Keywords: concrete, dialectical relationship, system, structure, performance, construction
I. Introduction
Concrete in a broad sense refers to a composite material with certain strength, rigidity and durability, which is composed of cementing materials (organic, inorganic or organic-inorganic composites), granular aggregates and other additives. At present, concrete made of inorganic cementitious materials in a narrow sense is widely used.
Concrete materials can be traced back to a very old historical period. The cementing materials used at first were clay, gypsum and hydraulic lime, and later pozzolana and hydraulic lime were used. Since 1824 J. As-pdin invented portland cement, the cementitious materials used to make concrete have undergone qualitative changes. Since then, the production technology of cement and concrete has developed rapidly, the dosage and application scope of concrete have been expanding day by day, and concrete materials have also developed into a variety of composite systems combining functions and structures to meet various performance requirements. At the same time, the development of concrete enriches the content of concrete science and technology research, and also brings new topics to concrete science research. The popularization and application of concrete science and technology further promotes the development of concrete. There are many dialectical relations in concrete things that follow the general law of dialectics of nature. In this paper, several problems are discussed in order to have a comprehensive understanding.
Second, the development of concrete is inseparable from the development of material economy in human society.
Although it is an accident that people found that clay can be used to make clay concrete in ancient times, the history of concrete development proves that the development of concrete is based on the material economy of human society. Pyramids built with gypsum concrete in ancient Egypt and the application of lime concrete in Qin Changcheng, China. They were all based on the relatively prosperous social economy and high productivity at that time.
In 1824, the invention of portland cement as a patent application itself is an economic and social phenomenon. Since then, the production of cement has followed the general economic law of economic commodity production, from simple small-scale workshop calcination and manual grinding to large-scale fully mechanized one-stop production line. Every link of its production development is influenced by the degree of social and economic development and the economic operation mechanism. At the same time, the large-scale production of cement and concrete has also stimulated and promoted the social and economic development. The commercialization and marketization of cement concrete completely push cement concrete to the market, so the production and development of cement concrete also depend entirely on the social, material and economic basis under the market mechanism. With the development of social economy and the demand of market and society, the variety and quantity of concrete are constantly innovating or increasing rapidly.
Looking back at the history of world civilization, concrete is one of the material pillars of world civilization today. Concrete materials are not only widely used in buildings, highways, bridges, water conservancy, tunnels and other infrastructure, but also in special projects such as marine development, geothermal engineering, waterproof and anti-corrosion engineering, atomic energy engineering and space development.
Third, the development of concrete is inseparable from the development of science and technology.
From a historical point of view, the development of concrete materials itself is a process of technological innovation, which has gone through the process from scratch, from simple to complex, from low to advanced, from primitive form to modernization, which not only reflects the progress of social economy and human material civilization, but also shows the course of scientific and technological development. Cementitious materials have experienced a leap in the quality of clay, gypsum, lime, cement and polymer. Three breakthroughs in reinforced concrete, prestressed concrete and polymer concrete. The construction of concrete has gone through completely manual operation, simple mechanical and manual labor construction mode, and now it is fully mechanized by manual control. Construction machinery has developed from simple mixing and vibration in the past to multi-functional complex series machinery; Building technology has also developed from simple technology in ancient times to high technology under the guidance of modern science. For example, the construction of underwater concrete has experienced bag construction and open-bottom tank (bag) construction, and gradually developed into high-tech construction methods such as conduit construction and pumping construction.
The technological innovation of concrete is a process of development with the development of various fields of natural science, which constantly provides theoretical basis and new research methods for the development of concrete, and various fields of natural science gradually penetrate into concrete; Concrete also provides a new subject for various fields of natural science. Testing and popularizing the basic principles of natural science; Natural science and concrete penetrate and combine with each other, forming a marginal subject of scientific and technological integration. With the rapid development of social economy, social science has gradually penetrated into specific scientific. The relationship between specific scientific and other disciplines is shown in figure 1. In recent years, the research and application of high-tech achievements have provided many new ideas for the research of concrete and achieved many breakthrough research results. The research methods and means of concrete have made new progress, and the research content of concrete has also deepened from the original macro-mechanical research to micro-research. Extensive research and in-depth discussion on concrete have enriched the content of concrete science.
Fourth, the application of system method in concrete.
Concrete itself is a system composed of cementitious materials such as cement and aggregates, which has a unique pore structure of concrete and follows the general laws of system science. The so-called system is an organic whole with certain hierarchical structure and function, which is composed of several interacting elements. System method is the general name of the method that comprehensively studies and processes the research object as a whole system according to the viewpoint and theory of system science. Systematic method is widely used in the research and control of concrete.
Four basic problems in concrete research, namely, concrete design, construction, structure and performance, constitute the regular tetrahedron structure of concrete system. The rheological properties and workability of fresh concrete and the structure of hardened concrete are determined by the design of some concrete components and the determined construction technology, and the structure of concrete determines the macro-mechanical properties and durability. Generally speaking, the demand for excellent performance of concrete must be reversed. Starting with the mix design and construction technology of materials, the performance of concrete is improved by optimizing the structure of concrete. The performance of concrete reflects the mix proportion, construction technology and structure of concrete. Through systematic research, concrete workers comprehensively consider the relationship between concrete design, construction, structure and performance, select functional materials (such as polymers or other additives), optimize mix design, and adopt advanced construction machinery and scientific construction technology to improve and optimize concrete structure, control concrete quality and obtain high-performance concrete. Specific improvement measures often start from three aspects: optimizing mix proportion, composite structure and new construction technology.
At present, the content of concrete research is mainly based on improving the performance of concrete, through the relationship between structure and performance. The information flow between the design, construction, structure and performance of new and old concrete will realize the self-organization optimization of concrete itself through the hard work of concrete workers and researchers, and the way of optimization is to modify concrete.
In the process of concrete research, black box principle, hypothesis theory and model simulation are often used to study and clarify the complexity of concrete internal structure. Considering concrete as a black box without knowing its structure and microstructure, an empirical hypothesis is put forward. Under the action of external stimulus (load or environment, etc.). ), the concrete black box will make a series of reactions. According to the hypothesis of excitation and response test, the black box is investigated, and the corresponding concrete constitutive model is established to explain the concrete structure and motion mechanism.
Five, specifically the unity of matter, information and energy.
Concrete itself is a system, which exchanges materials, energy and information with the external environment all the time. At the same time, concrete can be divided into many subsystems at all levels, and there is always the exchange of material energy and information between subsystems and between subsystems and parent systems. With the chemical reaction between cement and water, that is, the gradual hydration and hardening of cement, the new cement concrete mixture constantly produces new substances, transmits and exchanges energy, and responds to the changes of concrete rheological parameters and concrete porosity and interface properties. In the process of mechanical failure of hardened concrete, in addition to developing the exchange of material and energy, there are not only the information detected by ultrasonic and crack propagation instruments, but also the information that concrete needs to take some measures due to insufficient strength or other shortcomings. Ultrasonic wave and crack propagation reflect the changes of internal matter and energy (including the changes of energy form) after concrete is compressed. Non-destructive testing, such as ultrasonic testing and X-ray diffraction testing, reflects the damage information inside concrete materials through the emission, transmission and acceptance of energy. Energy and information are unified. The fracture mechanics of concrete unifies the intensity factors of stress field and displacement field at the crack tip of concrete with the strain energy release rate of concrete.
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