RHA and GGBS Paper for IEI 46th Engineers' Day.doc

7/29/2019 RHA and GGBS Paper for IEI 46th Engineers' Day.doc

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46th Engineers Day, September 15

The Institution of Engineers (India), A P State Centre

Development of Self Compacting Concrete

Using Rice Husk Ash and Ground Granulated Blast Furnace Slag

M V Seshagiri Rao, FIE, Professor, Department of Civil Engineering, JNTUH, Hyderabad.

Srinivasa Reddy V,MIE, Associate Professor, Department of Civil Engineering, GRIET, Hyderabad.

Swaroopa Rani M, Associate Professor, Department of Civil Engineering, JNTUK, Kakinada.

ABSTRACT

Self Compacting Concrete (SCC) as the name implies that the concrete requiring a very

little or no vibration to fill the form homogeneously. SCC is defined by two primary properties:

Ability to flow or deform under its own weight (with or without obstructions) and the ability to

remain homogeneous while doing so. The study explores the use of Ground Granulated Blast

Furnace Slag (GGBS) and Rice Husk Ash (RHA) to increase the amount of fines and hence

achieve self-compactibility in an economical way, suitable for Indian construction industry. The

main objectives of the present experimental investigations are to study the behavior of M20,

M40 and M60 SCC containing varying amounts of GGBS and RHA and to evaluate the Strength

Efficiency of GGBS and RHA combination in SCC. Test results substantiate the feasibility to

develop low cost SCC using GGBS and RHA.The SCC mixes produced with 30% GGBS

replacement of cement has shown improvement in 28 days Compressive Strength of about

31.04% in M20 grade and 20.83% in M40 grade. However, in case of M60 grade the requiredtarget strength was not reached when replaced with GGBS alone, so 5% RHA was added.

Keywords: Self Compacting Concrete, Rice Husk Ash (RHA), Ground Granulated Blast

Furnace Slag (GGBS), compressive strength, Strength efficiency factor.

INTRODUCTION

From several years, due to poor quality control and quality assurance at site, the problem

of durability of concrete structures has been a major issue to engineers. Sufficient compaction is

required to make durable concrete structures. Compaction of conventional concrete is done by

vibrating whereas over vibration can easily cause segregation and bleeding. Further, in

conventional concrete, it is very difficult to ensure uniform material quality and good density in

heavily reinforced locations of the structures.

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FIE - 015739/9 Email:[email protected] MIE-1463351 Email:[email protected]

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To overcome these problems, SCC was developed in Japan as a means to create uniformity in the

quality of concrete. Self-compacting concrete achieves this by its unique properties in fresh state

such as workability, water retention, workable time, green stability and early shrinkage. In the

plastic state, it flows under its own weight and maintain homogeneity while completely filling

any formwork and passing around congested reinforcement. Furthermore, in hardened state, it

possesses all important properties such as compressive strength, flexural and tensile strength,

elastic modulus, drying shrinkage, freeze-thaw resistance and carbonation resistance as

compared to conventional concrete. The concept of SCC was firstly proposed and applied to

prototype structure by Okamura in Japan in 1988. Later studies to develop SCC, including a

fundamental study on the workability of concrete, have been carried out by Ozawa and

Maekawa. SCC has now been used in construction with enthusiasm across Europe, America and

other parts of the world in both cast-in-situ and precast concrete work. Earlier, SCC relied on

very high content of cementitious paste and the mixes required specialized and well-controlled

placing methods to avoid segregation. But the high contents of cement paste made them prone to

shrinkage and generation of very high heat of hydration. The overall costs were also very high

and therefore, applications remained very limited. After a continuous research and development

which created a series of advancement in the field of SCC and it is now no longer a material

consisting of only cement, aggregates, water and admixtures.

The SCC is an engineered material consisting of cement, aggregates, water and admixtures withseveral new constituents like colloidal silica, pozzolanic materials, ground granulated blast

furnace slag (GGBS), micro silica, rice husk ash (RHA), chemical admixtures etc. to take care of

specific requirements such as high-flowability, high compressive strength, good workability,

enhanced resistance to chemical and mechanical stresses, lower permeability, enhanced

durability, resistance against segregation and ability to pass under dense reinforcement

conditions. The fluidity, deformability and high resistance to segregation enables the placement

of concrete without vibrations and with reduced labour, noise and less wear and tear of the

equipment. It also helps to shorten the construction period. Owing to all its properties, use of

SCC is constantly increasing all over the world. But the adoption has not been as fast as it should

have been due to its higher cost of production. In India, SCC is used in limited owing to lack of

awareness and the higher costs associated with its production.

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SCC is defined by two primary properties: Deformability and Segregation resistance.

Deformability or flowability is the ability of SCC to flow or deform under its own weight (with

or without obstructions). Segregation resistance or stability is the ability to remain homogeneous

while doing so. High range water reducing admixtures are utilized to develop sufficient

deformability. At the same time, segregation resistance is ensured, which is accomplished either

by introducing a chemical VMA or by increasing the amount of fines in the concrete. These

viscosity modifying admixtures are very expensive and the main cause of increase in the cost of

SCC. Self-compacting Concrete is considered to be the most promising building material for the

expected revolutionary changes at the job sites as well as on the desk of designers and civil

engineers. However, the basic principles of this material are substantially based on those of

flowing, cohesive, and superplasticized concretes developed in the mid of 1970's. The necessary

ingredients for manufacturing SCC are superplasticizers and powder materials (including

cement, fly ash, ground fillers or other mineral additions even in the form of fine recycled

aggregate) at an adequate content (> 400 kg/m3 of cement and filler), with some limits in the

maximum size of the coarse aggregate (< 25 mm).

The self-compacting concrete differs from conventional concrete in the following three

characteristic features, namely, (i) appropriate flowability, (ii) non-segregation, and (iii) no

blocking tendency. An increase in the flowability of concrete is known to increase the risk of

segregation. Therefore, it is essential to have a proper mix design. SCC should have:-1. Low coarse aggregate content

2. Increased paste content

3. Low water powder ratio

4. Increased super plasticizers dosage

5. Sometimes VMA can be used

Role of Superplasticizers

When we increase the slump of concrete over 175mm by increasing amount of water the

bleeding increases too much but with superplasticizers flowing concrete with slump level up to

250mm can be manufactured with no or negligible bleeding. The most important basic principle

for flowing and cohesive concrete (SCC) is the use of superplasticizers combined with a

relatively high content of powder materials in terms of Portland cement mineral additions ground

fillers and very fine sand.

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Viscosity Modifying Agents (VMA)

With these admixtures (0.1 to 0.2% by mass of cementitious materials) SCC can be made

with a reduced volume of fine materials. Viscosity Modifying Agent (VMA) may also be used to

reduce the segregation and sensitivity of the mix due to variation in other constituents especially

to moisture content.

Rice Husk Ash (RHA)

India is a major rice producing country, and the husk generated during milling is mostly

used as a fuel in the boilers for processing paddy, producing energy through direct combustion

and / or by gasification. About 20 million tones of RHA is produced annually. This RHA is a

great environment threat causing damage to the land and the surrounding area in which it is

dumped. Lots of ways are being thought of for disposing them by making commercial use of this

RHA. Rice milling generates a by product know as husk. 22 % of the weight of paddy is received

as husk. This husk is used as fuel in the rice mills to generate steam for the parboiling process.

This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this

husk is converted into ash during the firing process, is known as rice husk ash (RHA). RHA,

produced after burning of rice husk and sieved with 150 micron IS sieve., has high reactivity and

pozzolanic property. Indian Standard code of practice for plain and reinforced concrete, IS 456-

2000, recommends use of RHA in concrete but does not specify quantities. Chemical

compositions of RHA depend upon burning process and temperature. Silica content in the ashincreases when burnt at high temperatures. RHA produced by burning rice husk between 600C

and 700C temperatures for 2 hours, contains 90-95% SiO 2, 1-3% K2O and < 5% un-burnt

carbon ( Houston, D. F. (1972)),. Under controlled burning condition in industrial furnace

(Mehta, P. K. (1992)), RHA contains silica in amorphous and highly cellular form, with 50-1000

m2/g surface area. So use of RHA with cement improves workability and stability, reduces heat

evolution, thermal cracking and plastic shrinkage. This increases strength development,

impermeability and durability by strengthening transition zone, modifying the pore-structure,

blocking the large voids in the hydrated cement paste through pozzolanic reaction. RHA

minimizes alkali-aggregate reaction, reduces expansion, refines pore structure and hinders

diffusion of alkali ions to the surface of aggregate by micro porous structure. Portland cement

contains 60 to 65% CaO and, upon hydration, a considerable portion of lime is released as free

Ca(OH)2, which is primarily responsible for the poor performance of Portland cement concretes

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in acidic environments. Silica present in the RHA combines with the calcium hydroxide and

results excellent resistance of the material to acidic environments. Pozzolanic reaction of RHA

consumes Ca(OH)2 present in a hydrated Portland cement paste, reducing the susceptibility to

acid attack and improves resistance to chloride penetration. This reduces large pores and porosity

resulting very low permeability. The pozzolanic and cementitious reaction associated with RHA

reduces the free lime present in the cement paste, decreasing the permeability of the system and

improving the overall resistance to CO2 attack and resistance to corrosion of steel in concrete.

Highly micro porous structure RHA mixed concrete provides escape paths for the freezing water

inside the concrete, relieving internal stresses, reducing micro cracking and improving freeze-

thaw resistance.

The particle size of the cement is about 35 microns. There may be formation of void in

the concrete mixes, if curing is not done in properly. This reduces the strength and quality of the

concrete. RHA is finer than cement having very small particle size of 25 microns, so much so

that it fills the interstices in between the cement in the aggregate. That is where the strength and

density comes from. And that is why it can reduce the amount of cement in the concrete mix.

There is a growing demand for fine amorphous silica in the production of special cement and

concrete mixes, high performance concrete, high strength, low permeability concrete, for use in

bridges, marine environments , nuclear power plants etc. This market is currently filled by silica

fume or micro silica , being imported. Due to limited supply of silica fumes in India and thedemand being high the price of silica fume has risen in India. It has the potential to be used as a

substitute silica fumes or micro silica as a much lower cost, without compromising on the quality

aspect. RHA has excellent water resistance (impermeability) properties and is used in

waterproofing compounds to give amazing results. It lowers the heat of hydration and prevents

formation of cracks during casting. Rice Husk is burnt in controlled temperatures which are

below 700 degrees centigrade. This ash generated is amorphous in nature. The transformation of

this amorphous state to crystalline state takes place if the ash is exposed to high temperatures of

above 850 degrees centigrade.

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Table 1: Chemical Composition of RHA

SiO2 Silica 85 % minimum

Humidity 2 % maximum

Particle size 25 microns

Colour Grey

Loss on ignition at 800C 4 % maximum

pH value 8

Ground Granulated Blast Furnace Slag (GGBS)

Blast Furnace Slag is a by product obtained in the manufacturing of Pig iron in the Blast furnace

and is formed by the combination of earthy constituents of iron ore with lime stone flux.

Quenching process of molten slag by water is converting it into a fine, granulated slag of whitish

color. This granulated slag when finely ground and combined with OPC has been found to

exhibit excellent cementitious properties. Glass particles of GGBS are the active part and consist

of Mono-silicate (Q0-type), like those in OPC clinker, which dissolve on activation by any

medium. Glass content in GGBS is normally more than 85% of total volume. Specific gravity of

GGBS is approximately 2.80, which is lower than of OPC. Bulk density of GGBS is varying

from 1200-1300 kg/m3. GGBS is more closure to OPC in chemical composition in compare to

other mineral admixtures. Hydration products of GGBS are poorly crystalline Calcium Silicate

Hydrate broadly similar to that formed from hydration of OPC, but with lower Ca/Si ratio

(Jimenez et al., 2003). Due to lower Ca/ Si ratio, these hydrates have more alkali retention

capacity. Hydration products of GGBS effectively fill up the pores and increase the strength and

durability of concrete. GGBS requires activation to initiate hydration and the availability of a

medium for continuing the hydration process. Slag hydration can be activated by using alkalies,

lime, sulphate etc (Chemically activation), or by fine grinding (mechanically activation) or by

increasing temperature of concrete (thermal activation). Various alkalies activators like Sodium

hydroxide, Sodium carbonate, Sodium sulphate, Sodium silicate (water glass) etc. can be used

for slag. Water glass activated slag produced most cross-linked structures that results inincreased mechanical strength of hydration products, while Sodium hydroxide make hydration

process of slag more intensive (Garcia et. al., 2003). Due to higher activation energy of blast

furnace slag relative to OPC, it has advantage of thermal activation on its hydration.

Hydration products like alkailies, lime and heat of OPC are activate the hydration of GGBS

particles in blended cement concrete. Initially and during early hydration of concrete containing

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GGBS, the predominant reaction is with Alkalies hydroxide, but a subsequent reaction is with

Calcium hydroxide (Roy and Idorn, 1982). Reactivity of GGBS with OPC in blended concrete is

depends on chemical & mineralogical composition, glass content, fineness etc. of the GGBS.

Type of Portland cement employed and curing conditions also has a significant effect on the rate

of formation of hydration products in blended concrete. Reactivity of high glass content slag is

normally found more and greater fineness of slag also increases its reactivity due to increase in

surface area for reaction with activators. Use of rapid hardening cement in place of OPC

increases the reactivity of slag in blended concrete, due to more activators available at early age.

ACI (ACI 233R-95) recommends the use of Slag Activity Index (SAI) to evaluate its reactivity.

SAI is the percentage ratio of the average compressive strength of slag blended cement mortar

cubes (at 50% slag content), to the average compressive strength of reference cement mortar

cubes at a designated age. Based on SAI the GGBS is classified into three grades namely, Grade

80, 100 and 120. Blended concrete with grade 120 normally achieved strength of OPC concrete

at 3rd day and after, while concrete with grade 100 achieved at 7 th day and afterward. However,

concrete made with grade 80 GGBS will have a lower strength at all ages and not recommended

by ACI for use in structural concrete. Use of GGBS in concrete usually improves workability

and decreases the water demand due to higher smoothness of GGBS particles and increase in

paste volume of concrete. At higher replacement level (> 50%) the water demand may increased

for same workability (Sivasundaram and Malhotra, 1992). The possible reason for this is thegreater fineness of GGBS particle, which increases the surface area of binder in concrete at

larger replacement level. Segregation and bleeding chance in GGBS blended concrete is lower.

GGBS blending increases the setting time of concrete but gap between initial and final setting is

reduced. Setting time of blended concrete is reduced with increase in the fineness of GGBS.

Dose of air entraining agent require is higher for GGBS blended concrete in comparison to OPC

concrete, to produce same air entrainment. Use of GGBS in concrete reduces the hydration

temperature and also prolonged the time for peak temperature of concrete as shown in Figure 1

(Brooks and Al-Kaisi, 1990). Results related to creep and shrinkage shows the more detrimental

effect of drying environment, or need of an early water curing for better performance of GGBS

blended concrete.

Table 2: Chemical Composition of GGBS

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Oxides Quantity Remark

SiO2 30 - 35% -

Al2O3 8 - 22% Higher in Indian Slag

CaO 27 - 32% Lower in Indian Slag

MgO 7 - 9% -

Fe2O3 8 - 10% Higher in Indian Slag

GAPS IN THE RESEARCH ON SCC WITH GGBS AND RHA

A good amount of work is reported on SCC with Fly ash. Limited studies were done on the

behaviour of

a) SCC with GGBS.

b) SCC with RHA.

c) SCC with GGBS and RHA combination and its efficiency.

Considering this gap in existing literature an attempt has been made to study the strength

efficiency of GGBS and RHA in SCC

The main objectives of the present experimental investigation are:

1. To study the behavior of M20, M40 & M60 SCC with combinations of mineral

admixtures GGBS and RHA and find out compressive strength at 28 days for 10 to 35

percentage of GGBS replacement at an increment of 5%.

2. To evaluate the Strength Efficiency of GGBS and RHA combination in SCC.

MATERIALS USED

1. Ordinary Portland cement - 53 grade

2. Coarse Aggregate - 10mm size

3. Fine Aggregate

4. Ground Granulated Blast Furnace Slag (GGBS) and Rice Husk Ash (RHA)

5. Superplasticiser - Sulphonated Naphthalene Formaldehyde (SNF)

6. Viscosity Modifying Admixture (VMA) - Glenium Stream2

Mix Proportions

Mix designed for M20, M40, & M60 & modified as per EFNARC specifications. Finally arrived

SCC mix proportions are

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M-20

grade1: 2.11 : 1.95: 0.45

M-40

grade1: 1.60 : 1.60 : 0.38

M-60

grade1: 1.35 : 1.10 : 0.30

The following tests are made for each trial to study fresh properties

Slump flow

testFilling ability

V-Funnel test Filling ability (flow ability)

L-Box test Passing ability

EVALUATION OF STRENGTH EFFICIENCY FACTORS

An effort is made to quantify the 28-day cementitious efficiency of GGBS and RHA in SCC at

various replacement levels. The effect of the addition of GGBS and RHA on the strength of a

SCC mix may be modeled by using a Cementing Efficiency Factor (k). Strength Efficiency

Factor is defined as the ratio of the cementing efficiency of GGBS and RHA to the cementing

efficiency of the cement to which the GGBS and RHA is added. The term "efficiency factor" for

GGBS+RHA in concrete can be defined as the number of parts of cement that may be replaced

by one part of GGBS+RHA for obtaining same strengths. The strength efficiency factors are

mainly usefulto describe the admixtures GGBS and RHA combinations ability on the

compressive strength of SCC and quantify the replacement of cement by GGBS and RHA

combination on a one-to-one basis by weight. It was observed that this overall strength efficiency

of GGBS-RHA SCC was found to be a combination of efficiency factor ka and kpi.e.

k = ka + kp

k = overall strength efficiency factor ka = efficiency factor depending on age

kp = efficiency factor depending on percentage of replacement

From the present research studies, an effort is made to understand the fact that the optimized

GGBS+RHA combination enhances the strength and durability performance of SCC much more

than GGBS alone in SCC. So it is felt that efficiency concept can be used to understand the

behavior of GGBS and RHA combination as admixture in SCC when compared to GGBS alone

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in SCC. This is achieved by evaluating overall efficiency factor k for GGBS with different

replacement dosages at 28- day compressive strength on three grades of SCC mixes.

The Bolomeys empirical expression is frequently used to predict the strength of concrete

theoretically and well justifies when applied to hardened SCC. Efficiency factors found from

Bolomeys strength equation are used to describe the effect of the GGBS and RHA combination

replacement in SCC in the enhancement of strength and durability characteristics.

The Bolomeys equation is: S = A [(C / W)] + B ------ (1)

S is the compressive strength in MPa, C is the cement content in kg / m3,

W is the water content in kg / m3

Equation (1) has been practically reduced to following two equations

S = A [(C/W) 0.5]...... (2)

S = A [(C/W) + 0.5]...... (3)

The above two normalized equations represents two ranges of concrete strengths based on the

change in slope when P/W (powder-water ratio) is plotted against strength. It is found that the

equation (2) is useful for most of the present day concretes when an analysis was done on test

results available . Also the extensive data published by Larrard also mentions this equation in his

famous book, on 'Concrete Mix Proportioning A scientific approach. Therefore, equation (2)

can be generally used for re-proportioning GGBS+RHA SCC.

Strength efficiency factor, k, can then be computed using modified Bolomeys equationS = A [(C+ kG)/W) 0.5] ---------- (4)

where W/(C+ kG) is the water/effective binder ratio and kG is the equivalent cement content of

GGBS and RHA combination. It is recognized that mineral admixtures contribution to concrete

strength comes mainly from its ability to react with free calcium hydroxide produced during

cement hydration (Pozzolanic Reaction (PR)). The rate of this reaction, when compared to

Cement Hydration Rate (CHR) determines the value of k. When k=1, both PR and CHR would

be same. When k1 even at early ages.

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TEST RESULTS

Table 3: Fresh Properties of Ordinary Grade SCC (M20)

Percentage of GGBS

replacement

(by weight of cement)

0 10 15 20 25 30 35

Cement (kg) 400 360 340 320 300 280 260

CA (kg) 780 780 780 780 780 780 780

FA (kg) 844 844 844 844 844 844 844

Water (kg) 180 180 180 180 180 180 180

GGBS (kg) 0 40 60 80 100 120 140

Superplasticizer %

(by weight of powder)0.80 0.85 0.82 0.76 0.70 0.62 0.58

SLUMP TEST SLUMP in mm 760 765 750 730 755 760 750

T-50 Sec 3.08 3.43 3.89 3.42 3.12 3.89 4.09

V-FUNNEL T0 Sec 6.21 6.52 6.26 6.05 5.98 7.02 6.12

T5min Sec 8.03 8.53 8.48 7.59 7.92 8.68 7.92

L-BOX

T20 Sec 2.99 2.91 4.12 2.98 3.08 4.12 3.05

T40 Sec 4.02 5.86 5.05 5.15 4.83 6.15 5.98

H2/H1 0.98 0.99 0.97 0.98 0.99 0.98 0.89

Table 4: Fresh Properties of Standard Grade SCC (M40)

Percentage of GGBSreplacement


0 10 15 20 25 30 35

Cement (kg) 500 450 425 400 375 350 325

CA (kg) 800 800 800 800 800 800 800

FA (kg) 800 800 800 800 800 800 800

Water (kg) 190 190 190 190 190 190 190

GGBS (kg) 0 50 75 100 125 150 175

Superplasticizer %

(by weight of powder)

1.0 1.2 1.14 0.96 0.90 0.82 0.78

SLUMP TEST SLUMP mm 720 750 730 745 760 720 700

T-50 Sec 3.24 3.13 3.69 3.18 3.50 3.80 4.18

V-FUNNEL T0 Sec 6.54 6.18 6.25 6.20 6.2 6.78 6.95

T5min Sec 8.37 8.14 8.50 7.98 8.09 8.25 8.40

L-BOX T20 Sec 3.15 2.58 3.18 3.00 3.12 3.68 3.90

T40 Sec 5.25 5.13 5.25 5.18 5.15 5.59 6.18

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H2/H1 0.96 0.98 0.97 0.98 0.99 0.98 0.84

Table 5: Fresh Properties of High Strength Grade SCC (M60)

Percentage of GGBSreplacement


0 10 15 20 25 30 35

Cement (kg) 600 540 510 480 450 420 390

CA (kg) 660 660 660 660 660 660 660

FA (kg) 810 810 810 810 810 810 810

Water (kg) 190 190 190 190 190 190 190

GGBS (kg) 0 60 90 120 150 180 210

RHA (kg) 0 30 30 30 30 30 30

Superplasticizer %

(by weight of powder) 1.0 1.25 1.20 1.1 0.98 0.94 0.90

SLUMP TEST SLUMP mm 725 695 720 770 720 760 700

T-50 Sec 4.28 3.13 3.82 4.38 3.24 3.13 4.18

V-FUNNEL T0 Sec 7.01 6.08 6.68 6. 90 6.54 7.02 6.95

T5min Sec 8.56 7.86 8.90 9.12 8.37 9.14 8.56

L-BOX

T20 Sec 4.01 2.59 3.18 3.58 3.15 4.02 3.98

T40 Sec 6.28 5.13 5.25 6.56 5.25 5.98 6.25

H2/H1 0.86 0.84 0.97 0.95 0.96 0.98 0.88

Table 6: Optimized GGBS and RHA Combined Mixes

Gradecement

(kg)

CA

(kg)

FA

(kg)

RHA

(kg)

(by weight of

Cement)

GGBS

(kg)

(by weight of

Cement)

Water

(kg)

Superplasticizer %

(by weight of powder)

M20 280 780 844 3.60* 116.40 180 1.08M40 350 800 800 4.50* 145.50 190 1.14

M60 450 660 810 30** 150.00 190 1.40

* 3% of optimized 30% GGBS is replaced by RHA **5% RHA is added to optimized GGBS

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Table7: Compressive Strengths of Ordinary Grade SCC (M20), Standard Grade SCC

(M40) and High Strength Grade SCC (M60) at 28 days age

% of GGBS

Replacement

Compressive Strength (MPa)

M20 M40 M60

0 28.15 43.59 59.97

10 30.54 45.31 60.03

15 31.98 45.90 61.96

20 32.85 46.16 63.08

25 33.34 47.89 65.52

30 36.89 52.67 63.99

35 35.65 49.09 63.12

0

10

20

30

40

50

60

70

Com

pressiveStrength(MPa)

0 10 15 20 25 30 35

Percentage of GGBS Replacement

M20 SCC

M40 SCC

M60 SCC

Figure 1: Variation of Compressive Strength with % of GGBS

Table 8: Fresh and Hardened Properties of SCC Grades

Grade

Fresh Properties Hardened Properties

Slump Test V Funnel Test L Box TestCompressive Strength at

28 days N/mm2Slump

mm

T50

Sec

Time for

Discharge

T5 min

secH2/H1

M20 750 4.2 7.2 8.6 0.98 41.20

M40 760 4.0 5.9 8.35 0.98 58.25

M60 720 3.24 6.54 8.37 0.96 65.52

Table 9: Efficiency Factors for SCC Mixes

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%GGBS

Replacement


Efficiency Factor (k)

28 days

M20 M40 M60

0 - - 0.6710 1.66 1.21 0.89

15 1.70 1.23 0.97

20 1.75 1.24 1.31

25 1.77 1.39 1.02

30 1.80 1.56 0.98

35 1.59 1.36 0.67

Table 10: Efficiency Factors for SCC Mixes with GGBS and RHA

Grade%GGBS replacement


%RHA Replacement of GGBS


Efficiency Factor (k)

28days

M20 30 3 2.19

M40 30 3 1.90

Table 11: Comparison of Strength Efficiency factor k of GGBS+RHA SCC and GGBS

SCC at optimum % of replacement

Admixture

Efficiency Factor k

(For optimum % replacement)

M20 Grade M40 Grade M60 Grade

28 Days 28 Days 28 Days

GGBS 1.80 1.560.66

GGBS and RHA 2.19 1.90 1.31

DISCUSSIONS

1. The SCC mixes produced with 30% GGBS has shown improvement in 28 days

Compressive Strength of about 31.04% in M20 grade and 20.83% in M40 grade.

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2. However, in case of M60 grade the required target strength was not reached when

replaced with GGBS alone, so 5% RHA was added.

3. The RHA-GGBS based SCC mixes has shown an increase in compressive strength, when

compared with ordinary SCC mixes by 46.35 % in M20 , 33.63% in M40 and 7.60% in

M60

4. The use of GGBS and RHA combination as mineral admixture in SCC is well accepted

because of the possible strength and durability performance improvement in the SCC due

to improved rheological and hardened properties.

5. Efficiency of GGBS+RHA in SCC

1. For compressive strength of GGBS +RHA SCC, efficiency factor k for M 20 is

nearly 2.2 at 28 days, which means that in a given concrete, 1 kg of GGBS and

RHA combination, may replace 2.2 kg of cement without impairing the

compressive strength. Similarly at 28 days, for M 40 grade k value is 1.90 and for

M 60 grade k value is 1.31. Water content is kept constant for each SCC Mix.

2. On other hand, k for GGBS alone in SCC is 1.80 for M20 grade, 1.56 for M40

grade and 0.66 for M60 grade at 28 days, which means that in a given

concrete,1kg of GGBS may replace with 1.80 kg of cement in M20 grade ,1.56

kg of cement in M40 grade and with 0.66 kg cement for M60 grade withoutimpairing the compressive strength

CONCLUSIONS

1. By using mineral admixtures GGBS, RHA with suitable dosage of S.P and V.M.A, and

with proper proportioning SCC of acceptable properties in fresh and hardened state can

be produced.

2. The addition of RHA to GGBS mixes has shown enhanced performance in terms of

strength and durability in all grades of SCC. This is due to the presence of reactive silica

in GGBS and RHA combination (microstate) which offers good compatibility.

3. K.Ganesh babu and V.Sree Rama Kumar reported that the strength efficiency factor k

varies from 0.70 to 1.30 for percentage replacement levels varying from 10% to 80%.

They observed that the 28 days compressive strengths of concretes containing GGBS up

to 30% replacement were slightly above that of normal concrete and at all the other

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percentages the strengths were below that of normal concrete. This agrees well with the

observations made by our studies, where the optimum percentage of GGBS replacement

is 30% and the strength efficiency factor k ranged from 0.70 to 1.80 for 10% to 35 %

replacement levels. So based on our experimental investigations it can be correlated that

at 28 days Strength efficiency of GGBS in SCC is more than that of in normal concrete

whereas, Strength efficiency of GGBS and RHA combination in SCC is more than that of

GGBS alone in SCC.

4. The optimum dosage of GGBS was found to be 30% in SCC concrete which is similar to

that of the findings of Ganesh Babu and Sree Rama Kumar.

REFERENCES

1. Bronzeoak Ltd, Rice Husk Ash Market Study, ETSU U/00/00061/REP DTI/Pub URN

03/668, 2003.

2. Hwang, C. L., and Wu, D. S., Properties of Cement Paste Containing Rice Husk Ash,

ACI SP-114, 1989.

3. E. B. Oyetola and M. Abdullahi, The Use of Rice Husk Ash in LowCost Sandcrete

Block Production, Department of Civil Engineering, Federal University of Technology,

P.M.B. 65, Minna, Nigeria, June 2006.

4. Okamura, H. and Ouchi, M., (1999). "Self-compacting concrete- development, present

and future", Proceedings of the First International RILEM symposium on Self-Compacting Concrete, pp.3-14.

5. EFNARC. (2002). "Specifications and Guidelines for Self Compacting Concrete."

Available online at: www.efnarc.org

6. H Okamura and M Ouchi. 'Self-compacting Concrete-Development, Present use and

Future' Proceedings of the First International RILEM Symposium on 'Self-Compacting

Concrete'. Sweden, Proc 7, 1999, pp 3-14.

7. Okamura, Hajime, Ozawa, and Kazumasa: 'Mix Design for Self-Compacting Concrete'

Concrete Library of JSCE No. 25, June 1995.

8. Collepardi M, Collepardi S, Ogoumah ologat JJ, troli R.laboratory test and field

experiences of high performance SCCs. Proc of 3rd RILEM Int Symp on SCC, Iceland,

Aug. France; RILEM publications PRO 33;2003.p. 413-16.

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http://www.efnarc.org/http://www.efnarc.org/


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9. Babu, K. G., and Kumar, V. S. R., (2000), Efficiency of GGBFS in Concrete, Cement

and Concrete Research, Vol. 30, pp. 1031- 1036

10. A. Skarendahl, O. Petersson, Self-compacting Concrete-State oftheart report 174-

SCC, RILEM Technical Committee, France, Report 23. (2000)

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Documents

RHA and GGBS Paper for IEI 46th Engineers' Day.doc