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The Research on the Dynamic Compressive Behavior and Micro-meso Mechanism of Sulfate Attacked Concrete

Author: GuoMin
Tutor: LiuTieJun
School: Harbin Institute of Technology
Course: Civil Engineering
Keywords: sulfate attack strain rate effect dynamic compressive properties microscopic experiments random aggregate model
CLC: TU528
Type: Master's thesis
Year: 2012
Downloads: 43
Quote: 0
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Abstract


As one of the most widely-used materials in civil engineering, concrete is a kind oftypical strain-rate-sensitive materials whose strength and deformation capacity varysignificantly with the changes of loading rate. Concrete structures in service have towithstand not only static loadings, but also dynamic loadings such as seismic load, windload, wave impact and blast loading inevitably. Besides, concrete structures in servicewould suffer environmental corrosion which results in the loss of durability. And thesulfate attack is a complex and harmful influence factor of environmental corrosion.Thus it is meaningful to research the dynamic compressive properties and themechanism of concrete materials suffering from different degree of sulfate attack.Firstly, the dynamic compression experiments were done to the concrete materialsof different corrosion levels in the strain rate range of2×10-5/s10-3/s. Then thechanging rules of compressive strength, deforming capability and the failure pattern ofthe concrete materials which had been subjected to sulfate attack for0day,60days and120days were analyzed. The results showed that the compressive strength of concretematerials suffering different degree of sulfate attack all increased with the increasing ofstrain rate and the rate sensitivity of sulfate attacked concrete was more obvious thanthat of uncorroded concrete. However, the elastic modulus did not change significantlywith the increasing of loading rate. For concrete materials suffering from sulfate attackfor0day and60days, the peak strain increased with the increasing of strain rate. Butfor concrete materials suffering from sulfate attack for120days, the peak strainincreased at first, then decreased. The energy absorption capability increased with theincreasing of strain rate. And the energy absorption capability of concrete samples underthe same loading rate decreased with the increasing of sulfate attack time. Besides, thefailure pattern showed typical strain rate effect and the longer of corrosion time, themore serious of damage.Secondly, the microscopic tests of X-ray diffraction and scanning electronmicroscopy were done. Then the changing rules of the composition and microstructurewithin the concrete suffering different degree of sulfate attack were analyzed. Theresults showed that the content of ettringite increased and the quantity of Ca（OH）2decreased as sulfate attack going on. However the content of CaSO4·2H2O decreased at first, then increased as sulfate attack going on. The internal structure also became denseat first, then loose. And the contents of the crystals at different parts of concrete sampleschanged in different laws. The changes of microstructure and mineral composition ledto the redistribution of free water in the way of being more helpful to the occurrence ofviscous effect. As a result, the strain rate sensitivity of concrete had a change.At last, the mesomechanics model based on random aggregate model was builtaccording to the thought that concrete was taken as composite material that made ofaggregate, mortar and interface in the meso-level. With large-scale finite elementanalysis software ANSYS, the uniaxial compressive mechanical properties of concretewere researched and how sulfate attack influenced the mechanical properties of concretewere explored. The results showed that the interface was the weakest part of theconcrete and the greatest influence factor on mechanical properties of concrete. Andcorrosion depth and corrosion degree were the most important influence factors onmechanical properties of sulfate attacked concrete.

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