What causesd these blemishes on top of my slabs?

Check our colored concrete troubleshooting guide in the color section of our products page or contact our salesmen.

What makes high quality concrete?

Basic requirements for 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 Allied Concrete meet quality requirements. 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.

Why is too much mixing of water dangerous?

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.

What are typical concrete requirements for around-the-house patios, walkways, and driveways?

The contractor should provide the ready mix producer with the following basic information:

Maximum size of coarse aggregate
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 compressive 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.

What steps can be taken during construction to ensure good performance?

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.

Proper joint spacing is determined by multiplying the depth of the pour (in feet) by a minimum of 24 and a maximum of 36. The Maximum distance between joints is 15 feet apart. Your length should be no more than 1.5 times your width.

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.

What kind of performance should I expect from concrete placed around your home?

Quality concrete that has been 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.

If you have any other questions or concerns regarding concrete, our business, please do not hesitate to call our office at (209) 524-3177 or email us through our Contact Us page.