CDOT Specification

Class 6 Road Base Calculator — CDOT Specification Base

Q: What is CDOT Class 6 Road Base?

CDOT Class 6 is a 3/4-inch crushed aggregate road base specification defined by the Colorado Department of Transportation. It combines 100% crushed angular granite/gravel with non-plastic mineral fines engineered for high-altitude freeze-thaw durability.

Q: How many tons of Class 6 base are in a cubic yard?

One cubic yard of compacted in-place CDOT Class 6 road base weighs approximately 1.84 tons (3,675 lbs) based on 136 lb/ft³ density. When ordering loose material from a Colorado pit, calculate 1.55 tons per loose cubic yard.

CDOT Class 6 Aggregate Base Course (Section 304) is the premier crushed aggregate specification engineered for high-altitude freeze-thaw cycles and Rocky Mountain roadway foundations.

ASTM / AASHTO Verified

Compaction & Waste Factors Included

Dump Truck Capacity Dispatcher

Imperial Standard (yd³ & Tons)

Class 6 Road Base Calculator — CDOT Specification Base

Precision volume, tonnage, compaction shrinkage & dump truck dispatcher

CDOT Specification

1. Excavation Area & Compacted Depth

Length (ft)

Width (ft)

Compacted Depth (in)

Project Presets:

2. Compaction Shrinkage (%)

3. Grading & Waste Buffer (%)

Geotechnical Material Density: 135 lb/ft³ (1.82 Tons/yd³)

Compacted Dry Density (lb/ft³)

Material Price ($/Ton)

Material Estimation Output

Total Weight to Order (incl. buffers)

25.1

Tons (approx. 1.3 Tri-Axle Loads)

Compacted In-Place Vol 11.1 yd³ 300 cu ft in place

Loose Delivery Volume 13.8 yd³ +24% combined buffer

Lift Schedule 2 Lifts (3.8" ea) 7.5" total loose spread

Material Subtotal $778.00 Excl. freight & taxes

Engineering Recommendation:

For a 6.0" compacted Class 6 Road Base Calculator base, spread in 2 separate loose lifts of 3.8". Mist with water to achieve optimum compaction before running a 3,000+ lb plate compactor.

CDOT Highway Standard

CDOT Class 6 Aggregate Base Course (Section 304) Specification Sheet

CDOT Section 304 Class 6

Compacted Dry Density 136 lb/ft³ (2,178 kg/m³)

Weight per Volume 1.84 Tons / yd³

Sieve Gradation 3/4" (19mm) CDOT Class 6 Gradation

Compaction Factor +17% to +21%

Optimum Moisture (OMC) 5.5% – 7.5% by Weight

CBR Bearing Ratio 85% – 100% (High Bearing)

Governing Standard CDOT Standard Specifications Section 304 Class 6

Max Lift Thickness 3" to 4" Maximum per Pass

Liquid Limit LL < 30 Maximum (AASHTO T89)

Plasticity Index PI < 6 Maximum (AASHTO T90)

LA Abrasion Loss < 45% (AASHTO T96)

Crushed Fracture % Minimum 50% with 2+ fractured faces

Civil Engineering Math

How to Calculate CDOT Class 6 Base Volume, Freeze-Thaw Tonnage & Loads

Mathematical equations for CDOT Class 6 volume conversions, high-altitude compaction shrinkage (+17–21%), and mountain dump loads.

1 Surface Area

Area Geometry

Area = Length (ft) × Width (ft)

Determine the square footprint of your driveway, patio, slab, or pad. For curved shapes, break the area into offset rectangles.

2 In-Place Volume

Compact Volume

Vol (yd³) = (Area × Depth_in ÷ 12) ÷ 27

Convert design depth to volumetric units. This represents the final solid in-place compacted volume required after rolling.

3 Compaction Loss

Gross Loose Volume

Loose Vol = Compact Vol × (1 + 19%)

Quarries sell aggregate in its loose, aerated state. Adding 19% accounts for void compression under mechanical vibration.

4 Weight & Ordering

Quarry Tonnage

Tons = Vol (yd³) × 1.82 × 1.05 Waste

Convert volume to bulk weight using dense-graded stone density, adding 5% for site grading tolerance and edge bevel waste.

Real-World Numerical Example

Worked Calculation: 1,000 sq ft Driveway at 6" Compacted Depth

Target Material: Class 6 Road Base Calculator

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Step 1 — Calculate In-Place Volume:

1,000 sq ft × (6 ÷ 12 ft) = 500 cu ft ÷ 27 = 18.52 cubic yards

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Step 2 — Apply +19% Compaction & +5% Waste:

18.52 yd³ × 1.19 (shrinkage) × 1.05 (waste) = 22.95 loose cubic yards

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Step 3 — Multiply by Quarry Bulk Density (1.84 Tons / yd³):

18.52 compacted yd³ × 1.24 combined factor × 1.82 Tons/yd³ = 41.8 Tons total order weight

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Step 4 — Calculate Hauling & Estimated Material Cost:

42 Tons ÷ 20-ton Tri-Axle = 3 Dump Truck Loads | Quarry Stone Cost: ~$1386

Order Sheet Summary

Total Order Weight: 41.8 Tons

Loose Volume: 23.0 yd³

Truckloads Required: 3 Tri-Axle Loads

Estimated Quarry Price: $1386

CDOT CP 31 / AASHTO T27

CDOT Section 304 Class 6 Particle Gradation & Sieve Curve

Laboratory sieve gradation analysis for CDOT Class 6 3/4" base engineered with 100% crushed faces for intense friction interlock.

Standard Sieve Size % Passing (Design Target)

1 3/4" (19.0 mm)

Spec: 100% 100%

2 1/2" (12.5 mm)

Spec: 60% – 85% 72%

3 No. 4 (4.75 mm)

Spec: 30% – 65% 48%

4 No. 8 (2.36 mm)

Spec: 25% – 55% 38%

5 No. 200 (75 µm)

Spec: 3% – 12% 7%

Selected Sieve Analysis Spec: 100%

3/4" (19.0 mm)

Target Percent Passing

100%

Geotechnical Function:

CDOT Class 6 top size (100% must pass).

Dense-Grading Principle: Continuous particle distribution from top size to sub-75µm fines locks stone voids, reducing empty space from 35% to <12% under vibration.

Civil Estimating & Geotechnical Engineering Review

Peer-Verified

Formulas, density conversions, and lift recommendations are modeled after AASHTO M147 (Materials for Aggregate and Soil-Aggregate Subbase) and ASTM C33/D2922 standards. Reviewed by licensed civil engineers and heavy highway earthwork estimators.

• AASHTO M147 Compliant • ASTM C136 Sieve Analysis • ASTM D698 / D1557 Proctor Compaction

Frost Pavement Section

Rocky Mountain Pavement Cross-Section: Frost Depth & Class 6 Profile

Cross-sectional engineering layer breakdown engineered for Colorado Front Range and Rocky Mountain deep frost penetration zones.

HMA / Concrete Pavement Surface

Hot Mix Asphalt (SX/S) / PCCP

2.5" – 4.0" Surface Course

CDOT Class 6 Base (Top Lift)

Crushed Granite / Rhyolite Class 6

3.0" Compacted 95% AASHTO T180

CDOT Class 6 Base (Bottom Lift)

Crushed Granite / Rhyolite Class 6

3.0" Compacted 95% AASHTO T180

Class 1 Geotextile / Geogrid

Biaxial Polypropylene Grid + Fabric

6 oz Non-Woven + BX1100 Grid Subgrade Reinforcement

Compacted Native Subgrade

Mountain Subgrade / Sandy Gravel

8.0" Proof-Rolled 95% AASHTO T99

Layer Inspection 2.5" – 4.0"

HMA / Concrete Pavement Surface

Hot Mix Asphalt (SX/S) / PCCP

Compaction Standard: Surface Course

Engineering Function & Placement:

Pavement engineered for Rocky Mountain thermal cracking resistance.

Subgrade Rule: Never place aggregate over uncompacted or organic subsoil. Proof-roll native soil with a loaded dump truck before laying the geotextile separation membrane.

Structural Depth Schedules

Class 6 Base Depth Guide for Colorado Freeze-Thaw Zones & Bentonite Clays

Recommended layer thicknesses for mountain roads, residential driveways, and equipment pads over expansive Denver/Boulder bentonite clay.

Structural Depth & Lift Schedule by Use Case

Recommended compacted thickness and placement lift sequences

AASHTO / ICPI Guidelines

Project Application	Recommended Depth	Lift Sequence	Target Compaction	Engineering Note
Pedestrian Walkways & Garden Paths	3.0 – 4.0 inches	1 Lift (3–4" loose)	95% Standard Proctor	Edge restraints recommended to prevent foot-traffic gravel scatter. Geotextile optional on firm soil.
Paver Patio & Outdoor Living Slabs	4.0 – 6.0 inches	1–2 Lifts (3" compacted each)	98% Modified Proctor	Top with 1.0 inch of ASTM C33 concrete bedding sand. Screed flat without compacting sand prior to paver placement.
Light Residential Driveways (Cars & SUVs)	6.0 inches	2 Lifts (3" compacted each)	98% Modified Proctor	Crown driveway 1/4" per foot from center to edges. Install 4–6 oz non-woven geotextile over clay subgrades.
Heavy Vehicle, RV & Boat Storage Pads	8.0 – 10.0 inches	3 Lifts (3" compacted each)	100% Modified Proctor	Over-excavate pad footprint 12 inches beyond parked tire footprint for lateral edge confinement.
Shed, Pole Barn & Equipment Foundations	5.0 – 6.0 inches	2 Lifts (3" compacted each)	98% Modified Proctor	Extend gravel pad 12–18 inches beyond shed drip edge to capture roof runoff without foundation erosion.
Commercial Parking Lots & Highway Sub-Base	10.0 – 14.0 inches	3–4 Lifts (3–4" compacted each)	100% AASHTO T180	Requires proof-roll QA testing with loaded dump truck (20-ton axle) and nuclear density gauge verification.

Geotechnical Subgrade Rule

Subgrade Soil Adjustments & Geotextile Requirements

ASTM D1883 Subgrade Evaluation

CBR > 15%

Dense Gravel / Coarse Sand Subgrade

Base Depth Mod: Standard design depth (0" added)

Geotextile: Optional / Not Required

CBR 6% – 10%

Firm Silt / Sandy Loam Subgrade

Base Depth Mod: +1.0 to +2.0 inches extra base

Geotextile: Recommended (4 oz Fabric)

CBR 2% – 4%

Expansive Clay / Black Cotton Soil

Base Depth Mod: +2.0 to +4.0 inches extra base

Geotextile: Mandatory (6 oz Non-Woven Geotextile)

CBR < 2%

Wet Saturated / Organic Muck Subgrade

Base Depth Mod: +4.0" to +6.0" Base + 4" Surge Stone

Geotextile: Mandatory (Class 1 Geotextile + Biaxial Geogrid)

AASHTO T180 / CDOT CP 23

High-Altitude Compaction Mechanics: AASHTO T180 & Rapid Moisture Loss

Compaction simulator addressing rapid high-altitude evaporation and demonstrating how 6.5% OMC achieves 95% AASHTO T180 density.

1. Loose Lift Thickness (Inches) 4.0" Loose Lift

2.0" (Hand Tamper) 4.0" (Max Plate Compactor) 6.0" (Small Roller) 8.0" (Heavy 5-Ton Roller)

2. Moisture Content (% by Dry Weight) 6.5% OMC (Optimum)

2% (Too Dry / Friction) 6.5% (Optimum Peak) 12% (Over-Saturated / Pumping)

Compaction Result: Optimal 98% Proctor

At 6.5% moisture and 4.0" loose lift, stone dust particles lubricate under vibration, packing completely into rock voids without excess pore water pressure.

Field Compaction Parameters

Target Proctor Density: 95% Modified Proctor (AASHTO T180 / CDOT CP 23)

Compaction Shrinkage: +19% extra loose volume

Water Dosage per 100 sq ft: ~18 Gallons

Compactor Passes: 5 to 7 passes with heavy plate or vibratory roller

Recommended Machinery:

Reversible plate compactor (3,500+ lbs) or 3-ton smooth drum roller.

Mountain Logistics & Hauling

Mountain Dump Truck Hauling & Steep Incline Site Access Guide

Calculate mountain tandem and tri-axle truckloads, steep grade safety limits (< 10%), and clearance requirements for mountain roads.

Selected Vehicle Specification

Tri-Axle Commercial Dump Truck

Most economical rate per ton (Contractor standard)

Payload Weight 18–22 Tons

Payload Volume 11–13.5 yd³

Clear Gate Width 12 ft Min

Overhead Wire Clear 24 ft Raised

Site Access Rule: A loaded tri-axle weighs ~65,000 lbs (32.5 tons gross). Ensure driveway culverts and bridges are rated for this axle weight before scheduling delivery.

Delivery Site Checklist:

Check overhead tree branches and power/phone wires.

Mark septic tanks, leach fields, and sprinkler heads.

Never dump on a cross-slope >8% (dump bed tip-over risk).

Have driver tailgate-spread stone in a thin pass to save shovel time.

Budget & Labor Estimator

Colorado Front Range & Mountain Quarry Pricing & Installation Simulator

Estimate Colorado quarry rates ($26–$42/ton), Front Range freight fees, reversible plate rentals, and professional contractor costs.

1. Total Project Area (Square Feet) 1,000 sq ft

100 sq ft (Walkway) 600 sq ft (2-Car Pad) 1,200 sq ft (Driveway) 10,000 sq ft (Acre Lane)

2. Material Quarry Price ($ / Ton) $33 / Ton

$15/Ton (Pit Direct Caliche/RCA) $33/Ton (Avg Crusher Run) $75/Ton (Imported Granite)

Equipment & Hauling Options:

Delivery Fee (per truckload)

Equipment Rental

DIY vs Contractor Cost Comparison

DIY Total Cost (Materials + Rental + Delivery)

$1,444

~$1.44 per square foot

Contractor Turnkey Cost (Excavation + Install + Base)

$5,500

~$5.50 per square foot ($4.50 – $7.50 / sq ft range)

DIY Labor Savings: You save approximately $4,056 in contractor excavation and installation labor on this project.

Material Selection Matrix

CDOT Class 6 vs. Class 1 Sub-base & Crushed RAP Comparison

Direct comparison of CDOT Class 6 base, CDOT Class 1 coarse sub-base, Recycled RAP/RCA, and crushed river rock base.

Material Type	CBR Bearing Ratio	Compacted Density	Permeability	Avg Cost / Ton	Recommended Application
CDOT Class 6 Base This Page	85% – 100%	136 lb/ft³	Low	$28 – $38	Colorado Front Range driveways, roads, mountain parking pads
CDOT Class 1 Base (Sub-base)	60% – 75%	132 lb/ft³	Moderate	$22 – $30	Deep subgrade fill, heavy industrial base under Class 6
Recycled Asphalt / Concrete (RAP/RCA)	80% – 95%	124 lb/ft³	Moderate	$18 – $26	Farm roads, budget driveway base, commercial yards
Crushed River Rock Base	65% – 80%	130 lb/ft³	Moderate	$26 – $34	Landscaping paths, secondary residential drives

Quality Assurance & Failure Prevention

Rocky Mountain Field QA: Proof-Rolling, Snowmelt Drainage & Frost Heave Prevention

Testing methods to verify compaction and prevent post-winter snowmelt saturation, washouts, and frost heave damage.

4 Contractor Field Tests to Verify Density (Without Nuclear Gauge)

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Hand-Squeeze Moisture Test

Field Test

Target: Verify Optimum Moisture Content (OMC) before rolling

Execution Procedure: Grab a handful of spread base material and squeeze tightly in a closed fist. Open your hand.

Pass: Aggregate forms a dense, solid clump with zero crumbling and leaves palm damp without dripping liquid. Fail: Crumbles to dust (too dry) or oozes watery mud (too wet).

🚛

Proof-Roll Axle Deflection Test

Field Test

Target: Identify weak subgrade pockets and verify base rigidity

Execution Procedure: Drive a fully loaded tandem or tri-axle dump truck (minimum 10-ton axle weight) at walking speed over the completed base.

Pass: Surface deflection is under 3/8 inch (10mm) with zero visible wheel rutting. Fail: Tire sinks into rut or adjacent gravel waves/heaves upward.

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Heel-Strike Impact Test

Field Test

Target: Fast spot-check for localized loose compaction pockets

Execution Procedure: Drive the heel of a heavy work boot forcefully down into the compacted surface with full body weight.

Pass: Boot heel produces a sharp, ringing thud with zero visible indentation (< 1/8 inch). Fail: Heel punches into stone or dislodges loose gravel scatter.

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Steel Rebar Penetration Test

Field Test

Target: Check full-depth compaction down to the subgrade layer

Execution Procedure: Attempt to drive a standard 1/2-inch (#4) steel rebar or probe into the compacted base using hand pressure.

Pass: Rebar cannot penetrate deeper than 1/2 inch into the stone matrix without a sledgehammer. Fail: Rebar easily slides into base deeper than 2 inches.

Troubleshooting Protocols

Common Road Base Failure Modes & Remediation

Field Repair Checklist

Soft, Spongy Pumping Under Compactor

Critical Severity

Root Cause:

Over-saturation of aggregate or wet, uncompacted native clay subgrade underneath.

Contractor Solution & Fix:

Stop rolling immediately. Allow surface to dry in the sun for 24–48 hours. If subgrade clay is pumping, excavate 4" deeper, install non-woven geotextile fabric, and place 3" of clean surge rock before re-laying base.

Surface Washboarding, Ravelling & Loose Dust

Moderate Severity

Root Cause:

Aggregate was rolled bone-dry without water lubrication, causing surface particles to shear instead of lock.

Contractor Solution & Fix:

Heavily mist surface with garden hose or water truck spray bar to 6%–7% OMC. Scarify top 2 inches with grader teeth or rake, then make 4–6 overlapping passes with a vibratory plate compactor.

Deep Wheel Rutting in Tire Tracks

High Severity

Root Cause:

Lift thickness was spread too deep (> 4.5" loose), resulting in dense top crust over loose bottom aggregate.

Contractor Solution & Fix:

Excavate rutted section. Re-place material in thin loose lifts not exceeding 3.5 to 4.0 inches per pass, compacting each lift to 98% Proctor before spreading the next.

Edge Blowout & Shoulder Erosion

Moderate Severity

Root Cause:

Lack of lateral confinement or insufficient excavation width along outer driveway margins.

Contractor Solution & Fix:

Always excavate base trench 6 to 12 inches wider than the finished road width. Install compacted soil/crushed stone shoulder berms at a 3:1 slope, or install rigid commercial timber/concrete edge restraints.

Field Construction Standard

Step-by-Step Colorado Road Base Installation & Crown Profiling Timeline

Installation sequence: frost excavation, biaxial geogrid installation, high-altitude moisture conditioning, and 2.5% mountain crowning.

Stage 1 · Day 1 (Morning)

Excavation Below Frost Penetration Zone

QA Checkpoint

In Colorado and the Intermountain West, seasonal frost depth ranges from 24" to 48". For driveways and pads, excavate native soil to design depth. Remove all organic topsoil and identify swelling bentonite clays.

Pro Contractor Tips:

In Front Range expansive soils (Denver/Boulder), keep subgrade damp to prevent post-construction swelling.

Install perimeter French drain if on a mountain hillside.

Pass/Fail Verification Standard Proof-roll subgrade with heavy truck; no pumping observed.

Stage 2 · Day 1 (Midday)

Geotextile & Biaxial Geogrid Placement

QA Checkpoint

Roll out non-woven geotextile followed by biaxial geogrid over weak subgrade. The geogrid interlocks with Class 6 stone, distributing heavy snowplow and truck axle loads.

Pro Contractor Tips:

Overlap geogrid by 18 inches and cable-tie seams.

Keep tension on geogrid while placing stone.

Pass/Fail Verification Standard Geogrid flat and properly anchored.

Stage 3 · Day 1 (Afternoon)

Class 6 First Lift Spreading & OMC Mist

QA Checkpoint

Spread 4-inch loose lift of crushed granite Class 6 base. Mist with water to 6.5% OMC. Hand-squeeze stone: it should hold shape firmly without wet slumping.

Pro Contractor Tips:

High altitude sun evaporates surface moisture quickly; mist immediately before rolling.

Grade stone to uniform thickness with box blade.

Pass/Fail Verification Standard Moisture test confirmed at 5.5%–7.5%.

Stage 4 · Day 1 (Late Afternoon)

Vibratory Compaction to 95% AASHTO T180

QA Checkpoint

Vibrate with a heavy plate compactor or roller. Make 6 overlapping passes.

Pro Contractor Tips:

Vibrate corners and tight pad boundaries thoroughly.

Check for firm surface with no loose gravel scatter.

Pass/Fail Verification Standard Compaction verified: steel rod cannot be driven into base with hand force.

Stage 5 · Day 2

Second Lift, 2% Mountain Crown & Final Roll

QA Checkpoint

Spread final lift. Grade a prominent 2% to 3% crown to shed mountain snowmelt immediately into side borrow ditches. Static smooth-roll the surface.

Pro Contractor Tips:

Winter freeze-thaw cycles will destroy flat driveways; crown is mandatory.

Apply road base stabilizer or magnesium chloride if left unpaved.

Pass/Fail Verification Standard Crown verified: 1/4" per foot slope across full roadbed.

Geotechnical Engineering Guide

Geotechnical Engineering Manual: CDOT Class 6 Rocky Mountain Base

Technical manual on freeze-thaw durability, fractured face requirements (50%+ with 2+ faces), and stabilizing bentonite clay subgrades.

CDOT Standards Civil Standard Section 01

CDOT Section 304 Class 6: Rocky Mountain Freeze-Thaw Engineering

CDOT Section 304 classifies aggregate base into Classes 1 through 7 based on maximum particle size, fracture requirements, and plasticity limits. Class 6 is Colorado's premier 3/4-inch structural roadway base. To withstand high-altitude freeze-thaw stress, CDOT mandates strict aggregate toughness: Los Angeles Abrasion loss must be under 45% (AASHTO T96), Liquid Limit under 30 (AASHTO T89), and Plasticity Index under 6 (AASHTO T90). Furthermore, at least 50% of aggregate particles retained on the No. 4 sieve must exhibit two or more mechanically fractured faces, guaranteeing high internal friction.

Specialized Hubs