SPWA Fall Rural Roads Workshop Gravel Roads Material Analysis, - PowerPoint PPT Presentation

SPWA Fall Rural Roads Workshop Gravel Roads Material Analysis, Surfacing and Maintenance Manoj Jogi Saskatchewan Ministry of Highways & Infrastructure Saskatoon October 19, 2017

Basic Objectives of a Road 1. Support traffic loads 2. Protect roadbed from water infiltration 3. Minimize loss of surface material 4. Provide reasonable surface texture 5. Provide resistance to weathering

Typical gravel road section Credit: FHWA

Crown 1. Drainage from the road surface 2. Allow water to leave the road as a shallow, non erosive sheet ½ inch per foot or 4% crown recommended AASHTO recommends ½-1 inch foot crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

Crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

Maintaining Crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

Sections without crown Credit: FHWA

Parabolic crown • Less crown in the middle • No room for drainage Credit: FHWA

Parabolic crown • Blade wear at center • Modify usage to reduce wear Credit: FHWA

Placement for Surface Aggregates • Address all surface drainage issues before placement • Road instability issues must be addressed before placement • Flat ‘A’ crown profile, shape the subgrade Credit: Penn State University Center for Dirt and Gravel Roads Studies

Crown gauge Credit: FHWA Credit: Skorseth, 2015

Good vs Poor Construction 1 2 Credit: Maine 3 Dept. of environmental Protection

Aggregates / Soil Testing 1. Sieve Analysis Test • Categorize coarse-grained soils in terms of particle size distribution. 2. Atterberg Limit Test • Categorize fine-grained soils in terms of the material’s consistency (plasticity index). 3. Percent fracture • To determine percent fracture faces in coarse portion of the material Organic soils are generally not tested unless they pose a risk to the failure on a project.

Sieve Analysis Test Credit: Klimochko

Sieve Analysis Test Procedure for describing a coarse-grained soil in terms of particle size (gradation). Percent Passing Agg “A” Agg “B” Agg “C” Agg”D” 100% 92% 70% 40% 97% 82% 60% 0% 40% 52% 55% 8% 26% 48% 4% 12% 25% 1% 7% 7%

Importance of Sieve Analysis Sieve analysis test results on a coarse- grained soil indicates the following: • How clean or dirty the aggregate is. • How well the aggregate can compact • How will be the aggregate matrix in place • How suitable the aggregate is. • Confirm if aggregate is in ‘spec’?

Atterberg Limit Test

Atterberg Limit Test Used for identifying soil’s water content causing the material to pass from one condition state to another. • From liquid to plastic = Liquid Limit (w L ) • From plastic to plastic solid = Plastic Limit (w P ) Plastic Index (PI) = Liquid Limit (w L ) – Plastic Limit (w P )

Atterberg Limit Test Apparatus

Liquid Limit Test Apparatus Liquid Limit = soil moisture at which the bottom of the groove in soil sample closes approx. 12 mm after 25 rotations of crank.

Plastic Limit Test Apparatus In field roll the soil with water to thickness of a matchstick tip till it starts crumbling Plastic Limit = soil moisture at which the threads of soil sample start to break up when 3 mm in diameter.

Importance of Plastic Limit Value • Plastic Limit (w P ) value identifies the approx. optimum water content of a soil at which it should be compacted. • Soil goes into a plastic state – deforms without rebound

Importance of Plasticity Index Value • Plasticity Index (PI) value indicates the relative compressibility of a soil. • The higher a number, the more compressible the soil. • How well the soil can pack depends upon plasticity index • Good indication of binding characteristics

Determining Optimum Moisture Standard Proctor Test Optimum Moisture = 6.7 % 2260 Proctor Dry Density = 2234 kg/m3 2250 2240 Dry Density - kg/m3 2230 2 2220 3 2210 2200 2190 1 4 2180 2170 2160 6.7% 5 6 7 8 9 Percent Moisture Klimochko, 2008

Compaction vs. Optimum Moisture • Wet of optimum moisture - dried to optimum by blading or disking before compacting. • Dry of optimum moisture - it should be sprayed with water to get the soil to optimum before compacting.

Optimum Moisture vs. Soil Type Optimum moisture contents for various soil types are as follows: • Granular Base Course:  6 % • Sandy Glacial Till:  13% Low • Silty Glacial Till:  15 % 3 Plastic Clay • Clayey Glacial Till:  17% • Highly Plastic Clay:  30 %

Soil Compaction • Proper compaction equipment is essential. • Uniform water application is essential. • Work zones should be kept short ( ≈ 500 m) to help ensure uniform moisture application during compaction. • If sections are too long, compacting soil at optimum moisture content becomes more difficult to achieve.

Soil Compaction • Use sufficient amount of water. • Use sufficient number of passes. • Use proper equipment. Self propelled • Pneumatic or steel wheel • No steel rollers on steep grade

Soil Compaction • Check densities (Quality Control) • Check with Probe

Gradation Types • Open graded – has only a small percentage of aggregate particles in the small particle size range. This results in more air voids. • Gap-graded - contains coarse and fine-graded soil particles but no intermediate sizes. • Well/Dense graded – has a uniform distribution of all particles sizes.

Gradation Open graded Dense graded Gap graded

Surface gravel Stone + Sand + Fines (dust) Good gradation is a good blend of stones, sand and fines.

Properties for surface gravel Fracture Percent • Very important property • Crushing is needed for this • Better embedment than rounded aggregates • Resistance to movement under traffic better than rounded aggregates

Surface gravel • Ideally some amount of crushed stones (fractured faces) • More gravel than sand (excess sand = no stability) • Blending different sizes Excess No fines allows the pieces to lock fines together to form a strong tight surface Good gravel road can not be made with bad gravel Right amount of fines Credit: USDA Forest Service

MHI Traffic Gravel Specifications Sieve Percent by Weight Passing Designation Canadian Metric Sieve Series Type 101 102 103 104 105 106 108 109 75.0mm 100 50.0mm 55-85 100 40.0mm 63-92 31.5mm 100 100 22.4mm 63-92 63-92 100 100 100 18.0mm 63-92 63-92 63-92 100 5.0mm 0-40 0-40 0-40 40-70 0-40 0-60 40-70 45-80 2.0mm 0-25 0-25 0-25 20-45 0-25 0-45 20-45 25-60 400µm 0-20 0-20 0-30 Fractured 50.0 Minimum Face %

MHI Base Course Specifications Base Course Type 3505 - Jan 1996 Sieve Designation 31 33 35 Percent Passing (by weight) 50 mm 31.5 mm 100 25 mm 22.4 mm 18 mm 75-90 100 100 16 mm 12.5 mm 65-83 75-100 81-100 9 mm 5 mm 40-69 50-75 50-85 2 mm 26-47 32-52 32-65 900 µm 17-32 20-35 20-43 400 µm 12-22 15-25 15-30 160 µm 7-14 8-15 8-18 71 µm 6-11 6-11 7-12 Plastic Index 0-7 0-6 0-5 Fracture, Min (50/75 Blow) % Min 50 Lightweight pieces % Max 5

Properties for surface gravel AASHTO Soil aggregate surface course • Minimum 8% Sieve C D E passing 71µm Designation sieve and 75.0mm 100 100 100 50.0mm 100 100 100 • PI 4 – 9 25.0mm 100 100 100 • Maximum liquid 9.5mm 50-85 60-100 - 4.75mm 35-65 50-85 55-100 limit 35 2.0mm 25-50 40-70 40-100 400µm 15-30 25-45 20-50 75µm 5-15 5-20 6-20

Recycled asphalt (RAP) • Can be used but few issues • In hot weather it behaves as a weak pavement • Hard to maintain and can develop potholes • Good idea to blend 50/50 with virgin gravel • Good binding and workability with 50/50 blend Credit: Granite Construction Company

Properties for surface gravel • Top size 1 – 1.5 inch • Typical Ministry gravel is 22.5 mm (7/8 inch) top size • Desirable 8 to 15 % passing 71µm sieve (dust) – some amount of clay for binding • Plasticity, PI 4 - 9 range • Good abrasion resistance • Wet conditions -- Less PI and fines • Dry conditions -- Can have PI and fines on higher side of the range

Surface Gravel • Can be placed at in an 8” depth and compacted to 6”, • or in a 6” depth and compacted to 4½” • Higher top size (Coarse)for wet area • Lower top size (Finer) for dry area • Pneumatic rollers, Wobbly or 10 tonne steel roller can be used. • Pneumatic / rubber rollers work on most gravel surfaces and they do not crush the rock.

Aggregate Sampling Make sure the sample obtained is: • Representative (quartering) • Not segregated by sampling • Properly identified (label) Poor sampling makes test results misleading and worthless. Credit: Skorseth, 2015

Jar Test  Surface aggregate 8 – 15% fines (dust)  Base aggregate (0 - 7% fines)  More stones than sand desirable

Gradation for surface gravel Poor surface aggregate Credit: FHWA

Gradation for surface gravel • Good blend for surface gravel Coarse material Fine material Credit: Klimochko, 2008