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Behavior of RPC under Repeated Cyclic Loading

[M.Tech. Structural Engg.] CIVIL ENGG. DEPT. BEC. BAGALKOT 1

Chapter 1

INTRODUCTION

1.1 General study

Most of the Structures such as deck slab of bridge, highway and airfield pavements are often

exposed to repetitive (fluctuating) loads by moving traffic, which cause a structure to failure

at a load level below its static capacity. Thus, fatigue loads (repeated loads) should be taken

into consideration in the design of concrete structures.

Reactive powder concrete (RPC) is a new type of concrete material. Compared with

conventional concrete, RPC has ultra-high strength, high toughness and high durability.

Combining the technical benefits and in-place costs, RPC was found to meet the

prerequisites of value engineering particularly in airport and high pavements, in bridge deck

overlays, curtain walls, sewer pipes, cavitation and erosion resistance structures such as

spillways, sluiceways, bridge piers and navigation locks, precast concrete products,

earthquake resistance structures, missile silos and energy dessipaters.

Rational design of concrete structures requires an accurate knowledge of concrete properties

under anticipated loading conditions. A large volume of information is available on behavior

of RPC under static loading conditions. However, relatively limited information is available

on behavior of RPC subjected to dynamic loadings.

In many applications, particularly in pavements and bridge deck overlays, the flexural

fatigue strength and endurance limit are important design parameters because these

structures are designed on the basis of fatigue load cycles. Plain concrete has fatigue

endurance limit of 50 to 55 percent of its static flexural strength. In RPC using the same

cross section as plain concrete could result in longer life span or high load capacity or both.In this present work an attempt has been made to evaluate the fatigue behavior of the new

steel and polypropylene fibers reinforced RPC. Hence, the study of effects of repeated loads

on RPC are to be studied in particular.


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1.2 Fatigue

Structures that are subjected to repeated loads are susceptible to failure due to fatigue.

Fatigue is a process of progressive permanent internal changes in the materials that occur

under the actions of cyclic loadings. These changes can cause progressive growth of cracks present in the concrete system and eventual failure of structures when high levels of cyclic

loads applied for short times or low levels of loads are applied for long times.

Many concrete structures such as highway pavements, highway bridges, railroad bridges,

airport pavements and bridges, marine structure, etc. are subjected to dynamic loads. Fatigue

strength data of concrete and other materials that are used in these structures for obtaining

their safe, effective and economical design are needed. A low cycle fatigue is important for

structures subjected to earthquake loads.

Although fatigue research began almost one hundred years ago, there is still lack of

understanding concerning the nature of fracture mechanism in cementitious composite

materials due to fatigue. This is partly due to complex nature of structure of such materials

and their properties are influenced greatly by a large number of parameters. Fatigue behavior

of concrete is also influenced by several parameters such as type of loadings, stress level,

rate of loading, material properties, environmental conditions, etc. The concrete properties

are dependent upon the variables such as water-to-cement ratio, cement content, air content,

curing technique, age, admixture content, etc.

1.2.1 Terms Related to Fatigue

The following are the most common terms used in fatigue analysis of materials.

1. Maximum stress (f max ): It is the maximum value of stress cycle, tensile stress being

considered positive and compressive stress negative.

2. Minimum stress (f min): It is the lowest value of stress cycle, tensile stress being

considered positive and compressive stress negative.


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3. Stress level (S): This is defined as ratio of maximum stress in stress cycle to static

flexure stress.

4. Stress ratio (R): This is defined as ratio of minimum stress to maximum stress in

stress cycle.

5. Mean stress (f m): It is defined as an average value of the maximum and minimum

stresses in a stress cycle, that is, f m = 1/2 (f max + f min ).

6. Fatigue life (N): It is defined as the number of cycles which could be withstood for a

given experimental condition.

7. Fatigue strength (f): It is defined as the intensity of cyclic stress that can be withstood

for a given number of cycles.

8. Endurance limit or Fatigue limit (f e): It is defined as the intensity of cyclic stress that

can be withstood for a given number of cycles.

1.3 Objectives of the present study.

The main objectives of the study are:

To evaluate the fatigue performance of RPC by conducting flexural fatigue tests on

beams subjected to repeated cyclic loading.

To evaluate the fatigue performance of RPC with replacement of steel fibers by

different percentages of polypropylene fibers conducting flexural fatigue tests on

beams subjected to repeated cyclic loading.

Linear regression model is developed for prediction of fatigue life and the failure

stress.


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Chapter 2

LITERATURE REVIEW

2.1 History of Reactive Powder ConcreteThe RPC is a very-high-strength, high-performance concrete material formulated to optimize

those properties that are beneficial to, and minimize those properties that are detrimental to,

strength, durability, permeability, and toughness of concrete. The initial formulation of RPC

was developed by Bouygues S.A. in their laboratories in France. Engineers working for

Bouygues mixed numerous trial batches of various combinations of cements, sands, silica

times, and water-reducing admixtures and conducted fresh and hardened properties tests of

these mixtures to determine which combinations provided the most optimal properties. Theyevaluated their results to choose a small number of optimized mixtures that they called

reactive powder concrete.

Reactive powder concrete obtains its name from the behavior and composition of its

component materials. The component materials are the same as those that are normally found

in conventional concrete and differ only in percentages. Cementitious materials are cement

and silica fume, aggregates are sands, and water and high-range water-reducing admixtures

(HRWRA) are used to hydrate the cementitious materials and provide fluidity to the mixture.When additional stiffness of the mixtures is required, silica flour can be added and to provide

flexural strength and toughness, steel fibers are incorporated. Reactive powder concrete uses

the word powder in its name to emphasize that all dry particles are kept to small powder

sizes. This helps to promote its homogeneity. The word reactive is used in the name to

indicate that it is formulated to maximize the effect of its reactive components. Much effort is

taken to maximize the cementitious components of RPC. Table 1.1 describes the basic

principles that were employed to obtain RPCS high -performance properties. Reactive

powder concrete mixes are characterized by high silica fume content and very low

water/cement ratio. Coarse aggregate is eliminated to avoid weaknesses of the

microstructure; the addition of superplasticizer is used to achieve a low water/binder (cement

and silica fume) ratio and heat-treatment (steam curing) is applied to achieve high strength

[10].


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Table 1.1 Basic Principles for the composition of RPC

HomogeneityParticle sizes and composition chosen for optimumeffectReactive elements chosen for high silica content

Compactness Particle volumes and sizes chosen for optimum packingFormulated to produce very low porosity

MicrostructureHigh silica contents improves paste/aggregatehomogeneityHeat curing improves strength

Ductility Addition of micro-fibers provides ductility andtoughness

Reactive powder concrete mixes are characterized by high silica fume content and very low

water/cement ratio. Coarse aggregate is eliminated to avoid weaknesses of the

microstructure, the addition of superplasticizer is used to achieve a low water/binder (cement

and silica fume) ratio and heat-treatment (steam curing) is applied to achieve high strength

[10]. Owing to the fineness of silica fume and the increased quantity of hydraulically active

components, it has been called Reactive Powder Concrete. Silica fume is an essential

ingredient of RPC (a by-product of the fabrication of silicon metal, ferrosilicon alloys and

other silicon alloys) [9]. The material comprises extremely fine particles and not only fills up

the space between the cement grains, but also reacts with the cement. From a physical point

of view, the silica fume particles appear to be perfectly spherical, with diameters ranging

from less than 0.1 microns to approximately 2 microns, so that the average silica fume sphere

is approximately 100 times smaller than the typical cement particle [9].

From a chemical point of view, the silica fume behaves as if it were a crystal of

portlandite, Ca(OH) 2. In the descriptions of the Australian Standard (AS 3582.3), silica fume

is also known as condensed silica fume and microsilica, and contains no less than 85 %

silica dioxide (SiO 2). The earliest silica fume utilization was the use of 15 % silica fume to

replace cement in the construction of a tunnel in Oslo in 1952. Silica fume use became more

common in the late 1970 s when it was used as a supplementary cementitious material in

concrete in Europe, and in the early 1980 s in North America. Following work by Bache and

co-workers in Denmark and a significant research effort in the early 1980 s in other

countries, silica fume was rapidly accepted as a supplementary cementitious material for

concrete almost everywhere in the world in the following 5 years. The use of


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superplasticizers in concrete began in the 1960s and was a milestone in concrete technology.

Using such techniques the production of concrete of high compressive performance and

ductility was achieved, as high workability could be maintained at a very low water/cement

ratio [16]. High fluidity and good workability can be achieved through the addition of

superplasticizer, which enhances the microstructure of the concrete.

2.2 Development of RPC

RPC was developed by the French engineers in the 1990 s [12]. Richard and

Cheyrezy presented the initial composition in which they eliminated coarse aggregates to

enhance the homogeneity. The bond between the coarse aggregate and the cement paste are

the weakest links in the matrix, so to improve strength the coarse aggregates were removed

from the composition. However, other studies have indicated that addition of coarse

aggregate does not necessarily reduce the compressive strength. The use of the coarse

aggregates led not only to the decrease in cementitious paste volume fraction, but also

necessitated changes in the mixing process and in the consequent mechanical properties.

RPC containing coarse aggregate was more easily fluidized and homogenized. The mixing

time was found to be shorter than for RPC without coarse aggregates. Formulations with and

without coarse aggregate exhibited a similar behaviour under compressive loading, although

with somewhat different modulus of elasticity and strain at peak stress, which was dependent

on the stiffness of the aggregates. The lower paste volume fraction and the physical

resistance of the stiffer basalt aggregate resulted in a lower autogenous shrinkage of the RPC

containing coarse aggregates. The initial purpose of adding coarse aggregates was to reduce

the cement usage so that the costs of construction could be lowered. Work has been

undertaken where artificial aggregate was used to replace natural ones with clinker-

aggregates resulted in an increase of strength (by about 20 MPa) compared to natural

aggregates [18].

Observation of the microstructure shows that silica fume addition leads to significant

improvement. Owing to the size of particle of silica fume (1/100 of a cement particle). Hence

the space between cement particles can be filled by the silica fume particles. Hence the pores

and voids can be considerably reduced in the matrix. The porosity of RPC never exceeds 9%

by volume in the pore diameter range of 3.75 nm to 100 micron. The reaction between


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Portland cement and a supplementary cementitious materials results in a very dense

microstructure and an improved bond between the binder and the aggregate. Several

researchers indicated that a reduced capillary porosity and changed pore size distribution are

achieved as a result of silica fume addition [20]. With reference to hydration, the reaction of

the calcium hydroxide produced by the cement hydration with the silica fume, results in a

higher content of calcium-silicate-hydrate (CSH), the main source of strength in hardened

concrete.

The influences of silica fume and cement type on the performance of 200 MPa RPC

have been studied by Richard and Cheyrezy [11]. They concluded that an RPC mix with

CaOAl 2O3 - free cement used less water and achieved higher strength than RPC mixed with

CaOAl 2O3 content cement. They also developed an understanding of the effect of

superplasticizer type on the performance of RPC in terms of water -cement ratio and

compressive strength. They observed that the steel fibre shape and the aspect ratio do not

significantly affect the workability. The mechanical performances of these fibre-reinforced

materials appear to be essentially influenced by the amount of fibres dispersed inside the

cement matrix and the bond between the cement matrix and the fibres. Furthermore this bond

depends on the fibre characteristics (size, shape, and surface treatment). In the initial

research, heat treatment and pressure before and during setting had to be applied to achieve a

high strength. A minimum value of porosity is found to be obtained for pressed RPC with

heat treatments between 150 C and 200 C in the laboratory. The effect of curing techniques

has been investigated, and specimens under steam curing resulted in the highest compressive

strength as compared to both moist and air curing. In addition the effect of curing on flexural

strength is not found to be the same as that on compressive strength in silica fume concrete

[17].

2.3 Fatigue

General

The earliest work on fatigue of mortar specimen in compression was done by Considered in

1898 and concrete specimen by Van Ornum in 1903 (book of Rbk). Several researchers

including Batson, Ramakrishnan, Kesler, Tarto etc. presented information on studies


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concerning fatigue behavior of concrete and fiber reinforced concrete [1]. However,

substantial amount of research work on fatigue behavior of concrete began after 1930. This

report deals with investigations related to fatigue behavior of RPC made with steel fiber and

polypropylene fiber.

Parameters effecting the fatigue behavior of concrete

A large number of parameters are known to influence fatigue properties of plain concrete.

These include stress range, variation in loads, load history, rate of loading, rest periods, stress

gradients, material properties, etc. The material properties are influenced by cement content,

water-to-cement ratio, curing conditions, amount of entrained air, specimen size, aggregate

type and quality, moisture condition, age of concrete, etc.

2.3.1 Stress Level

The effect of varying load levels on fatigue is of special importance because this

condition is more representative of the actual conditions to which a structural component will

be subjected. Several studies indicated that the stress levels influences the fatigue strength

[all references]. In general, higher fatigue strength is obtained when the stress levels is

reduced.

Suresh Kumar et al (2) studied the effect the stress levels on flexural fatigue life of

High performance concrete. All specimens (100mm100mm500mm.) were simply

supported on a 400mm span and subjected to repeated loads of varying range and magnitudes

using third point loading systems. The number to repetitions to failure determined for three

stress levels 0.65, 0.70, and 0.75 for pavement quality concrete (PQC) and high volume fly

ash concrete (HVFA) and 0.65, 0.75, and 0.85 for silica fume concrete (SFC).

The scatter diagram of the test results for PQC, HVFAC and SFC are shown in Figure

2.1.The tests revealed that number of cycles increases as stress level decreases for PQC,

HVFAC and SFC.


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Figure 2.1 Scatter diagram Aravindkumar et al (3) performed an investigation to evaluate the effect of stress level on

conventional concrete (PCC) and HVFAC prisms (500mm150mm150mm) subjected to

repeated loads. Fatigue test specimens were tested under one-third point loading. PCC was

tested for eight stress levels (0.85, 0.81, 0.76, 0.71, 0.65, 0.61, 0.57, and 0.53) and HVFAC

was tested at seven stress levels (0.80, 0.75, 0.70, 0.65, 0.60, 0.54, 0.50). The test results of

PCC and HVFAC are tabulated in table 2.1and 2.2 respectively.

Table 2.1 Fatigue Life of PCC at Different Stress Levels


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Table 2.2 Fatigue Life of HVFAC at Different Stress Levels

Singh et al (4) aimed to find the two-million-cycle fatigue strengths of SFRC for different volume

fractions of steel fibres and compared with that of plain concrete. The specimens used for flexural

fatigue tests and static flexural tests were fiber concrete beams of size 500 mm100 mm100

mm. The specimens were cast in 9 batches, each batch consisting of 14 fibre concrete beams,

of which 4 were tested in static flexural condition to obtain the flexural strength of the batch

and the remaining 10 were tested in flexural fatigue condition at different stress levels to

obtain the fatigue lives of SFRC. The influence of increasing fiber content can be seen from

Fig.2.2 wherein the ordinate represents applied fatigue stress as percentage of the

corresponding static strength. Increasing the fiber content from 0.0% to at least up to 1.0%improves the fatigue performance significantly, but with further addition of fibres the

performance drops .


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Figure 2.2 S-N

relationships for steel fibre reinforced concrete 50% 50 mm+50% 25mm long fibres based on applied fatigue stress as percentage of static flexural stress.(a) V f =1.0%; (b) V f =1.5%; (c) V f = 2.0%

Girish et al evaluated the influence of stress levels on the flexural fatigue behavior of steel

fiber reinforced concrete [5]. The SFRC beam specimen of size 500mm x 100mm x 100mm

containing mixed steel fibers of size 50mm x 2mm x 0.6mm and 0.5mm 30mm in

different proportions were tested under two point flexural fatigue loading at various stress

levels (0.85, 0.8, 0.75, 0.7). It is observed that at the higher stress amplitude the concrete

specimens sustained fewer cycles to failure and as stress amplitude reduced the no. of cyclesto failure also increased gradually as shown in figure 2.3.

Figure 2.3 Fatigue Life at different Stress Ratio


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2.3.2 Rate of loading

The influence of the frequency of loading has been investigated by several researchers like

Rathby et al. The effect of this is illustrated in Fig. 2.4 where endurance curves are plotted

with the maximum stress in the fatigue cycle expressed as a proportion of the flexuralstrength. The lower endurance curve is based on strength values obtained at a rate of loading

equivalent to that applied in fatigue tests at 20 Hz. The upper curve is based on values

obtained from standard tests at a much slower rate of loading. In general strength values are

more readily obtainable for the standard rate of loading and therefore it is more convenient, if

less correct, to use the conventional strength (upper curve in Fig. 2.4) as a basis for

comparison; this has been done in subsequent analysis. Fatigue tests at two different

frequencies 4 and 20 Hz-showed no significant effect on fatigue performance within this

frequency range. Kesler has suggested that it is only when the strain levels are high enough

to produce significant microcracking that there is likely to be any appreciable effect of rate of

loading [6]. Since the static strength of concrete depends significantly on the rate of loading,

it is anticipated that fatigue performance would also be effected by this parameter. However,

in general, variations of the loading frequency have insignificant effects on fatigue strength

of concrete if the maximum stress level remains less than about 75% of the static strength.

However, for higher stress levels, fatigue strength decreases considerably with decreasing

frequency of loading. Under such conditions, creep effects become more dominant, probably

leading to a substantial reduction in fatigue strength with decreasing rate of loading..

Figure 2. 4 Typical endurance curves for flexural loading at 20 Hz.


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2.3.3 Age at time of loading

As expected, age and curing have a decisive effect on the fatigue strength. Concrete

inadequately cured is less resistant to fatigue than a well cured concrete at a given age. In

general, test data showed increase in fatigue strength of concrete with increase in age asshown in figure 2.5. At the same time there is a corresponding increase in the static strength.

If the fatigue loading is expressed as a proportion of the appropriate mean strength, all the

results lie close to an endurance curve very similar to that derived from constant amplitude

tests on beams cured for 6 months [6].

Figure 2. 5 Variation of fatigue endurance with age.

2.5 Advantages of RPC

The main advantage that RPC has over standard concrete is its high compressive

strength. Richard and Cheyrezy [6] demonstrated RPC with compressive strengths ranging


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from 200 to 800 MPa, and fracture energies up to 40kJ/m 2. Other advantages include low

porosity, improved microstructure and homogeneity, and high flexibility with the addition of

fibres. As a result of its superior performance, RPC has found application in the storage of

nuclear waste, bridges, roofs, piers, seismic-resistant structures and structures designed to

resist impact/blast loading. Owing to its high compression resistance, precast structural

elements can be fabricated in slender form to enhance aesthetics. Durability issues of

traditional concrete have been acknowledged for many years and significant funds have been

necessary to repair aging infrastructure. Reactive Powder Concrete possesses good durability

properties. Lower porosity and capillaries account for its endurance, RPC construction

requires low maintenance costs in its service life.

RPC usually incorporates larger quantities of steel or synthetic fibres and has

enhanced ductility and high temperature performance. This enables structural members to be

built entirely from RPC without the use of conventional transverse reinforcement, relying on

the RPC itself to resist all but the direct longitudinal tension [5].

Several landmark RPC structures exist:

Sherbrooke pedestrian bridge was erected in July 1997 in Quebec, Canada. It is the

worlds first major structure to be built with RPC. It has a 60m span of precast beams [5].

The Shepherds Gully Creek Bridge (in NSW, Australia) is a single span of 15m. It has a

width of 21m and is on a skew of 16 degrees. It is the first RPC construction for normal

highway traffic; it comprises four traffic lanes plus a footway [13].

Seoul Sunyudo footbridge (in South Korea) consists of two steel accesses carried by a

Ductal arch [13]. The span of the arch is 120 m constructed of Ductal, an ultra- high

performance concrete reinforced with fibres. Ductal is a commercial version of RPC.

Cavill and Chirgwin [15] reported that for a typical beam, the RPC solution has less than

35% of the volume of a conventional beam and need not contain any reinforcing bars;however this does not completely offset the higher cost of the materials. Saving in the

cost of the RPC solution can come from the significantly lower weight reducing the

supporting structure costs and reducing the erection costs. Consideration of life cycle

costs also favours an RPC solution.


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Sakata-Mirai Footbridge in Japan Sakata-Mirai Footbridge in Sakata in Japan does not

use any passive reinforcement. It is extremely light with dead weight of only 56 tonnes,

which is approximately one-fifth of the dead load of an equivalent conventional

prestressed concrete structure and results in an economic advantage of around 10% It is

shown in Figure 2.8.

Figure 2.6 Sherbrooke Footbridge, Canada

Figure 2.7 Shepherds Creek Road bridge, Australia Bridge open to traffic


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Figure 2.8 Sakata-Mirai Footbridge in Japan


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Chapter 3

EXPERIMENTAL DETAILS

3.1 Introduction

In order to investigate the behavior of RPC under repeated cyclic loading, several

experimental works have been undertaken. Details of materials employed, mix proportions,

mixing sequences, design of experiments, specimen preparation, experimental tests and

apparatus used will be presented in this chapter. In general, the experimental programme is

mainly to produce, to find out the optimal composition for producing RPC using local

available materials.

3.2 Details of RPC Materials

In this experiment, the constituents used in the RPC mixtures are different from the

conventional concrete mixtures, which include ordinary Portland cement, silica fume, silica

sand, quartz powder, superplasticizer, steel fibers, polypropylene fibers and water. Details of

each constituent are recapitulated as follows.

3.2.1 Ordinary Portland Cement

The cement used throughout the experiments is Ordinary Portland Cement (OPC)

(Table 3.1) that complies with IS: 12269-1987 and has a 28-day mortar compressive strength

of 53 MPa. The density is 3120 kg/m 3 and the fineness is 3390 cm 2/g. The initial and final

setting times are 30 minutes and 565 minutes respectively. The chemical composition is

given in Table 3.1 and confirms to IS: 4032-1985.

3.2.2 Silica fume

Silica fume 920 D from Elkem India Ltd. (Table 3.2) that complies with ASTM C

1240 95a and IS:15388-2003 is used for the present study. The silica fume is extremely

fine with particle size of 0.1 m. It exists in grey powder form that contains latently r eactive

silicon dioxide and no chlorides or other potentially corrosive substances. The dry bulk

density is 0.65 + 0.1 kg. The maximum dosage recommended in literature is about 30 % of


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cement content by weight. For optimum results in concrete, it was suggested to use in

conjunction with Polycarbocilyic ether superplasticizer from its range.

Table 3.1 Properties of 53 Grade OPC

Sl. No. Particulars Test Results IS 12269 Req.Chemical Properties:

1

CaO 0.7SO 3

2.8 SiO 2 + 1.2Al 2O3 + 0.65 Fe 2O3

Lime Saturation Factor (%)

0.86

0.80 Min

1.02 Max

2 TriCalcium silicate (C 3S) 45.38% -

3 DiCalcium silicate (C 2S) 27.06% -4 TriCalcium aluminate (C 3A) 7.04% -

5 Tetra Calcium Aluminoferrate (C 4AF) 13.44% -

6 Al 2O3 / Fe 2O3 Alumina Iron Ratio (%) 1.29 0.66 Min

7 Insoluble Residue (% by mass) 1.36 3.00 Max

8 Magnesia (% by mass) 0.86 6.00 Max

9 Sulphuric Anhydride (% by mass) 2.12 3.00 Max

10 Total Loss on Ignition (% by mass) 2.97 4.00 Max11 Total Chlorides (% by mass) 0.003 0.10 Max

12 Performance Improver: Limestone (%) 2.00 Not Specified

Physical Properties:

13 Fineness (Specific surface) 303 m 2/kg 225 m 2/kg Min

14

Soundness test

a. By Le Chatelier 0.8 mm 10.0 mm Max

b. By Autoclave 0.048 % 0.8 % Max

15

Compressive strength

a. 3 days 42.0 MPa 27.0 MPa Min

b. 7 days 54.7 MPa 37.0 MPa Min

c. 28 days 71.0 MPa 53.0 MPa Min

16 Specific gravity 3.15 Not Specified


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17 Particle Size Range 31 m 7.5 Not Specified

Manufacturer: UltraTech Cement Ltd

Table 3.2 Physical and chemical properties of silica fume

Sl. No. Properties Silica fume

1 Form Ultra fine amorphous powder

2 Colour Grey

3 Specific gravity 2.2

4 Bulk Density 700 kg/m Densified

5 Specific surface 25 m /g

6 Particle size ~15m

7 Sio 2 90%

8 H 2O 1%

9 Make Elkem

3.2.3 Silica Sand

The all of mixes were produced using silica sand which replaced the coarse aggregate

from conventional concrete. The silica sand was brought from Mangalore Karnataka. It is

yellowish-white high purity silica sand. The particle sizes used in the experiments is 90 m

600 m

3.2.4 Quartz Powder

The crushed quartz used in the experiments is white powdered quartz flour which acts

as additive for cement and sand particles and in turn increasing the density. The quartz flour

is brought from Bangalore, India. The particle size ranged from 10 m to 45 m is employed.

The specific gravity of quartz powder is 2.6.

3.2.5 Superplasticizer

The very low w/b (cement + silica fume) ratio used in RPC is only possible with the use of

superplasticizer (SP) to obtain its workability. In this research, the second generation of super


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plasticizer called glenium B-233 and ASTP G - 199 surtec from BASF India Ltd. were used.

The superplasticizer are an extremely high water-reducing agent that meets the requirements

for IS:9103-1999. Descriptions are provided in Table 3.3.

Table 3.3 Properties of Super Plasticizer Sl. No. Properties Glenium B-233 ASTP G-199

1 Type of S.P. Polycarboxylic ether Polycarboxylate polymer

2 Appearance Light brown Dark yellow

3 Density 1.09 1.12

4 pH Value 8 6

5 Sp.Gravity 1.1 1.2

6 Solid content 30% 40%

7Recommended

dosage0.5 to 1.5% 0.3 to 1.2%

3.3 Particle Size Distribution of RPC Materials

Table 3.4 Particle size distribution for Sand

Sieve (mm) Mass (g) % retainedCumulative %

retained% passing

4.75 0 0.0 0.0 100.02.18 8 0.4 0.4 99.61.75 14 0.7 1.1 98.91.00 18 0.9 2.0 98.00.60 51 2.6 4.6 95.50.50 60 3.0 7.6 92.50.30 710 35.5 43.1 57.00.25 695 34.8 77.8 22.20.15 395 19.8 97.6 2.50.09 42 2.1 99.7 0.4

0.063 7 0.4 100.0 0.0Pan 0 0.0 100.0 0.0

Total mass 2000 gm

Table 3.6 Particle size distribution for Quartz powder


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Sieve (mm) Mass (g) % retainedCumulative %

retained% passing

0.09 0 0 0 1000.075 25.20 25.24 25.24 74.760.063 54.65 54.73 79.97 20.03 pan 20.00 20.03 100.00 0.00

Table 3.5 Particle size distribution for Cement

Sieve

(mm)

Mass

(g)

%

retained

Cumulative

% retained

%

passing

0.15 - - - 100

0.09 3.53 3.53 3.53 96.47

0.075 45.61 45.66 49.19 50.81

0.063 43.99 44.04 93.23 6.77

pan 6.76 6.77 100.00 0.00


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Figure 3.1 Particle size distribution graph

The particle size distribution of cement, sand and quartz powder is shown in the figure 3.1.

The size of cement particle ranges from 60 - 200 m , the size of quartz powder is ranges

from 80 - 150 m and that of sand is ranging from 90 m to 4.0 mm. From the figure 3.1 it isclear that quartz powder will fill the void space between cement particles and sand particles.

3.5 Production Process of RPC

This research aims to study the production process utilizing local available materials

in India. RPC was produced under laboratory conditions, with the least complicated process.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.010 0.100 1.000 10.000

P e r c e n

t a g e p a s s

i n g

Particle size (mm)

Particle size distribution graph

Sand

Cement

QuartzPowder


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Since the properties of RPC are dependent on the type and quality of the materials used,

concreting practice, curing conditions, workmanship, etc., RPC mixes developed in one place

may not be applicable to another place where the local conditions are not quite the same.

Therefore, contextual information needs to be considered in the production of RPC. So far,

there is no guideline on how RPC could be produced in India and in world. The production

process of RPC in this research is based on some previous works by other researchers, as

well as our trial-and-error approaches.

3.5.1 Brief Production Guidelines

A set of brief production guidelines proposed for producing RPC using local available

materials in this study is summarized in the following:

A. Constituent materials and Content used

A 1 Cement

Ordinary Portland Cement (OPC) that complies with IS:12269-1987 is to be used for the

production of RPC. Cement with low or zero C 3A content is preferred as it would affect

the performance of RPC. The cement content normally used for the production of RPC is

700 1000 kg/m 3.

A 2 Mineral Additive

A 2.1 Silica fume

Silica fume that complies with IS:15388-2003 can be used. It is the smallest particle with

the average particle size of 0.1 m. For production of RPC, silica fume content is

normally 15-35% of the weight of cement.

A 2.2 Quartz Powder

Local white crushed quartz flour with particle size ranges from 10 m to 45 m is

employed which helps to reduce bleeding and segregation, and modify the CaO/SiO 2

ratio of the binder. The content is generally 20-30% of the weight of cement.

A 3 Aggregate (Silica sand)

Local silica sand with high purity of silica with average particles size ranges from 150

m and 600 m is used. It is dimensionally the largest granular material in RPC mix.

Silica sand constitutes the largest percentage in RPC mix, which is about 1.4 times the


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weight of cement.

A 4 Water

Water for mixing and curing concrete shall be clean, fresh water taken from the public

supply.

A 5 Chemical admixture

A chemical admixture is defined as a constituent material of concrete other than

cementitious materials, mineral additives, aggregates and water. The admixtures shall

comply and be used in accordance with the suppliers recommendation. For production

of RPC, superplasticizer which possesses extremely high water-reducing abilities that

meets the requirements for superplasticising admixtures according to IS:9103-1999

should be used. Any chemical admixtures containing chlorides are prohibited. Large

quantities between 3 and 3.5% by weight of binder are generally added to the RPC mix.B. Maximum Water-to Binder Ratio

The water-to-binder ratio of the RPC minimum shall obtained 0.14.

C. Mixing Procedures

C 1 Dry mixing powders (including cement, silica fume, quartz powder and silica sand)

for about 3 minutes with a low speed of about 140 rpm.

C 2 Addition of sixty percentage volume of water containing half amount of

superplasticizer, and mix for about 3 minutes with a higher speed of about 285 rpm.

C 3 Addition of the remaining water and superplasticizer, and mixed for about 10

minutes with a higher speed of about 285 rpm.

D. Curing

Water curing is the most convenient, practical and economical method in curing concrete.

Temperature of water at 27 + 1C is normally applied.

To achieve higher compressive strength of RPC at early edge accelerated curing at 65 0C

and 90 0C is useful.

3.5.2 Observation

Applying the above production guidelines for producing RPC, some observations are

made during concrete mixing. A long mixing time is required for the RPC mixes for ensuring

that dry-balled particles have become plastic-flowable. The mixing process for the RPC takes


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about 15 to 20 minutes to complete. The extended mixing time was necessary to fully

disperse silica fume, break up any agglomerated particles, and allow superplasticizer for

developing its full potential.. This also implies that RPC requires long mixing time because it

contains only very fine materials. It is suggested that mixers with a high speed are

recommended to break up any agglomerated particles so as to get a homogeneous and

cohesive mix, as well as shorten the mixing time.

3.5.3 Observations during the production of RPC

3.5.3.1 Observations during compaction

Since RPC requires the use of very low w/b ratio and very high cementitious materials

content, the RPC mixes are generally thick, sticky and viscous. Compaction on such a lowworkability concrete or mortar would be a problem. For w/b ratio as low as 0.14, compaction

by vibration table would not be applicable as there is not enough water content for proper

compaction to take place. Hand tamping using a tamping rod would be the only choice.

However, hand tamping done by different people would not be the same as the force that

each of them uses would be different. The void content in the bulk of particles in the paste

may vary greatly from good compaction to bad compaction. This may seriously affect the

performance of RPC. Adding more superplasticizer can increase the workability. However,

there is a limit to the dosage of superplasticizer that can be added. Overdosage of

superplasticizer can lead to chemical incompatibility problems and excessive retardation of

the setting time (Kwan, 2003). It is therefore necessary to find out an optimal mix that can

make compaction easy.

3.5.3.2 Industrialization problems

(a) High costs

Production of RPC places more stringent requirements on material selection and

optimization of composite materials than conventional concrete. In a typical RPC mix design,

the least costly components of conventional concrete (coarse and fine aggregates) have been

replaced by more expensive materials (Silica sand and quartz powder). Silica fume is also

incorporated in RPC. Requirements of RPC for high quality raw materials result in a


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substantial increase in cost over that of conventional concrete (about 3 to 4 times higher).

Moreover, the entire mixing time for RPC takes about 15 minutes which is much longer than

that of conventional concrete which takes only about 5 minutes; and the setting time for RPC

is longer because of the use of high dosage of superplasticizer. This lengthens the entire

construction period and thus increases the cost.

On the other hand, a very high speed mixer is needed to effectively break down those

fine particles, which also leads to high consumption of energy and cost. RPC, due to its high

cost, will not replace ordinary concrete where the conventional concrete can economically

meet the performance criteria (Dauriac, 1997). Though RPC has the potential to structurally

compete with steel, the high production costs of RPC may hinder the construction industry

from accepting such products.

(b) Lack of standards and code of practice

The state of knowledge of RPC is very low in the Indian construction industry. This

new concrete technology has not been acknowledged and vigorously researched locally,

resulting in a problem as the knowledge must be transferred to those doing the work so that

the advancement becomes a state of the practice involvement through research, development

and technology transfer stages is a key to the successful application of new concrete

technology in routine design and practice.

Since the mechanical properties of RPC are different from those of normal strength

concrete (NSC), the existing design codes which are only applicable to structures made of

NSC, need to be modified. For the full implementation of RPC, it would be a long term

process and may require many years of effort. Other barriers which may hinder the

construction industry from implementation of

RPC may include:

Inadequate research

No awareness of need for RPC

The production process to complicated

May got opposition from construction industries and market due to high cost


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Chapter 4MIX DESIGN OF RPC

The reactive powder concrete mixtures with different dosage of silica fume, and with

quartz powder are designed for different w/b ratio. Table 4.1 provides the details of the RPCmix design which are based on some published recommended compositions (Richard and

Cheyrezy, 1995; Cheyrezy et al., 1995; Washer et al., 2004; Shaheen and Shrive,2006). The

RPC mixes are produced using mortar mixer with a speed of about 140-285 revolutions per

minute (rpm). The mix design obtained using mix design procedure of high performance

concrete given by P.C.Aitcin [24].

The volume of cement content like 900 kg/m 3 are considered in the present study.

The Silica fume content of 15 - 20 % by weight of cement was considered. Quartz powder of10 - 20 % by volume of cement was added to the mixes. The superplasticizer of 4 % by

volume of cement was added to the mixes. The water binder ratio of 0.22 was selected for the

mixes.

The details of mix design are are given below:

Table 4.1 Properties of raw material

Sl.No. Material Specific gravity

1 Cement 3.15

2 Silica fume 2.2

3 Quartz Powder 2.6

4 Quartz sand 2.6

5 Super Plasticizer 1.1 to 1.2

6 Water 1


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The two different types of fibers used with different percentage in Control RPC as shown

below

Table 4.2 percentage of fibers used in RPC

Types of

fibers

Percentage of fibers used

Control RPC RPC RPCPP1 RPCPP2 RPCPP3

Steel fibers0 2% volume

of concrete

0 0 0

Polypropylenefibers

0 0 0.2% by

weight of

cement

0.275% by

weight of

cement

0.35% by

weight of

cement

Trial 1: Cement - 900 kg/m 3 and Silica fume - 20 % [without quartz powder]

Cement = 900 kg/m 3

Silica fume = 180 kg/m 3

Water binder = 0.18 % = 194.4 ltr

Super plasticizer = 2 % = 18 ltr

Volume of cement = 900/3.15 1/1000 = 0.285 Cum

Volume of Silica fume = 180/2.2 1/1000 = 0.081 Cum

Volume of water = 0.194 Cum

Volume of super plasticizer = 0.018 Cum

Volume of sand = [1 - (0.285 + 0.081 + 0.194 + 0.018)]= 0.422

= 0.422 2.6 1000

= 1097.2 kg

Extra water for SSD condition = 2 % = (216+23)


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= 240 ml

Table 4.3 Material proportion for 1 kg of Cement

Cement Silica fume Sand Water Superplastisizer

1 0.20 1.219 0.240 0.018

With quartz powder

Volume of quartz powder = 360/2.6 = 0.138 Cum

Volume of sand = 1 - (0.285 + 0.081 + 0.194 + 0.018 + 0.138)

= 1 - 0.716 = 0.284 2.6 1000

= 738.4/900

= 0.820 1200

= 984 gm


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Chapter 5RESULTS AND DISCUSSIONS

5.1 Static Compressive Strength

Standard 150x150x150 mm cubes were tested for 28 days compressive strength in

accordance with I.S. 516-1959 using Servo controlled compression testing machine of 3000

kN capacity. The maximum compressive load on the specimen was recorded as that load at

which the specimen failed to take any further increase in load. The compressive strength was

calculated by dividing the maximum compressive load obtained by area on which the load

was applied. Average of three samples was taken as the representative value of compressive

strength of each batch of concrete. The values of compressive strengths obtained are shown

in Table 5.1. Fig 5.1 shows the testing facility.

Table 5.1 Average Static Compressive Strength Test Results

Batch

No.

28 day compressive strength of concrete (Mpa)

Control

RPC

RPC RPCPP1 RPCPP2 RPCPP3

1 144.6

2 118.4

3 124.8

Average 129.26


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Fig. 5.1 Testing of Concrete Cube

5.1 Static Flexural Strength

To obtain the maximum and the minimum load limits for the fatigue tests, it was obligatory

to estimate the static flexural strength of concrete mixes. Standard 100x100x500 mm beam

specimens were tested for static flexural strength after of 28 days of curing under three-point

loading arrangement using a 500 kN closed-loop servo-controlled actuator. Static flexural

strength tests were carried out to determine the static flexural strength of all mixes prior to its

fatigue testing because once a specimen fails under fatigue loading, it is rather impossible to

determine the static flexural strength. The load was applied at the rate of 0.5 mm/minute.

Three specimens from a particular batch of concrete were tested and maximum load was

noted from the load-deflection curve. The rest of the specimens from a particular batch of

concrete were tested in flexural fatigue with the maximum and minimum loads in fatigue

tests being determined from the static flexural strength so obtained. Static flexural strength

test results for the mixes under study are presented in Table 5.2. The static flexural strength

of RPC 29.5 Mpa .


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Table 5.2 Average Static Flexural Strength Test Results

Batch

No.

28 day compressive strength of concrete (Mpa)


1 29.5

2 33.4

3

Average 31.45

5.3 Flexural Fatigue Analysis

After the static flexural strength of a particular batch was set up, remaining specimens were

from the same batch were tested in flexural fatigue. The fatigue parameters include static

flexural strength, stress level, stress ratio and loading frequency. The load cycle characteristic

value or stress ratio R is expressed as R= fmin/fmax, where fmin and fmax refer to the

minimum and maximum fatigue stress . The stress level S is expressed as fmax/fr, where fr

is the static flexural strength. The fatigue tests were performed with stress level ranging from0.5 to 0.3 and at constant stress ratio value of 0.1. The test was carried out in load control

mode using a continuous sinusoidal waveform with a loading frequency of 2 Hz. The test

was continued until the failure of limit was encountered. In this study, fatigue limit is defined

as when either the testing specimen fails or two million cycles limit reached without failure.

Table 5.3 Fatigue Life data obtained experimentally for Mixes under study

Stress Levels(S)

Mix


0.3 2000000

0.4 2000000


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0.5 1202000

From the fatigue test data obtained for the different types concretes under investigation S-N

curves are developed using linear regression models, considering log normal distribution.

The linear regression model is of the form (y = ax + c) in which stress ratio (S) is taken on Y-

axis and Log (N) values are taken on the X-axis.

Figure 5.2 Relationship between stress ratio (R) and Log (N)

y = -0.6783x + 4.6243R = 0.75

0

0.1

0.2

0.3

0.4

0.5

0.6

6.05 6.1 6.15 6.2 6.25 6.3 6.35

S t r e s s L e v e

l ( S )

Number of cycles (N)

RPC

RPC

Linear (RPC)


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Chapter 6

CONCLUSIONS1. The maximum compressive strength of 129.26 MPa is achieved with cement

content of 900 kg/m 3 with water binder ratio of 0.22.

2. The numbers of cycles increases as stress level decreases from 0.5 to 0.3.

FUTURE SCOPE

Stress strain characteristics of RPC under cyclic loading

Development of stability point curve under cyclic loading


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REFERENCES

report uma1

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