Microstructural and Durability of Alkali Activated Binders Based on Palm Oil Fuel Ash (POFA) and Fly Ash
Loading...
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
UNIVERSITI MALAYSIA SARAWAK
Abstract
Description
Ordinary Portland Cement (OPC) manufacture caused 5-8% carbon dioxide emission worldwide and the production of OPC is very unlikely to reduce as it is projected an increase in demand of production by 2050. Therefore, new binder innovations as construction materials is urgently needed. One of the latest innovations in construction materials is alkali activated binder (AAB). AAB is produced from the mixture of raw materials (precursor) and alkali activator solution. The precursors used in this study are Palm Oil Fuel Ash (POFA) and fly ash, while the alkali activator solutions are sodium hydoxide (NaOH) and combination of NaOH and sodium silicate (Na2SiO3) (mass ratio of 1:1). The main objectives of this study are to characterize the binding gel of alkali activated POFA and fly ash binders, to study the pore structure of AAB, and also to investigate the performance of AAB, as a function of precursor, activator, and curing age. Microstructural investigation was performed through Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDX). The samples were tested at 7, 28 and 90 days curing ages except the SEM-EDX test was conducted on all samples in 28 days. The water sorptivity test is to study the porosity of AAB. The samples also tested under sulfated environment. The binder gel formed in sole POFA is silica rich gel while sodium–alumina–silicate–hydrate (N–A–S–H) binding gel dominant in fly ash binder. When a combination of POFA and fly ash were used, N–A–S–H gel strongly influences the binder matrix. The choice of precursors and type of activator are the main factors in controlling porosity and mechanical strength of alkali activated POFA and fly ash binders. Alkali activated fly ash binder has the lowest coefficient of capillary absorption with highest mechanical strength compared to POFA binders. When comparing v the effect of activator used, NaOH activated pastes measured lower rate of capillary absorption and improved strength compared to NaOH and Na2SiO3 activated paste, for both POFA and fly ash. This implies that these materials have potential applications for strength performance, with differences in porosity which may impact the choice of binder application. All the pastes after sulfate attack are having reduction in compressive strength. The presence of the fly ash as the precursor influenced the increasing of the compressive strength. Binding gel types, the porosity and its mechanical strength, and phase evolution before and after sulfate attack of alkali activated POFA and fly ash based was established based on the analysis results.