Concrete Types

Regular Concrete

Regular concrete is the lay term far concrete that is produced by following the mixing instructions that are commonly published on bags of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa to about 40 MPa, depending on the purpose, ranging from blinding to structural concrete respectively. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

High-strength Concrete

High-strength concrete has a compressive strength generally greater than 6,000 pounds per square inch (40 MPA). High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.

In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength.

High-performance concrete

High-performance concrete (HPC) is a relatively new term used to describe concrete that conforms to a set of standards above those of the most common applications, but not limited to strength. While all high-strength concrete is also high-performance, not all high-performance concrete is high-strength. Some examples of such standards currently used in relation to HPC are:

• Ease of placement
• Compaction without segregation
• Early age strength
• Long-term mechanical properties
• Permeability
• Density
• Heat of hydration
• Toughness
• Volume stability
• Long life in severe environments

Self-compacting concretes

During the 1980s a number of countries including Japan, Sweden and France developed concretes that are self-compacting, known as self-consolidating concrete in the United States. This self-compacting concrete (SCCs) is characterized by:

• extreme fluidity as measured by flow, typically between 650-750 mm on a flow table, rather than slump(height)
• no need for vibrators to compact the concrete
• placement being easier.
• no bleed water, or aggregate segregation

SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear on formwork.

As of 2005, self-compacting concretes account for 10-15% of concrete sales in some European countries. In the US precast concrete industry, SCC represents over 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for road and bridge projects.

This emerging technology is made possible by the use of polycarboxylates plasticizer instead of older naphthalene based polymers, and viscosity modifiers to address aggregate segregation.

Pervious concrete

Pervious concrete is sometimes specified by engineers and architects when porosity is needed to allow some air movement or to facillitate the drainage and flow of water through structures. Pervious concrete is referred to as "no fines" concrete because it is manufactured by leaving out the sand or "fine aggregate". A pervious concrete mixture contains little or no sand (fines), creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly.

Pervious concrete pavement is a unique and effective means to address important environmental issues and support sustainable growth. By capturing rainwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting US Environmental Protection Agency (EPA) stormwater regulations. The use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA, and by other agencies and geotechnical engineers across the country, for the management of stormwater runoff on a regional and local basis. This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices. In doing so, pervious concrete has the ability to lower overall project costs on a first-cost basis.