Role of N-acetylcysteine in the management of COPD

The importance of the underlying local and systemic oxidative stress and inflammation in chronic obstructive pulmonary disease (COPD) has long been established. In view of the lack of therapy that might inhibit the progress of the disease, there is an urgent need for a successful therapeutic approach that, through affecting the pathological processes, will influence the subsequent issues in COPD management such as lung function, airway clearance, dyspnoea, exacerbation, and quality of life. N-acetylcysteine (NAC) is a mucolytic and antioxidant drug that may also influence several inflammatory pathways. It provides the sulfhydryl groups and acts both as a precursor of reduced glutathione and as a direct reactive oxygen species (ROS) scavenger, hence regulating the redox status in the cells. The changed redox status may, in turn, influence the inflammation-controlling pathways. Moreover, as a mucolytic drug, it may, by means of decreasing viscosity of the sputum, clean the bronchi leading to a decrease in dyspnoea and improved lung function. Nevertheless, as successful as it is in the in vitro studies and in vivo studies with high dosage, its actions at the dosages used in COPD management are debatable. It seems to influence exacerbation rate and limit the number of hospitalization days, however, with little or no influence on the lung function parameters. Despite these considerations and in view of the present lack of effective therapies to inhibit disease progression in COPD, NAC and its derivatives with their multiple molecular modes of action remain promising medication once doses and route of administration are optimized

EFFECT OF SELF-HEALING ON THE CHLORIDE DIFFUSIVITY AT EARLY AGE

International audienceThe chloride diffusivity of cementitious materials significantly affects the durability of civil engineering structures (e.g. reinforced concrete buildings) and the waste containment matrices (e.g. sediments, radioactive waste). Its influence becomes greater when cracks appear due to restrained shrinkage. The results of an experimental campaign on the chloride diffusion characteristics of uncracked, cracked and self-healed mortar specimens are presented at several ages. The mortar compositions are characterized by several contents of blast-furnace slag. The diffusion characteristics are measured by means of accelerated migration tests and solutions titration with silver nitrate to determine the steady state stage and the effective diffusion coefficient. The cracking size is monitored using optical microscopy. Results clearly show that self-healing is a positive phenomenon that limits and reduces the crack size, therefore leading to a decrease of the diffusion coefficient. Moreover, the addition of blast-furnace slag intensifies this trend due to the slow hydration kinetics of this type of hydraulic binder

EFFECT OF SELF-HEALING ON THE CHLORIDE DIFFUSIVITY AT EARLY AGE

International audienceThe chloride diffusivity of cementitious materials significantly affects the durability of civil engineering structures (e.g. reinforced concrete buildings) and the waste containment matrices (e.g. sediments, radioactive waste). Its influence becomes greater when cracks appear due to restrained shrinkage. The results of an experimental campaign on the chloride diffusion characteristics of uncracked, cracked and self-healed mortar specimens are presented at several ages. The mortar compositions are characterized by several contents of blast-furnace slag. The diffusion characteristics are measured by means of accelerated migration tests and solutions titration with silver nitrate to determine the steady state stage and the effective diffusion coefficient. The cracking size is monitored using optical microscopy. Results clearly show that self-healing is a positive phenomenon that limits and reduces the crack size, therefore leading to a decrease of the diffusion coefficient. Moreover, the addition of blast-furnace slag intensifies this trend due to the slow hydration kinetics of this type of hydraulic binder

Cementitious materials with mineral additions: impact on the self-healing kinetics and the products formation

International audienceGround granulated blast-furnace slags (GGBFS), as a hydraulic binder, are widely used for many years in engineering concretes. The French standards allow substituting 50% of Portland cement by GGBFS. This approach leads to a decrease in the CO2 emissions produced during clinkerisation process. Portland cement substitution by GGBFS can also improve the workability, decreases the hydration heat and increases the long-term compressive strength. GGBFS can also significantly improve the resistance to sulfate attack. Concrete structures made with GGBFS cement can be cracked at early age due to restrained shrinkage. This cracking can reduce mechanical and transport properties, leading to an increased risk of aggressive agents’ penetration. Self-healing of cracks, already observed on building sites, could partially overcome these durability issues.To understand the effect of GGBFS on self-healing kinetics and the type of self-healing products, five hydraulic binders were studied: two Portland cement (French and Canadian), two GGBFS (French and Canadian) mixed with Portland cement (named GGBFS formulation hereafter) and a French blended cement (62% of slag) named CEMIII/A. Each material was characterized by XRF, XRD, PZD test, fineness Blaine test and TGA. At 7 and 28 days, French and Canadian mortar specimens were cracked respectively to obtain three crack sizes: 50, 100 and 150 µm. The cracked specimens were then stored at 23 °C and 100% R.H for up to 6 months. The evolution of self-healing is followed by X-ray tomography or air-flow measurements. SEM with EDS were performed on the sawed samples to identify and analyze self-healing products.Results show that two main products are formed: (1) calcite by the carbonation of portlandite in the matrix, and (2) supplementary reaction products (mainly C-S-H with various C/S ratios), formed by the reaction of anhydrous particles. Both GGBFS formulations show a good self-healing potential but the kinetics of the phenomenon are slightly different. Mortar made with French GGBFS presents the best self-healing potential compared to the four others formulations. Mortar with Canadian GGBFS presents a similar behavior as Canadian Portland cement. These results can be explained by the material characteristics but also by their hydration kinetics. A hydration model is currently developed in order to investigate more deeply these observations

Experimental investigation and modelling of size effects on drying in concrete: application to a vessel of nuclear power plant

International audienc

Experimental studies of self-healing cementitious materials incorporating mineral admixtures

In order to limit the release of CO2 produced in cement manufacturing, clinker (the major cement component) is often partially replaced by mineral admixtures like blastfurnace slag. The use of mineral admixtures presents different advantages such as the recycling of industrial waste and the improvement of different material properties (workability, sulfate resistance, compressive strength at long term\u85). Nevertheless, several civil engineering constructions made with blast-furnace slag cement presented cracking at early age due to restrained shrinkage (autogeneous, thermal and drying shrinkage) that affects significantly the material transfer properties and their durability in aggressive environments (chloride, CO2). Under certain conditions however, it is known that cementitious materials present a self-healing capacity. The purpose of this research work is to study the beneficial influence of the natural selfhealing capacity of mortars with blast-furnace slag cement on the lifetime of civil engineering constructions. A new experimental device has been designed in order to understand the selfhealing capacity of mortars at early age. The novel apparatus allows developing micro-cracks in a mortar ring specimen by restrained shrinkage and monitoring the evolution of self-healing by gas permeability and effective diffusivity measurements. The effects of different slag contents (0%, 50%) and curing conditions (air conditioned room at 25±1°C and 45±5% R.H., in tap water) on the self-healing kinetics are studied. Optical measurements in 2D (optical microscope, SEM) and 3D (tomography), chemical analyses of the self-healing products and quantification of the properties of cement with blast-furnace slag (compression and tensile strength, autogenous and drying shrinkage, heat release) complete the study

Cementitious materials with mineral additions: impact on the self-healing kinetics and the products formation

International audienceGround granulated blast-furnace slags (GGBFS), as a hydraulic binder, are widely used for many years in engineering concretes. The French standards allow substituting 50% of Portland cement by GGBFS. This approach leads to a decrease in the CO2 emissions produced during clinkerisation process. Portland cement substitution by GGBFS can also improve the workability, decreases the hydration heat and increases the long-term compressive strength. GGBFS can also significantly improve the resistance to sulfate attack. Concrete structures made with GGBFS cement can be cracked at early age due to restrained shrinkage. This cracking can reduce mechanical and transport properties, leading to an increased risk of aggressive agents’ penetration. Self-healing of cracks, already observed on building sites, could partially overcome these durability issues.To understand the effect of GGBFS on self-healing kinetics and the type of self-healing products, five hydraulic binders were studied: two Portland cement (French and Canadian), two GGBFS (French and Canadian) mixed with Portland cement (named GGBFS formulation hereafter) and a French blended cement (62% of slag) named CEMIII/A. Each material was characterized by XRF, XRD, PZD test, fineness Blaine test and TGA. At 7 and 28 days, French and Canadian mortar specimens were cracked respectively to obtain three crack sizes: 50, 100 and 150 µm. The cracked specimens were then stored at 23 °C and 100% R.H for up to 6 months. The evolution of self-healing is followed by X-ray tomography or air-flow measurements. SEM with EDS were performed on the sawed samples to identify and analyze self-healing products.Results show that two main products are formed: (1) calcite by the carbonation of portlandite in the matrix, and (2) supplementary reaction products (mainly C-S-H with various C/S ratios), formed by the reaction of anhydrous particles. Both GGBFS formulations show a good self-healing potential but the kinetics of the phenomenon are slightly different. Mortar made with French GGBFS presents the best self-healing potential compared to the four others formulations. Mortar with Canadian GGBFS presents a similar behavior as Canadian Portland cement. These results can be explained by the material characteristics but also by their hydration kinetics. A hydration model is currently developed in order to investigate more deeply these observations