![Testing shotcrete: the slump test [Video]](https://bestsupportunderground.com/wp-content/uploads/2016/11/portada3.jpg)
Another essential test to measure the consistency of fresh shotcrete is the slump or Abrams cone test. As is the case with the flow table test, the methodology is simple and requires only basic tools, making it easy to replicate onsite.
The test is designed to measure shotcrete’s slump, or its consistency; which is of great importance to determine its pumpability and minimize pulsations in the concrete pump.
How does the test work?
The test includes the filling of a slump mould with three consecutive layers of concrete. Once the mould is removed, the difference in height between the shotcrete slump and the cone are measured and compared.
Our video details the different steps involved, in accordance with European regulation UNE-EN 12350-2:2009.
It’s important to ensure that the concrete is thoroughly mixed before beginning the process. Instructions for the test are as follows:
- Find a flat and level surface
- Clean and dampen the table surface and cone
- Place the cone in the middle of the table, and secure it in place
- Fill about a third of the cone with the first layer of shotcrete, then tamp 25 times with the tamping rod
- Repeat with the second and third layers
- Use tamping bar to ‘skim off’ any extra shotcrete, leveling it with the top of the cone. Clean off any spillage
- Carefully lift up the mould, making sure the concrete is not subject to any twisting or lateral movements
- Measure the height difference (h) between the highest point of the slump and the top of the cone
- The test should be carried out within a timeframe of 150 seconds from start to finish
What do you need?
You need the following to do the test:
- Mixing tray table(essentially a flat plank),
- A metallic conical mould cut at the top and bottom (height of 300 mm, with a diameter of 100 mm on the top and 200 mm at the base) with foot pieces,
- A tamping rod measuring around 600 mm
Test results
Make sure your slump is true, and retaining its overall shape, and that no portions have sheared off (shear slump), or that it has collapsed completely (collapse slump).
Putzmeister Underground recommends a slump value of between 180-220 mm (slump class S4-S5), in line with industry body EFNARC.
Failure to deliver within those parameters would mean the shotcrete is no adequate for the job.
Sources:
- European Committee for Standardisation (CEN), “Testing Fresh Concrete: Part 2: Slump Test”, Published 2009
- EFNARC, “Specifications & Guidelines for Self-Compacting Concrete”, Page 21, Published February 2002, Last accessed 23/08/2016
