Four Different Types of Concrete
"Regular" or "normal" concrete is the term used for the mix which is sold primarily for home use and is available at home improvement stores. It comes pre-mixed for the convenience of do-it-yourselfers and needs only to be mixed with water.
It can also be bought unmixed and then combined with the sand and aggregate by contractors or others who are confident of their skills and knowledge. The standard formula is one part of cement, two parts sand, and three parts fine, dry stone. After blending these ingredients, the mix is then combined with one-half part water for final use.
The strength of regular concrete is sufficient for cosmetic purposes, and light home projects. It cures quickly, in about 90 minutes. It is not recommended for areas where freezing and thawing cycles occur regularly.
High strength concrete, also called high-performance, has a much higher compressive strength than regular, which means it is considerably stronger and can bear greater weight. This concrete is prepared with a lower water-to-cement ratio, which makes the resulting product less workable. This can be a problem in situations where rebar (reinforcing bars) cages are being used to reinforce the concrete. In today’s world of technology, superplasticizers are often added to increase the workability of high strength concrete.
Pervious concrete is a mixture where air or water is able to seep into the concrete through voids. These voids are deiberate and are caused by the difference in the formula. The fine aggregate is reduced, meaning the cement is held together mostly by the larger aggregate. This type is used where groundwater replenishment is important, or when water needs to be able to drain directly through the concrete.
Self-compacting, also known as flowing or self-consolidated, is one type which is often used by builders to reduce labor costs. When using regular or high performance concrete, vibration is used to remove the air from the concrete. This vibration occurs on the outside of the building forms and causes stress and wear on the forms. Self-compacting concrete requires no vibration, so it reduces the stress and the forms can be re-used, saving even more money. These are important factors in the contracting business, because labor and materials are a large part of the total budget for construction.
This type of concrete is also very useful when working in areas like underground structures, or places where vibration is difficult or impossible such as the bottom of bodies of water like oceans and rivers. Although it is the same composition of aggregates, cement and water as high strength concrete, it has additives which help it flow.
Each type of concrete--regular, high-strength, pervious and self-compacting--has an important place in our world today.