Ph.D. Thesis Defense Announcement

Fundamental Understanding of NOx Sequestration Capacity and Pathways in Nano-TiO2

engineered Cementitious Materials

By

Qingxu (Bill) Jin

Advisor:

Dr. Kimberly E. Kurtis (CEE)

Committee Members:

Dr. Lawrence F. Kahn (CEE), Dr. Yuanzhi Tang (EAS), Dr. Emily Grubert (CEE), and

Dr. Jeffrey W. Bullard (CEE, Texas A&M)

Date & Time: Wednesday, October 16th, at 9:00 am

Location: Mason Building, Room 2119

The ubiquity of concrete in the urban environment and upscaling of nanomaterial production have prompted interest in the
incorporation of titania (TiO2) nanoparticles into cementitious materials. Air purification by TiO2-based cementitious materials
occurs by photocatalysts that capture nitrogen oxide species (NOx) from the atmosphere, oxidizing them into nitrite and nitrate
species. Because nitrite- and nitrate-based corrosion inhibitors are effective in improving corrosion resistance in reinforced
concrete, there is potential to develop nano-TiO2 engineered cementitious materials that transform NOx into corrosion inhibitors.
To provide guidelines for engineers and scientists to design such materials, a fundamental understanding of the NOx
sequestration capacity and pathways in cementitious materials is needed. This dissertation first develops a novel experimental
approach that combines water-based wet chemical extraction, UV-visible spectrophotometry, and ion chromatography to
quantify the NOx sequestration capacity in both plain and TiO2-modified cementitious pastes. Compared to plain cement pastes,
TiO2-modified cement pastes exhibit higher NOx uptake (in terms of nitrite and nitrate detected in the material) due to the
activation of photocatalytic reactions, greater surface area, and an increased amount of micropores with the addition of TiO2.
The detection of nitrite and nitrate ions in plain cement paste shows these materials have an intrinsic NOx sequestration
capacity but, the difference in NOx uptake between TiO2-modified ordinary portland cement (OPC) and calcium aluminate
cement (CAC) indicates that different NOx sequestration pathways occurred in these cements, which is likely due to differences
in chemical composition and hydrated cementitious phases.
To understand the NOx sequestration pathways in cementitious materials, various pure hydrated cementitious phases
were synthesized and their NOx uptake capacities were evaluated. Among non-carbonated phases, the highest NOx uptake
was measured in calcium silicate hydrate (C-S-H) phases. The NOx-converted nitrite and nitrate could either adsorb to the
surface of C-S-H or dissolve in pore solution. For aluminum (Al)-bearing phases, nitrite and nitrate ions were found to substitute
for the sulfate ions and form new phases. Because the main hydration product of OPC is a C-S-H phase and the primary
hydration product of CAC are aluminate-rich phases, the different NOx sequestration mechanisms and pathways between
C-S-H and Al-bearing phases explains the difference in the NOx uptake capacities of OPC and CAC. A synthetic calcite phase
was also examined in this research to investigate the effect of carbonation, which significantly improved NOx uptake capacity
compared to non-carbonated cementitious phases. The fundamental understanding of NOx sequestration pathways can be
used to design cementitious materials with optimized chemical composition for enhanced NOx sequestration and thus act as
corrosion inhibitors.