Increase the Strenght of Base and Subbase of Flexible Pavement by Adding Fledspar as Additive Material

The strength and durability of the flexible pavement is highly dependent on the quality of the aggregate material used for base and subbase layers. This is can be understand since 95 percent of the weight-volume of the base and subbase layer is aggregate. Therefore using a good quality and strong base and subbase material is very important. In this paper, which is a report of a reseacrh, Feldspar is used as stabilizer of base and subbase materlias of flexible pavement. Feldspar is a group rock-ftant forming tectosilicate minerals that made up about 41% of the earth’s continental crust by weight. 5 to 25% of Feldspar with increment of 5% by weight of the base and also subbase were added. Direct Shear and California Baring Ratio (CBR) test were conducted., beside water content and dry density test. The results of direct shear test show that cohesion of base and subbase materials decrease from 0,164 kg/cm2 of original base and subbase materials become 0,01 kg/cm2 for base and subbase material after adding with 25% of Feldspar, and angle of inernal friction increase from 47,670 become 49,800. Meanwhile the results of CBR test show that CBR value of base increase from 30% to 86,40%, as well as for subbase increase from 21,50% to 87,30% after adding with 15% of Feldspar. It can be concluded that adding aggregate of base and subbase with Feldspar the strenght improve signicantly, and the influence is the strengthening of the base and subbase layers.


Introduction
Flexible pavement usually consist of three layers which cover surface layer or wearing course layer at the top of the pavement, base layer which is placed directly under surface layer, and subbase layer which is placed under base layer and above the subgrade or road bed soil layer, as shown in Fig. 1.1.
In most asphalt pavements, the stiffness in each layer or lift is greater than that in the layer below and less than that in the layer above. This could be understood from the load distribution Fig. 1.2. where the stress at the surface layer is higher than that of the layer below. Therefore, the material used for the base and subbase must be durable aggregate and meet the spesification. According to [2], granular subbase material shall have a 4-day soaked CBR of not less than 30% when compacted at 100% of modified proctor AASHTO (T 180-D) and tested in accordance with AASHTO T 193, while base material must be crushed aggregate which shall have a 4-day soaked CBR of not less than 80% when compacted at 100% of modified proctor AASHTO (T180-D) and tested in accordance with AASHTO T 193. To get materials that can meet the specifications above, stabiliztion is performed using Feldspar on the existing aggregate base and subbase.

Research Methodology
This research was conducted in the Soil Mechanic Laboratory, Faculty of Engineering, Universitas Islam Sultan Agung (UNISSULA) of Semarang, Indonesia. Base and subbase materials was crushed stone obtained from Contractor's Base Camp located in Mangkang km10.00 of West Semarang.
Firstly some tests are carried out to determine the properties of the original aggregate of base and subbase, those tests were, determination of water content and dry density, CBR, and Dierct Shear tests. The original properties of aggregate base and subbase are given in Table 2.1. Secondly preparing Felsdpar which will be used as a stabilizing material. Feldspar is (KAlSi3O8 -NaAlSi3O8 -CaAl2Si2O8) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock [3]. Images of Feldspar are shown in Fig. 2.1 and Fig. 2.2. respectively [3]. Use as additive of aggregate base and subbase, the rocks of Feldspar was crushed into fine grains that pass sieve #

Increase the Strenght of Base and Subbase of Flexible Pavement by adding Fledspar as additive material
Journal of Advanced Civil and Environmental Engineering 61 100 or into fine particles of 0.15mm in diameter. So that it is obtained uniform particle of Feldspar with diameter 0.15mm.

Water content and dry density
Water content and Dry Density of original base and subbase and fledspar-base/subbase mixtures are shown in Table 3.1. It appeares that the water content as well as dry density increases with increasing of feldspar content in the aggregate of base amd subbase.

California Bearing Ratio (CBR)
The results of CBR test of original base and subbase and fledspar-base/subbase mixtures are shown in Table 3.2. and presented in the regression model in Fig. 3

Direct shear test
Direct shar test results consist of cohesion value 'c' and angle of internal friction 'φ' are given in Table 3

Conclusion
From overall test results and discussion then conclusions can be drawn as follows: 1. Analyzed using regression models, for CBR and Direct Shear test results, have a coefisien of determination R-square and coefficient of correlation R above 90%. This means the feldspar has a strong influence in improving the strenght of aggregate base and subbase. 2. Cohesion value after adding with Feldspar become zero, and angle of internal friction φ is significantly large, this means that the strenght of aggregate base and also subbase increases.