Early-age Thermal ((better)) Crack Control In — Concrete Ciria C660

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.

Higher cement content generally leads to higher peak temperatures.

Where ( E_c(t) ) is the early-age elastic modulus. C660 provides simplified tables for ΔT_allow for common concrete grades and restraint levels. early-age thermal crack control in concrete ciria c660

C660 is guidance , not a standard like Eurocode 2. However, Eurocode 2 (clause 7.3.2) references it for thermal cracking. Many project specifications now explicitly require "design to CIRIA C660 principles."

C660 acknowledges that modern cements behave differently than their predecessors. The document provides equations and charts to estimate the adiabatic temperature rise based on the cement content and type (e.g., CEM I, CEM IIA, etc.). For a 600mm thick raft with 35% ggbs

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

This is the danger zone. As the concrete cools to ambient temperature, it contracts. This contraction causes tensile stress . Early-age concrete has very low tensile strength (typically 10-15% of its compressive strength). If the restrained contraction exceeds the tensile capacity, early-age thermal cracking occurs. The risk

[ R \cdot \alpha \cdot \Delta T_{allow} \leq \frac{f_{ct}(t)}{E_c(t)} ]