IMPORTANCE OF THE ZERO POINT IN DCP TESTING OF FLEXIBLE PAVEMENTS FRANK NETTERBERG

1. IMPORTANCE OF THE ZERO POINT IN DCP TESTING OF FLEXIBLE PAVEMENTS FRANK NETTERBERG Pavement Materials & Geotechnical Specialist

3. ZERO POINT MODEL AT TOP OF KLEYN Granular (1975 on) : Base TMH 6 Standard method (1984) : Surfacing DE BEER Cemented (1989 on) : Surfacing

4. GRANULAR PAVEMENTS Structural capacity of granular pavements to an additional rut depth of 20 mm in millions of actual 80kN standard axle loads (MISA) (Kleyn, WinDCP): Capacity =Cm x 10-9(DSN800)3,5……………MISA

5. 3,83 – DN50 1,39 10 X 20 …….…… MESA SC20 = DSN200 CEMENTED PAVEMENTS Structural capacity (SC20) of lightly cemented pavements to an additional rut depth of 20 mm in millions of equivalent 80kN standard axles (MESA) (De Beer, WinDCP):

6. RELATIVE DAMAGE EXPONENT Relative damage (TRH 4: 1996 – COLTO 1996) or load equivalency (Kleyn and Savage, 1982) exponent : LEE = 0,044 (BN100)1,24………………n

7. THREE CASE HISTORIES • Twelve mostly stabilized sand base pavements under old, hard seals • One untreated and one cement-treated gravel base pavement under double seal • One new cement / emulsion-treated base pavement under new soft, bleeding, Cape seal • All DCP testing for the work presented here was carried out according to TMH 6: 1984 with the zero reference point at the top of the seal.

8. 55 YEAR-OLD THICK, HARD TRIPLE SEAL AFTER 1,5 MESA • SURFACING: Triple seal + 1 reseal (25 –30 mm in total) • BASES : 150 mm, mostly Kalahari sand • One neat sand (MAASHO CBR 50, GM 0,9; NP, but G7) control • One sand + 2 % sulphite lye (lignosulfonate) (G7? • Two sand + 4 or 8 % SS 60 emulsion (BT3?) • Five sand + 3, 5 or 10 % OPC or PBFC (C3 ? • Two sand + 4 or 8 % 30/35 EVT TAR (BT3?) • One “crusher-run” (G4) control • SUBBASE : 3 % PBFC-treated Kalahari sand (C4?)

9. Neat Kalahari sand base

10. 5 % OPC- treated sand base

11. Effect of zero point on mean capacity and load equivalency exponent of 12 pavements using granular model

12. 30 YEAR-OLD DOUBLE SEAL • SURFACING : Double seal + 1 slurry + 1 reseal (13 – 19 mm in total) • BASES: 150 mm calcrete gravel (GM 2,0) • One neat (PI 12, G6) • One 4 % PBFC (C3?) • SUBBASE : 2 % PBFC-treated calcrete (C4 ?) • TRAFFIC : 0,5 MESA

13. Neat gravel base section after patching

14. Effect of zero point on mean capacity and load equivalency exponent of two gravel-based pavements using granular model

15. NEW CAPE SEAL SURFACING : 19 mm Cape seal (with asphalt) BASE & SUBBASE : 300 mm “calcrete” + sand + 2,5 % CEM I + 1,5 % SS 60 (C3 / C4) TRAFFIC : 200 ESA

16. Typical base shear failure

17. Effect of zero point on single point estimates of structural capacity of one cemented pavement by the cemented model

18. CONCLUSIONS • (FOR CASES STUDIED) • INCLUDING THE SEAL YIELDED: • Higher capacity with Kleyn granular model with old, relatively hard & thick seals (also cemented model) • Generally lower capacity with De Beer cemented model with new soft, bleeding seal • MORE CONSERVATIVE : • Zero at top of base with Kleyn model • Zero at top of seal with De Beer model • Use what the model developer used! • But zero at top of surfacing allows for both models • Check average BN 100 manually if using WinDCP 5.1