Propriedades físicas e mecânicas de cimentos de ionômero de vidro encapsulados e não encapsulados

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Behaviour of grouted dowels used in precast concrete connections

This research deals with the behaviour of grouted dowels used in beam-to-column connections in precast concrete structures. The research focuses primarily on the theoretical and experimental analysis of the resistance mechanism of the dowels. The experimental programme included 15 models for analysing the following variations in dowel parameters: a) dowel diameters of 16, 20 and 25 mm, b) dowel inclinations of 0 degrees (i.e. perpendicular to the interface), 45 degrees and 60 degrees, c) compressive strength of classes C35 and C50 for the concrete adjacent to the dowels, and d) the absence or presence of compressive loads normal to the interface. The experimental results indicate that the ultimate capacity and shear stiffness of the inclined dowels are significantly higher than those of the perpendicular dowels. Based on these results, an analytical model is proposed that considers the influence of the parameters studied regarding the capacity of the dowel.

A new damage model for composite laminates

Aircraft composite structures must have high stiffness and strength with low weight, which can guarantee the increase of the pay-load for airplanes without losing airworthiness. However, the mechanical behavior of composite laminates is very complex due the inherent anisotropy and heterogeneity. Many researchers have developed different failure progressive analyses and damage models in order to predict the complex failure mechanisms. This work presents a damage model and progressive failure analysis that requires simple experimental tests and that achieves good accuracy. Firstly, the paper explains damage initiation and propagation criteria and a procedure to identify the material parameters. In the second stage, the model was implemented as a UMAT (User Material Subroutine), which is linked to finite element software, ABAQUS (TM), in order to predict the composite structures behavior. Afterwards, some case studies, mainly off-axis coupons under tensile or compression loads, with different types of stacking sequence were analyzed using the proposed material model. Finally, the computational results were compared to the experimental results, verifying the capability of the damage model in order to predict the composite structure behavior. (C) 2011 Elsevier Ltd. All rights reserved.

Mechanical analysis of conventional and small diameter conical implant abutments

PURPOSE. The aim of the present study was to evaluate if a smaller morse taper abutment has a negative effect on the fracture resistance of implant-abutment connections under oblique compressive loads compared to a conventional abutment MATERIALS AND METHODS. Twenty morse taper conventional abutments (4.8 mm diameter) and smaller abutments (3.8 mm diameter) were tightened (20 Ncm) to their respective implants (3.5 x 11 mm) and after a 10 minute interval, implant/abutment assemblies were subjected to static compressive test, performed in a universal test machine with 1 mm/min displacement, at 45 degrees inclination. The maximum deformation force was determined. Data were statistically analyzed by student t test. RESULTS. Maximum deformation force of 4.8 mm and 3.8 mm abutments was approximately 95.33 kgf and 95.25 kgf, respectively, but no fractures were noted after mechanical test. Statistical analysis demonstrated that the evaluated abutments were statistically similar (P=.230). CONCLUSION. Abutment measuring 3.8 mm in diameter (reduced) presented mechanical properties similar to 4.8 mm (conventional) abutments, enabling its clinical use as indicated. [J Adv Prosthodont 2012;4:158-61]

Performance estimation for concretes made with recycled aggregates of construction and demolition waste of some Brazilian cities

The aim of this paper is to verify the influence of composition variability of recycled aggregates (RA) of construction and demolition wastes (CDW) on the performance of concretes. Performance was evaluated building mathematical models for compressive strength, modulus of elasticity and drying shrinkage. To obtain such models, an experimental program comprising 50 concrete mixtures was carried out. Specimens were casted, tested and results for compressive strength, modulus of elasticity and drying shrinkage were statistically analyzed. Models inputs are CDW composition observed at seven Brazilian cities. Results confirm that using RA from CDW for concrete building is quite feasible, independently of its composition, once compressive strength and modulus of elasticity still reached considerable values. We concluded the variability presented by recycled aggregates of CDW does not compromise their use for concrete building. However, this information must be used with caution, and experimental tests should always be performed to certify concrete properties.

Cement-base bearing pads mortar for connections in the precast concrete: study of surface roughness

Bearing pads are used in precast concrete connections to avoid concentrated stresses in the contact area between the precast elements. In the present research, the bearing pads are Portland cement mortar with styrene-butadiene latex (SB), lightweight aggregate (expanded vermiculite-term) and short fibers (polypropylene, glass and PVA), in order to obtain a material with low modulus of elasticity and high tenacity, compared with normal Portland cement mortar. The objective of this paper is to analyze the influence of surface roughness on the pads and test other types of polypropylene fibers. Tests were carried out to characterize the composite and test on bearing pads. Characterization tests show compressive strength of 41MPa and modulus of elasticity of 12.8GPa. The bearing pads tests present 30% reduction of stiffness in relation to a reference mortar. The bearing pads with roughness on both sides present a reduction up to 30% in stiffness and an increase in accumulated deformation of more than 120%, regarding bearing pads with both sides smooth.

Abrasividade pendular e a resistência mecânica das rochas

Esse trabalho emprega o método para avaliar a abrasividade proposto por Golovanevskiy e Bearman (2008). Esse método, ensaio de abrasão por impacto deslizante (Gouging Abrasion Test), é realizado em condições de alta tensão/alto impacto de desgaste. O método consiste de uma ponteira cilíndrica com uma ponta cônica de 90º, que, em trajetória pendular, atinge uma amostra de rocha com energia de impacto de 300 J e velocidade da ordem de 5,2 m/s. O Gouging Abrasion Index (Gi) é calculado como sendo a média do diâmetro da ponta cônica, após desgaste, em milímetros e o resultado é multiplicado por 10. Esse trabalho verificou a adequabilidade do Gouging Abrasion Test, para um pequeno número de amostras de rocha, que representam, qualitativamente, os principais tipos de rocha encontrados em trabalhos de corte, perfuração e britagem no Brasil, e a sua correlação com outros ensaios consagrados como a resistência à compressão, o desgaste Amsler e a dureza Knoop. Essa análise mostrou alta correlação entre Gi e a dureza Knoop (R² = 0,94), baixa correlação com o desgaste

Some issues concerning the dynamic response and damage of composite laminates subjected to low velocity impact

Abstract. This thesis presents a discussion on a few specific topics regarding the low velocity impact behaviour of laminated composites. These topics were chosen because of their significance as well as the relatively limited attention received so far by the scientific community. The first issue considered is the comparison between the effects induced by a low velocity impact and by a quasi-static indentation experimental test. An analysis of both test conditions is presented, based on the results of experiments carried out on carbon fibre laminates and on numerical computations by a finite element model. It is shown that both quasi-static and dynamic tests led to qualitatively similar failure patterns; three characteristic contact force thresholds, corresponding to the main steps of damage progression, were identified and found to be equal for impact and indentation. On the other hand, an equal energy absorption resulted in a larger delaminated area in quasi-static than in dynamic tests, while the maximum displacement of the impactor (or indentor) was higher in the case of impact, suggesting a probably more severe fibre damage than in indentation. Secondly, the effect of different specimen dimensions and boundary conditions on its impact response was examined. Experimental testing showed that the relationships of delaminated area with two significant impact parameters, the absorbed energy and the maximum contact force, did not depend on the in-plane dimensions and on the support condition of the coupons. The possibility of predicting, by means of a simplified numerical computation, the occurrence of delaminations during a specific impact event is also discussed. A study about the compressive behaviour of impact damaged laminates is also presented. Unlike most of the contributions available about this subject, the results of compression after impact tests on thin laminates are described in which the global specimen buckling was not prevented. Two different quasi-isotropic stacking sequences, as well as two specimen geometries, were considered. It is shown that in the case of rectangular coupons the lay-up can significantly affect the damage induced by impact. Different buckling shapes were observed in laminates with different stacking sequences, in agreement with the results of numerical analysis. In addition, the experiments showed that impact damage can alter the buckling mode of the laminates in certain situations, whereas it did not affect the compressive strength in every case, depending on the buckling shape. Some considerations about the significance of the test method employed are also proposed. Finally, a comprehensive study is presented regarding the influence of pre-existing in-plane loads on the impact response of laminates. Impact events in several conditions, including both tensile and compressive preloads, both uniaxial and biaxial, were analysed by means of numerical finite element simulations; the case of laminates impacted in postbuckling conditions was also considered. The study focused on how the effect of preload varies with the span-to-thickness ratio of the specimen, which was found to be a key parameter. It is shown that a tensile preload has the strongest effect on the peak stresses at low span-to-thickness ratios, leading to a reduction of the minimum impact energy required to initiate damage, whereas this effect tends to disappear as the span-to-thickness ratio increases. On the other hand, a compression preload exhibits the most detrimental effects at medium span-to-thickness ratios, at which the laminate compressive strength and the critical instability load are close to each other, while the influence of preload can be negligible for thin plates or even beneficial for very thick plates. The possibility to obtain a better explanation of the experimental results described in the literature, in view of the present findings, is highlighted. Throughout the thesis the capabilities and limitations of the finite element model, which was implemented in an in-house program, are discussed. The program did not include any damage model of the material. It is shown that, although this kind of analysis can yield accurate results as long as damage has little effect on the overall mechanical properties of a laminate, it can be helpful in explaining some phenomena and also in distinguishing between what can be modelled without taking into account the material degradation and what requires an appropriate simulation of damage. Sommario. Questa tesi presenta una discussione su alcune tematiche specifiche riguardanti il comportamento dei compositi laminati soggetti ad impatto a bassa velocità. Tali tematiche sono state scelte per la loro importanza, oltre che per l’attenzione relativamente limitata ricevuta finora dalla comunità scientifica. La prima delle problematiche considerate è il confronto fra gli effetti prodotti da una prova sperimentale di impatto a bassa velocità e da una prova di indentazione quasi statica. Viene presentata un’analisi di entrambe le condizioni di prova, basata sui risultati di esperimenti condotti su laminati in fibra di carbonio e su calcoli numerici svolti con un modello ad elementi finiti. È mostrato che sia le prove quasi statiche sia quelle dinamiche portano a un danneggiamento con caratteristiche qualitativamente simili; tre valori di soglia caratteristici della forza di contatto, corrispondenti alle fasi principali di progressione del danno, sono stati individuati e stimati uguali per impatto e indentazione. D’altro canto lo stesso assorbimento di energia ha portato ad un’area delaminata maggiore nelle prove statiche rispetto a quelle dinamiche, mentre il massimo spostamento dell’impattatore (o indentatore) è risultato maggiore nel caso dell’impatto, indicando la probabilità di un danneggiamento delle fibre più severo rispetto al caso dell’indentazione. In secondo luogo è stato esaminato l’effetto di diverse dimensioni del provino e diverse condizioni al contorno sulla sua risposta all’impatto. Le prove sperimentali hanno mostrato che le relazioni fra l’area delaminata e due parametri di impatto significativi, l’energia assorbita e la massima forza di contatto, non dipendono dalle dimensioni nel piano dei provini e dalle loro condizioni di supporto. Viene anche discussa la possibilità di prevedere, per mezzo di un calcolo numerico semplificato, il verificarsi di delaminazioni durante un determinato caso di impatto. È presentato anche uno studio sul comportamento a compressione di laminati danneggiati da impatto. Diversamente della maggior parte della letteratura disponibile su questo argomento, vengono qui descritti i risultati di prove di compressione dopo impatto su laminati sottili durante le quali l’instabilità elastica globale dei provini non è stata impedita. Sono state considerate due differenti sequenze di laminazione quasi isotrope, oltre a due geometrie per i provini. Viene mostrato come nel caso di provini rettangolari la sequenza di laminazione possa influenzare sensibilmente il danno prodotto dall’impatto. Due diversi tipi di deformate in condizioni di instabilità sono stati osservati per laminati con diversa laminazione, in accordo con i risultati dell’analisi numerica. Gli esperimenti hanno mostrato inoltre che in certe situazioni il danno da impatto può alterare la deformata che il laminato assume in seguito ad instabilità; d’altra parte tale danno non ha sempre influenzato la resistenza a compressione, a seconda della deformata. Vengono proposte anche alcune considerazioni sulla significatività del metodo di prova utilizzato. Infine viene presentato uno studio esaustivo riguardo all’influenza di carichi membranali preesistenti sulla risposta all’impatto dei laminati. Sono stati analizzati con simulazioni numeriche ad elementi finiti casi di impatto in diverse condizioni di precarico, sia di trazione sia di compressione, sia monoassiali sia biassiali; è stato preso in considerazione anche il caso di laminati impattati in condizioni di postbuckling. Lo studio si è concentrato in particolare sulla dipendenza degli effetti del precarico dal rapporto larghezza-spessore del provino, che si è rivelato un parametro fondamentale. Viene illustrato che un precarico di trazione ha l’effetto più marcato sulle massime tensioni per bassi rapporti larghezza-spessore, portando ad una riduzione della minima energia di impatto necessaria per innescare il danneggiamento, mentre questo effetto tende a scomparire all’aumentare di tale rapporto. Il precarico di compressione evidenzia invece gli effetti più deleteri a rapporti larghezza-spessore intermedi, ai quali la resistenza a compressione del laminato e il suo carico critico di instabilità sono paragonabili, mentre l’influenza del precarico può essere trascurabile per piastre sottili o addirittura benefica per piastre molto spesse. Viene evidenziata la possibilità di trovare una spiegazione più soddisfacente dei risultati sperimentali riportati in letteratura, alla luce del presente contributo. Nel corso della tesi vengono anche discussi le potenzialità ed i limiti del modello ad elementi finiti utilizzato, che è stato implementato in un programma scritto in proprio. Il programma non comprende alcuna modellazione del danneggiamento del materiale. Viene però spiegato come, nonostante questo tipo di analisi possa portare a risultati accurati soltanto finché il danno ha scarsi effetti sulle proprietà meccaniche d’insieme del laminato, esso possa essere utile per spiegare alcuni fenomeni, oltre che per distinguere fra ciò che si può riprodurre senza tenere conto del degrado del materiale e ciò che invece richiede una simulazione adeguata del danneggiamento.

Physical and mineralogical changes of Hungarian monumental stones exposed to different conditions: stone-testing in-situ and under laboratory conditions

The Székesfehérvár Ruin Garden is a unique assemblage of monuments belonging to the cultural heritage of Hungary due to its important role in the Middle Ages as the coronation and burial church of the Kings of the Hungarian Christian Kingdom. It has been nominated for “National Monument” and as a consequence, its protection in the present and future is required. Moreover, it was reconstructed and expanded several times throughout Hungarian history. By a quick overview of the current state of the monument, the presence of several lithotypes can be found among the remained building and decorative stones. Therefore, the research related to the materials is crucial not only for the conservation of that specific monument but also for other historic structures in Central Europe. The current research is divided in three main parts: i) description of lithologies and their provenance, ii) physical properties testing of historic material and iii) durability tests of analogous stones obtained from active quarries. The survey of the National Monument of Székesfehérvár, focuses on the historical importance and the architecture of the monument, the different construction periods, the identification of the different building stones and their distribution in the remaining parts of the monument and it also included provenance analyses. The second one was the in situ and laboratory testing of physical properties of historic material. As a final phase samples were taken from local quarries with similar physical and mineralogical characteristics to the ones used in the monument. The three studied lithologies are: fine oolitic limestone, a coarse oolitic limestone and a red compact limestone. These stones were used for rock mechanical and durability tests under laboratory conditions. The following techniques were used: a) in-situ: Schmidt Hammer Values, moisture content measurements, DRMS, mapping (construction ages, lithotypes, weathering forms) b) laboratory: petrographic analysis, XRD, determination of real density by means of helium pycnometer and bulk density by means of mercury pycnometer, pore size distribution by mercury intrusion porosimetry and by nitrogen adsorption, water absorption, determination of open porosity, DRMS, frost resistance, ultrasonic pulse velocity test, uniaxial compressive strength test and dynamic modulus of elasticity. The results show that initial uniaxial compressive strength is not necessarily a clear indicator of the stone durability. Bedding and other lithological heterogeneities can influence the strength and durability of individual specimens. In addition, long-term behaviour is influenced by exposure conditions, fabric and, especially, the pore size distribution of each sample. Therefore, a statistic evaluation of the results is highly recommended and they should be evaluated in combination with other investigations on internal structure and micro-scale heterogeneities of the material, such as petrographic observation, ultrasound pulse velocity and porosimetry. Laboratory tests used to estimate the durability of natural stone may give a good guidance to its short-term performance but they should not be taken as an ultimate indication of the long-term behaviour of the stone. The interdisciplinary study of the results confirms that stones in the monument show deterioration in terms of mineralogy, fabric and physical properties in comparison with quarried stones. Moreover stone-testing proves compatibility between quarried and historical stones. Good correlation is observed between the non-destructive-techniques and laboratory tests results which allow us to minimize sampling and assessing the condition of the materials. Concluding, this research can contribute to the diagnostic knowledge for further studies that are needed in order to evaluate the effect of recent and future protective measures.

Laboratory study of grouted macadams impregnated with mine waste geopolymeric binder

A new type of pavement has been gaining popularity over the last few years in Europe. It comprises a surface course with a semi-flexible material that provides significant advantages in comparison to both concrete and conventional asphalt, having both rut resistance and a degree of flexibility. It also provides good protection against the ingress of water to the foundation, since it has an impermeable surface. The semi-flexible material, generally known as grouted macadam, comprises an open-graded asphalt skeleton with 25% to 35% voids into which a cementitious slurry is grouted. This hybrid mixture provides good rut resistance and a surface highly resistant to fuel and oil spillage. Such properties allow it to be used in industrial areas, airports and harbours, where those situations are frequently associated with heavy and slow traffic. Grouted Macadams constitute a poorly understood branch of pavement technology and have generally been relegated to a role in certain specialist pavements whose performance is predicted on purely empirical evidence. Therefore, the main objectives of this project were related to better understanding the properties of this type of material, in order to predict its performance more realistically and to design pavements incorporating grouted macadam more accurately. Based on a standard mix design, several variables were studied during this project in order to characterise the behaviour of Grouted Macadams in general, and the influence of those variables on the fundamental properties of the final mixture. In this research project, one approach was used to the design of pavements incorporating Grouted Macadams: a traditional design method, based on laboratory determined of the stiffness modulus and the compressive strength.

Comportement thermique des géopolymères obtenus à partir d'une argile kaolinite

The aim of this work is to study the thermal behavior of geopolymers derived from kaolinite (clay). The geopolymers were characterized by various technics: Thermal analysis (DTA, TGA and dilatometer), X-ray diffractography (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Certain physical properties of the products were equally determined: linear shrinkage of curing, percentage of water absorption and compressive strength. The results obtained after drying and thermal treatment showed that the products preserved their initial forms, but showed variable colours based on the temperatures they were treated at. The products obtained at 90, 300 and 500 °C contained hydroxysodalite. The synthesis of geopolymers is not complete at 300 °C (presence of kaolinite in the material) but the products obtained are quite consolidated. The geopolymers obtained have weak values of linear shrinkage of curing (less than 0.6 %) and the compressive strength increases from room temperature (4.9 Mpa) up to 400 °C (8.9 MPa) then becomes constant between 400 and 500 °C. The combination of results demonstrates the efficiency of the temperature parameter during the synthesis of geopolymers based on kaolinite. // L’objet de ce travail est l’étude du comportement thermique des géopolymères à base d’une argile kaolinite. Les produits obtenus ont été caractérisés au moyen de plusieurs techniques : analyses thermiques (ATD, ATG et dilatométrie), microscopie électronique à balayage (MEB), analyse par diffraction de rayons X (DRX), analyse infrarouge par transformée de Fourier (IRTF). Certaines propriétés physiques des produits obtenus ont également été déterminées : retrait linéaire de cuisson, pourcentage d’absorption d’eau et résistance à la compression. Les résultats obtenus montrent qu’après le séchage et à la fin du traitement thermique, les éprouvettes des produits conservent leur forme initiale mais présentent une variation de couleur en fonction de la température de traitement. Les produits obtenus à 90, 300 et 500 °C contiennent de l’hydroxysodalite. La réaction de synthèse géopolymère n’est pas encore terminée au moins à 300 °C (présence de kaolinite dans le matériau) mais les produits obtenus sont assez consolidés. Les géopolymères obtenus présentent de faibles valeurs de retrait linéaire de cuisson (inférieure à 0,6 %) et une résistance à la compression qui augmente de la température ambiante (4,9 MPa) jusqu’à 400 °C (8,9 MPa) puis devient constante entre 400 et 500 °C. L’ensemble de ces résultats permet de mettre en exergue l’efficacité du paramètre « température » au cours de la synthèse des géopolymères à base de kaolinite.

EFFETS DE L’INCORPORATION D’ADJUVANTS MINÉRAUX SUR LES PROPRIÉTÉS DE CIMENTS GÉOPOLYMÈRES A BASE DE SCORIES VOLCANIQUES

Volcanic ashes are raw materials from geological deposits with a range of chemical compositions. When combined with suitable alkali activators they can be converted to geopolymers cement at ambient temperature. In this work we have investigated the possibility of use bauxite and oyster shells as mineral admixture in volcanic ashes, to enhance the properties of geopolymers synthesized. Different methods of analyses such as Fourier Transform Infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and Scanning Electron Microscopy (SEM) were used to assess the variation of setting time, linear shrinkage and 28 days compressive strength of geopolymers paste. The bauxite and the oyster shells were characterized using inductively coupled plasma (ICP-AES), thermal analyses (DSC/ATG), FTIR and X-ray diffractometry. The results of these analyses has showed that bauxite and oyster shells are respectively source of Al2O3 and of CaO, and can compensate the deficiencies of these oxides in volcanic ashes. Adding mineral admixture dissolve slowly in high alkaline medium. Addition of about 20% of bauxite or 10% of oyster shells is seen to decrease the setting time respectively from 415 to 275 min and 195 min. Linear shrinkage decrease with percentage of bauxite or of oyster shells added. Efflorescence is reduced by adding 10% of bauxite. 28 days compressive strength of geopolymeric materials increase respectively for 4.77 and 7.52% for 10% of bauxite or 20% of oyster shells added. More than these percentage additive has a deleterious effect on compressive strength due to crystalized mineralogical phases of the admixture.

Elaboration et caractérisation de ciments géopolymères à base de scories volcaniques

Two types of volcanic ashes referenced as ZD (volcanic ashes from Djoungo) and ZG (volcanic ashes from Galim) were collected from two Cameroonian localities. They were characterized (chemical and mineralogical compositions, amorphous phase content, particle size distribution and specific surface area) and used as raw materials for the synthesis of geopolymer cements at ambient temperature of laboratory (24 ± 3 °C). The synthesized products were characterized by determining their setting time, linear shrinkage and compressive strength, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. The mineralogical composition, the amorphous phase content, the particle size distribution, the specific surface area of the volcanic ashes as well as the mass ratio of the alkaline solution (sodium silicate / sodium hydroxide) were the main parameters which influenced the synthesis of geopolymers with interesting characteristics at ambient temperature (24 ± 3 °C). The volcanic ashes (ZD) whose mineralogical composition contained anhydrite, low amorphous phase content and low specific surface area led to long setting times. Moreover, its products swelled and presented cracks due to the formation of ettringite and these resulted in low compressive strengths (7 to 19 MPa). The volcanic ashes (ZG) containing high amounts of amorphous phase and high specific surface area led geopolymers with setting times between 490 and 180 minutes and compressive strength between 7 and 50 MPa at ambient temperature of laboratory. The properties of geopolymers were improved when elaborated with a mixture of volcanic ashes and metakaolin (ZD–MK and ZG–MK). For geopolymers obtained from ZD–MK, the setting time was between 500 and 160 minutes while it was between 220 and 125 minutes for geopolymers obtained from ZG–MK. The compressive strength greatly increased between 23 and 68 MPa and 39 and 64 MPa for geopolymers obtained from ZG –MK and ZD–MK respectively. A comparative study of the properties of mixtures of metakaolin–alumina and volcanic ash–alumina based geopolymers shows that metakaolin is a good source of Al2O3 and SiO2 and which highly reactive with alkaline solution and produces geopolymers with better characteristics compared to volcanic ash based–geopolymer. The properties of volcanic ash–based geopolymer were also improved when amorphous alumina was incorporated into the volcanic ash. This additive is used to compensate the deficiencies in Al2O3 content in the volcanic ash. Compare to when volcanic ash is used alone 20 to 40 % incorporation of this additive corresponded to increases of the compressive strength by 18.1 % for metakaolin-alumina based-geopolymers and by 32.4 % for volcanic ash-based geopolymers.

Effects of adding Bauxite and Oyster shell on the properties of metakaolin-based geopolymer cements

This work has investigated the possibility of use bauxite and oyster shell as mineral admixtures,to enhance the properties of metakaolin-based geopolymer cements. Raw materials(metakaolin, bauxite and oyster shell) were characterized in the first time by determination of their chemical and mineralogical compositions, particles size distribution, specific surface area, thermal analysis and then in the second time use to synthesized geopolymers. Different methods of analysis such as Fourier Transform Infrared spectroscopy(FTIR), X-Ray Diffractometry (XRD), and Scanning Electron Microscopy (SEM) were used to assess the variation of setting time, linear shrinkage and 28 days compressive strength of geopolymer pastes. The results of these analysis has showed that bauxite and oyster shells are source of Al2O3 and CaO respectively, and also contain crystalline phases. The geopolymers obtained by mixing metakaolin and bauxite have their setting time between 235 and 420min and their compressive strength between 40 and 57MPa ; for those obtained by mixing metakaolin and oyster shell the setting time is between 330 and 485min and compressive strength between 40 and 58MPa . The addition of a moderate amount (20% by mass) of bauxite or oyster shell led to improve the compressive strength of a metakaolin-based geopolymer of 43% (metakaolin-bauxite-based geopolymers) and 45% (metakaolin-oyster shell-based geopolymers) and decrease the linear shrinkage. More than 20% mineral additive has a deleterious effect on compressive strength and increase the setting time. Keywords: Metakaolin ; Bauxite ; Oyster shell ; synthesis ; Optimization; Geopolymer cements.

DEVELOPMENT OF POROUS CONCRETE GEOPOLYMER USING HYDROGEN PEROXIDE AS BLOWING AGENT.

Metakaolin and volcanic ashes respectively called MK and ZG were used as aluminosilicate raw materials for the synthesis of porous geopolymers. The hydrogen peroxide was used as a blowing agent. The geopolymer prepared were characterized by Spectroscopy Fourier Transform Infrared (SFTI), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and the determination of some physical properties such as bulk density, total porosity, volume shrinkage, compressive strength and thermal conductivity was also carried out. The presence of pores in the geopolymer obtained is function of the percentage of hydrogen peroxide added, causing the concomitantly decrease in compressive strength, apparent density and thermal conductivity. The use of hydrogen peroxide as a blowing agent gave some thermal insulation properties to these geopolymers which could be close to the properties of some commercial insulation materials.