Reactive Powder Concrete
Reactive Powder Concrete (RPC) is a developing composite material that will allow the concrete industry to optimize material use, generate economic benefits, and build structures that are strong, durable, and sensitive to environment. A comparison of the physical, mechanical, and durability properties of RPC and HPC (High Performance Concrete) shows that RPC possesses better strength (both compressive and flexural) and lower permeability compared to HPC. This page reviews the available literature on RPC, and also presents the results of laboratory investigations comparing RPC with HPC. Specific benefits and potential applications of RPC have also been described.
High-Performance Concrete (HPC) is not just a simple mixture
of cement, water, and aggregates. It contains mineral components and chemical
admixtures having very specific characteristics, which give specific properties
to the concrete. The development of HPC results from the materialization
of a new science of concrete, a new science of admixtures and the use
of advanced scientific equipments to monitor concrete microstructure.
The concept of reactive powder concrete was first developed by P. Richard and M. Cheyrezy and RPC was first produced in the early 1990s by researchers at Bouygues’ laboratory in France2. A field application of RPC was done on the Pedestrian/Bikeway Bridge in the city of Sherbrooke, Quebec, Canada3. RPC was nominated for the 1999 Nova Awards from the Construction Innovation Forum. RPC has been used successfully for isolation and containment of nuclear wastes in Europe due to its excellent impermeability4.
The requirements for HPC used for the nuclear waste containment
structures of Indian Nuclear Power Plants are normal compressive strength,
moderate E value, uniform density, good workability, and high durability5.
There is a need to evaluate RPC regarding its strength and durability
to suggest its use for nuclear waste containment structures in Indian
Composition of Reactive Powder Concrete
RPC is composed of very fine powders (cement, sand, quartz powder and silica fume), steel fibres (optional) and superplasticizer. The superplasticizer, used at its optimal dosage, decreases the water to cement ratio (w/c) while improving the workability of the concrete. A very dense matrix is achieved by optimizing the granular packing of the dry fine powders. This compactness gives RPC ultra-high strength and durability6. Reactive Powder Concretes have compressive strengths ranging from 200 MPa to 800 MPa.
Richard and Cheyrezy1 indicate the following principles for developing RPC:
Table 1 lists salient properties of RPC, along with suggestions on how to achieve them. Table 2 describes the different ingredients of RPC and their selection parameters. The mixture design of RPC primarily involves the creation of a dense granular skeleton. Optimization of the granular mixture can be achieved either by the use of packing models7 or by particle size distribution software, such as LISA8 [developed by Elkem ASA Materials]. For RPC mixture design an experimental method has been preferred thus far. Table 3 presents various mixture proportions for RPC obtained from available literature1,3,9,10.
Table 1: Properties of RPC enhancing its homogeneity and strength
Table 2: Selection Parameters for RPC components
Table 3: RPC mixture designs from literature
The major parameter that decides the quality of the mixture is its water demand (quantity of water for minimum flow of concrete). In fact, the voids index of the mixture is related to the sum of water demand and entrapped air. After selecting a mixture design according to minimum water demand, optimum water content is analyzed using the parameter relative density (d0/dS). Here d0 and dS represent the density of the concrete and the compacted density of the mixture (no water or air) respectively. Relative density indicates the level of packing of the concrete and its maximum value is one. For RPC, the mixture design should be such that the packing density is maximized.
Microstructure enhancement of RPC is done by heat curing. Heat curing is performed by simply heating (normally at 90°C) the concrete at normal pressure after it has set properly. This considerably accelerates the pozzolanic reaction, while modifying the microstructure of the hydrates that have formed1. Pre-setting pressurization has also been suggested as a means of achieving high strength1.
The high strength of RPC makes it highly brittle. Steel fibres are generally added to RPC to enhance its ductility. Straight steel fibres used typically are about 13 mm long, with a diameter of 0.15 mm. The fibres are introduced into the mixture at a ratio of between 1.5 and 3% by volume1. The cost-effective optimal dosage is equivalent to a ratio of 2% by volume, or about 155 kg/m3.
Mechanical Performance and Durability of RPC
The RPC family includes two types of concrete, designated RPC
200 and RPC 800, which offer interesting implicational possibilities in
different areas. Mechanical properties for the two types of RPC are given
in Table 4. The high flexural strength of RPC is due to the addition of
RPC has ultra-high durability characteristics resulting from its extremely low porosity, low permeability, limited shrinkage and increased corrosion resistance. In comparison to HPC, there is no penetration of liquid and/or gas through RPC4. The characteristics of RPC given in Table 6, enable its use in chemically aggressive environments and where physical wear greatly limits the life of other concretes12.
Table 4: Comparison of RPC 200 and RPC 800
Table 5: Comparison of HPC (80 MPa) and RPC 2009
Table 6: Durability of RPC Compared to HPC10
Limitations of RPC
In a typical RPC mixture design, the least costly components of conventional concrete are basically eliminated or replaced by more expensive elements. The fine sand used in RPC becomes equivalent to the coarse aggregate of conventional concrete, the Portland cement plays the role of the fine aggregate and the silica fume that of the cement. The mineral component optimization alone results in a substantial increase in cost over and above that of conventional concrete (5 to 10 times higher than HPC). RPC should be used in areas where substantial weight savings can be realized and where some of the remarkable characteristics of the material can be fully utilized2. Owing to its high durability, RPC can even replace steel in compression members where durability issues are at stake (e.g. in marine condition). Since RPC is in its developing stage, the long-term properties are not known.
Experimental study at IIT Madras
The materials used for the study, their IS specifications and properties have been presented in Table 7.
Mixture Design of RPC and HPC
Table 7: Materials used in the study and their properties
Table 8: Mixture Proportions of RPC and HPC
* Fibre RPC ** Fibre HPC
Workability and density were recorded for the fresh concrete mixtures. Some RPC specimens were heat cured by heating in a water bath at 90°C after setting until the time of testing. Specimens of RPC and HPC were also cured in water at room temperature.
The performance of RPC and HPC was monitored over time with respect
to the following parameters:
Fresh concrete properties
The workability of RPC mixtures (with and without fibres), measured using the mortar flow table test as per ASTM C10915, was in the range of 120 – 140%. On the other hand, the workability of HPC mixtures (with and without fibres), measured using the slump test as per ASTM C23116, was in the range of 120 – 150 mm. The density of fresh RPC and HPC mixtures was found to be in the range of 2500 – 2650 kg/m3.
The compressive strength analysis throughout the study shows
that RPC has higher compressive strength than HPC, as shown in Fig. 1.
Compressive strength at early ages is also very high for RPC. Compressive
strength is one of the factors linked with the durability of a material.
In the context of nuclear waste containment materials, the compressive
strength of RPC is higher than required.
Fig 1: Compressive strength of RPC and HPC
he maximum compressive strength of RPC obtained from this study is as high as 200 MPa, while the maximum strength obtained for HPC is 75 MPa. The incorporation of fibres and use of heat curing was seen to enhance the compressive strength of RPC by 30 – 50%. The incorporation of fibres did not affect the compressive strength of HPC significantly.
Plain RPC was found to possess marginally higher flexural strength than HPC. Table 9 clearly explains the variation in flexural strength of RPC and HPC with the addition of steel fibres. Here the increase of flexural strength of RPC with the addition of fibres is higher than that of HPC.
Table 9: Flexural strength (as per IS 516) at 28 days (MPa)
*Normal Curing **Hot Water Curing
As per literature3, RPC 200 should have an approximate flexural strength of 40 MPa. The reason for low flexural strength obtained in this study could be that the fibres used (30 mm) were long. Fibre reinforced RPC (with appropriate fibres) has the potential to be used in structures without any additional steel reinforcement. This cost reduction in reinforcement can compensate the increase in the cost by the elimination of coarse aggregates in RPC to a little extent.
Fig. 2 presents a comparison of water absorption of RPC and HPC.
A common trend of decrease in the water absorption with age is seen here
both for RPC and HPC. The percentage of water absorption of RPC, however,
is very low compared to that of HPC. This quality of RPC is one among
the desired properties of nuclear waste containment materials.
Fig. 2: Water absorption of RPC and HPC
The non-destructive assessment of water permeability using the Germann Instruments equipment actually only measures the surface permeability, and not the bulk permeability like in conventional test methods. A comparison of the surface water permeability of RPC and HPC is shown in Fig. 3.
It can be seen from the data that water permeability decreases with age for all mixtures. 28th day water permeability of RPC is negligible when compared to that of HPC (almost 7 times lower). As in the case of water absorption, the use of fibres increases the surface permeability of both types of concrete.
Fig. 3: Surface Water Permeability of RPC and HPC
Resistance to chloride ion penetration
Results of rapid chloride permeability test conducted after 28 days of curing are presented in Table 10. Data indicate that penetration of chloride increases when heat curing is done in concrete. Total charge passed for normal-cured RPC is negligible compared to the other mixtures. Even though heat-cured RPC shows a higher value than normal-cured RPC, in absolute terms, it is still extremely low or even negligible (<100 Coulombs). This property of RPC enhances its suitability for use in nuclear waste containment structures.
The data also indicate that addition of steel fibres leads to
an increase in the permeability, possibly due to increase in conductance
of the concrete. The HPC mixtures also showed very low permeability, although
higher compared to RPC.
Table 10: Rapid Chloride Permeability Test (as per ASTM C 1202)
*Normal Curing **Hot Water Curing
Reactive Powder Concrete (RPC) is an emerging technology that lends a new dimension to the term ‘high performance concrete’. It has immense potential in construction due to its superior mechanical and durability properties compared to conventional high performance concrete, and could even replace steel in some applications.
The development of RPC is based on the application of some basic
principles to achieve enhanced homogeneity, very good workability, high
compaction, improved microstructure, and high ductility. RPC has an ultra-dense
microstructure, giving advantageous waterproofing and durability characteristics.
It could, therefore, be a suitable choice for industrial and nuclear waste
A laboratory investigation comparing RPC and HPC led to the following conclusions:
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