|FHWA > Engineering > Pavements > Concrete > Alkali-Silica Reactivity (ASR)|
How is lithium used to control ASR?
Lithium can be used effectively in new concrete as a preventative for future ASR susceptibility, and is being explored as an option for treating existing concrete showing signs of deterioration due to ASR. In new concrete, Lithium is used as an admixture. As treatment for existing concrete, lithium compounds are generally vacuum or electrochemically impregnated into the surface of the concrete for best results.
How is it used in early concrete?
The amount of lithium, as an admixture, required to suppress expansion depends upon the form of lithium, the nature of the reactive aggregate and the amount of alkali in the concrete. Many studies have shown that the expansion of concrete for a given aggregate depends on the amount of lithium relative to the amount of sodium plus potassium in the mortar or concrete mixture. This has led to the use of the molar ratio [Li]/[Na+K] for expressing the lithium dose in mortar and concrete mixtures, where [Li] is the number of moles of lithium and [Na+K] is the sum of the moles of sodium plus the moles of potassium present in the mixture.
Mc Coy and Caldwell’s (1951) data showed that expansion was largely eliminated if the lithium-to-sodium-plus-potassium ratio was equal to or greater than 0.74; i.e. [Li]/[Na+K] ≥ 0.74. A number of recent laboratory studies have confirmed this finding and [Li]/[Na+K] = 0.74 has become the “standard dose” for controlling ASR in concrete containing reactive aggregate.
The common lithium compound that is commercially available for use as a concrete admixture is a solution containing 30% lithium nitrate (LiNO3). To achieve a molar ratio of [Li]/[Na+K] = 0.74 requires the addition of 4.6 liters of 30% LiNO3 solution for every 1.0 kg of Na2Oe in the mixture (0.55 gallons of solution for every 1.0 lb of Na2Oe).
Although the "standard dose" of [Li]/[Na+K] = 0.74 appears to be sufficient to control expansion with a great many aggregates, it is not sufficient for all aggregate types (Lane, 2000; 2002; Durand, 2000; Tremblay, 2004), and higher doses are required. With some aggregates, a dose of 1.5 times the standard dose, i.e. [Li]/[Na+K] = 1.11, may still not be sufficient to suppress damaging ASR (Tremblay, 2004). It is recommended that amount of lithium required to control expansion with a particular aggregate is determined by appropriate testing methods.
To determine the amount of lithium required to control ASR with a specific aggregate, it is recommended that the combination of materials be tested using a modification of the concrete prism test (ASTM C 1293). The only modifications necessary are to add the required amount of lithium nitrate solution to the mix water and to correct the total water content for the water contained in the lithium nitrate solution. The test should be conducted at a range of different lithium doses to determine the minimum amount required to control expansion (< 0.040% at 2 years) with the aggregate under consideration.
How is it used in existing concrete?
Lithium nitrate has been applied to existing concrete structures affected by ASR through three methods: topical treatment, vacuum impregnation treatment, and electro-chemical impregnation treatment.
Several structures, including pavements, bridge decks and median barriers, have been treated by spraying the surface of the structure with lithium nitrate solution, most commonly using a 30% LiNO3 solution.
Figure A4b.F2. Spraying 30-percent lithium nitrate solution with a tanker truck on a concrete pavement near Mountain Home, Idaho.
Vacuum Impregnation Treatment
Vacuum impregnation is used to inject lithium nitrate into the concrete structure using negative pressure (by the vacuum), allowing the material to penetrate through the structure’s cracks. Several structures have been treated using this method, including a section of concrete barriers near Leominster, Massachusetts, a set of columns in Houston, Texas, and concrete girders in Corpus Christi, Texas.
Electrochemical treatments are based on an extraction technique (electrochemical chloride), using approximately 40 D.C. volts between the surface anode and the reinforcement steel in the concrete (which would serve as the cathode). The lithium solution would be left ponded at the surface, and its ion (+) would be repelled by the (+) charged anode, and drawn towards the steel reinforcement (-) ions. This treatment typically takes about 4 to 8 weeks.
In March 2006, two concrete columns in Houston, Texas were treated under the FHWA Lithium Technology Program using this treatment method, and the treatment took 8 weeks to complete.