Material Structure

Radiation Damage of Concrete Aggregates

Concrete is used heavily in shielding of nuclear power plants, and storage of nuclear waste. In such environments, exposure to radiation is inevitable. While concrete is optimal for shielding such radiation from the outside (due to its water content), collision of high energy radiation with the aggregates (i.e. rocks and gravel bound together by cement) can lead to amorphization and increases in reactivity. When this radiation damage occurs for aggregates containing silica, the result is alkali-silica reaction (ASR). ASR is commonly known to result in expansion, cracking, and ultimate failure of the concrete. This research uses molecular dynamics simluations, which model physical movement of atoms and molecules, to assess the extent and nature of this radiation damage. Results provide a basis for developing mitigation strategies to prevent ASR from occurring in concrete exposed to radiation.

Material Processes

Carbon Neutral Cementation by Direct Carbonation

Global carbon dioxide emissions, 8-10% of which originate from the cement industry, are a growing problem. Ordinary portland cement and calcium hydroxide both have the potential to carbonate, thus consuming some of this carbon dioxide. This research investigates the carbonation of both of these materials in liquid and supercritical carbon dioxide. High levels of carbonation (>80%) are achieved within two hours in both forms of carbon dioxide, and carbonation in the presence of silica sand results in the formation of stable pellets. Though cementation quality remains to be tested, carbon neutral cementation by such a means would not only mitigate emissions from the construction industry, but could be used to consume flue gas from coal fired power plants or other major emissions sources. Results provide a basis for further investigation into the production of carbon neutral building elements, and hold the potential to revolutionize the green construction industry.

Material Properties

Moisture Transport in Cement Paste Pore Networks

Cement paste is an inherently porous material. Moisture resides within these pores, and the movement of this moisture in and out of the cement paste dictates its durability (i.e. creep, shrinkage, cracking, and transport of corrosive ions). Particularly during the first drying, when cement paste in concrete is exposed to low relative humidities, irreversible changes in pore structure occur. This phenomenon is measured via sorption isotherms, which track the attachement or detachment of single or multiple layers of water molecules from the pore surfaces using weight change at a constant temperature. This research compares sorption data with isotherm models, and develops a means to predict a sorption isotherm using degree of hydration and the initial water-to-solid ratio of the cement paste. Results elucidate the factors contributing to durability problems in cement paste and concrete, and provide an approach to predict beforehand how well or poorly a given cement paste formulation will behave, and how long it will last in the field.