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Title: Microstructure, Mechanical Performance, and Chloride Binding of Seawater Cured Portlandite-Calcined Clay Binders

Author(s): Borno

Publication: Web Session

Volume: ws_S22_Borno.pdf

Issue:

Appears on pages(s):

Keywords:

DOI:

Date: 3/28/2022

Abstract:
This study presents an attempt to recreate ancient lime-pozzolana binders using slaked lime, calcined clay, and seawater. Calcined clay with blended minerals (kaolin and montmorillonite) was first mixed with portlandite at a 3:1 ratio to prepare different binder batches. Artificial seawater (water to binder ratio = 0.55) was then added to the binder batches to prepare paste samples. Paste samples were cured in the artificial seawater at around 23?. The microstructural development of the paste samples was studied using various experimental techniques including isothermal calorimeter, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). The compressive strengths of the paste batches after 7 and 28 days of curing in seawater were also measured. Additionally, the chloride and sulfate binding of the calcined clay paste samples were measured using X-ray fluorescence. Due to the alkalinity of seawater (pH = 8.3), it significantly activated the reaction between portlandite and calcined clay mixtures giving heat of reaction profiles similar to those of Portland Cement paste. The paste batches formed hydrocalumite and ettringite at the early stage of the curing (before 7 days). After more than 56 days of curing, the paste batched formed a dense microstructure containing amorphous gel, hydrocalumite, ettringite, and phillipsite (zeolite). 29Si and 27Al NMR spectra revealed that the amorphous phase primarily contained C-A-S-H and geopolymer gels. Additionally, the results show higher chloride and sulfate binding capacity of the calcined clay samples compared to that of the Ordinary Portland Cement (OPC) samples.