Concrete Pavements Conference 2013 12 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
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
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 dynamic @ 3 Hz 20 kn + 40 kn static 40 kn cyclic @ 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
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
Test set-up (South Africa) - section Dynamic load actuators ±55 230 ±20 80 20 kn 20 kn 120 mm dia x 80 mm high load cell 165 165 16 mm thick base plate on 3 mm rubber Concrete Timber pack 1 800 Crack inducer incision ±525 140 Rubber foundation Angle iron Crack/joint face > ¾ thickness 5
Aggregates Aggregate type South Africa Granite (19mm) Granite (37.5mm) Dolomite (19mm) Dolomite (37.5mm) America Limestone (25mm) Glacial gravel (50mm) ACV (%) 25 27 15 15 18 30 RD (kg/m 3 ) 2.65 2.65 2.86 2.86 2.61 2.58 Test Absorp tion (%) 0.33 0.33 0.20 0.20 0.61 - LA abra Stiffness sion (%) (MPa) 33 33 21 21 34 22 27.0 29.0 42.0 48.0 22.0 24.0 Sand grading (washed crusher sand) 100 90 Cummulative percentage passing 80 70 60 50 40 30 20 Grading Envelope Lyttleton Dolomite Rossway Granite 10 0 0.01 0.10 1.00 10.00 Sieve size (mm) 6
Concrete mix design South Africa Slab 2 Slab 3 Slab 4 Water (l) 185 201 185 Cement (kg) 335 360 335 Materials (/m 3 ) Sand (kg) 800 830 854 Stone (kg) Slabs 1 + 5 201 360 775 1025 America 1075 1115 1160 335 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
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* 24.5 38.7 50.0 20.0 30.0 36.7 27.2 45.0 57.5 29.0 41.7 50.0 27.7 41.5 55.0 27.7 38.5 48.2 29.8 43.5 49.3 27.5 39.3 45.0 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) 17-18 0.25 26.5 27.5 2 (37.5) 29.0 17-18 0.25 28.0 29.0 3 (19) 41.2 24-25 0.45 42.5 43.5 4 (37.5) 48.0 24-25 0.45 43.5 44.5 8
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 25 30.6 2.93 2.33 140 Glacial gravel 50 32.8 2.41 2.21 175 Limestone 25 34.8 2.47 2.17 90 Analysis of results Deflection Load transfer efficiency (LTE) Relative movement (RM) 9
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) 2.5 2.0 1.5 1.0 Dynamic dolomite agg. Dynamic granite agg. Static dolomite agg. Static granite agg. Static EverFE 0.5 19 mm aggregate 0.0 0.1 0.4 0.7 1.0 1.3 1.6 1.9 2.2 2.5 Crack width (mm) 10
LTE vs crack width 19 mm aggregate 100 90 Load transfer efficiency (%) 80 70 60 Dynamic dolomite agg. Dynamic granite agg. 50 Static dolomite agg. Static granite agg. EverFE static 40 0.1 0.4 0.7 1.0 1.3 1.6 1.9 2.2 2.5 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
Improvement of aggregate interlock equation - 1 3 x y ( x) = 114000 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 + 11.413 ) ( x) = 0.118(1 e (( v x)1. 881 agg ) where: y(x) = relative vertical movement (mm) x = crack width (mm) agg = nominal size of 20% maximum aggregate particles(mm) v = 0.136 for static loading (speed = 0 km/h) =0.035 for dynamic loading (speed = 80 km/h) 12
Effect of improved equation Relative movement (mm) 3.5 3.0 2.5 2.0 1.5 1.0 Dynamic 19mm agg. Static 19mm agg. Previous equation Improved equation - dynamic Improved equation - static 0.5 0.0 0.1 0.5 0.9 1.3 1.7 2.1 2.5 Crack width (mm) 13
Contribution of 5 th experiment Load transfer efficiency (%) 100 80 60 y = 100e -11.525x 40 R 2 = 0.9445 20 Aggregate interlock active zone y = 100e -1.6764x R 2 = 0.9649 Smooth joint zone y = 100e -6.5722x R 2 = 0.9278 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 -5.1197x R 2 = 0.9296 0 0.0 0.1 0.2 0.3 0.4 0.5 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
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
Thank you 16