Papers by Keyword: Freezing-Thawing Cycle

Abstract: In order to study the influence of freezing-thawing cycles on shear strength of seasonal frozen soil in northeast China, silty clay, typical soil in Jilin region, was selected. 20 groups of specimens were carried out by quick shear tests considering soil water content and the number of freezing-thawing cycling. The test results indicate that soil cohesion presents the slight fluctuation with the increase of water content, and the maximum value reaches around the peak of liquid limit. Internal friction angle of soil shows the sharp drop and the extent changes between 40% - 60%. The soil cohesion gradually declines with the increase of the number of freeze-thawing cycling. Therefore, the effect of the first freezing-thawing cycle on soil cohesion is obvious, and cohesion gradually tend to be stable after 7 freezing-thawing cycles. The final value of cohesion is approximate a third to a half of the unfrozen soil. The internal friction angle of soil increases with the augment of cycling number of freezing-thawing, which is related to the water content. The higher water content will bring about the greater growth rate of friction angle.

Abstract: The destructive effect of salt corrosion on concrete has attracted wide attention of civil engineering scholars nowadays. The west area in Jilin province is not only the typical frost soil region, but also is the most serious area with saline soil. In such environment damage of structural engineering often occurs under the action of freeze-thaw cycles and salt corrosion due to the lack of concrete durability. In this article Da’an city in Jilin is selected to be as the research area, and the physical and chemical properties of soil samples in spring are analyzed, the results indicate that the component of soluble salt in soil mainly includes Na⁺, HCO₃^-, Cl^-, and SO₄², and small amount of Mg²⁺, Ca²⁺, K⁺, and so on. In order to study the influence of different soluble salts on concrete durability under the condition of freeze-thaw cycles, quick freeze-thaw cycling tests on concrete durability are conducted respectively in sulfate, chloride and bicarbonate solution. Then the characteristics and laws of concrete corrosion damage under freeze-thaw cycles and salt corrosion damage are summarized.

Abstract: Biaxial compression tests are performed on 450mm*450mm*450mm cubic specimens of big aggregate concrete at five kinds of stress ratios,0:-1, -0.25:-1, -0.5:-1, -0.75:-1 and-1:-1 after exposure to freeze-thaw cycles of 50, 100, 150, 200, 250 and 300 times by employing a large static-dynamic true triaxial machine. Failure modes of the specimens are observed and described. The two principally static compressive strengths are measured. Based on the test data, the influences of the freeze-thaw cycles and stress ratios on the biaxial strengths of big aggregate concrete after exposure to freeze-thaw are analyzed respectively. The relationships between the ultimate compressive strength and freeze-thaw cycles, stress ratios are given respectively. The unified failure criterion with consideration of the influence of freeze-thaw cycles and stress ratios is proposed, which provides the experimental and theoretical foundations for strength analysis of big aggregate concrete structures subject to complex loads in cold environment. Key words: big aggregate concrete; freeze-thaw cycle; stress ratio; biaxial compressive strength; failure criterion

Abstract: A series of moisture content tests were carried out to study the changes in geogrid-reinforced clay moisture content under freezing-thawing cycles, the influences of compaction degree, reinforcement layers and initial moisture content of the soil on the soil moisture content under freezing-thawing cycles were discussed. We can see that the soil compaction degree is the first important factor to the moisture content, the change of upper lay clay moisture content is positive for the low compaction degree and negative for a high one; the reinforcement layers is the second important factor to moisture content, the upper lay moisture content reduces with the increasing of reinforcement layers, it is significant in the high compaction soil; the initial moisture content is the weakest factor, a big change of upper lay moisture content only appears when the initial moisture content is large and the soil compaction is low.

Abstract: The influence of limestone powder, lithium slag and air-entraining agent on frost resistance of concretes was investigated by freezing-thawing cycle tests. The elastic moduli and weight loss rates of concretes before and after tests were checked. The results show the introduction of limestone powder into concrete is disadvantageous to its frost resistance, which gets worse as limestone powder contents increase. Air-entraining agent used in concrete can improve its frost resistance. The frost resistance grades of concrete containing a certain of air-entraining agent (0.2-0.4‰) can reach F1500, while it is below F300 for limestone powder concrete which is absent of air-entraining agent. The addition of lithium slag into concrete is helpful to frost resistance, and optimum mixing amount is 10%.

Abstract: The influence of fly ash as cement replacement on pore structure, chloride penetration and frost resistance of recycled concrete is investigated by evaporable water test, chloride natural diffusion test, and freeze-thawing test. The experimental results indicate that adding fly ash to recycled concrete can decrease its porosity and improve its pore size distribution. Chloride penetration resistance of recycled concrete is enhanced firstly and then reduced with increasing of fly ash content. The best proportion replacing cement with fly ash is 20%. Fly ash content has a certain influence on the frost resistance of recycled concrete, and the frost resistance of recycled concrete only has been improved when the proportion of fly ash replacing cement achieves more than 20%.

Abstract: Mechanical properties experiments of air-entraining concrete after suffered to 0, 100, 200, 300 and 400 freezing-thawing cycles were performed. The experiment method, contents and result of strength and deformation of air-entraining after freezing-thawing cycle under biaxial compression were also introduced. The relationship between the strain corresponding to peak stress and cycle of freezing-thawing as well as the relationship between compressive strength and cycle of freezing-thawing were analyzed. The failure criterion of air-entraining concrete under biaxial compression was established.

Abstract: Biaxial compressive tests of plain concrete specimens suffering 0、25、50 and 75 cycles of freezing and thawing respectively in 3.5% sodium chloride solution imitated seawater were completed under four lateral constant stress rates. The tests were completed by using the large static-dynamic triaxial test system for concrete in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The biaxial compressive strength and deformation characteristics of concrete confined by lateral stress after suffering corrosive cycles of freezing and thawing were studied in a systematic way. On the basis of the tests, the failure criterion of concrete subjected to constant lateral compressive stress after suffering corrosive cycles of freezing and thawing was established in the stress-strain system. The conclusions can provide the testing and theoretical basis for deeper study of the concrete construction subjected to biaxial compressive combined loads in northern cold region or influenced by corrosive cycles of freezing and thawing nearby the coastal and offshore area.

Abstract: This paper discusses the sulfate resistance and frost of mass hydraulic concrete which containing fly ash, superplasticizer and a novel MgO-bearing expansive agent (HNM), at same time, the mechanisms and processes of sulfate attack on it have been proposed. Results showed that using a water/binder ratio of 0.48 in RCC containing 50 % fly ash and 8 % HNM a durability factor of over D300 can be achieved and sulfate resistance may be improved slightly.