Thermodynamic Modelling of CaO-Al2O3-SiO2-H2O-Based Cements

Most concrete is produced using calcium (alkali) aluminosilicate hydrate (C-(N-)A-S-H)-based cement. However, the chemistry of this phase in many cement-based materials is still not fully understood. This thesis presents a structural and thermodynamic investigation of C-(N-)A-S-H and C-(N-)A-S-H-based cements to provide insight into the chemistry of these materials. A mixed cross-linked and non-cross-linked tobermorite-like structural model for C-(N)-A-S-H is developed (the CSTM), which more appropriately describes the spectroscopic information available for this phase. Application of the CSTM to a Na2SiO3-activated slag cement cured for 56 and 180 days indicates the presence of a poorly-crystalline zeolite-like phase. The role of Al in cross-linking of C-(N-)A-S-H is also studied, which provides a more advanced description of the chemistry and structure of C-(N-)A-S-H than previously reported. A thermodynamic model for C-(N-)A-S-H (CNASH_ss) is derived, which greatly advances the utility of thermodynamic modelling of C-(N-)A-S-H-based cements by explicitly defining Al and alkali uptake in this phase. The chemistry of alkali-activated slag (AAS)-based cements is simulated using CNASH_ss and an ideal solid solution thermodynamic model for MgAl-OH-LDH that is also developed in the thesis. This analysis provides a good description of Na2SiO3-activated slag cement chemistry and accurately predicts chemical shrinkage in this material. Phase diagrams for NaOH, Na2SiO3, Na2Si2O5 and Na2CO3-activated slag-based cements are also simulated. These results can be used to design the chemistry of AAS-based materials. A detailed analysis of C-(N-)A-S-H solubility is presented, for Ca, Al, Si and alkali concentrations most relevant to C-(N-)A-S-H-based cements and at temperatures of 7-80°C. Solubility products for alkali-free C-(N-)A-S-H change slightly between 7°C and 80°C and as a function of Al/Si ratio. However, less soluble C-(N-)A-S-H is formed at higher Ca and alkali content. These results are important for understanding the stability of C-(N-)A-S-H in the majority of cement-based materials used worldwide

Implications of Emerging Vehicle Technologies on Rare Earth Supply and Demand in the United States

We explore the long-term demand and supply potentials of rare earth elements in alternative energy vehicles (AEVs) in the United States until 2050. Using a stock-flow model, we compare a baseline scenario with scenarios that incorporate an exemplary technological innovation: a novel aluminum–cerium–magnesium alloy. We find that the introduction of the novel alloy demonstrates that even low penetration rates can exceed domestic cerium production capacity, illustrating possible consequences of technological innovations to material supply and demand. End-of-life vehicles can, however, overtake domestic mining as a source of materials, calling for proper technologies and policies to utilize this emerging source. The long-term importing of critical materials in manufactured and semi-manufactured products shifts the location of material stocks and hence future secondary supply of high-value materials, culminating in a double benefit to the importing country. This modeling approach is adaptable to the study of varied scenarios and materials, linking technologies with supply and demand dynamics in order to understand their potential economic and environmental consequence

Local terrestrial biodiversity impacts in life cycle assessment:A case study of sedum roofs in London, UK

Urban development is a key driver of global biodiversity loss. “Green” infrastructure is integrated to offset some impacts of development on ecosystem quality by supporting urban biodiversity, a prominent example being green roofs. The effects of green infrastructures on urban biodiversity are not well understood and poorly included in life cycle assessment (LCA) methodology. Here, we present a novel methodology that quantifies the local impact of green infrastructures on terrestrial biodiversity—demonstrated here for sedum roofs in London, UK—and integrates within LCA. It relates energy provision by plants to the metabolic requirements of animals to determine what species richness (number of species) and species abundance (number of individuals) are supported. We demonstrate this methodology using a case study, comparing the life cycle impact of developing 18 buildings, with either asphalt concrete or sedum roofs, on ecosystem quality. We found the sedum roofs (0.018 km 2) support 53 species (673 individuals), equivalent to 1.3% of the development's life cycle impacts on ecosystem quality. Complete offsetting requires considerable reduction in transport use throughout the development's lifetime, and lower environmental impact material selection during construction (contributing 98% and 2%, respectively). The results indicate sedum roofs offer minor impact mitigation capacities in the context of urban development, and this capacity is limited for all green infrastructures by species richness in local species pools. This paper demonstrates the potential and limitations of quantifying terrestrial biodiversity offsets offered by green infrastructures alongside urbanization, and the need for realistic expectations of what role it might play in sustainable urban design.</p

Local Terrestrial Biodiversity Impacts in Life Cycle Assessment: A Case Study of Sedum Roofs in London, UK

Urban development is a key driver of global biodiversity loss. ‘Green infrastructure is integrated to offset some impacts of development on ecosystem quality by supporting urban biodiversity. A prominent example being green roofs. The effects of green infrastructures on urban biodiversity are not well understood and poorly included in life cycle assessment (LCA) methodology. Here, we present a novel methodology that quantifies the local impact of green infrastructures on terrestrial biodiversity – demonstrated here for sedum roofs in London, UKand integrates within LCA. It relates energy provision by plants to the metabolic requirements of animals, to determine what species richness (number of species) and species abundance (number of individuals) are supported. We demonstrate this methodology using a case study, comparing the life cycle impact of developing 18 buildings, with either asphalt concrete or sedum roofs, on ecosystem quality. We found the sedum roofs (0.018 km2) support 53 species(673 individuals), equivalent to 1.3% of the development’s life cycle impacts on ecosystem quality. Complete offsetting requires considerable reduction in transport use throughout the development’s lifetime, and lower environmental impact material selection during construction (contributing 98% and 2% respectively). The results indicate sedum roofs offer minor impact mitigation capacities in the context of urban development, and this capacity is limited for allgreen infrastructures by species richness in local species pools. This paper demonstrates the potential and limitations of quantifying terrestrial biodiversity offsets offered by green infrastructures alongside urbanisation, and the need for realistic expectations of what role it might play in sustainable urban design.<br/

YSTAFDB, a unified database of material stocks and flows for sustainability science

We present the Yale Stocks and Flows Database (YSTAFDB), which comprises most of the material stocks and flows (STAF) data generated at the Center for Industrial Ecology at Yale University since the early 2000s. These data describe material cycles, criticality, and recycling in terms of 62 elements and various engineering materials, e.g., steel, on spatial scales and timeframes ranging from cities to global and the 1800s to ca. 2013. YSTAFDB integrates this diverse collection of STAF data, previously scattered across various non-uniformly formatted electronic files, into a single data structure and file format. Here, we discuss this data structure as well as the usage and formatting of data records in YSTAFDB. YSTAFDB contains 100,000+ data records that are all situated in their systems contexts, with additional metadata included as available. YSTAFDB offers a comprehensive basis upon which STAF data can be accumulated, integrated, and exchanged, and thereby improves their accessibility. Therefore, YSTAFDB facilitates deeper understanding of sustainable materials use and management, which are key goals of contemporary sustainability science

Effect of Gypsum on the Early Hydration of Cubic and Na-Doped Orthorhombic Tricalcium Aluminate

The tricalcium aluminate (C3A) and sulfate content in cement influence the hydration chemistry, setting time and rheology of cement paste, mortar and concrete. Here, in situ experiments are performed to better understand the effect of gypsum on the early hydration of cubic (cub-)C3A and Na-doped orthorhombic (orth-)C3A. The isothermal calorimetry data show that the solid-phase assemblage produced by the hydration of C3A is greatly modified as a function of its crystal structure type and gypsum content, the latter of which induces non-linear changes in the heat release rate. These data are consistent with the in situ X-ray diffraction results, which show that a higher gypsum content accelerates the consumption of orth-C3A and the subsequent precipitation of ettringite, which is contrary to the cub-C3A system where gypsum retarded the hydration rate. These in situ results provide new insight into the relationship between the chemistry and early-age properties of cub- and orth-C3A hydration and corroborate the reported ex situ findings of these systems

Effect of gypsum on the early hydration of cubic and Na-doped orthorhombic tricalcium aluminate

The tricalcium aluminate (C3A) and sulfate content in cement influence the hydration chemistry, setting time and rheology of cement paste, mortar and concrete. Here, in situ experiments are performed to better understand the effect of gypsum on the early hydration of cubic (cub-)C3A and Na-doped orthorhombic (orth-)C3A. The isothermal calorimetry data show that the solid-phase assemblage produced by the hydration of C3A is greatly modified as a function of its crystal structure type and gypsum content, the latter of which induces non-linear changes in the heat release rate. These data are consistent with the in situ X-ray diffraction results, which show that a higher gypsum content accelerates the consumption of orth-C3A and the subsequent precipitation of ettringite, which is contrary to the cub-C3A system where gypsum retarded the hydration rate. These in situ results provide new insight into the relationship between the chemistry and early-age properties of cub- and orth-C3A hydration and corroborate the reported ex situ findings of these systems