corrosion resistance of m100 grade concrete using quartz sand and quartz fillers in hybrid fiber...

CORROSION RESISTANCE OF M100 GRADE CONCRETE USING QUARTZ SAND AND QUARTZ FILLERS IN HYBRID FIBER

REINFORCED SELF COMPACTING CONCRETE

INTRODUCTION

Performance of concrete is generally judged by strength

and durability properties. Probably the most important

durability issue with reinforced concrete is deterioration due

to reinforcement corrosion (Wallbank, 1989). A detailed

description of the corrosion process can be found in the

study of Rosenberg A, Hanson CM, Andrade C (1989). In the

alkaline cementitious environment, a stable oxide film is

formed on the steel surface which protects the interior steel

from corroding. However, corrosion starts due to the

carbonation of concrete leading to a reduction in the

alkalinity, or the presence of chloride ions causing pitting

damage of the protective film on the steel bar. The

corrosion product absorbs water and increases in volume.

By

Once the expansion becomes excessive, concrete

cracking will occur. Following the approach proposed by

Tuutti k (1982), the corrosion process can be divided into

two parts: an initiation (depassivation) stage and a

propagation (corrosion) stage. During the initiation stage,

corrosion agents such as chloride ions and carbon dioxide

penetrate into the concrete cover, but their concentration

around the steel reinforcement is not high enough to cause

corrosion yet. The end of the initiation stage or the

beginning of the propagation stage is the moment when

corrosion starts at threshold concentration of aggressive

species. Within the propagation stage, steel corrosion is

accompanied by the growth of radial cracks from the steel

bar, which will eventually lead to spalling of the concrete

cover.

ABSTRACT

Cement concrete is porous in its basic structure as a result of which permeation of air, moisture and other deleterious

agents occur, causing corrosion of reinforcement. Corrosion is defined as the deterioration of a material through a

chemical or electrochemical reaction with its environment. The phenomenon of corrosion of reinforcement bar in

concrete is a time dependent process. Under severe environmental conditions also, it takes years for the steel

reinforcement to be corroded and to cause deterioration of Reinforced Concrete (RC) structures. However when it

becomes imperative to evaluate the relative performance of different types of steel and binder in a short time, the

accelerated corrosion test can be adopted. Effort has been made to present the corrosion resistance of M100 High

Strength Self Compacting Concrete (HSSCC) with and without adding Hybrid fibers (Steel Fibers with aspect ratio 60:1

and Glass Fibers with aspect ratio 857:1). The specimens are tested after 28 days of curing. The corrosion process is

initiated by applying a constant voltage of 6 volts to the system in which concrete specimens of 100x200mm cylinders

with concentrically embedded rebar of 10mm are placed in NaCl solution of 1.2 molarity. The specimens are visually

inspected at regular intervals of time for the onset of cracks. The accelerated corrosion test is terminated after cracking

of the specimen is observed i.e., when there is onset of a large current increase corresponding to time and the results are

interpreted in a current-time graph.

Keywords: Corrosion Resistance, HSSCC (High Strength Self Composting Concrete) Hybrid Fiber, Electrochemical

Reaction, Cracking.

B. NARENDRA KUMAR * P. SRINIVASA RAO ** K.RAJESH *** R. KRISHNESWAR ****

* Associate Professor, Department of Civil Engineering, Hyderabad, India. ** Professor, Department of Civil Engineering, Jawaharl Nehru Technology University College of Engineering, Hyderabad, India.

*** M.Tech, Department of Civil Engineering, VNR Vignana Institute of Engineering and Technology, Hyderabad, India. **** B.Tech, Department of Civil Engineering, VNR Vignana Institute of Engineering and Technology, Hyderabad, India.

VNR Vignana Institute of Engineering and Technology,

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10 li-manager’s Journal on Structural Engineering Vol. No. 3 14l, 3 September - November 20

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Performance measurements of reinforced concrete

related to the corrosion of embedded steel may be based

on the type and condition of steel bar and thickness and

quality of concrete cover, properties of cement paste,

mortar, and concrete, and electrochemical conditions of

the reinforcement in contact with the solution, paste,

mortar, or concrete. Issues relating to reinforcement type

have been extensively discussed in the study by Haynes G,

Fasullo EJ and McCuen RH et al (1992), and the use of

galvanized steel, stainless steel, or coated reinforcement in

preventing chloride-induced steel corrosion in concrete

have been investigated by Rober H (1982) and

Rasheeduzzafar (1992). Cracking has been noted to

increase the likelihood of damage to reinforced concrete

Suzuki K (1990) and Beeby AW (1981). Cover to

reinforcement is considered of prime importance by some

researchers (Gu P, Beaudoin JJ, Zhang MH, Malhotra VM,

2000) while others believe that concrete type/quality is

more critical than the cover thickness. Further information

on concrete cover, its modification, cracking, and de-

lamination can also be found in the study by Babaei,

Hawkins and Rasheeduzzafar (1992).

1. Objectives

1. To investigate the corrosion resistance of M100 grade

self-compacting concrete.

2. To compare the resistance to corrosion b\w HSSCC and

high strength hybrid fibre self-compacting concrete

(HSHFSCC).

3. To observe the difference in cracking due to corrosion in

HSSCC and HSHFSCC.

2. SCC Materials

An ordinary Portland cement of 53 grades is being used in the

mix. Quartz sand is used as fine aggregate replacing river

sand by 100%. Aggregate of size ranging from 4.75mm to

20mm is used as coarse aggregate. MasterGlenium ACE 30

and Glenium stream 2 are used as Super plasticizer and VMA

respectively. Hooked end steel fibers of aspect ratio 60:1 and

CEM-FIL anti crack alkali resistant glass fibers of aspect ratio

857:1 are used in the mix.

3. Mix Proportion

Self-compacting concrete mix is made using 640kg/m3 of

cement, 64kg/m3 of micro silica and 160 kg/m3 of quartz

powder. 1.5% of cementations material is used as super

plasticizer and 0.25% of cementations material is used as

viscosity modifying agent has been taken from previous

study done by B. Narendra Kumar, P. Srinivasa Rao, K.Rajesh

(2013). Fibers are tuned to 1.5% of cementations material

P. Srinivasa Rao, Seshadri Sekhar.T and P.Sravana (2009). The

Quantities in the mix are as shown in Table1.

4. Batching, Mixing and Placing of HSHFSCC

The proportioning of the quantity of cementations material

(Cement, Quartz powder and micro silica), fine aggregate

(Quartz Sand), coarse aggregate, superplasticizer, VMA

steel and glass fibers were done using weight batching as

per the mix design. Water was measured in volume. All the

measuring equipment are maintained in a clean

serviceable condition with their accuracy periodically

checked.

The concrete used in the study is laboratory produced with

an electrically operated pan mixer 80 litre in capacity.

Buttering of the mixer (disposal of the first mix) was always

firstly conducted before the first intended batch. This is to

eliminate the effect of the mixer dryness/wetness condition.

The same mixing procedure was followed for all HSHFSCC

mixtures. Firstly, the total content of course aggregate and

fine aggregate were mixed in dry condition in the mixer

until uniform distribution was observed. Then cementations

materials (cement + quartz powder + micro silica) are

added and mixed until uniformity. Secondly, water and

chemical admixtures like SP and VMA are premixed in a

beaker and stirred lightly. The premixed solution (Water + SP

+ VMA) was added to the running mixer in about 3 - 4

intervals limiting the running time to 3 minutes. The mixer is

kept still for 30 seconds and at last the fibres were sprinkled

while mixing thoroughly for 2min until uniform mix is

Table 1. Mix Proportions Used

Materials

HSSCC

HSHFSCC

3Cement (kg/m ) 640 640

Micro Silica (kg/m3) 64 64

Quartz Powder (kg/m3) 160 160Quartz Sand (kg/m3) 887 887

Coarse aggregate (kg/m3) 797.53 797.53SP (% of P.C) 1.5 1.5

VMA (% of P.C) 0.5 0.5W/P ratio 0.20 0.21

Steel Fibers (% of P.C) - 0.75 Glass Fibers (% of P.C) - 0.75

11li-manager’s Journal on Structural Engineering Vol. No. 3 14l, 3 September - November 20

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obtained (this 2min mixing is done even though fibres were

not 3 added). Once the mixing time was completed,

concrete is placed and the rheological tests (slump flow

test, V-funnel test, L-box test and U-box test) were performed

in quick succession.

5. Testing of the Specimen

5.1 Properties of fresh concrete:

In order to determine the self-compatibility the following

test were conducted on fresh concrete

(I) Flow Table

(ii) V Funnel

(iii) L-box

In Flow Table test the diameter and T500 represent flowing

ability, where V Funnel and L Box represent the passing and

filling ability, which are presented in Table 2 and Table 3. The

flow properties in both the concretes are within limits in

accordance to EFNARC (2005) guidelines.

5.2 Properties of hardened concrete

The hardened properties like compressive strength, split

tensile strength and flexural strength of HSSCC and

HSHFSCC are presented in Table 4 and Table 5 respectively.

6. Preparation and Casting of Specimens

The concrete prepared is poured into cylindrical molds of

100x200mm. The reinforcing rods of 225mm length and

10mm diameter were taken and positioned concentrically

in 100x200mm cylindrical molds with 25mm cover at

bottom and 50mm projection at the top. Concrete in

molds is shown in Figure 1. The concrete is then allowed to

harden for in molds for 48 hours. Epoxy coating is applied to

the 50mm projection of reinforcing rod and specimens are

kept in curing tank for 28 days. Specimens ready for testing

are shown in Figure 2.

7. Act Materials

The equipment consists of a precision Voltage source

which feed current (micro ampere range) to the Concrete

specimens with rebar. The specimens can be kept inside

the Acrylic container with perforated Stainless steel

Table 2. Flow Properties of HSSCC

Table 3. Flow Properties of HSHFSCC

Table 4. Hardened Properties of HSSCC

Table 5. Hardened Properties of HSHFSCC

Figure 1. Specimen in Moulds

Test Method HSSCC

Flow TableDiameter (mm) 750

T (seconds)500 2

V Funnel T (seconds)f 6

T (seconds)5min 8

L box 0.9

Test Method HSSCC

Flow TableDiameter (mm) 714

T (seconds)500 5

V Funnel T (seconds)f 10

T (seconds)5min 12

L box 0.87

Test Method 7day (Mpa) 28day (Mpa)

Compressive Strength 85.35 109.18

Split Tensile Strength 1.85 4.23

Flexural Strength 9.83 13.45

Test Method 7day (Mpa) 28day (Mpa)

Compressive Strength 96.3 123.8

Split Tensile Strength 2.89 8.35

Flexural Strength 13.33 18.52

Figure 2. Reinforced Concrete Specimens


cathode of suitable diameter. NaCl solution is poured

inside the container for penetration into the concrete

specimen. Stable DC voltage is applied between the SS

cathode and the steel rod. The data acquisition monitors

the voltage and current of each concrete specimen. The

readings are acquired 4 for an interval of say 1 min (can be

settable by the user). The period of test can be set upto a

week. At the end of test the data can be transferred to a PC

which will provide all the readings. Graphical plot can be

done current with respect to time.

7.1 Assembly of ACT Equipment

·Power source- Eight channel Data Acquisition System

with PC interface (Figure 3).

·The time at which sudden raise of current will be noted

down for each cell

·LED display indicates the voltage applied to cells.

·Four line LCD display will indicate the current in each

cell.

·Logging period and the total test period can be set by

the user using the key switches

·The data are stored in the equipment.

·At the end of test a buzzer is activated. The data can

be transferred to the PC.

·Any time the stored data in the equipment can be

transferred to PC by pressing the INC continuously for

10 seconds.

·Acrylic tank 150Wx150Dx200H mm with Stainless steel

cathode of 150mm (Figure 4). Electrode clamps and

USB to connect laptop.

·Battery back up to provides continuous power for Eight

hours to the equipment alone with 12v110AH battery.

7.2 Chemicals Used

Sodium Chloride (NaCl)

Sodium Chloride of 99% with molarity 58.44 g/mol (Figure

5).

8. Test Procedure

The test can be carried out by varying the impressed DC

voltage, the result would be increased or decreased time

to failure. Various researchers used various voltages,

however six volt is found to be an adequate value to

complete the tests within a reasonable length of time. The

beauty of the test is that it continues 24 hours a day and 7

days a week continuously, the only attention that needs to

be given is frequent checking of the crack appearance

period. Early research indicated that three test specimens

are adequate for each type of mix or material. Test data

indicate that sufficient accuracy could be obtained since

the data analysis method used here averages the three

values. Judgment and expertise should be used where

premature specimen failure occurs. If one of the three

specimens fails the first few days and the other two

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Figure 3. Eight channel Data Acquisition System

Figure 4. Acrylic tank, Stainless steel mesh

Figure 5. NaClExtrapureChemical


continue for a long period, the data from the prematurely

failed specimen should not be used. Visual inspection of

this one specimen will probably show improper preparation

of the specimen. Longer time-to-failure and higher

resistance are indicative of improvement over the

standard mix and the ability to better deter the intrusion of

chloride to the reinforcing steel. Preliminary research results

established that a continuation of testing to a point where

cracks became 0.79mm and larger caused pollution from

seepage of corrosion products into the water. For the

purpose of these tests various researchers used various

chloride concentrations, based on the exposure level the

concrete structure will be exposed when put on use.

8.1 Accelerated Corrosion Test Setup

A rapid corrosion testing technique was used to compare

the corrosion performance of plain and blended cement

concretes. Similar cells with some differences 5 were

reported by other researchers (Al-Tayyib AJ, Al-Zahrani MM,

1990). The setup for accelerated corrosion test (also known

as impressed voltage test) is as show below. It consists of a

DC power supply, two stainless steel plates, a data logger,

test specimen and the container containing 1.2 molarity of

NaCl solution. Concrete Cylinder specimens 100x200 mm

with a centrally embedded steel bar are used for the

accelerated corrosion test. The specimens are tested at

the required age after preparation. The steel bar (anode/

working electrode) of the cylinder specimen is connected

to the positive terminal and the stainless steel plates

(cathode/ counter electrode) are connected to the

negative terminal of the DC power source.

The corrosion process is initiated by applying a constant

voltage to the system. The current response is continuously

monitored and recorded by the data logger. In addition

the specimens are daily inspected visually for the onset of

cracks.

The data logger is set at a sampling frequency of 24 hours

for recording the corrosion current of the circuit. The

accelerated corrosion test is terminated after cracking of

the specimen when the rate of increase of corrosion

current with time was negligible.

8.2 Data Analysis

An important fact of this test is definition of specimen failure.

In all cases test is considered to commence at the time of

application of the impressed current. Specimen failure is

defined as that time corresponding to onset of a large

current increase. The example in Figure 6 and Figure 7

illustrates schematically the generalized nature of current

variations in the constant voltage test method. Initially it can

be seen that some relatively small amplitude variations are

encountered; but after that at later stage a large increase

in current occurs. It is considered that this corresponds to

growth of a crack within the concrete and to a

corresponding decrease in electrical resistance. Crack

growth is sub sequent incremental and is comprised of

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Figure 6. Schematic Test Setup for Accelerated Corrosion Test

Figure 7. Test Setup for Accelerated Corrosion Test with 6-concrete specimens


successive stages of propagation, which relieves tensile

stresses, and arrestment, which gives rise to additional solid

corrosion products accumulation.

9. Precaution

In this test, the specimen is accompanied in some

instances by development of an aqueous solution on top

of the specimen surface as shown in Figure 8. The pH of the

top liquid has been found to be approximately 1.9,

presumably due to hydrolysis of initial corrosion products.

Because of this and also because of the relatively low

electrical resistance of the top liquid, corrosion can occur

pre-ferentially at this location. Occurrence of this can lead

to erroneous conclusions. In order to permit this liquid to

drain away from the reinforcing steel, the specimen

preparation procedure specifies a 100 slope to the top

surface.

10. Experimental Results

10.1 HSSCC without Fibers

The corrosion process is initiated by applying a constant 6

Voltage to the system. The current response is continuously

monitored and recorded by the data logger. In addition

the specimens are daily inspected 6 visually for the onset of

cracks. The data logger is set at a sampling frequency of 24

hours for recording the corrosion current of the circuit. The

accelerated corrosion test is terminated after cracking of

the specimen when (there is a considerable variation in

corrosion current vs time graph) the rate of increase of

corrosion current with time was negligible. The current in

three cells i.e., concrete specimens in channel-1, channel-

2 and channel-3 at the corresponding days are shown in

Table 6.

The results are presented using a current-time and also the

failure time and crack observed is represented in Figure 9.

For the specimens in channel-1, channel-2 and channel-3

the failure of specimens was observed at 11th day from

start of experiment and crack was observed on 12th day

from start of experiment. The failure specimens are shown in

Figure 10.

10.2 With Hybrid Fibers

For specimens with hybrid fibres also the same procedure is

followed as in without fibres. A constant 6 Voltage is applied

to the system with specimens in channel-1, channel-2 and

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Figure 8. Aqueous Solution on Top of Specimen Surface and Pit Corrosion Occurrence Terminating Test.

Table 6. Current at the corresponding day for HSSCC

Figure 9. Corrosion Current verses Time Graph for HSSCC

TIME in DaysCURRENT in µA

CH-1 CH-2 CH-3

1 51 57 69

2 47 60 68 3 51 66 68

4 59 73 64 5 60 70 67

6 64 72 73 7 72 70 72

8 78 68 72 9 83 69 73

10 92 67 75

11 82 61 67

12 110 86 89

13 106 78 80 14 101 72 80

15 93 63 76

Figure 10. HSSCC Specimens After Failure


channel-3 and the specimens are inspected daily for the

onset of visual cracks. The current in each channel on the

corresponding days is shown in Table 7.

The results are presented using a current-time and also the

failure time and crack observed is represented in Figure 11.

For the specimens in channel-1, channel-2 and channel-3

the failure of specimens was observed at 16th day from

start of experiment and crack was observed on 18th day

from start of experiment. The failure specimens are shown in

Figure 12.

11. Discussions

·The HSSCC specimens failed on 11th day where the

HSHFSCC specimen took 16 days to fail under the

same electrochemical reaction.

·After the failure of specimens the time taken for the

crack observed in HSHFSCC was delayed when

compared HSSCC.

·Inspection of specimens after concluding the test

showed that there are two to three small cracks on the

tensile surface of HSHFSCC specimens, whereas only

single crack of slightly more width was observed on

HSSCC specimens.

Conclusions

The accelerated corrosion setup used under the present

study has been found to be an efficient and simple tool to

compare the durability performance of concretes,

especially in terms of resistance of concrete against

reinforcement corrosion.

·The accelerated corrosion test results indicated that

the specimens with Hybrid Fibre had superior

performance and mostly yielded longer time to

corrosion cracking at similar curing condition and

testing age compared to those with no Fibre content.

·The presence of glass fibres helped in reduction of

plastic shrinkage and increase in uniformity of

HSHFSCC mix which resulted in more durability.

·Even after failure time HSHFSCC has taken

considerably more time for the crack to be observed

when compared to HSSCC specimens.

·In HSSCC specimens only a single crack was observed

whose width was slightly more than the cracks

observed in HSHFSCC.

·From the crack pattern observed on the tensile surface

of specimens it can be concluded that the presence

of fibres in HSHFSCC ceased the propagation of cracks

resulting in distribution of corrosion pressure into small

multiple cracks which gives more time to the structure

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Table 7. Current at the corresponding day for HSHFSCC

Figure 11. Corrosion Current verses Time Graph for HSHFSCC

Figure 12. HSHFSCC Specimens After Failure

TIME in DaysCURRENT in µA

CH-1 CH-2 CH-3

1 81 83 97

2 79 90 94 3 81 91 106

4 84 92 103 5 82 97 114

6 87 101 128 7 93 95 126

8 98 93 119 9 96 93 119

10 103 87 117 11 106 88 122

12 107 90 123 13 113 93 119

14 118 96 121 15 123 101 125

16 116 94 119

17 139 121 149

18 154 137 157

19 141 131 132

20 132 124 129


before failure.

Recommendation

In view of the assured self-compatibility property and

improved corrosion resistance capacity of HSHFSCC this

concrete can be adopted for structural applications,

especially where there is heavy congestion of

reinforcement in RC structures and for prestressed

structures.

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ABOUT THE AUTHORS

Singh

Professor, Department of Civil Engineering, Jawaharl Nehru Technology University College of Engineering, Hyderabad, India. He

B.Narendra Kumar is currently working as an Associate Professor in Department of Civil Engineering, VNR Vignana Jyothi Institute of Engineering & Technology, Hyderabad. He received his B.Tech in Civil Engineering, M.Tech in Structural Engineering and is pursuing his PhD at JNTU, Hyderabad.His research interests are SCC, special concretes and concrete mix designs.

Dr.P.Srinivasa Rao is currently working as an specialized in Structural Engineering .Research interests are Concrete

Technology, Structural Design, High performance Concrete, Prefabricating Structures, Special Concretes and use of Micro Silica, Fly ash in Building Materials. He has been associates with a number of Designs projects, for Number of Organizations and involved as a key person in Quality Control and Mix Designs.He has guided three Ph.D s and 100 M.Tech projects .Guiding 15 Ph.D students and delivered invited lectures in other organizations and institutions.Member of ISTE, Member of ICI and Member of Institute of Engineers.

K. Rajesh is currently pursuing his M. Tech. degree (Structural Engineering) in the Department of Civil Engineering, VNR Vignana Jyothi Institute of Engineering & Technology, Hyderabad.

R.Krishneswar currently pursuing his B. Tech. degree in the department of Civil Engineering, VNR Vignana Jyothi Institute of Engineering & Technology, Hyderabad.


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