Concrete Pavements Conference August Aggregate interlock efficiency at concrete pavement joints

Transcription

1 Concrete Pavements Conference August 2013 Aggregate interlock efficiency at concrete pavement joints Dr Anna-Carin Brink Introduction Background to SA study Load transfer through aggregate interlock Laboratory studies Analysis of results Improvement of aggregate interlock equation Conclusions and recommendation 1

2 Background to South African study Main objective - investigate existing methods for modeling aggregate interlock shear load transfer efficiency Provide an improved aggregate interlock equation for the new South African mechanistic concrete pavement design procedure Definition of load transfer Deflection load transfer efficiency: LTE δ = U / L ratio of deflection of unloaded slab to the deflection of the loaded slab 2

3 Laboratory studies Experimental design and test procedure Aggregates Concrete mix design Concrete material test results Experimental design and test procedure -1 Description South Africa America Slab thickness 230 mm 250 mm Concrete strength 35 MPa 24 MPa Aggregates Granite + dolomite Limestone + glacial gravel Load 20 kn 3 Hz 20 kn + 40 kn static 40 kn 3 Hz Actuators One each side of crack One on leave slab Subbase Rubber "Michigan" foundation Crack widths 0.1 mm to 2.5 mm 0.3 mm to 2.5 mm 3

4 Experimental design and test procedure - 2 Dynamic = load applied through two actuators, both sides of crack, speed 80km/h, frequency 3 Hz Static = single load one side of crack Cyclic = single load, frequency 3 Hz Timing of slab cracking South Africa within 24 hours after casting America When concrete split tensile strength exceeded 70% of 28-day strength 7 to 10 days after casting 4

5 Test set-up (South Africa) - section Dynamic load actuators ± ± kn 20 kn 120 mm dia x 80 mm high load cell mm thick base plate on 3 mm rubber Concrete Timber pack Crack inducer incision ± Rubber foundation Angle iron Crack/joint face > ¾ thickness 5

6 Aggregates Aggregate type South Africa Granite (19mm) Granite (37.5mm) Dolomite (19mm) Dolomite (37.5mm) America Limestone (25mm) Glacial gravel (50mm) ACV (%) RD (kg/m 3 ) Test Absorp tion (%) LA abra Stiffness sion (%) (MPa) Sand grading (washed crusher sand) Cummulative percentage passing Grading Envelope Lyttleton Dolomite Rossway Granite Sieve size (mm) 6

7 Concrete mix design South Africa Slab 2 Slab 3 Slab 4 Water (l) Cement (kg) Materials (/m 3 ) Sand (kg) Stone (kg) Slabs America kg type Ι cement per m 3 fresh concrete 5.5% air in fresh concrete 1.15 relative water content 0.72 workability Shuttering 7

8 Concrete test results SA - 1 Slab number 1 (19) 2 (37.5) 3 (19) 4 (37.5) Curing method water air water air water air water air Compressive strength (MPa) 7 days 28 days Time of test* Concrete test results SA - 2 Slab number 1 (19) Laboratory E (GPa) 21.0 Calculated E (MPa) K 0 (GPa) α E c,28 = K 0 + (GPa/MPa) αf cu,28 (GPa) (37.5) (19) (37.5)

9 Concrete test results USA Aggregate type Maximum size (mm) 28-day compressive strength (MPa) 28-day split tensile strength (MPa) Split tensile strength at cracking (MPa) 28-day fracture energy (N/m) Glacial gravel Glacial gravel Limestone Analysis of results Deflection Load transfer efficiency (LTE) Relative movement (RM) 9

10 Deflection SA - Crack width and subbase support = primary factors controlling slab deflection USA Crack width = primary factor controlling slab deflection Deflection vs crack width 19 mm aggregate 3.0 Deflection (mm) Dynamic dolomite agg. Dynamic granite agg. Static dolomite agg. Static granite agg. Static EverFE mm aggregate Crack width (mm) 10

11 LTE vs crack width 19 mm aggregate Load transfer efficiency (%) Dynamic dolomite agg. Dynamic granite agg. 50 Static dolomite agg. Static granite agg. EverFE static Crack width (mm) LTE - USA Stage I: tight crack (crack width <0.5 mm) 100% LTE Stage II: aggregate interlock (crack width 0.6mm 2.5 mm) Stage III: elastic deformation of foundation (crack width >2.5 mm) SA study indicated upper asymptote for 37.5 mm aggregate > 2.5 m 11

12 Improvement of aggregate interlock equation x y ( x) = agg where: 4.5 y(x) = relative vertical movement (mm) x = crack width (mm) agg = nominal size of 20% maximum aggregate particles(mm) Improvement of aggregate interlock equation - 2 y ) ( x) = 0.118(1 e (( v x) agg ) where: y(x) = relative vertical movement (mm) x = crack width (mm) agg = nominal size of 20% maximum aggregate particles(mm) v = for static loading (speed = 0 km/h) =0.035 for dynamic loading (speed = 80 km/h) 12

13 Effect of improved equation Relative movement (mm) Dynamic 19mm agg. Static 19mm agg. Previous equation Improved equation - dynamic Improved equation - static Crack width (mm) 13

14 Contribution of 5 th experiment Load transfer efficiency (%) y = 100e x 40 R 2 = Aggregate interlock active zone y = 100e x R 2 = Smooth joint zone y = 100e x R 2 = Lab Road Section 2 Road Section 3 Road Section 4 Expon. (Lab) Expon. (Road Section 2) Expon. (Road Section 3) Expon. (Road Section 4) y = 100e x R 2 = Relative movement (mm) Shift factor to calibrate laboratory data to field data F = l/(k*e subbase ) Where: k l E subbase = Subgrade modulus = Radius of relative stiffness = Subbase stiffness 14

15 Conclusions Increase in crack width increase in deflection, decrease in LTE, increase in RM Deflection tended to reach asymptote at crack width >2.5 mm LTE 50 mm glacial gravel = 80% at 2.5 mm vs 84% 19 mm dolomite South Africa blessed with good quality road construction materials and effective crushing techniques and maybe Australia as well? Recommendations Equation developed during SA study can be used with confidence EverFE gave good indication of results, specific pavement foundation model should be borne in mind Compare relative SA vs Australian aggregate characteristics 15

16 Thank you 16