Natural crushed aggregate (NCA) is the most common material for aggregate throughout the world. The consumption of the NCA itself is rising up through the years. Concrete structures and road construction are some of the most consuming aggregate material, especially NCA. Therefore, aggregate such as recycled concrete aggregate (RCA) has become an alternative material for some particular civil construction. The implementation of RCA as road construction material has been raised for a long time ago especially in road base layer. Road base layer as foundation for road pavement must provide an adequate strength to hold the working load on the pavement surface. RCA is more heterogeneous material compared to NCA as the RCA contain many substances, such as aggregate, cement, sand, and some additive substances. Hence, it effects the strength of the RCA as construction material. In this paper, the properties of the RCA are investigated to get the characteristic of the aggregate. Density, water absorption, aggregate crushing value (ACV), compaction, and penetration test (CBR) were conducted in this research. An improvement by using plastic strips as addition also proposed to strengthen the RCA as road base material.
This paper presents the findings on the improvement of California Bearing Ratio (CBR) value of soil subgrade using garnet waste. Soil subgrade are very important in construction of roadways and need more attention in strength. Many researchers found that soil subgrade in Malaysia need an improvement technique for the road constructions. One of the techniques is using garnet waste which is an industrial waste that is getting bulkier, and thus create opportunity to reduce and reuse the waste. The research aims to determine the properties of soil subgrade and garnet waste, to determine the CBR value of soil subgrade and to determine CBR value of soil subgrade mixed with garnet waste. Material properties testing for soil subgrade are sieve analysis and Atterberg limit; and garnet waste used sieve analysis and chemical composition. Compaction test in the mixed proportion are used to obtain the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) and CBR test was done using CBR-Marshall Tester. In this study, the result obtained from garnet waste have been used to observed their effect on CBR value of soil subgrade by varying the amount of garnet waste contain 20%, 40%, 60%, 80% and 100%. 100% garnet waste content showed the best result for the highest 43% CBR value. The CBR value of the soil showed judicious improvement after mixing with above 40% garnet waste in the soil subgrade. As a conclusion, the improvement of CBR value in soil subgrade using garnet waste is applicable.
Road base layer has a unique way to distribute the stresses. Unlike a concrete layer which relies on its flexural strength, the road base layer transmit its working load by grain-to-grain contact. Many aspects will affect this load transfer system, for example, the aggregate type, shape, and strength. In this research, the fibre optic sensing was used to obtain the strains of the load under the road base layer. By knowing the strains under the road base layer, then the load distribution characteristic on the road base layer can be obtained. Two samples were tested in this research. Sample A was a road base layer constructed from natural crushed aggregate (NCA), and sample B was constructed from recycled concrete aggregate (RCA). The dimensions of the samples are 1 m x 1 m with 200 mm of thickness. A gradual static load was applied on the road base layer surface and the fibre optic sensing will measure the strains at the bottom of the road base layer. A software simulation also conducted as a comparison for the mechanical test. The result shows that the distribution area of road base layer from RCA is smaller than road base layer from NCA which means it distributes less stress than road base layer from NCA. It means that NCA has a better grain-to-grain action compare to RCA.
Internal friction angle (φ) is one of the important parameter in a foundation engineering, especially in the stress distribution event. The higher value of the internal friction angle shows the higher of the material can withstand the lateral force. Cohesion factor (c) is also an integral part of the shear strength for the foundation material. In the granular soil such as sand or non-cohesive material, including aggregate, cohesion value usually assumed as zero, although some cohesion factor may be applied. In this research, two different materials were tested for their shear strength. The materials were Natural Crushed Aggregate (NCA) and Recycled Concrete Aggregate (RCA). Each material was also tested under two different circumstances. First, the materials were tested in a small-scale direct shear (SSDS) test with the maximum material size of 0.425 mm and 2.0 mm. Secondly, the materials were tested in a large-scale direct shear (LSDS) test with the graded size of aggregate according to road base layer specification. The SSDS showed the internal friction angle of NCA and RCA varies from 26.20 to 29.82 degrees. Whereas the LSDS showed the internal friction angle of NCA and RCA are 44.90 and 29.16 respectively. Both of SSDS and LSDS also showed the cohesion value of NCA and RCA.
The road base layer as a primary foundation for the flexible pavement needs to provide adequate strength for the working load. The road base layer which is constructed from a gradation of aggregate must distribute the stress as wide as possible to reduce the load per square area. The action of stress distribution on the road base layer mostly relies on its grain-to-grain interaction. This research used the natural crushed aggregate (NCA) and the recycled concrete aggregate (RCA) as the road base materials. Physical models were conducted to evaluate the stress distribution under a static load. The physical model was using a box with a dimension of 620 mm x 620 mm x 500 mm. There were three layers for the physical model such as the road base layer, sub-base layer, and subgrade layer. The thickness of each layer was 200 mm, 100 mm, and 200 mm respectively. A static load with a maximum of 20 kN in the increment of 1 kN was added. The result of the scaled-model was not as similar to the theory of Boussinesq related to the stress distribution. The characteristic of the materials will show a different behavior of the stress distribution.
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