Characterization of an Algerian natural pozzolan for its use in eco-efficient cement

WOS:000367756300007International audienceThe paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)(2), water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime constumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view

Characterization of an Algerian natural pozzolan for its use in eco-efficient cement

WOS:000367756300007International audienceThe paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)(2), water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime constumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view

Bâtiments construits en adobe salin, durabilité centenaire et confort thermique dans un climat désertique

International audienceL’adobe est un matériau à inertie thermique importante, mais il se caractérise par unefaible résistance mécanique soit en compression ou en flexion. L’utilisation d’adobesalin confectionné à l'aide d'un sable salin dans les bâtiments traditionnels dans la zonesaharienne de l’Algérie présente une meilleure protection de ces bâtiments vis-à-vis desintempéries et offre une bonne isolation thermique au bâtiment. Nos mesuresexpérimentales effectuées sur les bâtiments traditionnels existants montrent quel’ambiance intérieure est tempérée et la température intérieure est quasiconstante variant entre 31 et 33 °C, alors que celle de l’extérieur dépasse les 50 °C,marquant ainsi un écart journalier d'environ 17 °C. Cela influe positivement sur leconfort thermique des habitants. Ce matériau apporte, par conséquent, une solutionidéale aux habitants du Sahara, et apporte du confort thermique à l’intérieur dubâtiment sans recours à la climatisation électrique

Bâtiments construits en adobe salin, durabilité centenaire et confort thermique dans un climat désertique

International audienceL’adobe est un matériau à inertie thermique importante, mais il se caractérise par unefaible résistance mécanique soit en compression ou en flexion. L’utilisation d’adobesalin confectionné à l'aide d'un sable salin dans les bâtiments traditionnels dans la zonesaharienne de l’Algérie présente une meilleure protection de ces bâtiments vis-à-vis desintempéries et offre une bonne isolation thermique au bâtiment. Nos mesuresexpérimentales effectuées sur les bâtiments traditionnels existants montrent quel’ambiance intérieure est tempérée et la température intérieure est quasiconstante variant entre 31 et 33 °C, alors que celle de l’extérieur dépasse les 50 °C,marquant ainsi un écart journalier d'environ 17 °C. Cela influe positivement sur leconfort thermique des habitants. Ce matériau apporte, par conséquent, une solutionidéale aux habitants du Sahara, et apporte du confort thermique à l’intérieur dubâtiment sans recours à la climatisation électrique

Effect of thermo-activation on mechanical strengths and chlorides permeability in pozzolanic materials

The present research aimed to study the combined effects of natural pozzolana and curing on the compressive and flexural strengths of mortars; it also investigated the chloride permeability of concrete. To do that, Ordinary Portland cement (CEMI) was used and three concrete preparations were made by incorporating natural pozzolana at a rate of 10, 20 and 30% by weight of CEMI. Moreover, three curing methods were employed. The first one is a standard curing method, at temperature 20 °C, and 2 other thermo-activation methods at the temperatures of 40 °C and 70 °C, for a setting time of 4 h. The thermo-activation methods were used to accelerate the initial hydration, for the purpose of improving the strength of the prepared mortars and concretes at the early age. The results obtained indicate that, substituting natural pozzolana for CEMI with a level below 20% gives strengths comparable to those obtained with CEMI alone. The curing methods at 40 °C and 70 °C allowed increasing mortar and concrete strengths at the early age; however, it was found that the temperature of 70 °C reduces strengths, at later age. Natural pozzolana limits the penetration of chlorides. Keywords: CEMI, Pozzolana, Hydration, Strength, Temperature, Chloride

Influence du type d’addition minérale sur les propriétés de transfert des Bétons AutoPlaçants

La formulation des bétons autoplaçants (BAP) présente certaines spécificités dont un volume élevé de pâte et une quantité importante d’ajouts minéraux. Ces deux paramètres influencent sensiblement les propriétés de transfert de ces bétons. Dans ce travail, nous avons étudié l’influence de la nature et du pourcentage de plusieurs additions minérales sur certaines propriétés de transfert (la diffusion des ions chlore et la perméabilité au gaz) des BAP. Trois différentes additions minérales ont été testées : des fillers calcaires, de la pouzzolane naturelle et des cendres volantes. Ensuite, nous avons cherché une probable relation analytique entre ces propriétés et la résistance à la compression de ces bétons. Au total, douze formulations ont été étudiées, elles couvrent trois différentes classes de résistances (30 MPa, 50 MPa et 70 MPa) et quatre types de bétons: un béton ordinaire vibré, un BAP à base de pouzzolanes naturelles, un BAP à base de fillers calcaires et un BAP à base de cendres volantes. Les résultats montrent que la nature de l’addition minérale dans les BAP influe considérablement sur les propriétés de transferts de ces bétons. Après 28, 90 et 360 jours de cure, les BAP contenant de la pouzzolane naturelle représentent des performances très comparables à celles obtenues sur des BAP à base de cendres volantes et bien meilleures que celles obtenues sur des BAP formulés avec du filler calcaire. Indépendamment du type d’addition minérale, les résultats confirment l’existence d’une forte corrélation entre le développement de la résistance à la compression et les propriétés de transferts des BAP

Effect of mineral admixture on resistance to sulphuric and hydrochloric acid attacks in selfcompacting concrete

International audienceThis paper presents a detailed experimental investigation of the acid resistance of economical self-compacting concrete (SCC) prepared with natural pozzolan, immersed for up to 12 weeks in sulphuric acid (H2SO4) and hydrochloric acid (HCl) solutions. The results are compared with those from a control concrete and other SCCs prepared with fly ash and limestone filler. The different factors considered in this study were the effect of mineral admixture type and the strength classes (30, 50, and 70 MPa) of the concrete specimens. In total, 12 formulations were tested. Mass and compressive strength losses are the main properties investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were used to better understand the kinetics of deterioration of each type of concrete. The results show the positive influence of natural pozzolan on the behaviour of SCC under both sulphuric and hydrochloric acid mediums

Influence of natural pozzolan, silica fume and limestone fine on strength, acid resistance and microstructure of mortar

International audienceBased on an ongoing experimental programme, this research focuses on the effect of various supplementary cementitious materials (SCMs) (natural pozzolan (NP)/silica fume (SF)/limestone fine (LF) at various substitution levels) on the microstructure and mechano-chemical resistance of blended mortar. The paper primarily considers the characteristics of these materials, including their strength and the effects of aggressive chemical environments, by using sulphuric acid and nitric acid. The porosity and pore size distribution of the mortars are also examined using mercury intrusion porosimetry (MIP).The microstructural changes in pastes caused by SCMs and the acid attack of the solution are analysed and related to the phase composition found by X-ray diffraction (XRD). Microstructural investigations, such as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), were also used to support the explanation for these mechanisms.The results, according to ASTM C267, showed that the addition of natural pozzolan or limestone fine would improve the acid resistance of mortar, but at different rates depending on the proportion of SCMs. On the other hand, mortars with silica fume are severely damaged in the sulphuric acid environment

Influence du type d’addition minérale sur les propriétés de transfert des Bétons AutoPlaçants Influence of the type of mineral admixtures on the transport properties of self compacting concrete

La formulation des bétons autoplaçants (BAP) présente certaines spécificités dont un volume élevé de pâte et une quantité importante d’ajouts minéraux. Ces deux paramètres influencent sensiblement les propriétés de transfert de ces bétons. Dans ce travail, nous avons étudié l’influence de la nature et du pourcentage de plusieurs additions minérales sur certaines propriétés de transfert (la diffusion des ions chlore et la perméabilité au gaz) des BAP. Trois différentes additions minérales ont été testées : des fillers calcaires, de la pouzzolane naturelle et des cendres volantes. Ensuite, nous avons cherché une probable relation analytique entre ces propriétés et la résistance à la compression de ces bétons. Au total, douze formulations ont été étudiées, elles couvrent trois différentes classes de résistances (30 MPa, 50 MPa et 70 MPa) et quatre types de bétons: un béton ordinaire vibré, un BAP à base de pouzzolanes naturelles, un BAP à base de fillers calcaires et un BAP à base de cendres volantes. Les résultats montrent que la nature de l’addition minérale dans les BAP influe considérablement sur les propriétés de transferts de ces bétons. Après 28, 90 et 360 jours de cure, les BAP contenant de la pouzzolane naturelle représentent des performances très comparables à celles obtenues sur des BAP à base de cendres volantes et bien meilleures que celles obtenues sur des BAP formulés avec du filler calcaire. Indépendamment du type d’addition minérale, les résultats confirment l’existence d’une forte corrélation entre le développement de la résistance à la compression et les propriétés de transferts des BAP. Formulation of self compacting concrete (SCC) has some specific characteristics including a high volume of paste and a large amount of mineral admixtures. These two parameters influence significantly the transport properties of SCC. In this work, we studied the influence of nature and the percentage of several mineral admixtures on some transport properties (the ions diffusion and chloride gas permeability) of the SCC. Three different mineral additives were tested: the limestone fillers, the natural pozzolan and the fly ash. Then we looked for the analytical relationship between these properties and the compressive strength of concrete. A total of twelve formulations were studied, they cover three different compressive strength classes (30 MPa, 50 MPa and 70 MPa) and four types of concrete: ordinary vibrated concrete, a SCC containing natural pozzolan, a SCC based with limestone fillers and SCC containing fly ash. The results show that the nature of the mineral admixtures in SCC influence on the transport properties of these concretes. After 28, 90 and 360 days of curing, the SCC containing natural pozzolan represent very similar performance to those obtained on SCC containing fly ash and much better than those obtained on SCC formulated with limestone filler. Regardless of the type of mineral admixtures, the results confirm the existence of a strong correlation between development of compressive strength and transport properties of SCC

Influence of Mineral Admixtures on the Permeation Properties of Self-Compacting Concrete at Different Ages

International audienceDue to its specific properties, the study of self-compacting concrete (SCC) represents an area of research that has strong potential for development. However, in spite of the interest of researchers in this new material, SCC has not yet gained universal acceptance as a construction material, and its application remains limited. The development of an economical SCC with interesting properties in the fresh and hardened state is important for the acceptance of such a concrete. Algerian natural source Pozzolan is rarely used in SCC due to the absence of any thorough study of its properties. This study investigates the permeation properties of SCC mixtures made with this Algerian natural Pozzolan, compared with conventional vibrated concrete and other SCC mixtures containing fly ash or limestone filler. Additionally, the correlations between chloride diffusion and sorptivity, and between apparent gas permeability and chloride diffusion, were investigated. Results indicate that, despite its economic benefits, SCC incorporating natural Pozzolan presents very low permeation properties (for example: lower migration coefficients compared to the SCC mixtures with limestone filler or ordinary vibrated concrete (difference > 50 % for results of the 30 MPa strength class). The relation between chloride diffusion and sorptivity, and between apparent gas permeability and chloride diffusion, is also confirmed