aggregate gradation DPWH specifications
Aggregate Gradation for DPWH Specifications: What Batching Plants and Contractors Should Check
How to read a sieve analysis, choose the nominal maximum size and control fines so sand, gravel and base course meet DPWH and ASTM C33 requirements.
Most aggregate rejections on government projects are not about rock strength. They are about gradation: too many fines, a missing middle size, or a stockpile that no longer matches the sample the laboratory approved. This guide explains how gradation is measured, what the DPWH Standard Specifications and ASTM C33 ask for, and what to check before a truck is unloaded.
Why gradation matters
Gradation is the distribution of particle sizes in an aggregate. It controls two things a project cannot fix later:
- Workability and cement demand in concrete. A well-graded aggregate has fewer voids, so less paste is needed for the same slump. Gap-graded or single-sized material needs more cement and water and shrinks more.
- Density and stability in base course. A base that packs tightly under the roller carries traffic; one with too many fines holds water and fails under load.
A specification therefore gives a grading envelope: for each sieve, a minimum and maximum percentage passing. The material must fall inside the envelope on every sieve, not just on average.
Sieve analysis: how the number is produced
The test is ASTM C136 (AASHTO T 27), usually paired with ASTM C117 (AASHTO T 11), which washes out the material finer than 75 µm before sieving. Without the wash, clay coatings stay stuck to the coarse particles and the fines are under-reported.
The procedure in brief:
- Sample properly per ASTM D75: portions from several points of the stockpile, avoiding the segregated skin, reduced to test size with a splitter (ASTM C702).
- Use enough material. C136 sets a minimum dry test mass that rises with the nominal maximum size, from a few hundred grams for sand to several kilograms for coarse aggregate. Take the figure from the standard's table, not from habit.
- Dry, wash over the 75 µm sieve, dry again, then shake through a nest of sieves from largest to smallest, weigh what is retained on each, and compute the cumulative percentage passing.
- Plot the curve against the specification envelope.
For sand, also compute the fineness modulus (FM): the sum of the cumulative percentages retained on the 150 µm, 300 µm, 600 µm, 1.18 mm, 2.36 mm, 4.75 mm and 9.5 mm sieves, divided by 100. ASTM C33 requires an FM between 2.3 and 3.1, and successive deliveries should stay within 0.20 of the value used in the mix design.
Nominal maximum size and the 1/5, 1/3, 3/4 rule
Two terms cause confusion. Maximum size is the smallest sieve through which 100% of the aggregate passes. Nominal maximum size (NMS) is the smallest sieve through which most of the aggregate passes; a small amount may be retained on it. A "3/4-inch" gravel is nominally 19 mm: nearly all passes 19 mm, a little is retained, and everything passes 25 mm.
The NMS must fit the structure. ACI 318 limits it to no more than:
- 1/5 of the narrowest dimension between the sides of the forms,
- 1/3 of the depth of a slab, and
- 3/4 of the minimum clear spacing between reinforcing bars, or between bars and forms.
For a heavily reinforced beam with 25 mm clear spacing, 3/4 × 25 = 19 mm, so only a 19 mm or smaller aggregate is acceptable; a 37.5 mm "1-1/2 inch" gravel is out even if it is cheaper per cubic metre.
Fines: the fraction that fails most samples
"Fines" here means the material passing the 75 µm (No. 200) sieve: silt, clay and rock dust. Small amounts are harmless, and in base course a controlled amount helps the layer pack. Too much raises water demand, weakens the paste–aggregate bond, causes shrinkage cracks and, in base course, makes the layer moisture-sensitive.
ASTM C33 sets these limits on material finer than 75 µm:
- Fine aggregate: 3.0% maximum for concrete subject to abrasion, 5.0% for all other concrete. If the fines are dust of fracture from crushing and free of clay or shale, the limits rise to 5.0% and 7.0%.
- Coarse aggregate: 1.0% maximum, or 1.5% for crushed aggregate where the fines are dust of fracture essentially free of clay or shale.
The DPWH items for aggregate subbase and base course control fines differently. Besides the grading envelope, they limit the plasticity of the fine fraction (liquid limit and plasticity index) and require a minimum soaked California Bearing Ratio (CBR). Plasticity is the real gatekeeper: rock dust is non-plastic, clay is plastic, and two materials with identical sieve curves can behave completely differently on the road if one carries clay.
The DPWH items that govern aggregates
The DPWH Standard Specifications for Highways, Bridges and Airports (Volume II, 2013 edition) organise requirements by pay item, and DPWH amends individual items by department order. Item numbers and numerical limits are deliberately not reproduced here; the only version that counts is the edition named in your contract. What each item asks for is summarised below.
| DPWH item (by name) | What the specification controls |
|---|---|
| Aggregate Subbase Course | Grading envelope, plasticity of the fine fraction, minimum soaked CBR |
| Aggregate Base Course | Tighter grading envelopes, plasticity limits, abrasion loss, higher minimum soaked CBR |
| Crushed Aggregate Base Course | As base course, but from crushed material with a fractured-face requirement |
| Portland Cement Concrete Pavement | Coarse-aggregate abrasion and soundness limits, fine-aggregate grading |
| Structural Concrete | Aggregates by reference to the materials item; abrasion and grading limits |
| Aggregates (materials item) | The reference item for fine and coarse aggregate quality used by the concrete items |
A supplier's "base course" must be matched to the pay item. Subbase allows a coarser, dirtier product than base course, and crushed aggregate base course needs a crusher, not just a screen.
ASTM C33 for concrete aggregates
Most private-sector mix designs, and DPWH concrete items by reference to their materials item, lean on ASTM C33. Its coarse-aggregate gradings are numbered. The sizes seen most often in Philippine ready-mix are below, with the percentage passing each sieve as given in the standard's grading table; check them against the edition your mix design cites.
| Size No. | Nominal size | 25 mm | 19 mm | 12.5 mm | 9.5 mm | 4.75 mm | 2.36 mm |
|---|---|---|---|---|---|---|---|
| 57 | 25 to 4.75 mm | 95–100 | – | 25–60 | – | 0–10 | 0–5 |
| 67 | 19 to 4.75 mm | 100 | 90–100 | – | 20–55 | 0–10 | 0–5 |
| 7 | 12.5 to 4.75 mm | – | 100 | 90–100 | 40–70 | 0–15 | 0–5 |
| 8 | 9.5 to 2.36 mm | – | – | 100 | 85–100 | 10–30 | 0–10 |
In local trade usage, a "3/4" or "G1" gravel is usually meant to satisfy Size No. 67, and a "3/8" or "chips" product Size No. 8. These codes are not defined in any standard and vary between yards, so order by millimetre size and size number, as explained in gravel sizes explained.
A checklist for receiving aggregates
Before accepting a load into the stockpile:
- Compare the delivery to the approved source. Same quarry or river, same product. A change of source needs a new sieve analysis and a new mix-design check.
- Look at it. Excess dust, clay balls, mud coating, organic matter or shells are visible before any test; a jar settling test on sand, or a wash over a 75 µm sieve, catches a bad delivery early.
- Keep the sieve curve on file with whatever certificate came with the load, the date, the truck plate number and the stockpile it went into, and watch for drift toward the edge of the envelope.
Ask for the reports your specification requires before you order rather than after the truck arrives, because whether a source can issue a given report depends on that source and on how the material was tested. The tests behind a certificate, and what a good certificate looks like, are covered in quality checks for batching-plant aggregates.
Illustrative scenarios
These are hypothetical situations, not project records.
- Ready-mix plant. A new gravel delivery shows 18% passing 4.75 mm, well above the 0–10% allowed for Size No. 67. The mix is over-sanded, slump drops and cement demand rises. The plant flags the source and the supplier re-screens.
How Stone Depot Trading helps
Stone Depot Trading coordinates B2B sourcing and supply of limestone, sand, gravel and fly ash through trade partner companies from General Santos City. State the pay item or size number in the inquiry with the quantity, delivery site and schedule, and name the reports your specification requires. Which reports a source can actually issue depends on the material, the source, the specification and the testing arrangement, so availability and the documentation position are checked with the partner and reported back before quotation rather than assumed (see aggregates for a concrete batching plant).
FAQ
Do I need a washed sieve analysis?
Yes for concrete aggregates and for any base course where fines and plasticity are limited. Dry sieving alone under-reports the material finer than 75 µm, because clay coatings stay on the coarse particles.
What nominal maximum size should I use for slabs and columns?
Commonly 19 mm (3/4 inch) for reinforced structural concrete and 25 to 37.5 mm for mass concrete and pavements, subject to the 1/5, 1/3 and 3/4 rules in ACI 318 and to the project specification.
Can river gravel be used as DPWH base course?
It can qualify for aggregate subbase or base course if the grading, plasticity, abrasion and CBR requirements of the item are met. The crushed aggregate base course item is written for crushed material, so screened river gravel is unlikely to satisfy it.
Who performs the tests for DPWH work?
A testing laboratory accredited by DPWH; the DPWH Bureau of Research and Standards accredits private testing laboratories, and DPWH separately accredits contractors' and consultants' materials engineers by examination. The project's materials engineer will know the current requirements for the contract.
Request a quote
Send the pay item or standard, the size or grading, the quantity, the delivery location and the target dates through the quote form, by email to cjandulana@stonedepotph.com, or by call or Viber to +63 945 643 5233. Submitting an inquiry starts a sourcing conversation; it does not create a binding order.
Sources
- ASTM C33/C33M, Standard Specification for Concrete Aggregates — ASTM International (https://store.astm.org/c0033_c0033m-18.html)
- ASTM C136/C136M, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates — ASTM International (https://store.astm.org/c0136_c0136m-19.html)
- ASTM C117, Standard Test Method for Materials Finer than 75-μm (No. 200) Sieve in Mineral Aggregates by Washing — ASTM International (https://store.astm.org/c0117-23.html)
- DPWH Standard Specifications for Highways, Bridges and Airports, Volume II (2013 edition) — Department of Public Works and Highways
- ACI 318, Building Code Requirements for Structural Concrete — American Concrete Institute
- Application for Assessment as DPWH Accredited Private Testing Laboratory (BRS Form No. 1) — DPWH Bureau of Research and Standards (https://web.archive.org/web/20120816121113/http://www.dpwh.gov.ph/doing_business/accreditation/mat_test_lab/GUIDELINES_lab.pdf)
- Department Order No. 53, Series of 2010, Accreditation of Contractors'/Consultants' Materials Engineers — Department of Public Works and Highways (https://web.archive.org/web/20111108175400/http://www.dpwh.gov.ph/doing_business/accreditation/mat_engr/DO_053_S2010.pdf)
Disclaimer
This article is general information. Final suitability of any material must be confirmed against the buyer's project specifications, the approved mix design, laboratory test results and the project engineer's requirements. Stone Depot Trading coordinates sourcing and supply; it does not certify materials or guarantee acceptance by any agency.