i am geology student .Sir i have little knowledge about eng geology that why i face allot problems.Sir my question is what is mean by ASR and ACR test ?what is its importance? what type of properties are determine through these tests?and in concrete what ASR exibits?
Dear Amjad, Goodmorning and Fraternal Greetings!
Thankyou for your question, I apologise that I am in the field hence I could not give you answer early. Regarding ASR test, the following is the explanation to the best of my knowledge.
Alkali-silica reactivity is the process in which certain minerals (mostly glass type silica) in the presence of moisture are broken down by the highly alkaline environment of concrete producing a gel that expands creating tensile forces in the concrete matrix which cause cracking of the concrete. The cracking then allows more water to infiltrate into the concrete creating more gel, more expansion etc. Ultimately the concrete fails or disintegrates.
Features & Benefits
• Test can be carried out completely on site.
• Minimal operator training and no special equipment required.
• Utilizes only two environmentally safe dyes.
• Identifies ASR in concrete and differentiates ASR from other causes of degradation.
• Results obtained in less than five minutes are easy to interpret.
• Economic, fast and easy to use.
Field Test to identify Alkali Silica Reaction (ASR) in concrete, Two reagents are applied to the broken surface of a concrete core and the excess rinsed off. On contaminated concrete, the resultant stains reveal the presence of ASR. The stains also reveal the extent of the ASR in the concrete and indicate the stage of ASR progression. Yellow indicates that degradation has begun; pink warns that degradation is advancing.
ASR Detect™ is both a practical and a scientific tool. It's principal application is analyzing existing concrete structures. By identifying ASR deterioration in its earliest stages, ASR Detect™ facilitates the problem being identified when remediation techniques can be applied; for example, treating the concrete with a lithium-bearing solution to inhibit further deterioration. Where deterioration is advanced, ASR Detect™ provides a clear picture of the extent and depth of the damage.
As a scientific tool, ASR Detect™ can be applied to improving the understanding of where, how and why ASR occurs. That understanding is basic to developing ASR preventatives that allow high-alkali cements or poor-quality aggregates to be used in concrete mixes without risking the development of ASR.
Simply apply each of the two reagents to the broken surface of a concrete core drilled in a suspect structure, and rinse off the excess. On ASR contaminated concrete, the resultant stains reveal the presence of ASR.
The stains™ distribution shows the extent of ASR in the concrete, and their proximity to different components of the aggregate gives clues to the source of trouble. The two gels that are identified - one staining yellow, the other pink - indicate the stage of ASR™ progression. Yellow signals that degradation has begun. Pink warns that degradation is advancing.
Typically, ASR occurs in cracks and these cracks often cut through the aggregate and usually do not follow the aggregate-paste boundaries. ASR tends to fill air voids.
In contrast to the two established methods of ASR Detect™ion-petrographic analysis and uranyl acetate analysis, ASR Detect™ has numerous benefits.
Because the reagent stains are clearly visible even before the treated sample dries, a complete diagnosis is possible in less than 5 minutes. ASR Detect™ systems are relatively inexpensive. Petrographic analysis requires shipment to a laboratory, adding time and raising the costs to hundreds of dollars per sample, also the uranyl acetate reagent is almost prohibitively expensive. ASR Detect™ is simple enough to use in the field. Its reagent stains are visible to the naked eye and are distinctive enough to be recognized and interpreted by anyone with minimal training. Petrographic analysis requires specially trained technicians working in a well equipped laboratory. Therefore, the use of ASR Detect™ can considerably reduce the cost of diagnosis by reducing drastically the need for petrographic analysis.
The ASR Detect™ reagents present minimal danger to either human health or the environment. Uranyl acetate is radioactive and contains a heavy metal and therefore, has the potential to cause health and disposal problems.
ASR Detect™ provides information not only about the presence but also the severity of ASR. Its affordability allows an engineer to analyze enough samples to obtain an accurate diagnostic picture of an entire structure. The high cost of a petrographic analysis permits only a limited number of samples to be examined.
Dr D S Subrahmanyam