Title:
Hydration Effects of Limestone Replacement in High Volume Fly Ash Concrete
Author(s):
Aniruddha Baral
Publication:
Web Session
Volume:
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
10/17/2021
Abstract:
High volume fly ash concrete (HVFAC) provides lower-cost construction material with better durability, and enhanced sustainability metrics, but favorable early-age properties, such as setting time, air entrainment, and strength gain can be a challenge. Previous research has shown that accelerating the setting time of HVFAC can be achieved by replacing part of the cement with fine limestone powder. Fine limestone powder can accelerate the setting time of HVFAC potentially through two different mechanisms – (1) fine limestone can act as nucleation seeds and thus accelerate C-S-H precipitation, and (2) fine limestone can react with the aluminate phases present in fly ash to form monocarbonate and hemicarbonate phases. In this research, we investigated the setting time acceleration for cement replacement with both micro and nano limestone in HVFAC systems with polycarboxylate and lignosulfonate-based chemical admixtures using isothermal calorimetry. Nano limestone replacement accelerated the setting time more than micro limestone replacement. Moreover, the setting time acceleration by limestone replacement was higher in the class C fly ash mixes containing polycarboxylate-based admixture compared to lignosulfonate-based admixture. Further, the crystalline phases formed in the hydration reaction will be quantified with Rietveld XRD to provide a scientific explanation behind the observed set time acceleration both in terms of different crystalline phase formation and the role of limestone nucleation sites for accelerated C-S-H formation.