Date of Award

Fall 12-21-2019

Level of Access

Open-Access Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

Advisor

Warda Ashraf

Second Committee Member

Eric N. Landis

Third Committee Member

Roberto Lopez-Anido

Abstract

This study investigated the potential application of wollastonite as a cementitious material in both hydrated and carbonated binder systems. Wollastonite is naturally occurring low-lime calcium silicate (CaO.SiO2) mineral with a substantially lower carbon footprint compared to the ordinary Portland cement (OPC). The first part of this work presented the application of wollastonite as partial replacement of OPC in traditional hydrated cement-concrete system. Second part of this work evaluated the properties of carbonation activated binder produced using wollastonite as the primary ingredient.

For the first part of the thesis, ground wollastonite with 3.5 µm and 9 µm mean particle sizes were used to replace 10% to 50% by weight of cement in paste and mortar mixers. The influence of ground wollastonite was compared with that of ground limestone. The performance of cementitious mixtures containing ground wollastonite and ground limestone has been monitored through isothermal calorimeter, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM). Ground wollastonite was observed to accelerate the OPC hydration due to the filler effect. Ground wollastonite accelerated the hydration reaction of calcium silicate and calcium aluminate phases present in OPC. Wollastonite with mean particle size of 9 µm remained chemically inert up to 28 days of curing, whereas wollastonite with mean particle size 3.5 µm consumed some Ca(OH)2 due to a slow pozzolanic reaction in the hydrated system. Combining all these effects, up to 30% replacement of OPC by wollastonite with mean particle size 3.5 µm in hydraulic mortar mixer reduced the compressive strength by less than 10%.

In the second phase of the thesis, wollastonite with mean particle size 9 µm was cured CO2 containing environment in the presence of Amino Acids. The primary binding phase of CO2 activated wollastonite is CaCO3 and Ca-modified silica gel. The formation of inorganic CaCO3 minerals in natural environments occur in the presence of organic molecules which results in organic-inorganic hybrid materials (biominerals) with remarkable toughness and resilience. Inspired by this biomineralization process, this part of study focused on the effectiveness of biominerals to control the crystallization of CaCO3 in carbonated wollastonite system. Four different amino acids were used as the biochemical source, including L-valine (non-polar, hydrophobic), L-serine (polar), L-arginine (positively charged, basic) and L-aspartic acid (positively charged, acidic). The fracture properties of this system were monitored using a notched beam samples following the Jeng-Shah two parameter model. L-Aspartic acid was most effective in stabilizing amorphous CaCO3 (ACC) and reducing crystal size, and L-Serine stabilized both ACC and vaterite. Formation of these metastable CaCO3 polymorphs were found to increase the flexural strength up to 113%. Amino acids containing carbonated composites have been observed to lower up to 61% of the modulus of elasticity. Carbonated composites have the same energy for crack initiation, but because of metastable ACC, amino acid containing batches have up to 156% higher energy for crack propagation.

Available for download on Friday, December 10, 2021

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