Concrete setting

I attended a course last week on contract management. The speaker started talking about concrete, which happens to be something I am quite passionate about (read the blog description). So Calcium Chloride is an accelerator while sugar is a retarder. And if you know your concrete, Calcium Chloride is not that good for concrete, because Chloride attack causes corrosion of steel rebar, and Calcium encourages alkali-silicate reaction (if you have reactive aggregate) which deteriorates your concrete in the long run.

So what's the point anyway? Well, the speaker, some expert, said that there was a lawsuit involving some contractor whose concrete could not set during construction. And after checking the site log, it appears that during casting it started raining and the workers ran away. So according to him it's the contractors fault cos anything could have fallen into the concrete, e.g. soft drinks with sugar, when they ran away, causing the concrete to not be able to set.

So what's the big deal anyway? Well firstly, if its just a couple of soft drinks, only a small area would not be able to set, not the whole slab. Secondly, sugar is a retarder, but unless u put a whole lot in, I think the concrete will still set if you just wait it out yah? I don't know the facts of the matter, but seems to me like the guy missed the point entirely. I don't think it was contaminants that caused the concrete not to set at all. In fact I think it's most likely a combination of poor concreting and mix proportioning that caused the concrete to HEAT UP too much during casting. I think what happened was "Delayed Ettringite Formation" also known ask "Internal Sulfate Attack" which occurs quite rarely because the concrete has to heat up till over 70 degrees celcius during casting. And yes, concrete can get that hot in Singapore, you'll be surprised. That's why we usually cast in the morning.

So, what's the point again? It just baffles me that the expert won the court case without having to actually find out the actual cause of the concrete not setting. He just pointed to the site log that the site was unattended. Which means there might have been some undesirable practices that were not discovered and corrected....

Interestingly enough, I wonder how many of you civil engineers out there even know what "Delayed Ettringite Formation" is? First time you heard of it? Even in a place where setting concrete can potentially reach 70 degrees celcius?