Updating Bituminous Stabilized Materials Guidelines Mix Design Report Phase II

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4. CONCLUSIONS AND RECOMMENDATIONS The investigation on wet trafficking and fundamental characteristics of BSMs associated with moisture damage studied through APT (MMLS3) device approach. Based on the data of the study, the following conclusions and recommendations are drawn: The approach employed in wet trafficking in this study successful accomplished the objectives to, - investigate test procedure, which is applicable for BSMs on moisture exposure using APT device (MMLS3). - validate the behaviour of selected BSMs on moisture susceptibility - Correlate the validated behaviour of BSMs on MMLS3 to the MIST device testing system. - Make appropriate recommendations regarding the use of the APT device on screening BSMs based on moisture related damage for mix design 4.1 Load application - The used of APT Device (MMLS3) has shown potential in identification of BSMs distress under wet trafficking. It can therefore suitably be adapted for testing Bituminous Stabilised Materials (BSMs). - The use of vinite or reinforced rubber mat proves to minimise the direct abrasion of wheel to the specimen. However, the vinite layer seen not be effective once severe cohesion loss of BSMs occurred. - The new variables applied on MMLS3 i.e. 420kPa tyre pressure, 1.8kN wheel load, and speed of 7200wheel per hour, seemed to provide acceptable level of screening the BSMs in term of moisture susceptibility. - The new variables applied on MMLS3 also found to validate the results obtained with MIST testing device. - The influence on curing of BSMs on wet performance is significant. Long term cured BSMs withstanding significant number of load application (100 000 wet axles) with small ravelling. Whilst the equivalent BSMs with an accelerated laboratory cure withstand less wet axles before severe disintegrate. 4.2 Disintegration and ravelling - The disintegration of BSMs during MMLS3 test show that, wet trafficking has more damage in term of cohesion loss or stiffness reduction compared to dry trafficking. This suggests that cohesion loss occurred under traffic and the damage aggravated by pore pressure in the presence of water. 32
- No sign of significant initial densification occurred on BSMs. However, cohesion loss or stiffness reduction of the trafficked materials increases as number of load application increases. - The level of disintegration and ravelling on BSMs under wet trafficking, shows that cohesion loss and stiffness reduction develop progressively. The failure mechanism of BSMs is that severe reduction of cohesion or stiffness occurs, before exponential loss of materials occurred. - Sample preparation need care to ensure smoothness of the test surface. Briquettes that spalled during cutting show an early disintegration on wet trafficking. - The performance of BMSs exposed to moisture during trafficking shows significant differences. The long cured BSM-emulsion proves to be moisture resistant, than BSMs with laboratory accelerated curing. - The influence of the addition of the active filler in BSMs is vital for the improvement in moisture susceptibility. The results indicate that BSMs with addition of 1% cement is more moisture resistant compared to BSMs with addition of Lime or no active filler. However interesting results on the addition of 1% lime is that, the BSMs endure moisture resistant to a certain saturation level up to 80%, thereafter exponential disintegration occurred. 4.3 Testing Temperature - The MMLS3 wet trafficking and ITS tests were conducted at controlled 25 o C. It is obvious that the field temperature on BSMs varies significantly, however in South Africa moisture related damage occurred during rainfall period. During that period air temperature, do not exceed 30 o C. Therefore, BSM-layer being a base or subbase its temperature will not excess 25 0 C. 4.4 ITS test results - The comparison of the ITS Values in all BSMs show no significant difference, with exception of BSM-emulsion made of quartzites and no active filler. This indicates that ITS test is not particular sensitive to moisture effect. - From the analysis, long term cured BSM-Mixes proved to be highly moisture resistant compared to laboratory accelerated cured BSM-mixes. However the ITS results show insignificant difference between these BSMs. The lack of reliability and repeatability of the ITS test for use in ranking BSMs in terms of moisture susceptibility, should preclude its use for important applications of BSMs. - Ravelling-depth of 4mm under the MMLS3 wet trafficking appears to be critical. It is appropriate to extend testing beyond 4mm for better screening the BSMs. 33
Page 1 and 2: APPENDIX J Technical Memorandum Upd
Page 3 and 4: findings of the moisture damage tha
Page 5 and 6: Figure J.4: The measuring wheel of
Page 7 and 8: An electric calibration unit used t
Page 9 and 10: 2.2 BSMs for MMLS3 testing The inte
Page 11 and 12: Figure J.12: The side view of the b
Page 13 and 14: The set-up of the test before traff
Page 15 and 16: 3. TEST RESULTS The use of vinite o
Page 17 and 18: Table J.7: ITS results after wet an
Page 19 and 20: Table 11: Ravelling-depth after MML
Page 21 and 22: Table 15: Tensile Strength Retained
Page 23 and 24: The comparison of BSMs on Figure J.
Page 25 and 26: From Figure J.19 it can be seen tha
Page 27 and 28: 4.3 Saturation Level The moisture i
Page 29 and 30: Ravelling-Depth [mm 16 14 12 10 8 6
Page 31: From the study conducted in MIST de
Page 35: 5. BIBLIOGRAPHY ASPHALT ACADEMY. 20

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