Mechanical and durabiliry properties of environmentally friendly Ultra-High-Performance Concrete (UHPC)

International audienceThis paper deals with mechanical and durability performances of more sustainable Ultra-High Performance Concrete (UHPC) by integrating high volumes of Blast Furnace Slag (BFS). Three substitution rates of cement by slag are explored (30%, 50% and 80%). Results show that a slag content of 30% improves slightly the compressive strength of concrete, whereas the strength of UHPCs containing 50% and 80% of slag are significantly reduced, particularly at early age. At 3 days, when the slag content increases, the porosity of UHPC mixtures with high slag content increases. In contrast, at 90 days, the volume of capillary pores decreases greatly and the global pores network becomes finer, when cement is substituted by BFS. This, results in decreasing gas permeability (1.5-6 times) and chloride diffusion (up 4 times). Results show also that all tested UHPCs have quite the same CO2 depth, after an exposure of 1 year. Indeed, the decrease of porosity, when BFS is added, is balanced by the decrease of pH, which promotes CO2 diffusion.Le présent article traite des performances mécaniques et de durabilité d'un Béton Ultra-Haute Performance (BUHP) plus durable, avec des teneurs en laitier élevées. Trois taux de substitution du ciment par des laitiers des hauts fourneaux (LHF) sont explorés (30%, 50% et 80%). Les résultats montrent qu'une teneur de 30% de laitier améliore légèrement la résistance à la compression, alors qu'avec 50% et 80% de LHF, la résistance à la compression chute significativement. A 3 jours, lorsque la teneur en LHF augmente, la porosité du béton augmente. A 90 jours, la réaction des LHF induit une diminution de la porosité capillaire et le réseau poreux devient plus fin. Ainsi, la perméabilité au gaz et la diffusion des ions chlore diminuent significativement. Les résultats montrent aussi que tous les bétons testés ont une profondeur de carbonatation similaire, après une année d'exposition au CO2. En effet, la diminution de la porosité, due à l'ajout des LHF est équilibrée par la diminution du pH, qui favorise la diffusion de CO 2

Physico-chemical study of cementitious materials based on binary and ternary binders

This research aims to study the physico-chemical phenomena occurring during hydration process of binary and ternary cementitious matrices, combining Portland cement (PC), blast furnace slag(BFS) and limestone filler (LF). For this purpose, measurements of the reaction rate and mechanical performances were performed on 12 mineral binders prepared with the same water-to-cementitious materials ratio (w/cm = 0.32) and various dosages of PC, BFS and LF. Three parameters are quantified using thermo-gravimetric analysis: the advancement of hydration characterized by the degree of hydration, the evolution of the chemically bound water as well as the quantity of Portlandite produced. Results show clearly that the knowledge of these parameters allows predicting correctly the evolution of compressive strength and young modulus at early age. The synergistic effects of ternary binders, formulated with moderate additions of BFS and LF, manifested in the form of an increased amount of hydration products compared to predictions based on the individual effects of BFS and the LF in the binary systems

Analyse multi-échelles du retrait endogène des matrices cimentaires

L'objectif de ce papier est de modéliser le retrait endogène d'une pâte de ciment dès le premier contact eau-ciment jusqu'à 2 jours d'hydratation en se basant sur un modèle d'homogénéisation multi-échelle. Le retrait endogène est composé de deux déformations issues de deux mécanismes différents. Une première déformation d'origine chimique issue d'un bilan volumique global négatif des réactions chimiques d'hydratation, qui apparaît dès le premier contact eau-ciment. A partir de la prise, le matériau se rigidifie progressivement et la déformation d'origine chimique est freinée par le squelette solide du matériau pour donner naissance à un phénomène de dépression capillaire à l'origine de la deuxième phase de déformation (retrait d'autodessiccation). Les entrées du modèle mis au point sont essentiellement la composition chimique du ciment ainsi que sa finesse, le rapport eau-ciment (E/C), la température et les propriétés mécaniques des principales phases. Les sorties sont l'évolution des phases dans le temps, la réaction chimique d'hydratation, le module d'Young, la dépression capillaire, le retrait chimique et endogène

Stability Behavior of Lime Stabilized Gypseous Soil

In arid and semi-arid zones, gypsum (CaSO4.2H2O) is one of the soluble of the common minerals that found in soils. In Iraq, gypseous soils is a worldwide stability problem that causes extensive damage upon wetting, and occur in certain areas characterized by variation of climatic conditions. The results of the stability behavior of lime stabilized gypseous soil where present in this paper under different tests. These tests were erosion, leaching and soaking. Erosion test was conducted under different variables such as water temperature, water velocity and flow duration. The soil used in this study was taken from a site near Al – Hader district about (80 km) from Mosul city. Its main geotechnical index properties are liquid limit is (46%), plastic limit (22%) and specific gravity is 2.58. The amount of the gypsum was 20%. The soil samples were treated with optimum lime percent (4%) depending on the Illinois procedure. A gypseous soil with 20% gypsum content was used and stabilized with 4% lime. All stabilized soil samples were cured for 2 days at 490 C. The results indicate that, the loss in weight increased for samples subjected to the flowing water, further increase in weight losses with increasing flow duration. High water velocity causes increasing in weight losses and loss in gypsum content , more loss in weight and more loss in gypsum content, for all values of flow duration and water temperature. Unconfined compressive strength decreased during the soaking process and further decrease in strength with increasing soaking duration. The leaching effect causes a continuous increasing in the permeability value of unstabilized soil samples, while it has an insignificant effect on the permeability of lime stabilized soil samples. Leaching is a time-dependent process. The results showed that the pH values of natural and lime stabilized soil samples decreases during leaching process

Impact of Tufa Stone Powder as a Partial Replacement of Aggregate on the Mechanical Performance and Durability of Repair Mortar

The rehabilitation and reconstruction works are usually performed with a view to conserving these landmarks and maintaining them culturally, architecturally and structurally. From this perspective, the mortars utilized in these repairs must be suitable, physiochemically and mechanically, to the ancient materials used in these buildings. Accordingly, it was proposed to evaluate tufa stone powder, a waste product of one of the most widely found stones in the Loire Valley in France, as an ingredient in repair-work mortar mixtures (M1, M2) through partially replacing the fine aggregate it contains with different amounts of this powder (37%, 42%) by weight of mix. Additionally, a third manufacturing mortar (M3) was utilized with both prepared mortars (M1, M2) for comparison with the tufa stone. The mechanical properties (including flexural, compressive and shear strengths, and ultrasonic pulse velocity) and the durability properties (total porosity, thermal dilation and conductivity, capillary absorption, and water and gas permeability) of the three mortars were examined in addition to those of the tufa stone. The results revealed that the prepared mortar, M2, (having lower binder content and a higher amount of substitution with tufa stone powder) has the lowest mechanical performance in comparison with the other mortars, indicating that this mortar is more supple and loose than the authentic tufa masonry. The thermal and durability properties are comparable to that of the tufa stone existent in ancient monuments. Consequently, the prepared mortar (M2) is the most appropriate mortar, for utilization in repairing old landmarks in the Loire Valley in France

Physical Characterization of Natural Straw Fibers as Aggregates for Construction Materials Applications

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw

Étude numérique et expérimentale du retrait endogène au très jeune âge des pâtes de ciment avec et sans inclusions

NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Mechanical Behavior of Gypseous Soil Treated with Lime

International audienc

A multi-scales approach for the physico-chemical deformations of solidifying cement-based materials

At early stages of hydration, solidifying cementitious systems exhibit dimensionalvariations caused by their thermal, hydrous, chemical and microstructural evolutions. Ifrestrained, these deformations can induce the development of internal stresses high enough togenerate cracking of the hardening material. This study focuses on early-age autogenousstrain of cement-based materials, which develops following two main processes: Le Chateliercontraction (also called chemical shrinkage) and self-desiccation shrinkage. Chemicalshrinkage results from the difference of absolute density between reactants (anhydrous cementand water) and hydration products. Early-age self-desiccation shrinkage is generally attributedto the development of a negative capillary pressure in the porous network related to the waterconsumption by the hydration reactions. The purpose of this research work is to propose amultiscale approach to model the rate of autogenous shrinkage of cement-based materials atvery early-age, between 0 and 48h. Le Chatelier contraction is computed from the chemicalequations of hydration and the specific volume of each phase, whereas a homogenizationmethod based on the self-consistent scheme is applied to calculate the self-desiccationshrinkage. Computed results are discussed and analyzed. Good agreements betweenexperiments and simulations are achieved and a sensitivity study is performed to assess theinfluence of the cement fineness and the fraction of granular inclusion on early-ageautogenous strain

Analyse multi-échelles du retrait endogène des matrices cimentaires

Colloque avec actes et comité de lecture. Internationale.International audienceL'objectif de ce papier est de modéliser le retrait endogène d'une pâte de ciment dès le premier contact eau-ciment jusqu'à 2 jours d'hydratation en se basant sur un modèle d'homogénéisation multi-échelle. Le retrait endogène est composé de deux déformations issues de deux mécanismes différents. Une première déformation d'origine chimique issue d'un bilan volumique global négatif des réactions chimiques d'hydratation, qui apparaît dès le premier contact eau-ciment. A partir de la prise, le matériau se rigidifie progressivement et la déformation d'origine chimique est freinée par le squelette solide du matériau pour donner naissance à un phénomène de dépression capillaire à l'origine de la deuxième phase de déformation (retrait d'autodessiccation). Les entrées du modèle mis au point sont essentiellement la composition chimique du ciment ainsi que sa finesse, le rapport eau-ciment (E/C), la température et les propriétés mécaniques des principales phases. Les sorties sont l'évolution des phases dans le temps, la réaction chimique d'hydratation, le module d'Young, la dépression capillaire, le retrait chimique et endogène