TRANSPORTATION RESEARCH BOARD. Bases/Subbases for Concrete Pavements: State-of-the-Practice. Tuesday, April 15, :00-2:30 PM ET

Transcription

1 TRANSPORTATION RESEARCH BOARD Bases/Subbases for Concrete Pavements: State-of-the-Practice Tuesday, April 15, :00-2:30 PM ET

2 The Transportation Research Board has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to RCEP. A certificate of completion will be issued to participants that have registered and attended the entire session. As such, it does not include content that may be deemed or construed to be an approval or endorsement by RCEP.

3 Purpose Provide an overview of the design and construction of bases and subbases for concrete pavements and its impact on pavement performance. Learning Objectives At the end of this webinar, you will be able to: Discuss the fundamentals of bases and subbases for concrete pavements Understand the design, construction, and cost considerations of bases and subbases Understand European practices for base/subbase design and construction Understand the performance of various bases at experimental sections constructed at MnROAD

4 Bases and Subbases for Concrete Pavements Transportation Research Board Webinar 1:00 PM 2:30 PM Tuesday, April 17, 2018 Sam Tyson, P.E. Concrete Pavement Engineer FHWA Office of Asset Management, Pavements, and Construction

5 Bases and Subbases for Concrete Pavements TRB Committee/Webinar Sponsors AFD50 Design and Rehabilitation of Concrete Pavements AFH50 Concrete Pavement Construction and Rehabilitation

6 Bases and Subbases for Concrete Pavements Background: FHWA Publications Bases and Subbases for Concrete Pavements FHWA-HIF , August 2017 (revised) Precast Concrete Pavement Bedding Support Systems, FHWA-HIF , November references cited in those documents.

7 Bases and Subbases for Concrete Pavements David Hein, Applied Research Associates, Inc. Bernard Izevbekhai, Minnesota DOT Background Rigid pavement layer configurations Design considerations Materials Construction Base drainability Base stability Innovative initiatives Conclusions Webinar Organization Presentations 60 minutes Question & Answer Period 30 minutes

8 Samuel S. Tyson, P.E. Concrete Pavement Engineer Office of Asset Management, Pavements, and Construction Federal Highway Administration 1200 New Jersey Avenue, S.E. E Washington, DC Phone:

9 Bases and Subbases for Concrete Pavements 6

10 Outline Background Rigid pavement layer configurations Design considerations Materials Construction Cost Summary of MnROAD experience Conclusions 7

11 Background Need for bases and subbases well known for thousands of years Romans built over 50,000 miles of roads for troops and supplies Recognized the benefits of protecting the natural earth subgrade Roads such as the Apian Way constructed of multiple layers of stones and sloped to drain water away from the road 8

12 Apian Way 9

13 Early Base/Subbase Thickness Aggregate base/subbases were very thick until about the 1900s Increased use of bound materials Base/Subbase Thickness (in) Romans (200 AD) Typical Base/Subbase Thickness (Early European Designs) Telford (Early 1800s) Macadam (Early 1800s) Early 1900s 10

14 Use of Portland Cement Concrete Portland cement concrete originally used as a base Primary benefit was its ability to spread load over a larger area than granular or bituminous bound materials Less aggregate used Non-uniform and low strength, poor consolidation, curing and joint issues First used as a wearing surface in the late 1800s 11

15 PCC Construction, Early 1900s 12

16 Pavement Loading Loads applied to a PCC pavement spread over a large area of the base/subbase and subgrade This permits the use of thinner bases for rigid pavements than for flexible pavements 13

17 Rigid Pavement Layer Configuration Rigid pavement surface typically PCC Base supports construction traffic and to provide uniformity of support to the PCC surface 14

18 Rigid Pavement Layer Configuration Concrete Slab (JPCP, CRCP) 15 Base Course (agg., asphalt, cement) Subbase (unbound, stabilized) Compacted Subgrade Natural Subgrade Bedrock

19 Design Considerations 16

20 Design Considerations Pavement loading 3 to 5 times heavier than any highway or aircraft loading previously Westergaard Design Method chosen based on the Bureau of Public Roads and experience on test roads in California, Texas and Illinois 17

21 Design Considerations 18

22 Subgrade Support 19

23 Pumping Travel Approach slab Fault Leave slab Joint (or crack) Saturated support layer Movement of fines Wedge of injected fines 20

24 Frost Heave 21

25 Soil Expansion 22

26 Strength and Stiffness P Stress k = P Deflection 23

27 Support for PCC Base/subbase provides improved protection of the subgrade, a stronger support to the PCC The the design thickness of the PCC is not significantly affected by the k-value as the PCC modulus (stiffness) has a high relative stiffness: PCC ~ 5.000,000 psi Base/subbase ~ 30,000 psi Subgrade ~ 3,000 to 20,000 psi 24

28 Base and Subbase Types Unstabilized Dense graded aggregate base Open graded aggregate drainage layer Stabilized Cement-stabilized bases Cement-treated base Lean concrete base Cement treated open graded drainage layer 25

29 Base and Subbase Types Stabilized Asphalt-stabilized bases Asphalt dense graded base Asphalt-treated base Asphalt treated open graded drainage layer 26

30 Impact of Stiffness Stabilized bases contribute to achieving a high level of smoothness for concrete pavements A stiffer base layer does not guarantee performance and may cause other problems Optimal base strength reduces strains in the pavement and improves load transfer If the base is too stiff, it fails to conform to the changes in the shape of the slabs subjected to environmental loading (curling and warping) 27

31 Impact of Stiffness Stresses and deflections increase within the slabs and may cause cracks to develop Target compressive strength of CTB should be 300 to 800 psi and LCB, 750 and 1,200 psi VOID DAYTIME CURLING VOID VOID NIGHTTIME CURLING 28

32 Subbase Thickness Governed by the frost protection desired Depends on subgrade type, depth of frost penetration, and water near the subgrade 29

33 Base Thickness Depends on support required for the construction equipment and type and condition of the underlying subgrade Thicknesses in the range of 4 to 6 inches are most common 30

34 Unstabilized Bases Granular bases, are the most commonly used base types for concrete pavements Unstabilized bases exhibit excellent field performance at a lower cost Unstabilized bases include crushed stone, sandgravels, sands, and a variety of wastes and byproducts Materials should meet requirements of AASHTO M

35 Physical Requirements Less than 10 percent passing No. 200 sieve Plasticity Index < 6 and liquid limit < 25 Maximum particle size not exceeding one third of layer thickness Los Angeles abrasion resistance (AASHTO T 96) of 50 percent or less Permeability of approximately 150 ft/day and not exceeding 350 ft/day 32

36 Base/Subbase Gradations Sieve Designation Percent Passing Inch mm Grading A Grading B Grading C Grading D Grading E Grading F 2 in in ¾ in No No No No

37 Cement Treated Base Typically contain 2 to 5 percent cement Percent passing No. 200 sieve up to 35 percent Granular soils with plasticity index of < 10 (A-1, A-3, A-2-4, and A-2-5 soils) may be used 34

38 Lean Concrete Base Also known as econocrete, contains more cement than cement-treated base but less than conventional concrete May use lower quality aggregates 35

39 Open Graded Drainage Layers Small percentage passing the No. 200 sieve for untreated Asphalt cement contents between 1.6 and 1.8 percent Cement treated layers have water to cement ratio of 0.37 and a cement content of 185 to 220 lbs/yd 3 36

40 Open Graded Drainage Layers Should only be used when: Potential for moisture damage to pavement Medium to heavy truck traffic Proper design and construction Commitment to inspection and maintenance Outlets may include edge drains with outlet pipes or daylighted 37

41 Open Graded Drainage Layers Daylighted bases well suited for flat grades and shallow ditches Permeability of 500 to 800 ft/day (stable) May require a geosynthetic separator Bottom should be > 6 in above 10 year storm line 3 % cross slope May require maintenance 38

42 Open Graded Drainage Layers Reduced emphasis on treated OGDL layers Sacrifice high permeability for stability Potential issues with stability of anchored dowel baskets during hot weather Potential for aggregate stripping and collapse of the stabilized layer 39

43 Recycled Materials Recycled materials can be a good source of aggregate for base and subbase Recycled concrete is the most frequently used 40

44 Use of Recycled Materials Can be very angular and require more compaction effort than virgin aggregates Material should be checked for contaminants such as soil, wood, plaster, gypsum, plastic, rubber, etc. Some fines may stick to the processed coarse aggregates Wash the aggregates to reduce potential for leaching and clogging of the drainage system 41

45 Recycled Materials Other recycled materials include: Reclaimed asphalt pavement Mill tailings Waste rock materials 42

46 Construction (Unstablized) Homogeneous blending of material Maintain optimum moisture content for compaction Minimum, 95% standard proctor (AASHTO T 99) density (98% modified proctor (AASHTO T 180) for heavy traffic roads) Trimmed to ± ½ in. of the design profile grade Avoid any segregation of aggregates Wet prior to paving concrete 43

47 Construction (Cement Treated) Typically placed using an asphalt or concrete spreader and compacted with rollers Time to place, compact, and trim cement treated base is limited to about 4 hours Trim to ± ½ in. of the design profile grade Curing with a light fog spray of water or curing compound (0.15 to 0.25 gal/yd 2 ) Prevent bonding of the base to the PCC (thin layer of sand or two coats of wax-based curing compound) 44

48 Construction (Lean Concrete) Similar to conventional concrete Compressive strength of 750 and 1,200 psi Does not need joints Shrinkage cracks will develop but not reflect through the PCC slabs Should within ± ¼ in. of the design profile grade 45

49 Construction (Lean Concrete) Untextured surface to prevent bonding to the PCC slabs Bond breaker such as two coats of wax-based curing compound Do not want to be excessively stiff (if so, notch at PCC joints) Current German practice includes 0.2 in. thick polypropylene geotextile interlayer as a bond breaker 46

50 Construction (Asphalt Treated) Identical to the conventional asphalt Smooth surface May need to treat to reduce surface temperature during concrete placement Should be within ± ¼ in. of design profile grade 47

51 Cost Considerations Consider purpose of the base and locally available materials Evaluate using life-cycle cost analysis Inputs include the material cost and performance May be difficult to characterize 48

52 Relative Costs Base Type Relative Cost No base/subbase 84 Dense-graded unstabilized 100 Open-graded unstabilized 114 Lean concrete 122 Open-graded asphalt-treated 123 Open-graded cement-treated 124 Lean concrete 122 Dense graded asphalt

53 MnROAD Experience with Bases for Concrete Pavements (Sensor Lead Length DC to Philadelphia) 50

54 Reason for Existence Rigid pavements do not necessarily require a strong foundation More important that the foundation provides uniform support Needed to prevent pumping Better slab support uniformity than subgrade More stable working platform for construction equipment Control of differential frost heave

55 Some Initial MnROAD Test Cells 52

56 Typical MnDOT Gradations Class 6: >15 percent of material which shall be crushed Class 5: > 10 percent of material which shall be crushed Crushing: Weight of the material retained on a 3/4-inch sieve MnDOT Standard Spec for Construction 2018

57 Traditional Sub-surface Infrastructure Edge Drains MnDOT Class 5 Aggregate Base

58 Original MnROAD Test Cells PASB Aggregate Gradation Sieve size % Passing 1½ in (37.5 mm) in (25.4 mm) ¾ in (19 mm) /8 in (9.5 mm) No. 4 (4.75 mm) No. 8 (2.36 mm) 0-10 No. 30 (600 µm) 0-5 No. 200 (75 µm) 0-3 Class 5 Aggregate Base Sieve size % Passing 1½ in (37.5 mm) - 1 in (25.4 mm) 100 ¾ in (19 mm) /8 in (9.5 mm) No. 4 (4.75 mm) No. 10 (2.0 mm) No. 40 (400 µm) No. 200 (75 µm) 3-10

59 Innovative Items Geocomposite Joint Drain Class 5 Q Base

60 PSAB Drainability, Stability and Interfacial Bond

61 MnROAD Observation: Benefits of Good Drainage Drainable Vs Non Drainable Bases Importance of drainage / Performance PCC Roadways Class-5 Non-Drainable Base Class-5 Cell 12 PASB Cell 7

62 Drainage Related Degradation Non Draining Base Scouring PASB Cell 7

63 Open versus Dense Graded Base Pavement Age 18 years US inch JPCP 1.25 in Dia 15 ft panels on MnDOT Class 5. Coring water did not drain in 2 bad cores but drained well in region of 3 good cores US TH 52 4 lane Divided JRCP 1.0 inch Dowel and 27 ft long Panels. Joints were tight but cores were delaminated

64 Open versus Dense Graded Base USTH 59 2 Lane 8 inch thick JPCP 15 ft Panels OGAB. All Joints are in Perfect Condition Minimal Surface Distresses. USTH 14 2 Lane 8 in JRCP with 1.25 inch Dowels on Class 5. Widened Joints and Incipient Dowel Deterioration.

65 Ride Quality PASB vs Non-PASB IRI (M/KM) IRI_LWPCell 6 IRI_LWPCell 7 (PASB) 62

66 Sustainable Synthetic Subsurface Drainage Initiatives 7.5 inch recycled aggregate concrete test cell Non-skewed joints (15 ft intervals) In lieu of OGAB subbase Day-lighted geocomposite joint drainage + unsealed joints Non-woven geotextile interlayer 3 inch concrete overlay non-woven geotextile interlayer Non-skewed joints (15 ft intervals) In lieu of GJD/OGAB/PASB subbase

67 Base Stability Sudden appearance of widespread cracks in August 2012 on an OGAB Section Forensic Evaluation Cracking pattern atypical of temperature and locked joints Only MnROAD concrete cell built on OGAB One of the cells with RCC Shoulders Crack progression more predictable than 1st appearance Undermined Test Section Reliability Evaluation of Network OGAB Sections Remediation

68 Sinking Support Fundamentals Very little has been specifically done in relating this phenomenon to jointed plain concrete pavements with or without dowels Sinking support moment of a propped cantilever of displacement δδ is given by MM = 3EEEEEE LL 2

69 Sinking Support Concept For a simply supported beam with sinking support that the sinking support moment is M = 6EEEEEE LL 2 Introducing radius of relative stiffness R = EEE μμ 2 kk 0.25 From where induced moment for propped cantilever similar to a locked joint and a freely moving joint M = 3bbbb 1 μμ2 δδδδ 4 LL 2

70 OGAB Special August, 2012/

71 Forensics: Stepwise Approach 68

72 Ride Quality History and Joint IRI (m/km) LWP 306 RWP 406 LWP 406 RWP

73 DCP Before and After Stiffer Yet Less Stable!!

74 Gradation Before and After Gradations Before & After

75 MnROAD Undermining Experiment

76 OGAB Efficacy & Risk Early Distress No early Distress Odds Ratio Risk Ratio Network OGAB No OGAB MnROAD Void No Void Odds of OGAB showing early distress is 5 times as High OGAB Special increased risk of early failure by 100 (2.5-1) = 150% OR, RR >>1 OGAB early failure is not rare in the network OR, RR 1 Void induced distress may be rare in Test Cell 12

77 Innovation Geocomposite Joint Drain (GJD) 7 ½ inch recycled aggregate concrete GJD at Joints 4 ½ -7 ½ inch Class 1 (Non drainable) Existing silt subgrade

78 GJD Load Transfer Efficiency 75

79 Gravel/Sand Basis for Stability and Drainability

80 Innovative Bases: MnDOT Class 5 Q in. FRC 5 in. FRC 5 lbs/cy fibers 8 lbs/cy fibers 24 ft pave width 24 ft pave width 6 ft (W) x 6 ft (L) 6 ft (W) x 6 ft (L) joints joints 5 in. PCC no fibers 24 ft pave width 6 ft (W) x 6 ft (L) joints 5 in. FRC 11.7 lbs/cy fibers 24 ft pave width 6 ft (W) x 6 ft (L) joints 11 in. Class 5Q aggregate base 11 in. Class 5Q aggregate base 11 in. Class 5Q aggregate base 11 in. Class 5Q aggregate base 3.0 in. agg base (existing) 3.0 in. agg base (existing) 3.0 in. agg base (existing) 3.0 in. agg base (existing) Clay loam (A-6) subgrade (existing) Clay loam (A-6) subgrade (existing) Clay loam (A-6) subgrade (existing) Clay loam (A-6) subgrade (existing)

81 Conclusions Rigid pavements do not necessarily require a strong foundation The key to achieving the desired performance is uniform support to the concrete slabs Primary purpose of base/subbase layers is to prevent pumping Base/subbase provides a stable working platform for construction equipment 78

82 Conclusions Scouring and bottom joint deterioration are indicative of inadequate subsurface drainage Three enemies at work: water, water and water Traditional bases were not very drainable PASB, Class 5 Q optimizes drainability, stability and durability GJD indicate good initial performance (needs cost-benefit and sustainability evaluation) 79

83 Conclusions Sinking support and loss of support are not the same as settlement. LAR and DCP: insufficient OGAB aggregate stability prediction. Hydraulic fracture is recommended OGAB special section efficacy analysis: Risk ratio >> 1, Odds ratio >> 1 for early failure 80

84 Conclusions Best performance obtained by: Selecting a base/subbase to prevent pumping Using a material that will remain stable over time Material that does not exhibit excessive deflections under traffic loading Treat the surface to prevent bonding and reduce friction between the PCC and base Using specifications that will ensure uniform support Construct with grade controls that allow for consistent thickness and smoothness of concrete 81

85 Questions 82

86 Today s Participants Sam Tyson, Federal Highway Administration, Sam.Tyson@dot.gov David Hein, Applied Research Associates, Inc., dhein@ara.com Bernard Izevbekhai, Minnesota Department of Transportation, bernard.izevbekhai@state.mn.us

87 Panelists Presentations After the webinar, you will receive a follow-up containing a link to the recording

88 Get Involved with TRB Getting involved is free! Join a Standing Committee ( Search for AFD50 (Standing Committee on Design and Rehabilitation of Concrete Pavements) and AFH50 (Standing Committee on Concrete Pavement Construction and Rehabilitation) Become a Friend of a Committee ( Networking opportunities May provide a path to become a Standing Committee member For more information: Create your account Update your profile