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Negative aggregate transparency can occur in formed concrete when there is segregation of fines and associated water between the form-face and the coarse aggregate. It appears as mottled light areas similar in shape and size to coarse aggregate.
To reduce the liklihood of its occurence, stiffen the formwork; increase the sand content, use internal vibrators rather than external ones, dampen aggregates and ensure correct curing.
Acknowledgement: Concrete Sociey
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