Flow table test

The slump test is a procedure for the determination of the flow, a characteristic of the consistency of fresh concrete. The simple experimental set-up this concrete testing is also possible directly on the site. Colloquially, the performance of the experiment because of the typical noise is also referred to simply as a rattle.

The slump test is not applicable for foam concrete, and grained concrete with a maximum grain size of the aggregate of more than 63 mm. In addition, self-compacting concrete can not examine sufficiently accurate due to the standardized size of the test table.

Application and structural engineering background

The slump test plays an important role both on construction sites, as well as in the concrete manufacturing mixing plants. The test is used to check the consistency of the fresh concrete immediately before installation, or in the factory prior to being loaded on a truck mixer. Particularly important is the examination if due to the installation conditions (eg narrow reinforcement layout ) or due to requirements for the surface of the component (eg concrete ), a mixture with a given slump, so a given consistency, ordered.

If the fresh concrete to viscous ( stiff), it can come with installation cavities ( larger pores, gravel nests ). Often these cavities are only visual defects, can in extreme cases, but also affect the resistance of the member. In addition, the reinforcement is not directly enclosed by concrete and thus not protected against corrosion with deep cavities. Unless remedial measures are carried out, this creates after some time an additional weakening of the component.

Attempt

Accessories and environmental conditions

• Standardized flow table with hinged at one side and with a handle and a stop for limiting the lift height on the opposite side. Dimensions: 70 cm x 70 cm
• Truncated cone-shaped container that is open top and bottom. (Height: 20 cm, Diameter top: 13 cm, bottom diameter: 20 cm)
• Or similar bucket with water, soup ladle similar to moisten and clean the plate, smoothing trowel, small shovel
• Horizontal, solid, non- resilient underground
• Possibly shelter in heavy rain

Implementation

First, the plate of the table is moistened with water and the like with a trowel the resulting water film is peeled off. The surface should be slightly damp after. This will ensure that the consistency is not affected by the table. In a dry surface the slump would be lower. Too wet table would distort the result in the other direction. Subsequently, the truncated cone shape is put on the center and to be filled with a small blade with fresh concrete. Projecting concrete at the upper opening is scraped smooth and shape then pulled up. The concrete a piece spreads out wide. The movable side of the Ausbreittischs immediately after 15 times smoothly lifted to the stop ( 4 cm) and then dropped. Between each pass at least 1 second should take up no more than 3 seconds. Through the vibration, the fresh concrete is spreading further. Finally, the diameter of the resulting " concrete cake " is twice measured diagonally. The mean diameter in millimeters is the slump. The specification is always rounded to 10 mm.

Evaluation and measures

As described in the implementation of the result of the experiment, the diameter of the " concrete cake ". The consistency, or the consistency of the fresh concrete class can be the basis of this value with the adjacent table easily determined.

If ordered with a certain consistency concrete, provides the slump on the site the opportunity to check whether the target is actually present. If this is not the case, the slump can be increased, for example, flow agents. After the admixture of the composition of the test is then repeated. In addition, the examination of individual batches allows the mixing engineer at the concrete plant easily adjust the concrete mix and to adjust the system for future batches accordingly.

Pros and Cons

The great advantage of the experiment is the simple experimental setup and the quick feasibility. Spreading tables are built sturdy, a little prone to damage, easy to clean and they also do not require power. This allows the fresh concrete consistency are checked for virtually any construction site without much preparation.

Be disadvantageous to see is the manual performance of the experiment, or 15 beats. Since the standard allows for a relatively large time window of 1 to 3 seconds between two passages, a sample, it is possible the examiner fast or slow to " rattle " and so - intentionally or unintentionally - to influence the slump. Because of this large variability, DIN 1045-2 and DIN EN 206-1 prescribes a tolerance of ± 30 mm for compliance with the target value of consistency.

Norms and Standards

• DIN 1048 - Test methods for concrete
• DIN EN 12350-5 - Testing fresh concrete - Part 5: Flow