U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This report is an archived publication and may contain dated technical, contact, and link information |
|
Publication Number: FHWA-HRT-06-133 Date: March 2007 |
In 1951, McCoy and Caldwell published data showing that the incorporation of various lithium compounds (LiCl, Li2CO3, LiF, Li2SiO3, LiNO3, and Li2SO4) in mortars (ASTM C227) containing highly reactive Pyrex ® glass could control damaging alkali-silica reaction provided the lithium was present in sufficient quantity. Although little work was conducted in the 40 years that followed the publication of this paper, there has been renewed interest in the use of lithium as an admixture, starting with the work conducted under the SHRP program (SHRP-C-343), and the last 15 years has seen the publication of numerous papers on the subject. Detailed reviews of the literature have been published elsewhere (Folliard et al., 2005; Feng et al., 2005).
The amount of lithium 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.
McCoy 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.
At the time of writing this guideline, the only commercially available lithium compound for use as a concrete admixture is a solution containing 30 percent lithium nitrate (LiNO3). To achieve a molar ratio of [Li]/[Na+K] = 0.74 requires the addition of 4.6 L of 30-percent LiNO3 solution for every 1.0 kg of Na2Oe in the mixture (0.55 gal of solution for every 1.0 lb of Na2Oe), as shown in table 9.
Table 9. Example showing calculation of [Li]/[Na + K] molar ratio.
Specific gravity of 30% LiNO3 solution = 1.2 |
|
The accelerated mortar bar test (ASTM C1260) cannot be used to evaluate lithium without significant modification. Immersion of the mortar bars in the high temperature alkaline solution overwhelms the mortar bar with alkali and changes the [Li]/[Na+K]. Proposed modifications have included adding lithium to both the mortar mixture and the soak solution using the same [Li]/[Na+K] ratio. However, there is currently little information available to confirm whether the lithium dose determined using a modified version of the accelerated mortar bar test is similar to that determined using the longer-term concrete prism test and field experience.
The use of lithium nitrate solution, at the levels of addition necessary to effectively control expansion due to ASR, has no adverse effect on the properties of fresh and hardened concrete, even at dosages in excess of 10 liters per cubic meter. The use of lithium nitrate may slightly enhance the workability of concrete (i.e., there is a small water-reducing effect) and lead to small decreases in the setting time (i.e., slight set-accelerating effect).