Concrete Admixtures for Residential Retaining Walls

How Concrete Admixtures Benefit Residential Retaining Walls

There can be many benefits to using concrete admixtures when constructing a residential retaining wall. Using concrete admixtures can help exceed minimum engineering specifications and minimize conditions that contribute to failures of residential retaining walls.

Compressive strength

When concrete is mixed, using too much water will decrease the compressive strength of the cured concrete. When the excess water evaporates, it leaves voids filled with air instead of solid concrete. Water-reducing admixtures can reduce the amount of water required for the mix to be workable and placeable by about 5 to 40% in the concrete mixture, resulting in stronger concrete.

Concrete with greater than about 10% trapped air levels can reduce compressive strength  significantly. However, some amount of entrained air, typically between 5% and 8%, is desirable in concrete that will be exposed to freezing conditions. Using an appropriate air entrainer at an appropriate dosage allows the entrained air content to be controlled.

Flexural strength

As crucial as compressive strength, the flexural strength of the concrete also has to be considered. Flexural strength is similar to compressive strength but measures how much stress the concrete can withstand before the bending of the concrete creates failure conditions.

And like compressive strength, water absorption can be a factor in diminishing flexural strength. Using the same concrete admixtures as increasing compressive strength will also increase flexural strength. Additionally, macro or micro fiber is added to help increase flexural strength as well.

Permeability

The purpose of most residential retaining walls is to reduce soil erosion caused by water and to control water flow. However, concrete is a porous material that can absorb moisture and other chemicals if the concrete is mixed with a higher water-to-cement ratio.

Water absorption can lead to several concrete failures, such as:

• Shrinkage
• Cracking
• Freeze/thaw failures
• Corrosion of reinforcing rebar

Studies showed that carbon nanotube admixtures like EdenCrete® decrease concrete’s water absorption and permeability. Reducing water absorption and permeability helps concrete retaining walls stay in place longer.

Shrinkage

When excess water is used to mix concrete, the moisture evaporates during the initial curing process. This can cause the concrete shrink, and the process is known as drying shrinkage. The shrinking of the concrete can lead to crack development. Using shrinkage-reducing admixtures and proper curing processes can reduce this tendency.

Cracking

Cracking can be a result of strength and permeability issues. Where strength issues were already present, as indicated by cracking, the cracking contributes to further strength reduction. The inclusion of certain materials, such as fibers, can help reduce crack propagation.

Delaminating

This type of concrete damage is a surface detachment of the concrete from the rest of the retaining wall, usually due to bonding issues. Ensuring proper concrete mixing and the inclusion of fibers or EdenCrete® carbon nanotube-enriched admixtures can help reduce the tendency to delaminate.

Spalling

Spalling is evidenced by a pock-marked appearance on an exposed concrete surface.  Spalling accelerates further deterioration of the concrete because it opens up the concrete’s interior matrix to environmental exposure. Spalling is often due to water penetration and freezing in higher-permeability concrete.

Efflorescence

Efflorescence refers to deposits of minerals that water leaves behind as it evaporates from a concrete surface. These can be unsightly, and can be indicative of additional problems within the concrete. Using admixtures that reduce the water content in the concrete can help prevent efflorescence.

Freeze / Thaw

This condition is a common cause of concrete failure. When water fills air voids in a porous material like concrete and then freezes, it expands by about 9%  of its original volume, stressing the concrete. When the ice thaws, it leaves little cracks that will continue to develop the next time moisture fills the spaces and refreezes. Using an appropriate air entrainer at the correct dosage entrains tiny air bubbles in the concrete. These air bubbles provide space for any freezing water in the concrete to expand into, protecting the concrete from the stress that creates.

Corrosion Resistance

When the reinforcing rebar rusts or corrodes from increased moisture absorption of the concrete, this can cause cracking, delamination, and spalling. This occurs at a more accelerated rate in marine or coastal environments with exposure to salt water. Using a corrosion inhibitor can help mitigate damage from reinforcing steel corrosion.

Use Concrete Admixtures For More Durable and Long-lasting Residential Retaining Walls

With carbon nanotube admixtures from EdenCrete®, you can build a residential retaining wall that surpasses design specifications in strength while significantly reducing the moisture absorption and permeability of the concrete it’s made from. Contact us to learn more about how carbon nanotubes can help you in your residential retaining wall project.