Sustainable Alternative Materials in Unbound Granular Layers of Pavement Structures

Abstract

In Part 1 of this thesis, reclaimed cement concrete (commonly referred to as recycled concrete aggregate or RCA) and reclaimed asphalt pavement (RAP) are investigated as potential alternative construction materials for Granular B Type II subbase fill. Ontario Provincial Standard Specification (OPSS) 1010 currently allows the common use of processed reclaimed construction materials in a variety of road base, subbase and asphaltic concrete layers, with the notable exception of Granular B Type II, which at present may only include 100% crushed bedrock, talus, iron blast furnace slag or nickel slag. As more restrictions are placed on zoning and approvals for new natural aggregate extraction sites in Ontario, there is a need to better understand the performance of materials such as RCA and RAP as economically beneficial potential aggregate sources for granular base and subbase fill layers.

An experimental program was created to assess and analyze the performance characteristics of a series of different subbase test mixtures incorporating RCA and/or RAP, either pure or blended with crushed bedrock, and the impact of the inclusion of these materials when compared to a conventional 100% crushed bedrock test mix meeting OPSS 1010 requirements for Granular B Type II. The performance characteristics to be assessed were field compactibility, gradations before and after field compaction, physical properties, standard and modified Proctor tests, California Bearing Ratio (CBR), permeability, resilient moduli and lightweight deflectometer (LWD) resilient moduli.

Field testing programs conducted at Quarry 1 in Ottawa, Ontario and Quarry 2 in Burlington, Ontario indicate that the subbase test mixtures meeting OPSS Granular B Type II gradation requirements and incorporating different proportions of crushed rock, RCA and/or RAP exhibit similar field rolling compactibility relative to 100% crushed rock. Grain size analysis testing showed some aggregate breakdown in multiple test mixes, with only minimal increases in material passing the 75 µm sieve, which is crucial to preserving permeability and drainage characteristics. Tests using a lightweight deflectometer (LWD) were subject to substantial variability but indicated that mixes using elevated levels of RCA (50% and 100%) can potentially have lower in-situ moduli compared to the other blends tested.

Laboratory tests indicate that high replacement levels of RCA can be used in subbase materials as a substitute for 100% crushed rock while maintaining good water permeability characteristics and similar or higher resilient moduli in blends incorporating RCA and/or RAP. CBR testing results were similar across all test blends incorporating crushed rock and RCA, but also indicated that the inclusion of 30% RAP can potentially reduce the bearing capacity of the granular material by approximately 30-40% in comparison to all other blends which do not contain RAP. Based on the overall results of this study, RCA and RAP appear to be capable of successfully substituting for natural aggregates in Granular B Type II in a range of compositional proportions. It is recommended that test sections should be completed on highway contracts with subbase mixture blends incorporating RCA and/or RAP in order to verify their performance in pavement structures in the field.

In Part 2 of this thesis, foam glass lightweight aggregates (LWA) are investigated as a potential pavement engineering design alternative in order to mitigate roadway loading impacts upon underlying subgrade soils while promoting the sustainable and economical use of recycled waste glass. Foamyna Canada Inc. supplied the Centre for Pavement and Transportation Technology (CPATT) with two foam glass lightweight aggregate materials, designated in this thesis as LWA-A and LWA-B. Physical properties testing was carried out by CPATT, including grain size analysis, crushed particle content, flat and elongated particle content, Micro-Deval abrasion resistance, cyclic freezing-and-thawing resistance and resilient modulus testing procedures. These procedures were conducted in order to evaluate the LWA materials against locally applicable standards, namely Ontario Provincial Standard Specification document OPSS 1010 as currently used by the Ministry of Transportation of Ontario (MTO).

The laboratory testing detailed in Part 2 indicates that both LWA-A and LWA-B have a very consistent and repeatable gradation with a high percentage of coarse aggregates. Both foam glass materials have very high crushed particle contents and very low flat and elongated particle contents. Micro-Deval abrasion resistance, freeze-and-thaw resistance and resilient moduli were also excellent for both materials, while relative density testing indicated LWA material specific gravity values which were substantially lower than that of water. However, it was found that the gradations of these two tested materials do not satisfy the existing requirements of OPSS 1010, which were developed for natural aggregates and, as currently constituted, may not be appropriately adapted to artificial lightweight aggregates. The coarse nature of the LWA materials would be highly beneficial to ensure the stability of the granular layers and prevent upward capillary water movement into other layers of the pavement structure.

Pavement design calculations were carried out using the AASHTO 1993 empirical design procedure and found that utilizing foam glass LWA as a lightweight subgrade replacement fill material can result in substantially leaner pavement structures as compared to the use of conventional expanded polystyrene (EPS) geofoam blocks as an artificial subgrade. A life-cycle cost analysis (LCCA) procedure carried out on these pavement designs showed that the use of foam glass LWA as a lightweight fill material underlying pavement can result in overall cost savings of over 30 percent relative to pavement structures which are underlain by EPS geofoam. Overall, the two tested LWA materials showed excellent physical and mechanical characteristics, and would be suitable for use in pavement structures as innovative lightweight and environmentally friendly alternatives to natural aggregate materials.