Unconventional and Simplified Approach towards Unpaved Roads: Application of Geosynthetics

A field trial was carried out to investigate the performance of different unconventional geosynthetic materials in unpaved road construction over soft ground.The test site comprises of 25 m long, by 3 m wide test sections, built on a subgrade of undrained shear strength approximately 45 kPa . One isunreinforced and serves as a control section in the study, three sections includea geotextile, and one includes a geogrid. Each test section incorporated avariable thickness of sandy gravel base course material, between25 and 45 cmthick. They were loaded in sequence by a vehicle of standard axle load.Performance of the test sections was evaluated from measurements of rut depth, base course thickness, base course deformations, geosynthetic strain, and deformed profile of the geosynthetic, with increasing number of vehicle passes.The four geosynthetic materials used exhibited a broad range of stiffness and material properties ,but the general performance of the four reinforced sections was similar on the base course layers. On contrary thinner subgrades showed a significant difference between the geosynthetics Keywords: Geo-synthetic materials, geo-textile, geo-grid, unpaved road.

Generalized Interface Shear Strength Equation for Recycled Materials Reinforced with Geogrids

In this research, large direct shear tests were conducted to evaluate the interface shear strength between reclaimed asphalt pavement (RAP) and kenaf geogrid (RAP–geogrid) and to also assess their viability as an environmentally friendly base course material. The influence of factors such as the gradation of RAP particles and aperture sizes of geogrid (D) on interface shear strength of the RAP–geogrid interface was evaluated under different normal stresses. A critical analysis was conducted on the present and previous test data on geogrids reinforced recycled materials. The D/FD, in which FD is the recycled materials’ particle content finer than the aperture of geogrid, was proposed as a prime parameter governing the interface shear strength. A generalized equation was proposed for predicting the interface shear strength of the form: α = a(D/FD) + b, where α is the interface shear strength coefficient, which is the ratio of the interface shear strength to the shear strength of recycled material, and a and b are constants. The constant values of a and b were found to be dependent upon types of recycled material, irrespective of types of geogrids. A stepwise procedure to determine variable a, which is required for analysis and design of geogrids reinforced recycled materials in roads with various gradations was also suggested.

Unconfined Compressive Properties of Fiber-Stabilized Coastal Cement Clay Subjected to Freeze–Thaw Cycles

This study aimed to investigate the feasibility of using polypropylene fiber-cement-stabilized coastal clay as base-course material or foundation material for city sustainable development by assessing its mechanical performance. The influence of the number of freeze–thaw cycles and curing ages on the mechanical properties of ordinary cemented clay (OCC) and polypropylene fiber-cemented clay (PCC) was investigated by using unconfined compressive test. The experimental results show that the addition of fiber with 1% content can increase the strength as well as the ductility of cemented clay by 12.5% and 15.6%, respectively. The strength of PCC and OCC at 22d age was 1.5 times than at 7d age. Under differently timed freeze–thaw cycles, the mechanical performance of PCC is improved, and, better than that, OCC improves by 11.8% in strength, 16.5% in strain and by 5% in degree of damage, indicating that fiber can improve the freeze–thaw resistance of cemented clay. The frost resistance of PCC and OCC increases with the increase in curing age. Finally, the variation of strength of OCC was explained through the change of micro-structure while the strength enhancing mechanism of polypropylene fiber for cemented clay was also revealed.

Analyzing the Application of Different Sources of Recycled Concrete Aggregate for Road Construction

Because of the environmental, planning, and resource restrictions in the exploration and processing of natural aggregates, interest in better utilizing recycled aggregates in road pavement construction is increasing. Several researchers have investigated the characteristics of recycled concrete aggregate (RCAg) with the aim of understanding its performance as a base-course unbound material. As the pavement design techniques and the properties of re-processed RCAg in each country are non-homogeneous, previous international research on recycled aggregate cannot necessarily be incorporated in New Zealand’s pavement specifications. Moreover, RCAg is mainly sourced from vertical or horizontal concrete demolished structures. These sources of material have different engineering characteristics, and there is a lack of information about their performance. This paper investigates the difference between the properties of these two vertical and horizontal sources, and it evaluates their application as an unbound granular base-course material as opposed to an alternative layer in the pavement, for road construction in New Zealand. The physical properties of RCAgs engineering performance (durability) were evaluated through experimental laboratory-based tests. Also, the characteristics of the tested RCAgs were compared with the specification of base-course materials (NZ Transport Agency M4) in New Zealand, and their appropriateness for high-performing pavement construction layers was assessed. According to the tests results, the tested RCAgs have proven to meet the “premium” base-course grade product, and it is expected that recycled crushed concrete, if production processes are appropriately managed, could have great potential use as a base-course material in road construction and in some cases perform better than common natural aggregates.