There are only a few aggregates that we rely on as hardscapers. Though none is as increasingly important as 3/4 inch angular crushed stone or ASTM#57 stone. This stone has numerous applications in the field and has become more embraced as a base material for permeable or open graded base construction. Due to its drainage capabilities because it is a clean stone, it has many benefits for installers in many applications.
3/4 Crushed Stone
3/4 inch crushed stone is a useful aggregate in several applications of hardscaping and has become increasingly relied upon in permeable and open graded base installations where the water that enters the system is meant to freely drain through the base material and penetrate into the subsoil or be collected into a drainage system and exfiltrated out of the system.
It is defined as a self-compacting (though still does require mechanical compaction) aggregate that has a blend of size 5, 6, and 7 stone. It is not technically compacted, but actually properly oriented with mechanical compaction. It is a clear stone that allows the movement of air and water through it with minimal resistance, which helps in the proper drainage of systems as well as the ability to resist freeze-thaw cycles. With the installation of this material on top of a subgrade, it is important that a woven or non-woven geotextile is used to prevent the migration of material into the subgrade.
If your 3/4 inch crushed stone has fines in it, it is not a washed / clear / clean stone product. Additionally, if it has numerous round stones that have not been angular fractured, you will not achieve the proper compaction rate that is seen with an ASTM 57 stone. You want to ensure the quality of the aggregate that you are installing so that you can stand behind the final product.
What is Clear Stone
Clear stone refers to a washed aggregate product that is free of fine materials. The washing of the product reduces the amount of fine material within the aggregate mixture which ensures that there is minimal fines that will absorb moisture and reduce the free draining capability of the aggregate. When purchasing this stone, you will want to ensure that it is a clear stone meaning it has been washed and is free of fines.
3/4 Inch Clear Stone Applications
- Permeable Pavement Base
- Open Graded Base
- Retaining Wall Backfill
- French Drain and Other Drainage Solutions
In a permeable base, water that enters the system through the joints of the pavement moves freely with minimal resistance through the base material to enter the subgrade or to enter a drainage system that will exfiltrate the water out. This is achieved through the lack of fines in the aggregates that construct the base of this type of application. This is why a 3/4″ crushed clean stone is the suitable option for the base material in this application along with a clean aggregate for the bedding layer and a larger clean aggregate for just above the subgrade.
Sometimes referred to as the hybrid base, this is similar to that of a permeable base in that it requires a clean stone with no fines to allow the water to permeate through the system to enter the subgrade or drainage system to exfiltrate the water from the system. It is constructed of a 3/4″ clean stone base along with a clean stone bedding layer like High Performance Bedding.
ASTM 57 stone is an ideal aggregate for the backfill and core filling of retaining walls because of its drainage capabilities. The lack of resistance for water to flow through the aggregate and the collection of that water in a drainage system prevents hydrostatic pressure surcharge against the retaining wall.
The drainage capabilities of ASTM 57 stone allow for it to be the optimal aggregate for drainage solutions such as a French drain where a perforated drain is encased in the clean stone and wrapped in a non-woven geotextile to allow for water to enter the drainage pipe with minimal resistance and drain to the ideal area.
3/4 Clear Stone Compaction
Proctor compaction test is used to determine the optimal moisture content that a soil or aggregate will become densest. Aggregates with fines will need to achieve a minimum of 98% Proctor values to achieve proper compaction. However, with ASTM #57 stone you are unable to test using this. That is because it does not have fines in it to retain that moisture content.
ASTM 57 stone compaction is achieved through mechanical compaction of a reversible compactor, plate compactor, or roller in order to vibrate the individual stone facets to properly orient them. Typically you will see an 8% settlement of material in the installation of 3/4 inch clear stone after mechanical compaction is achieved. This settlement rate is lower than that of an alternative aggregate such as Granular A, making the most efficient use of aggregate in the installation process.
3/4 Inch Crushed Stone Calculator
Knowing how much aggregate you need for your project requires three measurements. You need to measure the length in feet, the width in feet, and the depth that you will need to cover with the aggregate. You can use this information to complete the formula below and to be able to calculate the total cubic yards of product that your project requires.
[Length (in feet) x Width (in feet) x Depth (in inches)] x 0.003 = Total Cubic Yards
If you have an irregular shape, you can break it down into square footage areas that are square / rectangular in shape and add them up or reduce the area that other objects will take up such as in a French drain scenario.