Best Practices for Concrete Road Pavement Construction

Transcription

1 Best Practices for Concrete Road Pavement Construction Mark B. Snyder, Ph.D., P.E. President, International Society for Concrete Pavements Vice-President, ACPA Pennsylvania Chapter

2 Concrete Paving

3 Critical Factors A good concrete mixture A good grade & trackline for paving Stringline management Continuous supply of concrete to paver Consistent concrete workability Well maintained paving equipment Proper operation of paving equipment Controlled density of concrete just the right vibration & finishing A skilled and dedicated crew 3

4 Key Properties of Concrete Workability Durability Strength (Workability and durability are as important as strength)

5 Aggregate Gradation CONTROLS workability!! Well-graded combined aggregate gradation will: Reduce water demand Lower drying shrinkage Increase workability Improve strength

6

7 Aggregate Bins 16 to 32 mm 8 to 16 mm 4 to 8 mm 0 to 4 mm 7

8 Cement The glue that holds concrete together More cement can mean more strength, but: Need more air entraining admixture for desired air Need more water, resulting in more drying shrinkage Increased risk of segregation with more paste More bleed water, increasing permeability Earlier sawing required Stiffer mixture Less fatigue capacity

9 Cementitious Materials Content Use no more cementitious material than is necessary to meet strength and workability Typical minimum is about 300 kg/m 3 for slipform SCMs may retard strength gain

10 Water-Cementitious Mat l Ratio Lower w/cm = higher strength, durability Slipform paving: 0.45 max (0.40 typ) Fixed-form paving/hand pours: 0.50 max (0.45 typ) For w/cm below about 0.40, autogenous shrinkage may be a concern.

11 Dowel Bar Options: many products are available

12 Dowels Bars Corrosion resistant dowels a must Stainless steel or zinc clad (~$12 to $20) FRP but effectiveness not proven yet Epoxy coated (low cost option) (~$4 to $5) 37 mm diameter minimum for t > 300 mm Can reduce no. of dowels middle 2 to 3 dowels not necessary May use 9 (5&4) or 10 (5&5) to reduce cost Length = 450 mm 12

13 FRP Dowels

14 Dowel Type Modifying FRP Dowel LT System Design for Structural Equivalence Diameter (mm) with Metallic Dowels Dowel Modulus, E (GPa) Applied Shear Force (kn) Metallic (300mm spacing) FRP (300mm spacing) FRP (300mm spacing) FRP (200mm spacing) Dowel Deflection at Joint Face (mm) Bearing Stress (MPa) There is additional deflection across the joint

15 Quality Starts from the Ground Up Roadbed (subgrade and subbase) design and construction are key to: Long-term performance Smoothness (initial and long-term)

16 What is Good Support? Uniformity in material and grading (most important!) Resistant to erosion Engineered to control subgrade soil expansion/frost heave

17 Place Base to Specified Tolerances Enhance pavement performance Minimize loss of concrete Minimize/eliminate thickness penalties Enhance smoothness

18 Stabilized Bases Stabilized bases SC, CTB, ATB, PATB Strength issue for SC/CTB/LCB Specify min/max values (7 DAY 5.0/8.0 MPa psi common) Base stiffness affects pavement performance Potential for random cracking high for very stiff bases

19 Bonded (match joints) Interface with Cement-Stabilized Base Unbonded: asphalt emulsion, curing compound (double-coat), 25 50mm asphalt concrete (Austria), 5mm thick geotextile (Germany), Geo-fabric, plastic sheet Fabric nailed inplace Geo-fabric bond-breaker over CTB at Denver Airport 5 mm geotextile over CTB (German practice)

20 Track Line & String Line Extend base 1 m beyond outside edge of pavement - keep it clean String line management very important to final smoothness of pavement STRINGLINE AIDS Use rigid stakes Use quality line Monitor & maintain line Paver sinkage!! 20

21 Stringlines Stringlines control the steering of the paver Stringlines control the elevation and slab thickness Stringline Elevation Sensing Wand Alignment Sensing Wand

22 Set Stringline Can be wire, cable, woven nylon, polyethylene rope, or another similar material Clean and tight splices Rigid stakes watch for staking errors Maximum stake spacing of 25 ft No perceptible sagging Adjust stake spacing to fit conditions See Staking Interval Calculator at apps.acpa.org for recommendations on curves

23 Stringline Considerations (cont.) Continually check tension Place winches at 300m Stringlines on both sides of paving? Some situations require cantilever or trusses for sensors to reach stringline

24 Stringless Paving: Example Leica s Direct Connect 3D Control System Software communicates directly with networked Microprocessor Control System

25 Concrete Placement Deposit concrete as close to paver as possible Avoid stop & go operation Maintain uniform speed & head No front end loaders or backhoes to distribute concrete 25

26 Concrete Placement Issues Do not add water to concrete in front of paver Reduced strength Reduced durability Proper vibration effort Control consolidation across paving width Provide just enough fines at surface for a tight finish

27 Consolidation The internal vibrators on the paver fluidize the concrete for extrusion Adequate consolidation Required around dowels and tie bars Throughout the slab

28 Poor Consolidation Lower in-place strength, honeycombing

29 Over-Consolidation Over vibration can cause settlement, loss of air void system, less durable concrete IMCP Manual

30 Vibrator Setup

31 Effect of Paver Speed on Consolidation

32 Vibrator Sensor Monitoring

33 Pre-placed bars Dowel Bars and Tiebars Staked adequately Cut/don t cut the tie wires Careful marking of location Inserted bars IMCP Manual

34 Staking Dowel Baskets

35 Baskets Dowel Bar Placement Issues Basket rigidity (wires/design) Basket stability cut shipping wires (?), anchor type/length, base stability Dowel debonding agent Basket length Mechanical implantation Consolidation around dowel bars Dowel debonding agent Dowel alignment

36 Dowel Bar Misalignment Categories

37 Dowel Misalignment Examples 37

38 Dowel Bar Alignment Testing German MIT SCAN Device Ultrasonic (MIRA) and GPR (Hilti) devices are also available. 38

39 Dowel Bar Misalignment Limits Skew (vertical or horizontal): Accept: < 15 mm per 450 mm Action: > 15 mm per 450 mm Horizontal Translation: Accept: < 50mm Action: >100mm or less than 75mm to edge Long. Translation : Accept: < 50mm Action: > 125mm Vertical Translation (Depth): Accept: <25mm and > 5mm clearance to saw cut Action: <65mm concrete cover (top or bottom) or <5mm clearance to saw cut

40 Dowel Bar Misalignment Single Dowel Total Misalignment (mm) Joint Score Weighting Factor, W < 15 mm mm mm mm 5 >38 mm 10

41 Dowel Bar Misalignment Joint Score Joint Score Risk of Joint Lockup < 5 Very Low 5 10 Low Moderate > 15 High Joint Score Limits: Accept: < 10 Action: All joints in MALL have JS >10 MALL= Maximum Acceptable Locked Length = 20m, including no more than 3 locked joints

42 Finishing Operations Minimize hand finishing do not over-finish Surface does not have to be super-smooth Longer straight edges produce smoother surface Do not add water to facilitate finishing if used, it should be fogged, not sprayed Finishers have final impact on smoothness and surface durability High Spalling Potential 42

43 Use 5-m float for smoothness Need for finishing is minimized by Selecting a workable mix 43 Properly operating the paving equipment

44 Concrete Texturing (affects safety & noise level) Common Methods Transverse tine (3 by 3 mm, random) out of favor!! Longitudinal tine (3 by 3 by 20 mm) better/preferred? Turf/broom drag Diamond grinding (for new??) 44

45 Exposed Aggregate Surface Step 1 - Curing compound + retarder - water-repellent coefficient > 90 % (first 24 h) Step 2 - Curing compound (applied after brushing) - water-repellent coefficient > 85 % 45

46 Brushing Machine Exposed aggregate surface 8 or 11 mm max size 46

47 D.Grnd (CO-202) Trf.Drag (Hvy) (CO-202) Brlp.Drag (Std) (IA-101-2) Brlp.Drag (Hvy) (IA-101-2) 3/4" L.Tine 1/16"D+Turf (IA-101-2) Rndm. L.Tine 1/8"D+Brlp (CO-202) Crpt.Drag-SnglSaw (KS-205) Crpt.Drag-NrmlSaw (KS-205) Trf.Drag (Hvy) (IA-101-2) 3/4" L.Tine 1/16"D+Turf (IA-101-1) D.Grnd 110 Deep-NrmlSaw (KS-205) Trf.Drag (Hvy) (IA-101-4) D.Grnd (IA-101-4) 3/4" L.Tine 1/16"D+Turf (IA-101-4) D.Grnd 110 Deep-SnglSaw (KS-205) 3/4" L.Tine 1/8"D+Turf (IA-101-2) D.Grnd 120 Deep-SnglSaw (KS-205) D.Grnd 120 Deep-NrmlSaw (KS-205) 3/4" L.Tine 1/8"D+Turf (IA-101-1) 1/2" T.Tine 1/16"D+Brlp (IA-101-2) Brm.Drag (MN-320) Brlp.Drag (Std) (IA-101-1) Trf.Drag (Std) (IA-101-4) 3/4" L.Tine 1/8"D+Turf (IA-101-4) D.Grnd 130 Deep-SnglSaw (KS-205) Brlp.Drag (Hvy) (IA-101-4) 1/2" T.Tine (GA-203) L.Groove (CO-202) Brlp.Drag (Std) (IA-101-4) 3/4" L.Tine 1/16"D+Brlp (IA-101-2) D.Grnd 130 Shlw-SnglSaw (KS-205) 1/2" T.Tine 1/16"D+Brlp (IA-101-1) 3/4" L.Tine 1/8"D+Brlp (Lng) (IA-101-2) Trf.Drag (MN-320) 3/4" L.Tine (ND-206) 3/4" L.Tine 1/16"D+Brlp (IA-101-1) D.Grnd 130 Deep-NrmlSaw (KS-205) D.Grnd (GA-203) 3/4" L.Tine 1/8"D+Brlp (CO-202) Trf.Drag (Std) (IA-101-2) 3/4" L.Tine 1/8"D+Brlp (Lng) (IA-101-4) 3/4" L.Tine 1/16"D+Brlp (IA-101-4) D.Grnd 130 Shlw-NrmlSaw (KS-205) Trf.Drag-SnglSaw (KS-205) 1/2" T.Tine 1/16"D+Brlp (IA-101-4) 1" L.Tine 1/8"D+Brlp (IA-101-4) 1/2" T.Tine 1/8"D+Brlp (IA-101-2) Trf.Drag (ND-323) 3/4" L.Tine 1/8"D+Brlp (Shrt) (IA-101-2) 3/4" L.Tine 1/8"D+Brlp (Lng) (IA-101-1) D.Grnd (IA-101-2) 3/4" L.Tine 1/8"D+Turf (CO-202) 1/2" T.Tine (GA-203) 3/4" L.Tine 1/8"D+Brlp (Shrt) (IA-101-4) Trf.Drag (Hvy) (IA-101-3) Brlp.Drag (Std) (IA-101-3) 3/4" L.Tine 1/8"D+Brlp (Shrt) (IA-101-1) Brlp.Drag (Hvy) (IA-101-3) 1/2" T.Tine 1/8"D+Brlp (IA-101-4) 3/4" L.Tine 1/8"D (Sine)+Brlp (CO-202) 3/4" L.Tine 1/16"D+Turf (IA-101-3) D.Grnd (IA-101-3) Trf.Drag (Std) (IA-204) 1/2" T.Tine (GA-203) D.Grnd (CO-305) 1/2" L.Tine 1/8"D+Brlp (IA-101-2) 3/4" L.Tine 1/4"D+Brlp (IA-101-2) 3/4" L.Tine 1/16"D+Turf (IA-204) Trf.Drag (Std) (IA-101-3) 3/4" L.Tine 1/8"D+Brlp (Lng) (IA-101-3) 1/2" T.Tine 1/16"D+Brlp (IA-101-3) 3/4" L.Tine 1/8"D+Turf (IA-101-3) 1" L.Tine 1/8"D+Brlp (IA-101-3) 1/2" L.Tine 1/8"D+Brlp (IA-101-1) 3/4" L.Tine 1/4"D+Brlp (IA-101-4) Trf.Drag (MN-319) 1" L.Tine (CO-305) 1/2" L.Tine 1/8"D+Brlp (IA-101-4) 3/4" L.Tine 1/8"D+Brlp (Shrt) (IA-101-3) 3/4" L.Tine 1/8"D+Turf (IA-204) 3/4" T.Groove (Bridge) (GA-203) D.Grnd (MN-319) 3/4" L.Tine-SnglSaw (KS-205) 3/4" L.Tine 1/16"D+Brlp (IA-101-3) 1/2" T.Tine (ND-206) 3/4" L.Tine 1/8"D+NoPreTex (IA-101-2) 3" T.Tine (ND-206) Rndm. T.Tine (1"/2"/3"/4") (ND-206) 1/2" T.Tine 1/8"D+Brlp (IA-101-3) 1" T.Tine (GA-203) 3/4" L.Tine 1/8"D+NoPreTex (IA-101-4) 4" T.Tine (ND-206) 1/2" T.Tine (GA-307) 3/4" L.Tine 1/8"D+NoPreTex (IA-101-1) 1/2" T.Tine (GA-307) Exp.Agg A (QC-340) 1" T.Tine (Skew) (ND-206) 1" T.Tine 1/8"D+Brlp (IA-101-2) 1" T.Tine 1/8"D+Brlp (IA-101-1) 3/4" L.Tine 1/4"D+Brlp (IA-101-3) 3/4" L.Tine-NrmlSaw (KS-205) 3/4" L.Groove (VA-336) 2/3" T.Tine 1/16"D+Turf (IA-204) 1/2" L.Tine 1/8"D+Brlp (IA-101-3) 3/4" T.Tine (IA-310) 3/4" T.Tine (ND-206) Rndm. T.Tine (Mrqtte.) (IA-310) Exp.Agg B (QC-340) 1/2" T.Tine (GA-307) 2" T.Tine (ND-206) 3/4" L.Tine 1/8"D+NoPreTex (IA-101-3) Rndm. T.Tine (5/8" Avg.) (NC-322) ShotPeened (QC-340) 1" T.Tine 1/8"D+Brlp (IA-101-4) 3/4" T.Tine (OH-325) 3/4" T.Tine (OH-325) 3/4" T.Groove (GA-307) 3/4" T.Tine (OH-325) ColdMilled (IA-204) Rndm. T.Tine (3/4"Avg.) (IA-310) 3/4" T.Tine (OH-325) 3/4" T.Tine (OH-325) 2/3" T.Tine 1/8"D+Turf (IA-204) 3/4" T.Groove (GA-307) 3/4" T.Tine 1/8"D+Turf (IA-204) 1" T.Tine (ND-206) 1" T.Tine 1/8"D+Brlp (IA-101-3) Rndm T.Tine 1/8"D+Brlp (WisDOT) (IA-101-2) 3/4" T.Groove (IA-204) T.Tine+Exp.Agg (QC-340) Rndm. T.Tine 1/16"D+Turf (3/4" Avg.) (IA-204) 3/4" T.Tine (IA-309) 3/4" T.Tine (IA-309) Rndm. T.Tine 1/8"D+Turf (3/4" Avg.) (IA-204) Rndm T.Tine 1/8"D+Brlp (WisDOT) (IA-101-1) 3/4" T.Tine (IA-309) Rndm T.Tine 1/8"D+Brlp (WisDOT) (IA-101-4) 1" T.Tine (GA-307) Rndm. T.Tine (ND-323) Rndm T.Tine 1/8"D+Brlp (WisDOT) (IA-101-3) Rndm. T.Tine (MN-319) Average OBSI Level and Variability (44-ft Avg, PWL=95%) (dba) Noise vs. Surface Texture Diamond Grinding Drag Longitudinal Tining Transverse Tining Longitudinal Grooving Transverse Grooving Other

48 Average OBSI Level (dba) Noise vs. Friction Diamond Grinding Drag Longitudinal Tining Transverse Tining Other Average DFT/CTM-Estimated SN40S (ASTM E 274 Skid Trailer, Bald Tire)

49 Concrete Curing Need to maintain adequate moisture & temperature regimes Inadequate curing leads to Excessive moisture loss at surface = plastic shrinkage cracking Weak surface => durability problems Excessive slab warping (built-in warp) Must assure timely curing behind paver

50 Ponding/continuous sprinkling Burlap/cotton mats Plastic sheeting Curing compounds Curing Methods 50

51 Curing Compounds Coating placed on concrete surface to prevent moisture loss Resin or wax based Clear or white-pigmented Advantages: Easy to use - not labor intensive Economical ASTM C 309 & AASHTO M148 (Type 2, Class B) All curing compounds are not created equal even if they meet specs Water retention is a key to successful curing

52 Curing Compound Application Time of application Apply as soon as surface sheen has disappeared Use automated equipment for uniform coverage Cover all exposed surfaces (incl. sides) Re-apply at joints after sawcutting Typical application rate: 4 to 5 m 2 /l ( ft 2 /gal) Curing time: Typically 72 to 96 hours Check nozzles regularly for uniform spray (avoid clogging)

53 53

54 Joint Sawing Why saw? Saw timing Sawing window Maturity testing HIPERPAV Early-entry saws Joint width Mixture effects

55 Joint Sawing

56 Factors that Shorten Window Sudden temperature drop High wind, low humidity High friction base Bonding between base & slab Porous base (PATB) Retarded set (delayed and shortened) Delay in curing application

57 Crack Prediction with HIPERPAV (free download)

58 Joint Sawing QA/QC Issues Check planned vs. actual locations Check sawcut depth Check sawcut carried through vertical edge 58

59 Joint Sealing Minimize infiltration of water and incompressibles Types Hot pour Silicone Compressive seals Reservoir preparation Clean Shape Current debate: to seal or not to seal?

60 Joint Sealing Approaches Conventional Approach Initial sawcut 3 mm Widening cut for sealant reservoir shape factor Single cut Approach 4 to 5 mm Narrow unsealed Narrow filled Narrow sealed 60

61 Joint Layout Critical to crack control Typically decided by engineer No knowledge of contractor, equipment, processes Hard to precisely place things like utilities Field adjustments can and should be made

62 If Joints Aren t Properly Adjusted

63 Field Adjustments are Necessary Adjust joints that are within 5 ft of a utility! Contractor must also consider impact of relocating joints!!!

64 Joint Layout Design EB237 Concrete Pavement Field Reference: Pre-Paving IS006, Intersection Joint Layout IS061 Design and Construction of Joints for Concrete Streets R&T Update 6.03 Concrete Roundabouts TB010 Design and Construction of Joints for Concrete Highways TB017 Airfield Joints, Jointing Arrangements and Steel TB019 Concrete Intersections: A Guide for Design and Construction

65 Summary: Cost of Poor Quality For highway agencies Traffic congestion & accidents Reduced service life Higher life cycle costs For contractor Corrective measures Partial payments Cost of claims (litigation) Liquidated damages

66 Acknowledgements American Association of State Highway and Transportation Officials (AASHTO) American Concrete Pavement Association National Concrete Pavement Technology Center (Iowa State University) Shiraz Tayabji, Fugro Consultants, Inc. U.S. Federal Highway Administration Pavement Technology Program U.S. National Highway Institute