Concrete Consolidation in ICFs

March 18th, 2010 | Common Troubleshooting, From the Field | Common Troubleshooting, concrete placement, consolidate, Darryl U, kelvin doerr

Concrete consolidation is a very critical component in the construction of ICF buildings. The consolidation of concrete in the ICF wall is more difficult to inspect after the pour because the forms stay in place. That is why internal vibration and proper concrete mix and placement is important to ensure that there are no voids or honey combing in the wall.

There are three main components that must be evaluated and addressed.  Consolidation is a function of all three components.

1. Concrete Mix
2. Placement
3. Consolidation

Concrete Mix Design for ICF

One of the most important aspects of concrete placement is the proper concrete mix design.  The flowability of the concrete is crucial.  A quality concrete mix can go along way to assure a successful and efficient concrete placement.  Proper concrete mix will save time on labor, facilitate concrete consolidation and provide for a successful Reward wall pour.  Cutting corners on the concrete mix can add cost and problems when you go to place concrete into the Reward walls.  Concrete mix can vary from region to region throughout the country, as the raw materials are different in various areas.  Because of the variance in materials and the importance of a quality concrete mix, the best advice is to work closely with the local concrete supplier.  Explain to the concrete supplier that you will be placing concrete in Reward insulating concrete forms.  Reward cannot provide the specific concrete mix design; we can only provide guidelines for the mix.

A proper Reward concrete mix will incorporate the following guidelines.  These guidelines must be conveyed to the concrete supplier.  They will have the most knowledge about the materials in the area to design the best mix for the Reward projects.

Concrete Compressive Strength

The 28-day compressive strength of the concrete must be specified to meet the strength used in the design of the Reward walls.  The minimum strength that should be specified is 2,500 psi.  A slightly higher compressive strength of 3,000 to 4,000 psi can help the flowability and pumpability of the concrete and provide additional strength to the walls with minimal or no additional costs.

Slump for Insulating Concrete Forms

The slump is an important criterion in the concrete mix to allow the concrete to flow and be pumped at an efficient rate.  Inadequate slump can create voids and honeycombs in the walls, or put excessive pressure on the forms during concrete placement.  Reward generally recommends a concrete slump of 5.5 to 6.5.  The core size of the forms will help determine the slump, and the smaller the core size the higher the slump. For example, the proper concrete slump for each size is listed in the table below.

Form Sizes	9″	11″	13″	15″ & 17″
ICF Concrete Slump	6.5″- 7″	6″-6.5″	5.5″-6″	5.5″
Course Aggregate Size	3/8″	3/8″-1/2″	1/2″-3/4″	3/4″

The slump specified must be the slump that arrives in the cement truck at the job site.  Water should not be added to the concrete at the job site.  Additional water will reduce the compressive strength of the concrete and affect the water to cement ratio.

Aggregate Size for ICF

The aggregate size is also important in providing concrete with the proper strength that will flow well through the insulating concrete forms.  A maximum aggregate size of 3/8″ to 1/2″ is recommended for the best results.  The risk of too large of aggregate in the forms could create the damming of the concrete within the forms resulting in a void.

As an example, again the smaller the core size needs the smaller aggregate. The proper aggregate for each size of core is listed in the table above.

Insulated Concrete Form Admixtures

Admixtures are ingredients in the concrete other than portland cement, water and aggregates.  Some of the effects of admixtures are to improve the pumpability, durability and workability of concrete and for weathering purposes.   There are many different types of admixtures available in different parts of the country.  Some of types of admixtures include air-entraining, water-reducing, superplasticizers, retarding and accelerating.  Fly ash, air, plasticizers and superplasticizers are common admixtures used in concrete in the insulating concrete form industry.  The concrete supplier should address admixtures at the concrete mix design stage.  The goal should be a good flowable concrete mix.

Be sure to thank our in-house ICF engineer Kelvin D and Darryl U for contributing to these posts. Next post we’ll go over concrete placement techniques.

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