How to Perform a Concrete Slump Test
Concrete slump testing sounds intimidating, yet it becomes quite easy with practice. Construction site managers, quality control technicians and engineers alike are encouraged to master concrete slump testing before beginning projects.
This is your step-by-step guide from Deslauriers’ concrete testing experts on how to perform a concrete slump test the right way.
How to Perform a Concrete Slump Test: A Quick Explanation of Concrete Slump
The slump analysis requires a consolidation of the concrete sample in a highly precise manner. A cone frustrum serves as the mold for concrete testing. The “slump” of concrete refers to the subsiding of the concrete as the mold is raised up after losing support.
The slump value refers to the height distance from the original surface and the displaced surface. The value is typically measured in either inches or millimeters.
The slump value ideal for one concrete application is not necessarily optimal for the next. A concrete slump that is particularly stiff is ideal for pavement and curb installations.
Alternatively, columns and casting walls with unique shapes and/or restricted reinforcement require a concrete mix that is malleable for a smooth flow. Such an easy flow ensures the concrete can slide into crammed spaces and also move around reinforcing steel.
Every contractor, engineer and construction site manager should be aware that concrete slump is dynamic as opposed to static. In other words, concrete slump changes. Factors ranging from temperature to position, time elapsed after batching and chemical admixture impact how the mix responds to testing.
All concrete slump testers should be aware that the subtleties of their actions affect the test outcome. If the placement is off or consolidated, the outcome will change. Moreover, if the slump cone is lifted too quickly or slowly, the outcome will also change.
How to Perform a Concrete Slump Test
Slump testing begins with a set of testing equipment. Deslauriers has your concrete slump testing needs covered. From steel slump cones to plastic slump cones, slump cone sets, economy base plates, scoops and strike-off bars, we’ve got everything you need.
At a bare minimum, testing requires a cone, a base, a scoop and a tamping rod. The entirety of the set must be wet to facilitate proper cleaning upon completion. Ideally, the slump test will be conducted within two and a half minutes of its beginning point for accuracy’s sake.
Be sure to err on the side of a larger rod that is of the graduated design style. Contrary to popular opinion, there is no need to use a tape measurer.
Fill the cone in three distinct increments. The last of the thirds should fill the cone to half its height. Each lift of the concrete is to be prodded with the rod at least 20 to 25 times. Begin the rodding along the outside, gradually working your way toward the middle in a spiral formation.
Penetrate the concrete mix to a level of once inch. Be sure to wear gloves while performing the concrete slump test as it has the potential to harm the skin.
Clamp the cone directly to the base for added security. Stand on the foot tabs to secure the testing equipment firmly in place. Start moving the scoop around in a circular motion, ensuring it is evenly distributed throughout the slump cone.
Grab your graduated tamping rod and work the mix, beginning on the outside. Push downward but don’t press the steel rod against the bottom of the cone. Push down and around 20 to 25 times before putting in the next lift of concrete.
Finishing the Slump Test
The last concrete placement is to be above the slump cone’s rim. The concrete is to pile up in the middle of the cone as it will move outward during the rodding process. Be sure to have a concrete scoop on-hand to ensure the cone is properly topped off for a straight edge.
Start moving the steel rod up and down for another 20 to 25 pushes. The tamping rod is used to strike the mix off smoothly yet not finish it, ultimately ensuring the excess concrete is removed for a level surface. Also, be sure to remove concrete that has accumulated along the base of the cone.
The next step is to lift the cone to conduct the test. Count to seven seconds when raising the cone. The concrete should remain firmly at the base. However, if the concrete moves away from the base, the test is to be conducted again.
Finally, raise the arm of the cone testing setup to gauge the distance from the arm’s handle to the surface of the concrete mass. Ideally, this distance will be between eight and nine inches.
The “Why” of Concrete Slump Testing
Concrete slump testing is a necessary analysis for all fresh concrete to be used for a wide array of purposes. Regardless of the specific application you have in mind, this test is essential for gauging the workability and consistency of fresh concrete.
Originally devised back in the early 1900s, concrete slump testing maintains the ideal slump value for a mixture that maximizes the placement of concrete. The test also facilitates proper consolidation and finishing.
Skip over the slump test and you won’t know whether your concrete is fully compliant. The aim is for the concrete batch you’ve selected to comply with the mix design approved for the project. If the concrete proves inefficient or otherwise flawed, it is unsuitable for placement.
Measuring the “W/CM” Value of the Concrete Slump
Above all, the purpose of the concrete slump test is to gauge the ratio of water to cement materials within a specific batch. The test ultimately determines if the concrete mix is sufficiently balanced.
The aforementioned water ratio to cement materials is referred to as the w/cm value. This value reflects the strength of the concrete.
In addition to concrete slump testing, other tests are conducted to gauge the following aspects of the fresh concrete:
- Unit weight
- Air Content
- Temperture
- Lab sample molding for strength
Such tests combine to gauge concrete properties after delivery to the project site.
Ideally, the fresh concrete test will be conducted just ahead of the time at which concrete placement occurs. Moreover, fresh concrete tests are to be repeated at intervals when pouring to determine if the product is sufficiently consistent.
Deslauriers has the Inside Scoop on how to Perform a Concrete Slump Test
Curious as to how to perform a concrete slump test? Ready to upgrade your slump testing setup? Explore Deslauriers’ Slump Cone Accessories or contact us for expert advice.
