New Concrete Paving and Construction
Proper Foundation Preparation is Essential for Long-Lasting Surfaces and Structures
An expert is needed for quality craftsmanship in concrete installation.
As with any paving project, the success of a concrete project begins with a solid foundation on soil that has been stabilized. Washtenaw County, for instance, contains many areas of expansive clay soil. Clay expands and contracts dramatically in response to moisture content. Often, it is necessary to remove 6-8 inches of clay and replace the clay with crushed concrete aggregate that is machine compacted before pouring the concrete. Keeping the concrete away from the clay will lessen the tendency for the concrete to expand and contract due to the absorption of excess moisture in the clay, or the reverse, dry clay that absorbs the moisture from the concrete. www.askthebuilder.com describes a typical concrete slab repair that would apply to this region of the country when the foundation is not properly prepared.
Residential sidewalks and driveways are generally poured at the depth of 4” with a 4000 PSI (pounds per square inch) load bearing capacity. Concrete poured in a depth greater than 4” needs to be reinforced with steel rebar that is suspended above the soil so that the concrete can grip onto the grooves of the steel bars from above and below in order to add extra strength. The apron of a driveway needs to be reinforced with steel because of the wear and tear from the turning of cars and delivery trucks. On average, concrete shrinks 1/16” every 10 linear feet. To compensate for the affects of the shrinkage, joints are cut in concrete sidewalks every 4-5 feet and in driveways every 10 feet.
Weather plays an important role in the quality of a concrete project. Sunny, hot, windy days dry the concrete rapidly. When concrete dries too quickly, the number of crystals that grow to ensure a strong durable concrete product are diminished. Homeowners that attempt their own projects are often tempted to add more water to the concrete on hot days to allow themselves more time to spread the product. Adding more water to concrete that has been mixed properly at a concrete manufacturing facility, changes the chemical makeup and will often result in spalling or shaling, which is when the top layer of the concrete starts to come off in flakes. This damages the concrete and lessens its integrity.
Cold weather also indicates special installation requirements. The ground cannot be frozen when pouring concrete. Concrete requires additional time to cure in cold weather. This slow set up time decreases the amount of crystals formed in the process, which leads to a weaker product. Chemical accelerators are often used in cold temperatures. The chemical accelerators speed up the curing process. Then, thermal heating blankets should be placed over the project for 4 days. The chemical reaction in the formation of concrete produces heat, therefore, the blankets keep the heat in so that concrete does not freeze before it has time to set up properly. Cement is air entrained, meaning it contains thousands of air bubbles that will expand and contract to absorb shock and adapt to weather changes.
Concrete projects need to be sloped properly. Rain and melt water needs to drain off concrete surfaces rapidly. Standing water may develop into ice patches in winter and also allow the water to seep into cracks causing greater cracking due to expansion and contraction over time. Concrete walkways and driveways are not simply poured and left to cure. As concrete stiffens a float is used over the concrete to drive stone aggregate down into the slab and to bring the sand and cement component to the top. Finishing concrete with a broom or other types of tools is an art. A well executed project needs to be perfect from the base to the finish to provide a quality product that is not only durable but pleasing to the eye.
Concrete projects take a lot of coordination and a team effort. For a project to be successful, the right tools and equipment must be ready and in working order, the correct amount of material must be ordered, the surface and forms must be prepared, the delivery needs to be scheduled, and an experienced team is needed to apply and finish the project. Although some smaller projects may be attempted by the do-it-yourself enthusiast, larger scale projects need to be executed by experienced professionals. Concrete is a complex material that needs special care and caution in its application. Due to its high alkalinity, wet concrete can cause 2nd to 3rd degree burns on skin.
Read more about the importance of proper concrete installation techniques at www.askthebuilder.com.
Tips for your Concrete Project
- Address soil and compaction issues
- Know the temperature and the affects it has on concrete
- Grade/slope the project for correct water drainage
- Do not add water to delivered concrete mix
- Pour concrete for appropriate depth according to the project
- Cut joints at appropriate intervals and depth to control cracking
- Seal your project every 2-3 years when using colored concrete
- Stamped concrete does not have voids = no weeds as in pavers
- Concrete will crack - repair cracks as they happen
- Color in Concrete
Living in Michigan means living with severe climate changes. Before adding color to your entire concrete driveway consider the effects of snow plow damage and eventual cracking of the surface. If you choose a solid colored concrete surface, future patches will be difficult to match. Even in non-colored concrete, patch work stands out and will not weather at the same rate as the older, existing concrete. If you are considering a colored concrete driveway, think about choosing a non-uniform color and design with extra cuts mixed in order to prepare for future repairs.
Sealers for Decorative Concrete
Sealers provide long-term protection and color enhancement.
Cure and seals, as you might expect, blend some of the benefits of cures and sealers. Like cures, they slow initial hydration of concrete to create a stronger product and minimize shrinkage cracking. They also provide mid-term protection of 6 to 12 months. These products are applied as soon as the concrete can be walked on.
Coatings provide long-term protection, the best chemical resistance, and color enhancement. They may also require special surface preparation for proper adhesion.
Inappropriate choice of product or faulty application will lead to a milky film to develop on the sealer. If corrective steps do not eliminate the film the sealer must be stripped off the surface. We recommend having your sealant applied by an experienced professional. Sealers need to be reapplied every 2-3 years.
Read more about decorative concrete installation, sealing and curing at www.concretenetwork.com.
Sealers for Routine Concrete
Although not as routinely performed on standard concrete projects, sealers may be utilized to prevent water and oil from passing through into the concrete. These sealers should be comprised of silanes and siloxanes not silicones. Silicones do not allow concrete to breathe, consequently, if temperatures drop below 32 degrees water vapor from soil would not be able to pass through to the surface.
Concrete Curbing vs. Asphalt Curbing
Concrete curbing is used along roadways and residential neighborhoods that have sidewalks. Concrete curbing is poured 12” under the surface and an additional 4” is exposed on the surface. This type of curbing stabilizes the asphalt or concrete paving sub base that is poured along side of it. The curbing directs water flow to drains.
Asphalt curbing is only used in parking lots. It is a much less expensive option compared to concrete curbing. It sits on top of the surface and often acts as a guide to direct water flow to drains. Asphalt curbing is susceptible to damage as it is not anchored into the ground and can be easily moved by snow plow blades.
Concrete Drain Collars and Catch Basins vs. Asphalt
When repairing or installing drain collars and catch basins budgeted money is well spent on concrete versus asphalt. Concrete is more stable and less susceptible to movement compared to asphalt. Concrete is more durable and able to tolerate greater PSI (pounds per square inch) pressure or load bearing strength. Since asphalt has more flex and movement, asphalt collars can erode which allows water to seep behind the bricks of the catch basin, which will erode the mortar on brick collar. This erosion requires manholes to be rebuilt at a faster rate compared to concrete.
Check to see if your contractor and contract include the following:
- A Michigan Builder’s License number is required for all concrete work outside of any residential structure including condominiums and apartment homes
- Workmen’s compensation and liability insurance documents
- One year warranty
- Fiber mesh in the mix design if 4” and wire mesh if 6” or thicker
- Enough concrete finishers to properly set the concrete according to the temperature to ensure the highest quality job
- Concrete redi mix not mixed at your site but delivered from a controlled factory setting in a concrete mixing truck
- Forms that are not warped