Shrinkage Compensating Concrete vs Shrinkage Reducing Chemicals
The shrinkage battle
When considering which approach to use to battle shrinkage, it is first important to understand the shrinkage you’ll encounter on the job: how much shrinkage and how that is going to affect the performance of the slab. Put very simply, shrinkage happens when moisture evaporates out of the concrete at a non-ideal rate as it hardens. Shrinkage occurs for different reasons in different concrete mixes, and it takes a seasoned expert to make judgements about the mix design that will work best on a given job.
There are a few types of shrinkage to consider before you decide how to battle against it. Drying shrinkage has to do with how water escapes from the concrete during the drying process. There is a good scientific explanation of this process in Concrete Construction
There is shrinkage that occurs in fresh concrete due to everyday environmental factors – hot or cold weather or a very rainy day. Chemical compounds aren’t generally going to help you with these environmental issues. This is why you want a concrete expert to work with you throughout the process who will know and understand the job. They can deliver valuable advice about the nuances of the mix.
To compensate or reduce?
Planning for the right kind of shrinkage requires applying the correct method.
The goal of shrinkage-compensating concrete is to proportion the mix so that it will increase in volume after setting to reduce early hardening. When this method is used appropriately for concrete floors, it can reduce cracking and provide other benefits such as allowing for greater joint spacing.
Shrinkage-reducing mixtures, or SRAs, rely on chemical additives to reduce the amount of shrinkage that occurs over time in concrete. Reducing shrinkage may result in a slight reduction in cracking but does not reduce the number of control joints and is not as effective in reducing curling. This is why FRICKS does not recommend SRAs.
How to decide which to use
No matter which approach you take, testing is essential, and should be conducted well before the date you intend to pour the concrete – at least a month and a half would be our recommendation. We also meet with our team, the construction team, and the project managers to go over a wide range of details and planning items regarding the project, the environmental concerns of the site, the type of testing methods to use, and small details about the job that could have a big impact.
Good planning combined with the benefits of having all the information you’ll need handy means that your mix experts can arrive at the right design for the job.