In brief
- Aggregate grading controls how much paste and water a mix needs, so a shift in fines or oversize changes strength and workability.
- Grading gaps survive because sieving, batching checks and pour records are the tasks nobody signs off at the end of a day.
- A client or supervisor can close the gap by requiring a sieve analysis, watching the stockpile and sampling cubes, and asking who signs each record.
Contents
Aggregate grading supervision gaps in Qardho show up as concrete that varies from load to load for no visible reason. If nobody checks the sand and coarse aggregate before batching, the mix design on paper and the mix in the mixer drift apart. The result is a pour that looks acceptable on the day and fails later under load, abrasion or salt. This is a supervision problem before it is a materials problem.
Why does aggregate grading drift when supervision is weak?
Grading drifts because aggregate arrives from more than one source and the stockpile is never sampled. Sand dug from a wadi, crushed stone from a quarry and material reclaimed from a previous delivery can sit in the same heap. Each has a different share of fines, mid sizes and oversize. When the loader takes from a different part of the heap, the grading changes without anyone touching the mix design.
Weak supervision lets that happen because sieving is slow and unrewarding. A sieve analysis takes time at the start of a job, not at the end, so it is easy to skip when the mixer is waiting. A supervisor who is also chasing deliveries, labour and the client has no spare hour for a wash test. Ask the project's engineer or the person who holds quality-control records what test records exist for the aggregate sources on site, then walk a recent site and look at how the aggregate was stored. If the heap has no separating bays, grading control cannot exist.
How does poor grading reach the finished concrete?
Poor mix consistency follows directly. More fines demand more water for the same workability. Oversize particles leave voids that paste must fill. A mix that was designed with one grading and batched with another can be over-sanded, harsh or bleeding, depending on the day.
On site the signs are practical, not theoretical. The mix may stiffen between loads, or slump may look right while the surface bleeds and weakens. Finishers may add water to keep up, which raises the water to cement ratio and cuts strength. General practice is to confirm the target grading, slump and cube testing regime against the project's specification and the engineer's instruction, because those limits belong to the design, not to a rule of thumb. In hot, dry conditions, over-sanded mixes also lose workability fast, so crews add water to place them. The defect appears months later as dusting, low strength or exposed aggregate.
What should a supervisor or client check on site?
Start with the stockpile. Ask how many aggregate sources are on site, whether they are kept in separate bays, and who samples them. Request the sieve analysis and the batching records for the pour, and check whether the grading matches what the mix design assumed. If no analysis exists, ask a laboratory for its rate and turnaround and have one done before the next structural pour.
Then watch the pour itself. Note every load, the slump, the water added and who signed for it. Take cubes and keep the labels with the record. One more check costs little: ask the supervisor to name the person who accepted the last delivery. If nobody owns that decision, nobody owns the grading. Confirm all limits against the project's specification and the engineer before you rely on them.
What to do next
Before any structural pour, treat the sieve analysis, the source list and the batching record as general practice for the concrete on site, and confirm the required records against the project's specification. Set a date to walk the stockpile together and agree who signs each pour record. If the test records do not exist, arrange one sieve analysis with a laboratory before structural concrete goes in.
Frequently asked questions
Do I need a sieve analysis for every concrete pour?
Not necessarily, but you should have an analysis that covers each aggregate source. Ask the engineer and the project specification what frequency applies, and repeat the test when the source or stockpile changes.
What does poor aggregate grading look like on site?
Watch for mixes that change between loads, bleeding surfaces, or crews adding water to keep placing. The surface may look fine while strength is below the design value.
Local reporting: this article is written for building work in Qardho and Puntland. Ground conditions, prices and rules differ between places; confirm the details for your own site.