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External self curing of concrete 2010

CHAPTER 1CHAPTER 1

INTRODUCTION

1.1 General

Construction industry use lot of water in the name of curing. The days are not so

far that all the construction industry has to switch over to an alternative curing system,

not only to save water for the sustainable development of the environment but also to

promote indoor and outdoor construction activities even in remote areas where there is

scarcity of water.

1.2 Curing of Concrete

Curing is the process of controlling the rate and extent of moisture loss from

concrete during cement hydration. It may be either after it has been placed in position

(or during the manufacture of concrete products), thereby providing time for the

hydration of the cement to occur. Since the hydration of cement does take time days, and

even weeks rather than hours – curing must be undertaken for a reasonable period of

time. If the concrete is to achieve its potential strength and durability curing may also

encompass the control of temperature since this affects the rate at which cement

hydrates.

The curing period may depend on the properties required of the concrete, the

purpose for which it is to be used, and the ambient conditions, i.e. the temperature andrelative humidity of the surrounding atmosphere. Curing is designed primarily to keep

the concrete moist, by preventing the loss of moisture from the concrete during the

period in which it is gaining strength. Curing may be applied in a number of ways and

the most appropriate means of curing may be dictated by the site or the construction

method. Curing is the maintenance of a satisfactory moisture content and temperature in

concrete for a period of time immediately following placing and finishing so that the

desired properties may develop. The need for adequate curing of concrete cannot be




overemphasized. Curing has a strong influence on the properties of hardened concrete;

proper curing will increase durability, strength, watertightness, abrasion resistance,

volume stability, and resistance to freezing and thawing and deicers.

Exposed slab surfaces are especially sensitive to curing as strength development.

And freeze-thaw resistance of the top surface of a slab can be reduced significantly

when curing is defective. When Portland cement is mixed with water, a chemical

reaction called hydration takes place. The extent to which this reaction is completed

influences the strength and durability of the concrete.

Freshly mixed concrete normally contains more water than is required for hydration

of the cement; however, excessive loss of water by evaporation can delay or prevent

adequate hydration. The surface is particularly susceptible to insufficient hydration

because it dries first. If temperatures are favorable, hydration is relatively rapid the first

few days after concrete is placed; however, it is important for water to be retained in the

concrete during this period, that is, for evaporation to be prevented or substantially

reduced. With proper curing, concrete becomes stronger, more impermeable, and more

resistant to stress, abrasion, and freezing and thawing. The improvement is rapid at early

ages but continues more slowly thereafter for an indefinite period.

Covering the concrete with an impermeable membrane after the formwork has

been removed.

By the application of a suitable chemical Curing agent (wax etc).

Curing by continuously wetting the exposed surface thereby preventing the loss

of moisture from it.

Ponding or spraying the surface with water is methods typically employed.

Department of CIVIL Engineering, A.I.T. Chikamagalur 2




1.3 Concrete can be kept moist (and in some cases at a favorable

Temperature) by three curing methods

1. Methods that maintain the presence of mixing water in the concrete during the

early hardening period. These include ponding or immersion, spraying or

fogging, and saturated wet coverings. These methods afford some cooling

through evaporation, which is beneficial in hot weather.

2. Methods that reduce the loss of mixing water from the surface of the concrete.

This can be done by covering the concrete with impervious paper or plastic

sheets.

3. Methods that accelerate strength gain by supplying heat and additional moisture

to the concrete. This is usually accomplished with live steam, heating coils, or

electrically heated forms or pads.

1.3.1 Ponding and Immersion

On flat surfaces, such as pavements and floors, concrete can be cured by

ponding. Earth or sand dikes around the perimeter of the concrete surface can retain a

pond of water. Ponding is an ideal method for preventing loss of moisture from the

concrete; it is also effective for maintaining uniform temperature in the concrete. The

curing water should not be more than about 11°C (20°F) cooler than the concrete to

prevent thermal stresses that could result in cracking. Since ponding requires

considerable labour and supervision, the method is generally used only for small jobs.

The most thorough method of curing with water consists of total immersion of the

finished concrete element. This method is commonly used in the laboratory for curing

concrete test specimens. Where appearance of the concrete is important, the water used

for curing by ponding or immersion must be free of substances that will stain or discolor

the concrete. The material used for dikes may also discolor the concrete. As shown in

Fig: 1.1





Fig. 1.1 Ponding method of water curing

1.3.2 Fogging and Sprinkling

Fogging (Fig. 1.2) and sprinkling with water are excellent methods of curing when the

ambient temperature is well above freezing and the humidity is low. A fine fog mist is

frequently applied through a system of nozzles or sprayers to raise the relative humidity

of the air over flatwork, thus slowing evaporation from the surface. Fogging

is applied to minimize plastic shrinkage cracking until finishing operations are complete.

Once the concrete has set sufficiently to prevent water erosion, ordinary lawn sprinklers

are effective if good coverage is provided and water runoff is of no concern. The cost of

sprinkling may be a disadvantage. The method requires an ample water supply and

careful supervision. If sprinkling is done at intervals, the concrete must be prevented

from drying between applications of water by using burlap or similar materials;

otherwise alternate cycles of wetting and drying can cause surface crazing or cracking.





Fig. 1.2 Fogging and sprinkling method of curing

1.3.3 Wet Coverings

Fabric coverings saturated with water, such as burlap, cotton mats, rugs, or other

moisture-retaining fabrics, are commonly used for curing (Fig. 03). Treated burlaps thatreflect light and are resistant to rot and fire wet, moisture-retaining fabric coverings

should be placed as soon as the concrete has hardened sufficiently to prevent surface

damage. During the waiting period other curing methods are used, such as fogging or the

use of membrane forming finishing aids. Care should be taken to cover the entire surface

with wet fabric, including the edges of slabs. The coverings should be kept continuously

moist so that a film of water remains on the concrete surface throughout the curing

period. Use of polyethylene film over wet burlap is a good practice; it will eliminate the

need for continuous watering of the covering periodically rewetting the fabric under the

plastic before it dries out should be sufficient. Alternate cycles of wetting and drying

during the early curing period may cause crazing of the surface.

Wet coverings of earth, sand, or sawdust are effective for curing and are often

useful on small jobs. Sawdust from most woods is acceptable, but oak and other woods

that contain tannic acid should not be used since deterioration of the concrete may occur.

A layer about 50 mm (2 in.) thick should be evenly distributed over the previously





moistened surface of the concrete and kept continuously wet. Wet hay or straw can be

used to cure flat surfaces. If used, it should be placed in a layer at least 150 mm (6 in)

thick and held down with wire screen, burlap, or tarpaulins to prevent its being blown

off by wind. A major disadvantage of moist earth, sand, sawdust, hay, or straw

coverings is the possibility of discoloring the concrete.

Fig 1.3 Wet coverings and Lawn sprinklers

1.3.4 Impervious Paper

Impervious paper for curing concrete consists of two sheets of Kraft paper

cemented together by a bituminous adhesive with fiber reinforcement. Such paper,

conforming to AASHTO M 171, is an efficient means of curing horizontal surfaces and

structural concrete of relatively simple shapes. An important advantage of this method is

that periodic additions of water are not required. Curing with impervious paper enhances

the hydration of cement by preventing loss of moisture from the concrete (Fig.04).As

soon as the concrete has hardened sufficiently to prevent surface damage, it should be

thoroughly wetted and the widest paper available applied. Edges of adjacent sheets

should be overlapped about 150 mm (6 in.) and tightly sealed with sand, wood planks,

pressure-sensitive tape, mastic, or glue. The sheets must be weighted to maintain close

contact with the concrete surface during the entire curing period. Impervious paper can





be reused if it effectively retains moisture. Tears and holes can easily be repaired with

curing-paper patches. When the condition of the paper is questionable, additional use

can be obtained by using it in double thickness. In addition to curing, impervious paper

provides some protection to the concrete against damage from subsequent construction

activity as well as protection from the direct sun. It should be light in color and no

staining to the concrete. Paper with a white upper surface is preferable for curing

exterior concrete during hot weather.

Fig 1.4 Impervious paper curing

1.3.5 Plastic Sheets

Plastic sheet materials, such as polyethylene film, can be used to cure concrete

(Fig. 05). Polyethylene film is a lightweight, effective moisture retarder and is easily

applied to complex as well as simple shapes. Its applications the same as described for

impervious paper. Curing with polyethylene film (or impervious paper) can cause patchy

discoloration, especially if the concrete contains calcium chloride and has been finished

by hard steel troweling. This discoloration is more pronounced when the film becomes

wrinkled, but it is difficult and time consuming on a large project to place sheet

materials without wrinkles. Flooding the surface under the covering may prevent

discoloration, but other means of curing should be used when uniform color is





important. Polyethylene film should conform to AASHTO M 171, which specifies a

0.10-mm (4-mil) thickness for curing concrete, but lists only clear and white opaque

film. However, black film is available and is satisfactory under some conditions. White

film should be used for curing exterior concrete during hot weather to reflect the sun’s

rays. Black film can be used during cool weather or for interior locations. Clear film has

little effect on heat absorption.

Fig 1.5: Plastic sheet curing

1.3.6 Membrane-Forming Curing Compounds

Liquid membrane-forming compounds consisting of waxes, resins, chlorinated

rubber, and other materials can be used to retard or reduce evaporation of moisture from

concrete. They are the most practical and most widely used method for curing not only

freshly placed concrete but also for extending curing of concrete after removal of forms

or after initial moist curing. However, the most effective methods of curing concrete are

wet coverings or water spraying that keeps the concrete continually damp. Curing

compounds should be able to maintain the relative humidity of the concrete surface

above 80% for seven days to sustain cement hydration. Membrane-forming curing

compounds are of two general types: clear or translucent; and white pigmented. Clear or

translucent compounds may contain a fugitive dye that makes it easier to check visually

for complete coverage of the concrete surface when the compound is applied. The dye





fades away soon after application. On hot, sunny days, uses of white-pigmented

compounds are base slab of a two-course floor. Similarly, some curing Compounds may

affect the adhesion of paint to concrete floors. Curing compound manufacturers should

be consulted to determine if their product is suitable for the intended application. Curing

compounds should be uniform and easy to maintain in a thoroughly mixed solution.

They should not sag, run off peaks, or collect in grooves. They should form a tough film

to withstand early construction traffic without damage, be no yellowing, and have good

moisture-retention properties. Caution is necessary when using curing compounds

containing solvents of high volatility in confined spaces or near sensitive occupied

spaces such as hospitals because evaporating volatiles may cause respiratory problems.

Applicable local environmental laws concerning volatile organic compound (VOC)

emissions should be followed. Curing compounds should conform to AASHTO M 148.

A method for determining the efficiency of curing compounds, waterproof paper, and

plastic sheets is described in AASHTO T 155. ASTM C1151, discontinued in 2000, also

evaluates the effectiveness of curing compounds. Curing compounds with sealing

properties are specified under ASTM C 1315. As shown in Fig:06

1.3.7 Steam Curing

Steam curing is advantageous where early strength gain in concrete is important

or where additional heat is required to accomplish hydration, as in cold weather.

Two methods of steam curing are used: live steam at atmospheric pressure (for

enclosed cast-in-place structures and large precast concrete units) and high-pressure

steam in autoclaves (for small manufactured units).

Steam curing at atmospheric pressure is generally done in an enclosure to

minimize moisture and heat losses. Tarpaulins are frequently used to form the enclosure.

Application of steam to the enclosure should be delayed until initial set occurs or

delayed at least 3 hours after final placement of concrete to allow for some hardening of

the concrete. However, a 3- to 5- hour delay period prior to steaming will achieve

maximum early strength. Steam temperature in the enclosure should be kept at about





60°C (140°F) until the desired concrete strength has developed. Strength will not

increase significantly if the maximum steam temperature is raised from 60°C to 70°C

(140°F to 160°F). Steam-curing temperatures above 70°C (160°F) should be avoided;

they are uneconomical and may result in damage. It is recommended that the internal

temperature of concrete not exceed 70°C (160°F) to avoid heat induced delayed

expansion and undue reduction in ultimate strength. Use of concrete temperatures

above70°C (160°F) should be demonstrated to be safe by test or historic field data.

1.4 Self curing of concrete

Self curing concrete is the one which can cure itself by retaining its moisture

content. A concrete can made to self cure by adding curing admixtures or by the

application of curing compounds.

1.4.1 Advantages of self curing

1. Reduces autogenously cracking.

2. Largely eliminates autogenously shrinkage.

3. Reduces permeability.

4. Protects reinforcement steel.

5. Provide greater durability.

6. Increases the early age strength.

7. Improved rheology.

8. Lower maintenance.

9. Higher performance.

10. Doesn’t adversely effects finish ability.





1.5 TYPE OF CEMENT

1.5.1 Ordinary Portland cement (O.P.C)

This is by far the most common cement in use. This is the basic type of cement

which is used on large scale in all general types of construction works. The details

regarding the composition and properties of this type of cement are given in IS: 269.

This cement is admirably suitable for use in general concrete constructions

where there is no exposure to sulphates in the soil or ground water.

These cements are available in different grades viz. 33, 43 and 53 grade.

1.5.2 43 grade Ordinary Portland cement

In these types of cements, the 28days cement strength is expected to have a

minimum value of 43 Mpa.

1.5.3 53 grade Ordinary Portland cement

In this type of cement, the 28 days cement strength is expected to have a

minimum value of 53 Mpa.

The use of high grade cement should not be taken for granted to yield high grade

[strength] concrete as the strength of concrete depends on the mixture of cement, sand,coarse aggregate and water. In fact, the cement’s grade has no relationship to the

strength of concrete. It is possible to produce concrete of wide-ranging strength using a

particular grade of cement. Moreover the “grade” has nothing to do with quality;

increase in the grade does not increase the quality of the cement.

Every structure has to satisfy the requirement of strength and durability. Strength is

the ability of the structure to withstand load. Durability refers to the period of troublefree life.





A structural cement of concrete may possess high strength, but may deteriorate

sooner than expected, making it a material of poor quality. Here the quality is with

reference to concrete and not that of the cement. A grade of cement can be said to be of

good quality if the concrete made with it satisfies both strength and durability

requirements.

The strength requirements [i.e. the strength of concrete] is satisfies by choosing the

proper amount of cement, limiting the amount of water, consolidating the mixture well

and curing the hardened concrete as long as possible. Durability on the other hand

depends on the several factors that are attributable both to the material and to the

exposed environment.

During a recent survey made in Chennai, the only grades of cement freely available

was found to be grade 53 and grade 43 was available on special order only and grade 33

was not found available.





CHAPTER 2CHAPTER 2

REVIEW OF LITERATURE

2.1 General

Construction industry is growing like day by day even in remote areas and

deserted regions. Even India and other countries are facing lot of problems in supplying

drinking water to their citizens. Hence construction industries are under pressure in

finding out alternative curing methods of curing concrete. The objective of curing is to

keep concrete saturated are nearly saturated as possible until the water fill the space in

the fresh cement paste have been sequentially reduced by the products of hydration of

cement [09]. Curing of concrete is complex phenomenon where the controlling process

is hydration of cement [10]. Hydration is an essential process of hardened concrete but

some micro cracking can occur as a consequence of hydration especially in HSC.

2.2 Self curing

The literature reports that the different compressive strength trends displayed by

cement paste and concrete specimen suggest that the presence of aggregate is

influencing the behavior of self curing concrete.

In the last 100 years there has been placed a certain amount of long lasting good

performing and economical concrete. However the deficiencies of much of concrete

have been obvious. In the last 75 years there have been great amount of knowledge

generated how to make the concrete better by best means of curing ACI committee 308

has studied the subjects since BRYANT MATHER called the industry’s attention to

“SELF CURING”.

Water retention of concrete containing self curing agents is investigated.

Concrete weight loss and internal relative humidity measurements with time were

carried out, in order to evaluate the water retention of self curing concrete. Non

evaporable water at different ages was measured to evaluate the hydration. Water

transport through concrete is evaluated by measuring absorption %, permeable voids %,

and water sorptivity and water permeability. The water transport through self curingconcrete is evaluated with age. The effect of the concrete mix proportions on the





performance of self curing concrete were investigated, such as cement content and w/c

ratio.

To achieve good cure, excessive evaporation of water from a freshly cast

concrete surface should be prevented. Failure to do this will lead to the degree of cement

hydration being lowered and the concrete developing unsatisfactory properties.

Curing can be performed in a number of ways to ensure that an adequate amount

of water is available for cement hydration to occur. However, it is not always possible to

cure concrete satisfactorily.

This paper is concerned with achieving optimum cure of concrete without the

need for applying conventional curing methods.

The guide to curing concrete is being re written to recognize the value of external

curing as an adjunct to internal curing.

Curing period is important for concrete in which it attains its maximum strength.

Normally all structures made of concrete are cured for a period of 28 days by the

application of water.

At present, meeting the requirements of drinking water is a global issue. Amidst

of this situation construction industry is growing rapidly. The scarcity of water is forcing

the construction industry to switch over to a curing method which can cure their

structures without the use of water. Self curing concrete is the only solution for these

problems. Looking at the demand of drinking water in all the metropolitan cities,

construction of highways and air fields in remote places where water curing is

practically not possible, deserted areas throughout the globe, etc forced to study on the

curing compounds and their performance.

Curing compounds are liquids which are usually sprayed directly on to the

concrete surface and they are an efficient and cost effective means of curing concrete

and may be applied to freshly placed concrete.





When used to cure fresh concrete, the timing of the application of the curing

compound is critical for maximum effectiveness. They should be applied to the surface

of concrete after it has been finished. As soon as free water on the surface has

evaporated and there is no water seen visible.

They may also be used to reduce the moisture loss from concrete after initial

moist curing or removal of form work. In case of columns and beams the application is

done after the removal of formwork on the horizontal surface; the curing compound is

applied upon the complete disappearance of all bleeding water.

After spraying, no further application of water or other material is necessary to

ensure continued curing. The concrete surface should not be disturbed until it has

sufficient strength to bear surface loads. The applied film should not be walked on

before it is fully dry and care should be taken to ensure that the film is not broken.

In case the concrete surface has dried, the surface should be sprayed with water

and thoroughly wetted and made fully damp before curing compound is applied. The

container of curing compound should be well stirred before use. It takes nearly 10 to 15

minutes for its drying and drying and it forms a thin water proofing film on the surface.

The fundamental conclusion shows that the efficiency test indeed is significant and

worthwhile test, yielding very reasonable test conclusion. Also at an age other than 7

days, a good correlation can be found between the compressive strength and the

evaporation.

B.Mangaiarkarasa and S.R.Damodaraswamy conducted compressive test on concrete

cubes of 150mm size, the curing compound used is CONCURE WB. Based on the

results of the investigation, they concluded the following.

Self curing concrete develops higher compressive strength then the water cured

concrete in three days.





Self curing concrete using wax based curing has an average efficiency of 84.0%.

Self cured concrete satisfies serviceability conditions also.

Self curing concrete can be practiced in pre fabrication units and in place of

water scarcity as well as exposed weather condition.

Whenever there is difficulty in water curing, self curing concrete will be very

economical in remote areas as well as in water scarcity area.

By adapting self curing compound concrete the sustainable development of

environment is maintained there is no doubt that self curing concrete play a vital role

and dominate the construction industry in future.

CHAPTER 3CHAPTER 3





EXPERIMENTAL METHODOLOGY

3.1 Introduction

External self curing concrete is the one which can cure itself by retaining its

moisture content. Concrete can made to self cure by the application of curing

compounds on the surface of the concrete. The curing compound is applied by means of

brushing or spraying.

3.2 Curing compound

The curing compound used is “CONCURE WB” which is a product of Fosroc

chemicals.

CONCURE WB is water based concrete curing compound based on a low

viscosity wax emulsion. It is supplied as a white emulsion which forms a clear film on

drying. When first applied to a fresh cementitious surface the emulsion breaks to form a

continuous, non-penetrating white coating. This dries to form a continuous clear film

which provides a barrier to moisture loss, ensuring more efficient cement hydration,

improved durability and reduced shrinkage.

3.2.1 Specifications of CONCURE WB

Base –wax

Shelf life – 12 months

Coverage – 3.5 to 5 m2/litre

Cost - Rs.90/litre

Specific gravity-0.98 at 25 °C

3.2.2 Features





single application

no other curing necessary

easy and safe spray application

endures hard wearing surface

3.2.3 Application procedure

The curing compound is applied by brush or by spraying while the concrete is

wet. In case of columns and beams the application is done after the removal of

formwork. On the horizontal surface, the curing compound is applied upon the complete

disappearance of all bleeding water.

After spraying, no further application of water or other material is necessary to

ensure continued curing. The concrete surface should not be disturbed until it has

sufficient strength to bear surface loads. The applied film should not be walked on

before it is fully dry and care should be taken to ensure that the film is not broken.

In case the concrete surface has dried, the surface should be sprayed with water and thoroughly wetted and made fully damp before curing compound is applied. The

container of curing compound should be well stirred before use. It takes nearly 10 to 15

minutes for its drying and drying and it forms a thin water proofing film on the surface.

As shown in Fig: 3.1.





Fig 3.1 Application of external self curing compound.

3.2.4 Uses of external self curing concrete

As a spray applied membrane to retain moisture in concrete for effective curing.

Suitable for all general concreting applications and of particular benefit for large

area concrete surfaces, such as airport runways, roads and bridgeworks.

It is also suitable for piece works. Where, it is difficult to curing.

It is also suitable for tunnel linings.





3.2.5 Advantages of external self curing concrete

Improved curing of concrete enhances cement hydration and provides a more

durable concrete.

Control of moisture loss improves surface quality, reducing permeability,

producing a hard wearing; dust free Surface and minimizing potential for surface

cracking and shrinkage.

Fugitive colour provides visual guide during application.

Water based, therefore, non-flammable.

Spray application reduces labour costs and eliminates the need for alternative

curing systems.





CHAPTER 4CHAPTER 4

TEST ON INGREDIENT MATERIALS

4.1 Introduction

The present investigation is carried out to study the behavior of normal and self

curing cured concrete and ingredient material by using O.P.C. 53 grade cement. The

tests were carried out at the Civil Engineering Laboratory of Civil Engineering

Department, AIT Chikamagalur.

4.2 Materials used and their properties

It is well known that strength of the concrete is dependent on the properties of its

ingredients. The materials used in the present investigations are as follows.

• 53 grade O.P.C.

• River sand as fine aggregate

• Quarried and crushed stone as coarse aggregate

• Potable water

4.3 Test on cement

The specific gravity, normal consistency, initial setting time, final setting time

and compressive strength of cement were found as per B.I.S specifications. The results

are tabulated in tables.

4.4 Test on fine aggregate

53 grade O.P.C. was used throughout the investigations. The cement was tested

according to B.I.S. specifications to determine its various properties. The overall





quantity of cement required for the investigation was procured in a single lot and stored

in the appropriate manner.

The specific gravity of natural sand was found according to the norms of the

Indian Standards and was used throughout in preparing the required mix of concrete.

Results are tabulated in table.

Sieve analysis of the fine aggregate was also carried out as per the B.I.S.

specifications to determine the grading zone. The results of sieve analysis are tabulated

in table.

4.5 Tests on coarse aggregate

The specific gravity of crushed stone aggregates of 20mm and downsize was

found according to the norms of Indian standards and were used for all concrete mixes.

The results are tabulated in table.

Sieve analysis of the coarse aggregate was also carried out as per B.I.S.specifications. The results are tabulated in table.

4.6 Specimen details

Two types of specimens namely cubes and cylinders were cast. Cubes were used

for compressive strength test and Cylinders for split tensile strength test.

4.7 Curing of the test specimens

The specimens are stored in the laboratory atmosphere for 24 hours from the

time of adding water to the ingredients. Temperature was maintained at 270 ± 20C. The

specimens were removed from the moulds after 24 hrs and then kept immersed in clean

water for the required age. The water in the tank was changed every week and the

temperature was maintained constant.





4.8 Testing of the specimens

The testing was carried out according to B.I.S. specifications.

Table4. 1 Results of test on cement

Particulars references

-

-

Type of cement 53 grade

O.P.C.

-------------

1 Normal Consistency 34.00 % IS:269-1958

2 Specific Gravity 2.85 IS:269-19763 Setting time (in min)

(a) Initial setting time

(b) Final setting time

80 min.

460 min.

IS: 269-1976

Should more

Than 30 min.

Should not be

More than 600min.

Table 4.2 Compressive Strength of Cement

Size of the specimen=70.6mm X 70.6mm X 70.6mm

Sl.No. Particulars Compressive strength in N/mm2

Type of cement 3 days 7 days 28 days

1 53 grade O.P.C 30.20 45.70 59.80

Table 4.3 Properties of the aggregate used





Sl

No.

Particulars Fine

Aggregate

Coarse

Aggregate

Reference

1 Specific gravity 2.50 2.60 IS:2386(partIII)-1963

2 Fineness

modulus

2.85 7.13 Is;2836(partIII)-1963

IS:383-1970

IS:460-1962

3 Grading zone Zone II 20 mm and

Downsize

IS 383-1963

Table 4.4 Sieve analysis of fine aggregate

Weight of sample taken =1000gm

Sl.No IS sieve

size

Weight

retained(gm)

Cumulative

Wt. retained

Cumulative % Wt.

retained

% finer

1 10mm 0 0 0 100.00

2 4.75mm 24 24 2.40 97.60

3 2.36mm 32 56 5.60 94.40

4 1.18mm 180 236 23.60 76.405 600μ 394 630 63.00 37.00

6 300 μ 282 912 91.20 8.80

7 150 μ 84 996 99.60 0.40

∑=285.40

Calculations

Fineness modulus = 285.40/100 =2.85

Table 4.5 Sieve analysis of coarse aggregate

Weight of sample taken =2000gms





Sl.No

IS sieve

Size

Wt.

retained

Cumulative

Wt.retained

Cumulative

% wt.retained

%finer

1 80mm 0 0 0 100

2 40mm 0 0 0 100

3 20mm 560 560 28.00 72.00

4 10mm 1152 1712 85.60 14.40

5 4.75mm 276 1988 99.40 0.60

6 2.36mm 09 1997 99.85 0.15

7 1.18mm 03 2000 100.00 0.00

8 600 0 2000 100.00 0.00

9 300 0 2000 100.00 0.00

10 150 0 2000 100.00 0.00

∑ =712.85

Calculations

Fineness modulus =712.85/100

=7.13

CHAPTER 5CHAPTER 5

TESTS ON FRESH CONCRETE

5.1 Workability of concrete

Workability is defined as the amount of useful internal work necessary to

achieve full compaction. It is also defined as the ease with which concrete can be placed

and degree to which it resists segregation. It is also given a new definition which





includes all the essential properties of the concrete in plastic condition i.e. mixing

ability, transportability, modulability and ease compaction.

5.1.1 Factors that affecting the workability of concrete

• Relative quantities of paste and aggregate.

• Plasticity of the paste itself.

• Maximum size and grading of aggregate.

• Shape and surface characteristics of aggregate particle.

Consistency of the concrete is an important component of workability and refers in a

way to the wetness of concrete. However it must be assumed that the wetter the mix

more workable it is. If a mix is too wet, segregation may occur resulting in honey

combing, excessive bleeding and sand streaking on the formed surfaces. On the other

hand if the mix is too dry it may be difficult to place and compact and segregation may

occur because of lack of cohesiveness and plasticity of the plastic.

In the present investigations workability connected with physical quantity is correlated

by slump test, compaction factor test and Vee-Bee consistometer test. The merit of Vee-

Bee test is that it simulates atleast in some respects, the compaction of concrete by

vibration in practice.

5.1.2 Slump test

Slump test gives an idea about consistency of concrete mix and indirectly

measures workability of the concrete. Depending on the slump values of concrete can be

classified into different categories as per IS: 1199-1959.

Table 5.1 Slump values of concrete mixes

Classification of concrete Slump value (mm)Stiff 0





Poorly mobile 10-30

Mobile 40-150

Cast mix >150

In this investigation work, slump test was conducted for all types of cement chosen for

grades M25 and the results are tabulated in the below table.

Table 5.2 Slump test values of ESC concrete mixes

Sl.No. Grade of concrete w/c ratio Slump (mm)

1 M25 O.P.C. 0.55 90

5.1.3 Compaction factor test

The compaction factor is defined as the ratio of weight of partially compacted

concrete to weight of fully compacted concrete. This test mainly deals with the amount

of energy required to compact a particular mix of concrete, which is a measure of

workability. The test gives a rough idea of workability of the given concrete mix.

Depending upon the compaction factor test values the concrete mix can be classified

into different categories as per IS: 1199-1959.





Table 5.3 Compaction factor values

Compaction factor Quantity of mix

0.95 Good

0.92 Medium

0.85 Bad(poor)

CHAPTER 6CHAPTER 6

TESTS ON HARDENED CONCRETE

6.1 Details of the standard specimens





Two types of specimens namely cubes and cylinders were cast. Cubes were used

for compression strength test and cylinders for split tensile strength test.The details of

the standard specimens used in the investigation are shown in table.

Table 6.1 Details of the standard specimens

Type of test Type of specimen Dimensions (mm)

Compression test Cubes 150 x 150 x 150

Split tension test Cylinder 100 x 200 depthᴓ

6.2 Test for compressive strength

The specimens were removed from the curing tank and its surfaces are cleaned

with cotton waste. They were tested in wet condition in a Compression Testing

Machine. The rate of loading was maintained at 140 kg/cm2/minute as per the

requirements given in the code of practice (IS: 516-1969). Three specimens of 150mm

cubes were tested for required age and the average value of compressive strength was

calculated. The results of compressive strength test were tabulated in table.

Table 6.2 Average Compressive strength of conventionally cured concrete

Type of cement Compressive strength, MPa (N/mm2)

3 days 7 days 28 days

OPC 53 grade 14.07 25.77 33.48





Table 6.3 Average Compressive strength of external self cured concrete

Type of cement Compressive strength, MPa (N/mm2)


OPC 53 grade 17.18 27.12 34.59

6.3 Tests for Split Tensile Strength

The tests were performed while they were in wet condition in Compression

Testing Machine. Three specimens were tested and the mean value was computed and

the results were tabulated in table 6.4





Table 6.4 Average Split tensile strength of conventionally cured concrete

Type of cement Split tensile strength, MPa (N/mm2)


OPC 53 grade 1.01 1.17 1.91

Table 6.5 Average Split tensile strength of external self cured concrete:

Type of cement Split tensile strength, MPa (N/mm2)


OPC 53 grade 1.06 1.30 2.31

CHAPTER 7CHAPTER 7

RESULTS AND DISCUSSIONS

7.1 Setting time of cement





The initial and final setting time of the cement (53 grade O.P.C) are shown in the

table (1).

7.2 Workability of concrete

The workability test results with respect to slump test are tabulated in table (6)

7.3 Compressive strength of concrete

Normally compressive strength of the concrete is a measure of quality of

concrete for a particular mix. The results of the compressive strength are tabulated in

table 7 & 8 and variations are shown in fig.

7.3.1 Comparison between the compressive strength of conventional cured

concrete and external self cured concrete

From the test results it is observed that the 3, 7 and 28 day’s compressive

strength of external self cured concrete is more than that for conventional cured

concrete.

It is observed that the increase in compressive strength of external self cured

concrete is about 22.10% at the age of 3 days, 5.24% at the age of 7 days and 3.32% at

the age of 28 days as compare to conventional cured concrete.

7.4 Splitting tensile strength of concrete

Split tensile strength is the method of determining tensile strength of concrete.

The results and variations of split tensile strength are tabulated in table 9 & 10. And

variations are shown in fig.





7.4.1 Comparison between the split tensile strength of conventional

cured concrete and external self cured concrete

From the test results it is observed that the 3, 7 and 28 days split tensile strength

of external self cured concrete is greater than that for conventional cured concrete.

It is observed that the increase in split tensile strength of external self cured

concrete is about 4.95% at the age of 3 days, 11.11% at the age of 7 days and 20.94% at

the age of 28 days as compare to conventional cured concrete.

CHAPTER 8CHAPTER 8

CONCLUSION AND SCOPE FOR FURTHER STUDIES

8.1 Conclusion





The following conclusions are drawn based on the present investigations.

• The variation between concrete cured conventionally and with self curing

compound is about 3.32% for compression strength and 20.94% for split tensile

strength.

• Hence self curing technique may be economically and efficiently adapted in

remote as well as in water scarcity areas.

• The surface of the self cured cement paste is less permeable to water vapour than

that of normal cured cement paste.

• Curing compound increases early strength of concrete than normal cured

concrete.

• Concrete with curing compound gives smooth and fine finished surface than

concrete without curing compound.

• About 100% of results have been attained in compressive strength with small

amount of water this method can be implemented in construction field.

8.2 Scope for further studies

• Based on the above studies and observations made, following works are

suggested for future studies.





• The study may be carried out for longer period beyond 28 days of curing.

• The study may be carried out to test the resistance of concrete against acid attack

and sulphate attack also.

• The study can be carried out for different grades of concretes with different

cements like Portland slag cement, Portland pozzolana cement, of different

grades.

• The study can be carried out for different field curing conditions and also for

different weather conditions.





Fig 1: Average compressive strength of conventionally cured concrete.

Fig 2: Average compressive strength of external self cured concrete.





Fig.3: Comparison between average compressive strength of external

self cured concrete and conventionally cured concrete





Fig.4: Average split strength of external self cured concrete.





Fig.5: Average split strength of conventional cured concrete.

Fig.6: Comparison between average split tensile strength of external

self cured concrete and conventionally cured concrete









Fig.7: EXTERNAL SELF CURING COMPOUND USED IN PIECE

WORK





Fig.8: Compression Testing Machine (Cube Testing)





Fig.8: Compression Testing Machine (Cylinder testing)









DESIGN OF CONCRETE MIX

(As per IS: 10262-2009)

DESIGN BY IS 10262-2009 METHOD

Design stipulations:

• Characteristic compressive strength required in the field at 28 days 25N/mm2

• Degree of quality control Good

• Type of exposure Mild

Test data for materials

Cement used Ordinary Portland cement

Grade of cement 53 grade

Specific gravity of cement 2.85

Specific gravity of fine aggregate 2.50

Specific gravity of coarse aggregate 2.60

Slump value 90 to 100mmMaximum size of aggregate 20mm

Fine aggregate falls into Zone-II

Target mean strength of concrete:

fck 1 = fck + (1.65 x S)

= 25 + (1.65 x 4.0)

= 31.60 N/mm2.

fck 1 = Target average compressive strength at 28 days,

fck= Characteristic compressive strength at 28 days,

s = Standard deviation





From table no.01 of IS10262-2009, S=4 N/mm2

Selection of water cement ratio:

From table no. of IS456-2000 maximum, W/C ratio =0.55

(For mild exposure condition)

Selection of water content:

From table 2 of IS10262-2009 for 20mm nominal maximum size aggregate and

fine aggregate conforming to grading zone 2 and for 25-50mm slump range maximum

water content per cubic meter of concrete =186 kg.

Estimated water content for 90mm slump = 186 + (6/100) x 186

= 197 Kg/m3

Calculation of cement content:

W/C ratio = 0.55

Cement content = 197/0.55

. = 358.18 Kg/m3

From table no.05 of IS456-2000 minimum cement

For mild exposure condition = 300Kg/m3





Therefore 358.183 Kg/m3 >300Kg/m3

Hence ok

Proportions of volume of coarse aggregate and fine aggregate content

From table 3, volume of coarse aggregate corresponding to 20 mm size

aggregate and fine aggregate zone2, for W/C ratio of 0.50=0.62

In the present water–cement ratio is 0.55 therefore volume of coarse aggregate is

required to be decreased to increase the fine aggregate content. As the water cement

ratio is lower by 0.10 the proportion of volume of coarse aggregate is increased by

0.01(at rate of -/+ 0.01 for every +/- 0.05 change in water cement ratio).

Here, W/C ratio = 0.55, therefore W/C ratio is increased by 0.05 correspondingly

the volume of coarse aggregate is lower by 0.01

Therefore, the volume of coarse aggregate = 0.61

Volume of fine aggregate = 1-0.61=0.39

Mix calculation:

The mix calculation per unit volume of concrete shall be as follows.





a) Volume of concrete = 1 m3

b) Volume of cement *

= 358.18 / (2.85 x 1000)

= 0.126 m3

c) Volume of water *

= 197 / (1 x 1000)

= 0.197 m3

d) Volume of aggregate = 1 - 0.126 - 0.197

= 0.677 m3

e) Mass of coarse aggregate = volume of aggregate x proportion of aggregate x

specific gravity of aggregate x 1000

= 0.677 x 0.61 x 2.60 x 1000

= 1073.72 Kg

f) Mass of fine aggregate = volume of aggregate x proportion of aggregate x

specific gravity of aggregate x 1000

= 0.677 x 0.39 x 2.50 x 1000

= 660.08 Kg

Mix proportion for 1 m3 concrete





W/C ratio Water

In litre

Cement

In Kg

Fine aggregate

In Kg

Coarse

aggregate in Kg

0.55 197 358.18 660.08 1073.72

1 1.84 3.00

BIBLIOGRAPHY

1. Data sheet on “Curing of concrete “, “Cement, concrete and aggregates”,

Australia, April 2006.





2. V.Mangiarkarasi and S.R.Damodeva swamy “Self curing concrete today’s and

tomorrow”s mud of constuructionneed of construction world” proceeding of the

international conference on “recent advances in concrete and construction

technology INCRAC AND CT 2005” ,Dec 7-9, 2005, SRMIST, Chennai, India.

Pp 423-434.

3. Ragu Prasad.P.S., “Comparative study of Blended Cement Composites with 43

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4. R.Marks, N.gowri Palana, R, Sun “Errly Age Properties of Self cured Concrete”.

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Bangalore.

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Concrete” Proceedings of the international conference on “Innovation and

Development of Concrete Materials and Constructions “ held at the University of

Dundee, Scotland , UK on 9-11 Sept 2002. Pp. 408-404.

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Retention Test for Curing Compounds” Materials and Structures/Materiaux ET

Constructions, Volume 35, Aug 2002, Pp. 408-404.

7. IS: 383, (1970), “Specification for coarse and fine aggregates from natural

sources for concrete”, (Second version), BIS , New Delhi

8. IS: 456, (2000), “Plain and reinforced concrete-code of practice”, BIS , NewDelhi





9. IS: 5816, (1999), “Splitting tensile strength of concrete-method of test”, BIS ,

New Delhi

10. IS: 516, (1959), (Reaffirmed 1999), “Methods for test of concrete”, BIS , New

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