Cemstone - Homeowner - Concrete Basics

CONCRETE BASICS

Ready-mixed concrete accounts for nearly 3/4 of all concrete.
Ready-mixed refers to concrete that is batched for delivery from a central plant instead of being mixed on the job site.
Every batch of ready-mixed concrete is tailor-made according to the specifics of the job.
Ready-mixed concrete is particularly advantageous when small quantities of concrete are needed.
Materials, such as water and some varieties of admixtures, are often added to the concrete at the job site after it has been batched to ensure that the specified properties are attained before placement.
In its simplest form, concrete is a mixture of paste and aggregates.
A remarkable trait of concrete is that it's plastic and malleable when newly mixed and strong and durable when hardened.
The key to achieving a strong, durable concrete rests in the careful proportioning and mixing of all ingredients.
A concrete mixture that does not have enough paste to fill all the voids between aggregates will be difficult to place and will produce rough, honeycombed surfaces and porous concrete.
A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is likely to shrink more and be uneconomical.
A properly designed concrete mixture will possess the desired workability for the fresh concrete.
Typically, a mix is about 10-15% cement, 60-75% aggregate, and 15-25% water. Entrained air may also take up another 5-8%.
The character of the concrete is determined by the quality of the paste.
The type and size of the aggregate mixture depends on the thickness and purpose of the final concrete product.
During placement, concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets.
For slabs, concrete is left to stand until the surface moisture film disappears. Then, a wood or metal handfloat is used to smooth off the concrete.

More Resources

Cold Weather Concrete

Concrete Calculator