Why is Concrete Better?
Concrete outperforms wood as a construction material, and won’t burden building owners with constant repair and maintenance costs. Versatile, long-lasting and durable, concrete is a cost-effective, sustainable choice for both residential and commercial building projects.
There are many reasons to choose concrete! Concrete is durable, low maintenance, has economic benefits, and is safe and free of harmful chemicals. In concrete’s life cycle, recycling is present from start to finish. Many wastes and industrial byproducts that would end up in landfills are used in the cement kiln or can be added to concrete mixes to provide desirable characteristics. Used concrete is recyclable and serves as aggregate in roadbeds or as granular material in new concrete. For many residential and commercial property owners, concrete is the paving material of choice. Some of the characteristics that lead people to choose concrete include:
Appearance – For many people, the light color and availability of attractive exposed aggregate finishes match their expectations better than dark asphalt.
Hardness – Unlike asphalt, concrete is solid, hard, strong, and retains those characteristics during hot weather. Asphalt can soften during hot summer days.
Rigidity – As a rigid, stone-like material, concrete resists deformation from vehicles or long periods of parking on its surface. Concrete driveway edges are also less subject to breakdown or deterioration.
Pothole & Weather Resistance – Potholes and other weather-induced damage are rare in concrete driveways. While cracking occurs with concrete, as on any material, other types of damage, such as roots growing through the surface, are much less frequent.
Versatility – For many homeowners, a driveway is more than just a road to the garage. Children use driveways for recreation, playing sports like basketball and riding skateboards, tricycles and other wheeled toys on them.
Neighborhood Standards – In many neighborhoods and developments, concrete driveways and sidewalks are the standard. In such neighborhoods, alternate material may detract from a home’s value, and may even be prohibited.
Value – In today’s market a concrete driveway costs just slightly more than an equivalent blacktop driveway and it is likely to have a much longer lifespan (10 years+). When cost is measured over the life of the driveway, concrete is significantly less.
Maintenance – As with any raw material, sealant and regular maintenance is going to be required. Concrete falls into the low maintenance category which also saves cost.
Does Concrete Crack?
Unfortunately, it’s very common for concrete to develop cracks, scaling, crazing, popping and pitting. All concrete has the tendency to crack, and it’s not possible to produce completely crack-free concrete. A common saying is that there are two guarantees with concrete. One, it will get hard and two, it will crack. Cracking is a frequent cause of complaints in the concrete industry.
Concrete expands and shrinks with changes in moisture and temperature. The overall tendency is to shrink, and this can cause cracking at an early age of the concrete. Irregular cracks are unsightly and difficult to maintain but generally don’t affect the integrity of concrete.
The most popular explanation for the concrete cracking is the freeze-thaw cycle in the winter. Concrete also cracks in the extreme sun, as it heats the concrete and causes it to expand. At the end of the day, the concrete contracts and regresses to its original, unbaked position.
Cracks that occur before hardening usually are the result of settlement within the concrete mass, or shrinkage of the surface (plastic-shrinkage cracks) caused by loss of water while the concrete is still plastic. Cracks that occur after hardening usually are the result of drying shrinkage, thermal contraction, or subgrade settlement. While drying, hardened concrete will shrink about 1/16 of an inch in 10 feet of length. One method to accommodate this shrinkage and control the location of cracks is to place construction joints at regular intervals. For example, joints can be constructed to force cracks to occur in places where they are inconspicuous or predictable. Horizontal reinforcement steel can be installed to reduce the number of cracks or prevent those that do occur from opening too wide.
Cracking can be the result of one or a combination of factors such as drying shrinkage, thermal contraction, restraint (external or internal) to shortening, subgrade settlement, and applied loads. Cracking cannot be prevented but it can be significantly reduced or controlled when the causes are taken into account and preventative steps are taken.
- Control joints (aka: Saw Cuts) in concrete driveways or slabs are simply pre-planned cracks. Control joints create a weak place, so that when concrete shrinks, it will crack in the control joint instead of randomly across the slab.
- It’s recommended to use sand on all concrete instead of salt. Salt will facilitate the freeze and thaw cycles that will then create the problem with pitting and cracking. When the temperature reaches 18 degrees, the concrete will freeze. At 35 degrees, it will melt and cause the cracking, pitting, crazing and scaling.
- With any concrete install, the edges are typically weaker than the middle, because there is a lack of support on the side. As a result, when you drive your car too close to the edge…or maybe even over the edge, that lack of support causes cracking and crumbling. Proper backfill is needed for this reason and also to allow for proper drainage.
You can have good design, adequate reinforcement, strong oversight and still experience cracks. A huge crack occurred down the middle of a 12 inches thick rebar reinforced slab poured at the Redstone Arsenal. The slab was engineered and supervised by the army core of engineers. The core of engineers decided to find out why it cracked, we’ll after they spent over $300,000.00 there findings were that concrete cracks. If the cracks aren’t more than a quarter inch wide with no vertical displacement there’s not a problem with the integrity of your job.
Using rebar will provide additional structural capacity for your driveway and is especially important if the slab will be exposed to heavy traffic. Reinforcement won’t prevent cracks, but it will help hold them together if they do occur. Reinforcement can be either wire mesh or ½-inch (#4) steel rebar placed in a grid pattern with a spacing between bars of approximately 12 inches. In either case, blocks should be used under the reinforcement to keep centered within the concrete.
There are several reasons why the combination of reinforcing steel and concrete works so well:
- The coefficient of thermal expansion is similar for concrete and steel, so when reinforced concrete freezes or gets hot, the two materials contract and expand similarly. If they didn’t, the combination would tear itself apart over time.
- The bond between reinforcing steel bars (rebar) and concrete is strong and efficient. The rebar has surface deformations (ridges) to further improve that bond. Due to the strong bond, the concrete effectively transfers stresses to the steel and vice versa.
- When the cement paste contacts the steel rebar, it forms a non-reactive surface film that inhibits corrosion. This passivation process helps rebar from corroding inside the reinforced concrete.
Concrete is a material high in compression strength and low in tensile strength. Steel, as a material, outperforms concrete 10:1 in compression strength and 100:1 in tension strength. However, steel costs about 50 cents per pound while concrete costs about 2 cents per pound. Thus economical reinforced concrete design uses steel to carry the tension stresses in a structural member and concrete to carry the compression stresses.