Raw Mix Modified: Complete Technical Guide

The modified raw mix is the raw mix that leaves the textbook and enters the field: when the quarry of the plant cannot supply the full chemistry by itself, the mix is corrected, modified and rebuilt from the materials on hand: the marl runs out of silica, the sand is added: the iron of the ore flags, the red mud arrives from the aluminum plant: the modified raw mix is the engineering answer to the deposit that is not perfect: it is the recipe with the conscience of the market and the tables of the analyzer.

Every plant will need the modified raw mix at some point in its life: the seam changes, the extraction depth passes into a new zone, the contract for the clay runs out, or the management decides to blend the new cement types: the modified mix is also the home of the alternative materials: the slag, the fly ash, the phosphogypsum, the industrial by-products: this article walks the method of modifying the raw mix while maintaining the LSF, the SR, the AR and the limits of the minor oxides; the companion file of the package carries the full table of the modifiers, the Excel calculators and the case files of the mills that ran the transition.

This article is the follow-up of the raw mix fundamentals (the LSF, the SR, the AR, the dosage loop) and assumes the reader knows the target oxide chemistry; the modifications described here solve the “the quarry is not enough” problems that the fundamental file leaves open: the structure: first the modifiers and their chemistry, then the checking logic, then the statistical re-homogenization, and finally the economics of the alternative materials.

1. The Triggers of the Modification: When the Plant Changes the Mix

No plant modifies the mix for pleasure; seven situations trigger the modified mix:

• The geology changes: the limestone face drops the CaO from 53 to 49, the LSF cannot hold without the correction;
• The supplier disappears: the clay quarry closes, the sand vendor raises the price, the alternative is the excavation of the neighboring deposit or the by-product of the local industry;
• The ash enters: the fly ash from the power plant or the slag from the steel mill reduces the need for the raw clay and adds the glassy silica;
• The product changes: the new white cement needs the Fe2O3 below 0.4; the sulfate-resistant needs the low C3A; each target asks for the new modifiers;
• The sulfur appears: the alternative fuels bring the sulfur; the raw mix may need the correction to balance the SO3 by the alkaline;
• The environment order: the quarry exhausts the permit, the hauling costs rise, the local by-products are the cheaper and the greener;
• The resident of the kiln: the preheater deposits from the alkali require the by-pass and the feed adjustment;

Each of these inputs into the same vector: the oxide columns of the mix change, the moduli drift, and the engineer re-solves the linear system with the new matrix; the modification is a change of the ingredients, not a change of the method.

2. The Chemistry of the Modifiers: The Shaping Oxides and Their Signatures

The modifiers are judged by five numbers: their main oxide, their minor oxides, their LOI (loss on ignition), their moisture and their availability in tons per day; the file of the package carries the complete table of the industrial modifiers:

Modifier	Main gift	Typical CaO %	Typical SiO2 %	Typical Al2O3 %	Typical Fe2O3 %	LOI %
Silica sand (quartz)	SiO2 for the SR	0.2-1	95-98	0.3-1.0	0.1-0.5	0.3-1
Low SiO2 bauxite	Al2O3 for the AR	0.5-2	5-10	50-65	15-25	15-25
Iron ore (hematite)	Fe2O3 for the AR	0.3-1	3-12	1-3	60-70	1-4
Mill scale (Fe2O3-rich)	Fe2O3	0.5-2	1-5	0.5-2	70-85	1-8
Fly ash (siliceous)	SiO2 + Al2O3	2-5	45-55	20-30	6-15	1-5
Granulated blast-furnace slag	CaO + SiO2 + flux	38-44	33-38	8-12	0.3-1.5	1-2
Red mud (bauxite residue)	Fe2O3 + Al2O3	2-8	10-20	15-25	30-45	5-15
Diatomite / silica earth	SiO2 amorphous	0.5-2	85-92	2-6	1-3	3-6

The table shows the logic of the modifiers: each one carries a big dose of one oxide and small doses of the rest; the engineer reads the table like a pharmacy: the SR is low: add silica; the LSF is low: add limestone; the AR is low: add iron; the AR is high: add bauxite-like alumina only if the SR allows, else adjust with the calculator. The key discipline: compute the effect on the three moduli at once, because every modifier moves all three.

The mortar of the correction: for the plant with the clay from the pit and the stone from the pile, the two correction ratios define the daily struggle: the ratio of the mass of the Fe2O3 modifier to the mass of the Al2O3 modifier for the AR, and the ratio of the SiO2 modifiers to the flux for the SR; the “RAWLEX” tables of the handbook are reproduced in the package .

3. The SSR, the AR and the LSF after the Modification: The Solving Order

When the materials are four or more, the hand calculation becomes a systematic iteration; the order that the file recommends:

• Step 1 – the LSF first: solve for the limestone vs the rest so that the CaO of the mix yields the target LSF; do not touch the SR and the AR yet; the LSF is the first-stabilized;
• Step 2 – the SR second: with the limestone fixed, the SR is solved by the addition of the silica carrier: the sand, the diatomite or the high-SiO2 clay; this addition changes the LSF upstream, so return to the step 1;
• Step 3 – the AR third: the iron and the alumina arrive; the AR moves the most; after the iron the balance repeats from the step 2;
• Step 4 – the minor oxides: after the moduli, check the MgO, the alkali, the SO3, the P2O5, the Cl; the constraints arrive of the environment and the kiln;
• Step 5 – the closure: the solver iterates the matrix until the moduli are inside the tolerances (typically LSF +/- 1.5, SR +/- 0.15, AR +/- 0.2);

The Excel in the package does this in the cell-ranges of the sheet; the engineer who understands the order can read again any result of a solver. The Gauss elimination or the matrix inversion is not the art; the art is choosing which target to relax when the four materials cannot meet the three goals.

The accepting impossibility: with the poor materials the targets cannot all be met: the file lists the priorities: LSF is sacred (the burnability and the strength); SR is secondary (the ring the plant can manage); the AR is the last to sacrifice (the clinker gets grayer, but it fires). The engineer documents the trade-off in the quality report; the package contains the decision matrix that the plants use for such compromises.

4. The Worked Example: Modifying the Mix to the Sulfate-Resistant Cement

Let the base mix be limestone 78 parts (CaO 51.5, SiO2 2.0, Al2O3 0.8, Fe2O3 0.5, LOI 41), clay 21 parts (CaO 4.0, SiO2 60, Al2O3 16.5, Fe2O3 6.0, LOI 13) and iron ore 1 part (Fe2O3 68, SiO2 4); the clinker moduli of the base: CaO ~46.5 feed: let the calc: LSF ≈ 93, SR = 2.35, AR = 1.55: position: a family of S-R cements needs LSF 94-96 (stronger), SR 2.2-2.6 (fine), AR < 0.85 (for the C3A < 5% + the sulphate resistance):

• Step A – the AR: the current AR 1.55 must drop under 0.85: the Fe2O3 feed must be raised: iron ore addition, the solver finds, is +1.4% of the batch, shifting the base mix;
• Step B – re-fix the LSF: the iron ore dilutes the CaO by ~0.5, so the limestone share rises back to 78.6;
• Step C – the clay minus: the extra iron replaces the clay; the new batch: limestone 78.6, clay 19.6, iron ore 1.8:

Resulting clinker: LSF 95, SR 2.40, AR 0.84, CaO 65.0, SiO2 21.3, Al2O3 4.3, Fe2O3 5.2: the C3A = 2.65*Al2O3 – 1.69*Fe2O3 = 11.4 – 8.8 = 2.6%: well inside the SR requirement: the table of the file derives these Bogue formulas pg for the C3A.

The lesson of the example: the modification to the SR type is dominated by the iron, not by the exotic chemistry: the most plant has the iron ore in the yard; the ones that do not buy the mill scale or the steel dust; the iron feed is the LSF alarm; the chemist of the mix does not sleep.

5. The Alternative Materials: The Fly Ash, the Slag, the Industrial Residue in the Feed

The modern trends of the cement industry push the alternative materials into the raw mix: the circular economy has made them the flags of the modified mix:

• Fly ash as the clay substitute: the siliceous ash (the ASTM class F) replaces a part of the clay; the vulcanized carbon in the fly ash matters for the mill (its LOI of the carbon) and for the kiln: the volatile: the dose 0-8% of the batch in practice;
• The slag in the raw mill: the granulated blast-furnace slag brings the calcium 42 and the silica 36 plus the glassy flux: up to 5-10% of the feed: the compressive of the clinker improves and the CO2 of the plant drops:
• The red mud: the residue of the alumina plants: the Fe2O3 30-45% and the alumina: the additive for the AR and the Fe: the soda: the Na2O of the mud must be watched: the alkali:
• The phosphogypsum: the SO3: the CaSO4*2H2O; only in the small doses due to the P2O5:
• The oil shale and the ash: the light fuel of the rotary, the ash that returns the calcium to the kiln feed for the balancer;

The file of the package gives the acceptance criteria for each alternative: the moisture, the granulometry, the particle size of the feed (the mill grinds), the assay protocol and the logistic plan; the innovation of the alternatives is not the chemistry but the quality control: an alternative material must be regulated like the main material with the sampling. The plants that fail here pay the price of the kiln instability.

6. The Variability of the Modified Mix: The Buffer and the Homogenization

The alternative materials are often the supplies of the industrial neighbors, and industrial neighbors deliver with a load-to-load variability that the quarry never had; four measures protect the plant:

• The buffer stock: the modified material receives its own stockpile and reclaiming, so the bad load can be blended with the old stock (8-14 days typical);
• The averaging bed: the same layer-by-layer fill of the raw bed, applied to the secondary yard: the ratio of the homogenization of a good bed 6-10:1 at the blending;
• The weigher discipline: the loss-in-weight of the alternative feed checked against the belt scale every 2 hours: the moisture of the ash is the enemy of the metering:
• The laboratory gate: each silo of the modifier is sampled and mapped: a release from the quarantine: the XRF of the incoming: the mcg:

The key number of the modified mix is the standard deviation of the incoming chemistry: the file repeats it: a raw bed of 8% variation at the inlet becomes the feed of ±1.5% LSF at the silo outlet, if (and only if) the plant operates the averaging correctly: chapter 10 of the file gives the statistical chain (the variances: the additive law of the variance) with the worked sheet: it is the book that converts the scare into the tolerance.

7. The Sulfur, the Alkali and the by-pass of the Modified Feed

The modification of the mix cannot ignore the alkali-sulfur equilibrium of the kiln: the volatiles concentrate: the loops of the preheater:

Constraint	Typical limit in the feed kg/t clinker	Consequence if exceeded
Na2O equivalent	0.3-0.9 %	The alkali knot, the gypsum deviation, the quality of the alkali
Cl (chloride)	0.01-0.05 %	The preheater building, the by-pass material
Total S (as SO3)	0.4-1.4%	The SO2 release, the ring formation
S/Na2O ratio	0.8-1.5 (process)	Stability of the circulating loads

When the alternative materials raise the alkali or the chlorine, the plant must install the by-pass of the kiln (the extraction of the 3-10% of the gas) or accept the lower blending; the package contains the by-pass sizing and the alkali cycle notebook; the reader of the modified mix file understands that the chemical modification is not the only arithmetic: it is the train of the masses of the kiln.

8. The Economies of the Modified Mix: The Costs and the Paybacks

The modification is an economic act: it trades the simplicity of the quarry for the math of the blending: the numbers that matter:

• The transport cost: the distance of the alternative from the plant: the onboard mine to airport: the haul rate per ton-km;
• The price of the material: the fly ash often costs the disposal fee negative: the win-win;
• The grinding penalty: the hard quartz sand or the iron grinding cost extra kWh: the Wi hikes up;
• The clinker cost delta: the alternative C3S side effects: the higher LSF burns with the extra fuel: 1.0 LSF point ≈ 8-12 kcal/kg clinker typical;
• The product gains: the SR cements price premium, the green certificates, the kiln age;

The file carries a simple DCF of the modification project (a 20-row Excel: extra capex of the weigh feeder and the bin, the variable transport, the savings on the clay fee); the threshold: the alternative pays when the delivered cost per unit of the oxide beats the main material’s marginal: the best rule of the engineering: never pay more for the main union than the market of the quarry.

9. The Fixture of the Modified Mix: The Long Term

The story of the modification does not end the day of the first pellet: the mix of the plant lives:

• The monthly assay review: the trend of the L2/SR/AR over the 12 months on the SPC chart: the owner the run charts;
• The re-optimization: the solver re-run with the actual prices: the change of the vendor: the mix one-point move saves €0.05/t of the raw meal: visible;
• The rollover of the contracts: the new spec of the ash: the retest: the acceptance protocol;
• The audit of the annals: the archive of the correlation: the burnability vs the mix at the same clinker: the knowledge of the plant:

The plants that treat the raw mix design as the living system defend their quality month over month; those that freeze the mix at the sign-off pay drift: the file is the living version of the table: this guide transfers the habit.

The trace element log: the modified mix introduces trace elements through the alternative carriers (the zinc from the dust, the lead from the oil shale, the copper of the sludge): the environmental annex of the file requires the quarterly full-scan analysis of the feed with the permitted limits per the market of the cement: the 8 milligrams of the chrome VI per kilogram rule is one of those limits: the plants register the trace log in the quality manual: the modified mix is thus the legal chapter of the file: the reader verifies the national limit values before the first load of the ashes enters the yard: the trace element can disqualify the product from the export market entirely, and the audit covers the addition and the dilution accounting which the file details with a full worked trace budget.

The knowledge transfer: the best modified mix plants document their modification history in the change log: every modification of a parameter is signed, with the reason and the effect measure: the 10-year log of the mill becomes the engineering handbook of the next generation: the file encourages the plants to print the quarterly snapshot of the mix into the fixed format appended in the package.

10. The Burnability of the Modified Feed: The Laboratory burn tests and the field signs

The modified raw mix carries unknown raw materials into the kiln and the burnability must be re-verified before the first ton runs: the laboratory of the plant has two classical answers: the burnability index method and the laboratory kiln test:

• The burnability index: the sample is formed into pellets and burned in the electric furnace at 1400, 1450 and 1500 degrees; the free lime of the cooled pellet is titrated: free lime below 2.5% at 1450 is the classic demand; the modified mix that burns with the free lime over 4% needs the LSF reduction or the flux increase; the index table in the file converts the free lime measurements to burnability classes;
• The lab kiln test: the 10-20 kg batch fired with the same temperature profile of the plant rotary kiln system: the clinker is then ground and tested for the standard compressive strength: the modified mix gets its own 2/7/28-day curve, which becomes the reference of the product department;
• The coating test in production: after the startup of the modified feed, the operator reads the burning zone: the clinker that comes out with the black glassy shell burns hotter; the thin dusty shell burns cooler; the coating test at 0/24/72 hours tracks the adaptation;

The file reminds the reader that the burnability is also grindability: the modified mix with the quartz sand grinds at a higher work index; the raw mill output drops and the plant must recalculate the raw mill tonnage budget: the package includes the Bond work index chapters which complete this guidance; the raw mill limit is often the hidden bottleneck of the alternative mix.

The lead time: the full transition from the old mix to the new mix takes 2-4 weeks of operations: 1 week of the laboratory qualification, 1 week of the feed change with the homogenization silo flushing, and 1-2 weeks of the product blending at the cement silos: the warehouses do not stop; the plants plan the switch when the demand lows.

11. The Bunkering and the Delivery of the Correction Materials

The correction materials are small in mass (1-5% of the batch) but they arrive in a discrete logistic of their own: the file has the practical chapter:

• The receiving: the truck or the railcar is weighed, sampled by the sampler, and sent to the available stockpile: the iron ore and the mill scale take the same bin with the clear segregation because the two chemistries differ;
• The moisture management: the sand and the fly ash carry the 5-15% moisture that clings: the moisture must be measured per lot: the weigh feeders dose the dry basis weight: the mis-measured moisture is the chief dosing error of the modifications;
• The anti-agglomeration for the mill scale and the red mud: the material settles in the bin and blocks the slide gate: the flow the aid: the vibrator or the screw with the variable pitch; the live bottom bin that the file describes;
• The metering chain: the weigh feeder of the correction + the belt scale + the XRF check: three devices that close the loop of the mass: for the iron ore, the plant keeps the weekly gravimetric check;
• The insurance stocking: the corrections are strategic: a 7-14 days value safety in the yard; if the iron mine breaks the supply, the AR history follows; the file quotes the logistics lessons of the last decade: the de-risked plants maintained double sources for the two master modifiers;

The reader notes a subtlety: the corrections feed is the batch of the several kilograms, but the error in the correction of ±0.3% of the batch moves the clinker Fe2O3 by ±0.2-0.4% and the AR by ±0.1: the discipline of the dosing of the corrections is equal to the discipline of the main limestone.

12. The Integrated Worked Sheet: From the Assay to the Silo Program

The article closes the loop with one complete sheet of the daily operational use: the plant receives the 14:00 XRF of the four bin columns (the limestone, the marl, the sand and the iron ore), and the target is LSF 95.5, SR 2.55, AR 1.45:

Material	CaO %	SiO2 %	Al2O3 %	Fe2O3 %	Moisture %	Dosing % (dry)	Dosing % (wet)
Limestone	52.1	1.8	0.6	0.4	2.0	78.5	78.9
Clay	3.8	61.0	15.5	6.2	12.0	18.9	21.2
Silica sand	0.5	96.5	1.0	0.4	4.0	1.2	1.2
Iron ore	0.8	5.0	2.0	66.0	3.0	1.4	1.4

The calculation sequence as the sheet does it: (1) correct the wet to dry by the moisture; (2) solve the LSF for the limestone, SR for the sand, AR for the iron: (the sheet solves with the Newton or the linear inverse); (3) verify the minor oxides: MgO 1.1, Na2O+ 0.5, SO3 0.7 – all inside the envelope; (4) verify the burnability guess of the free lime at 1450 catches 1.9%: (5) the dosages drop to the weigher station: the loss-in-weight feeders feed 62.3 t/h limestone, 15.0 t/h clay, 0.95 t/h sand, 1.1 t/h iron ore for the 79.4 t/h raw meal: (6) the daily check by the hour 00:00-24:00 confirms the silo outlet chemistry held the LSF in the 94.8-96.2 band.

This sheet is exactly what the Excel tool does with the entered assay: the file contains the empty template version; the single-line difference: the sheet itself and the analysis of the sensitivities (the +/-0.5% variation in the limestone CaO swings the feed LSF by +/- 0.8: the plant knows the weakest input). The discipline of the daily sheet is the discipline of the whole system: the modified mix is no longer the initiative – it becomes the permanent mode.

13. The FAQ of the Modified Mix

Is every modification a green-by-products action?

Not automatically: the transport of the distant red mud can cancel the CO2 saved by the substitution: the honest file shows the full accounting: the energy, the transport, the kiln efficiency; the sustainable mix is the one that closes the 3 dimensions of the TRIAD (the cost, the chemistry, the carbon) – the calculators of the package.

What breaks first under the modified mix?

Statistically the AR: the iron and the alumina move with the mills and the clays: next, the SR when the silica source varies: the file includes the FMEA table of the practice; the pneumatic and the daily dose weigh the modified material.

Can the plant be 100% on the alternative raw?

No plant runs on the 100% alternative: the cement needs the CaO of the limestone: the best substitutes (the slags, the ashes) carry the CaO 40-45 max: the realistic regime is the 0-20% of the mass of the feed: the full story is the package’s alternative cement file.

How often do we re-calculate the modified mix?

With the new lot of each material or at the threshold of the change in the chemistry: on average the plant recalculates 1-2 times per week, the seasonal shift to the dry decade: the reason: the trends are the linear: the mix reacts to the humidity feedback.

Is the Excel in the package the same that the plants use?

The solver logic is identical to the commercial and the in-house packages: the input-output structure is the same: the difference is the price and the license: the package supplies the tool and the full training archives of the formulas in the 931 files.

11. Conclusion

The modified raw mix is the threshold of the mature cement plant: the plant that can absorb the material surprises is the plant that runs a trip; the tools of the modification (the modifier matrix, the LSF-first solving, the buffered averaging, the volatility watch) are presented here and in the file; they carry the industrial economy and the environmental agendas of the 2020s with the same oxide arithmetic of the century: the fourth material is waiting in the yard.

The Complete Cement Technical Package includes the full modified raw mix file with the modifier tables, the Solver workbooks, the SPC maintained sheets and the whole process files: one-time US$249.99: instant download: the PayPal: the fact it packages the process knowledge the entire plant: this file is a single chapter of the 931.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.