Experimental Study On Freezing And Thawing Responses Of Vegetation-growing Concrete

The infrastructure constructions through or located in alpine area of our country are gradually increasing for the promotion of the western development strategy. These infrastructure constructions are benefit for human life and production, but at the same time they have damaged vegetations and led to a large amount of bare slopes too. As an excellent artificial ecological material, the main function of the vegetation-growing concrete is to restore vegetations by shallow layer protection. At present it was only implemented in part of the high temperature areas, such as the south China, the central China and the southwest of China. There were few reports about the successful ecological restoration through the common artificial ecological materials in domestic which have the similar working condition with vegetation-growing concrete.For the reason above, the vegetation-growing concrete is chosen as the research object to study the frost-heave and thaw-settlement properties of vegetation-growing concrete firstly. As well, it is tested for the anti-freeze and improvement combined with the measures of cement soil. The specific works and main research achievements are as follows:(1)Taken cold-end temperature, water content and plant generate as the influence factors, frost-heave experiments are carried out by different levels of single factor and orthogonal four levels of three factors for the vegetation-growing concrete, and it emphatically discusses the relationship between the frost-heave ratios and various factors in different initial conditions in the course of unidirectional freezing. Result shows that cold-end temperature, water content, plant generate all influence the frost-heave properties of the vegetation-growing concrete. The order of influence intensity by various factors is as follows:plant generate> water content> cold-end temperature. The frost-heave ratios of the vegetation-growing concrete will increase with the raising of the water content and cold-end temperature. But for the vegetation-growing concrete composed with clay, there is a turning point for water content. And in the two sides of this point, the frost-heave ratio takes on a large difference. Under the same conditions, the frost-heave effect of vegetation-growing concrete composed with clay is greater than that composed with sand. Then, the paper makes prediction models of frost-heave for vegetation-growing concrete.(2)On the basis of the frost-heave test, taken cold-end temperature, water content, plant generate and thawing temperature as influence factors, thaw-settlement experiments are carried out by different levels of single factor and orthogonal four levels of four factors for the vegetation-growing concrete, and it emphatically discusses the relationship between the thaw-settlement coefficients and various factors in different initial conditions in the course of bidirectional thawing. Result suggests that cold-end temperature, water content and plant generate all obviously influence the thaw-settlement characters of vegetation-growing concrete, while thawing temperature almost has no influence on them, and the order is as follows:plant generate> water content> cold-end temperature> thawing temperature. The thaw-settlement coefficients of the vegetation-growing concrete will increase with the raising of water content and cold-end temperature. But for the vegetation-growing concrete composed with clay, there is a turning point for water moisture too. And the thaw-settlement coefficient has a large difference in the two sides of this point. Under the same conditions, the thaw-settlement effect of vegetation-growing concrete composed with clay is greater than that composed with sand. Then, the paper makes prediction models of thaw-settlement for vegetation-growing concrete.(3)Combined with experiments of the frost-heave and the thaw-settlement for vegetation-growing concrete, the paper discusses the changes of shear strength and volume. Result indicates that the change of cold-end temperature has great influence on the shear strength indexes. Water content only has great influence on the cohesion, while the influence on the internal friction angle is not obvious. Thawing temperature almost has no influence on the shear strength indexes. There are little changes in volume after a complete process of frost-heave and thaw-settlement, while the micro structure of the material is disturbed obviously by the freezing and thawing action.(4)In the premise of without altering the proportions of raw materials, taken palm fiber, silica powder and surfactant as influence factors, anti-frost and improvement experiments are carried out by different levels of single factor and orthogonal five levels of three factors for the vegetation-growing concrete, and it emphatically discusses the mass loss and relative dynamic elastic modulus of the vegetation-growing concrete influenced by various factors under different conditions. It shows that the palm fiber, silica powder and surfactant all influence the frost resistance property of the vegetation-growing concrete. The order of the influence is as followed:the palm fiber> surfactants> silica powder. It also indicates that the best additive agent to improve the frost resistance property of the vegetation-growing concrete as followed:palm fiber:silica powder:surfactant=1:3:0.05. While the additive amount reaches 1.5% by weight of the dry plant generate, the frost resistance property of the vegetation-growing concrete can be improved about three times. It also shows that this additive agent hardly influences on plant's growth though the plant adaptability analysis of improved vegetation-growing concrete.Basis on the artificial ecological material of vegetation-growing concrete, the paper obtains the frost-heave and the thaw-settlement characteristics, and puts forward an optimal method and mixing proportion of the additive agent to improve the frost resistance property of the vegetation-growing concrete, firstly reporting the proper ecological material for slope vegetation restoration in alpine region. Research not only has important theoretical and practical significance for slope ecology restoration in alpine region, but also provides reference value to the research of similar ecological material.