Application of recycled waste materials for making a new and green pavement base/subbase
Creators: name: SABERIAN BOROUJENI, Mohammad
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400502
subject: Civil geotechnical engineering
classificationCode: 400505
subject: Construction materials

description: Construction and demolition (C&amp;D) materials, such as recycled concrete aggregate (RCA) and crushed rock (CR), as well as solid wastes, such as glass and scrap tyres, comprise a significant proportion of all the generated wastes around the world. Around 534, 531 and 20 million tonnes of C&amp;D wastes are generated each year in the USA, European Union, and Australia, respectively. Construction and demolition (C&amp;D) materials along with industrial and commercial wastes constitute more than 80% of the waste materials received for reprocessing in the state of Victoria, Australia. Therefore, reusing recycled materials can reduce carbon emissions up to 65%, in addition to significant cost savings. Thus, recycling and reusing of C&amp;D wastes is imperative in helping to alleviate this problem. Fortunately, solid recycled waste materials are being widely used in different civil projects such as pavement bases/subbases, permeable pavements, light-duty pavements, and backfilling of underground service pipes.

Annually, around 4 and 0.5 million tonnes of scrap tyres are stockpiled in the USA and Australia, respectively. Statistics show that over 50 million tyres are disposed to landfill in Australia each year, and surprisingly only less than 10% of them are locally recycled. Thus, managing the generated non-biodegradable waste tyres would be a challenging issue due to their sheer volume and size. Crumb rubber provides good water resistance with low absorption, low shrinkage, acid resistance, high impact resistance, and excellent thermal and sound insulation, and can improve the impact resistance, toughness and fatigue performance of base and subbase of roads.

On the other hand, the use of natural resources for making glass, and landfilling of waste glass is considered to be a further cause for environmental concerns. About 15, 10, and 1 million tons of waste glasses are annually stockpiled in the European Union, the United States, and Australia, respectively. Approximately 64 kg of feldspar, 176 kg of limestone, 190 kg of soda ash, and 560 kg of sand are conserved by recycling one ton of waste glass. Waste glass has been also used for different civil applications, such as an aggregate in asphalt, base, and subbase of pavements, aggregate in concrete, lightweight engineering material, and cementitious material.

In the first step of the project, the basic geotechnical properties of construction and demolition materials, including recycled concrete aggregate (RCA) and waste crushed rock (CR) were determined. Then, the properties of crumb rubber and crushed glass were evaluated. In the second stage, the effects of rubber size and rubber content on the geotechnical properties of RCA and CR were investiagetd through a series of geotechnical tests such as modified compaction, unconfined compression strength (UCS), California bearing ratio (CBR), Clegg impact hammer, dynamic lightweight cone penetration, aggregate crushing value (ACV), Los Angeles (LA) abrasion, resilient modulus, permanent deformation, and large-scale direct shear. Based on the tests¿ results, the optimum percentage of rubber was considered for the next stage, in which different amounts of crushed glass were added to RCA and CR containing the optimum amount of rubber, and the above-mentioned tests have been conducted on the mixed samples.

According to the results of the thesis, it was concluded that although the inclusion of rubber to the aggregates resulted in decreasing some of the strength properties, a few of the samples incorporating rubber could meet the minimum required strength values suggested by the relevant standards. Thus, the inclusion of 1% rubber to the aggregates provided a better response among the other samples containing rubber. This conclusion was made based on an in-depth comparison between the test results (i.e., the tests mentioned above). Also, carbonation (10% carbon) led to significant increases in the strength properties of the aggregates containing rubber (around 75% increase). In addition, increasing the temperature to more than 450 oC led to a collapse of the RCA samples with and without fine rubber. The maximum heating degree could be considered as 450 oC for base and subbase of pavements. Also, it was noticed that a higher temperature resulted in relatively higher strength values because of the melting of the rubber under high temperatures. Based on the test analysis, the optimum blend would be suggested as RCA with 1% rubber, which showed the highest strength compared to the other samples at high temperatures. It was also noticed that the freezing-thawing process had significant effects on the strength values regardless of rubber content added. Moreover, it was concluded that because of the fantastic ability of rubber particles in protecting the samples from freeze-thaw forces/deteriorations, it could make the blends a viable economic option for the construction of pavement base and subbase. In the end, by comparing the results of the effects of crushed glass on the properties of the aggregates containing 1% rubber obtained from a series of comprehensive experimental tests, it was concluded that the inclusion of 5% glass provided the highest properties and the best performance.

In this research, a new concept and method has been developed for for making a green and sustainable pavement base/subbase. The outcomes of this study will provide practical guidance on the application of waste materials. It will benefit local government, local community, construction and pavement industry, and recycling industry.