外文翻译-关键参数对水泥浆体干燥收缩的影响.doc

1、毕业设计(论文)外文资料翻译院 系专业学生姓名班级学号外文出处Cement and Concrete Research附件：1.外文资料翻译译文（约3000汉字）； 2.外文资料原文(与课题相关的1万印刷符号左右)。指导教师评语：指导教师签名：年月日Influence of key parameters on drying shrinkage of cementitious materialsAbstract Drying shrinkage can be a major cause of the deterioration of concrete structures. The contra

2、ction of the material is normally hindered by either internal or external restraints and tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The evaluation of the stress distribution in the material requires the knowledge of the “real” free shrin

3、kage deformation. This paper presents the results of a study performed to evaluate this deformation and obtain a better understanding of the behavior of concrete under drying conditions. Shrinkage tests were carried out on cement pastes, mortars, and concretes. The influences of different key parame

4、ters were evaluated: relative humidity, specimen size, water/cement ratio, and paste volume. The results indicate that between 48 and 100% relative humidity, the shrinkage of cement paste is approximately inversely proportional to relative humidity. Results also show that the ultimate shrinkage of p

5、astes and mortars measured on 50350 400-mm specimens does not differ much from the “real” shrinkage measured on 4832-mm specimens. Thus, for the specimen dimensions investigated in this study, the existence of a humidity gradient did not affect to a large extent the ultimate shrinkage strain. The in

6、fluence of the water/cement ratio, within the range investigated (0.350.50), was found to be relatively small. Conversely, paste volume was observed to have a very strong influence. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Cement paste; Concrete; Drying; Humidity; Shrinkage1. Introd

7、uction Drying shrinkage, together with its low tensile strength, is probably the most disadvantageous property of Portland cement concrete 1. Shrinkage generally leads to cracking and, even though it may not affect the structural integrity, durability problems are generally increased 2. This is part

8、icularly true in the case of concrete overlays and slabs on grade where drying occurs from one face only and shrinkage is hindered by external and internal restraints 3,4. The external restraint is due to the bond between the repair layer and the old concrete in the case of overlays, while, for slab

9、s on grade, it comes from the friction with the subgrade and the slab self-weight. The internal restraint is caused by the humidity gradient that exists in concrete until the hygrometric equilibrium with the surroundings is reached. Local shrinkage is directly related to pore humidity; there-fore, a

10、 gradient of shrinkage deformation exists throughout the drying process. Tensile stresses are thus induced in the concrete and may eventually overcome the tensile strength of the material and cause cracking and debonding of over-lays 5.To improve the design of concrete overlays and slabs on grade, t

11、he material behavior under drying has to be characterized more precisely. Presently, codes of practice (e.g., ACI, CEB) give fairly good models to predict shrinkage as a global deformation 6, but these models are unsuitable in some cases, for instance, to compute the stresses induced by a shrinkage

12、gradient. The determination of the “real” shrink-age strain of concrete (i.e. independent of the element size) as a function of local humidity is essential for this purpose. This study, which is part of a research program on the durability of thin concrete repairs, was performed to evaluate the free

13、 shrinkage deformation of cementitious materials and to characterize the influence of certain basic parameterson this deformation. Shrinkage tests were carried out on cement pastes, mortars, and concretes. The parameters studied were: relative humidity, specimen size, water/cement (W/C) ratio, and p

14、aste volume. 2. Test program To obtain a better understanding of the shrinkage phenomenon and to evaluate the “real” free shrinkage deformation, it is important to take into account the influence of key parameters such as the size of specimens and the relative humidity.Drying shrinkage measurements

15、were carried out on twodifferent sizes of specimens: 4832-mm and 5050400-mm prisms. The smaller specimens were considered thin enough to obtain approximately gradient-free shrink-age. It was shown in previous studies 7,8 that the thickness of cement paste specimens in the range of 1 to 3 mm does not

16、 affect equilibrium shrinkage.The shrinkage tests on the smaller specimens were per-formed at three relative humidity levels (48, 75, and 92%). These values range from the minimum occurring generally in moderate climates to close to full saturation conditions (100%). The larger specimens were all tested