Conco Companies FAQs
What do I need to do to prevent cracks in my concrete?
When it comes to concrete, random cracking is unsightly. But, due to the fact that concrete shrinks, it is going to crack. Our best defense for concrete cracking is to try to control where the cracks occur.
Cracks will appear at any time and place where the stress within the concrete to pull apart exceeds the strength of the concrete to hold itself together. Concrete will shrink at a rate of approximately 1/8 inch per 20 feet, and while it shrinks it will crack randomly. We can control this random cracking by pre-determined location of joints in the concrete.
What are some forms of joints?
ISOLATION JOINTS (also called expansion joints) – These are placed wherever complete separation between the floor and adjoining concrete is needed to allow them to move independently without damage. These isolation joints are often made with an asphalt-based cork-like material.
CONSTRUCTION JOINTS – These are placed in a slab where concrete operations are concluded for the day. However, if the concrete operation is interrupted long enough that a cold joint may appear, you should install a construction joint regardless of planned joint layout.
CONTROL JOINTS – (also called contraction joints) – These are intended to create straight lines of weakness in the concrete that the cracks will occur along. They should be created to a depth of one forth the slab’s thickness with a maximum joint spacing of 24 to 36 times the thickness of the slab.Control Joints can be formed with a jointer, also called a groover. They have a cutting edge or bit that makes narrow grooves in the slab. For a 4-inch slab the depth of the cutting edge should be one inch, for a 6-inch slab the edge depth should be 1.5 in, and for an 8-inch slab the edge depth should be 2 inches. The radius at the top of the groove should be 1/8 in. for floors and 1/4 to 1/2 in. for sidewalks, driveways or patios. Shallow groover tools should only be used for decorative applications.
SAW JOINTS – These are control joints that are sawed in, straight as possible, clean lines about 1/4 the thickness of the slab. Sawing should be done as soon as the concrete is strong enough to resist tearing or other damage by the saw blade. A slight raveling of the sawed edge is acceptable. It is important not to delay sawing too long because the concrete may crack before it is sawed, or it will crack ahead of the saw blade. Saw joints are usually preferred over joints with a groover tool on floors that will carry forklift traffic or other industrial vehicles.
What problems can occur due to high temperature, high wind and low humidity?
The National Ready Mixed Concrete Association (NRMCA) defines hot weather concreting as anytime during high temperatures in which special precautions need to be taken to ensure proper handling, placing, finishing and curing concrete. During the summer months you will most generally experience problems that require precautions being taken for hot weather concreting, but the associated climatic factors of high winds and dry air can occur at any time. These conditions often produce a rapid rate of evaporation of moisture from the surface of the concrete and an accelerated set time among other problems.
Hot weather is a major factor to consider when planning a concrete project. Too often it is assumed that not much can be done to combat hot and dry conditions. Many times the addition of large amounts of water is used to fight off rapid set times or to ease the placing and finishing process. These assumptions and practices often times prove to be detrimental to the concrete.
What is Fly Ash?
Fly ash is a carbon by-product of coal combustion, most often the result of coal-fired electrical generating facilities. It is cementitious material, meaning it’s chemical properties cause it to harden with water exposure. By itself, fly ash does not possess much compressive strength. However, when added to Portland Cement it develops strength characteristics very similar to cement. Because fly ash reacts with the binding elements of cement, its addition to concrete adds strength helps to remove harmful agents in the mix. In our area, fly ash is particularly beneficial as it tends to slow the generation of heat in the concrete during hot weather.
Why choose concrete over asphalt for a driveway?
While asphalt is a cheaper short-term solution, the initial cost savings is lost over the lifetime of the driveway. Quality concrete driveways will last more than 30 years with little maintenance, but asphalt driveways need regular periodic sealing coats to retard age-related cracking. Even high-quality asphalt driveways and parking lots will deteriorate more quickly than concrete, due to environmental factors. When considering to the added expenses of surface/crack sealers and asphalt’s shorter lifespan, the overall cost of using concrete is much lower, and produces a true long-term solution.