Performance of cementitious systems containing calcined clay in a chloride-rich environment: a review by TC-282 CCL.

In this review by TC- 282 CCL, a comprehensive examination of various facets of chloride ingress in calcined clay-based concrete in aggressive chloride-rich environments is presented due to its significance in making reinforced concrete structures susceptible to chloride-induced corrosion damages. The review presents a summary of available literature focusing on materials characteristics influencing the chloride resistance of calcined clay-based concrete, such as different clay purity, kaolinite content and other clay minerals, underscoring the significance of pore refinement, pore solution composition, and chloride binding mechanisms. Further, the studies dealing with the performance at the concrete scale, with a particular emphasis on transport properties, curing methods, and mix design, are highlighted.

Chloride-induced corrosion of steel in concrete-insights from bimodal neutron and X-ray microtomography combined with ex-situ microscopy.

Unlabelled: The steel-concrete interface (SCI) is known to play a major role in corrosion of steel in concrete, but a fundamental understanding is still lacking. One reason is that concrete's opacity complicates the study of internal processes. Here, we report on the application of bimodal X-ray and neutron microtomography as in-situ imaging techniques to elucidate the mechanism of steel corrosion in concrete.

Diffusion potentials in saturated hardened cement paste upon chloride exposure.

The diffusion potentials can cause significant errors in corrosion-related investigations of reinforced concrete structures (half-cell potential mapping, potentiometric sensors). Therefore, an improved understanding of the diffusion potentials in cement-based materials is needed. This study investigates the permselective behavior and its implication for the arising diffusion potentials.

Using micro-XRF to characterize chloride ingress through cold joints in 3D printed concrete.

Digital fabrication methods with concrete have been rapidly developing, with many problems related to component production and material control being solved in recent years. These processes produce inherently layered cementitious components that are anisotropic, and in many cases, produces a weak interface between layers, which are generally referred to as cold joints. While material strength at these interfaces has been well studied in recent years, durability has received less attention, even though cold joints can function as channels for aggressive agents, such as chlorides.

Speciation of iron(II/III) at the iron-cement interface: a review.

Steel is used as reinforcement in construction materials and it is also an important component of cement-stabilized waste materials to be disposed of in deep geological repositories for radioactive waste. Steel corrosion releases dissolved Fe(II/III) species that can form corrosion products on the steel surface or interact with cementitious materials at the iron-cement interface. The thermodynamically stable Fe species in the given conditions may diffuse further into the adjacent, porous cement matrix and react with individual cement phases.

Multiscale micromechanics modeling of plant fibers: upscaling of stiffness and elastic limits from cellulose nanofibrils to technical fibers.

The mechanical properties of natural fibers, as used to produce sustainable biocomposites, vary significantly-both among different plant species and also within a single species. All plants, however, share a common microstructural fingerprint. They are built up by only a handful of constituents, most importantly cellulose.

Does carbon footprint reduction impair mechanical properties and service life of concrete?

Unlabelled: The aim of this study is to evaluate how much the changes in the concrete mix design, which enable carbon footprint reduction, are impacting mechanical properties and predicted service life of concrete structure. The starting point of this study was concrete mix used in a recent reinforced concrete Pelješac Bridge in the Adriatic. In the first round of experiments the amount of cement in this initial mix was significantly lowered, without jeopardising workability of the mix.

A long-term study on structural changes in calcium aluminate silicate hydrates.

Unlabelled: Production of blended cements in which Portland cement is combined with supplementary cementitious materials (SCM) is an effective strategy for reducing the CO emissions during cement manufacturing and achieving sustainable concrete production. However, the high AlO and SiO contents of SCM change the chemical composition of the main hydration product, calcium aluminate silicate hydrate (C-A-S-H). Herein, spectroscopic and structural data for C-A-S-H gels are reported in a large range of equilibration times from 3 months up to 2 years and Al/Si molar ratios from 0.

A method for the mix design of low carbon concrete towards industrial production.

Unlabelled: The introduction of newly developed blended cements into the mass market is essential to ensure an effective reduction of the carbon footprint related to cement production. To facilitate this process, formulating mix proportions using pastes and/or mortars rather than concrete can be a great advantage. However, for the upscaling towards industrial concrete it is then essential to maintain the target rheological and mechanical properties, something that is all too often challenging.

Porewater compositions of Portland cement with and without silica fume calculated using the fine-tuned CASH+NK solid solution model.

Unlabelled: The CASH+ sublattice solid solution model of C-S-H aims to predict the composition of C-S-H and its ability to take up alkalis. It was originally developed for dilute systems with high water-solid ratios, and thus in this paper further optimized and benchmarked against measured pore solution compositions of hydrated Portland cement (PC) and PC blended with silica fume (SF) at realistic water-binder ratios. To get an improved agreement with the pore solution data, the stability of two CASH+ model endmembers, TCKh and TCNh, has been fine-tuned with standard Gibbs energy corrections of + 7.

The effect of paste composition, aggregate mineralogy and temperature on the pore solution composition and the extent of ASR expansion.

The reaction kinetics of the alkali silica reaction depends on the composition of the pore solution. The evolution of the pore solution composition in different cement pastes and concretes was studied. Pastes containing silica fume or metakaolin had the lowest amount of alkalis in the pore solution.

Durability of concretes exposed to high concentrations of CaCl and MgCl.

Unlabelled: In cold regions, calcium and magnesium chloride deicing salts damage concrete pavements due to the formation of certain deleterious chemical phases, including calcium oxychloride. While there is much research at a cement paste-scale, damage in concrete has been less studied. In this study, we evaluate concrete damage due to calcium and magnesium chloride and explain the roles of supplementary cementitious materials (SCM) replacement level, air entrainment, salt type, and exposure conditions in damage development.

Report of RILEM TC 281-CCC: outcomes of a round robin on the resistance to accelerated carbonation of Portland, Portland-fly ash and blast-furnace blended cements.

Unlabelled: Many (inter)national standards exist to evaluate the resistance of mortar and concrete to carbonation. When a carbonation coefficient is used for performance comparison of mixtures or service life prediction, the applied boundary conditions during curing, preconditioning and carbonation play a crucial role, specifically when using latent hydraulic or pozzolanic supplementary cementitious materials (SCMs). An extensive interlaboratory test (ILT) with twenty two participating laboratories was set up in the framework of RILEM TC 281-CCC 'Carbonation of Concrete with SCMs'.

Influence of the composition of high-strength concrete and mortar on the compressive fatigue behaviour.

The results of compressive fatigue investigations on four high-strength concretes and their corresponding mortars are presented. The influences of coarse aggregates generally, the substitution of basalt coarse aggregate by granite, the addition of silica fume and the variation of the water to cement () ratio are investigated systematically. The numbers of cycles to failure, the developments of strain, stiffness, dissipated energy and acoustic emission hits are focused on in the analyses.

Dimensional stability of cement paste and concrete subject to early-age carbonation curing.

Early-age carbonation curing of concrete is receiving more interest in terms of performance improvement and emission reduction. However, the volume change of cement-based products subject to carbonation curing may become a concern because of the potential carbonation shrinkage and its related shrinkage cracking. The purpose of this study was to investigate the dimensional stability of cement paste and concrete subject to the early-age carbonation curing.

Load-deformation behaviour of weft-knitted textile reinforced concrete in uniaxial tension.

Weft-knitted textiles offer many advantages over conventional woven fabrics since they allow the fabrication of doubly curved geometries without the need of stitching multiple patches together. This study investigated the use of high-strength continuous fibres as knitted textile reinforcement, focusing on various knitting patterns, fibre materials, coating types and spatial features to enhance the bond conditions between concrete and reinforcement. The bond is of particular interest since the contact surface of knitted textiles is fundamentally different due to their closed surface, compared to commercially available textile reinforcement, which is normally formed as orthogonally woven grids of rovings.

Functional and environmental performance of plant-produced crumb rubber asphalt mixtures using the dry process.

Incorporating crumb rubber (CR) using the dry process, directly in the asphalt mixture rather than into the bituminous binder requires no plant retrofitting, and therefore is the most practical industrial method for CR incorporation into asphalt mixtures. Nevertheless, very few large scale studies have been conducted. This work uses a holistic approach and reports on the functional and environmental performance of asphalt mixtures with different concentrations of CR fabricated employing the dry process in asphalt plants.

Tensile response of Ultra High Performance PE Fiber Reinforced Concretes (PE-UHPFRC) under imposed shrinkage deformations.

PE-UHPFRC is a new Ultra High-Performance Fiber Reinforced Concrete (UHPFRC), which is developed to reduce the environmental impact of conventional UHPFRC by replacing the steel fibers with synthetic ones and reducing the clinker content in the mix. The development of the dynamic elastic modulus, the evolution of free autogenous deformations and the eigenstresses development with age, under full and partial restraint conditions, were investigated for PE-UHPFRC and the results were put into perspective with that for conventional UHPFRC with steel fibers. Furthermore, the tensile responses of different mixes under imposed shrinkage were compared and discussed.

The ratio of shear to elastic modulus of in-plane loaded masonry.

When designing unreinforced masonry buildings, the wall stiffness and, consequently, the masonry elastic and shear modulus and are essential parameters. Current codes provide empirical estimates of the masonry elastic modulus and a ratio between the shear and elastic modulus, /. This ratio, commonly taken as 0.

Active control of properties of concrete: a (p)review.

Concrete properties to a large extent depend on mix design and processing, currently leaving only limited options to actively modify concrete properties during or after casting. This paper gives a (p)review on a more advanced active control of properties of concrete, based on the application of external signals to trigger an intended response in the material, either in fresh or hardened state. Current practices in concrete industry that could be considered as active control are briefly summarized.

A simplified model for the combined wicking and evaporation of a NaCl solution in limestone.

Salt weathering is one of the major causes of the damage both in cultural heritage as well as in civil engineering constructions. A special case develops when there is a continuous wicking of a salt solution into a material in combination with evaporation of the moisture at its surface. In this study we are interested in the case where the absorption rate is much higher than the evaporation and as a result a salt concentration will build up at the drying surface resulting in crystallization.

Performance of single skin masonry walls subjected to hydraulic loading.

Property owners are facing increasing threats from flooding and in response are likely to turn to products designed to waterproof or 'seal' the outside of the building in an effort to prevent the ingress of flood water. However, very limited research has been conducted on the effect of this sealing action and the consequent hydraulic load acting upon the structure of the building. The theoretical safe application of waterproofing products has been suggested to be between 0.

How models can make a difference for a sustainable future of the building industry.

Models play a vital role in science and technology and in the evolution of modern societies. They are used for describing processes and mechanisms, experimental observations, analyses and predictions. In spite of the fact that models are a reduction of reality, the achievements of modern societies are impressive and would have been inconceivable without the role of models.

An experimental study of cathodic protection for chloride contaminated reinforced concrete.

Cathodic protection (CP) is being increasingly used on reinforced concrete structures to protect steel reinforcing bars from corrosion in aggressive conditions. Due to the complexity of environmental conditions, the design specifications in national and international standards are still open to discussion to achieve both sufficient and efficient protection for reinforced concrete structures in engineering practices. This paper reports an experimental research to investigate the influence of chloride content on concrete resistivity, rebar corrosion rate and the performance of CP operation using different current densities.