Q. What makes good quality concrete?
A. There are several basic requirements for good quality concrete:

• Good materials-cement, aggregate admixtures and water 
• Proper proportioning of these materials 
• Thorough mixing 
• Skillful placing and finishing
• Proper curing

All of these requirements are important, and failure to satisfy any one of them will often result in a reduction in quality. The materials used by Ohio Ready Mix, Inc. meet quality requirements specified by groups such as the American Society for Testing and Materials and the Ohio Department of Transportation. The specifications relate to important properties such as amounts of nondurable substances permitted in aggregates and how fast the cement will set and gain strength. Multiple tests are conducted to verify that, the materials we use meet and exceed applicable specifications. 

Another key to having excellent concrete is proportioning. Proportioning is simply deciding how much of each ingredient will be put in the concrete. A temptation to use too much water generally results from an effort to make placing operations easier for the contractor. Overly wet concrete flows into the forms more readily, is easier to compact and to strike off.

Everything about overly wet concrete is easier-except the maintenance problems that will begin to appear on a surface that could just as easily have been trouble-free for many years.

Q.  Why is too much mixing water dangerous? 
A.  Simply because excessive water makes a more dilute cement paste. Not all of the water in any concrete reacts with cement and when there is an excessive amount of water it leaves small voids in the hardened paste. This makes the concrete weaker, more porous and less durable.

Q.  What are typical concrete requirements for around-the-house flatwork-patios, walks, driveways?
A.  The contractor should provide the ready mix producer with the following basic information:

• Maximum size of coarse aggregate. Usually, we recommend #57 stone. 
    
• Slump of the concrete. Slump is a measure of how readily a concrete flows. Slump values are determined by test. Increasing the water content increases slump, and a slump that is too high indicates that too much water may have been added to the concrete. A 4 to 5-inch slump will give a good, workable mix. A stiffer mix (lower slump) will usually be more difficult to place and a wetter, soupy mix won't be as strong and durable.
     
• Strength required. In severe climates where concrete will be exposed to freezing and thawing, a compresive strength of about 4000 pounds per square inch (psi) is a common specification. Strength is measured on standard test cylinders cured under standard conditions. A strength of 3000 to 3500 psi at 28 days is adequate for nearly all concrete not exposed to numerous freezing and thawing cycles or to deicing salts.
     
• Air-entrainment. Entrained air is air that is purposely incorporated into a concrete mix, primarily to make the concrete resistant to deterioration caused by freezing and thawing and the use of deicing salts. To be effective for this purpose the air content should be about 6 percent. The air bubbles also make the concrete easier to work because they act as a lubricant. For this reason some builders prefer to use air-entrained concrete for most flatwork around the home, whether or not the flatwork will be exposed to freezing and thawing.
  

Q.  What steps can be taken during construction to ensure good performance?
A.  The homeowner will want to be sure that, for flatwork, the underlying soil (subgrade) is well compacted by the contractor and not extremely wet or muddy when concrete is placed. Workers should also check the elevation of the subgrade by measuring down from a straightedge laid on the forms.

High spots should be removed; otherwise the slab will be too thin in spots. Low spots should be filled in and compacted; otherwise the buyer may pay for more concrete than is needed. Flatwork for driveways, sidewalks and patios is typically 3 1/2 to 4 inches thick.
Side forms should be set so that the finished concrete surface is sloped slightly for drainage. A slope of 1/4 inch per foot of width is recommended for driveway slabs.

Joints are needed in most concrete slabs. They control cracking by dividing the slab into square sections for driveways and patios, the joints should usually be spaced 10 feet apart or less. For sidewalks they are typically spaced only 4 or 5 feet apart. Joints must be cut to a depth of at least one inch. If the joints aren't cut deep enough or if no joints are provided, the slab will probably crack at random locations.

Where flatwork abuts another structure, it should be separated from the structure by an expansion joint. Usually a premolded strip of compressible material is inserted at locations such as the intersection of a driveway and garage slab or a patio and the foundation wall of a house.


Q.  What is meant by curing?
A.  A chemical reaction between cement and water makes concrete strong and durable. The purpose of curing is to make sure that little or no water is lost from the concrete during the early stages of this chemical reaction.

Q.  How is curing accomplished? 
A.  The newly placed concrete should be covered or sprayed with a material that will retain the moisture within the mix. Membrane curing compounds sprayed on the surface are the materials most commonly used. They are very convenient but they must be applied immediately after the concrete is given its final finish and care must be taken apply them thoroughly and uniformly. Coverings used to cure concrete include wet burlap, plastic sheets and Kraft paper. If burlap is used it must be kept continuously wet. The curing process should be continued for at least 72 hours and twice as long if the temperature is below 50 degrees F.
 

It is up to the contractor to cover the concrete and start  the curing process. But it is usually up to the homeowner to follow through from there and make sure that curing proceeds uninterrupted for the required time period.

Q.  How do you find a good contractor?
A.  First of all, don't pick him entirely on the basis of cost. In concrete work, as in any business, you get what you pay for. Cost should be a consideration, but it should not be the only consideration. Knowledge, competence, integrity and experience are the qualities to seek in a contractor. To obtain the names of qualified contractors, talk to the dispatchers or friends and family. Then take a look at a few of the contractors' completed jobs, particularly some that were done several years ago. If you like what you see, you can feel easier about seeking bids from them, knowing that they do good quality work.

Q.  What performance should you expect from concrete placed around your home?
A.  Good quality concrete-properly proportioned, mixed, placed, finished and cured-will give maintenance-free service for many years. Concrete work, properly done, will usually last much longer than the need for which it was originally installed. 

Q.  How do I know how much concrete to order?
A.  When you have measured the length and distance of the area you are interested in pouring, call our dispatch center and they will provide an exact measurement for your project.

Q.  What kind of reinforcement should I use in my concrete?
A.   Much of that depends on what the concrete is being used for.  In most cases, Fibermesh is an excellent no-hassle solution to providing additional strength.  We also suggest using rebar or wire depending on the use.

Community Storage  |  Duff Quarry  |  Mr. Concrete  |  Ohio Lumber

Ohio Ready Mix, Inc. 9016 S.R. 117, Box 305 Huntsville, Ohio 43324
Phone: 937.686.3112 Fax: 937.686.5125 E-mail: jduff@bright.net