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Concrete-Eating Robot Recycles Buildings

Posted date: 9:50 PM / comment : 0 , , ,

Concrete-Eating Robot Recycles Buildings

Building demolition demands a lot of heavy machinery to crush concrete and separate valuable materials for reuse. Often, those materials are transferred to offsite locations, which wastes time and resources. The process also wastes a lot of water in order to prevent harmful dust clouds from blooming. However, a Swedish student’s concrete-eating robot aims to change all that.
“The ERO Concrete Recycling Robot was designed to efficiently disassemble concrete structures without any waste, dust or separation and enable reclaimed building materials to be reused for new prefabricated concrete buildings,” explained Omer Haciomeroglu of the Umea Institute of Design of Design. ”It does so by using a water jet to crack the concrete surface, separate the waste and package the cleaned, dust-free material.”
The idea is to send in a fleet of the ERO robots that will scan buildings to determine the best route to execute demolition. Once the robot goes to work, using vacuum suction and electrical power, it erases the building.
“ERO deconstructs with high-pressure water and sucks and separates the mixture of aggregate, cement and water. It then sends aggregate and filtered cement slurry separately down to the packaging unit to be contained,” Haciomeroglu wrote. ”Clean aggregate is packed into big bags, which are labeled and sent to nearby concrete precast stations for reuse. Water is recycled back into the system.”
Turbulence dynamos strategically placed inside air suction chambers even provide a percentage of ERO’s energy needs. Once the last wall has been demolished, essentially nothing has gone to landfills or been sent away for additional processing.
“Even the rebar is cleaned of concrete, dust and rust and is ready to be cut and reused immediately,” Haciomeroglu stated. “Every bit of the load-bearing structure is reusable for new building blocks.”
So far the design remains a concept, but influential organizations are starting to take note. Last year, Haciomeroglu’s concept won in the Student Designs category of the International Design Excellence Awards.

The Progression of High Strength Concrete

Posted date: 6:00 PM / comment : 0 , ,

The Progression of High Strength Concrete

The definition of high strength concrete continues to change. This change occurs as the art of achieving a particular strength is reduced to practice, and the structural requirements push at the edge with needs for higher strength. One such example is the CN Tower in Toronto, with its required strength in 1976 of 5000 psi. At that time, this was difficult to achieve. Today 5000 psi concrete is routinely used and produced without special precautions.

In the manufacturing of high strength concrete, there are significant differences from those seen in practice just a few years ago. Cementitious components and content, admixtures aggregates and curing have changed. Once the province of high cement contents and silica fume, much of the developments over the last decade have revolved around a better understanding of, and attention paid to, the microstructure of the concrete. High strength concrete can be modeled as a three phase system -- the paste, the aggregate and the interface between them (Figures 1 and 2). By taking this approach, an engineered composite material can be designed.

Figure 1: Thin section of concrete showing microstructure of paste. Red arrows are typical flyash particles.
Figure 2: Thin section of concrete showing microstructure of paste. Note the relatively low degree of hydration of the slag particles (red arrows).
Actions taken to modify the interfacial transition zone between the aggregate and paste have increased the load transfer between the paste and aggregate; thereby increasing the strength of the concrete. It is the action of meta-kaolin, silica fume and other finely divided materials in modifying this interfacial transition zone that originally led to significant increases in strength. These materials were once used at high replacement levels, frequently greater than 10%. While high strength was often achieved, the workability and susceptibility to fracture of the concrete were problems that ultimately limited the strength.

In modern high strength concrete, blends of smaller quantities and fractions of silica fume result in large increases in strength without compromising the ability of the mixtures to be placed. In many cases, ternary or even quaternary blends of pozzolanic material with Portland cement are seen in practice.

One of the reasons for these blends is that the heat generated during the hydration process can cause residual stress within the paste, and reduce the strength of the concrete. While these types of effects can readily be removed in metals by annealing, no such process is available for concrete. The curing process must be engineered to control the hydration reaction so residual stresses are minimized. Temperature monitoring or other devices are used to track the progress and monitor the reaction that produces the binder.

The literature at the turn of the 20th century often referred to the curing process as annealing. While having very little to do with the concept of heat treating of metals, this curing, when performed properly, is a critical factor in the performance of higher strength concrete. Strengths up to 20,000 psi have been realized using pozzolanic materials, dispersants, limestone modified cements and careful attention to aggregate materials selection. The limestone acts to nucleate the reaction and reduces the quantity of unhydrated-cement.

Admixture technology has progressed. Stabilizing admixtures and dispersants with a low affinity for the solid surface, where a large fraction of dispersant remains in solution, has allowed mixtures to be held in a state of "suspended animation" while the concrete is placed. They can perform predictably, allowing scheduling of the construction process. Retarders, dispersants and stabilizers will increase the strength.

One of the difficulties that the designer of high strength concrete mixtures encounters is the ability to have workable concrete with very low water/cement ratios. Use of modern high-efficiency dispersants (super plasticizers) has led to observed autogeneous drying of materials due to hydration or vaporation due to high temperature. As a consequence, some very low water/cement ratio concrete have shown good performance in the laboratory but poor performance in the larger structural members, where the heat of hydration is not as readily dissipated and where the sample is not immersed in water for 28 or even 56 days. These limits are advancing by innovations such as the use of lightweight aggregate for internal curing and steel whiskers to distribute stresses.

Aggregate materials are no different. As the paste strength increases, and the interfacial transition zone densifies, the strength of the aggregate or the presence of fractures therein become a limiting factor. Reducing the maximum particle size and carefully selecting the geological origin of the materials can lead to significant improvements in strength.

Recognition by the design and construction team that the concrete strength does not need to be achieved at seven or 28 or even 56 days, but only as the structure is loaded, allows mixtures that have relatively low cement contents and very high pozzolanic replacement to achieve compressive strengths in excess of 15,000 psi.

Care must be taken in the production of high strength concrete in order to ensure that the performance of the concrete in situ is what was intended in the design. Raw materials, batching and handling at the plant and at the installation site must be controlled. Without an understanding of the importance of high strength concrete at the production plant and by the individual vehicle drivers, it will be more difficult to achieve performance of the structure.▪

Kevin A. MacDonald, FACI, is President and Principal Engineer for Beton Consulting Engineers LLC, Mendota Heights, MN. He was named a Fellow of ACI in 2004. Kevin can be reached at kmacdonald@betonconsulting.com.
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Prefabricated Construction Method

Posted date: 11:01 AM / comment : 0 , , ,

Prefabricated Construction Method

Prefabricated Construction Method
Prefabricated construction is a building process in which elements or modules of the structure are prefabricated at plants, then transported to the construction site for installation. Using this method can reduce  the time of building, also saving construction cost. Prefabricated construction is now widely applied for new houses or other building structures like bridge, tunnels,  culverts, water supply system…
The benefits of prefabricated construction method is from the  fabrication of standard components on factory floor. This  production is less time consumption compared to actual condition of construction process. The prefabricated elements are transported to the site for installing process. At the site, the modules are unloaded, moved into position with the support of heavy cranes, and assembled to form a designed building.
Together with the fast assembly, prefabricated construction also saves a lot of money on the construction project. By using standard patterns, the building materials are saved at the manufacturing factories. This help to reduce the waste in formwork and other materials that can occur during traditional building procedures.
Another considerable  profit using prefabricated construction method is the energy efficiency. Because the prefab elements of a panelized home are precut, they fit snugly together, making for a tighter edifice. This means less effort for heating and cooling, resulted  in lower energy bills.
The rapid development of prefabricated houses has led to the increasing of construction templates that homeowners have more choice for designs of their houses. By combining these templates, it is possible to design the layout of the house, specify the dimensions of each room, and build a home that is exactly to the specification of the owners. There are also complex building plans for prefabricated construction that can be adjusted slightly and still have the benefit of using materials of standard lengths, widths, and textures.
Prefabricated houses are not the only type of construction structures that can be produced using prefabrication construction method. As mentioned above, this method is widely used in many types of constructions like bridges, culverts or even swimming pools.

Reactive Powder Concrete.

Posted date: 10:37 PM / comment : 0 , ,

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.


HPC has achieved the maximum compressive strength in its existing form of microstructure. However, at such a level of strength, the coarse aggregate becomes the weakest link in concrete. In order to increase the compressive strength of concrete even further, the only way is to remove the coarse aggregate. This philosophy has been employed in Reactive Powder Concrete (RPC)1.

Reactive Powder Concrete (RPC) was developed in France in the early 1990s and the world’s first Reactive Powder Concrete structure, the Sherbrooke Bridge in Canada, was erected in July 1997. Reactive Powder Concrete (RPC) is an ultra high-strength and high ductility cementitious composite with advanced mechanical and physical properties. It consists of a special concrete where the microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. It uses extensively the pozzolanic properties of highly refined silica fume and optimization of the Portland cement chemistry to produce the highest strength hydrates1.
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 context. 
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:
  1. Elimination of coarse aggregates for enhancement of homogeneity
  2. Utilization of the pozzolanic properties of silica fume
  3. Optimization of the granular mixture for the enhancement of compacted density
  4. The optimal usage of superplasticizer to reduce w/c and improve workability
  5. Application of pressure (before and during setting) to improve compaction
  6. Post-set heat-treatment for the enhancement of the microstructure
  7. Addition of small-sized steel fibres to improve ductility
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
Property of
RPC		DescriptionRecommended ValuesTypes of failure eliminated

Reduction in
aggregate size		Coarse aggregates are replaced by fine sand, with a reduction in the size of the coarsest aggregate by a factor of about 50.Maximum size of fine sand is 600 µm
Mechanical,
Chemical &
Thermo-mechanical 
Enhanced mechanical propertiesImproved mechanical properties of the paste by the addition of silica fumeYoung’s modulus values in 50 GPa – 75 Gpa rangeDisturbance of the mechanical stress field.
Reduction in aggregate to matrix ratioLimitation of sand contentVolume of the paste is at least 20% greater than the voids index of non-compacted sand.
By any external source (e.g., formwork).
Table 2: Selection Parameters for RPC components
ComponentsSelection ParametersFunctionParticle SizeTypes
SandGood hardness
Readily available and low cost.
Give strength,
Aggregate		150 µm
to
600 µm		Natural,
Crushed
CementC3 S : 60%;
C2S : 22%;
C3A : 3.8%;
C4AF: 7.4%.
(optimum)		Binding material,
Production of primary hydrates		1 µm
to
100 µm		OPC,
Medium
fineness
Quartz PowderfinenessMax. reactivity during heat-treating5 µm
to
25 µm		Crystalline
Silica fumeVery less quantity of impuritiesFilling the voids,
Enhance rheology,
Production of secondary hydrates		0.1 µm
to
1 µm		Procured from Ferrosilicon industry
(highly refined)
Steel fibresGood aspect ratioImprove ductilityL : 13 – 25 mm
Ø : 0.15 – 0.2 mm		Straight
SuperplasticizerLess retarding characteristicReduce w/c_Polyacrylate based
Table 3: RPC mixture designs from literature
P. Richard and M. Cheyrezy1S. A. Bouygues3V. Matte9S. Staquet10
[1995][1997][1999][2000]
Non fibred12 mm fibres25 mm fibresFibredFibred
Portland Cement1111111
Silica fume0.250.230.250.230.3240.3250.324
Sand1.11.11.11.11.4231.431.43
Quartz Powder--0.39--0.390.2960.30.3
Superplasticizer0.0160.0190.0160.0190.0270.0180.021
Steel fibre----0.1750.1750.2680.2750.218
Water0.150.170.170.190.2820.20.23
Compacting pressure--------------
Heat treatment temperature20ºC90ºC20ºC90ºC90ºC90ºC90ºC

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 steel fibres.

Table 5 shows typical mechanical properties of RPC compared to a conventional HPC of compressive strength 80 MPa11. As fracture toughness, which is a measure of energy absorbed per unit volume of material to fracture, is higher for RPC, it exhibits high ductility. Apart from their exceptional mechanical properties, RPCs have an ultra-dense microstructure, giving advantageous waterproofing and durability characteristics. These materials can therefore be used for industrial and nuclear waste storage facilities1.
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
RPC 200RPC 800
Pre-setting pressurizationNone50 MPa
Heat-treating20 to 90°C250 to 400°C
Compressive strength (using quartz sand)170 to 230 MPa490 to 680 MPa
Compressive strength (using steel aggregate)--650 to 810 MPa
Flexural strength30 to 60 MPa45 to 141 MPa
Table 5: Comparison of HPC (80 MPa) and RPC 2009

PropertyHPC (80 MPa)
RPC 200
Compressive strength80 MPa200 MPa
Flexural strength7 MPa40 MPa
Modulus of Elasticity40 GPa60 GPa
Fracture Toughness<10³ J/m²30*10³ J/m²

Table 6: Durability of RPC Compared to HPC10

Abrasive Wear2.5 times lower
Water Absorption7 times lower
Rate of Corrosion8 times lower
Chloride ions diffusion25 times lower

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
Materials Used
The materials used for the study, their IS specifications and properties have been presented in Table 7.
Mixture Design of RPC and HPC
  • Considerable numbers of trial mixtures were prepared to obtain good RPC and HPC mixture proportions.
  • Particle size optimization software, LISA8 [developed by Elkem ASA Materials] was used for the preparation of RPC and HPC trial mixtures.
  • Various mixture proportions obtained from the available literature were also studied.
  • The selection of best mixture proportions was on the basis of good workability and ideal mixing time.
  • Finalized mixture proportions of RPC and HPC are shown in Table 8.
Table 7: Materials used in the study and their properties
Sl. No.SampleSpecific GravityParticle size range
1Cement, OPC, 53-grade
[IS. 12269 – 1987]		3.1531 µm – 7.5 µm
2Micro Silica
[ASTM C1240 – 97b]		2.25.3 µm – 1.8 µm
3Quartz Powder2.75.3 µm – 1.3 µm
4Standard sand, grade-1
[IS. 650 – 1991]		2.652.36 mm – 0.6 mm
5Standard sand, grade-2
[IS. 650 – 1991]		2.650.6 mm – 0.3 mm
6Standard sand, grade-3
[IS. 650 – 1991]		2.650.5 mm – 0.15 mm
7Steel fibres (30 mm)
[ASTM A 820 – 96]		7.1length: 30 mm & dia: 0.4 mm
8Steel fibres (36 mm)
[ASTM A 820 – 96]		7.1length: 36 mm & dia: 0.5 mm
920 mm Aggregate
[IS. 383 – 1970]		2.7825 mm – 10 mm
1010 mm Aggregate
[IS. 383 – 1970]		2.7812.5 mm – 4.75 mm
11River Sand
[IS. 383 – 1970]		2.612.36 mm – 0.15 mm
Table 8: Mixture Proportions of RPC and HPC
MaterialsMixture Proportions
RPCRPC-F*HPCHPC-F**
Cement1.001.001.001.00
Silica fume0.250.250.120.12
Quartz powder0.310.31--
Standard sand grade 21.091.09--
Standard sand grade 30.580.58--
River Sand--2.402.40
20 mm aggregate--1.401.40
10 mm aggregate--1.501.50
30 mm steel fibres-0.20--
36 mm steel fibres---0.20
Admixture (Polyacrylate based)0.030.030.0230.023
Water0.250.250.40.4
* 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:
Compressive Strength (as per IS 51613 on 5 cm cubes for RPC, 10 cm cubes for HPC), Flexural Strength (as per IS 516 on 4 x 4 x 16 cm prisms for RPC, 10 x 10 x 50 cm beams for HPC),
Water Absorption (on 15 cm cubes for both RPC and HPC),
Non destructive water permeability test using Germann Instruments (on 15 cm cubes for both RPC and HPC),
Resistance to Chloride ions Penetration test (on discs of diameter 10 cm and length 5 cm as per ASTM C 120214).
Results
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.
Compressive strength
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.
Flexural strength
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)
RPCRPC-FHPCHPC-F
NC*HWC**NC*HWC**NC*NC*
11121822810
*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.

Water absorption
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 incorporation of fibres and the use of heat curing is seen to marginally increase the water absorption. The presence of fibres possibly leads to the creation of channels at the interface between the fibre and paste that promote the uptake of water. Heat curing , on the other hand, leads to the development of a more open microstructure (compared to normal curing) that could result in an increased absorption.
Water permeability
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)
RPCRPC with fibresHPC
NC*HWC**NC*HWC**NC*HWC*
Cumulative Charge passed in Coulombs4
(less than 10)		94140400250850
ASTM C1202 classificationNegligibleNegligibleVery lowVery lowVery lowVery low
*Normal Curing     **Hot Water Curing
Summary
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 storage facilities.
A laboratory investigation comparing RPC and HPC led to the following conclusions:
  • A maximum compressive strength of 198 MPa was obtained. This is in the RPC 200 range (175 MPa – 225 MPa).
  • The maximum flexural strength of RPC obtained was 22 MPa, lower than the values quoted in literature (~ 40 MPa). A possible reason for this could be the higher length of fibres used in this study.
  • A comparison of the measurements of the physical, mechanical, and durability properties of RPC and HPC shows that RPC possesses better strength (both compressive and flexural) and lower permeability compared to HPC.
  • The extremely low levels of water and chloride ion permeability indicate the potential of RPC as a good material for storage of nuclear waste. However, RPC needs to be studied with respect to its resistance to the penetration of heavy metals and other toxic wastes emanating from nuclear plants (such as Cesium 137 ion in alkaline medium) to qualify for use in nuclear waste containment structures.
References
  1. Richard P, and Cheyrezy M, “Composition of Reactive Powder Concrete”, Cement and Concrete Research, Vol. 25, No.7, (1995), pp. 1501 – 1511.
  2. Aitcin P.C, “Cements of yesterday and today Concrete of tomorrow”, Cement and Concrete Research, Vol. 30, (2000), pp 1349 - 1359.
  3. Blais P. Y, and Couture M, “Precast, Prestressed Pedestrian Bridge - World’s first reactive powder concrete structure”, PCI Journal, Vol. 44, (1999), pp. 60 - 71.
  4. Dauriac C, “Special Concrete may give steel stiff competition, Building with Cincrete”, The Seattle Daily Journal of Commerce, May 9, 1997.
  5. Basu P.C, “Performance Requirements of HPC for Indian NPP Structures”, The Indian Concrete Journal, Sep. 1999, pp. 539 – 546.
  6. Bonneau O, Vernet C, Moranville M, and Aitcin P. C, “Characterization of the granular packing and percolation threshold of reactive powder concrete”, Cement and Concrete Research, Vol. 30 (2000) pp. 1861 – 1867.
  7. Goltermann P, Johansen V, and Palbol L, “Packing of Aggregates: An Alternative Tool to Determine the Optimal Aggregate Mix”, ACI Materials Journal, Sep-Oct. 1997, pp. 435 – 443.
  8. Elkem AS website – http://www.silicafume.net/
  9. Matte V and Moranville M, “Durability of Reactive Powder Composites: Influence of Silica Fume on the leaching properties of very low water/binder pastes”, Cement and Concrete Composites, 21 (1999) pp. 1 - 9.
  10. Staquet S, and Espion B, “Influence of Cement and Silica Fume Type on Compressive Strength of Reactive Powder Concrete”, 6th International Symposium on HPC, University of Brussels, Belgium, (2000), pp. 1 – 14.
  11. Bickley J. A, and Mitchell D, “A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: 1990-2000”, (2001), pp. 96 – 102.
  12. HDR Engineering Website on Reactive Powder Concrete, Last modified Nov. 1999, http://www.hdrinc.com/engineering/engres.htm
  13. Indian Standard Designation IS 516-1959, “Methods of Test for Strength of Concrete,” BIS, New Delhi, 2002.
  14. ASTM Standard Designation C1202-97, “Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration,” ASTM, Pennsylvania, 2001.
  15. ASTM Standard Designation C109-99, “Standard Test Method for Compressive Strength of Hydraulic Cement Mortars,” ASTM, Pennsylvania, 2001.
  16. ASTM Standard Designation C143-00, “Standard Test Method for Slump of Hydraulic Cement Concrete,” ASTM, Pennsylvania, 2001.
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