APROJECT REPORT

ON

INTERNAL CURING OF HIGH PERFORMANCE CONCRETE

SUBMITTED BY

SOMDATT DAHIYA

09EELCE055

IN PARTIAL FULFILLMENT OF

THE REQUIREMENT FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

CIVIL ENGINEERING

OF

GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN

UNDER THE GUIDANCE

OF

Er. Amit Daiya

DEPARTMENT OF CIVIL ENGINEERING

GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN

2012-2013

APROJECT REPORT

ON

INTERNAL CURING OF HIGH PERFORMANCE CONCRETE

-: SUBMITTED BY:-

Mr. RAMESH KUMAR 09EELCE044

Mr. SOMDATT DAHIYA 09EELCE055

Mr. YASHPAL SINGH 09EELCE063

Mr. ANKUR GUPTA 09EELCE004

Mr. MUKESH KUMAR 09EELCE027

Mr. SUNIL KR. SHARMA 10EELCE207

Mr. MANISH KUMAR 10EELCE205

Mr. RAGHVENDRA SINGH 10EELCE206

Mr. JITENDRA SINGH 10EELCE204

Miss. USHA MEENA 09EELCE059

Miss. SONIA GUPTA 09EELCE056

Mr. DHANRAJ MEENA 09EELCE0

UNDER THE GUIDANCE

OF

Er. Amit Daiya

DEPARTMENT OF CIVIL ENGINEERING

GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN

2012-2013

CERTIFICATEThis is to certify that, the project entitled

INTERNAL CURING OF HIGH PERFORMANCE CONCRETE

Submitted by

Mr. SOMDATT DAHIYA

Is a record of his own work carried out by him in partial fulfillment for the award of

BACHELOR OF TECHNOLOGY

IN

CIVIL ENGINEERING

Govt. engineering college, Bharatpur, rajasthan

Under my guidance during the academic year

2012-2013

Dr. Biswajit Acharya Er. Amit Daiya (Project Advisor) (Project Guide & H.O.D)

Date : Place:BHARATPUR

DEPARTMENT OF CIVIL ENGINEERING

GOVT. ENGINEERING COLLEGE, BHARATPUR

2012-2013

Acknowledgement

When we take a glance over our journey throughout the year, few respectful and friendly faces and encouragement come across our mind. What we remember the most is the immense help, guidance and teachings of our project guide Er. Amit Daiya without whom working in this project would have been walking on an unknown path. He who has taken sincere efforts to lead us, he who taught us how to plan, work and analyze and he who made us discover our hidden qualities will be always remembered by us for the teachings and principles he taught us during the project course. We would like to thank him for being such an excellent teacher, a perfect guide, a strict disciplinarian, an indefatigable leader and a true friend.

We are grateful to Er. Priyanka Gupta for their timely and valuable guidance. We are grateful for the guidance and kind support of Dr. Biswajit Acharya. We would like to extend our gratitude towards the supporting staff for being very helpful. We are very grateful to those who in the form of books had conveyed guidance in this project work.

At last, we would like to thank our friends and family for their support and encouragement throughout the

year.

Mr. SOMDATT DAHIYA

B.TECH CIVIL ENGINEERING

CHAPTER NO. DESCRIPTION PAGE NO.

0

ABSTRACT i

LIST OF TABLES ii

LIST OF FIGURES ii

1.

INTRODUCTION 1

1.1 OBJECTIVE 1

1.2 SIGNIFICANCE OF THE PROJECT 1

1.3 DEFINITION OF INTERNAL CURING 1

1.4 NECESSITY OF INTERNAL CURING 2

1.5 POTENTIAL MATERIALS FOR IC 2

1.6 ADVANTAGES OF INTERNAL CURING 2

1.7 CONCRETE DEFICIENCIES THAT IC CAN ADDRESS 3

1.8 IMPROVEMENTS TO CONCRETE DUE TO IC 4

1.9 SUMMARY 4

2.

SUPER ABSORBENT POLYMERS 5

2.1 GENERAL 5

2.2 SUPER ABSORBENT POLYMERS FOR IC 5

2.3 SUMMARY 6

3.

LITERATURE REVIEW 7

3.1 GENERAL 7

3.2 REVIEW OF LITERATURE 7

3.3 SUMMARY 13

4. EXPERIMENTAL PROCEDURE 14

4.1 CONSTITUENT MATERIALS USED 14

4.1.1 Cement 14

4.1.2 Aggregates 15

4.1.3 Super Plasticizers 16

4.1.4 Silica Powder 16

4.1.5 Super Absorbent Polymers 17

4.2 FRESH CONCRETE PROPERTIES 18

4.2.1 Slump Test 18

4.3 HARDENED CONCRETE PROPERTIES 18

4.3.1 Compression Test on concrete cubes 18

4.3.2 Tensile strength of concrete 19

4.3.3 Flexural Strength of concrete 19

4.3.4 Modulus of Elasticity 19

4.4 TESTING PROCEDURE 19

4.5 SUMMARY 20

5.

MIX DESIGN 21

5.1 DEFINITION 21

5.2 OBJECTIVE OF MIX DESIGN 21

5.3 FACTORS TO BE CONSIDERED IN MIX DESIGN 21

5.4 MIX DESIGN 22

6.

RESULTS AND DISCUSSION 25

6.1 FRESH CONCRETE PROPERTIES 25

6.2 MECHANICAL PROPERTIES 25

6.2.1 Compressive Strength 25

6.2.2 Split Tensile Strength 25

6.2.3 Flexural Strength 26

6.2.4 Modulus of Elasticity 26

6.3 COMPARISON OF RESULTS 27

6.4 SUMMARY 29

7. CONCLUSIONS 31

7.1 GENERAL 31

7.2 CONCLUSIONS 31

8.

SCOPE FOR FUTURE WORK 32

8.1 GENERAL 32

REFERENCES 33

PUBLICATIONS 36

i

ABSTRACT

Proper curing of concrete structures is important to ensure that they meet their

intended performance and durability requirements. Therefore an effective in situ curing is

necessary to maximize the degree of hydration and to minimize the cracking problems due to

drying shrinkage.

Traditional external curing could not achieve a desired effect due to the very low

permeability of high-performance concrete, so some researchers shifted their attention to

internal curing, a new curing method that may greatly enhance the curing effect on high-

performance concrete.

High-performance concrete, which has a low water-binder ratio (w/b) and is often

incorporated with highly active mineral admixtures such as silica fume, has been widely used in

long span bridges and high-rise buildings because of its excellent mechanical performance. It is

also accompanied with more severe self-desiccation at early ages, however, and is thus more

prone to autogenous shrinkage (AS) and cracking.

The low water-cement (w/c) ratio (below ~0.4) of HPC, which is necessary for the

enhancement of strength and durability, leads to a so-called self-desiccation of concrete, as a

result of the cement hydration process. This causes considerable volume changes known as

autogenous shrinkage, which in turn lead to concrete cracking. The internal curing (IC) of

concrete using small, well distributed water reservoirs seems to be able to solve this problem.

IC is the process by which water is provided throughout the concrete to enhance cement

hydration. Internal curing can be achieved in two different ways. (i) By partially replacing fine

aggregates by Light Weight Saturated Aggregates, (ii) By adding Super Absorbent Polymers.

Super Absorbent Polymers (SAP) are a group of polymeric materials that have the ability to

absorb and retain a significant amount of liquid from their surroundings and to retain the liquid

within their structure without dissolving.

In this study it is experimentally examined about the influence of IC on the mechanical

properties of HPC. Several percentages of SAP are added and the properties are analyzed.

ii

LIST OF TABLES

SL.NO. DESCRIPTION PAGE NO.

1. Table 1: Mix Proportion 24

2. Table 2: Fresh Concrete Properties 25

3. Table 3: Compressive Strength Results 26

4. Table 4: Split Tensile Strength 26

5. Table 5: Flexural Strength 27

6. Table 6: Modulus of Elasticity 27

LIST OF FIGURES

SL.NO. DESCRIPTION PAGE NO.

1. Figure1: Super Absorbent Polymer 6

2. Figure 2: SAP before and after addition of water 6

3. Figure 3: Moulds 24

4. Figure 4: Comparison of Compressive Strength 27

5. Figure 5: Comparison of Split Tensile Strength 28

6. Figure 6: Comparison of Flexural Strength 28

7. Figure 7: Comparison of Elastic modulus 29

8. Figure 8: Compression Test 30

9. Figure 9: Flexure Test 30

1

CHAPTER 1

INTRODUCTION

1.1 OBJECTIVE

To incorporate internal curing of HPC by means of Super Absorbent

Polymers.

To study the effect of different compositions of SAP on mechanical

properties of HPC.

1.2 SIGNIFICANCE OF THE PROJECT

Now-a-days HPC has become an object of intensive research due to its growing

use in the construction practice. However, low w/c ratio (below 0.4) of HPC, which

is necessary for the enhancement of strength and durability, leads to self desiccation

of concrete, as a result of cement hydration process. This causes considerable

volume changes, which in turn lead to cracking as well as strength reduction.

Internal Curing of concrete using small well distributed water reservoirs seems

to be able to solve this problem. In this study, the effect of Super Absorbent

Polymer as an agent for internal curing on mechanical strengths of concrete with

low w/c is investigated.

The effects of adding polymer on mechanical strength of concrete are studied

experimentally and the results are discussed.

1.3 DEFINITION OF INTERNAL CURING (IC)

The ACI-308 Code states that “internal curing refers to the process by

which the hydration of cement occurs because of the availability of additional

internal water that is not part of the mixing Water.” Conventionally, curing concrete

means creating conditions such that water is not lost from the surface i.e., curing is

taken to happen ‘from the outside to inside’. In contrast, ‘internal curing’ is

allowing for curing ‘from the inside to outside’ through the internal reservoirs (in

2

the form of saturated lightweight fine aggregates, super absorbent polymers, or

saturated wood fibres) Created. ‘Internal curing’ is often also referred as ‘Self–

curing.’

1.4 NECESSITY OF INTERNAL CURING (IC)

Conventionally, curing concrete means creating conditions such that water is

not lost from the surface i.e., curing is taken to happen ‘from the outside to

inside’. In contrast, ‘internal curing’ is allowing for curing ‘from the inside to

outside’ through the internal reservoirs (in the form of saturated lightweight

fine aggregates, super absorbent polymers, or saturated wood fibres) Created.

‘Internal curing’ is often also referred as ‘Self–curing.’

Often specially in HPC, it is not easily possible to provide curing water from

the top surface at the rate required to satisfy the ongoing chemical shrinkage,

due to the extremely low permeabilities often achieved.

1.5 POTENTIAL MATERIALS FOR INTERNAL CURING

The following materials can provide internal water reservoirs:

Lightweight Aggregate (natural and synthetic, expanded shale),

LWS Sand (Water absorption =17 %)

LWA 19mm Coarse (Water absorption = 20%)

Super-absorbent Polymers (SAP) (60-300 mm size)

SRA (Shrinkage Reducing Admixture) (propylene glycol type i.e.

polyethylene-glycol)

Wood powder

1.6 ADVANTAGES OF INTERNAL CURING

a. Internal curing (IC) is a method to provide the water to hydrate all the

cement, accomplishing what the mixing water alone cannot do. In low w/c

3

ratio mixes (under 0.43 and increasingly those below 0.40) absorptive

lightweight aggregate, replacing some of the sand, provides water that is

desorbed into the mortar fraction (paste) to be used as additional curing

water. The cement, not hydrated by low amount of mixing water, will

have more water available to it.

b. IC provides water to keep the relative humidity (RH) high, keeping self-

desiccation from occurring.

c. IC maintains the strengths of mortar/concrete at the early age (12 to 72

hrs.) above the level where internally & externally induced strains can

cause cracking.

d. IC can make up for some of the deficiencies of external curing, both

human related (critical period when curing is required is the first 12 to 72

hours) and hydration related (because hydration products clog the

passageways needed for the fluid curing water to travel to the cement

particles thirsting for water).

Following factors establish the dynamics of water movement to the unhydrated

cement particles:

i. Thirst for water by the hydrating cement particles is very intense,

ii. Capillary action of the pores in the concrete is very strong, and

iii. Water in the properly distributed particles of LWA (fine) is very

fluid.

1.7 CONCRETE DEFICIENCIES THAT IC CAN ADDRESS

The benefits from IC can be expected when

Cracking of concrete provides passageways resulting in deterioration of

reinforcing steel,

low early-age strength is a problem,

4

permeability or durability must be improved,

Rheology of concrete mixture, modulus of elasticity of the finished product or

durability of high fly-ash concretes are considerations.

Need for reduced construction time, quicker turnaround time in precast plants,

lower maintenance cost, greater performance and predictability.

1.8 IMPROVEMENTS TO CONCRETE DUE TO IC

Reduces autogenous cracking,

largely eliminates autogenous shrinkage,

Reduces permeability,

Protects reinforcing steel,

Increases mortar strength,

Increases early age strength sufficient to withstand strain,

Provides greater durability,

Higher early age (say 3 day) flexural strength

Higher early age (say 3 day) compressive strength,

Lower turnaround time,

Improved rheology

Greater utilization of cement,

Lower maintenance,

use of higher levels of fly ash,

higher modulus of elasticity, or

greater curing predictability,

5

higher performance,

does not adversely affect pumpability

Reduces effect of insufficient external curing.

1.9 SUMMARY

Definition, advantages and necessity of Internal Curing is studied in detail and the

materials those can be used for IC are analysed.

CHAPTER 2

SUPER ABSORBENT POLYMERS

2.1 GENERAL

Super absorbent polymers (also called slush powder) are polymers that can absorb

and retain extremely large amounts of a liquid relative to their own mass.

Water absorbing polymers, which are classified as hydro gels when cross-linked;

absorb aqueous solutions through hydrogen bonding with water molecules. A SAP's

ability to absorb water is a factor of the ionic concentration of the aqueous solution. In

deionized and distilled water, a SAP may absorb 500 times its weight (from 30–60 times

its own volume), but when put into a 0.9% saline solution, the absorbency drops to

maybe 50 times its weight.

The total absorbency and swelling capacity are controlled by the type and degree

of cross-linkers used to make the gel. Low density cross-linked SAP generally has a

higher absorbent capacity and swells to a larger degree. These types of SAPs also have a

softer and stickier gel formation. High cross-link density polymers exhibit lower

6

absorbent capacity and swell, but the gel strength is firmer and can maintain particle

shape even under modest pressure.

2.2 SUPER-ABSORBENT POLYMER (SAP) FOR IC

The common SAPs are added at rate of 0–0.6 wt % of cement. The SAPs are

covalently cross-linked. They are Acrylamide/acrylic acid copolymers. One type of SAPs

are suspension polymerized, spherical particles with an average particle size of

approximately 200 mm; another type of SAP is solution polymerized and then crushed

and sieved to particle sizes in the range of 125–250 mm. The size of the swollen SAP

particles in the cement pastes and mortars is about three times larger due to pore fluid

absorption. The swelling time depends especially on the particle size distribution of the

SAP. It is seen that more than 50% swelling occurs within the first 5 min after water

addition.

Fig.1 Super Absorbent Polymer

7

Figure 2: SAP before and after addition of water

2.3 SUMMARY

The physical and chemical properties of Super Absorbent Polymers and their

applications in the field of Civil Engineering is studied in detail in this chapter.

CHAPTER 3

LITERATURE REVIEW

3.1 GENERAL

In this chapter literature survey on the topics of application of internal curing to

high performance concrete with various materials and to measure various parameters

such as autogenous shrinkage etc., is presented.

3.2 REVIEW OF LITERATURE

8

3.2.1. “Mitigating Autogenous Shrinkage by Internal Curing” by M.R. Geiker et.al, American Concrete Institute, Special Publication. (15)

The use of internal curing is a highly effective means of mitigating autogenous

shrinkage in cement mortars (w/cm=0.35, 8 % silica fume). Two different sources of

internal water supply are compared: 1) replacement of a portion of the sand by partially

saturated lightweight fine aggregate and 2) the addition of super absorbent polymer

particles (SAP). At equal water addition rates, the SAP system is seen to be more

efficient in reducing autogenous shrinkage at later ages, most likely due to a more

homogeneous distribution of the extra curing water within the three-dimensional mortar

microstructure. A comparison of the water distribution in the different systems, based on

computer inodeling and direct observation of two-dimensional cross sections, is given.

3.2.2. “Internal curing of high-performance concrete with pre-soaked fine light

weight aggregate for prevention of autogenous shrinkage cracking” by Daniel

Cusson et.al, Cement and Concrete Research 38. (6)

The effectiveness of internal curing (IC) to reduce autogenous shrinkage cracking

in high-performance concrete (HPC) was investigated using different levels of internal

curing on four pairs of large-size prismatic HPC specimens tested simultaneously under

free and restrained shrinkage. Internal curing was supplied by pre-soaked fine

lightweight aggregate (LWA) as a partial replacement to regular sand. It was found that

the use of 178 kg/m3 of saturated LWA in HPC, providing 27 kg/m3 of IC water

eliminated the tensile stress due to restrained autogenous shrinkage without

compromising the early-age strength and elastic modulus of HPC. It was shown that the

risk of concrete cracking could be conservatively estimated from the extent of free

shrinkage strain occurring after the peak expansion strain that may develop at very early

ages. Autogenous expansion, observed during the first day for high levels of internal

curing, can significantly reduce the risk of cracking in concrete structures, as both the

elastic and creep strains develop initially in compression, enabling the tensile strength to

increase further before tensile stresses start to initiate later.

9

3.2.3. “High Performance Concrete Enhancement through Internal Curing” by

John Roberts, Northeast Solite Corporation. (13)

Internal curing (IC) in place of, or as an adjunct to, external curing can assure that

results contemplated through HPC will be achieved and improved. Problems resulting

from low water-cement (w/c) ratio concretes, such as autogenous shrinkage, have been

identified, and research and field experience show us how IC will resolve them. Concrete

can be improved by the substitution, for a small amount of natural sand in the mixture, of

an equal volume of crushed structural grade absorbent lightweight aggregate sand

(LWAS). Most expanded shale lightweight aggregates have the ability to absorb 15% or

more by weight of water and this absorbed water is immediately available to hydrate the

cement particles deprived of mixing water in low w/c ratio concretes. This occurs through

prompt release of the water as the concrete cures and the mixing water is used up.

3.2.4. “Extending internal curing to concrete mixtures with W/C higher than 0.42”

by Gaston Espinoza-Hijazin et.al, Construction and Building Materials. (11)

To obtain the required durability, strength and high performance during the life cycle of

the structure, curing concrete is crucial from the first hours after its setting. Therefore, an

effective in situ curing is required to maximize degree of hydration of cementitious

material and to minimize cracking problems due to drying shrinkage. Hydration starts

when mixing water contacts the cementitious materials, causing chemical reactions that

produce calcium silicate hydrates, which make concrete stronger, and other hydration

products such as calcium hydroxide and monosulphate. The formation of the hydration

products is associated with a reduction of the original volume, what is called chemical

shrinkage. Some part of the mixing water becomes chemically bonded to the hydration

products, some other adsorbed at the surface of the hydration products, and the rest

remains in solution at the capillary pores formed during hydration. Cementitious

materials get the water needed to promote hydration from the capillary pores, which

generates surface tensions that result in volumetric reductions known as autogenous

shrinkage when occurs in a closed isothermal system that is not subjected to external

forces. Internal curing (IC) is an effective method for improving performance of low W/C

10

–low permeability concretes because they require additional water to hydrate the

cementitious materials. Conventional concretes, on the other hand, contain enough water

to hydrate the cementitious materials, but are frequently not properly cured, allowing

drying and compromising strength gain and durability. The aim of this investigation is to

assess the effect of IC as a complement to traditional curing in relatively high W/C

concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive

strength, and permeability were measured in concretes with IC and without IC. Results

show that even under drying conditions, mixtures with IC exhibit 16% higher hydration,

19% higher compressive strength, and 30% lower permeability than their counterparts

with no IC. This suggests that IC can be very useful for improving performance in

concrete mixtures with relatively high W/C under poor curing conditions.

3.2.5. “Super absorbing polymers as an internal curing agent for mitigation of early-

age cracking of high-performance concrete bridge decks” by Bart Craeye et.al,

Construction and Building Materials. (3)

High-performance concrete (HPC) with low w/b-ratio experiences a considerable

chemical shrinkage and self-desiccation during its hydration process, leading to a rather

high autogenous shrinkage deformation during hardening. In case the free deformation of

the concrete is prevented, internal stresses are introduced, which can lead to premature

cracks. These early-age cracks can severely affect the durability of a concrete structure.

By adding super absorbing polymers (SAP) into the HPC as an internal curing agent, and

by adding additional curing water to the concrete mixture, the chemical shrinkage and the

self-desiccation during hydration of the concrete is counteracted and thus the autogenous

shrinkage of the HPC can be significantly reduced. Unfortunately, this process of internal

curing also has some disadvantageous effects on the mechanical properties. In search of

an optimization of the internal curing process, an extensive experimental program was

performed on HPC, using different degrees of internal curing, to assess the mechanical

and thermal properties of the HPC, and to evaluate the effectiveness of the performed

curing. The goal is to obtain a maximal autogenous shrinkage reduction and a minimal

strength reduction. The resulting effect on the early-age cracking risk is simulated by

means of finite element calculations. The simulations also include thermal stress

11

development due to the heat of hydration. In case 70 kg/ m3 of internal curing water is

provided via the SAP, an optimal reduction of the cracking risk is noticed, mainly caused

by the autogenous shrinkage reduction and the appearing expansive deformation peak

directly after setting takes place.

3.2.6. “Autogenous Shrinkage of Concrete with Super-Absorbent Polymer”, Wang,

Fazhou, Zhou, Yufei, Peng, Bo, Liu, Zhichao, Hu, Shuguang. (19)

The water-release process of prewetted super-absorbent polymer (SAP) particles

in cement paste is illustrated by a cracking viewer and it is found that water entrained by

SAP is almost exhausted after 7 days, producing many pores in the paste structure.

Meanwhile, the effects of SAP dosages and entrained water on internal relative humidity

(IRH), autogenous shrinkage (AS), and compressive strength of concrete are discussed.

Results indicate that incorporation of SAP obviously delays IRH decline and mitigates

AS at an early age; however, it negatively influences the pore structure of cement paste.

Thus, the compressive strength of concrete decreases with a higher content of SAP or

entrained water.

3.2.7. “Combating Shrinkage with Internal Curing”, Neville A.M (Properties of

Concrete, Fourth Edition, Prentice Hall) (16)

Shrinkage in concrete is related primarily to the cracking tendency in concrete

structures. Cracks affect concrete’s compressive strength, durability performance, and

aesthetic quality. Whether in the form of drying shrinkage, autogenously shrinkage,

plastic shrinkage, or other shrinkage mechanism, combating the volume instability of

concrete can be quite challenging for engineers and contractors.

3.2.8. “The use of lightweight fines for the internal curing of concrete”, by George

C. Hoff, Northeast Solite Corporation. (12)

The benefits of using lightweight aggregates in concrete to help reduce cracking

in slabs and bridge decks has been intuitively known for decades by the lightweight

aggregate industry but the reasons as to why this occurred were not extensively

examined and the benefits were not widely promoted. It was believed, and correctly so,

12

that the lower modulus of the LWA and the improved transition zone around the LWA

particles due to their generally vesicular surface, helped reduce stress concentrations

between the paste and the aggregate and those reductions subsequently reduced the

amount of early-age cracking in the concrete. In the 1980’s, the production of high-

strength concrete (HSC) became more common and, to accomplish it, came the use of

higher cement contents, supplementary cementing materials such as silica fume, fly ash

and blast furnace slag cement, and lower water-binder ratios as a result of the extensive

use of super plastizers. The term “high-performance” concrete (HPC) also emerged with

a focus on providing special properties of concrete above what would normally be

expected from concrete produced for general use. Most of the HPC was directed at

improved durability. The durability improvements came by reducing or eliminating the

transport mechanisms of the environment into the concrete and this generally followed

the same modifications of the mixture proportions that occurred for HSC.

3.2.9. “Internal Curing of High Performance Concrete Bridge Decks and Its Effects

on Performance, Service Life and Life-Cycle Cost”, by Daniel Cusson et. al,

National Research Council Canada. (5)

Internal curing with LWA has been successfully used recently in large

construction projects of normal-density concrete structures. Field observations reported

marginal pavement cracking, and tests indicated that 7-day flexural strengths reached

90% to 100% of the required 28-day flexural strength due to an improved cement

hydration. They also found that the compressive strengths of air-cured cylinders were

similar to those of wet-cured cylinders at all ages, suggesting that concrete with internal

curing is less sensitive to poor external curing practices or unfavorable ambient

conditions.

Although the benefits of internal curing for high performance concrete (HPC)

structures have been evidenced in laboratory and field investigations (such as those

previously mentioned), the literature does not provide any significant quantitative

information regarding the extent of service life that can be achieved by internal curing of

concrete structures. The objective of this paper is to provide reasonable estimates of

13

service life and life cycle costs for a typical concrete bridge deck made with internally-

cured HPC, using available test data from the literature, along with mechanistic models

and conservative engineering judgment.

3.2.10. “Internal Curing and Microstructure of High-Performance Mortars”, by

Dale P. Bentz et. al, Building and Fire Research Laboratory, National Institute of

Standards and Technology. (4)

While typically used to reduce early-age autogenous shrinkage and cracking,

internal curing will also strongly influence the microstructure that is produced in cement-

based materials. In this paper, the microstructure of a set of three different blended

cement high performance mortars produced with and without internal curing will be

compared. For these mortars with a water-to-cementitious materials ratio of 0.3 by mass,

internal curing has been provided by the addition of pre-wetted lightweight fine

aggregates. Their microstructures have been examined after 120 days of sealed curing

using scanning electron microscopy of polished surfaces in the back-scattered electron

imaging mode. Clear distinctions between the microstructures produced with and without

internal curing are noted, including differences in the un reacted cementitious content, the

porosity, and the microstructure of the interfacial transition zones between sand grains

(normal and lightweight) and the hydrated cement paste. These micro structural

observations will be related to previously measured performance attributes such as

autogenous deformation and compressive strength development.

3.2.11. “Self Curing Concrete – An Introduction”, Ambily.P.S. et. al, Concrete

Composites Lab, Structural Engineering Research Centre, Chennai.

Excessive evaporation of water (internal or external) from fresh concrete should

be avoided; otherwise, the degree of cement hydration would get lowered and thereby

concrete may develop unsatisfactory properties. Curing operations should ensure that

adequate amount of water is available for cement hydration to occur. This paper discusses

14

different aspects of achieving optimum cure of concrete without the need for applying

external curing methods.

3.3 SUMMARY

A detailed literature study was carried out based on the previous investigations

and the various parameters involved are also considered.

CHAPTER 4

EXPERIMENTAL PROCEDURE

4.1 CONSTITUENT MATERIALS USED

15

Materials that are used for making concrete for this study were tested before

casting the specimens. The preliminary tests were conducted for the following materials.

Cement

Fine aggregate

Coarse aggregate

Water

Silica fume

Super absorbent polymer

4.1.1 Cement

Cement used in construction is characterized as hydraulic or non-hydraulic.

Hydraulic cements (e.g., Portland cement) harden because of hydration, chemical

reactions that occur independently of the mixture's water content; they can harden even

underwater or when constantly exposed to wet weather. The chemical reaction that

results when the anhydrous cement powder is mixed with water produces hydrates that

are not water-soluble. Non-hydraulic cements (e.g., lime and gypsum plaster) must be

kept dry in order to retain their strength.

The most important use of cement is the production of mortar and concrete. The

bonding of natural or artificial aggregates to form a strong building material that is

durable in the face of normal environmental effects.

Specific Gravity of Cement (IS: 4031)

In concrete Technology, specific gravity of cement is made use of in design

calculations of concrete mixes, and it is also used to calculate its specific surface.

The specific gravity is defined as the ratio between the weight of given volume of

cement to the weight of an equal volume of water. The most popular method of

determining specific gravity of cement is by the use of kerosene which doesn’t react with

cement.

16

Initial and Final Setting Time of Cement

As soon as water is added to cement, hydration of cement starts which results in

changing the water cement mix from fluid to solid (setting). Initial Setting Time is that

time period between the times at which water is added to cement paste, placed in the

Vicat’s mould 5mm to 7mm from the bottom of the mould. It is usually desirable that

concrete should be placed and compacted before Initial Set has started and not disturbed

after.

In the second stage of hydration, hardening takes place and the Final Setting Time

is that time period between the time water is added to cement and the time at which

needle with annular collar attachment fails to makes an impression on the surface of

cement paste.

4.1.2 Aggregates 

“Fine   aggregate”   is defined as material that will pass a No. 4 sieve and will, for

the most part, be retained on a No. 200 sieve. For increased workability and for economy

as reflected by use of less cement, the fine aggregate should have a rounded shape. The

purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a

workability agent.

Coarse aggregate is a material that will pass the 3-inch screen and will be retained

on the No. 4 sieve. As with fine aggregate, for increased workability and economy as

reflected by the use of less cement, the coarse aggregate should have a rounded shape.

Even though the definition seems to limit the size of coarse aggregate, other

considerations must be accounted for.

Fine aggregates:

Usually sand or stone dust and its size is limited to 4.75mm gauge, i.e., passing

through 4.75mm IS sieve but retained on 75 micron sieve.

17

Coarse aggregates:

Broken stone/gravel and its size is 4.75mm gauge plus i.e., retained on 4.75mm IS

sieve.

All in aggregates:

Sieve analysis enables us to ascertain the proportions of different sizes of

aggregate. The results which are generally given as percentage of total aggregate passing

through each of sieve are considered as a method of standardization of grading of

aggregates for most economical mix and workability with minimum quantity of cement.

4.1.3 Super plasticizers

Superplasticizers, also known as high range water reducers, are chemicals used as

admixtures where well-dispersed particle suspensions are required. These polymers are

used as dispersants to avoid particle aggregation, and to improve the flow characteristics

(rheology) of suspensions such as in concrete applications. Their addition to concrete or

mortar allows the reduction of the water to cement ratio, not affecting the workability of

the mixture, and enables the production of self-consolidating concrete and high

performance concrete. This effect drastically improves the performance of the hardening

fresh paste. Indeed the strength of concrete increase whenever the amount of water used

for the mix decreases. However, their working mechanisms lack of a full understanding,

revealing in certain cases cement-superplasticizer incompatibilities.

4.1.4 Silica Powder

Silica fume in powder form is added to Portland cement concrete to improve its

properties, in particular its compressive strength, bond strength, and abrasion resistance.

These improvements stem from both the mechanical improvements resulting from

addition of a very fine powder to the cement paste mix as well as from the pozzolanic

reactions between the silica fume and free calcium hydroxide in the paste.

18

Addition of silica fume also reduces the permeability of concrete to chloride ions,

which protects the reinforcing steel of concrete from corrosion, especially in chloride-rich

environments such as coastal regions and those of humid continental roadways and

runways (because of the use of deicing salts) and saltwater bridges.

Effect of silica fume on different properties of fresh and harden concrete:-

a) Workability: With the addition of silica fume, the slump loss with time is directly

proportional to increase in the silica fume content due to the introduction of large surface

area in the concrete mix by its addition. Although the slump decreases, the mix remains

highly cohesive.

b) Segregation and Bleeding: Silica fume reduces bleeding significantly because the free

water is consumed in wetting of the large surface area of the silica fume and hence the

free water left in the mix for bleeding also decreases. Silica fume also blocks the pores in

the fresh concrete so water within the concrete is not allowed to come to the surface.

4.1.5 Super-Absorbent Polymer (SAP)

The common SAPs are added at rate of 0–0.6 wt % of cement. The SAPs are

covalently cross-linked. They are Acryl amide/acrylic acid copolymers. One type of

SAPs are suspension polymerized, spherical particles with an average particle size of

approximately 200 mm; another type of SAP is solution polymerized and then crushed

and sieved to particle sizes in the range of 125–250 mm. The size of the swollen SAP

particles in the cement pastes and mortars is about three times larger due to pore fluid

absorption. The swelling time depends especially on the particle size distribution of the

SAP. It is seen that more than 50% swelling occurs within the first 5 min after water

addition.

4.2 FRESH CONCRETE PROPERTIES

4.2.1 Slump Test

19

Fresh concrete when unsupported will flow to the sides and sinking in height will

take place. This vertical settlement is known as slump. The workability (ease of mixing,

transporting, placing and compaction) of concrete depends on wetness of concrete

(consistency) i.e., water content as well as proportions of fine aggregate to coarse

aggregate and aggregate to cement ratio.

The slump test which is a field test is only an approximate measure of consistency

defining ranges of consistency for most practical works. This test is performed by filling

fresh concrete in the mould and measure the settlement i.e., slump.

4.3 HARDENED CONCRETE PROPERTIES

4.3.1 Compression Test on Concrete Cubes

The determination of the compressive strength of concrete is very important

because the compressive strength is the criterion of its quality. Other strength is generally

prescribed in terms of compressive strength. The strength is expressed in N/mm2. This

method is applicable to the making of preliminary compression tests to ascertain the

suitability of the available materials or to determine suitable mix proportions. The

concrete to be tested should not have the nominal maximum size of aggregate more than

38mm test specimens are either 15cm cubes or 15cm diameter, 30cm used. At least three

specimens should be made available for testing. Where every cylinder is used for

compressive strength results the cube strength can be calculated as under.

Minimum cylinder compressive strength =

0.8 x compressive strength cube (10 cm x 10 cm)

The concrete specimens are generally tested at ages 1 day, 7 days and 28 days.

4.3.2 Tensile Strength of Concrete (Split Tensile Test)

20

Concrete is strong in compression but weak in tension. Tension stresses are likely

to develop in concrete due to drying shrinkage, rusting of reinforcement, temperature

gradient etc. In concrete road slab this tensile stresses are developed due to wheel loaded

and volume changes in concrete are available to determine this. Split test is one of the

indirect methods available to find out the tensile strength.

4.3.3 Flexural strength of Concrete

It is the ability of a beam or slab to resist failure in bending. It is measured by

loading un-reinforced 6x6 inch concrete beams with a span three times the depth (usually

18 in.). The flexural strength is expressed as “Modulus of Rupture” (MR) in psi. Flexural

MR is about 12 to 20 percent of compressive strength.

4.3.4 Modulus of Elasticity

It is the ratio between tensile stress and tensile strain of any material. It shows the

material’s tendency to be deformed elastically when a force is applied to it. This is

calculated from the stress – strain curve of that particular material.

4.4 TESTING PROCEDURE

Within the experimental research program concerning the development of

mechanical properties of a high performance reference concrete of grade M40 (REF) was

considered with the following composition, according to Table 1. The w/c-ratio is 0.32.

The w/b ratio is 0.30. The super plasticizer is poly carboxylic ether. Coarse aggregates

were chosen, having a particle size mainly varying between 2 mm and 20 mm. The silica

fume, containing more than 90% of amorphous SiO2, has a specific surface area of 20

m2/g. A previous study, with a similar HPC composition (w/b ratio of 0.33), indicates

tensile failure of the HPC after 6 days due to internal restraint of the autogenous

shrinkage. In order to mitigate this and to prevent early-age cracking, additional internal

curing water will be provided by means of SAP.

The SAP used, is a suspension polymerized, covalently cross linked acryl

amide/acrylic acid copolymer. The particle density is 785 kg/m3 (diameter between 80

21

µm and 150 µm) and has a water absorption capacity of 45 g/g after 5 min (the

approximate mixing time). Based on this absorption level, the amount of SAP to be added

to the concrete is estimated, aiming for an amount of internal curing water equal to 45

kg/m3 (SAP45), 67.50 kg/m3 (SAP67.5) and 90 kg/m3 (SAP90). This leads to a

corresponding SAP amount of respectively 1 kg/m3, 1.5 kg/m3 and 2.00 kg/m3. The

amount of curing water itself has to be added to the concrete during mixing. As

compensation, the sand content is reduced in order to obtain 1 m3 of concrete (Table 1).

Concrete mixes are made using a planetary mixer according to the following

mixing procedure: first the dry components (binder, fine and coarse aggregates, SAP) are

mixed for 1 min, and afterwards the water and super plasticizer are added and mixing

continues for another 4 min. An intensive experimental program is performed to study the

effect of internal curing on different types of concrete properties: (i) fresh properties

(slump and density); (ii) mechanical properties (compressive strength, flexural strength,

splitting tensile strength and elastic modulus).

4.5 SUMMARY

The detailed experimental program to be followed for the purpose of this project

and the tests to be carried out are studied in this chapter.

CHAPTER 5

22

MIX DESIGN

5.1 DEFINITION

Mix design is the process of selecting suitable ingredient if concrete and

determines their relative proportions with the object of certain minimum strength and

durability as economically as possible.

5.2 OBJECTIVE OF MIX DESIGN

The objective of concrete mix design as follows.

1. The first objective is to achieve the stipulated minimum strength.

2. The second objective is to make the concrete in the most economical Manner.

Cost wise all concrete’s depends primarily on two factors, namely cost of material

and cost of labour. Labour cost, by way of formwork, batching, mixing,

transporting and curing is namely same for good concrete.

5.3 FACTORS TO BE CONSIDERED IN MIX DESIGN

1. Grade of concrete

2. Type of cement

3. Type & size of aggregate

4. Cement content

5. Type of mixing & curing

6. Water /cement ratio

7. Degree of workability

8. Density of concrete

9. Air content

5.4 MIX DESIGN

23

Design Stipulations:

Grade Designation = M-40

Type of cement = P.P.C-43 grade

Fine Aggregate = Zone-II

Sp. Gravity Cement = 3.15

Sp. Gravity Fine Aggregate = 2.61

Sp. Gravity Coarse Aggregate = 2.65

Mix Calculation:

1. Target Mean Strength = 40 + (5 X 1.65) = 48.25 MPa

2. Selection of water cement ratio

Assume water cement ratio = 0.35

3. Calculation of cement content: -

Assume cement content 475 kg / m3

4. Calculation of water: -

475 X 0.35 = 150 kg which is less than 186 kg (As per Table No. 4, IS: 10262)

Hence o.k.

5. Calculation for C.A. & F.A.: (As per IS: 10262, Cl. No. 3.5.1)

V = [ W + (C/Sc) + (1/p) . (fa/Sfa) ] x (1/1000)

V = [ W + (C/Sc) + {1/(1-p)} . (ca/Sca) ] x (1/1000)

Where

V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the

volume of entrapped air,

W = mass of water (kg) per m3 of concrete,

24

C = mass of cement (kg) per m3 of concrete,

Sc = specific gravity of cement,

(p) = Ratio of fine aggregate to total aggregate by absolute volume,

(fa) , (ca) = total mass of fine aggregate and coarse aggregate (kg) per m3 of

Concrete respectively, and

Sfa , Sca = specific gravities of saturated surface dry fine aggregate and Coarse aggregate

respectively.

As per Table No. 3, IS-10262, for 20mm maximum size entrapped air is 2%.

Assume F.A. by % of volume of total aggregate = 36.5 %

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.365 ) ( Fa / 2.61 )] ( 1 /1000 )

=> Fa = 588.2 kg

Say Fa = 588 kg.

0.98 = [160 + (400 / 3.15) + (1 / 0.635) (Ca / 2.655)] (1 /1000)

=> Ca = 1159.37 kg.

Say Ca = 1159 kg.

Hence Mix details per m3

Cement = 475 kg

Water = 150 kg

Fine aggregate = 588 kg

Coarse aggregate = 1159 kg

Water: cement: F.A.: C.A. = 0.35: 1: 1.25: 2.42

25

Table 1: Mix Proportion

Fig.3 Moulds

Cement

(kg)

FA

(kg)

CA

(kg)

Silica Fume

(kg)

Super Plasticizer

(kg)

Water

(liter)

475 588 1159 25 5 150

26

CHAPTER 6

RESULTS AND DISCUSSION

6.1 FRESH CONCRETE PROPERTIES

The fresh concrete properties and thus the consistency of the concrete mixture can be

determined by means of the slump test and the flow test. Also the density of the fresh concrete

can be easily determined by measuring the net weight of a reservoir with a known volume filled

with compacted HPC.

Component Unit Ref SAP45 SAP67.5 SAP90

Slump mm 48 69 42 63

Density(Fresh) kg/m3 2488 2396 2354 2337

Density(28

days) kg/m3 2423 2379 2328 2300

Table 2: Fresh Concrete Properties

6.2 MECHANICAL PROPERTIES

6.2.1 Compressive Strength

Cube specimens with a side of 150 mm are produced and stored immediately

after mixing in a climate room. At the age of 1 day, 7 days and 28 days the compressive

strength tests are performed according to the IS Code procedures. The values are

tabulated in Table 3.

6.2.2 Split Tensile Strength

Tensile splitting tests are carried out on cylinders(diameter 150 mm, height 300

mm) also stored immediately after mixing in a climate room and tested at the age of 1

day, 7 days and 28 days (according to the IS Code). The results are given in Table 4.

27

6.2.3 Flexural strength

. For each composition, the Flexural strength is also determined on prism

specimens (side 150 mm, height 300 mm) at the age of 1 day, 7 days and 28 days

according to the IS Code procedures. The test results are tabulated in Table 5.

6.2.4 Modulus of Elasticity

For each composition, the Elastic modulus is determined on cylindrical specimens at the age of 28

days. The test results are tabulated in Table 6.

MIX

1DAY

STRENGTH (MPa)

7 DAYS

STRENGTH (MPa)

28 DAYS

STRENGTH (MPa)

% INCREASE AT 28 DAYS

REF 12.26 26.82 40.23

SAP45 14.27 36.5 54.75 36.1

SAP67.5 12.74 32.92 49.38 22.74

SAP90 11.74 31.92 47.88 19.02

Table 3: Compressive Strength Results

MIX

1DAY

STRENGTH (MPa)

7 DAYS

STRENGTH (MPa)

28 DAYS

STRENGTH (MPa)

% INCREASE AT 28 DAYS

REF 12.26 26.82 40.23

SAP45 14.27 36.5 54.75 36.1

SAP67.5 12.74 32.92 49.38 22.74

SAP90 11.74 31.92 47.88 19.02

Table 4: Split Tensile Strength

MIX 1DAY 7 DAYS 28 DAYS % INCREASE AT 28

28

STRENGTH (MPa) STRENGTH

(MPa)STRENGTH

(MPa)

DAYS

REF 12.26 26.82 40.23

SAP45 14.27 36.5 54.75 36.1

SAP67.5 12.74 32.92 49.38 22.74

SAP90 11.74 31.92 47.88 19.02

Table 5: Flexural Strength

MIX REF SAP45 SAP67.5 SAP90

EC (MPa) 35.3 46.9 41.9 39.3

Table 6: Modulus of Elasticity

The tabulated results were then expressed in the form of bar charts to compare the

properties between various mix proportions.

6.3 COMPARISON OF RESULTS

Comparison of Compressive Strength

REF

REF

REF

SAP45

SAP45

SAP45

SAP45

SAP6

7.5

SAP6

7.5

SAP6

7.5

SAP90

SAP90

SAP90

SAP90

SAP6

7.5

0

10

20

30

40

50

60

1DAY 7 DAY 28 DAY % INCREASE

Str

eng

th (

MP

a) REF

SAP45

SAP67.5

SAP90

29

Figure.4 Comparison of Compressive Strength

From the above graphical result comparison, it is clearly visible that addition of SAP

leads to increase in compressive strength. It is also can be noted that the effectiveness is

higher with SAP 45 composition.

Comparison of Split Tensile StrengthREF

REF

REF

SAP45

SAP45

SAP45

SAP45

SAP67.5

SAP67.5

SAP67.5

SAP67.5

SAP90

SAP90

SAP90

SAP90

0

10

20

30

40

50

60

1DAY 7 DAY 28 DAY % INCREASE

Str

eng

th (

MP

a) REF

SAP45

SAP67.5

SAP90

Figure.5 Comparison of Split Tensile Strength

From the above graphical result comparison, it is clearly visible that addition of SAP

leads to increase in split tensile strength. It is also can be noted that the effectiveness is

higher with SAP 45 composition.

Comparison of Flexural Strength

REF

REF

REF

SAP45

SAP45

SAP45

SAP45

SAP67.5

SAP67.5

SAP67.5

SAP67.5

SAP90

SAP90

SAP90

SAP90

0

10

20

30

40

50

60

1DAY 7 DAY 28 DAY % INCREASE

Str

eng

th (

MP

a) REF

SAP45

SAP67.5

SAP90

30

Figure.6 Comparison of Flexural Strength

From the above graphical result comparison, it is clearly visible that addition of SAP

leads to increase in flexural strength. It is also can be noted that the effectiveness is

higher with SAP 45 composition.

Comparison of Elastic Modulus

0

10

20

30

40

50

REF SAP45 SAP67.5 SAP90

Ela

stic

Mo

du

lus

(MP

a)

Figure.7 Comparison of Elastic Modulus

6.4 SUMMARY

The fresh concrete properties and the hardened concrete strength properties were

determined through experimental measurements and they were tabulated. The

comparison between the properties of different mix proportions were done through the

bar charts. Form the comparison it is noted down that the result is optimum at the mix

proportion SAP 45.

31

Fig 8. Compression Test Fig 9. Flexure Test

Fig 10. Split Tensile Test

32

CHAPTER 7

CONCLUSION

7.1 GENERAL

By adding super absorbing polymers (SAP) into the HPC as an internal curing

agent, and by adding additional curing water to the concrete mixture, the autogenous

shrinkage of the HPC can be significantly reduced and hence the strength properties can

be increased. Several mechanical tests were performed to evaluate the effect of internal

curing on the high-performance concrete properties and cracking behavior. Therefore one

reference composition was compared to three compositions with additional amount of

SAP, partially replacing the sand of the reference composition. In addition, this study

indicates the effectiveness of super absorbing polymers (SAP) as an internal curing agent

to prevent early-age cracking of high-performance concrete.

7.2 CONCLUSION

The main conclusions of this study are listed below:

– Addition of SAP leads to a significant increase of mechanical strength

(Compressive, Split tensile and Flexural strength).

– A higher and earlier heat production rate due to hydration is found for

higher amounts of SAP added to the reference concrete.

The effectiveness of internal curing by means of SAP applied to a high-performance

concrete is the highest if 45 kg/ m3 water is added by means of 1 kg/m3 SAP.

33

CHAPTER 8

SCOPE FOR FUTURE WORK

8.1 GENERAL

There is a scope for determining the influence of internal curing on

mechanical properties such as autogenous shrinkage, creep etc.

There is a scope to determine the influence of internal curing on thermal

properties such as heat of hydration, relative humidity etc.

There is a scope to determine the influence of internal curing on Indian

climatic conditions with different curing temperatures.

There is a scope for determining the influence of internal curing when

different admixtures are used in concrete.

34

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37

PUBLICATIONS

1. “Study on Mechanical Properties of High Performance Concrete using SAP as an

Internal Curing Agent”, National Conference on Advances and Innovations in

Civil Engineering, Mepco Schlenk Engineering College, Sivakasi.

2. “Study on Mechanical Properties of HPC using SAP as an Internal Curing

Agent”, National Conference on Modern Trends in Civil Engineering, Dr.

Sivanthi Aditanar College of Engineering, Tiruchendur.