CONCRETE 101

Ordering Concrete

To order a load of concrete, simply call the nearest LC Redi-Mix location and ask to speak with dispatch to set up a delivery.

The following information will be needed when plancing a concrete order:

  • Date and Time of Delivery
  • Jobsite location(address)
  • Quantity of concrete to be delivered
  • Application of concrete being delivered. For example, driveway, garage floor, footings…
  • What type of mix


Dispatchers can help figure quantities if needed.

The strength of most residential concrete is usually based on personal preference and/or local building codes.

Most commonly used mixes are from 3000 psi to 4000 psi, sack mixes are also available upon request.

It is important to tell the dispatcher what the concrete will be used for. Some examples of typical applications are: footings, walls, basement floors, driveways, sidewalks, and porch tops.



Choosing The Correct Concrete For Your Project

A basic concrete mix contains cementatious materials, water, aggregates and admixtures.

Portland cement, often referred to as simply cement, is the powder that gives the concrete its bonding characteristics. Other types of cementatious materials are fly ash, ground granulated blast furnace slag, and microsilica. These products are added to the concrete to affect desired characteristics of the concrete such as finishability, strength, and/or set times.

In our area of Northern Michigan, we offer two different types of coarse aggregate. The first type is a “local aggregate” or “round stone”, commonly used in all concrete that is not exposed to the weather and elements of nature. Concrete used in garage floors, basement floors and foundations have “round stone” coarse aggregate. The other main coarse aggregate is crushed limestone. It is mainly used in exterior concrete such as a driveway, sidewalk, patio, or porch top. The aggregate used does not affect the strength of the concrete.

Admixtures are used to control certain characteristics of the concrete. An air entraining admixture is a good example of a commonly used admixture. This particular admixture usually is in a chemical form and is added to the mix at the plant during the loading process. Air entrainment is necessary in exterior concrete which is exposed to the elements of nature, particularly moisture and the freeze-thaw cycle. Retarders, accelerators, and water reducers are other common admixtures. Fiber reinforcement is another form of a concrete admixture. Fibers are mainly used to control shrinkage cracks. Visit the Fibermesh web site listed in the “Partners & Links” section of this web site to see all the advantages of using fiber reinforcement. Our dispatchers can make suggestions, to help you decide what concrete mix is the best for your application.

Common ways to refer to concrete mixes would be by the “psi” or strength of the mix. For instance, commonly used mixes are 2500psi, 3000 psi, 3500 psi, and 4000 psi mixes.



Tips For Placing Concrete Slabs On Grade


GRADE PREPARATION

Grade preparation involves setting the grade elevation and creating a level and well compacted surface. Compaction can be obtained using a compactor, sprinkler, or both. During summer months it is beneficial to spray down the grade with water just before placing the concrete on the grade. This is beneficial for the curing process, and helps prevent shrinkage cracks, especially in dry, hot, windy conditions.

PLACING CONCRETE

Placing the concrete is typically done right from the truck. As soon as possible, screed off concrete with a screed board (a 2” x 4” is commonly used), and immediately bull float. It is critical to bull float the slab as soon as possible after screeding, delays in bull floating may cause surface problems later. The slab is usually ready to be edged after the concrete has been bull floated. If this is an exterior slab, a broom finish is recommended. A broom finish is obtained by pulling a broom across the surface of the concrete in one uniform direction. The broom finish is applied after all bull floating, grooving, edging and mag work has been done. If you are unsure as to when to broom your concrete, try a small sample piece next to the edge that you can easily fix with a hand mag if needed. Smooth troweled (interior) finishes require more time and labor, experienced help is recommended when attempting to finish floors.

CURING CONCRETE

After concrete has been placed, and finished, the process of curing the concrete begins. Curing concrete is basically controlling conditions that are in direct contact with the concrete to help it obtain maximum durability. One of the most common curing practices is to apply a curing agent to the exposed surfaces of the concrete. Curing agents are easily applied by either sprayer or roller, and are readily available from your local LC Redi-Mix location. Curing compounds allow the concrete to utilize its own moisture to obtain maximum durability. For the best results, most curing compounds should be applied after finishing operations have been complete, and normal traffic will not damage the surface of the concrete. Another method of curing concrete is to cover the concrete with a sheet of plastic, this will basically do the same thing as the curing compound by keeping the concrete in a moist condition. If plastic is used to cure the concrete, clear plastic is recommended over black plastic. It is recommended that all exterior concrete be sealed every year to help fight against deterioration from salt and chemicals. Concrete sealers are also available at your local concrete supplier.

CONTROLLING CRACKS

Concrete cracks are usually controlled by one of two different methods. The first is cutting the concrete in locations where it is likely to crack with a specially designed saw. Concrete saws can be rented from most rental stores. The other method is called ‘tooling’ or ‘grooving’ joints in the concrete. This practice is done while the concrete is in the plastic state. If concrete is not tooled, it is strongly recommended that it be cut no more than 24 hours after it has been placed to prevent uncontrolled shrinkage cracks. The recommended distance between joints is usually two to three times the thickness of the slab in feet. If a 4” thick slab is being placed, joints should be no more than eight feet to 12 feet apart.