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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. In addition, due to the difficulties associated with interpretation of field inspections of distressed concrete, it is often misdiagnosed leading owners to implement rehabilitation strategies that are ineffective with ASR. It is therefore important to implement procedures and methodology in the field that will successfully diagnose potential ASR reactivity as soon as possible so proper rehabilitation methods can be implemented that will be successful in extending the useful life of concrete pavement and structures.

Under the SHRP Program, the use of the uranyl (uranium) acetate fluorescence method was developed so that it can be utilized to monitor possible ASR prior to development of serious distress. The method, rapid and economical, is described in Section a. below. The method can be utilized both in the laboratory and in the field using portable equipment. While the method has proven useful in screening distressed concrete for potential ASR distress, it does present a few issues in its implementation which have prevented its widespread use in field inspections. The method utilizes a chemical solution which contains a slightly radioactive uranium isotope. While the level of radioactivity presents minimal risk, its use is regulated by a number of agencies and care must be taken in removing all materials from the inspections that have been in contact with the uranium.

Secondly, a portable UV light box must be utilized to visualize the test section after treatment with the uranyl acetate. A bushhammer fitted to an impact drill is needed to expose the surface. A vacuum is needed to collect all contaminated powder and chips. The UV light box, impact drill and vacuum used in the method require electricity, thus making it imperative to have either a source of electricity or a generator available at the site of inspection.

More recently, due to the difficulties encountered with the uranyl acetate method, the Department of Energy (DOE) Los Alamos Laboratories have developed a method that is easier to use, only requires easy to handle non-toxic reagents, and achieves visualization of ASR gel by the naked eye, thus not requiring a special light box. This method is described in Section b. below. This method is still experimental and not yet available in the marketplace. It is presented here because results to date are very promising and it is expected the method will be marketed in the form of a test kit within the next six months. Check back with this site for further information.

Use the following steps to prepare the uranyl acetate solution for ASR gel recognition. Be sure to wear protective eye wear (goggles or glasses) and rubber gloves while mixing the solution.

Procedure

This procedure can be used on any concrete surface to identify ASR gel. However, experience has shown that formed or sawed surfaces that have been exposed for years are not always satisfactory. Thus, it is best to use surfaces that are newly formed, such as fresh fractures, cores, and ground or sawed surfaces. In the field this can be accomplished by the use of a bushhammer, or by coring and fracturing a core. Thereafter, proceed with the following steps.

Step 1

Prepare surface to be examined as follows :

1. Old Formed, finished, or wearing surface :Use grinding wheel on electric drill or other means, such as a bush hammer, to grind off up to ¼ inch of concrete. Rinse with tap water.
2. Fractured surface :Break off piece from concrete structure or fragment and rinse freshly fractured surface with tap water.
3. New concrete core :Rinse off cylindrical surfaces after core retrieval. If core has been dried, rewet and wash with tap water, if necessary, to remove solids from coring slurry.

Step 2

Put on protective eyewear (goggles or glasses) and rubber gloves. Apply uranyl acetate solution from plastic squeeze bottle or sprayer. Only a momentary application of solution film is necessary to adequately wet the surface with solution.

Step 3

Allow solution to react for 3 to 5 minutes with any ASR gel that might be present on the surface. Then rinse surface with water. Remove protective eyewear (chemical goggles or glasses) and gloves.

Step 4

Put on UV absorbing protective eyewear. View the 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:

1. Once treated, the surface can be viewed at later ages without further solution application. However, it is advisable to first rewet the surface with water.
2. All liquids, powders and surfaces exposed to uranyl acetate, including any clothes that may have come in contact with the material, should be collected and disposed of properly according to federal and local rules and regulations.

The pictures below demonstrate how the method is applied in the field for ASR screening. Note methods used to insure that any material that comes in contact with uranyl acetate is collected for proper disposal.

FIG. 29 - Impact drill, UV-light viewing box, and vacuum used in preparing and removing test surfaces. Drill is fitted with bushhammer.

FIG. 30 - Bushhammered surface rinsed and ready for uranyl acetate application.

FIG. 31 - Drops of uranyl acetate solution being applied to vertical surface using plastic squeeze bottle. Note cloth held against concrete bushhammered surface to absorb excess solution.

FIG. 32 - Bushhammering treated surface to remove uranyl acetate contaminated layer. Note hose attachment to vacuum to collect powder and chips generated by bushhammering.

Interpretation

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 smearing during surface sawing or coring. Fractured surfaces eliminate this effect and most clearly reveal undisturbed ASR gel deposits. This smearing is not likely in a bushhammered surface.

Figures 33 through 36 illustrate typical occurrences of ASR gel as seen in ordinary and UV light. Interpretations are offered of representative occurrences of gel in distressed concrete.

FIG.33 - Fractured surface of concrete pavement core showing location of reactive granite gneiss particles (arrows), as photographed in ordinary light. There is no positive indication of ASR gel on this surface in ordinary light.

FIG.34 - Same fractured surface shown in Fig. 33 after uranyl acetate treatment. Green and bright yellow areas display ASR gel. Note band of ASR gel along periphery of granite gneiss particle (arrow) while interior of particle is free of reaction product. Film of ASR gel has spread over about one-half of surface shown.

FIG.35 - Badly cracked coarse aggregate and concrete from pavement showing severe cracking similar to that illustrated in Figs. 4 and 5. Cracking at pavement wearing surface was typical of that associated with ASR.

FIG.36 - Same field of view as shown in Fig. 35 but photographed in UV light after treating with uranyl acetate solution. Brown fractured coarse aggregate particle to left displays peripheral green film of ASR gel. Microcracks between triangular coarse aggregate particle to right and brown particle with peripheral band contain light greenish-yellow deposit of ASR gel. Crack with ASR gel extends above brown particle and along periphery of triangular particle. Development of ASR is confirmed by these observations.

Precautions

The following precautions must be taken when conducting the UV light examination for ASR gel.

1. WEAR UV LIGHT-ABSORBING PROTECTIVE GLASSES WHENEVER THE UV LAMP IS IN OPERATION. UV RADIATION WILL DAMAGE SIGHT IF POINTED FROM ANY ANGLE AT THE EYES. A protective glass is built into the field UV-light box.
2. Wear rubberized, waterproof lightweight gloves when handling uranyl acetate solution and concrete to which the solution has been applied. The uranyl (uranium) acetate is radioactive but emits only alpha radiation. Even though only dilute solutions are used, gloves must be worn for safety purposes and to avoid yellow discoloration of the skin.
3. Do not allow the uranyl acetate solution to come in contact with the skin and particularly the eyes. Wear chemical goggles or glasses when working with the solution.
4. Check with your state and local authorities regarding use of uranyl acetate in the laboratory and the field prior to implementation of test procedure and follow all existing rules and regulations.
5. Obtain MSDS for uranyl acetate and study carefully prior to use. Follow all recommended precautions. See health hazard information for further guidance.

HEALTH HAZARD INFORMATION

INHALATION :

Soluble uranium salts are moderately hazardous on inhalation. Coughing, sneezing and breathing difficulty may be expected and damage to kidneys and liver may occur after continued exposure.

INGESTION :

The toxicity rating is not high (slight to moderate) due to the low absorption rate of soluble uranium compounds. Solubility may be increased when material is dissolved in acetatic acid solution. However, gastrointestinal discomfort with vomiting and diarrhea may follow sizeable ingestions. Kidneys and liver may be damaged as well.

SKIN CONTACT :

Mild irritation, reddening and possible soreness may be experienced in cases of prolonged exposure to moist skin.

EYE CONTACT :

Absorption of soluble uranium compounds through eye tissues is reported. No specific symptoms of eye irritation by uranyl acetate have been found although the reddening and pain due to chemical substances can probably be expected. Reddening and burning may be increased when material is dissolved in acetatic acid solution.

CHRONIC EXPOSURE :

Principal hazards are kidneys and liver damage resulting from prolonged contact and absorption. Radioactivity induced tumors or malignancies are also possible.

AGGRAVATION OF PRE-EXISTING CONDITIONS :

Persons with pre-existing skin disorders or eye problems or impaired liver or kidney function may be more susceptible to the effects of the substance.

FIRST AID

INHALATION :

Remove to fresh air. Get medical attention for any breathing difficulty.

INGESTION :

If swallowed, induce vomiting immediately by giving two glasses of water, or milk if available, and sticking finger down throat. Call a physician immediately. Never give anything by mouth to an unconscious person.

SKIN EXPOSURE :

Remove any contaminated clothing. Wash skin with soap or mild detergent and water for at least 15 minutes. Get medical attention if irritation develops or persists.

EYE EXPOSURE :

Wash eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately.

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