PURPOSES : The purpose of this study is to present a cross section suitable for low-traffic road pavement considering the environmental characteristics of Vietnam. METHODS : The behavior of the pavement with respect to the axial load was numerically analyzed using the nonlinear finite element method. The elastic-plastic material model was applied to material properties such as subgrade, sub-base layer, and base layer, and whether the material yielded was determined. In order to evaluate the adequacy of the cross section of the Vietnamese low-traffic pavement, it was compared with the KPRP Lv 3 road pavement section. And it was compared with the newly proposed MAST composite Pavement. The design life of each pavement section was calculated using the results obtained from the pavement structural analysis. RESULTS : The cross section of the Vietnamese low-traffic road pavement, KPRP lv3, MAST composite Type1 road pavement did not satisfy the design criteria for fatigue cracking and rutting. MAST composite Type2 was analyzed considering CTAB having 100mm and 150mm thickness and compressive strength of 5MPa, 10MPa, 15MPa and 20MPa, and all of them satisfied the design criteria. CONCLUSIONS : The low-traffic road pavement section in Vietnam currently used is judged to be inappropriate, and the MAST Composite type 2 proposed in this study is evaluated as an appropriate alternative. Further studies such as field application are needed in the future.

PURPOSES : The objective of this study was to evaluate the field applicability of chip seals using recycled aggregates by comparing performance between natural aggregates and recycled aggregates for chip seals. METHODS : In order to check the performance of chip seals using recycled and natural aggregates, Bitumen Bond Strength (BBS) test, Vialit and bleeding tests were carried out. Cationic emulsions (RS(C)-2 and latex modified RS(C)-2L) were used in the tests. Granite aggregates were used as the natural aggregate and recycled aggregate from road wastes were used as the recycled aggregate. The aggregate was used with uniform gradation between 10 mm and 4.75 mm to clearly compare the performance difference between natural and recycled aggregates. RESULTS : Test results showed that the aggregate retention was low for both natural and recycled aggregates when applying RS(C)-2 (unmodified emulsion), but there was almost no difference between them when applying RS(C)-2L and RS(C)-2L-1 (modified emulsion) in the Vialit test results. In the bleeding tests, there was no bleeding for both natural and recycled aggregates when applying RS(C)-2 and RS(C)-2L. CONCLUSIONS: It was possible to apply chip seals using recycled aggregates in the field because the chip seals with recycled aggregates and RS(C)-2L (modified emulsion) showed aggregate retention similar to that of natural aggregates, and there was no bleeding.

PURPOSES : The objective of this study is to evaluate the effect of physical characteristics of emulsion asphalt and aggregate on performance of chip seal pavements. METHODS : In order to evaluate the performance of chip seal materials, the sweep tests and Vialit Plate Shock tests were conducted on the mixtures with five emulsion asphalt binders and three aggregate types. The sweep tests was intended to investigate the change of bonding properties between emulsion asphalt and aggregate with curing time. The Vialit Plate Shock test was used to evaluate the bonding properties of chip seal materials at low temperatures. RESULTS : Results from sweep tests showed that polymer modified emulsion asphalt can reduce the curing time by 1.5 hour comparing with typical emulsion asphalt. It is also found that the Flakiness Index of aggregates and absorption rate of binder are the major factors affecting the bonding properties of chip seal materials. The Vialit Plate Shock test results showed that the average aggregate loss of CRS-2 is ten times higher than CRS-2P No.2 indicating that the use of polymer additives in emulsion asphalt can improve the performance of chip seal materials in low temperature region. CONCLUSIONS : The use of polymer in emulsion asphalt can decrease the curing time of chip seal materials and increase the bonding properties between aggregates and asphalt binder. It is also concluded that the lower Flakiness Index and absorption rate of aggregates can improve the performance of chip seal pavement.