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Top 5 Myths and Misconceptions About Concrete

July 3, 2015

There are many myths and misconceptions about concrete – while some may be relatively harmless, others can cause problems if taken as truth. Here are just a few of the most popular ones…


  1. Concrete Hardens by Drying out

Concrete is cured first, then slowly dried out. It is the curing that turns the concrete into a permanently hard substance through the chemical reactions that occur in the presence of water. Premature drying would stop the fresh concrete hardening properly, and thus maintaining enough moisture in the mixture is crucial during the curing.


  1. You can Always Add Water to Increase the Workability of Concrete

Water should not be added to pre-mixed concrete to increase its workability, because diluting the chemicals that harden the concrete will lead to a weaker end result. Instead of water, plasticisers can be added to enhance the flow of the mixture. Only add more water if you can perform a slump test to ensure that you are not exceeding the maximum water-cement ratio.


  1. You can Estimate the Drying Time

You may have heard that you can accurately estimate the drying time of concrete by calculating slab depth. A rule-of-thumb like this unfortunately fails to take into account all the factors that affect drying time – for example, the availability of pathways within the mixture that let the water rise to the surface of the slab where it can evaporate. Ambient conditions, such as air movement and relative humidity, can also significantly influence the drying time.


  1. A Surface Test can Determine when Concrete is Dry

Since the surface is generally the only route for water to escape from a concrete slab, either a surface test or an absence of a sheen of water is often taken as evidence that bleeding within the slab has stopped. However, the moisture level at the surface does not necessarily reflect the overall condition of the slab. The only accurate way to determine if a slab is dry is to perform a relative humidity test at the correct depth.


  1. Concrete that is Flat and Level when Wet will Remain so

Concrete will go through changes in volume as it sets, hardens and dries. If there are significant differences in the moisture level and the temperature between the top and the bottom layers of the concrete slab, the edges may curl. Curling can be minimised with techniques that reduce the temperature and moisture differences.


Written by Roadmaster Concrete Mixers, the leading providers of volumetric concrete mixers throughout the UK and Europe.