Concrete Evaluation of Home in Paradise, California

Two samples for evaluation: bottom and side views.
Porous paste indicative of high water in concrete. (Petrographic photo)
Highly porous section of paste.
Porous section of paste with a large void.
Crystal growth in void in porous paste (SEM, 500x).
Crystal growth in void in porous paste (SEM, 700x).
Showing porous micro-structure of paste(SEM, 500x)  .

Around a decade ago, about 70 cubic yards of concrete was poured over a 10-day period at a residence in Paradise, California.  The concrete was placed in batches of 5 to 8 cubic yards each day. The concrete sustained cracks at several locations and some of the surfaces were scaled exposing aggregates on the top portion of the concrete. The owners contacted C3S to perform a concrete evaluation to determine the cause of the defects.

Two cored samples were submitted to C3S: one had a crack in the middle of the core and the other had no crack. The samples were evaluated by petrographic analysis and scanning electron microscopy.

Evaluation clearly showed evidence of re-tempering.  The amount of water added was excessive.  Estimated original water-to-cement ratio in paste was 0.46 +/- 0.02 while the water-to-cement ratio in the cracked concrete was 0.76 +/- 0.02. 

The images showed evidence of re-tempering during our concrete evaluation.