11” samples Submerged in 1N NaOH 80° C (176° F) 14-day test duration > 0.10 % expansion shows potentially ASR reactive aggregate

ASTM C 1293 3 x 3 x 11” samples Over water 38° C (100° F) 100% RH 1 to 2 year test duration > 0.04 % expansion shows potentially ASR reactive concrete

Effect of Fly Ash and Slag on Alkali-Silica Reactivity Fig. 3-21. Effect of different fly ashes and slag on alkali-silica reactivity. Note that some ashes are more effective than others in controlling the reaction and that dosage of the ash or slag is critical. A highly reactive natural aggregate was used in this test. A less reactive aggregate would require less ash or slag to control the reaction. A common limit for evaluating the effectiveness of pozzolans or slags is 0.10% expansion using this rapid mortar bar test (Detwiler 2002).

Colorado Springs Airport

Colorado Springs Airport

Colorado Springs Airport

Tri Services (Navy, Air Force, Army) DOD Guide Specifications for airfields 32 DOD airports have ASR Class F Fly Ash only

Mitigation of Alkali-Silica Reactivity in New Mexico R Mitigation of Alkali-Silica Reactivity in New Mexico R. Gordon McKeen, P.E. etal

> 35 % Class C required

> 40 % Class C required