建筑材料外文翻译--普通硅酸盐水泥中掺入硅灰和石膏对水化反应的影响(编辑修改稿)

建筑材料外文翻译--普通硅酸盐水泥中掺入硅灰和石膏对水化反应的影响(编辑修改稿)内容摘要：

been confirmed to take place even in the first few days, chiefly on the grounds of the consumption of Ca2+ ions in the liquid phase, but also of the uptake – in descending order – of OH– and K+ ions [13–17]. And on the other, the amount of heat released per gram of Portland cement in pastes with silica fume has been found to amply exceed the amount of heat released by the respective plain pastes [18]. Experimental Objective In light of these considerations on substances such as gypsum and silica fume。 the objective or purpose of the present study is, to analyze their overall effect on the hydration of two Portland cements with widely varying positions, with a view to limiting their use in high performance concrete. Materials and methods Two Portland cements with widely differing mineralogical positions were chosen for this study. One, with a very high C3A content, called PC1, and the other, with a minimum C3A content (1%) and a maximum C3S content, called PC2。 the other constituents were a very active pozzolanic mineral addition (silica fume, SF) and rich ground natural gypsum. Distilled water was used in the mortar in all cases. The chemical position, density and BET specific surface of the Portland cements and the addition are given in Table 1. The potential position of thePortland cements found from their chemical position and the Bogue equations was as follows: 51% C3S,16% C2S, 14% C3A and 5% C4AF for PC1 and 79% C3S, 2% C2S, 0% C3A and 10% C4AF for PC2. The different chemical and mineralogical positions of the two cements Portland are partly reflected in the difference in their densities。 their fineness, on the contrary, is parable. SF contains: over 90% SiO2, % SiO2 r – (reactive silica) [19, 20] and yet has a much lower density than quartz () and a very high specific surface. Its diffractogram, shown in Fig. 1, reveals the presence of cristobalite (C)。 the diffuse pattern is indicative of the substance’s primarily vitreous nature [21]. The pastes for the study were made by mixing each Portland cement separately with SF, in percentages by mass of 90/10 and 80/20, in the absence of gypsum or with sufficient amounts to bring the total SO3 content to %. Table 2 gives the setting times and water demand for 500g samples. These two physical parameters were determined as laid down in European standard EN 196, part 3 [22]. morphology had a significant effect on water demand. The SF spheres separated the Portland cement particles, making a greater surface area available for hydration. Moreover, given its density and specific surface, the silica fume prised a larger number of particles than the Portland cement replaced, significantly increasing the water demand. Pozzolanic activity was evaluated chemically by Frattini’s test [23], by paring the amount of calcium hydroxide in an aqueous solution covering the hydrated sample at 40186。 C for a given period of time (in this case, 48 h), with the solubility isotherm for calcium hydroxide in an alkaline solution at the same temperature. The indication of pozzolanic activity was defined to a lower calcium hydroxide concentration in the sample solution than on the solubility isotherm, due to its uptake in the pozzolanic reaction (=+result) (Fig. 2). The heat release pattern was ascertained by heat conduction calorimetry for pastes. Measurements were taken at a temperature of 25186。 C. Data were recorded during the first 48 h of hydration and the total heat released was puted by integrating the area under the rate of releaseage curve. This methodology is widely used to monitor hydration in pure Portland cement [1] as well as for cements containing mineral additions [24]. To obtain equally workable pastes, the water:cementitious material ratios used were for pure Portland cements, for mixes with 10% SF and for mixes with 20% silica fume. Results and discussion Figure 2 shows [OH–] and [CaO] determined at 48 h. Note that the pastes with SF showed pozzolanic activity at 48 h (., 6 days before its first specified age, 8 days [25]), in the case of PC1 at (additioncement) replacement rates of 10%, and in PC2 at rates of 15% or higher. Some of these mixes failed to show pozzolanicity at that age because the rate of the hydration reaction was so high that it could not be countered or pensated for by the fixation of the calcium hydroxide resulting from the pozzolanic reaction. Fig. 2 Pozzolanicity (Frattini test) at 48 h: results When gypsum was added to the samples, the [CaO] increased due to its partial dissolution in water, whereas [OH–] declined, partially because of the effect dilution of the Portland cement, although no pozzolanic activity was detected in any of the samples within the first 48 h. Figures 3 and 4 show the first 48h calorimetric curves for the samples containing PC1 and PC2, respectively. The first stage or induction period for plain PC1, visible in Fig. 3, shows a high rate of heat release due to initial hydrolysis and the hydration of the aluminous ph。