TABLE OF CONTENTS Slump, as it relates to concrete, is a measure of consistency equal to the decrease in height, measured to the nearest 1/4 inch (6 mm) of the molded mass immediately after it has been removed from this molded mass created by the slump cone.
The mold is in the form of a frustum (part of a solid cone intersected by the use of parallel lines) 12 inch (2.5 cm) high with a base diameter of 8 inches (2 cm) and a top diameter of 4 inches (1 cm).
This mold (slump cone) is filled with freshly mixed concrete in 3 layers, each being rodded with a 5/8 inch (15.9 mm) bullet-shaped rod 25 times. When the mold has been filled, the top is struck off and the mold is lifted. The amount by which the mass settles after mold removal is referred to as slump. A small slump is an indication of a very stiff mix and a very large slump is indicative of a very wet consistency
Recommended slumps are:
| Type of construction | Maximum slump (inches) | Minimum slump (inches) |
|---|---|---|
| Reinforced walls/footings | 3 (76.2 mm) | 1 (25.4 mm) |
| Caissons, substructure walls | 3 | 1 |
| Beams, reinforced walls | 4(102 mm) | 1 |
| Building columns | 4 | 1 |
| Pavements, slabs | 3 | 1 |
| Mass concrete | 2 (50.8 mm) | 1 |
Rule of Thumb: To raise the slump 1 inch (25.4 mm), add 10 pounds of water for each cubic yard of concrete. (One gallon of water equals 8.33 pounds.)
