What Is A Slump Test?

ASTM C143 – The purpose of the slump test is to determine the consistency of the concrete. This is a measure of the relative fluidity or mobility of the concrete moisture.

A technician will arrive at your site before concrete is placed. At a certain time, the technician will obtain a sample of

Technician rodding

Technician rodding the concrete in the cone to consolidate it.

the concrete. Testing of the concrete will be started within 5 minutes of obtaining the sample. The technician will follow ASTM C143 for the slump test of the concrete. After the concrete has been placed in the cone, rodded, and the cone pulled, the technician will measure how far the original displaced center of the cone has “slumped.” This number is called the slump and it is recorded to the nearest ¼ inch.

Technician pulling cone

Technician pulling the cone straight up to see how far it will slump.

Most projects have specifications for what the slump can be. Some have a maximum slump only. Some have a specification that says plus or minus one inch either way. Some clients need us to slump each truck as it is placed to ensure consistency.

Technician measuring

Technician measuring how far the original displaced center of the cone of concrete has slumped down.

Sometimes contractors need extremely stiff concrete to put through a curb machine (so it can be placed and remain standing).