Research On Concrete Framework And Structure Model

The use and research of concrete material have nearly 200 years' history. With the development of scientific research and technology, the components - structure - properties correlation of concrete is constantly to be revealed. During this period, we have gained a large number of valuable research achievements.On the one hand, concrete is a multi-level and non-homogeneous composite material. The non-homogeneous, non-linear, and anisotropic property makes the strength and deformation of concrete is very complex, thus it also leads to difficulties in the reach of concrete structure model. As many of the concrete structure model achieve different results, this important fact that the different space-arranged of the aggregate in concrete leading to different stress distribution is often overlooked.On the other hand, concrete design theory is still stuck in the structure model of cement paste, the core of which is still water-cement ratio theory. It has historical and academic limitations in the use of concrete and research guidance.The cement paste structure model of concrete mix design, using unit of water W, water-cement ratio W/C and the rate of sand Sp as the basic parameters, only water-cement ratio ensuring the strength and using the rate of water and sand as the goal of mix workability, does not reflect the interaction between the various components of concrete and the contribution to their strength. The main reason is: water-cement ratio theory has not established intrinsic link between the cement and aggregates. With the high-strength and high-performance concrete developed, high-strength concrete is dependent much more on strength of coarse aggregate skeleton. Traditional concrete theory is no longer adapted to the new developments.To this end, based on the theory of centroplasm hypothesis proposed by Wu zhongwei academician and the crystal principle, the thesis brings up a model of concrete framework structure. The author believes that the concrete is composed of coarse aggregate framework, mortar and interface transition area. The strength of concrete is from the three contributions. The framework structure is that coarse aggregates arrange in space, just like human being's skeleton. It depends on the volumetric ratio which is composed of coarse aggregate, cement and fine aggregate, which can be expressed by the rate of framework-mortar N. The mortar which is composed of hardened cement paste and fine aggregate plays a role of adhesive bonding of coarse aggregate in the framework and structure model, as the muscle does in our body. And fine aggregate in mortar plays a role of strengthening the model just like the fiber in muscle. The essential reason why concrete performance varies so much lies on that in addition to the structure formed by coarse aggregate, the major reason is the deviation causing by mortar in concrete and the standard cement mortar.The main work and results of the thesis include:1. Based on the in-depth analysis of existing concrete strength and structure the theory, the hardened cement paste model is proposed, and the C concrete model of the parameters based on water-cement ratio as well as the limitations of traditional concrete design theory is pointed out objectively. The J concrete model is proposed on the base of C concrete model. The model is based on the concept of the aggraegate-paste ratio J, considering the effect on concrete strength of aggregates-cement ratio and water-cement ratio in the whole, the contribution of aggregate on the strength of concrete is quantitative the first time and it truly reflects the physical nature that the strength of concrete which the cement and aggregate provide together. Based on the J parameter and the correlative strength theory formula f_cu=A_j·f_ce[1/J-B_j], unit water dosage W, aggregates-paste ratio J as essential parameters double parameter concrete design method is established. The part of the work supplements and improves the concrete strength and design theory.2. For the study of concrete mortar, the paper researches shape character by digital image processing (DIP method), sets up mortar deviating function and a function between the mortar slump and water quantity and also quantifies the effect of the aggregate distribution and particle shape characteristics on mortar property. The correlative results are cement-sand ratio function:(?), and deviating function:(?), and relationship between the mortar slump and water quantity:3. In view of the theory of concrete structure, the coarse aggregate has aunique status. This paper reaches its structure characteristics on a more in-depth and comprehensive study.(1) For the real state of concrete, the determination statistics of concrete aggregate coordination structure within the space coordinate of the form and the related calculations show that:At the vibrated state in the concrete specimens, the number of most aggregate coordination focus on 6 to 8; three basic unit of framework model are brought forward ; the strength test results of concrete framework structure model unit and compositions validate that the different distribution of the balls in concrete affect the aggregate concrete strength. (2)With the application of DIP techniques, using the sphericity and thickness/breadth ratio as the shaping character parameter, then make the characterization of coarse aggregate grain shape characteristics clear, so that the reach of coarse aggregate grain shape becomes more convenient. By studying the characteristics of coarse aggregate stacking, the function relationship between the coarse aggregate grain shape parameters and accumulation porosity (that is, filling density), the grain shape parameters and coordination number of framework structure are established, which makes research of the coarse aggregate in concrete from qualitative into quantitative.4. Framework-mortar ratio as the main parameters of the model, breaks through the parameters limitations of water-cement ratio and fully reflects the aggregate (coarse aggregate)framework structure role; the strength formula of framework (?) that is reasoned fromcompound principles, reflecting the various structural layers 'contribution to strength appropriately.5. Establishing the mathematic model of designing metho of framework concrete whichuses framework-mortar ratio N (or N_c), sand-cement ratio deviation D_j (or S_w), and unit water dosage W as essential parameters clears the structure of concrete design methods, including the three parameters determination and the relevant design process.The determination method of the various parameters in the design method is: framework-mortar ratio N: (?), sand-cement ratio deviating function:(?), and unit water dosage: (?)6. Using framework structure mode design for preparation of framework structure concrete and investigating the property of mechanics and durability.(1)The test results of the framework structure concrete and the traditional concrete indicate that: per cubic amount of cement can be reduced of 25kg, while the compressive strength is only 0.2% lower than traditional concrete, and folly meet the design requirements. At the same time, a comparative test of the concrete durability is made. The results show that properties of resistance to freeze-thaw, resistance to chloride ion permeability and resistance to carbonation can meet the design requirements. This shows that compared with traditional concrete, framework structure concrete is more economy.(2) The experimental results analysis of the resistance to freeze-thaw framework structure concrete shows that: ①Within a certain range (1.12～1.34), the smaller the framework-mortar ratio is, the better the frost resistance of concrete is. This is because: According to the framework theory, the framework-mortar ratio is larger, indicating that the coarse aggregate is more in concrete, the concrete is denser and the frost resistance is better. But the premise is that concrete mortar must have sufficient strength and durability to ensure their own and the interface do not occur freeze-thaw damage ahead.②Admixture such as fly ash and silica fume in the framework concrete, can effectively improve the frost durability of concrete, and the effect of silica fume admixture is better than fly ash.Concrete framework structure model theory is a new concrete theory after the mortar model theory. Since this mathematic model is on the basis of a physical model which could open out the essence of concrete microscopical structure, it will embody more adequately how much every ingredient in concrete has contributed to the integrated performance of concrete in real sense. The research work in this paper only provides a new idea for the concrete research, and a more in-depth and comprehensive research is expected to improve the system of concrete framework structure model theory.