In Central Iowa, concrete popouts are unfortunately an inevitable occurrence when it comes to concrete. They can be caused by a variety of environmental and aggregate reasons, but there are several things you can do in order to prevent and protect against concrete popouts.
What is a popout?
Popouts are blemishes in the concrete surface which occur as early as one to two days, and as late as years after the concrete is placed. These blemishes range in size from 1/16th of an inch to up to an inch in diameter.
In the Central Iowa area, our local aggregates include particles that may cause popouts. Ready mix producers all use aggregates that meet Iowa DOT specifications, and it is often assumed that meeting the IDOT specifications will ensure that popouts will not occur. This assumptions is simply not valid. When you travel along the interstate highway at 65 mph, a sand or even a larger aggregate popout is unnoticeable and insignificant. But take a driveway, a garage floor, patio, pool deck or any other high profile concrete project the popouts make the appearance aesthetically unappealing because it is noticeable.
Why do popouts sometimes occur?
When the glaciers from the last Ice Age receded northward through Iowa 10,000 years ago they deposited all types of soils, sand and rock. Many of these deposits contain small percentages of deleterious materials, including certain shales, iron oxide particles, unsound cherts, and other soft particles.
Ready mix concrete producers utilize the local sand and rock deposits that are available in their markets to make concrete as economical as possible for the end user. Often these are the same deposits mentioned in the previous paragraph – deposits that may contain materials that cause popouts.
Are popouts in any way harmful to the integrity of a concrete slab?
No. Popouts do not in any way decrease the life of a concrete slab. Popouts will not affect the structural serviceability of the slab now, or in the future. However as stated before some people may find these popouts aesthetically unpleasant.
What steps can be taken to minimize popouts?
For any high profile concrete project such as polished floors, patios, colored concrete, pool decks, sidewalks, driveways etc. it is recommended to use import sand in the concrete mix. Import sand comes from aggregate sources that contain minimal amounts of deleterious materials. For the Central Iowa area these sands are imported for Eastern Iowa or from Nebraska. There is added expense to ship this aggregate because of distances from these sources to the ready mix plants in Central Iowa. Many find the extra cost per yard for import sand too expensive and opt to use local sands in the ready mixed concrete they use, which increases the risk of popouts.
- Use import sand. Liberty Ready Mix always maintains a stockpile of import sand for our customers.
- Use only aggregates that meet standard specifcations.
- Use only cements that meet ASTM specifications.
- Use air-entrained concrete.
- Use concrete with lowest water content and slump possible for the application.
- Do not finish concrete with bleed water on the surface.
- Avoid hard-steel troweling where not needed, such as most exterior slabs.
- Use proper curing methods.
- Use proper sealing methods.