Having concrete poured on your property is a big deal. It can be very expensive and an integral part of your properties foundation. Many builders and homeowners have questions about concrete. Over the years we have compiled and answered some of the most frequently asked questions about concrete below.
- What is the difference between cement and concrete?
Contrary to popular belief, concrete and cement are not the same thing. Cement is actually a component of concrete, which is basically made up of three basic components: water, aggregate (rock, sand or gravel) and cement. Cement is a very fine powder made of limestone and other minerals, which absorbs water and acts as a binder to hold the concrete together. This combination, or concrete mix, will be poured and harden into the durable material that we are all familiar with. While cement is a construction material in its own right, concrete cannot be made without cement. These two terms are often incorrectly used interchangeably; however, concrete and cement are distinctly two separate products. Since concrete is derived from natural resources, there will be variations in color, texture and appearance, which is the inherent aesthetic expression, property and character of concrete’s natural patina.
- What are expansion joints, and why do I need them?
Expansion joints are joints left in between sections of concrete to allow safe movement of concrete throughout the year. Concrete, like any other material, expands and contracts with seasonal temperature fluctuations. Expansion joins are basically designed to mitigate the harmful results that these fluctuations have on concrete, and to absorb vibrations and permit soil movements due to earthquakes or ground settlement. Not incorporating expansion joints in your concrete project would result in hundreds or thousands of dollars in repair or replacement costs.
- What are control joints/grooves, and why are they necessary?
A control joint is simply a groove cut positioned on the surface of the concrete. Since all concrete has a tendency to crack, control joints, or relief joints as they are sometimes called, are designed to control and encourage crack formation, which happens naturally where there are differences in moisture levels and temperature variations in the atmosphere, to occur within those joints. Concrete shrinkage is in itself a normal process as it cures, and the lack of, or inadequate, control joints can produce unsightly and damaging cracking. Even if control joints are effectively placed to perform their intended function, unexpected small/hairline cracks can appear outside these joints; however, these cracks do not compromise the structural integrity, strength or longevity of the concrete, are cosmetic in essence and not covered under warranty.
- Why cure concrete, what does it mean and how long does it take?
Curing is one of the most vital and indispensable steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period, from five to seven days after placement for conventional concrete, the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds which seal in moisture.
Typically, concrete takes approximately 28 days to fully reach its design strength; and a considerable portion of concrete shrinkage is going to occur during this interval, particularly during the first week or less. Even though the concrete’s design strength is reached in about a month, concrete continues to harden for days or weeks after that point too. Since all concrete is derived from natural resources, it has an inherent tendency to react to thermal conditions, atmospheric fluctuations and will not cure and dry uniformly, resulting in some initial discoloration, which usually blends and cures out in a few months, similar to other natural and organic substances.
- After new concrete is poured, when can I walk or drive on it?
This is the most common question customers ask. Even though concrete takes around 28 days to cure, we know that most situations do not allow for that kind of cure time. We caution our customers to wait at least 24 to 48 hours before walking on new sidewalks, avoiding anything that would scuff or scratch the surface, such as dragging feet, rough foot traffic, large pets with sharp claws, etc. Stamped concrete and decorative finishes will take a little longer. After another week or two, normal foot traffic may resume, however, we advise our customers to avoid dragging heavy items, like trash cans, for another week or two.
As for driving on new concrete driveways, we recommend waiting seven to ten days for a small car or passenger car. For large, heavy vans or trucks, we recommend using utmost discretion and waiting the full 28 days.
- What can be done to protect & prolong the life of new concrete?
Sealing driveways, patios, sidewalk or other flatwork can greatly slow down the deterioration process caused by oxidization from the sun, water runoff and the overall use of your concrete driveway or sidewalk. A concrete driveway should be sealed every 2 to 3 years depending on the harshness of the seasons and various other factors, such as amount of traffic, sun exposure, use of salt and chemicals on roads, etc.
- Can we replace asphalt with concrete?
Absolutely; many of our customers were former asphalt driveway owners who realized that a concrete driveways can be a beautiful addition and add a substantial return of investment to your home. A wide variety of different colors and patterns to choose from can give your home a unique, one of a kind look: stamped concrete driveways, patterned concrete driveways, colored concrete driveways, textured concrete driveways, polished concrete driveways, concrete driveway overlays, concrete driveway staining and dyes. A properly installed concrete driveway with a little care and regularly scheduled maintenance can last up to 20 or even 30 years!
- What is the normal warranty on concrete projects?
D&B Concrete ensures high quality standards in workmanship and materials, and therefore, provides customers with a one-year warranty on workmanship against major cracks, major scaling or spalling and rock pops. Major cracking is defined as cracks wider than 1/4 inch and the total length of these major cracks must be more than 10% of the entire driveway’s edges and Joints, or more than 20% of an individual panel’s perimeter length. Major spalling, scaling or rock pops is defined as substantial surface disintegration greater than 10% of the entire driveway surface or more than 25% of any individual panel.
To keep your warranty in effect for one year, customers are advised to avoid the following practices that would render your warranty null and void: Never use or expose your flatwork to deicers containing sodium chloride, magnesium chloride, calcium chloride, ammonium sulphate or ammonium nitrate, as these chemicals cause surface defects in concrete. Avoid using any deicing chemicals on concrete less than two years old; the only safe material for traction on new concrete is sand. The National Research Council’s Strategic Highway Research Program tested deicing salts to see how they would etch and destroy concrete. The tests revealed that magnesium chloride did the least amount of damage; calcium chloride caused 26 times more damage to the concrete than magnesium chloride; and regular rock salt, sodium chloride, caused 63 times more damage.
This warranty does not cover the following: Damage caused by acts of God; damage caused by severe heaving of underlying ground; damage to concrete flatwork from deicing chemicals and road salt (typically found in driveways where wheels rest in normal parking spots); rock pops smaller than 3/4” diameter; physical damage (marks from ice chippers, snowplows, construction equipment, heavy trucks, etc.); damage or staining caused by organic matter or material; any concrete exposed to salt or chemical deicers; curb work and approaches, as these areas are subjected to harsh chemicals from snow plows.
- How thick should the concrete be?
If the driveway will be used by both passenger cars and light trucks or SUVs, then a minimum 4″ thickness should be adequate. Four inch thickness is also used for standard patios, sidewalks, porches and concrete slabs.
- What is reinforcement fiber concrete?
Fiber Reinforced Concrete is a composite material made of hydraulic cements, water, fine and coarse aggregate, and a dispersion of synthetic, small fibers which are distributed uniformly throughout the concrete matrix. Unlike welded wire reinforcement or rebar, which is specifically located in a single plane, syntheic fibers are distributed uniformly throughout the concrete matrix and their primary function is to modify micro and macro cracking. One of the important properties of fiber reinforced concrete is its superior resistance to cracking, thereby increasing structural strength, cohesion and integrity The synthetic fibers do not expand in heat or contract in the cold which helps minimize cracking. Finally, synthetic fibers help keep the concrete from spalling during impacts or fires.
- What necessary insurance should a concrete contractor have?
Most states require that contractors demonstrate proof of insurance as part of obtaining a trade license or registering. Contractor or business insurance will usually fall into two types, and D & B Concrete carries both:
Liability — Covers property damage and injuries caused by the contractor’s work. It will not normally pay the cost of repairing or replacing bad work; that’s the purpose of the bond.
Workers’ compensation — Provides payments to injured workers, without regard to who was at fault in the accident, for lost wages and medical services. It also provides benefits to the contractor’s family in the event of death. If the owner is the only employee, workers’ comp may or may not be required, depending on the state.