تاثير مصرف ماسه طبيعي بر خواص و رفتار بتن آسفالتي روسازيها

The effect Of Using Natural Sand On The Properties And Behavior Of Asphalt Paving Mixes

In hot-mix asphalt the shape and surface texture of fine aggregate particles have a vital effect on the resistance to permanent deformation of the mix. Due to availability and economical savings in comparison with crushed sand, there is a tendency of using mostly natural sand in pavement construction,which under poor joint inspection is sometimes used without perfect washing. The aim of this research was to investigate the effect of using natural sand, particularly in a soiled (as-dig) state, on the properties of asphalt concrete, and also to evaluate the sufficiency of the current method of design and control of asphalt mixes. Four types of aggregate blends with the same grading and a 60/70 penetration grade asphalt were used in the study to produce asphalt mixes. Aggregate blends were prepared using constant coarse and different fine fractions. The shape and surface texture characteristics of fine aggregates were determined by following standard laboratory procedures: one type of crushed sand, one type of natural river sand and a sand type consisting of a blend of the crushed sand and the natural sand. Results obtained from Marshall Method of Mix Design indicates that this design method does not comprise the sensitivity required to indicate the maximum allowable percentage of natural sand in asphalt mixes and so, further relevant complementary tests are needed. Results obtained from mix design tests, and also from unconfined compressive strength tests indicate that using natural sand particularly in a soiled state causes a reduction in the bearing and energy absorption capacity of the asphalt mixture, and intensifies the risk of occurrence of permanent deformation and bleeding in the asphalt concrete surfaces.