1、外文原文： The effects of supplementary cementing materials in modifying the heat of hydration of concrete Yunus BallimPeter C. Graham Received: 23 February 2008 / Accepted: 17 September 2008 / Published online: 23 September 2008 Abstract This paper is intended to provide guidanceon the form and extent t
2、o which supplementarycementing materials, in combination with Portland cement, modifies the rate of heat evolution duringthe early stages of hydration in concrete. In this investigation, concretes were prepared with fly ash,condensed silica fume and ground granulated blastfurnace slag, blended with
3、Portland cement inproportions ranging from 5% to 80%. These concretes were subjected to heat of hydration tests under adiabatic conditions and the results were used to assess and quantify the effects of the supplementarycementing materials in altering the heat rate profiles of concrete. The paper al
4、so proposes a simplified mathematical form of the heat rate curve for blended cement binders in concrete to allow a design stageassessment of the likely early-age timetemperature profiles in large concrete structures. Such an assessment would be essential in the case of concrete structures where the
5、 potential for thermally induced cracking is of concern. Keywords:Heat of hydration _ Fly ash _ Silica fume _ Slag _ Concrete 1 Introduction Supplementary cementing materials, such as ground granulated blastfurnace slag (GGBS), fly ash (FA) and condensed silica fume (CSF), are now routinely used in
6、structural concrete. Used judiciously, these materials are able to provideimprovements in the economy, microstructure of cement paste as well as the engineering properties and durability of concrete. They also alter the rate of hydration and can influence the timetemperature profile in large concret
7、e elements. This paper is aimed at an improved understanding of the way in which the early-age heat of hydration characteristics of concrete are altered by the addition of supplementary cementing materials (SCM), in combination with Portland cement, as a part of the binder. Importantly, in the desig
8、n and construction of large concrete elements, where the extent of temperature rise is of concern, our ability to reliably 宁波工程学院毕业设计（论文） -外文翻译 1 predict the early-age temperature differentials in the concrete requires a careful understanding of the rates at which heat is evolved during hydration 13
9、. In essence,the intention of this paper is to provide guidance on the form of the heat-rate function for concretes containing supplementary cementing materials. This is essential input information in the design and construction of large dimension and/or high strength structures where thermal strain
10、s are likely to lead to deleterious cracking and/or loss of durability. In the investigation reported here, concrete samples containing combinations of Portland cement with GGBS, FA or CSF were tested in an adiabatic calorimeter in order to determine their heat ofhydration characteristics. The test
11、programme was limited to binary blends of the materials, i.e., eachtest was limited to a combination of Portland cement and one supplementary material and all concreteswere prepared at the same water:binder (w/b) ratio. For each type of supplementary material, concretes were prepared with supplement
12、ary material replacing between 5% and 80% of the Portland cement,depending on the type of SCM. Concrete samples with a volume of approximately 1 l were tested in the adiabatic calorimeter. The adiabatic calorimeter that was used in the test programme is based on the principle of surroundinga concret
13、e sample with an environment in which the temperature is controlled to match the temperature of the hydrating concrete itself, thus ensuring that no heat is transferred to or from the sample and the rise in temperature measured is solely due to the heat Mevolved by the hydration process. This calori
14、meter has been described in detail by Gibbon et al. 4. Since the rate of evolution of heat during theMhydration of cementitious materials is influenced by Mthe temperature at which the reaction takes place, there is no unique adiabatic heat rate curve for aparticular cement or combination of cementi
15、tious materials. Comparisons of the heat rate performancesof materials must, therefore, be made on the basis of the degree of hydration or maturity. In this paper, the results are expressed in terms of maturity or t20 h, which refers to the equivalent time of hydration at 20_C. This form of expressi
16、on of the heat rate function and the justification for its use, is describedby Ballim and Graham 1. 2 Concrete materials and mixtures Concrete materials which are commonly used and readily available in South Africa were used in these tests. The Portland cement complied with SABS EN197-1, type CEM I
17、class 42.5 5 and the GGBS, fly ash and silica fume complied with SABS 宁波工程学院毕业设计（论文） -外文翻译 2 1491 Parts 1, 2 and 3 68, respectively. The oxide contents of the binder materials were determined by XRF analysis and the results are shown in Table 1. The range of replacement levels by each of the three s
18、upplementary materials used, together with the concrete mixture proportions. The concrete mixture proportions were kept the same throughout, except that the composition and relative proportion of the binder was changed as required. All the concretes therefore had a w/b ratio of approximately 0.67 an
19、d the water content was sufficient to compact the concrete by manually stamping the sample holder. All the mixture components, including the water, were stored in the same room as the calorimeter at least 24 h before mixing. This allowed the temperature of the materials to equilibrate to the room te
20、mperature, which was controlled at 19 1_C. A 1.2 l sample of each concrete was prepared by manual mixing in a steel bowl and the adiabatic test was started within 15 min after the water was added to the mixture. All the tests were started at temperatures between 18 and 20_C and temperature measureme
21、nt in the calorimeter was continued for approximately 4 days. The silica sand used in the concretes was obtained in three size fractions and these were recombined as needed for the mixing operation to ensure a uniform sand grading for each concrete. The stone used in the concrete was a washed silica, largely single-sized and 9.5 mm in nominal dimension. 3 Conclusions
