PermeNewal Vacuum Force and FMC Corporation's Renew^rLithium
Solution Attacks Alkali Silica Reaction


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   Complements of TECVAC, INC.

  Alkali Silica Reaction Testing

   From SHRP-C/FR-91-101

The only indisputable evidence that ASR has developed in concrete is the presence of ASR gel reaction products. In the early stages of reactivity, or under conditions where only small quantities are produced, ASR gel is virtually undetectable by the unaided eye, and revealed only with difficulty by a skillful observer using a microscope. Thus, ASR may go unrecognized in field structures for some period of time, possibly years, before associated severe distress develops to force its recognition and structure rehabilitation. Use of uranyl (uranium) acetate fluorescence method has been developed. This method can be used to monitor possible ASR prior to development of serious distress and to confirm ASR existence.

ASR is uniquely characterized by production of a gel-like reaction product. It is composed of essentially of silica, the alkalis (sodium and potassium), and calcium in the presence of water. Uptake of water by the gel is the primary factor determining volume changes associated with ASR. The gel may be present in large or minute amounts in aggregates, aggregate sockets, air voids, fractures, and on the surfaces of externally formed concretes. By application of uranyl acetate solution to a surface containing the gel, the uranyl ion substitutes for alkali in the gel, thereby imparting a characteristic yellowish-green glow when viewed in the dark using short wavelength (254 nanometer) ultraviolet light. ASR gel fluoresces much more brightly than the cement paste due to the greater concentration of alkali and, therefore, the uranyl ion in the gel.

EQUIPMENT AND
MATERIALS

 
The following equipment and materials are required to perform the test for the presence of ASR gel:
 

1. A source of 254 nanometer (short wavelength) ultraviolet (UV) light capable of producing a peak intensity of at least 1200uW/sq cm at 6 inches.

2. Powdered reagent grade uranyl acetate.

3. Plastic storage bottles and squeeze or spray bottles.

4. UV absorbing protective eye wear.

5. Protective eye wear for mixing chemicals.

6. Rubber gloves. (lightweight)

7. Provisions for admitting UV light from the lamp while excluding ordinary light. Viewing box for outside surface examination or dark room for core examination.

8. Surface preparation equipment to produce a fresh concrete surface or coring equipment.

 
1. Prepare dilute acetic acid solution by adding 5 mL of glacial acetic acid to deionized or distilled water to make up 200 mL of solution.

2. Add 5 g of uranyl acetate powder to the dilute acetic acid solution. Warm, but do not boil, to dissolve the powder.

3. Store in closed plastic bottles. Reagent solution has shelf life of a year or more.

 
While this procedure can be used on any concrete surface, experience has proved it best to investigate newly formed surfaces such as fractures, cores and sawed or ground surfaces.

Step 1. For old formed, old finish, wearing surface: Use a grinding wheel on electric drill or other means to grind off up to 1/4" of the concrete. Rinse with tap water.

Step 1. Fractured surface: Break off piece from concrete structure or fragment and rinse freshly fractured surface with tap water.

Step 1. New concrete core: Rinse off cylindrical surfaces after core extraction. Wash off coring slurry.

Step 2. With protective eye wear and rubber gloves on, apply uranyl acetate solution from plastic squeeze bottle or sprayer. It is only necessary to wet the surface.

Step 3. Allow the solution to react for 3-5 minutes and rinse the surface with water.

Step 4. Remove the rubber gloves and replace safety goggles with UV absorbing eye wear. View concrete surface using UV light in a darkened room or, when in the field, through viewing openings in a box that prevents light from reflecting on the concrete surface. Note: The surface can be viewed at later ages without further solution application. However it is advisable to first rewet the surface.

 
The presence of ASR gel will be revealed in UV light by a yellowish-green fluorescent glow. Deposits will be localized in cracks, air voids, certain aggregate particles and, in severe cases, as broad films in aggregate particles and fractured surfaces. Such films on sawed and cored surfaces may reflect as "smear" from sawing or cutting. Fractured surfaces eliminate this effect and most clearly reveal undisturbed ASR gel deposits.


Follow Precautions When Testing For ASR

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