Why the COA Matters More Than Price
In a global market where silica fume trades from Southeast Asia, Norwegen, and China at wildly different price points, the Certificate of Analysis is often the only technical document standing between your specification and a failed mix design.
A COA from a reputable producer documents chemical composition, physikalische Eigenschaften, and activity performance — tested batch by batch, against internationally recognized standards. A COA from an unreliable supplier may list impressive numbers that were measured once, years ago, on a different production run.
The difference between these two documents can mean the difference between a 100 MPa UHPC element and a durability failure at 10 Jahre. Before price, before lead time, before Incoterms — read the COA.
⚠ Critical Distinction
Confirm whether the COA covers the specific batch/lot being shipped, or is a generic “typical analysis” dokumentieren. Batch-specific COAs, cross-referenced against the shipment’s lot number, are the industry standard for serious procurement.
The Eight Parameters That Define Quality
Both ASTM C1240 and EN 13263 establish minimum requirements for silica fume used in concrete. Here are the parameters you must scrutinize on every COA — and what they mean for your mix.
Chemical · Primary
SiO₂ Content
ASTM C1240: ≥ 85% · EN 13263: ≥ 85%
The single most important figure. SiO₂ drives pozzolanic reactivity. Most construction applications target ≥ 90%; UHPC and HPC typically specify 92–96%. Higher grades yield denser C-S-H and tighter ITZ.
Physical · Fineness
Spezifische Oberfläche
Typically 15,000–25,000 m²/kg (WETTE)
Measured by BET nitrogen adsorption. Higher surface area = faster pozzolanic kinetics and better particle packing. Ensure the method is stated — BET results and Blaine values are not interchangeable.
Physical · Oversize
Aufbehalten 45 μm Sieve
ASTM C1240: ≤ 10%
Coarse particles do not react. Excessive oversize indicates poor production quality or agglomerated material. For UHPC and shotcrete, tighter limits (< 3–5%) are standard in project specs.
Physical · Moisture
Feuchtigkeitsgehalt
ASTM C1240: ≤ 3.0%
Moisture above threshold causes clumping, weight discrepancies, and handling problems in pneumatic systems. Critical for powder silica fume; verify against packaging integrity during shipment inspection.
Chemical · Combustion
Verlust bei Zündung (LOI)
ASTM C1240: ≤ 6.0%
LOI reflects unburned carbon and organics. Elevated LOI interferes with air-entraining admixtures, increases water demand, and suppresses pozzolanic efficiency. Premium grades often achieve ≤ 3.0%.
Leistung
Kraftaktivitätsindex (ORKB)
ASTM C1240: ≥ 105% bei 28 Tage
Compares mortar cube strength with and without silica fume. SAI ≥ 105% bei 28 days confirms reactivity. Learn how HSA measures and reports pozzolanic activity index for each grade.
Chemical · Durability
Chloride Content (Cl⁻)
IN 13263: ≤ 0.3% · Projects often ≤ 0.1%
Chloride triggers reinforcement corrosion. Particularly critical in marine structures, Tunnel, and parking decks. Many project specifications impose limits stricter than the standard minimum.
Chemical · Durability
Alkali Content (Na₂O eq.)
Typically ≤ 1.5% · Check project spec
Alkali-silica reaction (ASR) risk. While silica fume generally mitigates ASR when dosed correctly, high intrinsic alkalis from the silica fume itself can be counterproductive. Flag any value above 1.5%.
ASTM C1240 vs EN 13263: Side-by-Side
Most buyers operate under one of two standards frameworks. Understanding how they differ prevents misaligned procurement. For a full breakdown of ASTM C1240 requirements, refer to our dedicated reference guide.
| Parameter | ASTM C1240 | IN 13263-1 | Notes |
|---|---|---|---|
| SiO₂ Content | ≥ 85.0% | ≥ 85.0% | Same minimum; higher grades voluntarily exceed this |
| Feuchtigkeitsgehalt | ≤ 3.0% | ≤ 3.0% | Identical; confirm for densified vs. unverdichtet |
| Verlust bei Zündung | ≤ 6.0% | ≤ 4.0% | IN 13263 is stricter |
| Übergröße (45 μm) | ≤ 10% | Not directly specified | EN uses specific surface area as the fineness proxy |
| Spezifische Oberfläche | Not specified (informational) | ≥ 15,000 m²/kg (WETTE) | IN 13263 is explicit; ASTM reports informally |
| Chloride Content | Not specified | ≤ 0.3% | IN 13263 includes Cl⁻ limit; ASTM is silent |
| SO₃ Content | ≤ 1.0% | ≤ 2.0% | ASTM C1240 is stricter for sulfur |
| Kraftaktivitätsindex | ≥ 105% @ 28 D | Activity Index per EN 13263-2 | Different test protocols; not directly comparable |
✓ Procurement Tip
For projects in Europe or the Middle East under EU-influenced standards, specify EN 13263 Einhaltung. For North America, Gulf, and most Asian markets, ASTM C1240 is more commonly referenced. Always confirm which standard applies before issuing a purchase order.
Matching SiO₂ Grade to Application
Not all applications require maximum purity. Over-specifying grade increases cost; under-specifying risks performance. For a detailed breakdown of each grade’s characteristics, see our guide to micro silica fume grades and their uses.
| SiO₂ Grade | Typical Range | Best Suited For | Key Consideration |
|---|---|---|---|
| 85% Grad | 85–89% | General-purpose concrete, infrastructure, mass concrete | Most cost-effective; meets ASTM/EN minimum |
| 92% Grad | 90–93% | Hochleistungsbeton, Meeresstrukturen, precast | Balanced reactivity and economics; most widely specified |
| 94% Grad | 93–95% | UHPC, protective coatings, HPC bridges | Superior pozzolanic activity; lower LOI typical |
| 96% Grad | ≥ 96% | 3D-printed concrete, feuerfest, specialty grouts | Premium feedstock; demand lower chloride and alkali too |
Green Flags vs. Red Flags on Any COA
A well-prepared COA tells you as much by what it includes as by what it omits. Train your eye to spot both signals before committing to a supplier relationship.
✓ Green Flags
- ✓Lot/batch number traceable to shipment documentation
- ✓Test date within 6 months of shipment date
- ✓All eight standard parameters reported, not selected ones
- ✓Strength Activity Index tested and reported, not estimated
- ✓BET surface area stated with test method specified
- ✓ISO 17025-accredited laboratory seal or reference
- ✓Consistent results across multiple historical batches on request
✗ Red Flags
- ✗“Typical analysis” with no batch identifier or date
- ✗SiO₂ reported as a suspiciously round number (z.B., exactly 92.0%)
- ✗LOI missing or reported as “N / A” without explanation
- ✗No Strength Activity Index — only chemical data provided
- ✗Chloride content absent from document entirely
- ✗No laboratory name, stamp, or signatory on the document
- ✗Significantly different results across batches with no explanation
Densified vs. Unverdichtet: What the COA Should State
Physical form affects handling, dosing accuracy, and dispersion — but it should not affect chemical performance. When reviewing a COA, confirm the product form is explicitly stated. For a detailed comparison, see our article on the difference between densified and undensified silica fume.
For Densified Powder
Bulk density is typically 500–720 kg/m³. The COA should report bulk density clearly, as it directly affects volumetric batching accuracy. Oversize values may appear slightly higher than undensified product due to agglomeration — confirm the supplier performs de-agglomeration testing or provides BET surface area as the primary fineness metric.
For Undensified Powder
Bulk density falls in the 200–350 kg/m³ range. Expect higher sensitivity to moisture pickup in humid storage. The COA moisture figure should reflect fresh-production testing, not aged material. Specific surface area values are typically more directly comparable to raw production output.
⚠ Supplier Note
Henan Superior Abrasives supplies powder silica fume exclusively — both densified and undensified grades — and does not produce slurry. This ensures full SiO₂ concentration as stated on the COA, and avoids transport weight penalties on water content.
Your Pre-Purchase COA Review Checklist
Run through this checklist on every COA before issuing a purchase order. It takes under ten minutes and can prevent costly mix redesigns or jobsite rejection events.
10-Point COA Verification Checklist
- 01Batch Traceability: Is a specific lot or batch number present that can be cross-referenced with the shipping documentation?
- 02Test Date: Was the COA issued within 6 months of your intended order date?
- 03SiO₂ Confirmation: Does SiO₂ meet or exceed your specification grade (85 / 92 / 94 / 96%)? Is the test method stated (XRF recommended)?
- 04LOI Compliance: Is LOI ≤ 6.0% (ASTM) or ≤ 4.0% (IN 13263)? Does it fit your admixture compatibility requirements?
- 05Moisture Check: Is moisture content ≤ 3.0%? Is the product form (densified/undensified) clearly stated?
- 06Fineness Verification: Is 45 μm oversize ≤ 10%? Or is BET ≥ 15,000 m²/kg (IN)? Is the measurement method specified?
- 07SAI Performance: Is Strength Activity Index ≥ 105% bei 28 Tage? Is the 7-day value also available?
- 08Chloride Limit: Is Cl⁻ reported and within project-allowable limits (standard max 0.3%)?
- 09Alkali Content: Is Na₂O equivalent reported and below 1.5% or within your ASR-risk threshold?
- 10Laboratory Accreditation: Does the COA carry an accredited lab reference, signatory, and stamp — not just a supplier letterhead?
Frequently Asked Questions
Can I trust a COA provided directly by the supplier without third-party verification?
Supplier-issued COAs are standard practice and acceptable for most procurement. Jedoch, for large or long-term contracts, independent third-party testing from an ISO 17025-accredited laboratory provides an additional layer of confidence. Reputable suppliers welcome third-party sampling and do not restrict it.
At minimum, request historical COAs from multiple batches to verify consistency. A single perfect COA is less convincing than 12 months of stable batch data.
What’s the difference between BET surface area and Blaine surface area?
WETTE (Brunauer–Emmett–Teller) measures total surface area using nitrogen gas adsorption, capturing the high microporosity of amorphous silica particles. Blaine is an air-permeability method developed for Portland cement and severely underestimates surface area for silica fume.
Always confirm the COA uses BET when referencing surface area for silica fume. A value of 15,000–25,000 m²/kg (WETTE) is typical. If a supplier reports surface area without specifying the method, request clarification before accepting the figure.
The COA shows SiO₂ = 94.2%, but my test on received material shows 91.8%. What should I do?
A discrepancy of more than 1–2% is worth investigating. First confirm that both tests used the same method (XRF vs. gravimetric wet chemistry) — different methods can yield different results on the same sample. Confirm sample preparation was consistent and that your test laboratory is ISO 17025 accredited.
If methodology is aligned and the gap persists, document the discrepancy formally and contact the supplier with both COA and third-party results. A reputable exporter will co-investigate and provide replacement material or credit where confirmed.
Does high SiO₂ content always mean better concrete performance?
SiO₂ content is necessary but not sufficient. A 96% SiO₂ silica fume with elevated LOI, poor fineness, or high moisture may underperform a well-characterized 90% Grad. The SAI result is the most direct performance indicator — it reflects actual reactivity under standardized conditions.
For most structural concrete, A 92% SiO₂ grade with SAI ≥ 110% and LOI < 3.0% will outperform an uncharacterized 96% Material. Specify the full parameter suite, not just SiO₂.
How often should a supplier issue a new COA?
For active production, COAs should be issued on a per-batch or per-production-lot basis. Most serious producers run QC testing every 1–4 weeks depending on volume. For large export orders, a COA covering the specific production lot destined for your shipment is standard.
A COA that is more than 12 months old and not linked to a specific recent batch is a procurement risk. Silica fume chemistry is stable in proper storage, but an old COA does not confirm the current production stream meets specification.
Request Documentation · Henan Superior Abrasives
Ready to Review Our COA?
HSA provides batch-specific COAs with full ASTM C1240 and EN 13263 compliance data — SiO₂, LOI, ORKB, Feuchtigkeit, Chlorid, Oberfläche, and more — for every shipment.
Über Henan Superior Schorpfer (HSA)
Henan überlegene Schleifmittel is a China-based manufacturer and global exporter of silica fume (Mikrosilika), silicon carbide, and related industrial minerals, supplying concrete producers and construction materials companies across 30+ Länder. HSA produces densified and undensified silica fume powder compliant with ASTM C1240 und IN 13263, available in grades from 85% zu 96% SiO₂. We do not supply slurry — only concentrated, dry powder product. For COA documentation, technische Datenblätter, or product samples, contact our export team.
