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Heading: 1.1Transparent Aggregate
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We have received the question below with photo's to show examples, please go to the following link to view everything...



http://www.aggregateresearch.com/articles/21318/Forum-Question---Transparent-Aggregate.aspx



Dear Technical People on aggregateRESEARCH.com

Our company manufactures chemicals for the cast concrete industry. One of our customers is experiencing a strange phenomenum. They cast pavers in polyurethane rubber moulds. Upon demoulding we find that there is a spot associated with each stone below the surface which is darker than the surrounding area. We thought that this was due to differential drying out of the surface and that once the whole tile was completely dry these marks would disappear. However the spots remain. Sometimes the spots are lighter than the surrounding area!

I have been told this is called "Transparent aggregate " but no explaination for its occurance has been given. We call it Leopard spot !







Would you be able to assist me in any way giving an explaination of this even which now seems to plague us more and more.

Best regards,

John Souter
Redec Chemicals
Cape Town
South Africa


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Tania Hudson


Here's my take. This is called aggregate shadow and is where the "mortar layer" is thin over the aggregate. The water-cement ratio is lower in that thin layer thus a color change. Perhaps the vibration effort was intense as a cause. (Vibration energy is transferred through coarse aggregate.)
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Roy Keck
 
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