Curing is the maintenance of a satisfactory moisture content and temperature in concrete for a period of time immediately following placing and finishing so that the desired properties may develop.
In the past, most specifications for pervious concrete have called for the use of a one or two layer application of polyethylene sheeting for seven to ten days to protect the concrete from premature drying which leads to low strengths and raveling.
PerviouShield® has been developed over the past three years to not only eliminate the use of polyethylene sheeting which typically ends up in our landfills but to offer immediate curing protection to pervious concrete especially in windy or sunny conditions while leaving behind a densified surface which is much more abrasion resistant than typical pervious concrete once the curing compound has dissipated.
For the most effective way to cure pervious concrete, we strongly advise our customers to include HydroMax® Internal Curing Admixture into a well balanced pervious concrete mix design followed by the application of PerviouShield®to the finished product.
There are several products on the market now that claim to offer internal curing but by definition, internal curing is “the process by which the hydration of cement occurs because of the availability of additional internal water that is not part of the mixing water.” No other product can make such a claim.
How this works is that if you have a well balanced mix design that calls for 18 gallons of water per yard, then you would add an additional 3 gallons per yard that gets bound up by the HydroMax®. When the cement in the mix has used up all of the available batch water, then the cements pulls additional water from the HydroMax® and hydration continues offering higher strengths and a better product.
Another way to look at this is that in regular pervious concrete (old technology) we have seen that typically only about 55% of the cement becomes fully hydrated which is the reason for requiring poly curing for at least seven days. Once you remove the poly and any remaining moisture is allowed to escape the concrete, hydration STOPS and so does your strength gain. If a typical mix has 600 pounds of cement, the reality is only 330 pounds of it are doing what it needs to do, the rest becomes almost worthless.
With the introduction of internal curing with HydroMax®, we now see 95% of the cement becoming fully hydrated which is why we get such great strengths and reduced raveling issues compared to pervious that is not cured internally. Adding HydroMax® also allows us to reduce cement contents to a more user friendly level of around 520 pounds per yard, while producing a more fluid mix, of which 494 pounds of cement is working towards the higher strengths and durability we desire.
PerviouShield® is designed to work in conjunction with HydroMax® to protect the top surface of the pervious concrete for an extended period of time and allow the internal curing to continue for as long as 35 days and has the added benefit of having the densifier to make the wearing surface more abrasion resistant. Click here to learn more about PerviouShield® and how it can benefit your project.