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The study of alkali-activated slag (AAS) is motivated by the need for more sustainable alternatives to Portland cement (PC) within the construction industry. Specifically, AAS offers good mechanical and chemical properties. However, the influence of the activator on its pore structure and hydraulic conductivity remains unclear. Both pore structure and hydraulic conductivity are key parameters in understanding the drying process and could potentially explain the high drying shrinkage observed so far. The present study aims to investigate the pore size distribution and hydraulic conductivity of six distinct AAS/sodium hydroxide mortar compositions, with a particular emphasis on the effect of varying the activator’s molarity and the solution-to-binder ratio (s/b). This research uses the mass variation in different relative humidity (RH) conditions from experimental tests to model the pore surface area, the pore size distribution, and the hydraulic conductivity. From the results, it emerges that increasing the molarity from 0.5 to 8 M reduces the open porosity and refines the pore structure, while increasing the s/b from 0.5 to 0.8 increases the open porosity while refining the pore structure. In addition, high molarity compositions are not suitable for testing in high RH and natural carbonation conditions due to the occurrence of deliquescence. Moreover, the main drying mechanism in AAS is water vapour transport even at high relative humidity, contrary to what was observed in the literature for PC. Finally, the hydraulic conductivity of alkali-activated slag presents a minimum of around 85% RH against the 60–70% RH for PC, causing AAS to dry faster when the relative humidity decreases from 85 to 50%., SCOPUS: ar.j, info:eu-repo/semantics/published

With the global population on the rise, the construction industry has experienced significant growth in the last two decades. Cement, a key component in concrete production, contributes up to 8% of total CO2 emissions. This underscores the demand for concrete solutions that are durable, cost-effective, and environmentally friendly. Alkali-activated materials (AAMs) present a promising alternative to traditional cements, contributing to more eco-friendly concrete production. In this research, twelve mixture compositions are explored, incorporating various combinations of precursors (slag, fly ash) and activators (sodium hydroxide and sodium silicate). Different alkali dosages and solution-to-binder ratios are also considered. The independent and combined effects of these parameters are observed on the development of main binder properties through specific experimental equipment. The first part focuses on characterizing the setting behavior of these novel binders. Continuous non-destructive tests, including ultrasonic pulse velocity (UPV) measurements and isothermal calorimetry tests, are combined with traditional tests such as slump flow, Vicat, and uniaxial compressive strength tests. For characterizing viscoelastic behavior post-setting, a novel technique involving repeated short-term creep tests is employed. This approach allows continuous monitoring, facilitating the characterization of early-age elastic stiffness and creep properties. To model short-term creep behavior, a power-law creep function is utilized. For long-term creep, a logarithmic creep function is applied. Furthermore, a logarithmic trend is observed in the development of specific creep over an extended duration of loading. An adapted version of the Model Code 2010 is employed to fit the experimental data, showing good agreement in modeling the specific creep of slag-based mortar samples., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The necessity to house the worldwide growing population is making the production of Portland cement (PC) grow alongside with its CO2 emissions in the atmosphere. In order to reduce said emissions, the scientific community is looking for viable and greener alternatives with comparable mechanical properties and good durability. Alkali-activated materials seem to represent a possible replacement to PC, even though their long-term durability is still not fully understood.One of the main issues for the durability of construction materials is the volume stability in drying conditions, that is how the volume of the material decreases when exposed to environmental conditions. The main consequence of the volume contraction is the development of microcracks which reduce the mechanical strength, allow for water vapour and CO2 to penetrate further inside the material, and may also lead to failure of the structure. In order to assess the long-term durability of a material is therefore crucial to understand how it shrinks according to the different external conditions.The present study focuses on the activation of Blast Furnace Slag (BFS) using different sodium hydroxide solutions and takes into account three main aspects of durability: the tendency to cracking in restrained conditions, the pore structure and hydraulic conductivity of the material, and the drying shrinkage in free conditions. The first experimental campaign on restrained shrinkage has been conducted using the ring test coupled with the assessment of the mechanical properties both in sealed and drying conditions; the goal is to understand when the formation of microcracks takes place and what is the maximum deformation the material can endure before failure. The second experimental campaign modelled the total porosity, the pore size distribution, and the hydraulic conductivity of the material based on the mass variation of the material exposed to different relative humidity levels. Finally, the third experimental, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Alkali-activated slag (AAS) is emerging as a possible and more sustainable alternative to Ordinary Portland Cement (OPC) in the construction industry, thanks to its good mechanical and chemical properties. Conversely, the effects of its high drying shrinkage are still a concern for its long-term durability. This study aims to investigate the drying shrinkage behaviour of six AAS/sodium hydroxide mortar compositions and the main phenomena affecting their drying shrinkage behaviour. Specifically, the molarity, solution-to-binder ratio (s/b), autogenous shrinkage, creep compliance, microcracking, and carbonation are considered as possible causes of the differences between AAS and OPC. The results show that it is not possible to correlate the shrinkage magnitude with the molarity of the activating solution, while an increase in the s/b increases the drying shrinkage. Concerning the other factors, autogenous deformation remains significant even after a period of 112 days, while the creep compliance is definitely affected by the drying process but does not seem to affect the shrinkage magnitude. Furthermore, the presence of microcracks caused by the drying process definitely influences the drying shrinkage. Finally, carbonation depends on the molarity of the activating solution, even though its effects on the material are still unclear., SCOPUS: ar.j, info:eu-repo/semantics/published

The growing use of blends of low- and high-calcium solid precursors in combination with different alkaline activators requires simple, efficient, and accurate experimental means to characterize their behavior, particularly during the liquid-to-solid transition (setting) at early material ages. This research investigates slag-fly ash systems mixed at different solution-to-binder (s/b) ratios with sodium silicate/sodium hydroxide-based activator solutions of varying concentrations. Therefore, continuous non-destructive tests—namely ultrasonic pulse velocity (UPV) measurements and isothermal calorimetry tests—are combined with classical slump flow, Vicat, and uniaxial compressive strength tests. The experimental results highlight that high alkali and silica contents and a low s/b ratio benefit the early-age hydration, lead to a faster setting, and improve the early-age strength. The loss of workability, determined from the time when the slump flow becomes negligible, correlates well with ultrasonic P-wave velocity evolutions. This is, however, not the case for Vicat or calorimetry tests., SCOPUS: ar.j, info:eu-repo/semantics/published

The present work investigates the desiccation effects on a lime-treated silty clay and compare it with the non-treated equivalent material. Original experimental techniques have been developed to control suction conditions, to track volume variations and cracks occurrence upon drying. Free and constrained desiccations are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength and stiffness at various suctions. In addition, the effects of the compaction mode, dry density and suction on the tensile strength have been investigated in a systematic way. Those investigations have been performed on natural and lime-treated compacted silty clay in order to emphasize the benefits of the lime treatment in the triggering and/or mitigation of the cracking process. To simulate the field conditions of compaction and obtain specimens having geomechanical properties as close as possible to the real material on site, the particular kneading compaction process in a CBR mould was largely used, and the final specimens were cut at required sizes with a milling machine numerically controlled by computer (CNC). At the end, generalized effective stress framework with an effective stress parameter calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil specimens. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks that are triggered at higher suctions. So, lime treatment plays a favourable role in the reduction of shrinkage and crack occurrence of soft soils subject to drying., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

This study aims to compare the developments of mechanical properties and autogenous shrinkage related properties of alkali-activated materials-based concrete (AC) and ordinary Portland cement-based concrete (OC) against curing age and degree of reaction. Temperature Stress Testing Machines are utilized to monitor the evolution of the internal tensile stress and the cracking occurrence in the restrained concrete. It is found that AC shows lower tensile strength-to-compressive strength ratios than OC. The mechanical properties of both OC and AC can be modelled by a power law against the degree of reaction. AC shows higher autogenous shrinkage, but later cracking than OC when under restrained condition. However, the degrees of reaction at which AC and OC cracked are very similar. From the autogenous shrinkage, the elastic modulus and the self-induced stress, the elastic and creep deformations of the concrete can be calculated. AC is found to show much higher creep coefficient than OC., Materials and Environment

This study aims to compare the developments of mechanical properties and autogenous shrinkage related properties of alkali-activated materials-based concrete (AC) and ordinary Portland cement-based concrete (OC) against curing age and degree of reaction. Temperature Stress Testing Machines are utilized to monitor the evolution of the internal tensile stress and the cracking occurrence in the restrained concrete. It is found that AC shows lower tensile strength-to-compressive strength ratios than OC. The mechanical properties of both OC and AC can be modelled by a power law against the degree of reaction. AC shows higher autogenous shrinkage, but later cracking than OC when under restrained condition. However, the degrees of reaction at which AC and OC cracked are very similar. From the autogenous shrinkage, the elastic modulus and the self-induced stress, the elastic and creep deformations of the concrete can be calculated. AC is found to show much higher creep coefficient than OC., SCOPUS: ar.j, info:eu-repo/semantics/published

Over the last 15 years, bulk hydrophobic treatment of cementitious materials with silanes and siloxanes is in the scientific focus. They are beneficial in terms of reducing water uptake by capillarity, however, this is often followed by an impact on cement hydration leading to the decrease in structural properties of cement matrix. The aim of this paper is to study the influence of different incorporation modes of a silicone-based hydrophobic agent used for the bulk hydrophobic treatment of mortars, and to evaluate their effect on cement hydration and the early age properties. Two different incorporation modes are compared: an emulsion of silane and silicone resin and microencapsulation of silicone resin. Each of these is incorporated in mortars prepared with CEM I and CEM III/A. Based on the combined measurement of isothermal calorimetry, electrical resistivity, ultrasonic pulse velocity, compressive strength, thermal expansion coefficient and autogenous deformation at early age, it is shown that the emulsion, as a delivery method of hydrophobic agent, affects the early age mechanical behavior of cement-based systems, for both types of cements. The microencapsulation on the other hand, prevents these effects from occurring, and is therefore suitable for bulk hydrophobic treatment., SCOPUS: ar.j, info:eu-repo/semantics/published

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The present work analyses the impact of the substitution of natural coarse gravel and sand by recycled gravel and sand on the concrete behavior under free and restrained condition since setting. The methodology presented in this paper associates a Temperature Stress Testing Machine (TSTM) with free shrinkage tests and other experimental advanced techniques, such as direct tensile testing and the monitoring of elastic properties using repeated loading testing. It is observed that the cracking sensitivity decreased with recycled concrete content in spite of lower tensile strength. This is due to the major influence of relaxation, but also damage and coupling effects. These phenomena contributed to a decrease of the stresses with different magnitude and kinetics. For concretes with recycled gravels, the major stress reduction was attributed to relaxation. The reduction of elastic modulus due to damage appeared from the first 24 h while creep seemed to develop later, as tensile stress to strength ratio became higher. Concrete with recycled sand had a different behavior with earlier creep development and lower damage., SCOPUS: ar.j, info:eu-repo/semantics/published

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