Base Design Considerations for Jointed Concrete. Dan G. Zollinger, Ph.D., P.E. Texas A&M University, College Station, TX, USA

Transcription

1 Base Design Considerations for Jointed Concrete Dan G. Zollinger, Ph.D., P.E. Texas A&M University, College Station, TX, USA

2 Discussion What is Erosion Effects on Performance Erosion Testing Use of Erosion In Design Field Assessment of Erosion

3 Jointed Plain Concrete Pavements (JPCP): Design Features Surface smoothness Thickness Design Load Transfer Surface Texture & Durability Concrete Mix Design Subgrade Subbase or base

4 JPC Pavement - Loaded Slab Behavior s θ h z 0 - w 0 total v z Reinforcing steel v i

5 Field Testing SS Ba sin Area j1 j 2* 0

6 Faulting Distress

7 The Three Main Elements of Erosion Rate of Erosion of the base/subbase Existence of Moisture under the slab Traffic Erosion

8 The Role of Moisture US 81/287 Cores Debonded AC base Debonded AC base Debonded AC base Debonded AC subbase AC base bottom AC base bottom AC base bottom AC base bottom AC subbase top Section 1 Section 2 Section 3

9 Jointing and Sealing Practices Making an initial saw cut to control cracking Making a second saw cut to create a reservoir for joint sealant Cleaning and preparing the reservoir faces Placing a backer rod in the reservoir, to keep the sealant from adhering to the bottom of the reservoir and to create a curved bottom surface for the sealant. Placing sealant material in the reservoir

10 LTPP Faulting Data Sections State and Section ID AL 1_3028 CA 6_3013 CA 6_3017 CA 6_3019 CA 6_3021 CA 6_3024 CA 6_7456 IN 18_3002 NE 31_3018 OK 40_3018 SD 46_6600 WY 56_3027 AL 1_4007 AL 1_4084 AR 5_3073 AR 5_3074 AR 5_4021 LA 22_4001 NE 31_4019 Pavement Type JPCP JPCP JPCP JPCP JPCP JPCP JPCP JPCP JPCP JPCP JPCP JPCP JRCP JRCP JRCP JRCP JRCP JRCP JRCP

11 Faulting Depth, mm Average Wet-days per Year, day Estimated Average Faulting Depth Estimated Average Faulting Depth Average Wet days per Year AL 1_3028 CA 6_3013 CA 6_3017 CA 6_3019 CA 6_3021 CA 6_3024 CA 6_7456 IN 18_3002 NE 31_3018 OK 40_3018 SD 46_6600 WY 56_3027 AL 1_4007 AL 1_4084 AR 5_3073 AR 5_3074 AR 5_4021 LA 22_4001 NE 31_4019 Wet days in LTPP database is defined as the number of days for which precipitation was greater than 0.25 mm for year 0

12 Faulting Depth, mm Faulting Depth, mm Faulting and Number of Wet days 25 Estimated Average Faulting Depth 25 Estimated Average Faulting Depth 20 y = 0.097x R 2 = y = 0.192x R 2 = Average Annual Wet Days, day Average Annual Wet Days, day JPCP Sections JRCP Sections Average faulting depth is estimated at the 100 million ESAL repetitions based on LTPP faulting data

13 Sustainability of Pavement Pavement condition Good Extended good condition by sustainable design Extended good condition by preservative maintenance Maintenance level Preservative Moderate Poor Critical point to Sustainability Restoration Remove and replace Pavement life (Time) Reduce slab deflection by improving Slab thickness Joint/crack load transfer Subbase and subgrade support Sustainable Pavement Design

14 Erosion Mechanisms: What s Needed? Do our Current Design Procedures or Test Methods Account for These Mechanisms? Water Florida vs Arizona Climate? Seal or no seal? Interstate Hwy vs retail parking? Pathway Erosion Load Erodible Medium Clay vs sand vs stabilized clay vs aggregate base?

15 PCA Method

16 AASHTO MEPDG

17 Hamburg wheel-tracking device (HWTD)

18 Erosion Results CTS HWTD erosion Test on cement treated subgrade

19 Average Erosion Depth (mm) Erosion Results CTB % CTB 4% CTB 6% CTB 8% CTB Number of Load HWTD erosion Test on cement treated base

20 Erosion Test and Shear Stress Model Sample Diameter = 6 inch Deflection Measuring Points 1.85 inch Concrete Subbase 158 lb Subgrade (Neoprene Pad) inch 1 inch 3/8 inch (1 ) i p b u V s 2 1 L E 1 i sb X 21 c base hb i E c e p h E x h i na 2 1 %E 1 P(σ 0) fe n fc f F

21 Consideration of Erosion In Design s θ total z 0 - w 0 v z v i h Reinforcing steel Damages the Slab/Subbase Interface Lowers Friction Reduces Composite Slab Thickness Reduces k-value Increases Stress Bending Stress Shear: Loss of LT

22 Partially Bonded System he u h 1 x xh 2 e p eb x e 3 2 Eh 4 c e p e 2 e-p e e e 12 1 k Ec 2 e e e e e 2 he e-p (x = degree of bond; = coeff. of friction) Notes on h e-p: e-u 121 k 1) ; h h ; derived from basin area 3) A m sp 2)s a b c ; s P h ; ; ; load induced pressure eu c eu f eu 2 f v v h eu 12 h y h 2 e u p 2 eu 4) and e p e e 1 he p he p h e-u y p e-p e h e-p Transformed Section

23 ln(-ln(x)) Equivalent Interlayer Friction x Where sp e 2 σ e = ; (for FWD plate loading) 2 s e a b e c e he P = Applied FWD load (F) a, b, c = , , and (for FWD plate loading) h c = Concrete slab thickness (L) = Load induced vertical pressure (FL -2 ) ( 0.7 psi) σ v h h A e p h eu eb eu h eu 2h e he hc v 12 eu p e 1 B ln(m u) Where A = e B 2 B = 0.039y y = Ln(μ)

24 Erosion Testing f i Di %E e f 0 w E x f x 21 1 e w E 1 x f x 21 e Where %E = Percent of erosion = Fault i Fault 0 f i f 0 = Level of faulting per load cycle i = Ultimate faulting D i = Damage ratio per load cycle i (D i = N i /N f ) α ρ N i = Erosion initiation shift factor = Erosion rate factor = Calibration factor = Effective ESAL per load cycle i

25 Faulting (inch) Erosion-Based Design Process 0,70 0,60 0,50 0,40 0,30 0,20 0,10 0, Year Base Curve 80% Flow Factor ft/day Subbase Permeability 180 Rainy Days Determine Traffic Base Cohesive Strength Calc Shear Stress Estimate NWD Determine Erosion Damage Determine Interlayer Frictional Resistance and Reduced k-value Determine Composite Thickness Determine Loss of LT Determine Bending Stress ADTT

26 Erosion Model f N f f N f i 1 2 % E D i ; D= ; N 10 k e k r ; r= 0 f Where %E = Percent of erosion f i f 0 = Level of faulting per load cycle i = Ultimate faulting D i = Damage ratio per load cycle i (D i = N i /N f ) = Erosion initiation shift factor α = Erosion rate factor ρ = Calibration factor N i = Effective ESAL per load cycle i 26

27 Presence of Moisture Ni Damage, Di %Wet Days N f N i = Effective ESAL N W = P% 365 P% = p 1 p 2 (1 + p 3 ) P% is a adjustment factor that contains three factors : p 1 : Probability of the Rain ( # of wet days/ 365) p 2 : Surface Inflow Factor p 3 Subbase Drainage Factor

28 1 %E ( 1 Prob(σ 0 fe n ) fc ff 3w n 0 ft ; 0 2 e k e S f cohesive or shear strength; f q tan c Interlayer Friction Model f i Di %E e f 0 he u h 1 x x h 2 e p e e eb F

29 Field Evaluation of Erosion Damage Flow Tests (Infiltration Test) Ground Penetration Radar (GPR) Falling Weight Deflectometer (FWD) Core Samples Toward South TS 3 Hot Pour Sealants TS 2 Silicone (Poor Condition) TS 1 Unsealed

30 Falling Weight Deflectometer (FWD) Drops on : Joints (Approach Slab and Leave Slab) Center of the Slab Edges and Corners J5 J2 J1 J3 1 %E 1 P(σ 0) fe n fc f F

31 Equivalent Thickness h 3 e p 4 m 12 k 1 2 b Ec h e-p Equivalent Thickness lm Measured Value k b Back-calculated Based on Cores E c

32 GPR Testing

33 Erosion Results h e TS1 Afternoon Read Position J1 J3 J5 J2 he TS 2 Afternoon Read Position J1 J3 J5 J2 he he 12 J5 J1 10 J2 J3 8 6 TS1 TS J1 J3 J5 J2 Falling Weight Deflectometer (FWD)

34 % Erosion Erosion Results %E TS3 TS2 TS1 Position J1 J2 J5 Erosion % Position J1 J2 J5 Erosion % Position J1 J2 J5 Erosion % TS3 TS2 TS J1 J2 J5 Slab Position Erosion % J5 J2 J1 J3

35 Erosion Results CRC

36 Conclusions Erosion leads to loss of support and faulting Subbase shear strength is key to erosion resistance Field evaluation reveals that slab corners and edges are susceptible to erosion Considering erosion effects may also help to avoid overly conservative designs and better material/traffic combinations

37 FWD Testing Pattern 1 %E 1 P(σ 0) fe n fc f F

38 Hamburg wheel-tracking device (HWTD) Subbase material 25.4 mm (1 in.) thick placed on a neoprene Jointed concrete block 25.4 mm (1 in.) thick. A wheel load of 71.6 kg (158 lb) is applied at a 60-rpm load frequency Measurements consist of the depth of erosion Vs the number of passes

39 Material Material Location Material Moisture When Tested Test Condition Erodibility (mm/million passes) SP FL Optimum Wet 3200 Clay TX Saturated Wet 15200

40 Dynamic Foundation Modulus (K dyn ) k b * 0 wp w 0 2 e Where P w 0 = wheel load (F) = center plate deflection (L) w * a a 1 ln e e 2 (center of slab loading)