title: Recycled asphalt pavement - fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations.
abstract: In this research, a low-carbon stabilization method was studied using Recycled Asphalt Pavement (RAP) and Fly Ash (FA) geopolymers as a sustainable pavement material. The liquid alkaline activator (L) is a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), and high calcium FA is used as a precursor to synthesize the FA-RAP geopolymers. Unconfined Compressive Strength (UCS) of RAP-FA blend and RAP-FA geopolymer are investigated and compared with the requirement of the national road authorities of Thailand. The leachability of the heavy metals is measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standards. The Scanning Electron Microscopy (SEM) analysis of RAP-FA blend indicates the Calcium Aluminate (Silicate) Hydrate (C-A-S-H) formation, which is due to a reaction between the high calcium in RAP and high silica and alumina in FA. The low geopolymerization products (N-A-S-H) of RAP-FA geopolymer at NaOH/Na2SiO3=100:0 are detected at the early 7days of curing, hence its UCS is lower than that of RAP-FA blend. The 28-day UCS of RAP-FA geopolymers at various NaOH/Na2SiO3ratios are significantly higher than that of the RAP-FA blend, which can be attributed to the development of geopolymerization reactions. With the input of Na2SiO3, the highly soluble silica from Na2SiO3reacted with leached silica and alumina from FA and RAP and with free calcium from FA and RAP; hence the coexistence of N-A-S-H gel and C-A-S-H products. Therefore, the 7-day UCS values of RAP-FA geopolymers increase with decreasing NaOH/Na2SiO3ratio. TCLP results demonstrated that there is no environmental risk for both RAP-FA blends and RAP-FA geopolymers in road construction. The geopolymer binder reduces the leaching of heavy metal in RAP-FA mixture. The outcomes from this research will promote the move toward increased applications of recycled materials in a sustainable manner in road construction.
authors.affiliation: School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand. Electronic address: menglim.hoy@gmail.com.
authors.forename: Menglim
authors.initials: M
authors.lastname: Hoy
authors.affiliation: School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand; Center of Excellence in Innovation for Sustainable Infrastructure Development, Suranaree University of Technology, Thailand. Electronic address: suksun@g.sut.ac.th.
authors.forename: Suksun
authors.initials: S
authors.lastname: Horpibulsuk
authors.affiliation: Department of Civil Engineering, Mahanakorn University of Technology, Thailand. Electronic address: runglawa@mut.ac.th.
authors.forename: Runglawan
authors.initials: R
authors.lastname: Rachan
authors.affiliation: School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand; Center of Excellence in Civil Engineering, Suranaree University of Technology, Thailand. Electronic address: avirut@sut.ac.th.
authors.forename: Avirut
authors.initials: A
authors.lastname: Chinkulkijniwat
authors.affiliation: Department of Civil and Construction Engineering, Swinburne University of Technology, Victoria 3122, Australia. Electronic address: aarulrajah@swin.edu.au.
authors.forename: Arul
authors.initials: A
authors.lastname: Arulrajah
mesh_terms: D060729:Coal Ash / Q000737:chemistry*; D019245:Compressive Strength; D060389:Construction Industry; D003252:Construction Materials; D015386:Hazardous Substances / Q000032:analysis* / Q000633:toxicity; D006838:Hydrocarbons / Q000737:chemistry*; D019216:Metals, Heavy / Q000032:analysis* / Q000633:toxicity; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D059027:Recycling; D013499:Surface Properties
chemical_list: D060729:Coal Ash; D015386:Hazardous Substances; D006838:Hydrocarbons; D019216:Metals, Heavy; D011108:Polymers; C006647:asphalt
keywords: Geopolymer; Heavy metals; Leachate analysis; Microstructure; Pavement structure; Recycled asphalt pavement