An overview of the remaining challenges of the RILEM TC 274-TCE, testing and characterisation of earth-based building materials and elements

Based on the RILEM Technical Committee 274-TCE work, this paper is a discussion of the remaining engineering challenges faced by earthen architecture. The assessment of earth material performances requires the development of appropriate procedures and standards. This is discussed in particular for the characterisation, hygrothermal behaviour, mechanical behaviour, and durability of earth materials. One other important challenge, since one of the main advantages classically put forward, is its ecological performance, is a proper assessment of life cycle assessment of earth materials, elements and buildings. Moreover, the paper develops why the approach to earthen construction must be different compared to the dominant construction materials, to preserve its ability to contribute to the ecological transition in the construction sector. In particular, the needs of using local soils, with an architectural approach coping with the limits of the materials, and developing an architectural optimisation to preserve the earthen materials multifunctionality rather than selecting a sole property to be maximised. Lastly, the findings of the paper can be used to develop a holistic approach to earthen construction to foster the development of new earthen architecture projects.

Advancing cement-based materials design through data science approaches

The massive scale of concrete construction constrains the raw materials’ feedstocks that can be considered – requiring both universal abundance but also economical and energy-efficient processing. While significant improvements– from more efficient cement and concrete production to increased service life – have been realized over the past decades through traditional research paradigms, non-incremental innovations are necessary now to meet increasingly urgent needs, at a time when innovations in materials create even greater complexity. Data science is revolutionizing the rate of discovery and accelerating the rate of innovation for material systems. This review addresses machine learning and other data analytical techniques which utilize various forms of variable representation for cementitious systems. These techniques include those guided by physicochemical and cheminformatics approaches to chemical admixture design, use of materials informatics to develop process-structure-property linkages for quantifying increased service life, and change-point detection for assessing pozzolanicity in candidate supplementary cementitious materials (SCMs). These latent variables, coupled with approaches to dimensionality reduction driven both algorithmically as well as through domain knowledge, provide robust feature representation for cement-based materials and allow for more accurate models and greater generalization capability, resulting in a powerful design tool for infrastructure materials.

Recent developments in reactivity testing of supplementary cementitious materials

Identification and rapid characterization of novel supplementary cementitious materials (SCMs) is a critical need, driven by shortfalls in conventional SCMs. In this study, we present a discussion of recently developed reactivity tests – the R3 test, the modified R3 test, the lime strength test, and the bulk resistivity index test. These tests measure reactivity parameters such as heat release, bound water, calcium hydroxide consumption, strength, and bulk resistivity. All tests can screen inert from reactive materials. To additionally differentiate pozzolanic and latent hydraulic materials, two parameters, for example, calcium hydroxide consumption and heat release, are needed. The influences of SCM bulk chemistry, amorphous content, and fineness on measured reactivity are outlined. Reactivity test outputs can predict strength and durability of cement paste/mortar/concrete; however, caution must be exercised as these properties are influenced by a variety of other factors independent of reactivity. Thoughts are provided on using reactivity tests to screen materials for concrete durability.

Life Cycle Assessment of alkali activated materials: preliminary investigation for pavement applications

The capital investment in the US for construction and maintenance of the infrastructure road network is $150 billion/year. Investments in OECD countries will likely stabilize, while other countries will face an exponential growth of investments for infrastructures driven by the development of metropolitan cities. Continued “business-as-usual” practice for portland and asphalt cement concrete pavement construction ignores the increasing warning calls for the identification of more sustainable and less energy intensive paving materials. Alkali activated materials concrete (AAM) have been studied with growing interest during the last three decades. AAM show promising results in terms of mechanical performance, while also having a global warming potential impact 30-80% less than that of portland cement concrete. The global warming potential of AAM is closely dependent on the: 1) activating solution used to activate the raw material and 2) origin of the raw material. Specifically, the impact of the transport for both of these components is ~ 10% of its global warming potential. Hence, to increase the adoption of AAM for pavements, it is fundamental to analyze the existing literature to clarify the link between environmental impact and mechanical performance, identifying opportunities for applications that are tailored to the local availability of raw material.

Opportunities and challenges for engineering construction materials as carbon sinks

Population growth and urbanization over the coming decades are anticipated to drive unprecedented demand for infrastructure materials and energy resources. Unfortunately, factors such as the degree of resource consumption, the energy-intensive nature of production, and the chemical-reaction driven emissions make infrastructure materials production industries among the greatest contributors to anthropogenic CO2 emissions. Yet there is an often-overlooked potential environmental benefit to infrastructure materials: most remain in use for decades and their long service lives can facilitate extended storage of carbon. In this perspective, we present an overview of recent technological advancements that can support infrastructure materials acting as a global, distributed carbon sink and discuss areas for further research and development. We present mechanisms to quantify the extent to which the embodied carbon will be removed from the carbon cycle for a long enough period of time to provide carbon sequestration and climate benefit. We conclude that it is possible to unlock the vast potential to engineer a carbon sequestration system that simultaneously meets societal need for expanding infrastructure systems; however, complexities in how these systems are engineered must be systematically and quantitatively incorporated into materials design.

Numerical simulation of multi-layer 3D concrete printing

This paper presents a computational fluid dynamics model fit for multi-layer 3D Concrete Printing. The numerical model utilizes an elasto-visco-plastic constitutive model to mimic the flow behaviour of the cementitious material. To validate the model, simulation data is compared to experimental data from 3D printed walls. The obtained results show that the numerical model can reproduce the experimental results with high accuracy and quantify the extrusion load imposed upon the layers. Such load is found to exceed the material’s yields stress in certain regions of previously printed layers, leading to layer deformation/flow. The developed and validated numerical model can assist in identifying optimal printing strategies, reducing the number of costly experimental print failures and human-process interaction. By doing so, the findings of this paper helps 3D Concrete Printing move a step closer to a truly digital fabrication process.

Pavement energy harvesting technologies: a critical review

The world energy consumption is constantly increasing and the research point towards novel energy harvesting technologies. In the field of pavement engineering, the exploitable sources are the solar radiation and the vehicle load. At present, these systems are able to convert the sunlight into electricity thanks to some solar cells placed under a semi-transparent layer (photovoltaic roads), or they can harvest thermal heat by means of solar thermal systems. The thermal gradient of the pavement can be exploited by thermoelectric generators, by heat pipes or by heat-transfer fluids (i.e. water) pumped into a medium (asphalt solar collectors, porous layer or air conduits). The traffic load can be exploited by piezoelectric materials, able to convert the vehicle load into an electrical charge. The aim of this paper is to describe the main pavement energy harvesting technologies, pointing out positives and negatives and providing indications for further optimizations. Finally, the systems are compared in terms of initial cost, electrical output, efficiency and technology readiness level.

Concrete damage due to oxidation of pyrrhotite-bearing aggregate: a review

Oxidation of pyrrhotite-bearing aggregates is one of the major causes of concrete damage in numerous buildings in Trois-Rivières in Canada and Connecticut in the USA. In the presence of moisture and oxygen, pyrrhotite oxidizes to generate iron-and sulfate-rich secondary minerals that cause internal sulfate attack. Iron sulfides are accessory minerals of different rock types. The distribution of sulfides is often very heterogeneous in terms of aggregate particles, even at the level of the quarries in which some areas may contain copious amounts than others, which complicates the sampling method. Pyrrhotite is a complex mineral with varying chemical composition, crystallographic structure, and specific surface area. These factors influence the reactivity of pyrrhotite. Therefore, it is challenging to control the quality of the aggregate sources. In this study, recent advances in the identification and quantification of pyrrhotite to diagnose complicated cases are presented, and a performance-based approach for the quality control of new sources of aggregates is introduced. The performance-based approach is preferred because it eliminates the influence of the oxidation of pyrrhotite.

Sharp Front analysis of moisture buffering

Moisture buffering describes the use of materials with high water-vapour sorption capacity to provide humidity control in interior spaces. Established models of the moisture dynamics of buffering are derived from conventional Fickian vapour-diffusion equations. We describe an alternative analysis using a Sharp-Front formulation. This yields a similar expression for the moisture effusivity, several consistent scalings and a new definition of the moisture penetration depth. Features of the model are compared with some published experimental data. A new sorption buffer index is a measurable experimental property that describes the water-vapour buffer strength of the material.

Progress and opportunities in modelling environmentally assisted cracking

Environmentally assisted cracking phenomena are widespread across the transport, defence, energy and construction sectors. However, predicting environmentally assisted fractures is a highly cross-disciplinary endeavour that requires resolving the multiple material-environment interactions taking place. In this manuscript, an overview is given of recent breakthroughs in the modelling of environmentally assisted cracking. The focus is on the opportunities created by two recent developments: phase field and multi-physics modelling. The possibilities enabled by the confluence of phase field methods and electro-chemo-mechanics modelling are discussed in the context of three environmental assisted cracking phenomena of particular engineering interest: hydrogen embrittlement, localised corrosion and corrosion fatigue. Mechanical processes such as deformation and fracture can be coupled with chemical phenomena like local reactions, ionic transport and hydrogen uptake and diffusion. Moreover, these can be combined with the prediction of an evolving interface, such as a growing pit or a crack, as dictated by a phase field variable that evolves based on thermodynamics and local kinetics. Suitable for both microstructural and continuum length scales, this new generation of simulation-based, multi-physics phase field models can open new modelling horizons and enable Virtual Testing in harmful environments.