Effect of chloride salt, freeze–thaw cycling and externally applied load on the performance of the concrete
Introduction
The evaluation of durability and service life for concrete structures is quite important and complicated, and it has been discussed in previous papers [1], [2], [3], [4], [5]. Performance deterioration caused by a monodamaging process, such as freeze–thaw cycling, is not consistent with the real conditions to which concrete structures are actually exposed. It has been found that the deterioration of concrete could be accelerated when subjected to dual-damaging processes, e.g., simultaneously subjected to both external loading and freeze–thaw cycling [6], [7]. Moreover, deterioration of concrete becomes more severe when subjected to multidamaging processes, e.g., simultaneously exposed to external load, freeze–thaw cycling, chloride or sulphate attack and so on. In this paper, the concrete with different strength levels when exposed to mono-, dual- and multidamaging processes was investigated, and the improvement from steel fiber to resist against the performance degradation in concrete was discussed as well.
Section snippets
Materials
The 525# R(II) Portland cement, river sand with fineness modulus 2.36, coarse aggregate of crushed basalt stone with maximum size of 10 mm, XP-II superplasticizer, steel fibers with length of 20 mm and aspect ratio of 40, respectively, were used in the test. The proportions of the various concrete mixes with three strength levels are given in Table 1.
Test methods
Tests of concrete specimens (40×40×160 mm) subjected to freeze–thaw cycling or to externally applied load in water or in a NaCl solution (3.5% by
Effect of NaCl solution on the frost resistance of the concrete
There is much difference in frost resistance of the concrete specimens between that tested in fresh water and in the chloride solution. Concrete with good frost resistance often scaled severely in a NaCl solution when subjected to freeze–thaw cycling, the weight losses of concrete specimens reaching failure threshold earlier in a NaCl solution than in water. Fig. 1a and b gives the weight losses of the plain concrete (C40NPC, C60NPC and C80NPC) subjected to freeze–thaw cycling in water or in a
Conclusions
Severe surface scaling occurred when the plain concrete was subjected to freeze–thaw cycling in a 3.5% NaCl solution, in which the weight losses of the concrete were larger than those in water. Due to the decline of the freezing point of the salt solution, the ultimate freeze–thaw cycles of the concrete in a NaCl solution were about 20% higher than those of the concrete exposed to the freeze–thaw cycling in water, while the losses in the dynamic modulus of elasticity of the former were fewer
Acknowledgements
The authors thank the key program from the National Natural Science Foundation of China, Grant No. 59938170, for the financial support. Jiangsu Research Institute of Building Science, which supported the experimental work, was greatly acknowledged as well.
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