In brief
- Segregation during transport starts when a drum turns too slowly, a chute drops the mix too far, or a truck waits with the load standing.
- Ask for the delivery note, the drum revolution count and the discharge time on every truck, and refuse a load that arrives separated or dry.
- Match the crew's transport experience to the pour size before work starts, and agree in writing what happens to a rejected load.
Contents
Concrete transport experience gaps in Gabiley show up when the crew running the truck and the chute has not handled a pour of this size before. The mix leaves the plant or mixer in specification, then segregates on the way or at discharge. Coarse aggregate sinks, paste rises and the concrete that reaches the formwork is no longer the concrete that was batched.
What does limited transport experience do to the mix?
Transport experience is the knowledge of how long a drum can turn, how fast, and how the mix behaves when it is finally tipped. A driver who has only carried short loads may not know that a drum left almost still lets heavy aggregate settle, or that a fast discharge into a deep drop separates the paste from the stone. General practice for truck mixing is a limited number of drum revolutions at mixing speed and a controlled rate at discharge, but the exact figures belong in the project specification. Confirm them with the engineer before the first truck moves. On a Gabiley site, ask the batching plant or mixer operator what revolutions the drum has run and how long the load has been standing. If nobody can answer, the load is a guess.
Where does segregation before placement start?
Segregation before placement starts at the point where the mix is allowed to move without being remixed. Three places matter on a typical Somaliland pour:
- The drum. A load that sits with the drum stopped, or turns at a crawl, settles. Free water rises and the top of the load turns watery.
- The chute. A long free fall from the chute into the formwork, or a chute run that is too steep, throws the coarse aggregate ahead of the mortar.
- The wait. Trucks queued at the gate with engines off and drums still lose workability as the day heats up.
Ask the supervisor to record arrival time, discharge time and drum revolutions on each delivery. Walk the pour and look at what lands in the formwork: a stony, dry pile under the chute with watery mortar running to the edges is a sign to stop and check. Confirm acceptance criteria with the project engineer rather than relying on a rule of thumb.
How do you detect a project experience mismatch?
A mismatch appears before the pour, in the questions the crew cannot answer. Ask the transport lead three things: how long the run takes loaded, what the drum speed setting is, and what the plan is if a truck is rejected. A crew with relevant experience answers without checking a phone. Request the batching plant's delivery records from a recent pour of similar size, or walk a site where the same crew has just finished. Look at the formed surface: honeycombing, a weak top layer and exposed stone can point back to how the concrete travelled. Check the contract for what a rejected load means for payment and programme, and agree the rejection procedure in writing before the first truck arrives. Where the municipal engineer's office holds records of nearby pours, ask whether they can be reviewed.
What to do next
Before the next pour in Gabiley, write a one-page transport plan: route, run time, drum revolutions, discharge method, maximum standing time and the rejection procedure. Ask the engineer to confirm the limits against the specification, then brief the driver and the receiving crew together. Keep the signed plan on site and record every delivery against it.
Frequently asked questions
Can we add water to a concrete load that arrived too stiff?
No. Water added at the truck raises the water to cement ratio and lowers the strength the mix was designed for. If a load arrives too stiff to place, reject it under the procedure agreed with the engineer.
Who should check concrete deliveries on a Gabiley site?
The receiving supervisor checks each load against the delivery note and the transport plan, then records arrival, discharge and any visible separation. The project engineer confirms the acceptance criteria.
Local reporting: this article is written for building work in Gabiley and Somaliland. Ground conditions, prices and rules differ between places; confirm the details for your own site.