Volume 69

doi: 10.4028/www.scientific.net/AST.69

Paper Title Page

Authors: Pavel Vasiljevich Krivenko
Abstract: Beginning from 1957, a scientific school in Kiev (USSR) headed by Victor Glukhovsky has been developing a new direction in binding/cementitious/ materials. Taken as background was discovery of binding properties of the alkali metal compounds when they act not only as activators of hardening but are responsible for the formation of main structural elements of the alkali- activated cements – zeolite-like compounds of different types. Just these hydration products, analogues to natural zeolites of the Na2О(K2О)•Al2О3 •(2- 4)SіО2•2Н2О type, were identified in the ancient concretes (Ancient Greece, Ancient Rome, Egypt, Syria). Durability of the ancient concretes and similarity of their structure with that of the alkaliactivated cement concretes allowed to predict their high durability. High performance properties of the alkali- activated cement concretes are supported by over 50-year experience of service of the structures made from them.
Authors: Vlastimil Bílek
Abstract: Alkali-activated concretes are relatively well-known composites. They show good mechanical properties, good resistance to the attack of a variety of chemical media and some other suitable properties. For their practical application various problems must be solved. In this paper some effects of the composition of the alkali activator and the composition of the binder on setting time, workability, efflorescence, leaching, strengths, shrinkage development, freezing and thawing resistance are studied with respect to a low price of the materials.
Authors: Zong Jin Li, Fei Qiao, Chung Kong Chau
Abstract: The recent development of two types of environmental friendly cementitious materials, magnesium oxychloride cement and magnesium phosphate cement, at HKUST are presented. Both of them can develop high strength without heat treatment under elevated temperature, i.e. the bonding of these cementitious materials can be achieved at low temperature through chemical reaction, as opposed to fusion or sintering at high temperature. The preparation process of the two cements can not only save a lot of energy but also emit no carbon dioxide. For magnesium oxychloride cement, our research includes parametric study of the formulation, strength development, water resistance, and also identification of phase composition in the cement paste. Magnesium phosphate cement is mainly applied as rapid repair material in civil engineering. In this paper, the formulation, mechanical properties and performance in patch repair of mortar specimen including strength, bond ability to old concrete substrate, volume stability are studied.
Authors: Christian Kaps, Marc Hohmann
Abstract: Two types of geopolymeric networks have been prepared and characterized: aluminosilicatic binders(1) generated of metaclays for composite cements and iron-phosphate binders(2) formed of iron oxyhydroxites for applications in strong acidic environments. The focus of the investigations was on the influence of the thermal(1) or the acidic(2) activation on the structure and properties of the materials. In both cases, the amount of present water plays an essential role.
Authors: Yun Sheng Zhang, Wei Sun, Zong Jin Li
Abstract: Geopolymer is a novel type of inorganic cementitious materials, which has become a hot topic across the world. Geopolymerization process of metakaolin in alkaline solutions shows important effects on final properties of hardened geopolymer. In this paper all the possible reaction pathways involved in the dissolution-reorientation-polycondensation process of metakaolin in alkaline solution were studied according to thermodynamic theory. The corresponding reaction energy of every possible pathway was also calculated using computation chemistry methodsemi- empirical AM1 calculation. The optimum reaction pathway was analysized based on the energy-minimized principle. The calculation results showed that highly alkaline accelerated the dissolution of 6-membered tetrahedron rings of SiO4 or AlO4 tetrahedron representing the molecular structure of metakaolin during dissolution process. Si-Al hybrid reorientation should theoretically be primary reorientation pathway during reorientation process. Framework clusters should be primary polycondensation products during polycondensation process. The above studies enhanced our understanding of formation mechanisms of metakaolin in alkaline solutions related to geopolymerization.
Authors: Monique Tohoué Tognonvi, Sylvie Rossignol, Jean Pierre Bonnet
Abstract: Consolidation of cementitious and geopolymeric materials involves silicate-based gel formation. This in situ mechanism is difficult to identify because it occurs in a complex and developing system representing only a minority phase. A study based on the behaviour of acidified sodium silicate solutions in alkaline medium, was therefore initiated in order to define the conditions of irreversible setting. A concentrated sodium silicate solution ([Si]=7 mol/l, pH=11.56, Si/Na=1.71) was used as starting solution. 29Si NMR spectroscopy, SAXS and elementary chemical analyses (ICP-AES) were used to characterize the various solutions. Acidification of initial solution, leads in a range of relatively low pH and silicon concentration to various gels formation: (i) reversible transparent gels made up of aggregates of particles (Si7O18H4Na4) and which do not change over time, (ii) soluble white gels that lead to gradual formation of a soluble solid consisting of colloid composition of NaSi1.87O4.24, (iii) “irreversible” gels which provide a syneresis phenomenon leading to formation of a strongly consolidated solid made up of soluble phase rich in sodium similar to white gels (NaSi1.87O4.24) and an insoluble phase type silica of composition NaSi12.66O25.82.
Authors: Monique Tohoué Tognonvi, Séka Simplice Kouassi, Toyotaka Maeda, Julien Soro, Sylvie Rossignol, Jean Pierre Bonnet
Abstract: Consolidation of cements and geopolymers can be explained by the formation of alkali silicate or alumino-silicate gels formed in situ during materials setting. To control such a system, a study concerning the use of sodium silicate gel as binder was initiated to manufacture consolidated materials with different size distribution of silica. The gels used as precursor of binder were synthesised by acidifying with hydrochloric acid, a concentrated sodium silicate. Consolidated materials were obtained by mixing the previous solution before gelation with granular materials (fine silica powder and sands). The existence domain of consolidated materials depends on the size distribution of sand. Consolidation of material is strong when the amount of silica is high. This result suggests a dissolution / precipitation reaction between gel and silica. Therefore, consolidation could be explained by the dissolution of small particles of silica and their precipitation into the grain boundary of sand. Mechanical properties are closed to those of cement materials.
Authors: Chayanee Tippayasam, Sansanee Boonsalee, Suvimol Sajjavanich, Chiara Ponzoni, Elie Kamseu, Duangrudee Chaysuwan
Abstract: Geopolymer has been developed as an alternative material to Portland cement. Geopolymer is based on the polymerization of alkaline activation and oxide of silicon and aluminium. These oxides can be found in many pozzolanic materials such as metakaolin and the wastes from industries and agricultures in Thailand, e.g., fly ash, bagasse ash and rice husk ash. Pozzolanic materials were selected as source materials for making geopolymers into 4 different types. Sodium hydroxide concentration of 10 Molar (10MNaOH) and sodium silicate (Na2SiO3) solutions were used as alkaline activators by the mass ratio of Na2SiO3/NaOH at 1.5. The mixtures were cast in 25×25×25 mm. cubes. After casting, the geopolymers were cured at 80๐C for 24 hrs. in an oven and then at room temperature for 7 days. The pozzolanic materials effects, the Si/Al molar ratio and the Na/Al molar ratio were studied and characterized. An X-ray fluorescence (XRF) was chosen to determine the percentages of silica and alumina in order to verify the proper ratio of the fly ash, Rice husk ash, Bagasse ash and Metakaolin.The study also included the impact on mechanical and physical properties such as compressive strength, water absorption, density and porosity.

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