171 research outputs found
Elucidating the Fresh and Hardened Properties of Limestone Calcined Clay Cements through Data Analytics
Limestone calcined clay cements (LC3) are a broad class of blended mineral compositions that are alternatives to conventional Portland cement (PC) and are one of the most promising technologies to achieve carbon neutrality in the concrete industry. However, a mechanistic understanding of fresh and hardened properties of LC3-based pastes, mortars, and concrete, as well as empirical design approaches are lacking. This dissertation addresses these knowledge gaps by developing composition-property linkages with the purpose of facilitating the transition of LC3 from the laboratory to practice. Specifically, the influence of LC3 composition on early hydration kinetics, rheological properties, compressive strength development and durability assessed by surface resistivity test is investigated. The compositional design space considers variations in water-to-solids ratio, proportions of constituent materials (PC, calcined clay or “metakaolin” (MK), limestone (LS)), added gypsum content, limestone particle size and superplasticizing admixture dosage. The composition-property linkages are established by combining laboratory data with data analytics approaches including Machine learning (ML).
A guiding hypothesis is that the sulfate balance (defined in this dissertation as time difference between the maximum of silicate peak and the sulfate depletion point measured during isothermal calorimetry), influences both the fresh (i.e., rheology) and hardened properties (e.g., compressive strength, surface resistivity) of LC3. To examine this, first, a non-parametric kernel regression technique Nadaraya-Watson (NW) estimator is applied to the heat evolution curves obtained from isothermal calorimetry, allowing quantification of the influence of compositional factors on early hydration kinetics (e.g., slope of silicate peak, sulfate depletion point) in a novel way. Thereafter, linkages between composition and sulfate balance are established first and then the hypothesis of the role of sulfate balance in influencing fresh and hardened properties of LC3 is tested in further chapters. Next, to predict the rheological behavior of LC3, domain knowledge is embedded in ML in the form of five physicochemical predictors, all based on composition. The ML modeling approach helps to elucidate the diversity of mechanisms through which the MK component dominates the rheological behavior of LC3, both directly and through its interactions with the other mineral constituents. Analytical measures (e.g., changes in portlandite and bound water contents over time) show how microstructural development translates to compressive strength and surface resistivity development. For instance, LC3 mortar strength over 28 days of hydration can be accurately predicted not only from its portlandite content over time, but also shows strong correlation with concrete surface resistivity development. Finally, a multi-objective optimization tool is developed to simultaneously predict LC3`s global warming potential and compressive strength development, which are two parameters central in the industrywide shift in cement compositions. Overall, this dissertation provides new foundational understanding of LC3`s early hydration kinetics and property evolution that supports the concrete industry`s adaptation to LC3; this work provides insights that not only rely on empirical findings but also generates models and analytical techniques that can be used to accurately predict fresh and hardened properties based on LC3 composition.Ph.D
Data-driven method for enhanced corrosion assessment of reinforced concrete structures
Corrosion is a major problem affecting the durability of reinforced concrete structures. Corrosion related maintenance and repair of reinforced concrete structures cost multibillion USD per annum globally. It is often triggered by the ingression of carbon dioxide and/or chloride into the pores of concrete. Estimation of these corrosion causing factors using the conventional models results in suboptimal assessment since they are incapable of capturing the complex interaction of parameters. Hygrothermal interaction also plays a role in aggravating the corrosion of reinforcement bar and this is usually counteracted by applying surface protection systems. These systems have different degree of protection and they may even cause deterioration to the structure unintentionally.
The overall objective of this dissertation is to provide a framework that enhances the assessment reliability of the corrosion controlling factors. The framework is realized through the development of data-driven carbonation depth, chloride profile and hygrothermal performance prediction models.
The carbonation depth prediction model integrates neural network, decision tree, boosted and bagged ensemble decision trees. The ensemble tree based chloride profile prediction models evaluate the significance of chloride ingress controlling variables from various perspectives. The hygrothermal interaction prediction models are developed using neural networks to evaluate the status of corrosion and other unexpected deteriorations in surface-treated concrete elements. Long-term data for all models were obtained from three different field experiments.
The performance comparison of the developed carbonation depth prediction model with the conventional one confirmed the prediction superiority of the data-driven model. The variable importance measure revealed that plasticizers and air contents are among the top six carbonation governing parameters out of 25. The discovered topmost chloride penetration controlling parameters representing the composition of the concrete are aggregate size distribution, amount and type of plasticizers and supplementary cementitious materials. The performance analysis of the developed hygrothermal model revealed its prediction capability with low error. The integrated exploratory data analysis technique with the hygrothermal model had identified the surfaceprotection systems that are able to protect from corrosion, chemical and frost attacks.
All the developed corrosion assessment models are valid, reliable, robust and easily reproducible, which assist to define proactive maintenance plan. In addition, the determined influential parameters could help companies to produce optimized concrete mix that is able to resist carbonation and chloride penetration. Hence, the outcomes of this dissertation enable reduction of lifecycle costs
Comminution in the Minerals Industry
Size reduction processes represent a significant part of the capital as well as the operating cost in ore processing. Advancing the understanding of and improving such processes is worthwhile since any measurable enhancement may lead to benefits, which may materialize as reductions in energy consumption or wear or improved performance in downstream processes. This book contains contributions dealing with various aspects of comminution, including those intended to improve our current level of understanding and quantification of particle breakage and ore characterization techniques that are relevant to size reduction, as well as studies involving modeling and simulation techniques. The affiliations of the authors of the articles published in this book span 14 countries around the globe, which attests to the highly international nature of research in this field. The themes of the manuscripts also vary widely, from several that are more focused on experimental studies to those that deal, in greater detail, with the development and application of modeling and simulation techniques in comminution. Size reduction technologies more directly addressed in the manuscripts include jaw crushing, vertical shaft impact crushing, SAG milling, stirred milling, planetary milling, and vertical roller milling. Ores involved directly in the investigations include those of copper, lead–zinc, gold, and iron as well as coal, talc, and quartz
Advances in Binders for Construction Materials
The global binder production for construction materials is approximately 7.5 billion tons per year, contributing ~6% to the global anthropogenic atmospheric CO2 emissions. Reducing this carbon footprint is a key aim of the construction industry, and current research focuses on developing new innovative ways to attain more sustainable binders and concrete/mortars as a real alternative to the current global demand for Portland cement.With this aim, several potential alternative binders are currently being investigated by scientists worldwide, based on calcium aluminate cement, calcium sulfoaluminate cement, alkali-activated binders, calcined clay limestone cements, nanomaterials, or supersulfated cements. This Special Issue presents contributions that address research and practical advances in i) alternative binder manufacturing processes; ii) chemical, microstructural, and structural characterization of unhydrated binders and of hydrated systems; iii) the properties and modelling of concrete and mortars; iv) applications and durability of concrete and mortars; and v) the conservation and repair of historic concrete/mortar structures using alternative binders.We believe this Special Issue will be of high interest in the binder industry and construction community, based upon the novelty and quality of the results and the real potential application of the findings to the practice and industry
Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete
An experimental evaluation of the crack propaga
tion and post-cracking response of macro
fiber reinforced concrete in flexure is c
onducted. Two types of structur
al fibers, hooked end
steel fibers and continuousl
y embossed macro-synthetic fibers are used in this study. A fiber
blend of the two fibers is evaluated for spec
ific improvements in the post peak residual load
carrying response. At 0.5% volume fraction, both
steel and macrosynthetic fiber reinforced
concrete exhibits load recovery at large
crack opening. The blend of 0.2% macrosynthetic
fibers and 0.3% steel fibers shows a significa
nt improvement in the immediate post peak load
response with a significantly smaller load drop and a
constant residual load carrying capacity
equal to 80% of the peak load. An analytical
formulation to predict fle
xure load-displacement
behaviour considering a multi-linear stress-
crack separation (σ
-w) relationship is developed.
An inverse analysis is developed for obtaining the multi-
linear σ
-w relation, from the
experimental response. The
�
-w curves of the steel and
macrosynthetic fiber reinforced
concrete exhibit a stress recovery after
a significant drop with increa
sing crack opening.
Significant residual load carrying capacity is attained
only at large crack separation. The fiber
blend exhibits a constant residual
stress with increasing crack sepa
ration following an initial
decrease. The constant residual stress is
attained at a small crack separation
Durability potential of Portland limestone cement concrete
There is an increasing global concern that has led to efforts to lessen the carbon footprint of the cement industry and make concrete manufacturing more sustainable by using other types of materials as supplements or alternatives, primarily for Portland cement (PC). This research work is concerned with the analytical systemisation, including the analysis, evaluation and structuring of global published experimental results, of ground limestone (GLS) used in concrete as a partial replacement of PC. The work is focussed on the physical and chemical characterisation of GLS and its effects on pore structure (in terms of porosity, water absorption and sorptivity), compressive strength and the durability of the concrete in terms of the carbonation and chloride ingress and the corrosion of steel reinforcement, including a statistical modelling of the carbonation of concrete with Portland limestone cement (PLC). Overall, it is suggested that, though the use of GLS up to 25% with PC should not impair the pore structure, the limit on GLS content for its effect on strength is likely to be about 15%. This should be considered where a higher proportion of GLS content is allowed in the standards. It is also shown that the carbonation rate and chloride ingress into concrete increase with increasing GLS content
Supplementary Cementitious Materials in Concrete
The articles featured in this Special Issue cover different aspects of the design, testing, and application of various types of supplementary cementitious materials in concrete. The results of the research, conducted by over 50 international universities and scientific centers, prove the great interest in the SCM topic
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