Date post: | 30-Dec-2015 |
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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.
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