The Effect of Lithium-Based Admixtures

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Title: The Effect of Lithium-Based Admixtures

Author(s): M. D. A. Thomas, D. Stokes, and T. Rodgers

Publication: Special Publication

Volume: 217

Issue:

Appears on pages(s): 483-498

Keywords: admixture; alkali-silica reaction; concrete; durability; lithium

Date: 9/1/2003

Abstract:
The ability of lithium-based compounds to suppress deleterious expansion due to alkali-silica reaction (ASR) in mortar and concrete was first demonstrated over 50 years ago. Lithium nitrate solution is now marketed in North America as a chemical admixture for inhibiting ASR; the product currently available is a 30% solution of LiNO3. The purpose of the study reported here was to determine to what extent a chemical admixture based on lithium nitrate influences the properties of fresh and hardened concrete when used at the dosage levels required to suppress expansion due to ASR. This was done by comparing the fresh and hardened concrete properties of a number of mixtures with and without the admixture. The constituent materials and concrete mixture proportions used in the study were based on those currently approved for the Class AA Structural Concrete for a major highway project in Albuquerque, New Mexico. These materials included a Type II portland cement, Class F fly ash, a reactive aggregate, and water-reducing and air-entraining admixtures. The water-to-cementitious-material ratio of the concrete was in the region of W/CM = 0.35. All of the concretes tested had either no air entrainment, or air contents in the range of 5% to 7%, slump values between 100 mm to 125 mm and strengths in the region of 32 MPa to 36 MPa. The use of lithium nitrate solution, at the levels of addition necessary to effectively control expansion due to ASR, appeared to have no adverse effect on the properties of fresh and hardened concrete, even at dosages in excess of 10 litres per cubic metre. Changes in the measured slump, air content and setting time of plastic concrete were generally insignificant. Tests on sawn concrete samples confirmed that the use of lithium had no impact on the hardened air-void parameters. Physical testing of hardened concrete showed that the use of lithium had little significant or consistent effect on the concrete strength or its durability as defined by the resistance of specimens to the penetration of chlorides or cyclic freezing and thawing.