Keywords

1 Introduction

In Japan, the research of high-strength concrete began around 1970 years ago. At that time, admixtures with better water reducing performance than general water reducing agents were successively developed in Japan. The concrete in Japan is developing towards high strength concrete with low water consumption and low water cement ratio. The strength of concrete is greatly promoted by the use of new water reducing agents and the application of silica fume. Because silica fume has strong pozzolanic properties and is a mixture of ultra-fine particles, it makes the concrete structure compact, and it is easy to produce high-strength concrete above 50 N/mm2, so it is widely used in actual structures and prefabricated components (originally PC piles). Ultra-high strength concrete, which exceeds l00 N/mm2, has developed since 1990. With the further development of research, the research and application from 100–150 to 150–200 MPa has gradually developed, creating another miracle in the field of materials and structures. Under a series of studies and engineering applications, a series of mature systems and measures have been formed for mix proportion design, structural design, production management and quality management of ultra-high performance concrete.

Through reading and sorting out the literature, this article has sorted out six important application cases of ultra-high performance concrete, including project overview, mix proportion design, strength, providing learning and reference for domestic and foreign scholars, and contributing to the development and application of ultra-high performance concrete.

2 Engineering Project Cases

The perfect combination of ultra-high performance concrete and high-strength reinforcement (yield load of 440 MPa) has made high-strength and high-performance materials an important step forward. They have been used in many building structures in Japan, and have been widely used in 100–150 MPa [1,2,3,4]. Even 150–200 MPa [5,6,7,8,9,10,11] ultra-high strength concrete has been used in actual engineering projects. See Table 1 for the engineering projects applying 150–200 MPa UHPC.

Table 1 The engineering projects applying 150–200 MPa UHPC
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Table 1 shows the basic information of six 150–200 MPa ultra-high performance concrete projects, which are mainly applied to the structural columns at the bottom core of the frame structure system of super high-rise buildings to improve the utilization rate of building area and the seismic performance of buildings. The buildings involved are widely used, but the common point is that the building structure is more regular.

3 Concrete Raw Materials and Mix Proportion

3.1 Concrete Raw Materials

According to statistics, the requirements for raw materials of ultra-high performance concrete above 150 MPa are obtained, and the raw materials are shown in Table 2.

Table 2 Main parameters of concrete raw materials
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Table 2 shows that, Silica fume composite cement is widely used in Japan, which has better hydration reaction and grading density, while ordinary Portland cement is mainly used in China; The compactness of concrete is well guaranteed by strictly calculating the proportion of fine aggregate and coarse aggregate. Low water cement ratio is one of the technical requirements of ultra-high performance concrete. The development and application of ultra-high performance water reducing agent greatly improve the working performance of low water cement ratio concrete, which is the key factor. Fiber is an important factor in the application of ultra-high performance concrete to building structures. Organic fiber could improve the fire and explosion resistance of concrete, and steel fiber could improve the ductility and ultimate strength of concrete. The strict requirements for various materials have realized the application of ultra-high performance concrete.

3.2 Mix Proportion

Mix proportion is the key link to realize the application of ultra-high performance concrete materials. The mix proportion parameters are listed in Table 3.

Table 3 The concrete mix ratio parameters
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Table 3 shows that, the aggregate grading of ultra-high performance concrete is relatively strict. The proportion of silica fume composite cement to coarse and fine aggregates makes it have a high compactness, so as to achieve high strength; High performance water reducing agent makes concrete with low water cement ratio still have high workability. Raw materials and mix proportion are the key to achieve ultra-high performance, and have important guiding significance.

4 Concrete Performance

Different curing processes are selected for different production methods, the curing process is the key to ensure the strength and working performance of concrete. Table 4 shows different manufacturing, curing process, strength, etc.

Table 4 The performance analysis of concrete obtained under different production processes for different mix ratios
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Table 4 shows that, whether cast-in-situ or factory prefabricated, heating curing is an optimal and even necessary curing process, which can guarantee the optimal performance in the fastest and best way. Heating curing includes warm water tank curing (40 °C), heating plate curing (90 °C) and steam curing (90 °C). The warm water tank curing and steam curing are applicable to the production process of the supporting prefabrication plant, the heating plate curing and steam curing are applicable to the supporting on-site casting production process, and the steam curing (90 °C + 120 h) is the most selected curing process. The test strength meets the requirements of design strength, and reasonable production process and curing process are effective guarantees for compressive strength.

5 Conclusion

With the development of high-performance materials, ultra-high performance concrete has been applied in Japanese building structures; At the same time, it lays a foundation for the development of new materials and new structural systems.

Silica fume composite cement material and solid grading analysis theory are the key technical supports for the development of ultra-high performance concrete in Japan; The development of super high performance water reducing agent is the core technology for the development of super high performance concrete, which solves the problems of high viscosity and low flow performance; Organic fiber and steel fiber solve their fire resistance, explosion resistance and ductility.

The curing process is the key to its ultra-high compressive strength. Through comparative analysis, it is found that steam curing (90 °C + 120 h) is more reasonable and suitable for large-scale and standardized production and application.

The research and application of ultra-high performance concrete in building structures in Japan have formed perfect technical standards and management measures, which provide guidance for our research and application.