In brief
- A slump test only protects the pour if the sample comes from the right truck, is taken at the right point, and is recorded while the concrete is still workable.
- When one person supervises several pours, tests get sampled from the chute, timed loosely, and written up as pass or fail with no numbers.
- A client can close the gap by asking for the tester's method, watching one test, and keeping dated records on site.
Contents
Poor slump testing supervision lets changes in concrete workability pass unnoticed until the formwork comes off. A slump test measures how far a cone of fresh concrete settles after the mould is lifted. It shows whether the mix can be placed and compacted with the equipment on site. When no one independent watches the test, the number on the record may not describe the concrete in the truck. This article explains how slump testing supervision gaps arise on a Somaliland site and how to close them.
Where do slump testing supervision gaps start?
They start when the person who ordered the concrete also controls the test. On a busy day the batching plant, the pump operator and the site team all want the pour to continue. If the supervisor is also managing labour, steel fixing and deliveries, the slump test becomes a formality. The sample may be taken from the first chute discharge rather than from the middle of the load. The cone may be filled in two lifts instead of three, or the rodding may stop early. Each shortcut changes the result without anyone writing it down. The test is then filed as a pass even though no one performed it to method.
What does a missed workability change do to the work?
It hides the reason a mix no longer places or finishes well. A slump outside the specified range can mean the plant added water, the aggregate moisture changed, or the cement content drifted. If the test result is recorded as acceptable, the site loses the only early warning it had. The crew then adds water at the pump to keep the concrete moving. That raises the water to cement ratio, which lowers strength and raises the risk of shrinkage cracking. Concrete can also stiffen between batching and discharge, especially where ambient conditions are hot or dry, so a mix that left the plant within range may not be within range on arrival. Check the project specification for the conditions it sets. A useful record shows the slump figure, the time, the truck number and the location in the pour. General practice for slump testing is set out in recognised test standards, and the project specification or engineer should confirm the acceptance limits for each element.
How do you spot a supervision gap on site?
You spot it by watching the test, not the paperwork. Arrive unannounced at the start of a pour or a wall. Ask the tester to show the cone, the base plate, the tamping rod and the measuring rule. Watch where the sample comes from. A sample taken from the first discharge or from the pump hopper does not represent the load. Watch whether the cone is filled and rodded in the specified number of layers, and whether the cone is lifted steadily without sideways movement. Ask for the slump figure in millimetres, not a tick in a box. Then compare the figure with the batch ticket and the pour location. If the record holds only signatures and the word "ok", the supervision may not be testing anything. Walk a recent slab and look for plastic shrinkage cracks, cold joints or a dusty surface as questions to raise, not as proof.
What to do next
Before the next pour, agree in writing who takes the slump sample, where it is taken, and who records the figure. Ask the supplier for the batch ticket and the specified slump range. Then stand at the discharge point for the first two trucks and watch the test from sample to reading. Keep the signed records in one file on site, and check them against the pour locations before the formwork is struck.
Frequently asked questions
How often should slump tests be taken on a pour in Borama?
The project specification or engineer should state the frequency. If the specification is silent, agree a frequency in writing before the pour starts, and record which trucks were tested.
Can a slump test tell you the strength of the concrete?
No. It only shows workability at the time of testing. Strength comes from the mix design, the water to cement ratio and curing. Ask the laboratory for cube or cylinder test results from the same batch.
What if the contractor refuses to let you watch the slump test?
Check what your contract says about inspection rights and testing. Raise it with the project manager in writing before the next pour. If the concrete has already been placed, ask for the batch tickets and test records for that day.
Local reporting: this article is written for building work in Borama and Somaliland. Ground conditions, prices and rules differ between places; confirm the details for your own site.