Influence de la température sur la thixotropie des bétons autoplaçants

L objectif de cette thèse est d étudier l influence de la température sur la thixotropie des bétons autoplaçants (BAP). L intérêt de ce travail s inscrit dans la perspective d optimiser les formulations des BAP dans une large gamme de température. Un plan factoriel composite centré a été adopté dans le but de minimiser le nombre d essais tout en étudiant les effets des facteurs (température et dosage en agent de viscosité (AV)) et leurs interactions sur les propriétés rhéologiques des BAP.La première phase de l étude consistait à quantifier la thixotropie du béton juste après le malaxage et durant la période dormante en fonction du dosage en AV à des températures comprises entre 11.3 et 30.7C selon le protocole proposé par Wallevik sur le rhéomètre BML4. Les résultats ont montré que l indice de thixotropie présente un minimum respectivement pour un dosage en AV de 0.28 % (par rapport à la masse d eau) et une température de 24C. Cependant, ce protocole ne permet pas d étudier la déstructuration des BAP, facteur recherché par exemple dans les coulages multicouches. Nous avons donc été amenés à retenir un protocole utilisé dans les gels et appelé protocole Dolz. L application de ce dernier aux pâtes de ciment et aux BAP a permis de mettre en évidence une nouvelle grandeur, le potentiel de déstructuration K. Les valeurs du potentiel K montrent qu au delà d un certain dosage en AV et d une certaine température, apparaissent des phénomènes d encombrement qui réduisent le potentiel K. Ainsi, le potentiel K apporte des informations complémentaires pour l aide à la sélection de dosages adéquats du couple superplastifiant agent de viscosité en fonction de la température de coulage.The aim of this thesis was to study the influence of the temperature on the thixotropy of self-consolidating concrete (SCC). The research significance comes within the perspective to optimize the design of SCC in a wide range temperature. A factorial composite experimental plan was carried out in order to minimize the total number of tests while studying the effects of factors (temperature and dosage of viscosity modifying admixture (VMA)) and their interactions on the rheological properties of SCC. The first phase of the study was to quantify the thixotropy of concrete proportioned with various dosage of VMA at different temperatures ranging from 11.3 to 30.7C just after mixing and at different time during the dormant period using the protocol proposed by Wallevik in BML4 rheometer. The results indicated that the values of thixotropy index present a minimum respectively with a VMA dosage of 0.28 % (by mass of water) and a temperature of 24C.On the other hand, this protocol does not allow studying the destructuration of SCC, useful factor needed for example in the multi-layer casting. We therefore had to retain a protocol used in gels and called Dolz protocol. The application of this last to cement pastes and SCC has revealed a new grandeur, the potential of destructuration K. The values of K show that beyond a certain dosage in VMA and a certain temperature, the congestion phenomena appear that reduce the potential K. In this case, the potential of destructuration provides complementary information to assist in the selection of appropriate dosages of couple superlasticizer-VMA whatever the casting temperature may be.ARRAS-Bib.electronique (620419901) / SudocSudocFranceF

Sustainable concrete: Potency of sugarcane bagasse ash as a cementitious material in the construction industry

ACLThe aim of this research is to determine the mechanical and durability properties of sugarcane bagasse ash (SCBA) as a partial replacement to Ordinary Portland Cement (OPC) in concrete. The SCBA was partially replaced at the percentage of 5 %, 10 %, 15 % and 20 % by weight of cement for a mean target strength of 27 MPa. A slump range of 130–150 mm was maintained constant throughout the experiment procedures. A total of 120 cubes and 30 rectangular beams were tested and the results were compared with control concrete. To evaluate the behaviour of SCBA on concrete, different tests were conducted on the concrete specimens namely, compressive strength, flexural strength, water absorption, water penetration, carbonation and ultrasonic pulse velocity. The results demonstrated that at 120 days of curing, compressive strength increased by 2.6 % and 1.7 % for 5 % and 10 % replacement level. The water absorption increased by 255 %, 390 %, 438 % and 488 % for 5 %, 10 %, 15 % and 20 % replacement level. The other tests showed decreased flexural strength and ultrasonic pulse velocity and increased water penetration and carbonation depth. The study inferred that 10 % replacement of OPC by SCBA exhibited positive performances and can be considered a suitable cementitious material in the construction industry

A sustainable approach in using construction and demolition waste materials in concrete

International audiencePurpose The purpose of this paper is to investigate the potential use of construction and demolition waste materials (C&DWM) as an alternative for natural fine aggregates (NFA), in view to solve the disposal problems caused due to landfills. In addition, to evaluate its suitability as a sustainable material, mechanical and durability properties have been performed on different proportions of concrete blending and the results recorded were compared with the reference concrete values. Design/methodology/approach In this research, the NFA were replaced at the proportion of 25%, 50%, 75% and 100% of C&DWM with a constant slump range of 130 mm–150 mm. This parameter will assess the consistency of the fresh concrete during transportation process. The characteristics of the end product was evaluated through various tests conducted on hardened concrete samples, namely, compressive strength, flexural strength, depth of penetration of water under pressure, rapid chloride penetration test, carbonation test and ultrasonic pulse velocity (UPV) test. All results recorded were compared with the reference concrete values. Findings The results demonstrated that the use of C&DWM in concrete portrayed prospective characteristics that could eventually change the concept of sustainable concrete. It was noted that the compressive and flexural strength decreased with the addition of C&DWM, but nevertheless, a continuous increase in strength was observed with an increase in curing period. Moreover, the increase in rapid chloride penetration and decrease in UPV over time period suggested that the concrete structure has improved in terms of compactness, thus giving rise to a less permeable concrete. The mechanical tests showed little discrepancies in the final results when compared to reference concrete. Therefore, it is opined that C&DWM can be used effectively in concrete. Originality/value This study explores the possible utilisation of C&DWM as a suitable surrogative materials in concrete in a practical perspective, where the slump parameter will be kept constant throughout the experimental process. Moreover, research on this method is very limited and is yet to be elaborated in-depth. This approach will encourage the use of C&DWM in the construction sector and in the same time minimise the disposal problems caused due to in landfills

Effect of temperature on early-age properties of self-consolidating concrete equivalent mortar

ACLIn this study, the effect of material temperature during casting on fresh properties, hydration kinetics, and early-age compressive strength of self-consolidating concrete (SCC) was evaluated. Concrete equivalent mortars (CEMs) based on SCC mixture designs with water-to-binder ratios of 0.41 and 0.45 were investigated. The SCC mixtures are targeted for infrastructure and building construction and precast applications. The CEMs were prepared at temperatures ranging from 8 to 36°C. Superplasticizer (SP) and air-entraining agent (AEA) demand were evaluated for the CEM mixtures made with different supplementary cementing material (SCM) and limestone filler types. Test results showed that the ambient temperature can significantly affect the SP and AEA demand, hydration kinetics, and compressive strength after 1 d of age. According to the ultraviolet–visible spectrophotometry (UV/Vis) test, the absorption rate of polycarboxylate-based SP decreased with temperature. In contrast, the sensitivity of polynaphthalene sulfonate-based SP to temperature was minimal. Relationships between the variations of different admixture contents, heat flux, and compressive strength with temperature were developed. For a constant slump flow and air content, the demand of the SP and AEA, heat flux, and 1-d compressive strength of CEMs increased linearly with material temperature

Impression 3D pour paroi composite à base de terre et de lin

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3D-Printable Materials Made with Industrial By-Products: Formulation, Fresh and Hardened Properties

Growing in the field of construction, 3D printing allows to build non-standard shapes and to optimise the use of resources. The development of printable materials requires good control of the fresh state of the material—between mixing and printing, a printable material has to evolve from fluid matter to be pumpable (extrudability) up to a matter supporting its own weight and those of superior layers (buildability). Our researches are focused on printable materials used in large printers, i.e., printers able to build structural pieces for buildings. As many pumps and printers can be used to achieve a wide range of parts, this paper presents a simple method to provide valuable guidance to users when a decision needs to be made about printable materials. In this context, our researches both try to maximise the use of industrial by-products to reduce the environmental cost of printed material and to propose tests easy to carry out in the field. Consequently, on the one hand, some printable materials that mainly include quarry washing fines have been developed and, on the other hand, Fall cone and Vicat tests have been used to determine the printability limit. By not focusing on a single formula, the novelty of this paper is to present to readers some parametric models, i.e., a methodology that can be used according to their own devices and applications. Based on a design of experiments, 20 formulas have been tested. Parameters that influence the quality of printing are highlighted. Mechanical tests results at hardened state and shrinkage measurements are also shown to demonstrate the ability of some formulas to be structural materials: compressive strengths at 28 days between 7.50 MPa and 18.40 MPa

Evaluate the influence of starch on earth/hemp or flax straws mixtures properties in presence of superplasticizer

In this paper, we study the influence of two types of starch on earth hemp or flax straw mixtures at fresh and hardened states. The main goal is to propose new non-load bearing earthen for indoor. The mass percentage of starch/binder (S/B) in mixtures was fixed at 1% of mass. The VEBE consistometer test has been used to fix a similar consistency between mixtures. The targeted workability has to allow an easy introduction of materials in the moulds. Adding both of starch has shown a positive effect on mixtures workability at the fresh state and mechanical resistances at the hardened state. At hardened state, mechanical and thermal-acoustic performances have been measured on laboratory samples and blocks at real scale. Results have shown a significant effect of starch on mechanical strengths

3D-Printable Materials Made with Industrial By-Products: Formulation, Fresh and Hardened Properties

International audienceGrowing in the field of construction, 3D printing allows to build non-standard shapes and to optimise the use of resources. The development of printable materials requires good control of the fresh state of the material—between mixing and printing, a printable material has to evolve from fluid matter to be pumpable (extrudability) up to a matter supporting its own weight and those of superior layers (buildability). Our researches are focused on printable materials used in large printers, i.e., printers able to build structural pieces for buildings. As many pumps and printers can be used to achieve a wide range of parts, this paper presents a simple method to provide valuable guidance to users when a decision needs to be made about printable materials. In this context, our researches both try to maximise the use of industrial by-products to reduce the environmental cost of printed material and to propose tests easy to carry out in the field. Consequently, on the one hand, some printable materials that mainly include quarry washing fines have been developed and, on the other hand, Fall cone and Vicat tests have been used to determine the printability limit. By not focusing on a single formula, the novelty of this paper is to present to readers some parametric models, i.e., a methodology that can be used according to their own devices and applications. Based on a design of experiments, 20 formulas have been tested. Parameters that influence the quality of printing are highlighted. Mechanical tests results at hardened state and shrinkage measurements are also shown to demonstrate the ability of some formulas to be structural materials: compressive strengths at 28 days between 7.50 MPa and 18.40 MPa

Study on the Replacement of Construction &Demolition Waste Materials as Fine Aggregates inthe Production of Low Strength Concrete

ACLThe construction industry is searching for a more ecological material which can provide a good sustainability and also have the eco-friendly label. The quest to protect the environment has enabled researches to find alternate materials which can fit the concrete matrix to produce a concrete that can meet the demand of the construction industry. The purpose of this research is to substitute traditional materials with construction and demolition waste by keeping the same slump value and by replacing natural fine aggregates (NFA) with Construction and Demolition Waste (C&D) materials and investigate their properties on fresh and hardened concrete. To determine and compare the properties, different tests were performed to evaluate the workability, density, compressive strength, flexural strength and absorption of each concrete mix. The results demonstrated that, construction and demolition waste materials with a define slump range decreases the compressive strength and flexural strength, and the water absorption increases with increasing C&D content

Synthesis and evaluation of starch-based polymers as potential dispersants in cement pastes and self leveling compounds

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