It starts at the rock face
A quarry is a bench cut into a deposit of rock, in Algeria most often limestone, under a mining title issued by the national mining agency and renewed under the 2025 mining law. A surface rock drill bores a pattern of holes into the bench, explosives are placed and fired by a licensed team, and the blast brings down a pile of fragmented rock, the muck pile, whose size distribution depends on the drilling pattern and the charge. A loader or an excavator feeds this rock into trucks or directly into the primary crusher. The quality of the final sand is already being decided here: a hard, clean, unweathered rock gives strong, clean aggregates; a rock with clay seams gives harmful fines that the plant will have to remove.
The circuit, stage by stage
A typical three-stage circuit for fine aggregate; plants differ in detail.
Feeding and scalping
A hopper and a vibrating feeder meter the rock into the circuit; a grizzly or scalping screen takes out the natural fines and soil before they enter the crusher.
Primary crushing: the jaw crusher
Two jaws, one fixed and one moving, squeeze the rock until it breaks and falls through the gap; the primary reduces blocks of several hundred millimetres to a product of roughly 100 to 200 mm.
Secondary crushing: cone or impact crusher
A cone crusher squeezes the rock between a rotating mantle and a bowl; an impact crusher throws it against plates. Both bring the material down to a few tens of millimetres and begin to shape the grains.
Tertiary crushing: the vertical shaft impactor
A VSI accelerates the stones in a rotor and throws them against an anvil ring or a bed of rock, breaking them on their weak planes; this is the stage that produces cubical grains and most of the crushed sand.
Screening
Multi-deck vibrating screens split the stream into the fractions sold, 0/3, 3/8, 8/15 and so on, and send oversize back to the crusher it came from; this closed circuit is what gives a controlled curve.
Fines control and stockpiling
Dust is captured by spraying or extraction, and the fines content of the sand is adjusted by screening, air classification or washing; conveyors build the stockpiles the trucks load from.
Why the tertiary stage decides sand quality
Jaw and cone crushers work by compression and leave flaky, elongated grains, which is acceptable for a sub-base but not ideal for concrete and asphalt. Impact crushing, and especially the vertical shaft impactor, breaks the rock along its natural planes and rounds the corners, giving a more cubical, better-graded product and generating the sand fraction in quantity. A plant that sells fine aggregate for concrete and asphalt therefore lives by its tertiary stage: its rotor speed, the wear of its parts and the feed it receives set the curve and the shape of the sand. This is also where grinding and milling machines come in for the finest products.
What decides the output of a plant
The factors a buyer should ask about when a project needs a high and steady rate of supply.
| Factor | Effect | What to ask the supplier |
|---|---|---|
| Rock hardness and abrasiveness | Harder rock means slower crushing and faster wear | Which rock, and what are its Los Angeles and Micro-Deval values |
| Feed size and blasting | Well-fragmented feed keeps the primary flowing | How is the quarry face worked |
| Crusher settings and wear parts | The closed-side setting and the wear of liners move the curve | How often are settings and liners checked |
| Screen area and decks | Screening is often the bottleneck | Which fractions can be produced simultaneously |
| Closed circuit | Oversize returned to the crusher stabilizes the product | Is the circuit closed on the sand fraction |
| Moisture and fines | Wet or clayey feed blinds the screens | How are fines controlled; is the sand washed or classified |
| Stock and haulage | Stockpiles absorb peaks; trucks set the delivered rate | Stock on the ground; own trucks or hired |
Consistency is the product
For the buyer, the value of a plant is not its peak tonnage but the sameness of its sand from week to week: the same curve, the same fines, the same cleanliness. That consistency comes from a steady feed, from maintenance of the crushers and screens, and from testing at the plant, with grading and sand equivalent run on production samples and recorded. Projects that need high production rates, such as a large concrete pour programme or the layers of a long road, should ask to see those records and visit the plant; the stockpiles, the state of the screens and the dust control say a great deal in ten minutes.
Frequently asked questions
What are the stages of a crushing plant?
A typical plant has a primary stage (a jaw crusher that breaks blasted rock to roughly 100–200 mm), a secondary stage (a cone or impact crusher that brings it to a few tens of millimetres), a tertiary stage (often a vertical shaft impactor that shapes the grains and produces sand) and screens that sort the fractions and return oversize to the crushers.
What is the difference between a jaw crusher and a cone crusher?
A jaw crusher breaks large blocks by squeezing them between a fixed and a moving jaw and is used as the primary crusher, while a cone crusher squeezes already-reduced rock between a rotating mantle and a bowl and is used as a secondary or tertiary crusher for finer, more uniform products.
What is a VSI crusher used for?
A vertical shaft impactor (VSI) throws stones at high speed against an anvil ring or a rock bed so that they break along their natural planes; it is used in the tertiary stage to produce cubical grains and crushed sand for concrete and asphalt.
How are fines controlled in crushed sand?
By screening, by air classification or by washing, after dust has been limited at source with water sprays and extraction; the target fines content is the one the project specification asks for, and the methylene blue test checks that the remaining fines are not clayey.
How much aggregate can a crushing plant produce?
It depends on the size of the crushers and screens, the hardness of the rock, the fractions produced at the same time and the organization of the quarry and haulage; rather than a headline tonnage, a buyer should ask for the sustained rate the plant can hold for the fractions it needs and the stock available.
How ETAHG can help
SARL ETAHG operates its own quarry and stone crushing plant, Carrière Djellal El Gharbi at Oued Sdeur near Aïn El Ibel in the wilaya of Djelfa, with crushing and grinding machines that produce high-quality fine aggregates and are especially suited to projects requiring high production rates, and it hauls with its own trucks and tipper semi-trailers. Visits to the plant can be discussed when a project is in preparation. See fine aggregate production and the fleet page.