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Studies of Control on Cracks on Construction of High-Strength Concrete Ctructures

Author: ChenZhaoXiong
Tutor: ChenBin
School: Chongqing Jiaotong University
Course: Structural Engineering
Keywords: crack control high-strength concrete autogenous shrinkage drying shrinkage curing internal curing hydration heat control
CLC: U445.57
Type: Master's thesis
Year: 2009
Downloads: 195
Quote: 0
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Abstract


The current development in bridge architect is that bridge constructions are getting lighter and lighter. To achieve a light construction, high-strength concrete is used for pre-stressed concrete bridges, especially long-span beam bridges, in order to reduce the cross-section as well as the dead load of the bridges. It is well known that the dead load of bridge construction accounts for above 90% of the total weight borne by traditional long-span beam bridge. To use high-strength concrete can therefore significantly lighten the dead load of bridge constructions and thus improve the bearing capacity of bridges. In addition, to use transverse pre-stress on the roof slab and vertical pre-stress on the web of bridges can increase the length of flange plate as a consequence of which the thickness of the roof, floor and web of bridges can be reduced. The reduction of the thickness of the roof, floor and web of bridges can further reduce the dead load of bridge constructions.However, since the w/c ratio of high-strength concrete is close to the theoretical w/c ratio, water loss in concrete caused by interior hydration process is a very serious problem which, as a result, leads to the autogenous shrinkage of concrete. Once the shrinkage was restricted, the concrete cracked.Traditional curing methods are not sufficient to ensure IRH of high-strength concrete, because high-strength concrete is denser than normal concrete. Furthermore, since more cement is used in high-strength concrete than in normal concrete, hydration heat is significantly higher in high-strength concrete than in normal concrete. How to ensure IRH of high-strength concrete and how to reduce the thermal stress resulted by hydration heat in massive high-strength concrete are thus central questions which affect the quality of concrete constructions.This paper deals at first with the characteristics of concrete at its earlier stage. The author lists different types of cracks which often happen at the earlier stage of concrete, and names the reasons which lead to the cracks. He analyses why concrete shrinks at its earlier stage and points out that concrete shrinkage is directly related to IRH: the higher IRH is, the more concrete shrinks.The crack can be avoid,if the IRH of concrete would be retain a high level.Secondly, a variety of curing methods for concrete are compared in this paper. The author analyses how different curing methods ensure IRH and temperature of concrete and compares the advantages and disadvantages of these curing methods. He comes to the conclusion that curing of concrete should be taken both in terms of exterior and interior of concrete. Reached a conclusion that using internal curing could reduce the shrinkage of high-strength concrete and the probability of crack caused by shrinkage significantly.Last but not least, the emergence of hydration heat of concrete, the reason for thermal crack in concrete as well as the effectiveness of various methods to reduce thermal crack have been analysed in this paper. The author uses computer to simulate the rise of temperature in concrete resulted by hydration and reaches the level almost equivalent to the real temperature field. He uses further this temperature field to estimate the stress field. This computer simulation could be of significant use for persons in the practice who control the thermal crack of concrete.

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CLC: > Transportation > Road transport > Bridges and Culverts > Bridge Construction > The works > Concrete and reinforced concrete works
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