Bituminous Street 2 General Information
Street Inspector Project Orientation • Before Mix Comes to the Project: • Study the Project Special Provisions and Plans. • Familiarize yourself with: • Typical sections, different mixtures, widths, thicknesses, etc. • Review and discuss the Project with your Supervisor: • Check areas that might require repair work. • If new grade, check for soft spots. • Introduce yourself to the job superintendent: • Discuss plans and provisions. • Discuss any specific concerns or known problem areas. • Document or record any agreements made during discussions. • Set up a communication system between Plant and Street.
Communication • A successful project depends on good communication between the Contractor and the Inspector and their ability to work together. • The Inspector should immediately notify the Contractor of any deficiencies observed on the project. • The Contractor and the Inspector should always keep an open line of communication and a respectful working relationship.
Inspector ResponsibilitiesCan include • Sampling asphalt at the refinery, terminal or mix plant. • Sampling hot-mix at the plant and behind the paver. • Testing asphalt and hot-mix. • Investigating aggregate at source for compliance with specification requirements. • Monitoring proportioning and mixing procedures at the plant or project site.
Inspector Responsibilities (Cont.) • Determining asphalt content and aggregate gradation in the plant. • Determining and verifying mix properties for comparison with target properties of the mix design. • Determining that contractor’s equipment meets specification requirements.
Inspector Responsibilities (Cont.) • Inspecting the handling, lay down, and rolling operations at the jobsite. • Determining thickness of compacted mixture. • Determining density and percent compaction of the finished pavement. • Marking of coring locations • Keeping accurate records. (Diaries and other project documentation)
Areas of Concern for the Street Inspector • Mixture Design • Mixture Delivery • Mixture Placement • Verification Sampling • Mixture Compaction • See MnDOT’s Inspector’s Job Guide for Construction 2006 (pages 27-33)
Areas of Concern for the Street Inspector • Mixture Design Ram pressure 600 kPa 1.25o Marshall Gyratory
Mixture Design • Problems relating to mix design can affect the mix on the roadway: • Stability • Workability
Aggregates in Hot Mix • Key to Non-Rutting Pavements • Crushed Aggregate in both coarse and fine • Adequate Void Properties
Areas of Concern for the Street Inspector • Mixture Delivery
Mixture Delivery • Problems relating to mixture delivery that can affect the mix on the roadway: • Segregation • Cold Weather • Release Agents
Mix Deficiencies –Visual Indicators • Blue Smoke (Excess moisture) • Stiffness (Cool Temperatures) • Bleeding (Excess AC and/or moisture) • Lean, dull look (Too little AC content) • Segregation (Aggregates, Truck loading) • Contamination (Aggregates, Equipment)
Areas of Concern for the Street Inspector • Mixture Placement
Mixture Placement • Street Inspector Responsibilities: • Ensure each load of mix is ok. • Weigh tickets are correct. • Watch for deficiencies in the mat during placement and make sure corrections are made if necessary. • Pay attention to details such as lift thickness, proper crown, properly constructed and matched joints, and surface texture and uniformity. • Monitor mix temperature. • Keep a street diary. • See additional information in MnDOT’s Inspector’s Job Guide for Construction
Inspection of the Mat • Mat Problems: • Defects that occur in the asphalt mixture during or soon after the lay-down and compaction operations. • Two primary categories of mat problems • Equipment related • Mixture related • See Page 195 of US Army Corps of Engineers “Hot-Mix Asphalt Paving Handbook”.
Areas of Concern for the Street Inspector • Sampling • Quality Control (QC) Samples • Quality Assurance (QA) Samples • Verification Samples
Sampling Tonnage • Samples are to be taken at random locations. • Determine planned tonnage for mixture to be produced and divide by 1000. Round to next higher hole number. • EX: 3,500 (tons planned) /1000 = 3.5 = 4 tests required • Testing rate is accelerated at mixture start-up: • 1 test per 500 tons for first 2,000 tons • If the first random number of the day falls at less than 50 tons sample at 50 tons.
Sampling Location • Behind the paver sampling is still considered the most representative sample location. However,…. • Alternate sampling locations are allowed when approved by the Engineer. • Truck box sampling is identified as an alternate sampling location (procedure on web). • When an alternate sampling location is approved and used the daily verification sample must still be taken from behind the paver.
Quality Control (QC) Samples • Sample location determined by contractor (Use ‘random’ numbers) • Sample taken and tested by contractor • Split in half – test one half and mark and save other half for 7 working days • Sampling frequency – 1 per 500 ton for the first 2000 tons, then 1 per 1000 ton. (Materials Control Schedule-minimum)
Quality Assurance (QA) Samples • The half of the Quality Control sample that is saved for 7 working days • Also may be referred to as the ‘QC split’ sample • Sampling frequency – same as the QC sample • Tested only when situation dictates
Verification Samples • Sampled by Agency or witnessed by agency if obtained by others • Tested by Agency or Agency representative • One half of sample given to Contractor and must be tested by Contractor • Frequency – one per day per mix type (If more than one project – sample each project)
Verification Samples (Cont.) • Transport to testing lab ASAP • Agency’s results to be available within 2 working days from time of delivery • Record test results on the Test Summary Sheet • Compare results for allowable tolerances • If tolerances are not met take appropriate action
Areas of Concern for the Street Inspector • Mixture Compaction
Purpose of Compaction • Increases Stability • Reduces Air Voids • Increases Density • Smoothes the Surface
Compaction • Specification 2360 requires all pavements be compacted with Maximum Density Method unless otherwise specified in the contract or as noted in Specification Section 2360.6C. • Section 2360.6C discusses Ordinary Compaction.
Maximum Density • Density cores to be taken by the end of the next working day after placement and compaction. • Core holes are to be refilled and compacted with HMA within 24 hours of coring. • $100 penalty per working day per lot for core holes not filled. Page 38
Ordinary Compaction (2360.6C) • By Specification, used for: • Minimum planned paving thickness is less than 1.5 inches. • Thin lift leveling • Driveways • Areas which cannot be compacted with standard highway equipment. • Or can be specified in Special Provisions as density acceptance method.
Ordinary Compaction • No cores are cut. • Must use a control strip (growth curve) to establish rolling pattern. • Two test points are established and the density at each point is measured by a portable nuclear gauge or approved alternate after each roller pass, take and average 2 readings (180 degrees apart) at each location. Typically, rolling is suspended when testing shows a decline in density with each additional roller pass.
Coring Locations • Inspector determines and marks coring locations on a random basis. • The inspector can estimate the days/nights total paving quantity towards the end of the shift (use plant production rates, typical day info, contractor targets, etc.) and mark the cores under the protection of the paving traffic control. Page 37
LOT DETERMINATION • Daily tonnage (See Summary Sheet) • Table 2360.6-B2a of the Specifications • Use Random Numbers • Three cores per lot (Two different locations and one ‘companion core’ for the agency) Page 37
Random Numbers From Random Number Table 0.74 0.60 0.01 0.27 If 4 lots are each 2500 ft: Lot #1: 2500 x 0.74 = 1850 ft. Lot #2: 2500 x 0.60 = 1500 + 2500 = 4000 ft. Lot #3: 2500 x 0.01 = 25 + 5000 = 5025 ft. Lot #4: 2500 x 0.27 = 675 + 7500 = 8175 ft.
Core Testing(2360.6B3) • The Contractor shall schedule the approximate time of core testing during normal project work hours so the Inspector may observe and record the saturated surface dry (SSD) weight and the immersed weight of the cores. Page 38
Black - Gold Bituminous Cores
Will it Fit ! *#*” Transporting Cores
Easier & No Core Damage Transporting Cores
(SSD) Saturated Surface Dry This will effect Density Wrong Little Over Board (LOB) Correct (SSD)
Is the Moisture Gone ? Not Sure Weigh and record weight of cores Continue drying for another 15 minutes Reweigh & record any weight loss And continue drying for another 15 minutes Repeat until no more weight loss….
Oven Drying Cores (After) Completely Dry
Density Lots (2360.6B2) • A narrow shoulder (<6 ft. wide) that is paved in the same pass as a driving lane or separately will normally be compacted by the Ordinary compaction method. • Mixture compacted under Ordinary compaction is excluded from lot density requirements and that tonnage is also excluded from incentive/disincentive payment. Page 37
Joint Density Requirements(2360.6B2a) • If the random number falls on an unsupported (unconfined) joint cut the core with the outer edge of the core barrel 1 foot away from the edge of the top of the mat (center of 4” core barrel 1 foot 2 inches away from edge). • If the random number falls on a confined joint cut the core with the outer edge of the core barrel 6 inches + 0.5 inch away from the edge of the top of the mat (center of 4” core barrel 8 + 0.5 inch away from the edge of the top of the mat. Page 38
Reduced Density Provision (2360.6B5) • Minimum density is reduced by one percent for the first lift constructed on aggregate base, reclaimed or cold inplace recycled base course and first lift on a roadway with a 7 ton or less spring load restriction and first lift on PCC pavements. • Incentives are excluded when density is reduced. • The Contractor can request that reduced density be waived, except on concrete. The request and approval shall be made after the first days paving and before the third days paving begins. Page 39
DENSITY • What is the required density? • What does the requirement mean? • What values are needed? • Where do the numbers come from? • What is the calculation?