Graduation Semester and Year
Spring 2025
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Civil Engineering
Department
Civil Engineering
First Advisor
Dr. Warda Ashraf
Abstract
The calcined clays are of great interest nowadays because of their potential to reduce the carbon footprint of the cement industry, while also enhancing the durability of concrete. Typically, this cementitious material is produced by calcining natural clays at a temperature range of 600 to 800℃, which also consumes energy. A limited number of studies have been carried out to determine if this temperature and the associated energy consumption can be further reduced. The aim of this study is to investigate the effect of the co-calcination of clay with alkaline hydroxide as a potential pathway to enhance the reactivities of calcined clay with high impurity and reduce their production energy requirements. Medium to low-grade clay was calcined with varying dosages of NaOH. The results showed that increasing NaOH content during co-calcination reduced the polymerization of the aluminosilicate network. However, higher Al content in the clay led to the recrystallization of sodium aluminosilicate (nepheline) in the presence of greater NaOH dosages. In contrast, for low-grade clay, the dissolution of both Al and Si improved with increasing NaOH content. Additionally, the amorphous content increased alongside the depolymerization of the aluminosilicate network. As a result, the pozzolanic properties, including R3 heat release and portlandite consumption, were enhanced through co-calcination. The calcination temperature and NaOH dosage were optimized specifically for this low-grade clay, with a temperature of 600°C and 2.5% NaOH by weight determined as the optimal combination. This optimization considered factors such as pozzolanic performance, the effectiveness of the alkali fusion system in minimizing free Na₂O leaching, compressive strength, and energy requirements for calcination. Furthermore, the effects of co-calcining individual clay minerals (kaolinite and montmorillonite) and certain non-clay minerals (quartz and feldspar) with varying NaOH dosages were evaluated. The study revealed that the polymerization of the silicate network in quartz and the aluminosilicate network in clay minerals decreased in the presence of NaOH during calcination. Consequently, the dissolution of Al and Si improved, enhancing pozzolanic properties. The findings revealed that the efficiency of co-calcination, including the dissolution of reactive Al and Si as well as the consumption of portlandite, decreased with increasing Al2O3: SiO2 in the precursor. Notably, this approach enabled the effective utilization of certain minerals by enhancing their Si dissolution by approximately 300% and portlandite consumption by 250% after 28 days. However, this approach was found to be highly dependent on the clay mineralogy. This method provides a promising approach to enhance the reactivity of clay with inert impurities like quartz, particularly where the availability of 1:1 clay minerals is limited, thus expanding their potential as SCM.
Keywords
Calcined clay, Aluminosilicate, Dissolution, Kaolinite, Montmorillonite, Quartz, Supplementary cementitious materials
Disciplines
Structural Engineering
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Borno, Ishrat Baki, "INSIGHTS ON THE ROLE OF CO-CALCINING CLAY WITH ALKALI HYDROXIDES" (2025). Civil Engineering Dissertations. 510.
https://mavmatrix.uta.edu/civilengineering_dissertations/510