Cement Heat of Hydration

[connect2]

So doing a small, lower end, mass concrete pour, the section is a 1.4m x 1.4m x 50m beam with a standard C1 concrete 35Mpa, 280 kg/m³ type 10 cement with 120 kg/m³ slag. Sealed the exposed top, left the forms on and covered the whole thing with insulated tarps for 3 days. Through the weekend ambient temp varies from 18 to 25^oC. Monday, three days later, it was hot and uncomfortable to stand on. Had no thermal couples but took readings after the form was removed and the concrete on the o/s face was +/- 42^oC. Hot and I can only imagine what the temp was inside the beam. Cracking on the top of the beam followed all the stirrup lines.

Is there a question here?
Yes what are your thoughts of what's occurred? My first thought is that at the batch plant they didn't do the slag substitution? The concrete temp at time of placement was running 19.6^oC to 23^oC.

 

[hokie66]

A combination of things, probably. It would have been a lot better to have reduced the concrete temperature at placement. The cracks sound a lot like plastic settlement cracks around the reinforcement due to inadequate consolidation.

 

[connect2]

Thanks hokie66 for the reply.

Yes as with concrete likely a combination of things. Ready mix suppliers are so tight lipped now a days. Getting any information off them is impossible.

Isn't a consolidation issue though but yes have seen that problem. I didn't ask for chilled water or ice in the mix because with the 30% slag substitution and the minimization of the core and o/s face temperature differential with insulated tarps i thought that I was pretty well covered, pardon the pun, on early age thermal cracking possibilities.