Staff Answer
Mar 09, 2026 - 01:48 PM
I pored a new concrete slab and it has excessive pop outs created from Lignite. which ASTM addresses how much lignite a concrete should have
The exact ASTM that governs lignite limits in concrete.
If you have some lignite we recommend sealing the concrete with SealGreen Concrete Sealer with Salt Defense Technology. - This sealer will reduce the future pops of lignite. Give us a call 913-681-3451 if you have questions.
ASTM C33 — Standard Specification for Concrete Aggregates
This is the primary ASTM standard that sets maximum allowable lignite and other lightweight deleterious materials in fine and coarse aggregates used for concrete.
According to search results:
- ASTM C33 allows 0.5–1% lignite in concrete sand (fine aggregate). shuntool.com
- Excess Lignite is known to cause popouts, staining, and surface defects. CivilWeb Spreadsheets
(Values vary slightly by region/spec revision, but these are the standard ranges referenced in industry and search results.)
|
Aggregate Type |
Max Lignite Allowed (ASTM C33) |
|
Fine Aggregate (Sand) |
0.5–1.0% lignite by mass shuntool.com |
|
Coarse Aggregate |
Typically 0.05% lignite (per similar international standards) CivilWeb Spreadsheets |
WHAT IS LIGNITE?
Lignite is:
- Lightweight
- Porous
- Water‑absorbing
- Soft
So, during finishing and curing, lignite particles float upward, and later:
- Absorb moisture → expand → popouts.
- Break down → leave holes or black marks.
Even tiny amounts within ASTM limits can still cause popouts, especially in slabs with a smooth finish. CivilWeb Spreadsheets
How to Confirm the Lignite Content
Producers typically use:
- Burn tests (measure weight loss after lignite burns off)
- Wet washing / flat-bottom classifiers to remove lignite from sand shuntool.com
If your slab has widespread popouts, the sand may have exceeded ASTM C33 limits — or barely met them but still contained enough lignite to cause issues.
What You Can Do Next
Here is a practical path forward:
1. Document the popouts
- Photograph patterns, density, and size.
- Note whether they appear after wetting/drying cycles.
2. Ask your ready‑mix supplier for:
- ASTM C33 compliance report for the aggregates used.
- Lignite content test results (burn test or equivalent)
3. If lignite content exceeds ASTM C33
You may have grounds for:
- Supplier remediation
- Surface repair compensation
- Replacement of affected areas (in severe cases)
4. Mitigation options
- Surface grinding + densifier
- Polymer-modified resurface.
- Thin-bonded overlay
- Full-depth repair (if structural or widespread)
At what amount of lignite in a concrete slab is too much and needs to be replaced completely?
Condensed version: there is no ASTM “X% lignite = replace the slab” limit. ASTM only limits lignite in the aggregates, not the finished concrete.
Here is how it actually breaks down:
- ASTM C33 sets maximum coal & Lignite in aggregates, roughly:
- Fine aggregate (sand): about 0.5–1.0% by mass
- Coarse aggregate: lower, around 0.25% or less
These limits are about aggregate quality, not a trigger to tear out concrete. - ASTM does not say:
“If your slab has more than X% lignite, you must replace it.”
Instead, it is performance-based: is the slab structurally sound and durable?
So, when is it “too much” in practice?
- Usually cosmetic only → no replacement:
- Small popouts, scattered.
- Shallow (⅛–¼ in deep)
- No scaling, no map cracking, no rebar issues
- Can be ground, patched, or overlaid.
- Consider replacement or major remediation if:
- Popouts are extremely dense (every few inches)
- They keep recurring after repairs.
- Popouts are deep, exposing coarse aggregate or rebar.
- You see wider distress: scaling, delamination, structural cracking, loss of cover.
In other words:
- ASTM C33 tells you the producer may have supplied out-of-spec aggregate if lignite is high.
- But the decision to replace the slab is based on condition, not a specific lignite percentage.
Add New Comment