Concrete Repair, Rehabilitation and Retrofitting II – Alexander et al (eds)
© 2009 Taylor & Francis Group, London, ISBN 978-0-415-46850-3

Performance of Reactive Powder Concrete (RPC) with different curing conditions and its retrofitting effects on concrete member
T.P. Chang, B.T. Chen, J.J. Wang & C.S. Wu
Department of Construction Engineering, National Taiwan University of Science and Technology,
Taipei, Taiwan, ROC

ABSTRACT: The material performance of Reactive Powder Concrete (RPC) with two different curing conditions, water-curing of 25ºC and steam-curing of 85ºC and 95% relative humidity, were studied experimentally. The reinforcing effects of the RPC with two wrapping thicknesses of 10 and 15 mm, respectively, on the surface of cylindrical concrete specimen were evaluated. Major experimental results show both the engineering properties and indices of durability of RPC with steam-curing at four different ages have substantially increased except for the supersonic pulse velocity and dynamic moduli of elasticity and shear. The ratio of increase of compressive strength of cylindrical specimens retrofitted with 10 and 15 mm of wrapping RPC are in the range of 9.5 to 38.0%.
1

INTRODUCTION

Reactive powder concrete (RPC), a cement-based composite material well known for the ultra-highstrength, high-durability and low-porosity, made its international debut in 1994 (Richard, 1994). The advance mechanical and physical properties of RPC are obtained by optimizing packing density of concrete mixture with precise gradation of all mix particles, and by using highly refined silica fume to improve the microstructure of hydrated cement pastes through the pozzolanic reaction. To produce a very high compressive strength of RPC, applications of pressure before and during setting and heat-treating after setting are normally required. Compressive strengths of 200 to
800 MPa, moduli of elasticity of 50 to 60 GPa and flexural strength of 6 to 13 MPa have been achieved with RPC (Richard, 1995).
On the other hand, maximum compressive strengths for the commonly used normal weight concrete in most concrete structures are in the range of 30 to 60 MPa with the corresponding moduli of elasticity of 14 to 35 GPa (Mindess et al. 2003). Due to advantage of the super material properties, RPC has been applied to many real constructions where the substantial weight savings of structure can be appreciated and where its distinguished features of material property can be fully utilized (Adeline &
Cheyrezy 1998, Etinne et al. 2001, Rebentrost &
Cavill 2006). In a typical RPC mix proportioning, in order to enhance the homogeneity and optimize the density of concrete granular mixture, the coarse

aggregates of conventional concrete are totally eliminated such that the amounts of fine aggregate,
Portland cement and silica fume need to be substantially increased.
Because the least costly components of conventional concrete have been replaced by more expensive ingredients and the required addition of steel fiber in order to increase the tensile strength, the cost of RPC is estimated to be 5 to 10 times higher than that of traditional High-Performance Concrete. As a result, a cost-effective application of RPC is used for concrete repair and retrofit (Lee et al. 2007). In this study, the material performance of RPC with two different curing conditions, water-curing of 25ºC and steam-curing of 85ºC and 95% relative humidity were evaluated by comparison on the changes of engineering properties and indices of durability.
2

EXPERIMENTAL PLAN

The experimental plan in this study was composed two major parts. The first part was the evaluation of the variations of material properties of reactive powder concrete (RPC) resulting from two different curing conditions, water-curing of 25ºC and steamcuring of 85ºC and 95% relative humidity. The second part was the evaluation of the reinforcing effects of RPC when it was used as a retrofitting material to cast circumferentially on the surface of the cylindrical normal weight concrete specimen. Such circumferential RPC layer provided a confining effect.

1203

2.1

Table 2.

Specimen preparation

The composition of normal weight concrete (NC) with water-to-cement ratio (W/C) of 0.6 is given in
Table 1.
Ordinary Type I Portland cement complying with
ASTM C 150 was used. Natural crushed gravel (maximum size of 10 mm) and river sand (specific gravity of 2.65, fineness modulus of 2.82) were used as the coarse and fine aggregates respectively. The NC was used to cast cylindrical concrete specimens with three different diameters, φ100 × 200 mm, φ80 × 200 mm and φ70 × 200 mm, respectively, as shown in Figure 1.
After demoulding, the specimens were cured in saturated lime water for 28 days. Then, each of two latter types of smaller cylindrical specimens was placed into a φ100 × 200 mm steel mold and cast with fresh RPC to form a circumferential layer of thickness of 10 and
15 mm, respectively, as the retrofitting material.
The composition of RPC with a water to cement ratio (W/C) of 0.193 used in this study is given in
Table 2. In practice, in order to reduce the cement hydration heat and increase the capability of sulfate resistance, either Type II or Type IV Portland cement can be used. In this study, Type II Portland cement of the fineness of 314 m2/kg using air permeability test was utilized. Imported silica fume was used which contains about 94.6% of SiO2. Its particle sizes were in the range of 0.67 to 5.02 μm with a specific surface area more than 20,000 m2/kg. Based on test result by

Table 1.

Composition of normal weight concrete (NC).

Cement kg/m3 392

SP* kg/m3 235

C.A.# kg/m3 0.98

Water kg/m3 F.A.$ kg/m3 592

1044

#

$

*SP = superplasticizer; C.A. = coarse aggregate; F.A. = fine aggregate.

(a)

( b)

200 mm

φ 70 mm

200 mm

φ 80 mm

200 mm

φ 100 mm

( c)

Figure 1. Three types of cylindrical NC specimens: (a) φ100 × 200 mm, (b) φ80 × 200 mm and (c) φ70 × 200 mm.

Composition of RPC.

Ingredient

Amount kg/m3 Ingredient

Amount kg/m3 Cement

553

Silica fume

79

Water

165

Quartz powder Superplasticizer
Fly ash
Blast furnace slag

41
166
184

Quarter sand
Steel fiber

184
1227
156

ASTM C 1240 standard, the loss of ignition (LOI), reactivity index at 7 days and specific gravity were
0.97%, 98.47 and 2.22, respectively.
The quartz flour having a particle sizes in the range of 2.41 to 15.02 μm and a specific gravity of 2.70 was used to activate the reactivity of RPC during the cement hydration under elevated curing temperature.
The mixture of quartz sand was composed of four different sizes of ground quartz particles in the range of
75 to 600 μm, which forms a major compact skeleton of granular assembly of RPC. Imported straight fiber plated by a thin layer of copper to avoid corrosion was used. Its diameter and length were 0.2 mm and
16 mm, respectively. To maintain a good workability, polycarboxylate based superplasticizer in liquid form was used.
The fly ash contained about 51.2% of SiO2 and
24.3% of Al2O3. Its fineness and specific gravity were
311 m2/kg and 2.17, respectively. The slag contained about 64.9% of SiO2 and 41.8% of CaO. Its fineness and specific gravity were 800 m2/kg and 2.85, respectively. To obtain a good consistency of fresh RPC, a proper order of mixing the ingredients was used.
First, the fine granular components of RPC in dry state, i.e., cement, silica fume, fly ash, blast furnace slag, quartz sand, and quartz powder were mixed for
3 to 5 minutes with low-speed gear to have a uniform mixture. The water and SP were mixed in advance and then added gradually to the dry granular mixture while it was still in a round container stirred by a rotating propeller eccentrically for another 2 to
5 minutes until the cement paste had a proper consistency and flowability. Finally, the steel fibers were spread into the cement paste and continuously mixed for another 2 to 3 minutes with middle-speed gear to complete the mixing of fresh RPC.
Cylindrical φ50 × 100 mm paper mold was used to cast the RPC specimens for the test of compressive strength. Beam specimen of 40 × 40 × 160 mm in a steel mould was used to test the flexural strength.
Cylindrical RPC specimens of φ100 × 200 mm were

1204

also cast for the tests of ultrasonic pulse velocity, electrical resistivity, and chloride permeability. After these fresh RPC specimens were cured in laboratory under ambient temperature for 24 hours, they were demoulded. Two kinds of curing conditions were used afterwards. The first one was that the RPC specimens were cured in a steaming chamber at a temperature of
85ºC for three days and then submerged in the saturated lime water until the day of testing. The second one was the RPC specimens were continuously cured in the saturated lime water until the day of testing.
To increase the density of mixture and ultra high strengths of RPC, an elevated temperature of 250 to 400ºC and a pressure of 50 MPa can be applied simultaneously to the fresh RPC during setting stage
(Richard, 1994, 1995). In order to keep the strength and modulus of elasticity of RPC at hardened state be as close as possible to those of the base NC solid cylindrical specimens, no additional pressure was applied. The curing temperature was also kept at a relatively lower value of 85ºC.
2.2

RPC was obtained according to ASTM C597. A fourelectrode measuring instrument was used to obtain the electrical resistivity of RPC specimens.
In general, either the ASTM C642 or
BS1881:122 standards can be used for the water absorption test of RPC specimens. In this study, the latter was referred to. The cylindrical specimens were dried in oven for 24 hours first and then its oven-dried weight was measured denote by WD. Then the dried specimens were saturated completely in water for one hour, one day, three days and seven days, respectively.
Then the specimens were taken out of water, wiped out the excessive water on the surface of specimen with cloth and measured its saturated weight denoted as WW.
The water absorption ratio Ra is simply defined as
Ra =

WW − WD
× 100%
WD

(1)

The chloride permeability test was performed according to ASTM C1202.

Experimental variables for performance evaluation Two types of indices to evaluate the performance of
RPC at ages of 3, 7, 14 and 28 days were conducted:
(1) Engineering properties including the compressive strength, splitting tensile strength, flexural strength, dynamic modulus of elasticity and dynamic shear modulus; (2) Durability properties including electrical resistivity, ultrasonic pulse velocity, water absorption and chloride permeability.
Procedures of ASTM C31, C192 and C617 standards were followed to obtain the compressive strengths of RPC cylindrical specimens. The thirdpoint-loading method was used to test the flexural strength with a stress rate of 0.866 to 1.213 MPa, as shown in Figure 2(a). The splitting tensile strength of
RPC specimens was obtained according to ASTM C
469 standard. The dynamic moduli of elasticity and shear and the resulting dynamic Poisson’s ratio were obtained according to ASTM C215 standard tested by a C.N.S. Erudite Resonant Frequency Tester as shown in Figure 2(b). The ultrasonic pulse velocity of

(a)

(b)

3
3.1

RESULTS AND DISCUSSION
Engineering properties of RPC

The engineering properties of RPC under two different curing conditions are shown in Tables 2 and 3.
The results in Tables 1 and 2 indicate that the compressive strengths of RPC specimens cured with the steam increase by ratios of 17.0 to 23.7% at four ages. Both the ratios of increase of 13.5 to 17.9% for the splitting tensile strengths and 19.3 to 25.8% for the flexural strength are also observed. Because the

Table 2. Engineering properties of RPC under watercuring of 25ºC.
Properties
Compressive strength (MPa)
Splitting tensile strength (MPa)
Flexural strength
(MPa)
Dynamic Young’s modulus (GPa)
Dynamic shear modulus (GPa)
Dynamic Poisson’s ratio Figure 2. (a) Third-point-loading method for flexural strength of RPC specimens; (b) Resonant Frequency Tester.

*D = day.

1205

3D*

7D

14D

28D

84

87

93

106

11.9

13.1

13.2

13.4

15.5

18.6

–

22.0

44.1

44.6

45.3

46.0

17.4

18.1

18.5

19.1

0.27

0.23

0.22

0.20

Properties

3D*

Compressive strength (MPa)
Splitting tensile strength (MPa)
Flexural strength
(MPa)
Dynamic Young’s modulus (GPa)
Dynamic shear modulus (GPa)
Dynamic Poisson’s ratio 7D

14D

28D

101

106

115

Compressive strength (MPa)

Table 3. Engineering properties of RPC under steamcuring of 85ºC and 95% relative humidity.

124

13.5

14.9

15.1

15.8

19.5

22.2

–

22**

41.0

45.5

45.6

45.7

16.2

18.5

18.5

18.8

0.27

0.23

0.23

0.21

120
110
100
90
80
70
60
50
40
30
20
10
0

RPC at 7 days

Tensile strain -0.002 -0.001

Compressive strain
0

0.001 0.002 0.003 0.004

ε

*D = day, **: dubious test results will be ignored.

Figure 4. Typical stress-strain curve for RPC specimen.

Table 4. Durability properties of RPC under water-curing of 25ºC.
Properties

(a)

(b)

Figure 3. Typical failure modes of RPC specimen after testing: (a) Compressive test; (b) Splitting tensile test.

Electrical resistivity
(kΩ-cm)
Ultrasonic pulse velocity (km/s)
Water absorption ratio (%)
Chloride permeability
(Coulomb)

3D*

7D

14D

28D

7.0

13.9

48.9

145

4.51

4.53

4.61

4.62

0.69

0.90

0.96

1.02

–

–

–

528

*D = day.

pozzolanic reaction resulting from the ingredients of silica fume, fly ash and blast furnace slag in the
RPC mixture will be activated energetically by the high temperature and moisture of curing steam. Such pozzolanic reaction causes a denser microstructure of
C-S-H cement hydrate and results in a faster development of strength gain. The strength development for the RPC specimen cured in the water under ambient temperature is apparently much slower. On the other hand, the increases of dynamic moduli of elasticity and shear, and Poisson’s ratio are insignificant, only in the range of −0.7 to 2.0%. These three measured values are not very sensitive to the changes of other material properties of RPC with the increase of ages.
Typical failure modes of RPC specimens from the compressive and splitting tensile tests are shown in Figure 3(a) and (b) respectively. It is noted that, unlike the normal weight concrete specimens with the failure modes of either in crushed state or two

separated pieces, these failed RPC specimens are still kept together by the steel fibers. Typical stress-strain curve for the RPC specimens.
3.2

Durability properties of RPC

The durability properties of RPC under two different curing conditions are shown in Tables 4 and 5. The results in Tables 4 and 5 indicate that the electrical resistivity of RPC specimens cured with the steam increases drastically by ratios of 333.8 to 5485.7% at four ages. Both the ratios of decrease of 0.04 to 3.4% for ultrasonic pulse velocity indicate that this property is not sensitive to the changes of other material with ages. The ratios of decrease for water absorption are in range of 49.0 to 66.7% imply this test method although is rather simple but seem to properly reflect

1206

Table 5. Durability properties of RPC under of RPC under steam-curing of 85ºC and 95% relative humidity.
Properties

3D*

Electrical resistivity
(kΩ-cm)
391
Ultrasonic pulse velocity (km/s)
4.36
Water absorption ratio (%)
0.23
Chloride permeability
(Coulomb)
–

7D

14D

547

551

Table 6. Increase of compressive strengths of cylindrical normal weight concrete specimen retrofitted by the circumferential RPC layers of different thickness.

28D
629
Properties

4.46

4.59
0.43

0.52

–

–

Ratio of increase %

36.09

–

39.51

9.5

−49.80

38.0

4.62

0.34

Average
Compressive
strength*
MPa

307

Control set
Retrofitted with layer of
10 mm
Retrofitted with layer of
15 mm

*D = day.

the function of pozzolanic reaction activated by the steam curing.
3.3

Retrofitting effects of RPC

Because the addition of steel fibers, RPC has a rather high tensile strength and impact resistance compared with the normal weight concrete. The failure mode will change from the brittle to the ductile. These two good material properties of RPC are the major advantages to consider it to be used as the retrofitting materials. On the other hand, unlike the conventional retrofitting sheet-type material such as Carbon Fiber
Reinforced Polymer (CFRP), RPC needs to have certain amount of thickness and inherent high stiffness when it is used to retrofit the column-type structural members. As a result, the strengthening mechanism for the cylindrical normal weight concrete specimen wrapped and retrofitted by an outer ring layer of RPC ought to be divided into two parts: axial composite effect and circumferential confining effect. In this study, the Poisson’s ratios of RPC and NC are 0.22 and 0.20, respectively. These two values are too close to develop a apparent circumferential confining effect. Thus, the concept of transformed composite section was used to account for the composite effects on the axial stress due to the additional strengthening of RPC at the circumferential layer. The stress of composite cylindrical specimen at the failure load
Pmax is calculated by the following equation:

σc =

Pmax
AN + nAR

(2)

where AN and AR are the cross-sectional areas of NC and RPC, respectively; n = E R /E N , and ER and EN are the moduli of elasticity of RPC and NC respectively.
Using Eq. (1), the experimental ultimate compressive

stresses of composite cylindrical specimens encircled with a retrofitting RPC layer of thicknesses of 10 mm and 15 mm, respectively, were calculated and shown in Table 6. The average compressive stresses were increased from 9.5% (10 mm thickness of layer) to
38.0% (15 mm thickness of layer).
4

CONCLUSION

Major experimental results show that the compressive, splitting tensile and flexural strengths of RPC with steam-curing increase substantially. However, the increases of dynamic moduli of elasticity and shear, and Poisson’s ratio are not very sensitive to the changes of other material properties of RPC with the increase of ages. Similar trend is also observed for the supersonic pulse velocity of RPC which is also insensitive to curing condition. Water absorption test is rather simple but seems to be able to provide distinguishable change of material properties resulting from the apparent pozzolanic effects due to steam cuiring. Increases of compressive strength of cylindrical specimens retrofitted with 10 and 15 mm of wrapping RPC are 9.5% and 38.0%, respectively.
REFERENCES
Adeline, R. & Cheyrezy, M. 1998. The Sherbrooke Footbridge: the first RPC structure, FIP 98, Amsterdam,
May.
Etienne, D., Causse, M. & Behloul, M. 2001. Design and building of Seoul Peace Footbridge, Third International
Arch Bridge Conference, Paris, 865–876, September.
Lee, M.G., Wang, Y.C. & Chiu, C.T. 2007. A preliminary study of reactive powder concrete as a new repair material, Construction and Building Materials 21, 182–189.
Mindess, S., Young, J.F. & Darwin, D. 2003. Concrete,
2nd Ed., Prentice Hall.

1207

Rebentrost, M. & Cavill, B. 2006, Reactive powder concrete bridges, 6th Austroads Bridge Conferences, 12–15
September, Perth, Australia.
Richard, P. & Cheyrezy, M. 1994. Reactive powder concretes with high ductility and 200–800 MPa compressive strength, ACI Spring Convention, San Francisco,
April.

Richard, P. & Cheyrezy, M. 1995. Composition of reactive powder concretes, Cement and Concrete Research,
25(7): 1501–1511.
Tanaka, Y., Musya, H., Ootake, A., Shimoyam Y. & Kaneko,
O. 2002. Design and construction of Sakata-Mirai footbridge using reactive powder concrete, Proceeding of the
1st fib Congress, Osaka, Japan, October.

1208