The RILEM technical committee on Performance-based Asphalt Recycling TC 308-PAR is dedicated to advancing research, promoting knowledge exchange, and disseminating information related to asphalt material recycling. Within this framework, Task Group 1 (TG1) “Performance-based Evaluation of Cold Recycled Asphalt Mixtures” concentrates on aligning laboratory testing methods with the real-world performance of cold recycled asphalt mixtures. To this end, TG1 members collaborated to share the various cold recycling practices adopted in their respective countries. This collaboration aimed to compare specific procedures, technical specifications, and expected performance outcomes. The participants diverse backgrounds, spanning differences in road classifications, traffic loads, climatic conditions, and availability of materials, enabled the development of a comprehensive overview of current methodologies and provided insights into the potential expansion of cold recycling applications. The comparative study of national practices has been structured into two papers: Part I focuses on the constituent materials and mixture composition, while Part II addresses testing protocols and the construction process. In detail, Part II reports a critical comparison of testing procedures, mechanical characteristics, construction methods and quality control procedures used in Italy, Canada, Poland, Brazil and USA, either adopted by selected road administrations or established by reference standards. Accordingly, all initial assumptions, terminology, definitions, and the general context presented in Part I should be considered fully referenced and applicable. This paper focuses on recycling techniques using both cement and bitumen as binders. Conversely, although the use of cement alone is a recognized and widely applied technique, as reported in Part I, Part II does not consider it, since a greater degree of uniformity in procedures and knowledge has already been achieved and shared worldwide.

The durability of wastewater treatment plants has been a major concern for decades due to their significant economic and health importance. Structures built with concrete are subject to severe deterioration linked to aggressive chemical and biological exposure conditions. Portland cement concrete is particularly vulnerable to such attacks leading to major damages in the structures. One of the strategies to protect this concrete from the effects of biodeterioration is applying a thin coating based on calcium aluminate cement. These materials were proved to have a superior resistance to biodeterioration compared to ordinary Portland cement. However, the cracks initiated in the protected structure that might reach the coating raise questions on its ability to fulfill its protective role. This paper aims to study the effect of the crack on the durability of the coating using a biological laboratory test, the BAC test, which simulates the real conditions encountered in a sewer system. The calcium leached from the specimens exposed to the biogenic sulfuric acid attack was monitored in two campaigns of the BAC test. Each campaign was performed on reference OPC-based uncoated specimens and coated specimens with the CAC-based coating: uncracked and cracked with two ranges of crack width between 150 and 200 µm and between 400 and 500 µm. The leaching results demonstrate that the protective function was not altered by the effect of the cracks when comparing the reference uncoated specimen to the coated ones. The SEM-EDS observations show the existence of a newly-formed phase in the few hundreds of micrometers from the exposed surface of the coated specimens. This phase was composed mainly of calcium, sulfur and aluminum and was probably a mix of AH3 and ettringite. The formation of this phase near and inside the crack opening could possibly act as a physical barrier that prevents further deterioration.

With over 8% of global carbon emissions worldwide, the cement industry is challenged to lower its carbon footprint. Replacement of clinker in cementitious systems becomes crucial. Sound research proved that kaolinitic clays with as low as 40% kaolinite can have a high reactivity as SCM. Further research studies found a synergy between the aluminates in calcined clays and the carbonates in limestone that led to the proposal of a ternary binder called Limestone Calcined Clay Cement, LC3, consisting of 50% Portland Cement, 30% calcined clay and 15% limestone. This paper presents the efforts of a group of members from 41 universities and 17 industrial partners through the RILEM Technical Committee 282 – CCL: Calcined Clays as Supplementary Cementitious Materials. The work was oriented to fill existing information gaps on characteristics of clay minerals, the process of clay calcination, hydration of cementitious systems containing calcined clay and limestone, fresh and hardened properties of concrete, standardization, and durability of concrete produced with binders containing calcined clay and limestone. The TC 282-CCL has published 10 whitepapers, with a strong contribution to a better knowledge and understanding of the role of calcined clay in cement and concrete.

The cement and concrete industries are currently facing the urgent and arduous challenge of decarbonisation and material circularisation for improved resource efficiency. The pursuit of new raw materials and binders that will improve sustainability is urgent, especially as end-of-pipe carbon capture and storage (CCS) technologies have not yet been scaled up economically even after five decades of research and large investments. On the other hand, society is facing the colossal issue of managing mineral wastes which are produced in several Gts per year globally, posing a massive environmental and societal liability. Many of these mineral wastes have elemental and mineralogical profiles that make them good candidates for use as clinker raw feed or supplementary cementitious materials. Although the published research on the topic is extensive, it is not organised, lacking a systematic comprehensive approach, making valorisation challenging. RILEM TC UMW was developed to address this gap and create a framework for realising the potential of upcycling mineral wastes focusing on using powders as either clinker raw feed or other binder applications while excluding discussion on calcined clays and mineral carbonation.

This Technical Letter examines the mechanical behaviour of bio-aggregate building materials (BBM), focusing on their performance under compressive, flexural and shear loading. The study synthesises the findings of various RILEM technical committees and recent research, highlighting the unique properties of BBM compared to conventional concrete. The paper discusses the factors influencing the mechanical behaviour of BBM, including bioaggregate type, volume fraction, morphology, mineral matrix, mix design, casting process and curing conditions. It presents detailed analyses of the BBM response under different loading conditions, highlighting the different phases observed during testing. The use of Digital Image Correlation (DIC) as an advanced measurement tool to capture BBM deformation is explored, providing insights into the heterogeneity and local behaviour of the material. The importance of the Interface Transition Zone (ITZ) between bio-aggregates and matrix is highlighted, with a focus on its formation and impact on mechanical properties. The paper also outlines the perspectives of a new technical committee aimed at harmonising test procedures and developing scientific data analysis methods for BBM. This comprehensive review provides valuable insights for researchers and practitioners working with bio-based building materials, paving the way for improved understanding and standardisation of the mechanical characterisation of BBM.

In November 2023 this journal published “Thermal conductivity of porous building ma­terials: An exploration of new challenges in fractal modelling solutions”. That paper gauges four fractal building materials’ thermal conductivity models, concluding that fractal-geometry-based approa­ches appear “a promising method” as they “demonstra­te high reliability in repro­ducing experimental data”. This discussion of the pa­per aims to shine a different light on the potential of fractal thermal conductivity models. It shows that good agreement with experimental data usually ori­ginates from calibration of various “physical” factors comprised in these models, with the fitted numbers commonly deviating from physical rea­lity. Moreover, exemplary instances reveal that good agreement with experimental data is obtained des­pite misinterpretation of measured outcomes or critical defects in model development, or, exceptio­nally, due to fabrication of validation information. This discussion does hence not share the pa­per’s positive opinion on the prospects of fractal-geometry-ba­sed ther­­mal conductivity models, and advises caution instead.

This paper presents perspectives and progress in the emerging field of architected infrastructure materials. Recent developments in advanced and additive manufacturing with construction materials have led to new capabilities to define, design, and shape the internal arrangement and overall morphology of materials. In contrast to conventional casting techniques used in the construction of civil engineering materials, such advancements have allowed for purposeful designs of materials into specific morphologies across scales, referred to as architected infrastructure materials. Contrary to monolithic construction materials, architected materials present new opportunities to engineer enhanced mechanical properties and unique performance characteristics in civil infrastructure components through design. Here, we present an overview of the field and the research gaps in design, manufacturing, and materials mechanics. An overview of a few design opportunities, including bio-inspired strategies is discussed. Current advancements in the field are presented focusing on cement-based, non-hydraulic, and cementitious composite architected materials. The existing studies on bouligand, cellular, lattice, auxetic, tabulated, and gradient architected construction materials and their mechanically advantageous characteristics are reviewed. The future directions and perspectives for the field are outlined with respect to the current research gaps and upcoming opportunities.

Though the technical knowledge to make cement and concrete more sustainable already exists, implementation of solutions lags behind the rate needed to mitigate climate change and meet the targets set by the Sustainable Development Goals. Whilst most of the focus around the built environment is on embodied carbon, we stress an important but neglected dimension: partnership (SDG17). Effective partnerships can be powerful enablers to accelerate sustainable solutions in cement and concrete, and let such solutions transfer from academia to the market. This can be achieved through knowledge generation, solution implementation, and policy development, among other routes. In this article, we share five recommendations for how partnerships can address neglected research questions and practical needs: 1) reform Science, Technology, Engineering and Mathematics (STEM) education to train “circular citizens”; 2) map out routes by which cementitious materials can contribute to a “localization” agenda; 3) generate open-access maps for the geographical distribution of primary and secondary raw materials; 4) predict the long-term environmental performance of different solutions for low-CO2 cements in different geographical areas; 5) overhaul standards to be technically and regionally fit for purpose. These approaches have the potential to make a unique and substantial contribution towards achieving collective sustainability goals.

The needs for research on cementitious materials are reviewed with a focus on Europe. These are considered under 8 topics: clinker production, alternatives to Portland cement, composite cements based on Portland clinker, concrete, admixtures, durability, recycling, digitisation in concrete construction, and, carbon capture and use or storage; finally, the key research questions and their potential for CO2 reduction are summarised in a “Watermelon” diagram with a list of 30 key questions to be addressed (see Appendix).

Concrete is one of the most used materials after water. Largely owing to this, its environmental impact is substantial, although its embodied carbon per unit volume or mass is low when compared to most alternatives. This, along with the broad availability, good strength, durability and versatility of concrete means that it will remain a material of choice, although more efficient ways of using it must be found. Structurally optimized building components are a means to do this as they can save about 50% material. Unfortunately, however, such elements are presently too expensive to produce owing to them requiring non-standard formwork. It is an objective of digital fabrication to propose solutions to this issue. In this con-text, Digital Casting Systems (DCS) have advanced material control strategies for setting-on-demand in digital concrete processing. Thereby, the formwork pressure is reduced to a minimum, which opens possibilities of rethinking formworks as systems that are dynamically shaping, millimetre thin or weakly supporting the material cast inside. In this paper we present a brief overview of millimetre thin formworks and summarize the first realization of concrete elements that utilizes the mechanics of paper folding to make millimetre thin formworks up to 2.5 meters high. Such formworks could initially be flat packed, erected into shape, and eventually peeled-off and recycled in established material streams. This would reduce waste and transport cost, while offering a surface finish that meets the expectations for exposed concrete surfaces.