See attached image. On concrete samples I cut with a saw, there is discoloration in the cement matrix (see light black vs. grey matrix). Does anyone know what would cause this discoloration.
The concrete was made in a cement mixer, so the aggregates and cement should be mixed consistently. A self-consolidating mix was used that incorporates a plasticizer, accelerator, viscosity modifier, and a air entrainer.
Thanks
Dear Mathews,
how many days of curing and what type of curing (by air or under water) are passed ?
External light color in my experience is due to drying process so close to surface carbonation is more effective, while internally is still darkwe because is more efficient hydration of Portland cement minerals. I think is quite normal this variable color from inside to outside. Of course if you had used also pozzolanic raw materials like fly ash or grey microsilica you could see some changing in color of cement matrix. Last thing , even cutting with metal chainsaw can modify the color when the saw meets different raw materials (cement past and aggregates with different mineralogy, size and shape of particles) , but all of these reasons don’t affect the strength development of concrete.
Hoping to be useful .
Best regards
Alex Reggiani
It would be interesting to cut twice at right angles to the first cut, and test the strength of the three regions.
What type of cement have you used? It seems that you added some SCM additive and some kind of seggregation occured at the mixing stage.
Best regards
Łukasz
Did you use slag cement?
https://www.concreteconstruction.net/how-to/greening-of-slag-cement-concrete_o
https://www.sciencedirect.com/science/article/abs/pii/S0958946516307703
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