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  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 3341-3346 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The chemistry of the calcium alumino-sulphate hydrates has been reassessed using the methods developed in a previous paper [10]. Ettringite does not have a constant solubility product. The rise in the ionic activity product of solutions in equilibrium with “ettringite” as a function of pH and sulphate activity is attributed to disordering of the crystal structure. This is due to removal of aluminium from the calcium aluminate hydrate columns which form the framework of the ettringite structure. The columns are terminated by these defects and estimates of the expected column length under various conditions are made. Qualitative explanations of changes in the stability of “ettringite” with respect to calcium aluminate monosulphate hydrate and of the action of certain admixtures on Portland cement are made on this basis.
    Type of Medium: Electronic Resource
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  • 22
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 19 (1984), S. 150-158 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper reports mechanical property measurements for Portland Cement paste free from fabrication artifacts (e.g. bubble-type voids), and compares them to published results both for normal and new high strength cement. Removal of large voids (above 100μm) by vacuum de-airing leads to an increase of ∼ 15% in mean flexural strength and a small decrease in fracture toughness. This increase in flexural strength is predictable from the tied-crack model previously proposed to explain the notch-sensitivity behaviour of hardened cement paste, and for which direct experimental evidence was obtained. It is suggested that factors such as moisture content are at least as important as large voids in controlling mechanical properties. It is concluded that the much increased strength of the new polymer-containing cements must result from improvements to the microstructure other than the simple elimination of voids.
    Type of Medium: Electronic Resource
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 19 (1984), S. 150-158 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper reports mechanical property measurements for Portland Cement paste free from fabrication artifacts (e.g. bubble-type voids), and compares them to published results both for normal and new high strength cement. Removal of large voids (above 100μm) by vacuum de-airing leads to an increase of ∼ 15% in mean flexural strength and a small decrease in fracture toughness. This increase in flexural strength is predictable from the tied-crack model previously proposed to explain the notch-sensitivity behaviour of hardened cement paste, and for which direct experimental evidence was obtained. It is suggested that factors such as moisture content are at least as important as large voids in controlling mechanical properties. It is concluded that the much increased strength of the new polymer-containing cements must result from improvements to the microstructure other than the simple elimination of voids.
    Type of Medium: Electronic Resource
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  • 24
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 16 (1981), S. 649-659 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanism of transverse-ply failure in cross-ply laminates of glass fibre thermoset composites has been investigated. It is shown that fibre debonding initiates failure, the debonds subsequently joining up to form a transverse crack nucleus. In the epoxy system investigated fibre debonding causes an observable whitening effect and small modulus change; this effect is reversible in that rebonding can be brought about by further heat treatment. It is shown that in the case of the polyester system the larger thermal strains introduced during the curing cycle cause debonding of the composite and therefore the whitening effects are not observed on application of load. Simple models for the prediction of the observed effect of glass fibre volume fraction on transverse failure strain are proposed.
    Type of Medium: Electronic Resource
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  • 25
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 3686-3694 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Tricalcium silicate (C3S), the major phase of Ordinary Portland Cement (OPC), occurs in several polymorphic forms depending on the amounts and types of impurity ions present. The hydration products of triclinic, trigonal and monoclinic C3S samples have been studied for a comparison with the silicate hydration products of OPC, using TEM and SEM. In the early stages, less than one day, there are distinct differences observed between the products on the surfaces of grains of different crystal structure but later all three appear similar. This suggests a common mechanism of hydration at later times, irrespective of structure, but the influence of the foreign ions in the first few hours is significant.
    Type of Medium: Electronic Resource
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  • 26
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 402-410 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The hydration of tri-calcium aluminate in the presence of gypsum has been examined by electron optical methods as a function of pH and hydration time. The location of the alumino-sulphate phase has been related to the solubility of aluminate ions from the precursive platelet phase. At pH ∼ 11.5 the alumino-sulphate precipitate is crystalline and precipitates from solution. When first formed it is deficient in calcium and sulphate with respect to ettringite. If the deficiency is too great, transformation to calcium aluminate monosulphate hydrate may occur as an intermediate step before the equilibrium phases are obtained. At a higher pH (∼ 12.5) the fibres of alumino-sulphate are smaller and more rounded. Long tubular fibres similar to those seen in portland cement were not observed. This has been explained as a consequence of using pure tricalcium aluminate, rather than alkali-containing material. The information obtained has been used to predict the effect of some inorganic additives on the phases produced during the setting of portland cement.
    Type of Medium: Electronic Resource
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  • 27
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 1059-1071 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The environmental stress corrosion cracking of epoxy/glass fibre crossply, unidirectional coupons and single E-glass filaments have been compared. At initial applied strains 〉 0.15% the resin does not protect the fibres as shown by their equivalent failure times. The failure occurs in the environment and planar fractures occur because of the localized stress in the load bearing plies adjacent to a transverse crack in the 90° ply of the 0°/ 90°/0° coupons. These transverse cracks result from stress corrosion of the glass/resin interface, which leads to a reduction of the transverse cracking strain. At applied strains 〈 0.15% fracture occurs within the unexposed half of the coupons and is thought to be caused by rapid transport of glass corrosion products where they crystallize within the coupon. This phenomenon is also responsible for the progressive transverse cracking that occurs in both the 0° and 90° plies of the unimmersed half of the crossply coupon under zero load.
    Type of Medium: Electronic Resource
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  • 28
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 19 (1984), S. 2677-2690 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanical properties of one of the new high strength polymer modified hydraulic cements have been investigated. An important parameter for the material is the amount of polymer present, and the properties are found to be dependent upon the degree of drying. For example, in the wet state, polymer content has little effect upon ultimate flexural strength, but does cause nonlinearity in the stress-strain behaviour. Although increasing polymer content causes a reduction in the initial tangent modulus, it is shown that retardation of hydration may account for this. In the dry state, increasing polymer content leads to increasing flexural strength, fracture toughness and failure strain, but leaves initial elastic modulus relatively unchanged. It is concluded that removal of pores is not the principal strengthening mechanism since strength increases are consequent upon water removal from the microstructure in the presence of the polymer. A fibrillar pull-out model is proposed to explain the observed behaviour of both “wet” and “dry” material and ordinary Portland cement paste, which shows good correlation with experimental results. The principal effect of the polymer is to act as an adhesive at the interface between interacting CSH fibrils.
    Type of Medium: Electronic Resource
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  • 29
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 1533-1539 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The temperature dependence of the thermal strains in the longitudinal direction of the transverse ply ε tl th , of 0°/90°/0° epoxy and polyester laminates, has been determined from the thermal variation of the deflection of an unbalanced beam. These results have been compared with those predicted from known values of the linear expansion coefficients,α t andα l. There is good agreement between the experimental and calculated values of thermal strain for the epoxy composite. Good agreement for the polyester laminates can only be obtained when the values ofα t used are those for wet laminates. The large thermal strains previously reported for the polyester laminates can therefore be explained by small quantities of water in the matrix which are not readily removed during post-curing.
    Type of Medium: Electronic Resource
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  • 30
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1983), S. 1522-1532 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The temperature dependence of the linear expansion coefficients in the longitudinal (α l) and transverse directions $$(\alpha _{t_1 } and \alpha _{t_2 } )$$ of unidirectional glass fibre laminates and their matrix resins (α m) has been studied. The results for the dry, fully post-cured polyester, epoxy resins and laminates have been found to be consistent with the predictions of the Schapery equations. An anomalous moisture phenomenon, in the form of a peak in theα m (T)/T andα t (T)/Tcurves for the polyester resin and laminates has been observed. A difference between $$\alpha _{t_1 }$$ and $$\alpha _{t_2 }$$ has been observed for partially cured polyester laminates, which is also perturbated in the presence of water. Both these moisture effects, which are not found in the epoxy specimens, are considered to result from a two-phase polyester matrix and the latter to continued curing below the softening point of the resin. These results have a considerable consequence on the magnitude of the thermal strains which develop in polyester composites.
    Type of Medium: Electronic Resource
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