Table 1: performance comparison of ordinary concrete materials, High performance concrete and ultra-high performance concrete (reactive powder concrete) compressive strength of ordinary concrete NSC high performance concrete HPC ultra-high performance concrete UHPC (MPa) 20-40 40-96170-227 Water-binder ratio 0.40-0.700 0.24-0.350.14-0.27 Cylindrical splitting tensile strength. 2.5-2.8-6.8-24 Maximum aggregate particle size (mm)6544 20-62 Air permeability K (40 C in K (24 hours) (mm) 3x 1000 Water absorption (225 hours) (kg/mm) 2x10 2.4x. (mm/s) 1 x10 4.9x10 2x10 carbon dioxide1surface erosion 0.08 surface erosion 0.0 1 poisson ratio 0.1-0.2. X 10 fluidity without self-shrinkage (workability) (mm) slump measurement slump measurement 150- 155 The design theory of ultra-high performance concrete with air content of 4-8% 2-4% 0 is the maximum accumulation particle accumulation theory. Particles with different particle sizes of its constituent materials form the densest filler in an optimal proportion, that is, the gaps between millimeter particles (aggregates) are filled with micron particles (cement, fly ash and mineral powder), and the gaps between micron particles are filled with submicron particles (silica fume). As early as 193 1 year, Anderson established the mathematical model of the maximum packing density theory. However, it was not until the end of 1970s that the first generation of ultra-high performance concrete designed and prepared by this model was born in the IET Cement Ogbeton Laboratory in aalborg, Denmark, which was called CRC(Compact Reinforced Composite). The mechanical properties of CRC are basically the same as the current UHPC, and the highest compressive strength exceeds 400MPa. It uses sintered bauxite as aggregate and steel fiber to improve the toughness of the material, so it is called "composite material". Restricted by the performance of superplasticizer at that time, CRC or early UHPC was sticky, not easy to be vibrated and compacted, and not convenient for cast-in-place application. In 1990s, cooperative research projects were carried out in Europe, and related research was also widely carried out around the world. This material has gained a new name "RPC". The reason why "UHPC" was formed in this century is that, compared with the early CRC or RPC, with the improvement of design theory, the appearance of super-efficient water reducer (polycarboxylic acid system) and the progress of preparation technology, this material has the construction performance of ordinary concrete, even can realize self-compaction, can be cured at room temperature, and has the conditions for wide application.
The differences between UHPC and ordinary concrete or high-performance concrete include: coarse aggregate is not used, silica fume and fiber (steel fiber or composite organic fiber) must be used, cement consumption is large, and water-binder ratio is very low. The composition of UHPC is shown in Table 2.
Table 2: Basic composition of UHPC ultra-high performance concrete kg/m wt% Portland cement (type V) 700-10 27.0-38.0 silica fume 230-320 8.5-9.5 Ground quartz sand 0-230 0.0-8.0 fine sand 760-/kloc-. ) and thin-walled structures, as well as high wear and corrosion environment. At present, UHPC has been applied in some practical projects, such as long-span footbridges, highways and railway bridges (see Table 3 for examples), thin-walled silos, nuclear waste tanks, steel cable anchorage reinforcing plates, ATM machine protective shells and so on. It can be expected that there will be more and more applications.
Table 3: Concrete composition and performance of the first UHPC highway bridge in France. Composition material: portland cement with kg/m performance 1 1 14 slump fluidity 630~640 mm silica fume 169 28d characteristic compressive strength (fck). 175 MPa 0-6mm aggregate 1072 28d characteristic tensile strength (ftk) 8 MPa fiber: 0.3mm diameter x20mm length 234 28d characteristic tensile strength after cracking 9. 1 MPa superplasticizer 40 elastic modulus 64 GPa water 209 specific gravity 2800 kg/m water/cementitious material ratio is 0./. References: Proceedings of the Third International Symposium on High Performance Computing: 20031October 6 -9 -22, Orlando, Florida.