November 2, 2026
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TL;DR
Construction aggregates are the sand, gravel, crushed stone and manufactured or recycled particles that make up most of a concrete mix and carry the load in a base course. The No. 4 sieve (4.75 mm) splits coarse from fine, AASHTO M 43 numbers such as No. 57 set the coarse sizes, and the state DOT spec in your contract sets the final gradation.
Order by that spec number with a current test report, and price the load delivered. Delivery can be a large share of the final cost, especially when aggregate travels a long way.
What construction aggregates do in a build
Construction aggregates give a structure its bulk and its load path. They take up most of the volume of concrete, form the stone skeleton of asphalt, and as an unbound layer they spread wheel and footing loads into the subgrade while letting water drain out.
Four jobs cover most of it:
- Concrete and asphalt: aggregate is the filler the binder coats. ASTM C33 sets grading and quality for concrete aggregates, from organic impurities in sand to abrasion and soundness in stone.
- Base and subbase: a dense-graded layer under pavement, slabs and pads. Its fines fill the voids so it compacts hard.
- Drainage and bedding: clean, open-graded stone around pipe, behind walls and in French drains, where water has to move.
- Armor and erosion control: rip rap and large stone on slopes, outfalls and channel banks.
USGS figures show where the tonnage goes. Of an estimated 870 million metric tons of construction sand and gravel produced in 2025, about 42% went into portland cement concrete, 20% into road base and coverings, and 12% into construction fill. About 72% of the 1.5 billion metric tons of crushed stone was used as construction aggregate, mostly for road construction and maintenance.
On a site plan, aggregate rarely works alone. Select fill, subgrade soil and stone base are layered together, and Soil Connect's guide to the dirt & aggregate material mix covers how those layers are chosen for a given load and soil.
Types of aggregate by source
The main types of aggregate by source are natural sand and gravel from pits, crushed stone from quarries, recycled concrete and asphalt, and manufactured aggregate such as slag and expanded shale. Source sets particle shape, consistency and, through the haul, the delivered price.
Table: Aggregate sources at a glance
| Source | How it is produced | Typical products |
| Sand & gravel pits | Dug or dredged, then washed and screened | Concrete sand, pea gravel, bank run, fill |
| Quarries | Drilled, blasted, crushed and screened rock | No. 57 stone, crusher run, screenings |
| Recycled | Old concrete or asphalt crushed and sized | Recycled base, backfill, coarse RCA |
| Manufactured | Industrial byproduct or kiln-expanded mineral | Air-cooled slag, expanded shale, clay or slate |
Crushed stone and natural gravel compete for many of the same jobs. USGS notes that crushed stone is often substituted for natural sand and gravel, and that recycled asphalt and portland cement concrete are increasingly used in place of virgin aggregate, though recycled material still supplies a very small share of the total.
USGS counts 3,500 crushed stone quarries and 6,500 sand and gravel pits in its 2025 estimates. About 70% of the crushed stone was limestone and dolomite, 14% granite and 6% traprock. The USGS mineral commodity data page also posts quarterly shipment surveys by state.
Local geology decides which source wins. Where quarries are few, Soil Connect's article on the growing demand for gravel finds higher delivered prices.
Coarse aggregate vs fine aggregate
Coarse aggregate is the fraction retained on the No. 4 sieve (4.75 mm), and fine aggregate is the fraction that passes it. FHWA and state DOTs such as Iowa draw the line at that sieve, and ASTM C33 grades each side separately.
Fine aggregate under ASTM C33 is natural sand, manufactured sand or a blend. Its grading band runs from 100% passing the 3/8 inch sieve and 95 to 100% passing the No. 4, down to 0 to 10% passing the No. 100. Virginia's spec splits it the same way into natural sand and stone sand, and caps natural sand passing the No. 200 sieve at 3% for concrete exposed to abrasion and 5% for other concrete. Stone sand whose fines are dust of fracture gets 5% and 7%.
Coarse aggregate under C33 can be gravel, crushed gravel, crushed stone, air-cooled blast furnace slag or crushed hydraulic-cement concrete. Common coarse sizes such as No. 57 and No. 67 allow no more than 10% passing the No. 4, so nearly everything in a coarse stockpile stays on that screen.
Table: Fine vs coarse aggregate for concrete
| | Fine aggregate | Coarse aggregate |
| Size boundary | Passes the No. 4 (4.75 mm) sieve | Retained on the No. 4 sieve |
| Common materials | Natural sand, manufactured or stone sand | Gravel, crushed stone, slag, crushed concrete |
| Grading set by | ASTM C33 fine aggregate band | ASTM C33 or AASHTO M 43 size number |
| What it controls | Workability, finish, paste demand | Strength, stiffness, the bulk of the volume |
A ready-mix plant buys the two fractions separately. Crusher run carries both in one product.
Aggregate sizes & gradations
Aggregate sizes for road and bridge work follow AASHTO M 43, also published as ASTM D448. Each size number is a gradation band, the share of the sample that must pass each sieve, and the number alone tells an estimator the top size and how clean the stone is.
The system numbers stone from 1, the largest at 4 inches, to 10, the smallest at 3/8 inch. Multi-digit sizes are blends, so No. 57 combines sizes 5 and 7, and an FHWA study counts 19 M 43 gradations in all. Virginia's Table II-3 lists the same numbered sizes, tested by sieve analysis under AASHTO T27.
Table: Four common size numbers (VDOT Table II-3, percent passing by weight)
| Size No. | 100% passes | Passing No. 4 | Passing No. 8 |
| No. 57 | 1 1/2 in | 10% max | 5% max |
| No. 67 | 1 in | 10% max | 5% max |
| No. 8 | 1/2 in | 10 to 30% | 10% max |
| No. 10 | 3/8 in | 85 to 100% | Not set |
No. 57 and No. 67 differ mainly at the top. No. 57 allows stone up to 1 1/2 inch, with 95 to 100% passing 1 inch. No. 67 tops out at 1 inch, with 90 to 100% passing 3/4 inch. Both keep 10% or less passing the No. 4, and Virginia caps coarse aggregate at 1% passing the No. 200 by washing, which is what makes them clean.
Gradation describes the curve as a whole. Penn State's aggregate primer notes that every AASHTO size is technically open graded: few fines, open voids, good drainage, poor compaction into a dense mass. Dense-graded material runs from the top size down to dust, like Virginia's 21A base, which allows 6 to 12% passing the No. 200. Blending fines into an open size is what yards still call modified stone.
Yard names vary by region. Put the size number and spec section on the order.
Crushed stone, crusher run & aggregate base
Crushed stone is quarried rock broken to size, crusher run is the unscreened, all-in product of that crushing, and aggregate base is a spec-graded layer, often crushed, compacted under pavement or slabs. Crusher run and base both carry plasticity limits, but only the base is produced to an approved job-mix formula.
Crushed stone is sold as single size numbers such as No. 57 and as blends. Its angular, broken faces interlock and compact better than rounded gravel, which is why many base specs call for crushed material.
Crusher run, in the words of the VDOT road and bridge specifications, contains all of the sizes produced when the original aggregate is reduced through a series of crushers to the maximum size specified. VDOT Section 205 sets three sizes with top sizes of 2 1/2, 1 1/2 and 1 inch, caps the liquid limit at 25 and the plasticity index at 3, and lists its uses as backfilling and bedding pipe and box culverts, maintaining traffic and building all-weather private access pavements.
Aggregate base is the engineered version. VDOT Section 208 calls Type I aggregate base crushed stone, crushed slag or crushed gravel, with at least 90% of crushed gravel retained on the No. 10 sieve showing a fractured face. Size 21A must fall between 6 and 12% passing the No. 200 and 21B between 4 and 7%, each within a job-mix tolerance.
Rip rap for slopes & channels
Rip rap is large, durable stone placed to stop scour on slopes, outfalls, ditches and channel banks. Its classes vary by state DOT, and two states can size the same job in different units.
Table: Two ways states class rip rap
| Virginia (VDOT 414, by stone weight) | Pennsylvania (R-series, by size) |
| Class AI: 25 to 75 lb | R-3: 2 to 6 in |
| Class I: 50 to 150 lb | R-4: 3 to 12 in |
| Class II: 150 to 500 lb | R-5: 4 to 18 in |
| Class III: 500 to 1,500 lb | R-6: 9 to 24 in, up to R-8 at 15 to 42 in |
Virginia also requires rip rap exposed to wave action to be igneous or metamorphic rock, and sets the bedding as crushed stone of at least Grade B. Penn State's primer notes that the R designations come from the National Crushed Stone Association, and that loose terms such as shot rock and surge stone carry no exact spec.
Recycled concrete aggregate & lightweight aggregate
Recycled concrete aggregate is old concrete crushed, cleaned of steel and soil, and screened to a gradation. Lightweight aggregate includes shale, clay and slate expanded in a rotary kiln. One trades on cost and reuse, the other on low weight.
FHWA's recycled concrete technical advisory (T 5040.37) describes the process as identical to producing virgin aggregate, apart from removing steel and contaminants. For RCA going into new paving concrete, it recommends more than 90% cement paste and aggregate, asphalt under 1% and absorption under 10%. It advises against fine RCA, and where fine RCA must be used, no more than 30% of the sand.
FHWA lists lower-grade uses for removed concrete too: granular base and subbase, bedding, backfill and granular embankment. Virginia permits crushed hydraulic-cement concrete as crusher run if it meets the physical requirements of Section 203, but not in subsurface drains with perforated pipe or as base where geotextile fabric is used. USGS lists 37 million metric tons of recycled material in its 2025 crushed stone estimates.
Lightweight aggregate made from expanded shale, clay and slate is fired in a rotary kiln at over 1,000 degrees Celsius, according to the Expanded Shale, Clay and Slate Institute. Gases form inside the softened particles and leave a uniform pore system as they cool. ASTM C125 calls an aggregate low density when its bulk density is under 70 lb per cubic foot. For scale, Caterpillar's density table lists loose crushed stone at 2,700 lb per cubic yard, which works out to 100 lb per cubic foot.
- ASTM C330: lightweight aggregate for structural concrete
- ASTM C331: lightweight aggregate for concrete masonry units
- ASTM C332: lightweight aggregate for insulating concrete
ESCSI lists masonry units, high-rise buildings, bridge decks and lightweight geotechnical fill among the main uses. Soil Connect's aggregate FAQ adds that lightweight aggregates reduce structural load and improve thermal insulation.
How to order from aggregate suppliers
Order from aggregate suppliers with four things fixed: the spec and size number, the quantity in tons, a current test report and a delivered price. Most quarries and pits sell by the ton, so convert the plan volume first.
- Pull the spec. Copy the size number or class and the governing section, such as AASHTO M 43 No. 57, VDOT 21A or rip rap Class II, onto the purchase order.
- Figure the volume. Length x width x depth in feet, divided by 27, gives cubic yards.
- Convert to tons with an in-place factor from your DOT or supplier, then add the waste allowance your estimator sets.
- Ask for test data: a recent sieve analysis against your band, plus the quality tests the spec names, such as soundness or abrasion.
- Compare delivered quotes. Ask each source for the price per ton, the freight per load and the tons each truck can legally carry.
A worked example shows the math. A 30 by 40 foot slab with a 4 inch stone base needs 30 x 40 x 0.333 = 400 cubic feet, and 400 / 27 = 14.8 cubic yards in place.
Table: Loose weights for 14.8 cubic yards of base stone (Caterpillar's table)
| Material | Loose lb per cubic yard | Tons per cubic yard | Tons at loose weight |
| Crushed stone | 2,700 | 1.35 | About 20 |
| Gravel, dry, 1/4 to 2 in | 2,850 | 1.43 | About 21 |
| Gravel, wet, 1/4 to 2 in | 3,400 | 1.70 | About 25 |
Those are loose weights, and the 14.8 yards are compacted in place, so 20 to 25 tons is a floor. An Illinois DOT District 5 plan memo converts aggregate base to tons at 1.8 tons per cubic yard, which puts this base near 27 tons. Caterpillar notes that weight varies with moisture, grain size and compaction, so confirm the factor with your supplier. At the roughly 15 tons per truck in Soil Connect's capacity article, that is two loads.
Supplier checks go beyond price. Soil Connect's guide to vetting aggregate suppliers covers reputation, documentation and project fit. For a job that is also importing or exporting soil, the Find Dirt marketplace handles dirt, soil and aggregates, and a Soil Connect Dirt Specialist contacts you within 1 business day.
What they do
By source
Coarse vs fine
Sizes
Base stone
RCA & lightweight
Ordering
Construction aggregates FAQ
Frequently asked questions
Which types of gravel work as a base?
Of the common types of gravel, crushed, dense-graded products make the best base: crusher run, a state base such as Virginia's 21A, or crushed gravel with a high share of fractured faces. Their fines fill the voids, so the layer compacts hard. Clean No. 57 stone drains well but does not compact into a dense mass, so it suits drainage layers and open-graded designs better than a tight, dense base.
How much aggregate does a slab need?
Multiply length by width by base depth in feet and divide by 27 for cubic yards in place. A 30 by 40 foot slab with 4 inches of base needs 14.8 cubic yards. Loose weights of 1.35 to 1.70 tons per cubic yard give 20 to 25 tons, but compacted base weighs more. At the 1.8 tons per cubic yard an Illinois DOT district uses for aggregate base, plan on about 27 tons plus waste.
Can Soil Connect source aggregate with dirt?
Yes. Soil Connect is an online marketplace for dirt and aggregates, and its Find Dirt form takes a free-text material type and a quantity, so a project can list its fill and its stone base together. A Soil Connect Dirt Specialist contacts you within 1 business day, and the team can also connect contractors with dirt options that are not on the platform.
Is recycled aggregate as strong as virgin stone?
Not quite in concrete. FHWA's technical advisory, citing ACI 555R, reports compressive strength 5 to 24% lower with coarse recycled aggregate alone, and 15 to 40% lower with coarse and fine together, compared with similar virgin mixes.
As base or backfill, recycled concrete aggregate is judged by the same gradation and physical tests as virgin stone. FHWA lists base, subbase and backfill among its uses, and Virginia allows it in crusher run.
Aggregate & fill material guides
Keep reading
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Construction aggregates guide: Types, sizes & how to order
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