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UHP Flexible Concrete for Critical Structures

Concrete with compressive strength more than 150MPa is called ultra high performance concrete (UHPC). Most specifically its applications are in high rise buildings, bridge, flyover and underground tunnel structures, where more than 70% materials consumption is possible to cut. This would be visually clear from Fig.1. Due to its high compressive strength, UHPC structural components are much smaller in size than their typical concrete counterparts. If the overall material weight (dead load) of girders/beams used in a certain steel structure bridge/flyover is 110kg/m, bridge of similar load bearing capacity constructed with UHPC will be of 141kg/m. Interestingly, for ordinary reinforced concrete bridge, this weight will be 528kg/m, which is about 3.72 times higher whereas. pre-stressing can only save 11.74% materials with the expense of additional arrangements are required for the pre-stressing system.

Figure 1: Relative sizes of beams of bridges constructed with various materials for similar level of load bearing capacity.

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Besides, the extremely low dead weight of the structures, another unique behaviour of the fibre reinforced UHPC is its high level of flexibility, Fig.2.

Figure 2: Deformation of conventional and UHPC under laboratory test condition

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Figure 3: High strength ductile steel (left) and polymeric (right) fibres.

In the case of flexible UHPC, high strength ductile fibres (steel or polymeric, Fig.3) play the main role. The bending strength and deflection behaviours of the cast slab depend on the strength and flexibility of the fibres used. Usually, steel fibres provide better bending strength. For better combination of bending strength and defection, combination of steel and polymeric fibres are also practiced. The bending strength vs. defection behaviours of various UHPC are shown in Fig.4.

Here it is to be mentioned that for UHPC no coarse aggregates are use. Along with cement, all materials used here will be in powder form and the powder like materials reacts with each other in presence of water. So, this type concrete also termed as reactive powder concrete (RPC). A typical mix proportion of UHPC is given below.

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