If you are sourcing blast-furnace slag for a cement blend, the offer has to name one form. Ground powder and unground granule are different cargoes, different mill instructions and different disputes. A line that says only "slag" is not a quotation we will send, and it is not a quotation a mill should accept. Fineness belongs in the brief when the plant will dose powder. Moisture and stowage belong in the same recap, because they decide the tonnes that arrive and the space the ship must have.
The abbreviations GBFS, GGBS and GGBFS, and the difference from coarser unground slag, are set out in GBFS, GGBS and laitier. This note is the buying brief: what to lock before an Algerian lot is offered on the GBFS line.
What buyers mean by slag for a blend
"Slag cement" is used for three different purchases, sometimes in the same week.
The first is a finished cement the buyer wants to import, already ground, already blended, sold as cement. That file belongs on cement, with a cement type and a packing format. It is not closed by shipping a constituent and hoping the receiver will call the powder cement.
The second is the constituent itself. The mill will intergrind it with clinker and a sulfate source, or blend it with cement it already holds. The buyer is not asking us to deliver a branded cement. They are asking for blast-furnace slag in a form their mill can use. That is the file this note is about.
The third is a loose request from a trading desk that has heard slag is available and wants "a slag cargo" to show a mill later. There is no blend, no fineness and no discharge constraint. We can listen. We cannot offer. A blast furnace slag supplier who prices that request is guessing which solid the mill will reject.
French-speaking buyers often write laitier. In a blend conversation it means the slag constituent, not the finished cement. It still does not say ground or unground. We answer with the form, not with a translation.
The blend ratio is the mill's number. Some plants are allowed a modest slag share in a general cement. Others are set up for a slag-rich cement and the slag is most of the mill feed. We do not publish a replacement rate for Algerian supply. We ask what the quality book already permits, and we qualify a lot against that book.
The decision: one form in the offer
One offer carries one form. If the buyer can take either powder or granule, those are two qualifications and two stowage conversations. They can run in parallel. They are not one sentence with "seller's option" at the end. That option means the ship arrives with whichever solid was easiest to load. The silo and the discharge gear were built for one of them.
The decision that sets the form is who grinds. A mill with spare finish-mill capacity, or with a dedicated slag mill, often wants the granule. Moisture, size and glass content then matter more than a Blaine figure, because the buyer will make the fineness. A mill that is already full, or a grinding station that doses ground materials from separate silos, wants the powder. Fineness is then a condition of the contract, measured by the method the receiving lab uses, and the grinding happened before the bill of lading.
Switching form after the ship is fixed is how a good sample becomes a rejected cargo. The recap names the form in words. "Slag in bulk" on the bill of lading is too thin if the dispute is powder versus granule.
There is a second decision inside the form: one lot, one quality. Topping up a short granule cargo with a finer screened pile, or blending two grinding campaigns to make a stem, is a new product. If it has to happen, it is agreed before loading, sampled as the combined lot, and described as such. It is not a quiet operational fix on the night shift.
A third decision is whether the blend should be slag at all. A plant whose standard and whose customers expect a natural pozzolan should not be sold slag because a slag lot is the one on the berth. The comparison sits in pozzolan in cement. We would rather lose the slag inquiry than put the wrong constituent in a cement the buyer has to stand behind.
Specifications the brief has to lock
Fineness is locked when the cargo is ground. The brief states the method and the target: Blaine, residue on a named sieve, or a particle-size curve. "Fine" is not a method. Say whether the figure is a minimum or a band, and what a coarse tail means. Mills argue about that tail more often than about the average, because it blinds a separator even when the mean looks acceptable.
For an unground granule the brief states the size range, the limit on oversize lumps, and the limit on dust the mill does not want to lose at the grab or flood the filter with. Granule that has been rehandled for months can carry more fines than a fresh granulator pile. The size on an old datasheet is not the size on the berth.
Glass content and activity stay questions on the qualified lot. We do not print them. The buyer says whether they have a minimum glass content, by which method, and whether activity is a contractual test or a mill trial they will run after discharge. Early-age strength and 28-day strength do not move together. A slag cement sold on two-day numbers can fail its customers with a slag that would have looked fine on a 28-day index alone. Put the ages in the brief.
Chemistry is a list of limits the buyer already enforces, not a window we invent. CaO, SiO2, Al2O3, MgO, sulfide, and sometimes chloride or alkali, are the usual lines. Magnesia and sulfide are where blends diverge: acceptable beside one clinker, awkward beside another. We match the buyer's limits to the lot. We do not back-solve a "typical slag" analysis to fill an empty template.
Moisture is a specification and a commercial clause at the same time. The buyer states what the mill and the handling can accept. The contract states whether the weight is wet or dry, how moisture is sampled, and what occurs if the result sits above the agreed figure. Leaving moisture as "about normal" is how a correct chemical cargo becomes a weight claim.
Sulfate balance is the mill's work. Slag changes the gypsum the cement needs. We do not prescribe the gypsum rate. We do say that a blend trial without a sulfate check is an incomplete trial, and that the slag offer will not pretend to be the cement formula.
Uses in the blend, and the wrong constituent
The proper use is a cement blend the plant controls. Intergrinding clinker, gypsum and slag is the common path. Blending already ground slag with cement, or with separately ground clinker, is the other. They do not share a fineness problem or a silo plan. The brief says which path the plant will run. A powder that suits a blender can be the wrong feed for a mill that expected a granule.
Colour, setting and heat are use constraints. A mill selling a pale cement will reject a darker lot even when strength passes. A mill selling mass concrete may want the slower heat. Ask which of those the customer notices.
The cargo is still not cement. Discharge does not become a slag cement because the slag was good. The mill grinds or blends, controls sulfate, and tests the product it sells. If what you need is the finished binder, say so and we will look at cement supply instead of dressing a constituent up as cement.
The wrong constituent is the one that shares a purpose and not an identity. Natural pozzolan also replaces part of the clinker in some plants. It is specified differently, it reacts differently, and it is the subject of pozzolan in cement, not of a slag offer. Air-cooled slag graded as aggregate can come from a blast furnace and still be useless in the finish mill. Fly ash and limestone filler are other additions. If the standard allows more than one, the shipment names one. A hold loaded with "supplementary cementitious material, quality to be typical" is a hold we will not fix.
A last wrong product is the right slag at the wrong fineness. Chemistry can match and the cargo can still be unusable: too coarse for the silo discharge the plant has, or so fine and dry that it floods the filter and the truck loading. Fineness is not a detail to "see on arrival".
Packing, moisture and stowage
The working format for a blend supply is bulk maritime. Bags and big bags are for a trial or a plant that cannot take bulk, qualified as their own lot. A container that performed well does not licence the next bulk stem. The bag may have been dried. The bulk pile may not have been.
Moisture is in the mass you pay for. Granule holds water in the pores. Powder takes water if the hatch is open in rain. A draft survey reports wet mass. On a dry basis, that draft becomes dry tonnes only with a moisture result both sides trust. Write the sampling rule before loading: where increments are cut, how the composite is split, which lab runs the test, and how fast. A single grab from the top of the pile will not survive a discharge argument. On a wet basis the contract still needs a ceiling, the buyer's figure checked against the lot. Above it, the buyer pays for water the mill may have to dry.
Stowage is fixed with the form. Powder and granule do not occupy the same cubic metres per tonne, and a wetter granule changes the figure again. We do not keep a house factor called "slag". The ship and the receiver's gear decide spout, grab or belt. A powder on a grab-only ship is a dust claim. A granule into a silo with no screen is a lump claim.
Do not finish a short granule parcel with ground slag so the ship sails full. The receiver cannot separate them at the grab. If two forms must move on one vessel, they are two holds and two sampling regimes. Previous cargo matters: chloride, sugar or a chemical that poisons cement is a reason to refuse the ship. Load port, rate and laycan go in the recap with the form and the moisture basis. Algeria is not one berth. The buyer nominates tonnage after that recap, not before it.
Documents, inspection and Incoterms
The quality certificate has to name the form in words a silo operator understands. "Slag" is not enough. Ground or unground granulated blast-furnace slag, plus the fineness or size method, is the minimum. Chemistry follows the contract list. Moisture is on the certificate when it corrects the weight or when it is a rejection limit. Glass and activity appear only if those tests were run. A blank is more honest than a figure borrowed from another campaign.
The commercial set is the usual one: invoice, packing list if there is packing, bill of lading, certificate of origin when the destination asks, and the quality certificate tied to the loaded lot. The bill of lading description should match the commercial invoice. If one says slag and the other says ground granulated blast-furnace slag, the mismatch is small until a bank, a customs entry or a claim reads both.
Inspection is agreed in the same breath as moisture. Independent sampling at loading, a sealed split for the receiver, and a referee laboratory named before anyone is angry, prevent the argument in which each side trusts only its own oven. Some buyers accept the producer's certificate for a first ship and add independent inspection from the second. That is a reasonable sequence if it is written down. It is a poor surprise if the buyer announces a referee after the hatches close.
Weight is draft survey, belt scale, or both, and the contract says which figure the invoice uses. A draft without a moisture correction is a wet weight. Calling it the dry shipped quantity because "the slag looked dry" is not a method.
Incoterms allocate the ship and the risk. FOB leaves the vessel to the buyer, which suits a mill that already has tonnage on the berth rotation. CFR and CIF put freight with the seller. CIF adds insurance. None of them defines the slag, the moisture basis or the sampling plan. Those clauses are written beside the Incoterm. A clean FOB recap with no form and no moisture line is an incomplete recap, however correct the three letters are.
How Algerian slag supply is qualified
NAGTAR qualifies supply from Algeria against the brief, with selected partners. We do not treat the country as a standing pile of blend-ready slag. Granulation and grinding are campaigns. A stockpile left from an earlier campaign can be the right chemistry and the wrong moisture, or the right granule and no grinding slot in the window you need. The file says which of those is true.
We start from the form you named. If the available material is coarser, we do not relabel it to match the word in your email. Either grinding can be done to the fineness method you stated, and that ground lot is what we sample, or we tell you the form that exists and you decide whether the mill can take it. A quotation that quietly substitutes granule for powder is the generic "slag" offer in a more polite sentence.
The laboratory sample is a screen. It is often drier and more even than the edge of the pile that will be loaded. Passing the screen means the lot is worth a ship conversation. It does not replace a loading sample. Fineness, moisture, and any glass or activity test you made contractual, are confirmed on the lot by the agreed method. Where a result does not exist, the offer says so.
A monthly blend programme and a single stem are qualified separately. The monthly case needs a view on whether the form repeats, not a promise that every campaign will photocopy the first certificate. We will not write that promise. We will tell you what has to be retested on each stem so the mill is not relying on last quarter's fineness.
Origin is the works that made the lot, documented as such. A trading description that says Algerian slag, with no link to the lot you sampled, is not a qualification. Your cement will carry your name. The constituent should be traceable to the pile that was tested.
What to send before a price is discussed
Price on an unnamed form is a number neither side can defend. Send the brief to the GBFS line first. A price conversation starts when the lot and the form are the same thing.
- One form, in words. Ground or unground. If you can accept either, say so and expect two paths, not one optional offer.
- The blend: intergrind or blend, the cement or standard you sell, and the slag share you are allowed to use. A range is enough.
- Fineness or size, with method, and what a miss means.
- Moisture: wet or dry weight, the ceiling you care about, and how you want it sampled.
- Chemistry limits you already apply, and whether glass or activity is a contract test or a later mill trial. Do not ask for a published index.
- Volume and rhythm: one stem, or a monthly intake. Trial tonnes are a different lot from the first full hold.
- Discharge: silo, grab, spout, rain constraint, truck rate.
- Incoterm, load-port ideas if you have them, and whether the invoice weight is draft or scale.
- Inspection: independent at loading, or producer certificate plus a referee clause.
- Date the mill can receive, and the date a sample result stops being useful.
If you also need clinker or finished cement, put that in the same message as its own block. If you are choosing between slag and pozzolan, say that before we sample the wrong powder.
Why will you not quote slag without a form?
Because the word covers at least two cargoes a mill cannot swap at the hatch. Ground granulated blast-furnace slag and unground granule differ in fineness, moisture behaviour, stowage and discharge. A single price on "slag" hides which one the seller intends to load. We quote one specified form per offer. If you need a comparison, ask for two offers and keep them separate through sampling and through the fixture.
Does fineness belong in the first brief?
Yes, when you are buying powder. Name the method your laboratory will use and whether the target is a minimum or a band. When you are buying granule to grind yourself, fineness is your mill's result, and the brief should lock size, dust and moisture instead. Adding a Blaine figure to a granule purchase creates a test the cargo cannot pass, because nobody has ground it yet.
How should moisture be handled on a bulk cargo?
Decide wet weight or dry weight before the ship is fixed. Dry weight needs a sampling rule and a laboratory, agreed in the contract, so the draft survey can be corrected. Wet weight still needs a ceiling the mill can handle. Granule holds water in the pores. Powder takes water if it sits in rain. Neither case is covered by the word "bulk" or by the Incoterm alone.
Can one shipment mix slag and cement?
Not in the same hold, unless the receiver has a written plan to keep them apart, which is unusual and rarely worth it. Slag for blending and finished cement are different products, different specifications and usually different customers inside the same company. If you need both, they are two files. Cement is quoted as cement. Slag is quoted as one form on the slag line. Combining them on one bill of lading to "simplify" the purchase is how the wrong solid reaches the wrong silo.
Is pozzolan an acceptable stand-in on a slag offer?
No. A plant can choose pozzolan instead of slag for a blend, and some standards allow either, but the choice is made in the brief, not at loading. Pozzolan is qualified on its own terms, discussed in pozzolan in cement. Substituting it into a slag stem because the slag form was short is a different product. The mill's trial, the activity test and the dosage would all be wrong.
What does a supplier need before naming a ship?
The form, the fineness or size method, the moisture basis, the volume, the discharge limit and the Incoterm. With those, we can say whether an Algerian lot can be qualified and whether a berth and a ship type make sense. Without them, a named ship is a guess about cubic metres and about what the grabs will pick up. Send the list above. The ship conversation follows the lot, not the other way round.