Coupling machine learning with thermodynamic modelling to develop a composition-property model for alkali-activated materials

Alkali-activation is one of the most promising routes for utilisation of versatile aluminosilicate resources. However, the variations of chemical compositions in these resources have increased the challenge of designing alkali-activated materials (AAMs) with multiple sources, posing the demand for establishing composition-property correlations that can represent a wide range of AAMs. This study proposes a data-driven approach to develop such composition-property correlations combining machine learning with global sensitivity analysis and thermodynamic modelling. The strength performance of alkali-activated concretes was investigated for a benchmark study (196 data inputs). The impact of the five key chemical compositions, CaO–SiO2–Al2O3–MgO–Na2O, has been assessed. The results show that despite the use of different aluminosilicate precursors, there appear to be coherent connections between bulk binder chemical compositions, phase assemblages, and the performance of AAMs. The composition-property correlations established via machine learning can be used to facilitate the on-demand design of AAMs utilising varying aluminosilicate resources.</p

A spatially-varying relaxation parameter Lattice Boltzmann Method (SVRP-LBM) for predicting the effective thermal conductivity of composite material

Functional filler-reinforced composite materials play critical roles in thermal management in various engineering applications. In this study, an in-house coded spatially-varying relaxation parameter Lattice Boltzmann Method (SVRP-LBM) solver has been developed for predicting the effective thermal conductivity (ETC) of simulated composite materials. A randomly dispersed filler generator (RDFG) incorporating Monte Carlo random sampling method has been developed for reconstructing the microstructure of composite materials. The artificial composite materials with functional fillers of different geometries and particle size are studied. The SVRP-LBM is validated against FVM perditions and theoretical models. The spatially-varying relaxation parameters method has been used to reflect materials with different thermophysical properties, including the interfacial contact resistance between the matrix-filler interfaces. It is demonstrated that the lowest relaxation parameters should be around 1.0 in order to achieve a higher accuracy of LBM predictions. The effects of filler geometry and particle sizes on the ETC are also assessed. The shape and orientation of the anisotropic filler have strong effects on the ETC. After the geometry of the filler in the numerical models being adjusted accordingly to the real fillers, the predictions show good agreement with experimental data. All in all, the SVRP-LBM solver has shown good capability and accuracy for predicting the ETC of composite material.</p

Improved Durability and Sustainability of Alkali-Activated Slag Cements

This study established the fundamental relationships between slag chemistry and reaction kinetics of sodium carbonate-activated slag. The application of the smart chemical addition CLDH for sodium carbonate-activated slag based on the understanding of slag chemistry, has not only made the sodium carbonate activator a plausible option for implementation, but more of a better option with performance advantages. The knowledge developed in this study about the ionic interaction between chlorides and individual reaction product filled in gaps in literature, and becomes a useful tool whose usage is not limited to tailing of sodium carbonate-activated slag, but also for optimising mix design of all types of AAS for achieving better performance

Assessing the long-term structural changes of metakaolin geopolymers encapsulating strontium loaded ion-exchanger

Zeolite-type inorganic ion-exchangers are extensively used in the nuclear industry to remove fission product radionuclides from contaminated process water and in groundwater cleanup. A significant amount of ion-exchangers loaded with concentrated radioactive isotopes of Sr are generated every year, and this is a particularly pressing issue in the Fukushima Daiichi site, where minimising the environmental release of these radioisotopes is currently the focus of much work. Encapsulation of these granular radionuclide-loaded ion-exchangers, which are often stored as slurries, into a stable solid waste form (as required for disposal) with a low leaching rate of toxic ions is challenging but critical for the safety of long-term geological disposal. Metakaolin geopolymers are attracting interest in the immobilisation of nuclear wastes. However, only limited information is available from the literature regarding the stability of key ion-exchangers in geopolymer binders, and the potential modifications occurring in the binder materials as a function of interactions with the ion exchangers. In this study, an ion exchanger representing those used in the Fukushima Daiichi wastewater treatment process, loaded with inactive isotopes of Sr, was encapsulated using metakaolin-based geopolymers. Different alkali cations were used as activators and the effects of different reaction temperatures were also assessed. The phase evolution, dimensional stability, and changes in microstructure of the geopolymer binders containing Sr-loaded ion-exchanger were characterised up to 1 year, to provide important information for evaluating the partitioning of Sr between the pore solution, ion-exchangers, and the binder

The effects of biomineralization on the localised phase and microstructure evolutions of bacteria-based self-healing cementitious composites

Microbially induced calcite precipitation (MICP) is one of the most effectivemechanisms to achieving self-healing abilities in cementitious composites. However, there has only been limited understanding of the effect of the MICP process on the mineralogy and microstructure of the cementitious matrix closely mixed with the healing products. This study systematically assessed the effect of biomineralization on the localised cementitious binders at micro and atomic level combining different characterisation techniques (i.e. XRD, FTIR and μCT). The results show that, in addition to the formation of CaCO3 polymorphs that close the crack space, the MICP process will also modify the phase assemblages near the healed cracks. For the first time we observed that when the most common source of calcium for the MICP process (calcium hydroxide) is limited, ettringite and C-S-H can also act as the providers of the calcium for the biomineralization process to take place. The detailed microstructure characterisations support that, apart from the dense thin layer (around 0.5 mm) of healing products formed on the surface of the cracks, loose particle-like calcium carbonate crystals can also form in pores and voids, suggesting that healing can also be generated in deeper sections of the crack. The outcomes of this study advance the fundamental understanding of the MICP process in Portland cement binders, and will also assist the further evaluation of the durability performances of these self-healed cementitious composites

Thermodynamic modelling of phase evolution in alkali-activated slag cements exposed to carbon dioxide

Carbonation of cementitious materials induced by their interaction with atmospheric CO2 is one of the main degradation mechanisms threatening their durability. In this study, a novel thermodynamic model to predict the phase evolution of alkali-activated slags exposed to an accelerated carbonation environment is presented. This model predicts the phase assemblages of carbonated alkali-activated slag cements, as a function of CO2 uptake under 1 v/v % CO2 conditions, considering the bulk slag chemistry and activators used. The changes taking place during the carbonation process regarding the physicochemical properties of the main binding gel, an alkali calcium aluminosilicate hydrate (C-(N)-A-S-H), the secondary reaction products CaAl and MgAl layered double hydroxides, and amorphous aluminosilicate gels, were simulated and discussed. The predictions of the thermodynamic model are in good agreement with experimental data retrieved from the literature, demonstrating that this is a valuable tool for predicting long-term performance of alkali-activated slag cements

Uptake of chloride and carbonate by Mg-Al and Ca-Al layered double hydroxides in simulated pore solutions of alkali-activated slag cement

Chloride ingress and carbonation are major causes of degradation of reinforced concrete. To enable prediction of chloride ingress, and thus to improve the durability of structural alkali-activated slag cement (AAS) based concretes, it is necessary to understand the ionic interactions taking place between chlorides, carbonates, and the individual solid phases which comprise AAS. This study focused on two layered double hydroxides (LDH) representing those typically identified as reaction products in AAS: an Mg-Al hydrotalcite-like phase, and an AFm structure (strätlingite), in simulated AAS pore solutions. Surface adsorption and interlayer ion-exchange of chlorides occurred in both LDH phases; however, chloride uptake in hydrotalcite-group structures is governed by surface adsorption, while strätlingite shows the formation of a hydrocalumite-like phase and ion exchange. For both Ca-Al and Mg-Al LDHs, decreased chloride uptakes were observed from solutions with increased [CO₃²⁻]/[OH⁻] ratios, due to the formation of carbonate-containing hydrotalcite and decomposition of AFm phases, respectively

Seizing the window of opportunity to mitigate the impact of climate change on the health of Chinese residents

The health threats posed by climate change in China are increasing rapidly. Each province faces different health risks. Without a timely and adequate response, climate change will impact lives and livelihoods at an accelerated rate and even prevent the achievement of the Healthy and Beautiful China initiatives. The 2021 China Report of the Lancet Countdown on Health and Climate Change is the first annual update of China’s Report of the Lancet Countdown. It comprehensively assesses the impact of climate change on the health of Chinese households and the measures China has taken. Invited by the Lancet committee, Tsinghua University led the writing of the report and cooperated with 25 relevant institutions in and outside of China. The report includes 25 indicators within five major areas (climate change impacts, exposures, and vulnerability; adaptation, planning, and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement) and a policy brief. This 2021 China policy brief contains the most urgent and relevant indicators focusing on provincial data: The increasing health risks of climate change in China; mixed progress in responding to climate change. In 2020, the heatwave exposures per person in China increased by 4.51 d compared with the 1986–2005 average, resulting in an estimated 92% increase in heatwave-related deaths. The resulting economic cost of the estimated 14500 heatwave-related deaths in 2020 is US$176 million. Increased temperatures also caused a potential 31.5 billion h in lost work time in 2020, which is equivalent to 1.3% of the work hours of the total national workforce, with resulting economic losses estimated at 1.4% of China’s annual gross domestic product. For adaptation efforts, there has been steady progress in local adaptation planning and assessment in 2020, urban green space growth in 2020, and health emergency management in 2019. 12 of 30 provinces reported that they have completed, or were developing, provincial health adaptation plans. Urban green space, which is an important heat adaptation measure, has increased in 18 of 31 provinces in the past decade, and the capacity of China’s health emergency management increased in almost all provinces from 2018 to 2019. As a result of China’s persistent efforts to clean its energy structure and control air pollution, the premature deaths due to exposure to ambient particulate matter of 2.5 μm or less (PM2.5) and the resulting costs continue to decline. However, 98% of China’s cities still have annual average PM2.5 concentrations that are more than the WHO guideline standard of 10 μg/m3. It provides policymakers and the public with up-to-date information on China’s response to climate change and improvements in health outcomes and makes the following policy recommendations. (1) Promote systematic thinking in the related departments and strengthen multi-departmental cooperation. Sectors related to climate and development in China should incorporate health perspectives into their policymaking and actions, demonstrating WHO’s and President Xi Jinping’s so-called health-in-all-policies principle. (2) Include clear goals and timelines for climate-related health impact assessments and health adaptation plans at both the national and the regional levels in the National Climate Change Adaptation Strategy for 2035. (3) Strengthen China’s climate mitigation actions and ensure that health is included in China’s pathway to carbon neutrality. By promoting investments in zero-carbon technologies and reducing fossil fuel subsidies, the current rebounding trend in carbon emissions will be reversed and lead to a healthy, low-carbon future. (4) Increase awareness of the linkages between climate change and health at all levels. Health professionals, the academic community, and traditional and new media should raise the awareness of the public and policymakers on the important linkages between climate change and health.</p

Characterization of supplementary cementitious materials by thermal analysis

Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required