Working with concrete in winter

Dr Bill Price offers some essential advice merchants can give their customers on working with concrete in the colder months.

Good organisation is always an important part of any project but, as winter approaches, industries that involve outdoor construction need to thoroughly consider weather conditions while planning and executing their operations.

Temperature plays a large role in any construction project. It doesn’t seem that long ago that the Beast of the East wreaked havoc on building projects across the UK – and doubtless, we could well be looking at less than desirable weather conditions early in 2019.

 

Let’s look at the impact that freezing temperatures can have upon concrete and how your customers can work around this.

 

Winter preparation

 

Perhaps the most critical factor in construction operations carried out in cold weather is ensuring that mortar gets adequate heat for normal cement hydration. The usability and strength development of concrete is, of course, affected by temperature and therefore, additional care must be taken when working with concrete in colder periods. Cement will not hydrate sufficiently at low temperatures (typically below 3 degrees), which, of course, increases the risk of slow setting, poor strength gain and frost damage.

 

It seems obvious to say, but this can be easily managed by avoiding mixing or laying concrete when the air temperature is below 5ºC and falling.

 

It’s also important to keep the mix above 5ºC for 48 hours after the concrete has been placed.  Freezing temperatures significantly reduce the compressive strength, the bond strength and also decreases the water penetration resistance of masonry. If the newly placed concrete does fall below freezing before developing enough strength, it will result in cracking, scaling and crumbling of the mortar.

 

If there is any risk of frost during this period, protect with an insulation quilt sandwiched between two sheets of polythene sheeting, but the best advice is to wait for a warmer day before doing these jobs.

 

 

 

 

 

 

 

 

 

Wind and rain

 

It’s not just frost that you need to consider. A great deal of judgment is required to perform construction projects in wind and rain. Across the board, it’s important to know what kinds of equipment and products can handle extreme weathers in construction.

 

Severe wind can cause premature drying as a result of increased evaporation. For this reason, it’s important to make the necessary arrangements to tackle the risk before laying concrete in a windy area. Consider putting up wind barriers to protect your work and cover the work with plastic sheeting, making sure that the sheeting is secure.

 

Rain too, can cause problems. Mortar should be kept moist for 36 hours to allow it to fully cure. However, a heavy rain may wash the lime out of the mortar, weakening the bond between the bricks and the mortar. Protecting new mortar from the elements with a water-resistant tarp or plastic sheeting is essential to slow curing and help form a strong bond.

 

The right product

 

Another significant factor to consider in the colder months is the quality of the concrete mix itself. Opt for a leading manufacturer to ensure your product is air-entrained.  Air-entrained mixes contain billions of microscopic air pockets that relieve internal pressure on the concrete by providing small chambers for water to expand into when it freezes. This gives the concrete increased resistance to freeze/thaw degradation.

 

Packaging is also important when protecting against the elements. Often, the winter months can see cement spoilt when left open outside. To keep cement dry and prevent wastage, look for products that are available in weather resistant packaging and tubs. It sounds simple but doing this will save you the time and money associated with purchasing more cement.

 

Tools

To prolong the life of your tools and materials in the winter, and save money in the process, it’s important to give them extra care. The annoying job of chipping away at hardened dirt or mortar and removing rust in spring, can be prevented by keeping your tools clean and well-oiled throughout the colder months. After all, good tools are quite an investment!

Dr Bill Price is National Technical Commercial Manager in Tarmac’s cement business Tarmac Blue Circle