دانلود رایگان ترجمه مقاله سیلیس آموروف در بتن در مدت زمان اولیه هیدراتاسیون – الزویر 2014
دانلود رایگان مقاله انگلیسی سیلیس آموروف در بتن با کارایی فوق العاده بالا: در مدت زمان اولیه هیدراتاسیون به همراه ترجمه فارسی
عنوان فارسی مقاله: | سیلیس آموروف در بتن با کارایی فوق العاده بالا: در مدت زمان اولیه هیدراتاسیون |
عنوان انگلیسی مقاله: | Amorphous silica in ultra-high performance concrete: First hour of hydration |
رشته های مرتبط: | مهندسی عمران، شیمی، شیمی آلی، شیمی تجزیه، مدیریت ساخت، سازه |
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نشریه | الزویر – Elsevier |
کد محصول | f142 |
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بخشی از ترجمه فارسی مقاله: 3.4.2. انحلال منافذ 4. نتیجه گیری
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بخشی از مقاله انگلیسی: 3.4.2. Pore solution Na+, K+, Ca2+, OH−, SO4 2− ions and silicate ions (e.g. H3SiO4 −) will be in the pore solution quickly after water addition to a cement [8,9]. They are formed from highly soluble alkali sulfates on the cement clinker surface (K2SO4, Na2SO4 and Na2SO4·3K2SO4), the setting regulation agent (gypsum, bassanite and anhydrite), calcium oxide and the initial dissolution of clinker minerals (mostly alite and aluminate phase) [9]. Fig. 12 shows the analytic ion concentrations and pH values in pore solutions from the different UHPC pastes. The analytic results refer to total element concentrations nominated as: Na, K, Ca, sulfate and silicate. In detail, measured sulfur is most likely sulfate (SO4 2−). The occurrence of different silicate species will be discussed later in this section. Measured concentrations of Na, K and sulfate are below the maximum possible values (in mmol/l: Na = 300, K = 350 and sulfate = 1190, calculated from the analytical composition of the cement and w/c = 0.23 by mass) in all pore solutions. A certain amount of sodium and potassium is bound in the unhydrated clinker minerals. The sulfate concentration is diminished by the precipitation of ettringite [14] which was also detected in XRD. Ca and silicate may be dissolved from setting regulation agents, alite and silica. Measured pH values correspond to similar pastes [62]. Pastes containing pyrogenic silica show slightly lower concentrations for all measured elements than samples with silica fume. Remarkably, in the pore solution of pastes with Stoeber particles, K and Na concentrations drop by a factor of about 10−3 , sulfate by about 10−1 , whereas the silicate concentration increases. This lack in Na, K and sulfate is untypical for a cementitious paste. In addition, the concentration of Ca in pastes containing silica fume and Stoeber particles is significantly higher than the saturation concentration of Ca2+ ions for lime (approx. 22 mmol/l). Different interactions at the interface between silica particles and the pore solution depending on the silica type may be assumed from the results and are discussed in the following. 4. Conclusions In this study, the effects of different types of silica (Stoeber particles, silica fume and pyrogenic silica) on the hydration of UHPC pastes were investigated within the first hour. Two different reaction sequences for silica (paths I and II) can be observed in a cementitious environment: either silica dissolves followed by a pozzolanic reaction (path I) or C–S– H phases from the hydration of alite nucleate at its surface (path II). The silica reactivity was discussed considering different properties of silica. Surface silanol group densities, total contents of silanol groups and solubilities in alkaline suspensions indicate that Stoeber particles should be by far the most reactive, followed by pyrogenic silica and the less reactive silica fume. A different reactivity ranking is postulated (pyrogenic silica N silica fume ≈ Stoeber particles) if the specific surface area is considered which is twice as high for pyrogenic silica as for silica fume or Stoeber particles. Silica reactions were further traced in UHPC pastes within the first hour of hydration by investigating the solid phases and the pore solution. The results give no indication for the reactivity ranking assumed from the specific surface area or for any reaction following path I or II. Instead, silica particles seem to attract cations (Na+, K+ and Ca2+) from the pore solutions and form alkali silicate oligomers and calcium silicate oligomers. These oligomers might be held as a layer around the silica particles and form an aqueous, amorphous gel phase. The extent of the assumed oligomerization depends on the silica reactivity postulated from the surface silanol group density and the total content of silanol groups. Indeed, it seems to be high enough in pastes with Stoeber particles to bind almost all alkali ions in alkali silicate oligomers. The corresponding decline of alkali ions in the pore solution may have an impact on the subsequent processes because alkali ions accelerate the hydration of alite [69,70]. Therefore, the alite hydration in UHPC pastes containing Stoeber particles might not be as fast as in UHPC pastes containing other silica. Reaction path I seems to be more likely for Stoeber particles than for the less reactive pyrogenic silica and silica fume. Further studies should investigate the effect of silica with different reactivities for an extended observation period to fully clarify the influence on the hydration (path I, II or both) and the resulting properties of UHPC. |