For a 600mm thick raft with 35% ggbs and a 15°C differential limit, C660 might let you pour without any active cooling. The saving? Tens of thousands in pipes, pumping, and labour. The risk? Quantified, not guessed. CIRIA C660 transformed early-age thermal cracking from a "black art" into an engineering calculation. It recognises that young concrete is not a weak version of old concrete—it's a different material entirely , one that generates its own heat, changes stiffness by the hour, and needs to be managed dynamically.

This isn’t a materials failure. It’s a heat failure. And for decades, the industry relied on blunt-force rules of thumb. Then came . Beyond "Don't Let It Get Too Hot" Before C660 (published in 2013, superseding the legendary CIRIA C91), thermal control was often reduced to a single mantra: keep the peak temperature below 70°C . But that misses the real enemy: the temperature differential (ΔT) between the hot core and the cooler edge.

Next time you see a hairline crack in a new foundation, ask: was that load, shrinkage… or a thermal differential that no one measured?