What are the "new materials" in civil engineering?

The new materials in civil engineering include the following materials: \xd\1 High-performance concrete (HPC)\xd\ requires high durability, high strength and excellent workability, which are firstly reflected in high early strength, high acceptance strength and high elastic modulus; Followed by high durability. It can protect steel bars from corrosion, and can also keep concrete strong and durable when used under other harsh conditions; Finally, it has high workability, pumpability and easy dressing. Fluidized concrete with large slump can be prepared without segregation; The pumping pressure can be reduced and the dressing is easy. When pouring in winter, the setting time of concrete is normal, the strength increases faster than that of ordinary concrete, and it is not frozen in low temperature environment, but the slump of pouring concrete in high temperature environment is normal and the hydration heat can be controlled. \xd\1.1 Low-strength concrete \xd\ This material can be used for filling, padding and isolation of foundation and pile foundation, as well as for subgrade or filling holes, and can also be used for underground structures. In some specific cases, low strength concrete can be used to adjust the relative density, workability, compressive strength, elastic modulus and other performance indexes of concrete, and it is not easy to produce shrinkage cracks. \xd\1.2 Lightweight Concrete \xd\ Lightweight concrete made of natural lightweight aggregate (such as pumice, tuff, etc.), industrial waste lightweight aggregate (such as slag, fly ash ceramsite, spontaneous combustion coal gangue, etc.) and artificial lightweight aggregate (such as shale ceramsite, clay ceramsite, expanded perlite, etc.) has the advantages of low density, high relative strength, good thermal insulation and frost resistance. Using industrial waste residue, such as abandoned boiler cinder, coal gangue from coal mine and fly ash from thermal power station, to prepare lightweight concrete can reduce the production cost of concrete, turn waste into treasure, reduce the pollution of cities or factories, and reduce the land occupied by accumulated waste, which is also beneficial to environmental protection. \xd\1.3 Self-compacting concrete \xd\ Self-compacting concrete does not need mechanical vibration, but relies on its own weight to make concrete compact. Although the fluidity of this kind of concrete is high, it can still prevent segregation. The methods for preparing this kind of concrete are as follows: (1) The volume of coarse aggregate is 5% of the volume of solid concrete; (2) The volume of fine aggregate is 4% of the mortar volume; (3) the water-cement ratio is .9 ~ 1.; (4) Conduct fluidity test to determine the dosage of superplasticizer and the final water-cement ratio, so as to obtain the optimal composition of the material. The advantages of this kind of concrete are: there is no vibration and noise in site construction, and it can be constructed at night without disturbing people; Harmless to workers' health; The quality of concrete is uniform and durable; It is also easy to pour when the reinforcement arrangement is dense or the component shape is complex; The construction speed is fast, and the on-site labor is small. \xd\2 Concrete with high content of fly ash \xd\ With the deepening of people's understanding of the inherent potential of fly ash, such as particle shape effect, pozzolanic activity effect and micro-aggregate effect, and the rapid development of concrete admixture technology, the view that fly ash is another necessary component of concrete after admixture is being accepted by more and more people, and the content of fly ash is also increasing. The United States, Britain, Canada and other countries, which are more advanced in concrete technology, have started the research and application of concrete with high content of fly ash since the mid-198s. \xd\ The significance of using a large amount of fly ash lies not only in saving limited engineering materials, but also in its environmental and social benefits. Cement is a product with high energy consumption and high environmental pollution. It is an inevitable trend to use cement as little as possible and use various industrial waste residues as much as possible to make concrete a material for sustainable development of mankind. In the western lT industry countries with particularly strict environmental protection requirements, special attention is paid to the secondary development and full utilization of various industrial wastes. With the rapid development of China's economy and the rapid improvement of people's living standards, environmental and social benefits will be paid more and more attention, and the full development and utilization of industrial waste residue will become an inevitable choice. \xd\3 New energy-saving wall materials \xd\3.1 New masonry materials \xd\ Walls with masonry structure usually rely on masonry materials with low thermal conductivity and good thermal insulation performance, so as to achieve the purpose of small heat transfer of the wall. This kind of materials mainly include hollow earth-drilling bricks, aerated concrete blocks, ordinary concrete and small concrete hollow blocks such as fly ash, coal grindstone and pumice, and thermal insulation mortar is used as masonry cementing material. \xd\ In recent years, energy-saving walls composed of thermal insulation materials and traditional wall materials (such as solid clay bricks and concrete) or new wall materials (such as hollow bricks and hollow blocks) have been developed and applied. Commonly used thermal insulation materials are mineral wool, glass wool, foamed plastics, expanded perlite, aerated concrete and other materials, and the composite materials are clay solid bricks, concrete hollow bricks, hollow blocks and other masonry materials. The composite wall has a layer of thermal insulation material with small thermal conductivity, and the thermal insulation performance of the wall is better than that of the wall built with single material, and the energy saving effect is more remarkable. However, the price of thermal insulation materials is relatively high, and at the same time, it is necessary to match the main structural form of the building, and it is best to adopt the structural form of frame structure and non-bearing wall. \xd\3.2 New-type composite wallboard \xd\ New-type energy-saving composite wallboard is composed of high-efficiency thermal insulation materials, external wall panels and internal wall panels. According to the standard size or modulus, it can be industrialized in the factory, including doors, windows and other components, which can be manufactured integrally with the wallboard, transported to the construction site and installed on the structural frame, thus forming the external protection structure of the building, which is the main architectural form adopted by developed countries in recent years. The composite wallboard used in this kind of building does not bear external force, and its thickness is generally 1 ~ 15 mm, with light weight, good thermal insulation performance, accurate size and high construction efficiency. \xd\4 FRP composites \xd\ Civil structures are mainly plagued by two major problems, premature degradation and insufficient structural functions. In recent years, fiber reinforced polymer (FRP) has become a feasible way to solve these structural problems. Engineering practice shows that FRP composite materials can adapt to the development of modern engineering structures to large span, towering, heavy load, high strength and light weight and withstand harsh conditions, and meet the industrialization requirements of modern construction technology, so they are being more and more widely used in bridges, various civil buildings, marine and offshore, underground engineering and other structures. There are two ways of application: one is to replace steel bars or steel pipes and directly apply them to new structures; Second, it is used for the maintenance and reinforcement of old structures to achieve good architectural effects. \xd\5 Intelligent materials \xd\ The service life of large-scale civil engineering structures and infrastructure is as long as decades or even hundreds of years. During its use, due to the adverse factors such as environmental load, fatigue effect, corrosion effect and material aging, the structure will inevitably produce damage accumulation, resistance attenuation, and even lead to unexpected accidents. In order to effectively avoid the occurrence of unexpected accidents, it is necessary to strengthen the health monitoring of such structures and facilities. \xd\, an intelligent material called carbon fiber smart concrete material, has been applied in large-scale civil engineering health monitoring. \xd\ It is a fiber-reinforced cement-based composite material with chopped or continuous carbon fiber as filling phase and cement slurry, mortar or concrete as matrix. The resistivity of this kind of material has a certain corresponding relationship with its strain and damage, so the strain and damage of carbon fiber concrete can be monitored by testing the change of its resistivity. Carbon fiber reinforced concrete also has the characteristics of simple construction technology, excellent mechanical properties and good compatibility with concrete structures. Therefore, it can not only be used to monitor the traffic flow and load of roads, but also meet the requirements of health monitoring technology for large civil engineering structures and infrastructure. In addition, the electrothermal effect and electromagnetic shielding characteristics of carbon fiber reinforced concrete also have important application value in temperature adaptation and electromagnetic interference resistance of concrete structures. \xd\ Nano-materials have ultra-high strength, superplasticity and some special electrical properties that conventional objects do not have because of their ultra-fine particle size. Nano-materials have been applied in many fields and achieved remarkable effects of strengthening, toughening and intelligence. As a traditional material, concrete's performance can't meet the higher requirements of social development, and intelligent concrete has become a new development direction. Nano-materials also endow concrete with intelligent characteristics. The resistivity of cement-based nanocomposites changes linearly with strain, and it has high sensitivity and repeatability. As an intrinsic intelligent material, cement-based nanocomposites have high strength and good conductivity, and have broad development prospects.