Independent Cement and Lime lists out the dos and don’ts of cold weather concreting to help achieve the desired outcomes without extending finishing times.
Dos and Don’ts
Do use an accelerator in the mix. This can either be an accelerating admixture or extra cement.
Don’t place the mix too wet. The wetter the mix, the longer the finishing times due to more bleed water.
Don’t place the concrete on frozen ground. This will reduce the concrete temperature and cause delayed bleeding.
Do remove water, ice and frost from trenches, formwork and reinforcement.
Do compact the concrete by vibration to release bleed water from the concrete matrix.
Don’t bull-float the surface of the concrete excessively as it will trap the water in the concrete and slow down bleeding. Tip: A bull-float with a piece of flat, dressed timber bolted to the face will open the pores of the concrete and allow bleed water to escape more readily.
Do remove excess bleed water from the concrete surface by dragging a length of hose or rope across the surface.
Don’t play with the concrete surface. Tip: Take a break and do the final finishing operation when the bleed water has disappeared and the surface can be marked only with a press of the finger.
Do start curing as soon as possible.
Don’t forget: Finishing time is the time from when the last concrete placed was bull-floated to the completion of final finishing.