Matthew R. Hall

Post-processing pathways in carbon capture and storage by mineral carbonation (CCSM) towards the introduction of carbon neutral materials

Carbon dioxide capture and storage by mineral carbonation (CCSM) is a technology that can potentially sequester billions of tonnes of carbon dioxide (CO2) per year. Despite this large potential, the costs of CCSM are currently too high for a large deployment of the technology and new systems are being investigated to attempt to overcome these limitations. To improve this situation, the successful development of post-processing routes creating marketable carbon neutral products could help the deployment of mineral carbonation. This work investigates the current market for CCSM products and the role they can play in decreasing the overall cost of CCSM technology. The current global market for the raw commodities, primarily cement additives, fillers and iron ore feedstock which could be produced by rock and/or industrial waste/by-product mineralisation, is about 27.5 Gt and can be easily flooded assuming 10% of the global CO2 emissions sequestered by CCSM. The CCSM technology chosen will play a very important role in the products created, available post-processing routes and accessible markets if the resultant materials are of high purity. Low-value applications such as fill for land reclamation may represent the only viable opportunity at the current state of the technology, bearing in mind that these materials are competing with low-cost materials (i.e. crushed rock) and that the size distribution of the carbonated materials may need significant alteration to make them potentially useful. However, there is a lack of information available on the quality of the CCSM products towards access to high-value markets such as micro-silica and PCC. In summary, CCSM post-processing might be viable only in niche high-value markets, while low-value applications such as land/mine reclamation are potentially more feasible and could be able to absorb Gts of CCSM products.

Influence of the Thermophysical Properties of Pavement Materials on the Evolution of Temperature Depth Profiles in Different Climatic Regions

The paper summarizes the relative influence of different pavement thermophysical properties on the thermal response of pavement cross sections and how their relative behavior changes in different climatic regions. A simplified one-dimensional (1D) heat-flow modeling tool was developed to achieve this by using a finite difference solution method for studying the dynamic temperature profile within pavement constructions. This approach allows for a wide variety and for daily varying climatic conditions to be applied, where limited or historic thermophysical material properties are available, and permits the thermal behavior of the pavement layers to be accurately modeled and modified. The model was used with available thermal pavement materials properties and with properties determined specifically for the study reported in this paper. The pavement materials included in the study comprised both conventional bituminous and cementicious mixes and unconventional mixtures that allowed a wide range of densities, thermal conductivities, specific heat capacities, and thermal diffusivities to be investigated. Initially, the model was validated against in situ pavement data collected in the United States in five widely differing climatic regions. It was found to give results at least as good as others available from more computationally expensive approaches such as two-dimensional (2D) and three-dimensional (3D) finite-element (FE) commercial packages. The model was then used to compute the response for the same locations where the thermal properties had been changed by using some of the unconventional pavement materials. This revealed that reduction of the temperature range by several degrees was easily possible (with implications for reduction of rutting, fatigue, and the urban heat island effect) and that depth of penetration of peak temperatures was also achievable (with implications for winter freeze and thaw). However, the results showed that there was little opportunity to displace the peak temperatures in time.

Enhancing thermal properties of asphalt materials for heat storage and transfer applications

This paper considers extending the role of asphalt concrete pavements to become solar heat collectors and storage systems. The majority of the construction cost is already procured for such pavements and only marginal additional costs are likely to be incurred to add the necessary thermal features. Therefore, asphalt concrete pavements that incorporate aggregates and additives such as limestone, quartzite, lightweight aggregate, copper slag, and copper fibre are designed to make them more conductive, or more insulative, or to enable them to store more heat energy. The resulting materials are assessed for both mechanical and thermal properties by laboratory tests and numerical simulations and recommendations are made in regard to the optimum formulations for the purposes considered.

Thermal, mechanical and microstructural analysis of concrete containing microencapsulated phase change materials

This paper studies the thermal, mechanical and microstructural aspects of concrete containing different amounts of microencapsulated phase change materials (PCMs). In addition, numerical simulation is carried out to study the potential application of PCM-modified concrete for reduction in summer surface temperature. It is shown that increasing PCM content in concrete led to lower thermal conductivity and an increase in the heat storage ability of concrete. However, the compressive and flexural strength of concrete significantly decreased. Microstructural analysis showed that PCMs appear to remain intact during mixing; however, PCM particles appear to fail by bursting under loading, creating hemispherical voids and crack initiation points as well as possible entrapped air behaviour. The result of numerical simulation revealed that reduction in summer concrete pavement surface temperature by several degrees was possible, with implications for reduction in concrete thermal stresses, shrinkage and urban heat island effect.

Ni Mg mixed metal oxides for p-type dye-sensitized solar cells

Mg Ni mixed metal oxide photocathodes have been prepared by a mixed NiCl2/MgCl2 sol-gel process. The MgO/NiO electrodes have been extensively characterized using physical and electrochemical methods. Dye-sensitized solar cells have been prepared from these films, and the higher concentrations of MgO improved the photovoltage of these devices; however, there was a notable drop in photocurrent with increasing Mg(2+). Charge extraction and XPS experiments revealed that the cause of this was a positive shift in the energy of the valence band, which decreased the driving force for electron transfer from the NiO film to the dye and, therefore, the photocurrent. In addition, increasing concentrations of MgO increases the volume of pores between 0.500 and 0.050 μm, while reducing pore volumes in the mesopore range (less than 0.050 μm) and lowering BET surface area from approximately 41 down to 30 m(2) g(-1). A MgO concentration of 5% was found to strike a balance between the increased photovoltage and decreased photocurrent, possessing a BET surface area of 35 m(2) g(-1) and a large pore volume in both the meso- and macropore range, which lead to a higher overall power conversion efficiency than NiO alone.

Nanocomposite materials for rapid-response interior air humidity buffering in closed environments

Three different mesoporous silica (MS) samples were selected as template materials for designing novel, high-performance desiccants to give rapid-response temperature and humidity buffering in closed environments. The aim was to investigate how the functional properties of the MS materials can be tuned to suit differing psychrometric conditions in closed environments, and to inform the design process by conducting sensitivity analysis using building performance simulation software. Their humidity buffering performance was compared with other materials using WUFI Pro v5.1 to conduct numerical hygrothermal simulations. The MS materials had more than two orders of magnitude greater humidity buffering than traditional interior building materials (e.g. painted gypsum plaster) due to their high vapour storage capacity and high dynamic vapour sorption (DVS) response rates. Analysis showed that the gradient of the w 50–w 80 portion of the absorption branch isotherm is the most sensitive parameter when using the hygrothermal numerical model as a design tool for materials tuning.

Thermophysical Optimization of Specialized Concrete Pavement Materials for Collection of Surface Heat Energy and Applications for Shallow Heat Storage

Great potential exists to use pavement structures to collect or store solar energy for heating and cooling of adjacent buildings, for example, airport terminals and shopping malls. Therefore, pavement materials comprising both conventional and unconventional concrete mixtures with a wide range of densities, thermal conductivities, specific heat capacities, and thermal diffusivities were investigated. The thermophysical properties were then used as inputs to a one-dimensional transient heat transport model to evaluate temperature changes at various depths at which heat might be abstracted or stored. Results indicated that a high diffusivity pavement (e.g., one that incorporated high conductive aggregates or metallic fibers, or both) could significantly enhance heat transfer as well as reduce thermal stresses across the concrete slab. However, a low diffusivity concrete could induce a more stable temperature at shallower depths and enable easier heat storage in the pavement, which would help to reduce the risk of damage caused by freeze–thaw cycling in cold regions.

Micro-Silica for High-End Application from Carbon Capture and Storage by Mineralisation

Waste silica remaining after the Carbon Capture and Storage by Mineral carbonation (CCSM) could represent a potential pozzolan material for partial replacement in concrete. The objective of this work was the production and testing of cement gel cubes with the residual-silica by-product obtained from the accelerated carbonation of Mg-silicate rocks. The silica produced was characterised in terms of its chemical composition, morphology and LOI. Also, the silica was used as an additive to the cement (CEM I class) in order to assess the effect on (28 days) compressive strength in comparison with a cement control specimen. The influence of different cement replacement percentages (5% and 10wt.% silica) were determined by measuring initial setting times and compressive strength. The compressive strength of the cement specimens with 5 and 10wt.% silica as pozzolan replacement of Portland cement were 3% and 8% higher than the control cubes indicating that the residual silica powder may have pozzolanic properties. However, high LOI and magnesium content might represent a limit in high-end applications and further work is required to identify optimised CCSM conditions able to reduce the impurities in the silica by-product and to establish their potential as a pozzolan.

9 – Soil stabilisation and earth construction: materials, properties and techniques

: This chapter describes the advantages and disadvantages of soil stabilisation, within the context of both soil mechanics and construction materials, and with specific reference to stabilised compressed earth construction, i.e. rammed earth and stabilised compressed earth blocks. Each of the key types of inorganic binder stabilisers are discussed at length including specific sections on high-calcium and naturally hydraulic hydrated limes, Portland cement and composite cements including pozzolanic materials and bituminous emulsions. In addition, stabilisation technologies such as synthetic and natural binders, including polymers, resins and adhesives, as well as fibre reinforcement are included. The chapter gives advice on stabiliser type selection and dosage rates with regard to compatibility with key soil characteristics, complemented by details of a selection tool and decision chart.

Enhancement of Soil Thermo-Physical Properties Using Microencapsulated Phase Change Materials for Ground Source Heat Pump Applications

Soil can be modified with Phase Change materials (PCM) in order to enhance its thermo-physical properties and energy storage for ground source heat pump applications. This paper studies thermo-physical properties of soil modified with different amount of microencapsulated PCM. It is shown that increasing PCM amount in soil lead to lower thermal conductivity and increase of volumetric heat capacity of PCM-modified soil across the PCM melting temperature range. In addition, numerical simulation is performed to study the potential application of PCM-modified soil for reduction of temperature variations in ground. The result of numerical simulation revealed that temperature variation under PCM-modified soil can be reduced by up to 3°C compared to conventional soil. This could improve the Coefficient of performance of a heat pump system by more than 17%.