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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).

For example:

Alkali
Molecular
Compound
Molecular
Li
7
LiNO3
69
Na
23
LiOH.H20
42
K
39
Na2Oe
62

Moles of lithium in 1 liter of 30%-LiNO3 solution

Specific gravity of 30%- LiNO3 solution = 1.2
Mass of 1 liter of 30%- LiNO3 solution = 1200 g
Mass of LiNO3 in 1 liter = 30/100x (1200) = 360g
Number of moles of LiNO3 = 360/60 = 5.217 moles

Moles of sodium + potassium in 1 kg of Na2Oe

Number of moles of Na2Oe ini 1 kg Na2Oe =1000/62 = 16.13 moles
Number of moles of Na = 2 x 16.13 = 32.26

Volume of 30% - LiNO3 solution required for [Li]/[Na+K] = 0.74

Molar ratio for 1 liter 30%-LiNO3 solution per 1 kg Na2Oe = 5.217/32/26 = 0.162
Volume of 30%-LiNO3 solution for molar ratio of 0.74= 0.740/0.162=4.6 liters per 1 kg 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.

Topical 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 Photo. Spraying 30-percent lithium nitrate solution with a tanker truck on a concrete pavement near Mountain Home, Idaho. This photo shows a closeup view of a water truck spraying lithium nitrate on an A S R-affected pavement near Mountain Home, Idaho.

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.

Figure A4b.F3. Photo. Typical vacuum impregnation setup. Photo shows the side of a concrete barrier with extensive cracking covered by a red plastic mesh taped to it. A spiral plastic tube is adhered to the top of the mesh, near the top of the barrier by the contractor. The vacuum has been turned on, and the lithium is being vacuumed across the barrier, first starting in the lower right corner and radiating out towards the center of the barrier.
Figure A4b.F3. Typical vacuum impregnation setup.

Figure A4b.F4. Photo. Vacuum impregnation treatment in Houston on a concrete column. A metal slab is being applied to the side of a concrete column, and manages to stay on through a vacuum process. Several plastic clear tubes, taped together, are adhered to the metal slab, with one main grey tube attached to a compressor that let the solution penetrate the structure.
Figure A4b.F4. Vacuum impregnation treatment in Houston on a concrete column.

Electrochemical Treatment

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.

Figure A4b.F5. Photos. Electrochemical lithium treatment process. There are three photos of columns in Houston, Texas, that were selected for electrochemical treatment. The photo on the left shows irrigation tubes, wood splices, and metal strips placed on the column. The metal strips are attached to titanium mesh that runs inside holes drilled into the sides of the column. The photo in the middle shows a cellulose layer being applied to the side of a column. The photo on the right shows plastic sheeting placed on all sides of the column. The gutters attached under the sheeting collect excess lithium for reuse.
Figure A4b.F5.  Electrochemical lithium treatment process.

 
Updated: 04/07/2011
 

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