The need to constantly improve the quality and properties of manufactured products leads to the development of hybrid materials that combine different elements, complementing one another. Fiber-reinforced mortar is one of those products, as the fibers are used to improve cementitious materials' flexural weakness. Experimental data on different metallic fibers dispersed in mortar demonstrate the correlation between early-age rheological properties and long-term mechanical strength. Both quantities depend on the ratio of the solid volume fraction of the fiber to a critical solid volume fraction characteristic of the form factors of the fiber. It is demonstrated that both effects arise from the packing stress of the fibers in the mortar when their concentrations are close to their maximum packing fraction. Geometrical arguments are used to explain how this critical volume fraction is related to the fiber form factor. Then, it enables the building of master curves using geometrical arguments.

The very early age flocculation of a cement based paste, in which cement is partially substituted by a calcined clay, metakaolin, is studied. We use rheological and ultrasonic reflection to monitor the evolution of the elastic properties of the paste with time, and light scattering to follow the change of its relaxation modes at small scales. We show that, at very early ages, of the order of hundreds of seconds after the paste preparation, a network of flocculated particles establishes, which manifests by a slow down of the dynamics of the relaxation modes of the paste at small scale. Then, this network consolidates and the macroscopic elastic modulus of the paste progressively increases with time, leading eventually to the setting of the paste. These observations show that, whatever the degree of replacement of clinker by metakaolin, a connected network establishes at very early times after the paste preparation, although the kinetics of flocculation slows down with clinker replacement.

This work examines the influence of iron oxide nanoparticles (Fe 3 O 4 NPs) on neutron and gamma-ray radiation shielding characteristics of Portland cement paste. Experimental evaluations were supplemented with theoretical studies using NXCom program. Portland cement pastes with 5, 10, 15, 20, and 30 wt% of nanomagnetite cement replacement were produced. Moreover, rheological, early strength development, compressive strength, and mercury intrusion porosimetry (MIP) tests were performed. The results showed that increasing the amount of Fe 3 O 4 NPs in a mix leads to a gradual increment in measured viscosity and yield stress. High nano-Fe 3 O 4 content substantially impeded the early strength development process and led to a decrement in the 7- and 28-day compressive strength of cement paste. The MIP studies exhibited a gradual increment in total porosity, and average pore volume, as nano-Fe 3 O 4 content was increased. All the macroscopic cross-sections of slow, fast and thermal neutrons constantly increased as a result of the addition of magnetite nanoparticles, with their variations being markedly linear. Similarly, gamma attenuation test results indicated that the addition of Fe 3 O 4 powder enhances the shielding capability of paste in the energy range of interest (0.08–2.614 MeV). In conclusion, Fe 3 O 4 nanoparticles can be successfully used in producing lead-free cementitious composites with improved gamma-ray and neutron shielding properties. However, certain drawbacks related to an increment in matrix porosity and thus a decrement in mechanical performance should be taken into account.

The aggregation behavior of an attractive colloidal silica suspension under oscillatory flow is studied using rheological measurement. We show that the competition between the aggregation of the particles and the aggregate breakup under external stress leads to a non-monotonous evolution of the elastic modulus with time. Remarkably, under certain conditions, the elasticity is not an increasing function of time but exhibits a maximum. The value of the maximum of the elastic modulus depends on the applied shear amplitude and the ionic strength of the suspension. Scaling laws that describes the evolutions of the elastic modulus as a function of the salinity and of the deformation amplitude are proposed and discussed.

Open dataset for publication Sikora P., El-Khayatt A.M., Saudi H.A., Liard M., Lootens D., Chung S.-Y., Woliński P., Abd Elrahman M. Rheological, mechanical, microstructural and radiation shielding properties of cement pastes containing magnetite (Fe3O4) nanoparticles. International Journal of Concrete Structures and Materials (2023), 17, 7. https://doi.org/10.1186/s40069-022-00568-y File 1 - X-ray diffractogram and particle size distribution (laser granulometry) data - *.opju (Origin)File 2 - Rheological test results - *.opju (Origin)File 5 - Mechanical peformance (early strength - ultrasounds and compressive strength) and density test results - *.opju (Origin)File 4 - Mercury intrusion porosimetry test data - *.opju (Origin)

The industry is responsible for 65% of greenhouse emissions, contributing to dramatic and irreversible climate changes. Among all the industries, construction is the most carbon and material demanding. Therefore, shortand long-term solutions should be quickly found to reduce both materials needed and their carbon footprint. With more than 20 GT produced per year, concrete and mortar are the most used construction materials. Even if they have a low carbon footprint compared to steel, glass, or wood, their massive volume consumption generates more than 3 GT of carbon dioxide annually. This paper exposes how to reduce the carbon-intensive clinker by up to 75% by substituting two different grades of Ground Calcium Carbonate (GCC), reaching the 50% carbon emission reduction target of the Paris climate agreement. As an alternative to the still limited resources of conventional Supplementary Cementitious Materials (SCMs), using different grades of GCC reduces the water needed and, therefore, the clinker required for a specific strength. We demonstrate that this reduces the carbon footprint by up to 50% for concrete and mortar with similar mechanical properties. A theory is proposed, linking materials' strength and relative porosity, giving an excellent relation and explaining the impact of the clinker substitution with GCC. Ecological concretes and mortars with improved performances could then be obtained, demonstrating a possibility of reducing in the short term 50% of the carbon emission of concrete and mortar by using broadly available grades of low carbon footprint Ground Calcium Carbonate.

The replacement of traditional cement with high clinker content should be achieved quickly to lower the carbon footprint of mortar and concrete. Cement is responsible for about 70% of the carbon footprint of cementitious materials. Current research suggests that the use of limestone and metakaolin or calcined clay could replace the current four gigatons of clinker produced. Here, binary systems composed of limestone/cement and metakaolin/cement are first studied to determine the individual impact of fine limestone and diverse fine metakaolins on the flow and compressive strength of the material. The flow properties are correlated with the surface areas of clinker and metakaolin and are almost independent of the limestone content. A model based on a linear relationship between compressive strength and porosity is used to estimate the reactivity of cement, limestone and metakaolin. An excellent correlation is obtained with the two binary systems and confirmed with the ternary systems using the same reactivity factors. The presented model allows the determination of the impact of each of the three components on compressive strength development. Limestone and metakaolin accelerate the hydration of clinker, leading to higher early strength, proportionally to their surface area. The reactivity of metakaolin is also found to be directly related to its mean size or surface area.

The need to constantly improve the quality and properties of manufactured products leads to the development of hybrid materials which combine different elements complementing one another. Fiber reinforced mortar is one of those products as the fibers are used to improve the flexural weakness of cementitious based materials. In this paper, a set of experimental data shows the impact of the fiber concentrations and their form factor on both the mechanical and the rheological properties. It is demonstrated that both effects arise from the packing stress of the fibers in the mortar when their concentrations are close to their maximum packing fraction. Geometric arguments are used to explain how this critical volume fraction is related to the fiber form factor. Then it enables the building of master curves using geometrical arguments.

Cement suspensions behave as a complex fluid from the rheological point of view as they are non-Newtonian fluids and their rheology is time dependent. The early-age hydration kinetics is mainly studied because of the importance of the determination of the initial and final setting time for all the applications of the cementitious materials. The particles within the fresh cement suspension are subject to several interactions which tend to cause aggregation of particles. The dynamics of the systems play an important role in the evolution of the size, density, and mechanical strength of these aggregates over time, and consequently control the macroscopic behavior. In this paper, the dynamics of several white portland cement suspensions with water to cement ratios from 0.25 to 0.46 have been studied. The motion of cement particles was characterized via multispeckle diffusing wave spectroscopy (MSDWS) in back scattering geometry, and the dynamics were described in terms of an autocorrelation function data. At all water to cement ratios, the dynamics of the particles slows down as a function of time. But at intermediate water to cement ratios, the consolidation of the particles networks occurs through temporally heterogeneous rearrangements of the particles. Such rearrangements do not occur at higher water to cement ratios. This behavior is correlated with a loss of flexural rigidity of the set cement.

The environmental impact of ordinary Portland cement (OPC) can be decreased by using alternative precursors, such as non-ferrous metallurgy slags (NFMS), which can be alkali-activated to form an inorganic polymer binder (IP). However, an IP demands the use of a high molarity alkali-solution, which is expensive, has a relative high environmental footprint and limits the use of superplasticizers. In order to tackle these challenges, hybrid binders are proposed, which consist mainly of NFMS, a minor amount of OPC and are activated with a low molarity NaOH solution, in which the superplasticizers can be used effectively. A self-compacting hybrid paste with high early-age strength was developed step-by-step by investigating the effect of different amounts of raw materials on the reactivity, identified by semi-adiabatic calorimetry, and strength development. The obtained optimal hybrid binder formulation was (in wt%) 70 NFMS, 10 ground granulated blast furnace slag, 10 OPC, 8 limestone, 0.9 NaOH, 0.8 plasticizer and 0.3 bassanite; for a water-powder ratio of 0.19, the compressive strength was 20, 41 and 61 MPa at 1, 7 and 28 days, respectively. This study demonstrated that a hybrid binder can be produced from mainly NFMS, which can increase their valorisation potential.

Additive manufacturing (AM), also referred as 3D printing, is a technology that enables building automated three-dimensional objects in a layer-by-layer manner. AM of cement-based and alkali-activated composites has gathered attention over the last decade and is one of the most rapidly developing civil engineering fields. Development of proper mixture compositions which are suitable in fresh and hardened state is one of the key challenges of AM technology in construction. As the behaviour of cement-based materials (CBM) and alkali-activated materials (AAM) is determined by chemical and physical processes at the nano-level, incorporation of nano- and micro-sized admixtures has great influence on the performance of printable composites. These modifications are attributed to the unique reactivity of nanoparticles associated with their small size and large surface area. This review paper summarizes recent developments in the application of nano- and micro-particles on 3D printable cementitious composites and how they influence the performance of 3D-printed construction materials. The research progress on nano-engineered CBM and AAM is reviewed from the view of fresh and hardened properties. Moreover, comparison between nano- and micro-sized admixtures including nanosilica, graphene-based materials, and clay nanoparticles as well as chemical admixtures such as viscosity-modifying admixtures and superplasticizers is presented. Finally, the existing problems in current research and future perspectives are summarized. This review provides useful recommendations toward the significant influence of nano- and micro-sized admixtures on the performance of 3D printable CBMs.

This study presents the experimental results of an investigation on the effects of nanosilica (NS) on the material characteristics of printable mortars used for additive manufacturing. Printable cement mortars based on Ordinary Portland Cement, limestone filler and silica sand were modified with different dosages of nanosilica (from 2% to 6% by weight of binder) and its influence on their hydration, rheological, mechanical and transport properties was assessed. The study showed that NS accelerates significantly the setting and hardening of printable mortar, while reducing its open time. Moreover, an increment of yield stress, together with an increment in NS dosage, was found to have occurred. The incorporation of an optimal NS dosage results in a noticeable increase in the compressive strength and alteration of the pore structure as determined by the MIP measurements. Moreover, transport properties of the produced mortar are significantly improved due to incorporation of NS. In addition to the microstructure refinement, Micro-CT and scanning electron microscopy (SEM) studies revealed that 3D printed mortars exhibit pore anisotropy in accordance with the printing direction. However, incorporation of NS in the mixture resulted in improved buildability, thus decreasing pore anisotropy. (C) 2021 The Author(s). Published by Elsevier Ltd.

We investigate the flow of a concentrated suspension of colloidal particles at deformation rates higher than the discontinuous shear-thickening transition shear rate. We show that, under its own weight, a jet of a concentrated enough colloidal suspension, simultaneously flows while it sustains tensile stress and transmits transverse waves. This results in a new flow instability of jets of shear-thickening suspensions: the jet is submitted to rapid transverse oscillations, that we characterize.

Concrete compressive strength is a critical design criterion for concrete elements and should, as a consequence, be carefully controlled to ensure structural integrity and intended functionality. As the cementitious binder of concrete hydrates, its strength and elastic modulus increase with time as concrete transitions from a fluid with suspended particles to a rigid but porous solid. Porosity of the material decreases as hydration products fill available space to create a densified structure. Ultrasonic instruments are able to continuously measure the material properties of cementitious materials. This is a significant advantage over destructive, quasi-static compression test of cylinders or cubes at discrete time intervals. Here, we estimate the elastic modulus and compressive strength of a cement paste or concrete from the amplitude of a reflected ultrasonic wave. A series of cement pastes and concretes are tested in quasi-static compression to establish a correlation between compressive strengths estimated from ultrasonic methods and classical compression test. The differences between the compressive strengths obtained by quasi-static compression tests and ultrasonic wave reflection differ by ±20% over a range of compressive strengths spanning more than 3 decades.

This study investigates the effects of seawater and nanosilica (3% by weight of cement), on the fresh and hardened properties of cement pastes and mortars produced with two types of low heat cements: Portland pozzolana cement (CEM II) and blast furnace cement (CEM III). The heat of hydration, initial and final setting times, rheological properties, strength development, sorptivity and water accessible porosity of the cement pastes and mortars were determined. The data reveal that cement type has a significant effect on the reaction rate of cement with seawater and nanosilica (NS). Specimens produced with slag-blended cement exhibited a higher cement reaction rate and the composite produced exhibited better mechanical performance, as a result of the additional reaction of alumina rich phases in slag, with seawater. Replacement of freshwater with seawater contributes mostly to a significant improvement of early strength. However, in the case of slag-blended cement, 28 day strength also improved. The incorporation of NS results in additional acceleration of hydration processes, as well as to a decrease in cement setting time. In contrast, the addition of NS results in a noticeable increment in the yield-stress of pastes, with this effect being pronounced when NS is mixed along with seawater. Moreover, the use of seawater and NS has a beneficial effect on microstructure refinement, thus improving the transport properties of cement mortars. Overall, the study has showed that both seawater and NS can be successfully used to accelerate the hydration process of low heat blended cements and to improve the mechanical and transport properties of cement-based composites.

Concrete, mortars, and grouts in fresh state can be pumped, sprayed and now even printed with additive manufacturing. For this type of materials, the knowledge of flow properties is crucial for adequate control during its applications. The thixotropy of cementitious materials must be taken into account due to the benefits of the change of viscosity especially in self-levelling applications. In this study, a rheological approach is used to characterize the thixotropy of a cement paste and to study both the physical and chemical thixotropies. White Portland cement pastes to cement ratios of 0.25. 0.34, 0.40 and 0.46 were prepared. For all pastes a commercial high range water reducing admixture (HRWRA) was used in concentrations of 0.04%, 0.120% and 0.360% and for samples with 0.360% concentration, the same mixes have been done with the addition of a commercially available viscosity modifying admixture (VMA). Results show that by measuring the viscosity over-time it is possible to uncouple the contribution of the chemical and physical thixotropy. An empirical mathematical model has been proposed in order to identify physical and chemical aging over time, finding that in the first instants the physical aging grows exponentially, followed by a linear growth ascribed to chemical aging. The addition of additives only affects the physical aging but does not interfere with chemical thixotropy. This approach could be suitable to predict and control the thixotropy of cement pastes and mortars.

Ultrasounds plays a major role in Non-Destructive tests. An important application is the monitoring of the hardening process in cement-based materials. It was recently proven that ultrasound echoes reflected from the interface between a transmitting medium and the cement paste carry information about the status of the chemical process responsible of the cement hardening. In application like e.g. the monitoring of bridges or tunnels during construction, these sensors should be deployed in remote sites where they should work autonomously for days. Unfortunately, no electronics is currently available which satisfies the requirements for an industrial use. In this paper a completely configurable, embedded ultrasound system, capable of managing up to 8 ultrasound transducers, is presented. The proposed “smart” sensor can be remotely controlled through a web-based user-friendly interface, is portable, and can be programmed to perform a series of tests scheduled along days or months. An example of cement hydration process monitoring is presented to show the performances and versatility of the proposed system.

Concrete is composed of sands, aggregates and cement powders mixed in water to produce a chemical reaction, named Hydration, that causes concrete hardening. The monitoring of the compressive strength during hydration is crucial to assess the concrete quality. The standard approach used to measure concrete strength consists of a manual and expensive process made by crushing concrete cubes in a compression machine. A non-destructive method based on monitoring the reflection coefficient of the ultrasound waves at the interface where the material is poured can replace the standard approach. In this work we present a system that embeds all the electronics needed for generating, acquiring and processing the ultrasound signal for automatically monitoring the concrete strength during and after the hydration process.