11

Chapter 2

LITERATURE REVIEW

2.1 STATUS OF RIGID PAVEMENTS IN INDIA

With a road network of 3.3 million km, carrying 65 per cent of freight and 85 per

cent of passenger traffic, the road traffic is set to grow at 7-10 per cent, while

vehicular traffic is expected to grow at a rate of 10 per cent in India. Though the road

network in India has increased by seven-fold in the last 45 years, the national and

state highways which carry majority of the traffic have increased by only 2 per cent

[1]. Of the 3.3 million km road length in India, the share of concrete roads is very

small. Though they have higher initial cost of construction, the concrete roads are

now being preferred in India owing to their qualities like lower life-cycle cost, better

surface condition, precise in design, long life, resistance to tangential stresses and low

maintenance cost. In the developed countries when the concrete roads were

constructed years ago, the rapid increase in traffic volume and high levels of heavy

truck traffic, which pavements must now carry, were not anticipated [2]. Hence it is

required to relook at the methods of forecasting the traffic volume for the purpose of

design. The pace of road construction in India was limited in the past but recently the

two programmes have given a boost to road construction namely, National Highway

Development Project’s (NHDP’s) Golden Quadrilateral, 5864 km (almost completed)

and North South East West corridor (NSEW), 7300 km (completed 4863 km) and the

Pradhan Mantri Grameen Sadak Yojana(PMGSY). The advent of expressways and

dual two-lane carriageway national highways has created a paradigm shift in the road

construction in India [1].

One of the most profound causes of the poor conditions of the roads in India is the

overloading of the pavements by allowing movement of the overloaded vehicles with

12

axle load in excess of the standard design axle load and by continuing the use of the

deteriorated roads even after their service life. The axle load spectrum for the design

of the pavements is derived from the existing traffic (surveyed) or assumed in case of

a new road, and the cumulative standard axles (CSA) considered for the design will

be used-up much quicker before the road attains the design life if the vehicles are

overloaded, thus leading to faster deterioration of the pavements [3]. Further, the

roads which are designed and constructed or being constructed for a specific volume

of vehicular traffic, should sustain greater traffic than anticipated, in the near future.

Repair and rehabilitation of these roads shall be an on-going priority to increase their

service life. The traditional methods of repair and rehabilitation incur high

replacement costs and cause several days of traffic interruption, especially in heavy-

traffic areas, such as major intersections, and on toll ways, where congestion/delay is

most prevalent [2]. This situation particularly warrants in case of concrete roads. It is

hence necessary to initiate the study on the fast- track construction and rehabilitation

of concrete roads, mainly for the rigid pavement portion of dual two-lane National

Highways and Expressways of India. One of the most important components of fast-

track construction of concrete roads is the design of suitable concrete mixtures. Fast-

track concrete mixtures do not require the use of special materials or out-of the

ordinary techniques but selection of materials including admixtures demands extra

care [2, 4, and 5]. Review of literature on the failure causes of rigid pavements;

properties and role of alternate cementitious materials and chemical admixtures in

concrete; features of high early-strength concrete in fresh and hardened state at early

and later age; alternate curing methods and durability aspects of concrete assume

greater importance in the study on accelerated rehabilitation of rigid pavements.

13

2.2 FAILURE OF RIGID PAVEMENTS

The defects apparent on rigid pavements may be due to deterioration of the

concrete, restrained volume-change stresses, or overload evidenced by pumping

and/or structural breaks [6]. The basic distress in concrete roads is formation of

cracks. Uncontrolled transverse and longitudinal cracks that occur during concrete

pavement construction are due to various reasons and full-depth repairs are the only

solutions in most of the situations. Further, unfortunately some concrete pavements do

not crack at the saw cuts and instead crack at unplanned locations. The common terms

for these early cracks are “random cracks” or “uncontrolled cracks.” The reasons for

uncontrolled cracks are due to factors like saw timing, saw cut depth, weather &

ambient conditions, conditions of base and sub base, quality of concrete, joint

spacing, rapid evaporation of surface moisture and so on [7]. Concrete structure is an

assembly of operating systems that experience temperature, air pressure and vapor

pressure gradients. Seasonal and diurnal fluctuations in outdoor conditions provide

variability and direction of the gradients and these operating conditions can aggravate

or accelerate premature failure of the structures [8]. Concrete roads are vulnerable to

attacks from atmospheric agents. Collepardi [9] in his technical paper has mentioned

that delayed ettringite formation (DEF) in the hardened concrete which occurs after

months or years due to sulphate attack in rigid hardened concrete was responsible for

cracking and spalling of concrete. The paper explained that the sulphate attack could

be internal which occurs in a sulphate free-environment by the late sulphate ions

release from either cement or gypsum-contaminated aggregates or could be external

when environmental sulphate (from water or soil) penetrates into a concrete structure.

Lee et al. [10] have investigated the premature deterioration of Iowa concrete

highway in U.S.A. In the case of Iowa highway, the sulphate ions that promoted

14

delayed ettringite formation were derived from the oxidization of Pyrite (FeS2) which

was found in coarse aggregate of the concrete. The delayed ettringite formation was

found to be the prime reason for the deterioration of the concrete. It was observed that

in poorly performing concrete, ettringite completely filled many small voids, occurred

as rims lining the margin of larger air entrainment voids and as microscopic

disseminations in the paste. These findings are useful in selection of coarse aggregate,

though this is always a matter of constraint in a particular area where pavement is to

be constructed or rehabilitated. Akoto and Niles [11] have explained the various types

of distresses and repair restoration techniques for rigid pavements. Depending on the

condition of crack width, spalling and faulting condition, they have recommended

repair and restoration techniques. Shallow spalling, shallow cracking, pop-outs and

scaling were the reasons mentioned for partial depth repair and it was advised that

partial depth repair should be limited to the top one-third of the pavement and should

not bear on dowel bar. The distress identified for the full depth repair were blowup

and corner crack of low severity, D-cracking, joint deterioration (with faulting≥ 6

mm), spalling(with faulting≥ 6 mm) and transverse cracking all of moderate severity

and longitudinal cracking of high severity(faulting ≥12 mm). They have concluded

that Concrete Pavement Restoration (CPR) technique was cost effective compared

with asphalt overlay and could save fuel consumption by as much as 20 per cent.

Sinha et al. [12] in their paper on the causes of cracking of concrete roads have

identified the causes for initial cracking of concrete roads which include curling and

warping of slabs due to temperature and moisture gradients from the top to the bottom

of the slab. Drying process of concrete was also identified as one of the reasons for

early cracks. They have concluded that uncontrolled cracks were due to complexity of

inter-relating factors governing the behaviour of concrete. The observations of the

15

authors suggest that ingredients, mix design and curing methodology play vital role in

the causes of distress in concrete roads. Phull and Rao [13] have reported that the rise

in heat of hydration due to hydration process which peaks at 72 hours after pouring of

concrete, low thermal conductivity of concrete along with shrinkage and creep effects

were responsible for discontinuous internal micro-cracks. The authors have reported

that fatigue of concrete pavements had assumed very high significance due to heavy

axle loads and high traffic volumes and hence have stressed for fatigue adequacy to

increase service life of concrete roads. Analysis presented in their paper explained

that even small changes in the magnitude of the parameters governing fatigue could

adversely affect the fatigue life of the concrete pavements, like even 1 per cent

reduction in concrete strength or 0.5 per cent reduction in pavement thickness could

bring down the fatigue life of the pavement by 13 to 55 per cent. The authors have

given suggestion for the rationalization of concrete pavement design methodology of

IRC: 58-2002, considering load and temperature stresses simultaneously for the

fatigue check. Kapila [14] has assessed cause of cracking of a newly built road in

Ethiopia and found three simultaneous conditions for the cracking of the road,

namely, clayey soil mass forming the sub-grade/embankment and surrounding with

large fine fractions, presence of vegetations in terms of mature trees like Eucalyptus

in the close proximity of road and absence of regular source of water supply to meet

the water requirement of trees. Gupta [15] in his paper on repair and improvement of

damaged cement concrete pavement has given various causes of damage of rigid

pavements like weak sub grade soil, faulty mix design of concrete, poor workmanship

etc. and concluded that causes of damage of cement concrete pavements should be

established first, then and only then the repair and improvement work should be done

accordingly. The author suggested that if cement concrete of the pavement layer was

16

of poor quality where it could be broken by a hammer and coarse aggregates could be

taken out easily then the re-laying of new cement concrete pavement should be done.

It is a known fact that the cracks in concrete initiate when the stress reaches the

strength limit of the concrete but they can only grow if the energy required to break

the material is supplied. Therefore the crack formation at early and later age in

concrete can be studied using energy criterion of fracture mechanics but the

application of fracture mechanics to assess the early age cracking of concrete roads is

still in its infancy [16]. Hence from the review of the literature on the pavement

distress, it is clear that assessment of failure patterns of concrete roads is essential to

decide about the type of accelerated repair or rehabilitation.

2.3 PAVEMENT CONCRETE IN PLASTIC STATE

In case of accelerated partial or full-depth repairs where new concrete layer has to

be laid, the primary requirement is the design of high early-strength concrete mixtures

with suitable qualities in fresh and hardened state and with excellent durability

characteristics. There is lot of misconception about the requirement of workability of

such concrete mixtures. Higher workability with superplasticizers that unnecessary

increase cost of concrete production is not warranted in pavement concrete. The

workability of PQC mix at site, as obtained when placed in front of the slip form

paver is of great significance. Lower workability of 20-25 mm slump is desirable for

smooth functioning of pavers [17]. Momin et al. [18] have given a brief account of

rigid pavement construction technology for Mumbai-Pune Expressway, where OPC in

the range of 305 to 425 kg per cubic metre of concrete was used. They suggested

slump of such concrete to be typically low in the range of 15 to 30 mm, as higher

slump might cause breaking of the edges of the road. Bissonnette et al. [19] have

published a paper on the deformation characteristics of Slabs-on-Ground. The

17

deformations studied were drying shrinkage, curling and joint opening for normal-

strength and high-strength high flowable concrete mixtures. The slabs made with a

flowable high-strength concrete produced the greatest curl heights and largest joint

openings even though the standard drying shrinkage values were lower than those

obtained for the plain concrete. The study indicated that some intrinsic characteristics

of the concrete, such as high stiffness, low creep, and self-desiccation, could be

detrimental to the performance of slabs-on-ground. Hence it is advisable to have

lower workability of pavement concrete.

2.4 CEMENTITIOUS MATERIALS

The cement concrete pavement generally consists of PQC slab as wearing course,

the base course of Dry Lean Concrete (DLC) that serves as platform for supporting

PQC slab and granular subbase. PQC is the most important part of cement concrete

and often laying of PQC is warranted in the rehabilitation of pavements. PQC for

construction and rehabilitation is typically produced with OPC. Of late supplementary

cementitious materials or by-products are being promoted to address environmental

issues and to increase durability characteristics of concrete. Fly ash and GGBS are

being utilized in the production of concrete, either in the form of partial replacement

to OPC or in the form of blending with cement clinker. Utilization of fly ash is very

limited in fast-track construction and currently there is no record of GGBS ever

employed in fast-track construction. [2]. PPC (fly ash based) and PSC are the two

blended cements being manufactured by the cement industry in India. Numbers of

papers, published in reputed journals have explained the advantages of using them to

impart desirable characteristics to concrete. Use of these blended cements in

transportation structures is very less, particularly in India. Heat of hydration is one of

the major factors in mass concreting. Concrete roads are always susceptible to early

18

cracking due to heat of hydration. Heat of hydration is now considered as aging

parameter in the concretes, modeled for early age behaviour. Heat of hydration can be

controlled by using blended cements [20, 21]. Naik et al. [22] have investigated

mechanical properties and durability of concrete made with blended fly ash and

compared them with that of normal and unblended fly ash concrete. They studied a

mixture without fly ash, and the other containing 35 per cent ASTM Class C fly ash.

Additional mixtures were composed of three blends of ASTM Class C and Class F fly

ash while maintaining a total fly ash content of 40 per cent of the total cementitious

materials. Conventional water curing was adopted for the specimens. Investigation of

mechanical properties included assessment of compressive and flexural strength of

concrete. The results revealed that the quality of mixture prepared with blending of

Class C fly ash with Class F fly ash was comparable or better than that of reference

mixture and mixture produced with unblended Class C fly ash. Blending of fly ash,

therefore, lead to comparable or better quality and reduced cost in concreting. Roesler

et al. [23] in their report on long life concrete pavement strategy have included

information on opening strength for different fast-track paving projects as given by

The American Concrete Pavement Association (ACPA). It is mentioned in the report

that the materials used by different agencies to achieve high early-strength concrete

were, ASTM Type I cement with accelerators, and ASTM Type III cement with

mineral admixtures such as fly ash or silica fume, and other proprietary fast setting

hydraulic cement concrete products. Erande and Limaye [24] have given a brief

account of concrete mix design and its optimization for Mumbai-Pune Expressway

where the cementitious material used was, 43 Grade OPC. They suggested attempting

the use of PPC in the production of concrete, especially in summer season to exploit

its low heat of hydration. Concrete technologists believe that the geo-climatic

19

conditions in India are suitable for the use of blended cement to tackle the problems

of durability due to its vast coastline and to take care of the tropical curing conditions

in most part of the country. Concrete produced with blended cements which contain

mineral admixtures is found to be superior to the concrete produced at construction

site with same mineral admixtures, as cement plants have better infrastructure to

monitor the quality of blended cements and adjustment of optimum proportion of

clinker with slag and fly ash is not possible in concrete plants or at sites. Further,

optimization of particle size and sulphate content is possible only in cement factories

[25]. Mailvaganam [8] in his paper on concrete repair and rehabilitation remarked that

amidst the global forces that were shaping the repair and restoration industry, there

was a shift in the manner that scientific research was carried out on the deterioration

process and the evaluation of repair materials. He mentioned that in addition to

focusing on high performance materials, future challenges would include the

development of more environmentally benign materials and the effective utilization of

by products and waste materials. Bouzoubaa et al. [26] have studied the mechanical

properties and durability of concrete produced with High-volume fly ash (HVFA)

blended cement produced in a cement plant. The test results were compared with

normal concrete. The results showed that to obtain slump and air content similar to

those of the control concrete, the use of HVFA blended cement required increased

dosages of the high-range water-reducing admixture and the air-entraining admixture.

The use of HVFA blended cement resulted in lower compressive and flexural

strengths at early ages (before 28 days) and higher mechanical properties after 28

days as compared with those of the control concrete made with ASTM Type I cement.

According to Collepardi [9] blended cements particularly pozzolanic and blast furnace

slag cements should be preferred instead of high early strength Portland cements to

20

control delayed ettringite formation in concrete. Barnett et al. [27] have investigated

the early-age strength development of concrete containing slag cement to give

guidance for its use in fast-track construction. The authors have found out that the

early-age strength of concretes with similar 28-day strengths and cured at 20 °C were

adversely affected by increasing levels of slag cement. The early-age strength

contribution of slag cement, however, was greatly improved by high curing

temperatures; for example, the strength development of slag cement concretes cured

under adiabatic conditions had comparable strengths to the portland-cement concrete

from either 2 or 3 days onward. Chahal et al. [28] in their paper which details about

the use of PPC in construction works have mentioned several advantages of PPC (fly

ash blended). They also have mentioned about various references like Indian

Standards’ Specifications, Indian Road Congress, and Indian Railways etc. which

speak about the PPC. In the conclusion of their discussion the authors have

recommended the use of PPC conforming to IS:1489 (Part-I):1991, for the

construction works in place of 33 grade OPC. Further, they categorically have

recommended the use of PPC in hydraulic structures, mass concreting works and in

aggressive conditions of environment. The quality of fly ash and its grinding with

cement clinker have been emphasized by the authors. Ravishankar et al. [29] have

investigated the combined effects of fly ash and rice husk ash in the concrete for rigid

pavements. Strength properties of M40 concrete were investigated by varying

percentage replacement of cement by fly ash (5 to 25 per cent) and rice husk ash (5 to

15 per cent). Compressive, split tensile and flexural strengths were evaluated. Apart

from control mix, three series of mixtures (in each series 5 mixtures) were prepared

for investigation. Replacement of cement by rice husk ash was kept constant as 5, 10

and 15 per cent in first, second and third series respectively and replacement of

21

cement by fly ash was varied from 5 to 25 per cent, at an interval of 5 per cent. The

results revealed that high strengths of order 55 MPa could be produced by partial

replacement of cement by the combination of 15 per cent rice husk ash and 10 per

cent fly ash. The results were encouraging to allow these waste products in the

pavement concrete mixtures from the consideration of strength requirement but the

durability studies on these mixtures were not undertaken by the authors. Pane and

Hansen [30] have performed early-age experiments on creep, thermal and

autogeneous deformations, early-age stress development, and hydration kinetics for

blended cement concrete. They used mineral admixtures like blast-furnace slag, silica

fume and fly ash in the production of concrete. Temperature effect was included in

the early-age stress prediction models and it was reported that the use of blended

cements to be beneficial in reducing the risk of early-age cracking as their presence

influenced the relaxation modulus of concrete significantly. Hale et al. [31] have

studied properties of concrete mixtures containing slag cement and fly ash for use in

transportation structures. Twelve mixtures with same amount of cement, fine

aggregate, coarse aggregate and with water-cementitious material ratio of 0.44 but

prepared with different proportions of slag and fly ash were tested for cylinder

compressive strength at 3, 7, 28, 56, 90 days, flexural strength at 28 day, splitting

tensile strength at 28 and 90 days, modulus of elasticity at 28 and 90 days and

shrinkage up to 100 days. The results showed that replacement rates of 15 per cent for

fly ash and 25 per cent for slag cement improved long-term concrete properties

without much sacrifice in early age properties. The addition of slag cement was

largely positive, whereas the addition of fly ash produced mix results. Pathak [32] in

his technical paper on pozzolana cement has reported that 10 per cent of the concrete

produced in the world utilized fly ash either in blended cements or during the

22

production of concrete at site, whereas it is only 5 per cent in case of India. As regards

to the permission given by different Indian codes and standards for the use of blended

cements, the author reported that though IS 456:2000 (Code of Practice for Plain and

Reinforced Concrete) and IRC 15:2002 (Code of Practice for Construction of

Concrete Roads) permitted use of PPC, Ministry of Road Transport and Highway

(MORT&H) under its clauses 602 and 1000 has barred its usage. It is well known that

OPC when combines with water shows only primary reactions, which liberate lime.

Because the compounds of such reactions are weak in resisting chemical attacks, the

concrete becomes prone to expansion and cracking. That is, using OPC alone could

introduce an element of risk in concrete durability. But cements with pozzolanic

materials undergo a secondary reaction, where they combine with lime to give

additional products of hydration that are denser and show higher ultimate strengths,

become impermeable and hence durable. Due to lower density and high volume per

mass, PPC is more efficient in filling voids. Use of PSC for concrete roads is not in

vogue worldwide because of the limited availability of GGBS. However, in India,

GGBS is available and slag based cements can be satisfactorily used in concrete roads

[1]. Kadkade and Mishra [33] have provided an account of fly ash blended cement

concrete pavement, used for the construction of Yamuna Expressway. PPC of more

than 400 kg per cubic metre of concrete was used in the mix design PQC, which had

target flexural strength of 4.88 MPa. The mix design for DLC too had PPC as

cementitious material. Construction of Yamuna Expressway demonstrated the use of

blended cement in PQC on a large scale.

2.5 HIGH EARLY STRENGTH

Early-age strength of concrete is the primary requirement of accelerated

construction and rehabilitation. Researchers in the past have modified properties of

23

concrete using different types of high early-strength cements, accelerators, mineral

additions etc., and employed alternate curing methods to enhance early strength gain

of concrete. Accelerators are found to be excellent viable options due to the degree of

easiness they offer during mixing operations. But limited application of accelerator is

seen in fast-track construction and generally only calcium chloride is tried as

accelerator. Further, addition of accelerator is not only useful in getting early high

strength in concrete, but it also helps in increasing its wear resistance depending on

curing age [2]. Calcium chloride is the most widely used accelerator and the exact

mechanism of Calcium chloride is not well understood. Hundreds of papers are

published on its effect on concrete. It increasers the rate of C-S-H formation thereby

increasing the early strength. It is added at the rate of 0.1 to 0.7 % by mass of

cement. [34]. Cheung et al. [35] have reviewed hydration kinetics of Portland cement

concrete containing different admixtures including accelerators, whose primary

acceleratory target is the aluminate phase, normally resulting in rapid workability

loss. The authors have cautioned about some cases of concretes where the sulphate

gets depleted prior to the main silicate peak, due to either inadequate added sulphate

or more active aluminates as a result, acceleration can be diminished and this impact

of sulphate balance is strongly seen with non-chloride accelerators, which in some

cases have been shown to become retarders in severely under-sulphated conditions.

Hence suggesting the road map for future research, the authors have concluded that a

number of the specific requirements like type of cement, mineral admixtures,

alternate curing techniques etc. were needed to model the behaviours of accelerators

in concrete. Therefore the authors have stressed for modeling the behaviour of

accelerator in the pavement concrete for the requirement of high-early strength.

Kovler and Roussel [36] have reviewed the literature related to the properties of

24

fresh and hardened concrete published after the 12th International Congress on the

Chemistry of Cement held in Montreal in 2007. In the review on the effect of

chemical admixtures on the properties of concrete, the authors have mentioned about

the research on the role of corrosion inhibitors, air-entraining agents and water-

reducing agents but research on the accelerator was not discussed. Mailvaganam et al.

[37] have studied the effects of chloride, non-chloride accelerators and

superplasticizer on the physio-chemical properties of two types of concrete, prepared

with fly ash and slag as 30 per cent replacement to normal Portland cement and

compared with the reference mix containing 100 per cent normal Portland cement.

Two series of mixes utilizing different admixture dosages and cured at two

temperatures (22°C and 5°C) were investigated. The compressive strength results and

temperature time curves indicated that at 22°C all three admixtures were effective in

offsetting the early strength reduction due to cement replacement. With the exception

of fly ash mixes, 28 day strengths were close to and in some instances exceeded the

strength of the 100 per cent Portland cement mixes. At lower temperatures (5°C) the

performance of conventional accelerating admixtures was marginal. Popovics et al.

[38] have investigated 4 rapid hardening cements, namely magnesium phosphate

cement for cold and regular weather use, magnesium phosphate cement for hot

weather use, aluminium phosphate cement and regulated set cement for the purpose

of quick repair of the concrete pavements. Compressive strength, x-ray diffraction

and scanning electron microscopy (SEM) tests were conducted as part of mechanical

and physiochemical tests on the concretes produced with these cements and water

reducing agents. Test results revealed that magnesium phosphate based cements

exhibited rapid strength gain in comparison to their other counterparts.

Physiochemical investigations provided limited information about the nature of the

25

hydration process of the cements. The authors did not study the durability attributes

of such concretes. Popovics [39] has studied the strength-increasing effects of a

chloride-free accelerating admixture on various Portland cement pastes, mortars and

concretes with or without other admixtures. The results were preliminary in nature

but the available experimental evidence showed that the tested chloride-free

accelerator was capable of increasing the strengths of a wide variety of cementitious

compositions including Portland cement, epoxy, pozzolana and combinations of

these. Smith [40] has investigated effects of two non-chloride accelerating agents

namely, sodium thiocyanate and calcium nitrate to achieve initial set of two brands of

ASTM Type I cement at 21 °C and at 4 °C. The results obtained were compared with

that of calcium chloride accelerator. Test results revealed that low or moderate

dosages of the two non-chloride accelerators could reduce time to achieve initial set

by l to 2 hours. It was also observed that effectiveness of the accelerator depended on

the type of cement and all three of the accelerators were more effective at 4 °C than

at 21 °C. The results highlighted the importance of type of cement and atmospheric

temperature for the effectiveness of accelerator. Rezansoff and Corbett [41] have

assessed effect of a chloride-based strength-accelerating admixture on the tensile and

compressive strength development of concrete under both wet and dry curing.

Tension and compression tests were made at regular time intervals up to 91 days.

Tension tests included the split cylinder, the modulus of rupture, and a pullout test.

Both strength-accelerated concretes showed reduction in the split cylinder tensile

strength averaging 10 and 11 per cent for wet and dry curing, respectively, at 91 days

relative to the compressive strength, when compared to the tensile strength achieved

for the control concrete without accelerating admixture. It was found that the

equations provided by concrete codes to estimate tensile strength based on

26

compressive strength of normal concrete were not applicable to concretes with

accelerating admixtures, since tensile strength acceleration might be much less than

compressive strength acceleration with calcium chloride or a chloride-based

accelerator. This was further complicated with dry curing since tensile strengths

might drop significantly with time. Ansari et al. [42] have discussed the development

and testing of two high early-strength concrete mixes. Fast-track concrete was

prepared with ASTM Type I Portland cement and a non-chloride-based hardening

accelerator. The concrete was used in full-depth repair of jointed concrete slabs on an

interstate highway in New Jersey of USA. A comprehensive experimental

programme was implemented for examining the strength gain capability as well as

the practicality of concrete mixes for field implementation. Soroushian and

Ravanbakhsh [43] have studied properties of high-early strength concrete for full

depth repairs of concrete pavements, produced using calcium chloride accelerator.

High cement content of 500 kg per cubic metre and 3.2 per cent of accelerator by

weight of cement were used to prepare concrete mixtures. Cellulose fibers and air-

entraining agent were used as additives to impart durability attributes to concrete as

generally high-early strength concretes were seen vulnerable to shrinkage and micro

cracks thus limiting the service life of concrete repairs performed with such concrete.

The strength properties, measured by compression and flexure tests and durability

property assessed by shrinkage, air-permeability abrasion resistance and freeze-thaw

resistance, were compared with normal concrete and high-early strength concrete

without cellulose fibers. It was found that addition of cellulose fibers helped reduce

the cement and accelerator contents by approximately 10 to 20 per cent while still

satisfying the early-age strength requirements of 8 hour opening time. Processed

cellulose fibers actually increased the resistance of concrete to restrained shrinkage

27

micro-cracking and cracking. Laboratory studies confirmed that the air permeability

of large restrained specimens could be reduced with the addition of processed

cellulose fibers. Lee et al. [44] presented a technical report which described

constructability and productivity analysis of the fast-track pavement reconstruction

on I-15 at Devore, which was located near San Bernardino in USA. They concluded

that the 72-hour closure was the most economical scenario when compared to other

types of closures from the perspective of construction schedules, road user delays,

and construction costs. Two concrete slab mix designs were compared: Early-age

ASTM Type III Portland Cement Concrete and Fast-Setting Hydraulic Cement

Concrete. They considered 2.8 MPa as the flexural strength for opening of repaired

pavements. It was found that two materials took approximately the same overall

project completion time. Hence they concluded that Fast-Setting Hydraulic Cement

Concrete was not the most economical solution. In his paper on accelerated

construction of cement concrete pavements, Nemati [45] has suggested that the

opening time to traffic on the new or rehabilitated pavement should be based on

achievement of required strength only. The paper discussed rapid construction of an

intersection where an Asphalt Concrete intersection was reconstructed with Portland

Cement Concrete Pavement over the weekend in 70 hours, where the use of ASTM

Type III cement was seen to be more beneficial in achieving the early strength. Water

reducing admixtures were used in the concrete which indirectly helped in getting

early strength due to less water demand. Barnett et al. [46] have investigated early-

age strength development of concrete containing slag cement, cured with different

curing temperatures so as to give guidance for its use in fast-track construction. The

percentage slag cement of the total binder in concrete was varied from 0 to 70 in 4

intervals. A total of 15 concrete mixtures were tested for the target 28-day mean

28

strengths of 40, 70, and 100 MPa. The standard and adiabatically-cured cubes were

tested in compression at 1, 2, 3, 5, 7, 14, 28, and 91 days. The early-age strength of

concretes with similar 28-day strengths and cured at 20 °C (68 °F) were adversely

affected by increasing levels of slag cement. The early-age strength contribution of

slag cement was greatly improved by high curing temperatures. The later-age

strength of these concretes under adiabatic curing conditions depended on both the

binder and the strength grade. In some cases, the ultimate or 28-day strength of the

concrete was unaffected by the higher curing temperatures experienced during

adiabatic curing. Ramseyer et al. [47] in their paper on economic and fast-track

rehabilitation of concrete pavements and bridge decks, have demonstrated the

production of very early strength concrete mixtures with low shrinkage properties

using ASTM Type I and Type III Portland cements, where it was found that very

early strength concrete with minimal Type III cement content was possible. For the

tested very early strength mix, decrease in the Type III cement content did decrease

the shrinkage but negatively impacted the early age strength gain required. Increasing

the Type I cement content was necessary to increase the early strength. It was also

investigated that addition of air-entraining agents increased the shrinkage of concrete.

Compressive strength of 20.7 MPa at six hours was the requirement of the mixes

which had variable and constant accelerator (conforming to ASTM C 494 as a Type

C admixture) dosage in different programme. When the dosage of accelerator was

variable, the mix with maximum accelerator dosage recorded maximum compressive

strength with both types of cements. Buch et al. [48] have experimentally evaluated

high-early strength concrete mixtures used in full depth repairs. In their study, 14

different concrete mixtures were tested for compressive and flexural strengths,

freeze-thaw resistance and microstructure properties. The produced concrete

29

contained ASTM Type I and Type III cements in the range of 425 to 525 kg per cubic

metre. The accelerators calcium chloride and non-chloride were used to hasten the

strength development with most of the mixtures devoid of reducers. The specimens

were air-cured in the moulds before testing. The initial design criteria included a

minimum compressive strength of 13.8 MPa (2000 psi) and a flexural strength of 2.1

MPa (300 psi) within the 6-8 hour opening time criteria. Of the 28 batches 19 did not

achieve the desired 6-8 hour compressive strength, with three of the mixtures that

achieved the desired early strength undergoing high temperature curing. The

investigations demonstrated the importance of increased temperature in achieving

early strength. For the specific cements used, the cement type had a notable impact

on various measures of early concrete strength, with Type III cements producing

higher strengths at a given age than Type I cements. All the high-early strength

mixtures had significantly high levels of micro-cracking hence authors have

recommended durability-related testing on such mixtures to ensure longevity of the

repair. Ghafoori et al. [49] have used Calcium chloride of constant dosage of 2 per

cent by weight of cement as an accelerating admixture in early opening-to-traffic

concretes which are also known as fast-track concretes. They investigated a total of

11 concrete mixtures made with 4 different cement factors, namely: 386, 446, 505

and 564 kg/m3 and 3 different cement types, namely: ASTM Type I, III and V

Portland cements, at early-age and at full maturity. The laboratory test specimens of

prisms and cylinders were cured in insulating boxes for pre-designated period of

time, sufficient to attain the minimum compressive strength for opening-time

requirement. The compressive strength of 20.7 MPa, corresponding to a flexural

strength of 4.5 MPa was the requirement for all the concrete mixtures for opening-to-

traffic time. Most of the mixtures achieved the opening-time strength in about 8

30

hours. Upon removal from the insulation boxes, half of the specimens were directly

immersed in 5 per cent sodium sulphate solution for 270 days and remainder were

cured in lime saturated water tank for 28 days before immersing in 5 per cent sodium

sulphate solution for again 270 days. Length change, loss of compressive strength

and mass loss were studied by the authors. Though fast-track concrete mixtures

showed excellent sulphate resisting attributes, the mixtures that allowed to mature

prior to sulphate attack exhibited better strength and durability characters than those

exposed to sulphate attack immediately at the opening time. The investigations

proved the importance of curing for strength and durability of fast-track mixtures

containing accelerators. Studying the behaviour of accelerators in the strength

evolution and setting times of cement pastes at early age, Aggoun et al. [50] in their

work on the effect of some admixtures on the setting time and strength evolution of

cement pastes at early ages, have remarked that research on accelerators dated back

to 1962 where calcium formate (Ca(CHO2)2) was first used as set accelerator.

Stressing the requirement of chloride free accelerators, the authors opined that

calcium chloride had been in the past the most widely used set accelerator in concrete

but the presence of chloride caused serious problems regarding corrosion of

reinforcement bars and this had renewed the interest to develop a number of chloride

free accelerators. They tested three types of accelerators namely calcium nitrate

which acted as set accelerator as there was marginal hike of compressive strength at

early age (1 and 3 day), TEA and TIPA which acted as hardening accelerator with

more than 50 per cent hike in compressive strength at early age(1 and 3 days). The

experimental findings by the authors on the behaviour of accelerators in the cement

paste can be applied to the fast-track concretes as it is the cement which is the binder

for aggregates in concrete and chemistry of cement is nothing but chemistry of

31

concrete. Cangiano et al. [51] have demonstrated the production and use of rapid

hardening concrete for the reconstruction of deck slab of small span bridge at

Brescia, Italy. Ordinary lime stone crushed aggregates of maximum size 10 mm,

cement content in the range of 600-650 kg/m3 and water-cement ratio of 0.25-0.27

were used for the production of concrete for the design strength of 60 MPa. No silica

fume, or accelerating admixture or pozzolanic materials were used. This rapid

hardening concrete was able to reach more than the design strength in one day. Use

of high content of cement and small size of coarse aggregate are the limitations of

this work. Khokhar et al. [52] have used mineral admixtures (fly ash and GGBS) to

get optimization in the early strength of concrete. Their study did not include any

accelerating admixture. It was observed in their study that the reduction in water

content and use of superplasticizer were not enough to obtain the design strength for

mixtures with the higher percentages of fly ash. Micro-fillers were used to improve

workability and early-strength. Micro-fillers did not participate in the chemical

reactions, but their better performance could be attributed to their action as an

accelerator during early cement hydration, as they would provide nucleation sites for

the hydration of the C3S and C2S, shortening the dormant stage and accelerating the

hydration reactions. To improve the performance of concrete mixture containing

mineral additions, an optimization method was introduced. To increase the early- age

strength, w/b ratio was reduced. Optimization was done to reach a compressive

strength of 10 MPa at 48 hours. However, the use of micro-fillers needs further

investigation taking into account its proportional use and durability factors. Riding et

al. [34] in their investigation on early age strength enhancement of blended cement

systems by combination of chloride and non-chloride accelerators have found that the

combination of DEIPA and Calcium chloride increased the early age strength of

32

mortar by increasing the degree of cement reaction. The mortar mixtures were

produced with low alkali and high alkali cement in combination with a typical slag,

and a Class F Fly Ash. The mortar strengths at 1 and 7 days were tested. The

combination of DEIPA and Calcium chloride enhanced the 1-day compressive

strengths of the High Alkali cement and slag blend by 14-19 per cent, the Low Alkali

cement and slag blend by 28-33 per cent and the Low Alkali cement and Class F Fly

Ash blend by 28-62 per cent. The admixtures however, did not significantly affect the

7 day or 28 day compressive strengths. Despite higher degrees of hydration DEIPA

mainly accelerated the aluminate phases. The authors particularly took the study of

DEIPA as there had been many studies on TEA and TIPA, but very few on DEIPA.

The technology of early strength development in concrete is continuously evolving.

Use of new ingredients in such concrete is being researched and there are some

positive outcomes but the application of such ingredients in the production of

concrete is still in its infancy and it takes some time to optimize their usage. Zhang et

al. [53] have used nano-silica to increase early strength and to reduce setting time of

concretes with high volumes of slag. They have assessed effects of nano-silica

dosages, size and dispersion methods on strength development of high volume slag

mortars. The results indicated that the incorporation of a small amount of nano-silica

reduced setting times, and increased 3 and 7-day compressive strengths of high-

volume slag concrete, significantly, in comparison to the reference slag concrete with

no silica inclusion. The strengths of the slag mortars were generally increased with

the decrease in the particles size of nano-silica at early age.

2.6 CURING

The most important phase of concrete after casting is curing, and it assumes

greater importance in high-early strength concretes, produced with different types of

33

cement. The term curing of concrete involves a combination of conditions that

promote the cement hydration, namely time, temperature and humidity conditions,

immediately after placement of the concrete mixture into formwork [54]. The

necessity for curing arises from the fact that hydration of cement can take place only

in water-filled capillaries, so in order to obtain a good mortar or concrete, the placing

of an appropriate mixture must be followed by curing in a suitable environment

during the early stages of hardening and a loss of water by evaporation from

capillaries must be prevented [55, 56]. There are many methods by which concrete

can be cured to achieve desired strength and durability. Conventional moist curing,

steam curing, high temperature steam curing, membrane curing etc. are the different

methods of curing. Conventional moist curing is always preferred wherever it is

feasible. In areas that suffer from paucity of water, membrane curing is a viable

option, especially for concrete pavements, as the application of membrane curing

compound is practicable and relatively easy. High temperature curing can give quick

strength to concrete; its application in pavement structures poses certain practical

problems. Membrane curing using different water and acrylic based curing

compounds is practically feasible for pavement concretes owing to the simplicity of

its application. Exhaustive experimental data in the form of research findings is

available about the effect of different curing on the properties of concrete. In one of

the early investigations on membrane curing, Rhodes [57] conducted laboratory and

field tests to compare the effect of storage conditions on the physical properties,

warping, temperature control, strength and abrasion resistance of concrete cured with

membranes and with wet burlap. A survey of pavements cured with clear membranes

in spring and summer showed that cracking, when occurred at all, was found

predominantly in pavements laid in the morning hours. Comparing white-pigmented

34

membranes with the usual wet-curing conditions in the field, membrane curing was

found to be efficient, practicable and about as half as expensive as wet curing under

the same conditions. Fattuhi [58] has investigated the effect of liquid based curing

compounds on the fresh and hardened properties of concrete. In the first series, fresh

concrete specimens sprayed with compounds were placed inside cabinets, maintained

at different environmental conditions. In the second series, hardened concrete cubes

brushed with compounds were either exposed to atmospheric conditions or placed in

environmental cabinets. Test results on fresh concrete specimens indicated a wide

variation in the curing efficiencies (25-89 per cent) depending on compound type and

environmental conditions. Low efficiencies (below 47 per cent) were noted for 70 per

cent of the tested compounds. For the hardened concrete cubes, compressive strength

test results generally indicated higher efficiencies (80-100 per cent). Austin et al. [59]

have compared the influence of curing methods on the strength and durability of

concrete produced with slag cement, with that of the normal concrete in a simulated

arid climate. Four curing regimes were investigated to encompass the range of

practical methods encountered on site. Specimens were placed in the hot environment

immediately after casting and conditioned for up to 28 days. The strengths of the slag

concretes were higher than that of the normal control concrete at all test ages (7, 14

and 28 days) when good curing was provided. Partial cement replacement with slag

therefore offered the potential to produce stronger and more durable concrete in hot

climates. The disadvantage of slag concretes was that they proved to be more

sensitive to poor curing than normal concrete with both strength and permeability

getting seriously impaired. Huyke-Luig [60] has investigated the effect of various

curing conditions on the compressive strength-gain of concrete in the tropical region.

In the experimental programme, the strength gain with age of concrete up to 1 year,

35

with different compressive strengths and under different initial and subsequent curing

conditions in warm and high-humidity climates, was determined. The initial curing

techniques evaluated were those most widely used in practice and were intended to

represent actual, imperfect construction practice. The subsequent curing conditions

were artificially modeled to simulate dry and rainy climates. Of the curing methods

evaluated, ponding was found to be the most effective, followed by intermittent

sprinkling, unsealed plastic covers, and curing compound. Wang et al. [61] have

studied moisture loss in concrete due to membrane curing. It was revealed that the

drying of concrete at early ages did not follow the “three-phase theory” and exhibited

two peak rates in moisture evaporation. When curing compounds were applied, the

rate of moisture loss from concrete was reduced immediately and the second peak was

eliminated. It was also found that the effectiveness of membrane curing depended

crucially on the time of its application and the generic type of the curing compound.

Ramezanianpour and Malhotra [62] have studied the effect of four curing regimes

namely, moist curing, curing at room temperature after demoulding, curing at room

temperature after two days of moist curing and curing at 38 °C with 65 per cent

relative humidity, on the mechanical and durability properties of concrete produced

with fly ash, slag and silica fume. The water-cementitious materials ratio of all the

concrete mixtures was kept constant at 0.50, except for the high-volume fly ash

concrete mixture, for which the ratio was 0.35. Compressive strength at various ages

and resistance to chloride ion penetration was assessed. The results indicated that the

reduction in the moist-curing period resulted in lower strengths and more permeable

concretes. The strength of the concretes containing fly ash or slag appeared to be

more sensitive to poor curing than that of the control concrete, the sensitivity

increasing with the increasing amounts of fly ash or slag in the mixtures. The

36

incorporation of slag or silica fume, or high volumes of fly ash in the concrete

mixtures, increased the resistance to chloride ions and produced concretes with very

low permeability. Mailvaganam[63] in his paper on chemical admixtures in concrete

has suggested membrane curing for cost effectiveness and durability, with a

maximum allowable water loss of 0.55 kg/m2 at 37.8±1.10 °C, when compared with

curing by using plastic sheets, wet burlap and retaining the shuttering for a specified

number of days, as neither of the first two methods were carried out for a sufficient

duration in the field because of the difficulty of ensuring continuous wetness and the

cost associated with keeping shuttering in place often precluded the use of this

method. Erande and Limaye [24] have suggested an increase in the quantity of

application of curing compound to 250 ml/m2 from 200 ml/m2 for making them more

effective in retaining moisture in freshly laid concrete. Aldea et al. [64] have studied

effect of three curing conditions namely, autoclaving (175°C, 0.5 MPa), steam curing

(80°C) and normal curing (28 days, 20°C, and 100% relative humidity) on the

properties of 4 concrete mixtures with slag as partial replacement to cement from 0 to

75 per cent in three equal intervals. The properties examined included mechanical

properties (compressive and tensile strength), transport properties (chloride

permeability and chloride penetration) and micro-structural properties (pore structure

and phase composition). Steam curing resulted in lower compressive strength and

Chloride permeability and penetrability significantly decreased with increasing slag

replacement except for autoclave curing. They concluded that for improved durability,

room temperature curing was the best. Zhang and Zhang [65] have demonstrated the

effect of moist curing in tropical regions at different temperatures on the strength and

other properties of concrete, produced with Portland cement (ASTM Type I) and 20

mm maximum size aggregate. The authors found that the strength of concrete cured at

37

higher temperature to be higher. The concrete was cured at 20 °C and 35 °C for 28-

days with varied water-cement ratio from 0.3 to 0.7, with an increment of 0.05.

Capillary porosity of concrete cured at 20°C was found to be lower. Huo and Wong

[66] have studied early-age behaviour of high performance concrete deck slabs under

different curing methods. The paper highlighted the importance of curing technique

and its duration in the strength and durability characteristics of concrete, where it was

stressed about proper curing to maintain satisfactory moisture and temperature,

particularly at the early-age of concrete. ASTM Type 1 cement, fly ash (class C) and

silica fume were used to prepare the concrete. Three moisture-curing methods and one

membrane curing method were used in the tests, which were: (1) wet burlap blankets,

(2) cotton mats, (3) curing compound, and (4) polyethylene blankets. The properties

assessed were, early-age shrinkage development, temperature change, and

evaporation rate. Moisture-curing methods could effectively reduce concrete

temperature due to hydration heat during early-age. Cotton mats and burlaps retained

more moisture on the concrete surface and reduced the temperature in concrete during

the very early-age. The findings of the paper are important to know the suitability of

curing technique for high performance concrete from the early-age deformation view

point. Al-Gahatani [67] has carried out an experimental study on the effect of three

types of curing methods, namely wet burlap, water based and acrylic based membrane

forming curing compounds, on strength and durability properties of concrete

produced with plain and blended (fly ash and silica fume) cements. The properties

investigated were compressive strength, shrinkage (plastic and drying) and pulse

velocity. It was observed that the strength developed in the concrete specimens, cured

with wet burlap was higher than in the specimens cured by membrane forming curing

compounds but specimens cured with curing compound exhibited higher efficiency in

38

decreasing plastic and drying shrinkage strains than that cured by covering with wet

burlap. The efficiency of acrylic based curing compound was higher than water base

curing compound. The curing efficiency of acrylic based curing compound, in terms

of compressive strength was in the range of 84-96 per cent. Yilmaz and Turken [68]

have studied the effect of curing materials on the compressive strength of concrete

produced with multiple admixtures like cold weather concreting admixture, set

retarding admixtures etc. The curing materials used in the study were paraffin

emulsion based curing material, hydrocarbon resin based curing material, acrylic

dispersion based curing material and acrylic resins. The experimental study revealed

that each chemical curing material used in the study presented various results,

differing from each other, for concrete specimens produced with no admixture and

different chemical admixture. They inferred that a given curing material which

increased the strength of concrete produced with any type of admixture could reduce

the strength of concrete produced with another type of chemical admixture and

alternatively, a curing material giving appropriate results for concrete specimen

produced without any chemical admixture could give inappropriate results for

concrete produced with other chemical admixtures. Hence they suggested that the

compatibility of curing material with admixtures in concrete should be assessed

before its application in the site.

2.7 STRENGTH PROPERTIES

Many construction agencies specify compressive strength of concrete for quality

compliance. In case of concrete roads it is the flexural strength which governs the

design. Hence it is required to know both the compressive and flexural behaviour of

concrete, particularly of high early-strength concrete, with features like blended

cements, chemical admixtures, alternate curing etc. There is limited information on

39

the flexural strength of such concrete. In their study on flexural strength of concrete,

Yener and Chen [69] have examined the differential influence of six differential

parameters namely; aggregate size, aggregate shape, water-cement ratio, age of

concrete, curing conditions and cement types to assess flexural strength and breakoff

strength, where breakoff strength test was similar to the process of testing cantilever

beam subjected to a concentrated force at the end. The variables included ASTM

Type I and Type III cements, dry and moist curing regimes with 7 and 28 days as

curing period , 12.5 mm and 25 mm as size of aggregate , smooth and angular as

shape of aggregate and water-cement ratio (varied from 0.35 to 0.53) in six equal

intervals. It was experimentally established by the authors that the rupture due to

flexural loading in most of the concretes was usually controlled by the aggregate-

cement bond except in concretes of high strength and concretes made with weak

aggregates. The experimental results proved that neither the aggregate shape nor the

size had any effect on the flexural and breakoff strengths of concrete. It was found

that the water-cement ratio, cement type, curing regime and curing age had significant

effect on the test results. The flexural strength increased rapidly after the age of 7 days

up to 28 days. Highlighting the failure mechanism of concrete under flexure, the

authors suggested that flexural failure was governed by weak-link theory, according

to which the failure gets initiated at the weakest section within the uniform moment.

The formation of the weakest section may be during production of concrete due to

inadequacy in mixing, compacting etc. Effects of admixture and blended cements and

the early-age (before 7 days) flexural behaviour of concrete were not part of the

investigation. Roesler et al. [23] in their report on the design and construction issues

for long life pavement strategies, prepared for California Department of

Transportation, have opined that the main concern with opening the rehabilitated

40

concrete to traffic was premature cracking of the slabs and if the flexural strength of

the concrete was not sufficient to resist the applied truck loads, then flexural fatigue

cracking would result. The report has given a list of the recommended opening

strength for a variety of pavement features taken from Federal Highway

Administration Washington D.C., where the required strength for opening to traffic

was based on fatigue analysis and the estimated number of Equivalent Single Axle

Loads (ESALs) the pavement could resist before fatigue cracking. The required

minimum flexural strength for all pavements was 2,068 kPa. Hence looking at the

significance of flexural strength in pavement concrete, it is ideal to specify pavement

concrete on the basis of flexural strength but it may be convenient to control it largely

on the basis of compressive strength, as estimation of flexural strength is rather

difficult. Initially concrete should be tested extensively to ensure that required flexural

strength is attained so as to establish relationship between compressive and flexural

strengths for a particular mix where any significant change detected in the

compressive strength could lead to reconfirmation of flexural-compressive strength

relationship [24]. Buch et al. [48] have recommended that if the concrete compressive

strength was to be used during construction to estimate flexural strength, the

relationship should be established for the actual job mix. This particularly warrants in

high-early strength mixes. There are some encouraging informations on the flexural

behaviour of concrete made with blended cements. Hale et al. [31] have found that

addition of slag cement increased the modulus of rupture. The authors also found out

that the source of cement had little effect on the modulus of rupture of the control

mixtures. For all the mixtures, the modulus of rupture results ranged from 4.6 MPa to

6.4 MPa. In the Delhi-Metro Rail Project, the concrete produced with fly ash

exhibited about 25 per cent higher flexural strength than normal concrete [32].

41

2.8 DURABILITY

Durability of concrete in general and fast-track concrete in particular is very

important. The rehabilitated or repaired concrete road using fast-track concrete

mixtures should show excellent durability attributes so as to avoid premature failure

after repair. Permeability, early-age shrinkage and freeze-thaw resistance are the

parameters generally evaluated to assess the durability of concrete. Hence review of

these properties of concrete is of paramount importance, especially of the concretes

produced with admixtures, different cements and cured with different curing methods.

Cement composition has major role in the durability of concrete. Concrete made with

modern cements comply with the specified 28-day strengths at higher water-cement

ratios and lower cement contents in comparison with the old cements, but with the

rapid hydration due to high C3S and cement particles spaced more widely apart due to

high water-cement ratio, the pore size distribution which determines permeability will

comprise predominantly of large and possible interlinked pores. Such an open and

continuous pore structure of hydrated cement paste is more permeable to aggressive

ions and solutions than one of similar porosity with fine and discontinuous pores.

Permeability is a pre-eminent criterion of durability; therefore, concrete made with

modern cements although satisfying strength requirements, is likely to be more

permeable, less dense and hence less durable [70]. Durability of the concrete is often

not affected by rapid gain of concrete strength whereas factors like permeability and

water cement ratio affect the durability [4]. Whiting and Nagi [71] have carried out

tests on the strength and durability of highway concrete used for rapid repair, typically

used for full depth repairs. Compressive strength, tensile strength, freeze-thaw

resistance and air-void characteristics were tested for the concrete. Durability results

were mixed, with those mixes having marginal air contents or using chloride

42

accelerators showing significant deterioration in freeze-thaw testing. Nagi et al. [72]

have studied the durability aspects of concrete used for early opening of repaired

highways. A variety of concretes mixes using different types of rapid strength

cements and admixtures, used for full-depth repair (slab replacement) of concrete

pavements and for bridge deck overlays in the states of Ohio, Kentucky, and Georgia

of USA were assessed. Durability evaluation of these mixtures included freeze-thaw

resistance, characterization of the air-void system, deicer scaling tests, and

measurement of chloride permeability. Specimens for these tests were prepared in the

field and were subject to standard field curing. Poor freeze-thaw performance of many

of the pavement repair mixes indicated that many questions still remained regarding

durability of concretes designed for early opening applications. It was particularly

observed that the use of calcium chloride reduced freeze-thaw resistance and hence its

avoidance was recommended in concrete. Al-Amoudi et al. [73] have studied the

effects of magnesium- sulphate and sodium- sulphate on the durability performance of

plain blended cement mortars. ASTM Type I, Type V, and blended cements, made

with fly ash, silica fume, and blast furnace slag, were exposed to sodium-sulphate and

magnesium-sulphate solutions. The performance of these cements in both the

environments was evaluated by measuring expansion and determining reduction in

compressive strength. The deterioration of the mortars due to the chemical exposure

was attributed to the initial reaction of these sulphates with calcium hydroxide. Higher

reduction in strength was observed in plain cement mortar specimens compared to

blended cement mortar specimens upon exposure to sodium-sulphate environment.

The strength reduction was, however, observed to be relatively lower in plain cement

mortar specimens exposed to the magnesium-sulphate environment compared to that

in blended cement mortar specimens. Expansion was observed to be higher in both

43

plain and blended cement mortar specimens exposed to the sodium-sulphate

environment compared to expansion measured in specimens exposed to magnesium-

sulphate environment. The expansion in plain and fly ash-blended cement mortar

specimens, exposed to sodium-sulphate was higher than in silica fume, blast furnace

slag, and low water-cement ratio mortar specimens. The higher expansion in plain

cement mortar specimens exposed to the sodium-sulphate environment could be due

to the formation of secondary ettringite. Saricimen et al. [74] have performed the

permeability and other durability tests on plain and blended cement concrete, cured in

field and laboratory conditions. Class F fly ash with 20 per cent cement replacement

was used in the pozzolanic cement concrete specimens. The concrete was tested at

early and at later age and it was found that fly ash cement concrete specimen were

less permeable. The authors commented that since pozzolanic reaction was highly

dependent on good curing practice, there was often concern about the effect of curing

on the permeability of pozzolanic cement concretes. Mangat and Khatib [75] have

investigated sulphate resistance of concrete produced with fly ash, silica fume and

slag. The concrete was prepared with different proportions of these mineral additions,

with a total cementitious content of 350 to 450 kg per cubic metre of concrete and

0.45 as water-cementitious material ratio. The concrete specimens were cured for 14

days after casting under different temperatures (20°C and 45°C) and humidity (25, 55

and 100) before immersion in sulphate solution. Results showed that cement

replacement by 22 and 32 per cent of weight by fly ash produced maximum sulphate

resistance. An 80 per cent replacement of cement by GGBS improved the sulphate

resistance of concrete; whereas 40 per cent replacement had contrary effect. 5 to 15

per cent replacement of cement by silica fume improved the sulphate resistance of

concrete considerably. Vieira et al. [76] have studied the influence of water curing on

44

the durability characteristics of fly ash concrete used for road pavement. Abrasion

test, determinations of compressive strength, capillary absorption, oxygen

permeability and open porosity, were performed on concrete mixtures with different

cement and fly ash contents, using limestone coarse aggregate and natural siliceous

sand. The results showed that fly ash concretes could develop satisfactory resistance

to abrasion, even with large amounts of cement replacement. In general, concrete

performance was improved with longer water curing times. Experimental studies on

the durability parameters like permeability, weight loss, resistivity, chloride

diffusivity of PPC, PSC and OPC concretes of grades M30 and M45, has confirmed

that some of the above durability parameters of PPC and PSC concretes were higher

than that of OPC concrete [25]. Basheer et al. [77] in their review paper on the

assessment of the durability of concrete from its permeation properties, have

discussed different transport mechanisms such as water absorption, permeability and

diffusion and the general principles adopted for their test methods. The durability

parameters such as chloride ingress, corrosion due to chloride ingress, carbonation

and freeze-thaw deterioration were also discussed. From the reported results it was

evident that all the transport processes were inter-related. The authors concluded that

the above mentioned transport processes were important physical properties of

concrete in relation to the durability parameters discussed and hence they opined that

the durability of concrete could be assessed by the measurement of concrete transport

processes. Naik et al. [78] have tested high volume fly ash pavement concrete for

strength and durability. The investigation was undertaken to examine the performance

characteristics of concrete pavements made with high volumes of Class F and Class C

fly ash. Compressive strength, resistance to chloride-ion penetration, and density of

concrete were tested using specimens from in-situ pavements. Test results indicated

45

better pozzolanic strength contribution and higher resistance to chloride-ion

penetration for concrete mixtures made with Class F fly ash relative to that made with

Class C fly ash. Aydin et al. [79] have studied the effect of ASTM Class C fly ash on

the sulphuric acid resistance of concrete. Cement was replaced with fly ash up to 70

per cent. The concrete specimens were cured by water and alternatively by steam.

Test results indicated that sulphuric acid resistance of steam-cured concrete could be

improved significantly by incorporation of fly ash. The deterioration rate of steam-

cured Portland cement concrete (control samples without fly ash) subjected to

sulphuric acid attack was much higher than that of standard-cured one. This could be

due to the more permeable microstructure of steam-cured samples caused by rapid

formation of CSH. However, above 40 per cent fly ash replacement level, steam-

cured concrete showed lower degradation than water-cured one. The results indicated

that sulphuric acid resistance of steam-cured concrete could be improved by

incorporation of fly ash, whereas the improvement in acid resistance by incorporating

fly ash was negligible in standard-cured concrete. These results are very important to

understand the effect of method of curing on the acid resisting property of concrete

produced with fly ash, as pavement concrete may also experience chemical attack like

acid rain due to increasing levels of environmental pollution. Banthia et al. [80] have

performed permeability tests on concrete specimens subjected to a compressive stress

to understand the permeability attributes of concrete at early (1-3 days) age. It was

found that the presence of a compressive stress below a certain threshold value

decreased the permeability, but there was significant increase in the permeability of

concrete when the applied stress exceeded this threshold value. The authors opined

that the increase in permeability due to applied stress depended upon the overall stress

history. Gonen and Yazicioglu [81] have presented laboratory studies of the concrete

46

containing mineral admixtures, silica fume and fly ash. The concrete mixtures were

subjected to short-term and long-term tests that included compressive strength,

porosity, capillary absorption, wet-dry cycle and accelerated carbonation. The test

results confirmed that mineral admixtures improved the performance of concrete. The

beneficial effect of fly ash was observed in relatively longer time. Adding of both

silica fume and fly ash slightly increased compressive strength, but contributed more

to the improvement of transport properties of concretes. Glasser et al. [82] have

reviewed the literature on the durability of concrete that undergoes detrimental

chemical attacks. Micro-structural alteration in concrete resulting from carbon

dioxide, chloride and sulphate attacks, formation of ettringite and thaumasite are

discussed in the review. Stressing on the importance of mineralogy of cement in

understanding and controlling the chemical attack, the authors opined that the

permeability of concrete and hence the sulphate attack could be controlled by the use

of cementitious materials. The effect of mix design parameters on the compressive

strength, depth of water penetration and chloride permeability was investigated by

Ahmed et al. [83] with a view to develop possible relationships between these

parameters and to suggest compliance criteria. ASTM C 150 Type I cement, silica

fume and fly ash were used in the production of concrete mixtures. The experimental

findings revealed that, the compressive strength, depth of water penetration and

chloride permeability were significantly influenced by the type of cementitious

materials and water-cement ratio. The quantity of the cementitious materials content

did not significantly influence the aforesaid properties. Relationships between the mix

design parameters and compressive strength, depth of water penetration and chloride

permeability were developed by the authors. They presented the compliance criteria

for compressive strength, depth of water penetration and chloride permeability. These

47

guidelines were for crushed limestone coarse aggregates and the authors suggested

similar guidelines for other types of coarse aggregates. Correlation between

compressive strength and certain durability indices of plain and blended cement

concretes was assessed by Al-Amoudi et al. [84]. Plain, silica fume and fly ash

cement concrete specimens prepared with varying water to cementitious materials

ratio and cementitious materials content were tested for compressive strength, water

permeability, chloride permeability and coefficient of chloride diffusion after 28 days

of water curing. The investigations revealed that for concrete with water to

cementitious ratio higher than 0.5, water permeability of plain cement concrete was

higher than that of fly ash cement concrete. Further, for the same water to

cementitious ratio and cementitious materials content, the chloride permeability of

plain cement concrete was more than that of silica fume and fly ash cement concretes.

The authors have developed the correlation equation relating strength and durability

which helps in assessing the durability of concrete made of different cementitious

materials. Pereira et al. [85] have studied the influence of natural coarse aggregate

size, mineralogy and water content on the permeability of structural concrete. Good

quality granite, basalt, calcareous and marble natural coarse aggregates, obtained from

different quarries, were used to produce structural concretes. Concretes were

produced with constant volume proportions, workability, mixing and curing

conditions using different sizes of each aggregate type. Their experimental findings

revealed that aggregates’ mineralogy had no effect on concrete permeability whereas,

aggregate size and water content had significant role in the permeability of concrete.

Many experimental results have shown that the permeability of concrete made with

blended cements was lower than that made with plain Portland cement concrete. The

validation of this fact in the field is reported by Pathak [32] in his technical paper

48

which mentioned about the concrete used in the Delhi Metro Rail Project where the

permeability of fly ash based concrete was about 47 lower than that of non-fly ash

concrete. But Hoseni et al. [86] in their review paper on the effect of mechanical

stress on the permeability of concrete have reported the experimental findings which

showed that at low stress levels, regular Portland cement concrete (with no mineral

admixture) had better resistance to the permeation of water than a mix containing fly

ash. In all likelihood, this was due to the unhydrated cement particles that tend to

block the pores due to siltation in the pore fluid. The authors further stated that there

was vast discrepancy between the results from various ‘permeability’ tests due to lack

of equilibrium in the fluid flow and concluded that cyclic loading was more

detrimental to permeability than monotonic loading. Guneyisi et al. [87] have studied

the effects of cement type, curing condition and testing age on the chloride

permeability of concrete. The research variables included cement type (plane and four

blended cements), water to cement ratio (0.45 and 0.65), curing conditions

(uncontrolled, controlled and wet curing) and testing age (28, 90 and 180 days). The

test results revealed that the selected parameters had greater effect on the chloride

permeability of concrete. The chloride permeability decreased significantly with the

enhancement of curing procedure. The concretes made with blended cements

exhibited higher reduction in chloride permeability with time than those made with

the plain Portland cement, which was due to modification of pore structure. Concrete

cured under uncontrolled curing exhibited unexpected variations in the chloride

permeability.

49

2.9 SUMMARY

The distress of the rigid pavements, suitability of repair and rehabilitation methods

for rigid pavements based on the type and severity of distress, accelerated

rehabilitation of the pavements involving different type of cementitious materials,

admixtures and curing methodologies are reviewed in this chapter. The strength and

durability attributes of concretes in general and pavement concrete in particular,

produced with different cementitious materials, admixtures and cured with various

curing methods are also reviewed. From the critical review of the existing literature, it

is concluded that there is a certain scope to the value addition of the literature on the

repair and rehabilitation of the rigid pavements. The reported literature on the fast-

track pavement concrete mixtures is limited. In India the construction of the concrete

roads was almost non-existent for 50 years due to scarcity of cement and easy

availability of bitumen, hence the research and development in pavement concrete

was also non-existent during this period [88]. There is paucity of information on the

behaviour of blended cements in the pavement concrete, particularly in the fast-track

pavement concrete. The application of non-chloride hardening accelerator in

pavement concrete for high early-strength requirement is also limited, so also the use

of curing compounds [2]. There are few durability studies on fast-track pavement

concretes. The research findings on the combined effects of type of cement

(particularly of India), method of curing and non-chloride hardening accelerator in the

mechanical (at early and later age) and durability properties of pavement concrete are

not yet reported and hence an experimental study in this direction is warranted,

particularly by using the revised guidelines for concrete mix proportioning as given

by IS: 10262 2009 [89].