Concrete is the most widely used construction material in the world whose production is an energy and water intensive process, with profound environmental impact (e.g., responsible for 5-8% of anthropogenic CO2 emissions). Most concrete is manufactured using Portland cement (PC) clinker, which is mainly produced by reacting limestone (calcium carbonate), clay (silica, alumina, and iron), and other ingredients such as alumina and iron oxide at temperatures up to 1450 °C. The main reaction product of PC hydration is calcium silicate hydrate (C-S-H) gel, which precipitates as nanometer sized particles containing a quasi-two-dimensional, polymerized layered structure. C-S-H acts as the primary binding phase in the hydrated PC matrix. Concretes can be made more environmentally friendly by safely sequestering industrial wastes. When these industrial wastes are incorporated, there is an impact on the properties of the C-S-H phase. Understanding the relationships between C-A-S-H synthesis, chemistry and mechanical properties is needed to obtain concrete with desired properties and help formulate processes to reduce its carbon footprint.
We are bringing forth several state-of-the-art techniques to understand these relationships. We are also investigating sensors embedded in cement for building integrity for building material integrity.
- High pressure studies of C-A-S-H to understand concrete failure mechanisms (David)
- Sensors for building health monitoring (David)
Recently Completed Projects
High-Temperature Materials for Thermionic Energy Conversion
Thermionic energy converters are based on the emission of electrons from a hot cathode and their collection by a cooler anode. In this process, they convert heat directly into electricity and have the potential to achieve high efficiencies comparable to those of conventional heat engines. We collaborated with a team (consisting of Prof. Howe at Stanford, Prof. Igor Bargatin at Penn, and Spark Thermionics) to develop a microfabricated, close-gap thermionic energy converter for directly converting heat from a combustion source into electricity. One key challenge was associated with the cathode, which needed to be highly conductive and survive temperatures as hot as 2000 °C in an oxidizing environment. We developed processes for fabricating a SiC-protected W cathode and investigated its long-term stability under harsh environments of relevance to TECs.
High Surface Area Nanomaterials for Supercapacitors
Electrochemical storage devices, in particular batteries and supercapacitors, are devices with the potential to meet the energy storage demands of the future. Batteries are high energy capacity devices which store energy through redox reactions in the bulk material of the device. Supercapacitors are high power devices which store energy in the electrochemical double layer. We developed and characterized the performance of several classes of materials for high-energy density supercapacitor. In particular, we investigated high surface area (i.e., high storage capacity) electrode materials including porous silicon nanowires grown from bulk silicon, silicon carbide nanowires, and graphene. By understanding the relationship between synthesis conditions and material properties (e.g., conductance, porosity, and stability), we were able to achieve the highest energy and power storage densities reported in a silicon nanowire-based supercapacitor electrode.