Thick concrete raft slabs generate enormous heat from the hydration of the cement. Slabs such as this will be getting up to 60-70 degrees internally and will take weeks to cool down. Consideration has to be given to using as low a cement content as possible. Use 56 days strengths or use a fly ash or GGBFS mixes. Use mixes with large aggregates, 40mm maximum size for instance, if possible and practical The pours take planning in terms of the logistics of getting the concrete in there with pre pour meetings between all the parties involved to ensure you have backup at plants and for the pumps, can you reach all the site, where do you park the trucks waiting to get onto the pumps? Have you got the staff necessary for both ensuring trucks don’t run out of driver hours and the staff on site won’t get too tired. Following the pour you need to monitor the temperatures at the surface and in the middle to avoid a significant temperature differential (20 degrees)from the inside to the outside. To avoid that difference requires insulation and you can play the temperature, removing the insulation to help the slab cool and covering again once the difference gets up towards 20 degrees. Conslab’s manager in Christchurch Glyn Sutton is an expert in the practicalities of these large pours.
View our largest concrete pour to date being the 1850m3 pour for Leighs Construction (Video courtesy of Leighs) in Christchurch on the ANZ building, Firth supplying the concrete with JFC Pumps pumping. Click on the link below.