Hitherto, limestone has been recognised as a suitable substitute for cement replacement. The present study was an experimental investigation of the properties of Portland limestone cement and the effects of water-to-cement (w/c) ratio on performance of concretes containing it. The Portland limestone cement concrete specimens (containing 14% limestone) with w/c ratio of 0·35, 0·45 and 0·55 were experimentally compared to ordinary Portland cement concrete specimens. The results demonstrated that w/c ratio has a prominent effect on the performance of Portland limestone cement concretes, with higher w/c resulting in weaker performance. Therefore Portland limestone cement containing 14% limestone can be considered as a low-cost, effective and available supplementary cementing material.
Milling was carried out in flowing argon but was interrupted at regular time intervals to take samples for X-ray diffraction (XRD). Because of exposure to air during the interruptions the powder was partly oxidized. The oxides formed did not appear in XRD patterns because they were of extremely fine grain size. As a result of the loss of V and W through oxidation, free carbon was also found in the final powder. The lattice parameter of the (V,W)C powder increased with milling time up to a maximum, then it decreased, which suggests that the amount of W in (V,W)C increased with milling time up to a maximum and then decreased. The crystallite size of the (V,W)C powder was calculated from the X-ray data and was found to be in the nm range (down to approximately 8 nm). Subsequent uninterrupted milling produced a powder which was freer from oxides and free carbon. (C) 2008 Elsevier B.V. All rights reserved.
Internal curing (IC) is an effective method for improving performance of low W/C - low permeability concretes because they require additional water to hydrate the cementitious materials. Conventional concretes, on the other hand, contain enough water to hydrate the cementitious materials, but are frequently not properly cured, allowing drying and compromising strength gain and durability. The aim of this investigation is to assess the effect of IC as a complement to traditional curing in relatively high W/C concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive strength, and permeability were measured in concretes with IC and without IC. Results show that even under drying conditions, mixtures with IC exhibit 16% higher hydration, 19% higher compressive strength, and 30% lower permeability than their counterparts with no IC. This suggests that IC can be very useful for improving performance in concrete mixtures with relatively high W/C under poor curing conditions. [All rights reserved Elsevier].
Internal curing (IC) is an effective method for improving performance of low W/C - low permeability concretes because they require additional water to hydrate the cementitious materials. Conventional concretes, on the other hand, contain enough water to hydrate the cementitious materials, but are frequently not properly cured, allowing drying and compromising strength gain and durability. The aim of this investigation is to assess the effect of IC as a complement to traditional curing in relatively high W/C concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive strength, and permeability were measured in concretes with IC and without IC. Results show that even under drying conditions, mixtures with IC exhibit 16% higher hydration, 19% higher compressive strength, and 30% lower permeability than their counterparts with no IC. This suggests that IC can be very useful for improving performance in concrete mixtures with relatively high W/C under poor curing conditions. (C) 2010 Elsevier Ltd. All rights reserved.
Internal curing (IC) is an effective method for improving performance of low W/C – low permeability concretes because they require additional water to hydrate the cementitious materials. Conventional concretes, on the other hand, contain enough water to hydrate the cementitious materials, but are frequently not properly cured, allowing drying and compromising strength gain and durability. The aim of this investigation is to assess the effect of IC as a complement to traditional curing in relatively high W/C concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive strength, and permeability were measured in concretes with IC and without IC. Results show that even under drying conditions, mixtures with IC exhibit 16%higher hydration, 19%higher compressive strength, and 30%lower permeability than their counterparts with no IC. This suggests that IC can be very useful for improving performance in concrete mixtures with relatively high W/C under poor curing conditions.
Sintered (Ti,W)C carbides were prepared from (Ti,W)C solid solution powder at 1510degC. The powder was produced by milling a mixture of carbon and oxides and then reducing it at 1200degC for 1h. The sintered (Ti,W)C carbides demonstrate full density, excellent hardness and fracture toughness values ( rho: 98-100%, HVN: 19-21GPa, KIC: 6.4-7.7MPam 1/2). These homogeneous (Ti,W)C carbides have considerable potential for use in structural applications. [All rights reserved Elsevier]
Tritium exposed samples, including doped graphite, SiC coated graphite, tungsten coatings fabricated by vacuum plasma spraying, and polycrystalline tungsten, were examined by beta-ray-induced X-ray spectrometry in an argon atmosphere. The changes in the X-ray spectra with time were followed for a maximum time of 100 h. The results indicated that the SiC coated graphite absorbed the most tritium and the polycrystalline tungsten the least. Preliminary computer simulations were performed to analyze the depth profiles of tritium in these materials. (C) 2010 Elsevier B.V. All rights reserved.
Abstract Given any compact, Hausdorff space K and 1 < p < ∞ , we compute the Szlenk and w ⁎ -dentability indices of the spaces C ( K ) and L p ( C ( K ) ) . We show that if K is compact, Hausdorff, scattered, C B ( K ) is the Cantor–Bendixson index of K , and ξ is the minimum ordinal such that C B ( K ) ⩽ ω ξ , then S z ( C ( K ) ) = ω ξ and D z ( C ( K ) ) = S z ( L p ( C ( K ) ) ) = ω 1 + ξ .
The annealing behaviour of Ti(C(0.5)N(0.05))-40 wt.% W and Ti(C(0.5)N(0.5))(0.6)-40 wt.% W mechanically alloyed powders was investigated using XRD, TEM, SEM and DTA techniques. It was observed that the reaction start and finish temperatures between constituents were lower in the system that had higher residual lattice strains after milling. The compositions of the intermetallic compounds and solution phases formed were dependent of the milling conditions and the annealing temperature. Thermal alloying was observed during annealing of Ti(C(0.5)N(0.05))-40 wt.% W mechanically alloyed products, whereas de-mixing of W-rich phases from the metastable solid solution occurred during annealing of the Ti(C(0.5)N(0.5))(0.6)-40 wt.% W milled powders. (C) 2011 Elsevier Ltd. All rights reserved.
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