Research On Uniaxial Compression Performance Of Concrete Under Freeze-thaw Cycles And Carbonation

Concrete structure, as a dominant role in our national infrastructure construction, is widely used in various fields. With the development of the times, the service environments of concrete structures and the damage effects which impact concrete durability are becoming more and more complex. Freeze-thaw cycles and carbonation, among the damage effects are the most common ones. Currently, the studies on concrete durability, such as the relevant deterioration mechanism, theoretical models, test methods, and even the methods for prevention, improvement and repair, all remain at the level of research on the effect of a single factor, while in practice the construction damages and deterioration occur due to loads and multiple environmental damage factors. Therefore, it’s of great importance to study the mechanical performance of concrete under the effect of freeze-thaw cycles and carbonation effect, which helps make full use of the strength of concrete material and improve design level.This paper, as the subsequent part of National Natural Science Foundation Project (grant number:50978224):research about mechanical performance of reinforced concrete and prestressed concrete structure under freeze-thaw cycles, carried out the experimental study of concrete performance under uniaxial compression with the impact of freeze-thaw cycles and carbonation effect, and the following work has been done:1. Freeze-thaw cycle test and carbonation test were carried out to prepare for the subsequent strength performance test. During freeze-thaw cycle test, the frost resistance of concrete was assessed from three aspects:relative dynamic modulus of elasticity, mass loss, and the surface damage condition. During carbonation test, indicator was sprayed to confirm if the concrete specimens was fully carbonized.2. Compressive strength of concrete cube specimens under freeze-thaw cycles and carbonation effect was tested. The test results indicated that in the freeze-thaw group, with the increase of freeze-thaw cycles the compressive strength of concrete cube specimens reduced constantly, presenting a linear trend, while for the freeze-thaw & carbonation group a non-linear decline trend was shown. Besides, the specimen size conversion coefficient showed a linear decline trend as the number of freeze-thaw cycles increased.3. Uniaxial compression performance of concrete prism specimens under freeze-thaw cycles and carbonation effect was tested with disc spring energy dissipation device.Test results showed that with the increase of freeze-thaw cycles, the compressive peak stress declined constantly to a linear trend, and it declined even faster for the concrete specimens of standard size. The compressive peak strain and compressive ultimate strain increased exponentially with the increase of freeze-thaw cycles, and the increase trend was slower for specimens from freeze-thaw & carbonation group. The specimen size conversion coefficient reduced linearly with the increase of freeze-thaw cycles. In the freeze-thaw group, it’s found that for the stress-strain curve of uniaxial compression strength of concrete prism specimens, there’s a concave phase at the initial loading stage, while for the freeze-thaw & carbonation group this concave phase was not obvious. Better fitting results were achieved with the application of sectional model to fit the uniaxial compression stress-strain curves of freeze-thaw group and freeze-thaw & carbonation group.4. Concrete microstructure test was carried out. RapidAir 457 image analyzer was applied to test concrete specimens, and concrete antifreeze evaluation was based on characteristic parameters, including air content in concrete, air void spacing factor, etc. Metallographic microscope was used to continuously observe representative pores. Micro-structure test results corresponded to macro test result.