Hydraulic SlumpHydraulic Slump

EquipmentEquipment

Slump cone & pan

5/8” x 24” long bull-nose rod

Concrete scoop

12” ruler

Bucket & sponge

PreparationPreparation

Using the sponge, moisten the pan and the inside wall of cone

Stand on cone fins

ProcedureProcedure

Using the scoop, carefully place the concrete in the slump cone

Fill the cone 1/3 full (by volume)

ProcedureProcedure

Using the rod, rod the concrete 25 strokes; do not strike the bottom

Start around the perimeter with the rod slightly inclined and spiral in toward the center

ProcedureProcedure

Continue the procedure for the second and third layers

Rod the layers just slightly into the preceding layer.

Do not strike the side of the cone.

ProcedureProcedure

Overfill the cone on the last layer.

If the level of the concrete drops below the top of the cone, stop rodding, add more concrete and resume the count

ProcedureProcedure

Strike off the excess concrete using the rod as a striker

Use a sawing and rolling motion

ProcedureProcedure

Clean the concrete from around the base of the cone

While holding the cone in place by the hand-holds, step off of fins and hold cone down with hands

ProcedureProcedure

Lift the cone in a single straight-up motion in 3 to 5 seconds

Turn the cone upside down and place it next to the subsided concrete

ProcedureProcedure

Place the rod across the base of the inverted cone.

Measure from the bottom of the rod to the displaced center of the concrete

Record to the nearest ¼”

How Do We Manage This?How Do We Manage This?

The Problem: “Slump Is Always On The Move”

“Target” or “Slump Not To Exceed” will be specified by the engineer in the specification.

Ie, 3” plus or minus 1” Ie, not to exceed 4”

Slump decreases with time at varying rates

Dependent on many factors including:◦ cement content and characteristics◦ Temperature◦ admixtures that are used

Slump loss is particularly a problem when concrete is being transported long distances or if placement is delayed.

Strength is CompromisedStrength is Compromised

Result Of Adding Water to the Truck:

Solutions:Solutions:Some mixing water is held back at the plant

and added at the job site as long as:

Addition of water does not exceed specified W/C ratio Addition of water does not exceed specified slump

RULE OF THUMB: One gallon of water per yard of concrete will increase slump one inch

READ: “CONCRETE IN PRACTICE: JOBSITE ADDITION OF WATER”

Another Solution: Another Solution: Superplasticizers & Water ReducersSuperplasticizers & Water Reducers

Acceptance of superplasticizers allows us to maintain desired water-cement ratios or reduce them while maintaining workability for placement.

Use of superplasticizers will also allow placement of concrete at slumps higher than the typical 3" with a lower water-cement ratio.

MUST BE APPROVED BY ENGINEERMUST BE APPROVED BY ENGINEER

REMEMBER:REMEMBER:

Any modifications to the concrete at the jobsite MUST be measured and recorded for quality assurance purposes!