Recycled asphalt pavement - fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations

Menglim Hoy; Suksun Horpibulsuk; Runglawan Rachan; Avirut Chinkulkijniwat; Arul Arulrajah

doi:10.1016/j.scitotenv.2016.08.078

Recycled asphalt pavement - fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations

Sci Total Environ. 2016 Dec 15:573:19-26. doi: 10.1016/j.scitotenv.2016.08.078. Epub 2016 Aug 19.

Authors

Menglim Hoy¹, Suksun Horpibulsuk², Runglawan Rachan³, Avirut Chinkulkijniwat⁴, Arul Arulrajah⁵

Affiliations

¹ School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand. Electronic address: menglim.hoy@gmail.com.
² 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.
³ Department of Civil Engineering, Mahanakorn University of Technology, Thailand. Electronic address: runglawa@mut.ac.th.
⁴ 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.
⁵ Department of Civil and Construction Engineering, Swinburne University of Technology, Victoria 3122, Australia. Electronic address: aarulrajah@swin.edu.au.

PMID: 27544652
DOI: 10.1016/j.scitotenv.2016.08.078

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/Na₂SiO₃ ratios 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 Na₂SiO₃ reacted 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/Na₂SiO₃ ratio. 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.

Keywords: Geopolymer; Heavy metals; Leachate analysis; Microstructure; Pavement structure; Recycled asphalt pavement.

MeSH terms

Coal Ash / chemistry*
Compressive Strength
Construction Industry
Construction Materials*
Hazardous Substances / analysis*
Hazardous Substances / toxicity
Hydrocarbons / chemistry*
Metals, Heavy / analysis*
Metals, Heavy / toxicity
Microscopy, Electron, Scanning
Polymers / chemical synthesis
Polymers / chemistry*
Recycling*
Surface Properties

Substances

Coal Ash
Hazardous Substances
Hydrocarbons
Metals, Heavy
Polymers
asphalt