Understanding the role of slag on geopolymer hardening and microstructural development

Puligilla, Sravanthi

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Description

Title

Understanding the role of slag on geopolymer hardening and microstructural development

Author(s)

Puligilla, Sravanthi

Issue Date

2011-08-25T22:10:56Z

Director of Research (if dissertation) or Advisor (if thesis)

Mondal, Paramita

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• User friendly geopolymer
• Ultrasonic Wave Reflection (UWR)
• fly ash-slag geopolymer
• hardening rate
• salicylic acid methanol extraction method
• Fourier transform infrared spectroscopy
• pore solution extraction

Abstract

The main objective of the present work was to understand the evolution of early age properties for successful application of geopolymer as an alternative binder. The early age properties like hardening (stiffening) and setting will determine the removal of formwork and thus the time of construction. The study was performed on user-friendly geopolymers obtained by using Class F flyash/slag/K-silicate/H2O. This involves the use of low concentration alkaline activators and low-temperature curing. A detailed investigation of microstructural development and hardening rate was presented for flyash and slag based geopolymers. Flyash and slag precursors were treated with potassium hydroxide-silicate activator of modulus 1.25 keeping SiO2/K2O = 5.1. For the first time in this study, ultrasonic wave reflection method along with Proctor penetration were used to determine the stiffening rate of geopolymers and their results correlated well. Microstructural development was investigated using SEM/EDS while the reaction rate was monitored through the use of semi-adiabatic calorimetry. An increase in the stiffening rate was observed with the addition of slag. It was concluded that the calcium dissolving from slag influences the early age properties significantly. Possible hypothesis to explain the role of slag on microstructure development and increased rate of stiffening is presented. Microstructural changes responsible for hardening were studied by characterizing geopolymer solids using Fourier transform infrared spectroscopy (FT-IR). The main drawback of using FT-IR was that Si-O-T (T =Al, Si) vibrations from the initial ash, geopolymer product and calcium silicate hydrate, yields an overlapping spectrum bands resulting in a broad hump which is difficult to interpret. This was resolved by separating the spectrum by selectively dissolving calcium silicate hydrate and geopolymer product. Calcium silicate hydrate and geopolymer product were selectively dissolved by salicylic acid extraction method and hydrochloric acid respectively. These extraction methods revealed the presence of calcium silicate hydrate in the samples supporting the theory. The pore solution extracted from geopolymer at various time intervals was also characterized through inductively coupled plasma spectroscopy for various ions like silicon, aluminum and calcium. As variation in ion concentrations was too high between multiple trials, no correlation could be established between the rate of product formation and change in ion concentration. The work on pore solution analysis will be repeated in the future after validating the test set up with more traditional system like cement paste and comparing data with existing literature.

Graduation Semester

2011-08

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http://hdl.handle.net/2142/26051

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Copyright 2011 Sravanthi Puligilla

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