Reactive powder Concrete
Reactive Powder Concrete (RPC) was developed by P. Richard and M. Cheyrezy and was first produced at Bouygues’ laboratory in France2 early 1990s. In July 1997, the Sherbrooke Bridge in Quebec, Canada3, became the world’s first structure to be constructed entirely out of Reactive Powder Concrete. Due to its extreme low permeability it is also being used for containment of nuclear waste in Europe4.
Reactive Powder Concrete (RPC) is basically a special concrete where the microstructure is optimized by precise gradation of all the constituent particles to produce a maximum possible density. This results in achievement of a composite with extremely high strength (compressive strengths ranging from 200 MPa to 800 MPa) and also high ductility (due to addition of steel fibers) along with improved mechanical and physical properties (low permeability etc.). RPC also extensively uses the pozzolanic properties of highly refined silica pozzolans and optimization of the Portland cement chemistry to produce the highest strength hydrates1 without use of course aggregates. Thus RPC is a Ultra High Strength Concrete (UHSC).
2. Composition of Reactive Powder Concrete
RPC is essentially composed of very fine powders:
• Quartz powder
• Silica Pozzolan (Microsilica, Silicafume etc.)
• Steel fibers (optional)
• Super plasticizer
The aim is to achieve a very dense matrix using extremely low water/binder (w/b) ratio (0.13-0.24) and by optimizing the granular packing of the dry fine powders. The resulting compactness gives RPC ultra-high strength and durability6. Table 1 shows the various components of RPC and their selection parameters.
3. Reactions taking place
• Cement hydration
2C3S + 6H C3S2H3 + 3CH
2C2S + 4H C3S2H3 + CH
• Pozzolanic reaction at normal curing
CH + S + H C3S2H3
• Pozzolanic reaction at hot curing
(C2S + C3S) +S+ 4H C5S6H5
4. Basic principles
The following principles are kept in mind while carrying out the mix design of RPC:
• Elimination of coarse aggregates to enhance homogeneity
• Enough OPC hydrate (calcium hydroxide) to utilize the pozzolanic properties of silica pozzolans.
• Optimization of the granular mixture to enhance the compacted density
• Use of super plasticizer to reduce w/b and improve workability
• Improved compaction by application of pressure (before and during setting
• Post-set heat-treatment to enhance the microstructure and increase hydration of cement and silica pozzolan.
• Addition of small-sized steel fibers to improve ductility
5. Factors affecting strength
• Water to binder ratio
The water to binder ratio is the most important factor in determining strength of concrete. Normally lower the w/b higher is the strength because the porosity decreases. The optimal w/b for RPC comes out to be about 0.2. The strength reduction at w/b lower than 0.2 may be due to lack of water to achieve sufficient compaction and hydration for strength...