What is the difference between cement and concrete?

 

Although the terms cement and concrete are often used interchangeably – cement is not concrete nor is concrete cement. Cement consists of various mixtures of clay and limestone and is actually one of the basic ingredients used to make concrete. When cement is mixed with other basic ingredients - sand, gravel or crushed stone, and water - the cement and water react to form a paste that glues the remaining ingredients into a hard stone like mass which is known as concrete.

 

Why does concrete crack?

 

All concrete cracks. Cracking is caused when concrete contracts during the drying, curing, hardening process, and the bond between the cement paste and the aggregates is not strong enough to endure that stress.

 

When installed properly, concrete is one of the most durable and long lasting products you can use. It is important that concrete contractors follow established guidelines with respect to concrete placement. Following are the main reasons concrete cracks:

 

• Excess water in the mix
• Rapid Drying of the concrete
• Improper strength concrete poured on the job
• Lack of control joints

Why is temperature important, can it be too hot or cold?

Concrete gains strength through a chemical reaction that involves hydration of the cement paste. Temperature extremes make it difficult to properly cure concrete. Too much water is lost by evaporation on hot days. If the temperature nears freezing, hydration slows and almost stop. Under these conditions, concrete ceases to gain strength and other problems develop. In general, the temperature of new proper concrete placement is between 50 F and 85 F. Placement of concrete outside of these ranges requires unique preparation.

 

Is slump important and what is it?

 

Slump is used as a measure of the consistency of freshly made concrete, and is most often associated with the amount of water added to the concrete mix to increase ease of flow and placement (the higher the slump, the wetter the mix). 

If too much water is added to increase slump beyond the design specification, it can result in reduced-strength potential for the concrete and possible surface deterioration. 

What decorative finishes are available?

 

Today, due to the advances in concrete finishing technology, mix and design, concrete can take on just about any shape, pattern, texture or color. Thus special finishes are possible and limited only by your imagination and the skill of your concrete contractor.

Some of the special finishes available include: exposed aggregate finishes, colored concrete finishes, stamped concrete finishes, engraved concrete finishes, stained concrete surfaces, and sawed and pattern-grooved concrete finishes.

 

What controls the strength of concrete?

The primary components that control the strength of concrete are the water and the cement contents. These two components are commonly referred to as the water/cement ratio. While properly graded sand and stone, and their relative amounts can affect the overall strength of the mix, the water/cement ratio has the greatest effect on the strength of the mix.