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Title: Mix design, fresh and hardened properties and microstructural characterisation of alkali-activated concrete based on PFA/GGBS blends
Author: Rafeet , Ali Mohsin Issa
ISNI:       0000 0004 6059 5421
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2016
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Alkali-activated concrete (AAO) has recently emerged as a potential candidate to replace the conventional Portland cement concrete (PGC) in several applications due to its low CO2 footprint and promising mechanical properties. However, the absence of a widely accepted standardised mix design method for AAC limits its commercialisation. Moreover, some technical problems such as the need for elevated temperature curing and the lack of sufficient data on both hardened and fresh properties of AAO among others played a major role in limiting the industrial uptake of this green alternative. In this thesis, fly ash from coal fired power stations and ground granulated blast furnace slag from iron production have been investigated as binders to replace Portland cement. The influence of salient parameters such as percentage of GGBS in PFA/GGBS blend, paste content, binder content, water-to-solid ratio (w/s) on setting time, workability and compressive strength of AAC is investigated. The findings obtained from this investigation helped to suggest mix design guidelines for PFA/GGBS AAC to achieve a wide range of compressive strength (20-70 MPa) and consistency classes (S1-S5) with “optimized" binder content in the range of 320-350 kg/m3. The main reaction product observed in 100% PFA systems cured at 70 °C was low Ca geopolymer gel (N-A-S-H). Blends with 20% GGBS content and higher (cured at 20 °C) exhibited higher reactivity and microstructural development and the extent of reactivity increased with the increase in GGBS content. Higher GGBS blends i.e. 60/40 and 30/70 showed solid and compact microstructure compared to low GGBS blends in agreement with higher compressive strengths obtained in those blends. C-A-S-H binding gel was detected as the main reaction product in blends with 20% GGBS and higher. Alternative silicate activators produced from rice husk ash (RHA), glass cullet (GC) and microsilica were found to be effective with PFA/GGBS blends and gave comparable strengths compared to commercial silicate activators. These alternative activators can reduce both the cost and the embodied energy of AAC.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available