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Developing maturity methods for the assessment of cold-mix bituminous materials

Thomas A. Doyle, Ciaran McNally⇑ , Amanda Gibney, Amir Tabaković

UCD School of Civil, Structural & Environmental Engineering, University College Dublin, Ireland

h i g h l i g h t s

" A maturity function was developed for conditioning effects on cold-mix materials.

" A correlation between maturity and stiffness was identified.

" Method was applied to assess climatic effects on cold-mix pavements in service.

a r t i c l e i n f o

Article history:

Received 15 May 2012

Received in revised form 9 August 2012

Accepted 20 September 2012

Available online 12 October 2012

Keywords:

Asphalt materials

Cold-mix

Emulsion

Maturity methods

Curing

Conditioning

Stiffness modulus

a b s t r a c t

Cold-mix bituminous materials offer a sustainable, cost effective alternative to traditional hot-mixes. Dif-

ficulties however can be encountered when specifying cold-mix materials due to the strong influence of

time and temperature on material performance. In the field of concrete technology maturity methods are

routinely used for assessing materials of known curing history. This research presents the development of

a maturity approach for the assessment of cold-mix bituminous materials and its application for predict-

ing the effect of climatic variations on in situ mixture performance. A strong correlation was observed

between the calculated maturity and the measured stiffness for a range of conditioning temperatures

and durations thus enabling the prediction of long and short-term material performance in situ where

ambient conditions are known.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

Cold-mix pavement materials are defined as bituminous mate-

rials mixed using cold aggregates and binder [1]. By eliminating

the need to heat the large volumes of aggregate substantial sav-

ings, both financial and environmental, can be achieved in compar-

ison with traditional hot-mix materials. Furthermore, because the

compactability of the material is not related to the mix tempera-

ture, cold-mixtures are portable and are therefore ideally suitedfor use in the construction and maintenance of rural roads as they

remove the need for portable hot-mix asphalt plants [2].

Despite the potential environmental and cost benefits associ-

ated with cold-mixes, there are a number of factors hindering their

wider use. These include an inconsistent approach internationally

to specifying this material and an incomplete understanding of

the strength development of cold-mixes when in service. Foremost

however is the lack of suitable assessment criteria for cold-mixes.

Serfass et al. [3] describe cold-mixes as evolutive materials. They

gain strength slowly as the material dries, developing strength

over time in a manner more akin to a cementitious material [4].

This is in contrast to hot-mix materials which gain strength quickly

as the material cools. Consequently traditional assessment meth-

odologies developed for hot-mixes are often not best suited to

cold-mixes. In this context, the objective of this research was to

facilitate the use of cold-mix bituminous materials in Ireland by

providing a maturity-based prediction method for long-term andshort-term performance.

2. Conditioning regimes

Accelerated curing is required for cold-mix materials prior to

laboratory testing due to its low initial strength to simulate the

medium to long-term performance of the material in situ [1]. The

long-term stiffness of the material will not be achieved until a sub-

stantial reduction of the moisture content has occurred. The prin-

cipal difficulty involved in the testing of cold-mixes is combining a

test of short duration with the requirement to simulate the

working environment of the material. Leech [5] reported that the

0950-0618/$ - see front matter 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2012.09.008

⇑ Corresponding author. Address: UCD School of Civil, Structural & Environmental

Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland. Tel.:

+353 1 716 3202; fax: +353 1 716 3297.

E-mail address: [email protected] (C. McNally).

Construction and Building Materials 38 (2013) 524–529

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o n b u i l d m a t

http://dx.doi.org/10.1016/j.conbuildmat.2012.09.008mailto:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2012.09.008http://www.sciencedirect.com/science/journal/09500618http://www.elsevier.com/locate/conbuildmathttp://www.elsevier.com/locate/conbuildmathttp://www.sciencedirect.com/science/journal/09500618http://dx.doi.org/10.1016/j.conbuildmat.2012.09.008mailto:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2012.09.008

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laboratory simulation of in situ curing was the most unsatisfactory

part of cold-mix emulsion mixture design. Later Muthen [6]

attributed the limited application of Foamix technology in South

Africa to the lack of a well-documented standardised mix-design

procedure.

2.1. Existing laboratory conditioning regimes

A number of commentators have investigated the multitude of laboratory conditioning regimes in use for the accelerated curing of

cold-mixtures [1,7,8]. A review of the literature was conducted and

a summary of conditioning regimes used and recommended for

cold-mixtures is presented in Table 1. It can be seen that a number

of the references specify multiple different oven conditioning re-

gimes, designed to simulate different periods of in situ condition-

ing. Three distinct temperature ranges are identified in the table;

ambient 20 C, 38–40 C, and 60 C. With the exception of Ruckel

et al. [9] a conditioning temperature of 60 C dominated for almost

30 years [4,6,10–15]. A conditioning temperature of 40 C gained

wider use in the late 1990s. Typically conditioning at 40 C was

undertaken for a period of 3 days [1,6,8,9,16]; however other dura-

tions also appear in the literature [9,13,17]. Curing regimes at

ambient temperature have more recently been used to overcomethe difficulty correlating accelerated laboratory testing to in situ

conditions. SABITA [13] included two ambient temperature condi-

tioning regimes of 7 and 28 days in its recommended curing proto-

cols for emulsion mixtures.

2.2. In situ conditioning simulation

The proposed equivalent in situ conditioning duration simu-

lated in the laboratory is included for a number of the regimes in

Table 1. There is a clear trend evident in the table with the increase

in both duration and temperature of conditioning in the laboratory

correlating to an extended duration of in situ conditioning. On the

other hand there is considerable variation in the particular values

from different researchers and little has changed since Ruckel etal. [9] reported that correlation between laboratory and field data

from different locations was problematic with Thanaya et al. [2]

reporting a similar difficulty in 2009.

Ruckel et al. suggested that curing the specimens for 3 days at

40 C simulates 1 month of conditioning in the field. This contrasts

with the recommendations of the Asphalt Academy (2002; cited

[7]) who suggest that this conditioning regime simulates 6 months

of conditioning in situ. A similar range of equivalent in situ condi-

tioning times is apparent for 3 days of conditioning at 60 C. Acott

(1980; cited [1]) equated this laboratory regime to a very broadtime span of 23–200 days of field curing whereas Maccarrone

[11] estimated that this simulates an equivalent of 1 year of field

curing.

2.3. Correlating conditioning regimes

Previous research by Doyle et al. [18] outlined a study to enable

the correlation of different laboratory conditioning methods in

which cold-mix bitumen emulsion material was tested for strength

gain for a range of conditioning temperatures and conditioning

durations. They identified a logarithmic increase for the stiffness

of the material over time. They found that by varying time and

temperature it is possible to achieve a significant range of perfor-

mance values. However, they note that the objective is not to max-imise the stiffness but rather to best represent what the material

can achieve in the field. In situ cold mix materials gain strength

over time and consequently each of the values of strength and stiff-

ness achieved in the course of testing has relevance to a particular

age of that material in situ. Brown and Needham [19] and Ozsahin

and Oruc [20] reported a similar profile of stiffness gain for a num-

ber of cold-mix materials including a number of mix additives such

as Portland cement, hydrated lime and calcium chloride also incor-

porating variation in the bituminous binder content.

2.4. Maturity methods

The maturity method is commonly used in the concrete indus-

try to determine the strength of the material after cycles of curingat varying temperatures [21,22]. There are a number of approaches

Table 1

Summary of conditioning regimes recommended for cold-mixes.

Oven conditioning In situ equivalent Foam (F) or emulsion (E)

T (C) t (days)

Kekwick [7] 60 1,3,7 F, E

Bowering [4] 60 3 F

Bowering and Martin [10] 60 3 Early field life F

Acott (1980); cited Jenkins [1] 60 3 23–200 days F

Muthen [6] 60 3 F

Maccarrone [11] 60 3 1 year F, E

Ramanujam and Jones [12] 60 3 F

Sabita [13] 60 2 E

Kishore Kumar et al. [14] 60 2 28 days E

Yan et al. [15] 60 2 F, E

NRA [17] 40 28 1 year F, E

Thanaya et al. [2] 40 18–21 E

O’Prey [8] 40 7 F

Ruckel et al. [9] 40 3 30 days F

Jenkins [1] 40 3 F, E

Asphalt Academy (2002); cited [7] 40 3 6 months F

Kim and Lee [16] 40 3 F

Sabita [13] 40 2 F

Ruckel et al. [9] 40 1 7–14 days F

Asphalt Institute; cited Ruckel et al. [9] 38 1 1 week E

Brown and Needham [19] 20 100 + 1 @60 C 1 year E

NRA [17] 20 28 1 month F, ESabita [13] Ambient 28 F

Sabita [13] Ambient 7 F

Ruckel et al. [9] Ambient 1 1 day F

T.A. Doyle et al. / Construction and Building Materials 38 (2013) 524–529 525

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of varying complexity available and can be also used to reliably

estimate the in situ strength of concrete. The procedure originated

with the use of increased temperatures to accelerate the curing of

concrete and the consequent need for a method to describe the

combined effects of time and temperature. The use of maturity

methods stemmed from the fact that the hydration of cement

accelerates with increased temperature and that concrete gains

strength with the progress of hydration. Therefore the strengthcan be expressed as a function of the time–temperature combina-

tion. Furthermore the effect of seasonal temperature on the

strength gain of concrete is also well documented [23].

2.4.1. Concrete maturity functions

A number of different maturity functions have been proposed

for the prediction of concrete strength. Neville [23] reports that a

number of researchers have sought to improve on existing matu-

rity methods due to the original methods not being applicable to

a wide range of conditions. He noted that where improvements

were recorded they were typically at the expense of introducing

complications. Carino and Lew [21] traced the development of

maturity methods for concrete back to McIntosh, Nurse, and Saul

in the 1950s. The product of time and temperature was proposedto describe the maturity resulting in the Nurse–Saul maturity func-

tion, Eq. (1).

M ¼Xt

0

ðT T 0ÞDt ð1Þ

where M is the maturity index, C h (C days); T is the average con-

crete temperature (C) during the time interval Dt ; T 0 is the datum

temperature (usually taken to be 10 C [6]), t is the elapsed time

and Dt is the time interval (hours or days).

In 1954 Rastrup (cited [24]) introduced the equivalent time as

an alternative method defined as the time required at the reference

temperature to achieve the same maturity as the actual cured

material. Neville [23] maintains that despite the development of

increasingly complex maturity methods, the original maturity

function remains a useful tool in practice.

3. Experimental testing

For the purpose of this study a cold-mix emulsion mixture was produced using

a limestone aggregate, a moisture content of 4% and a binder content of 3.3%. The

binder used was a cationic emulsion containing 64% bitumen. The aggregate used

was selected to conform with the clause 800 series of unbound materials for road

pavements [25]. This mix design was based on previous work conducted by Doyle

et al. [18] which found the mix to produce a compacted density of 2172 kg/m 3 and a

compactability of 84.8%. Three sets of eight 150 mm diameter specimens were pro-

duced by gyratory compaction. Mechanical performance was assessed using the

ITSM test in accordance with IS EN 12697-26 [26] using a test temperature of

20 C. Specimens were conditioned in a thermostatically controlled air chamber

with uncontrolled humidity at temperatures of 20

C, 40

C, and 60

C. Repeatedtesting of the specimens was carried out after intervals of accelerated curing of

increasing duration.

Three phases of accelerated conditioning were used to investigate the strength

development of the material. The initial period of conditioning was of 12 and

15 months duration for the specimens conditioned at 40 C and 20 C respectively.

The second phase of conditioning was at ambient room temperature of approxi-

mately 18 C for a period of 6 months. Finally the specimens were subjected to a

conditioning temperature of 60 C. The set of specimens initially conditioned at

60 C was not suitable for further testing due to the elevated stiffness already

achieved and the likelihood that further conditioning at a reduced temperature

would have little or no effect on the specimens.

3.1. Results of specimen conditioning

The conditioning study carried out in the course of this study identified a signif-

icant range of stiffness modulus values for materials of identical composition as a

result of variation in the conditioning regime. The results from the initial phaseof specimen conditioning are presented in Fig. 1. The stiffness values achieved for

conditioning at 40 C were approximately double the values achieved at 20 C for

the same duration. The 60 C conditioning regime resulted in further elevated stiff-

ness values and bears no relation to the expected curing rate in situ.

4. Developing a maturity function

4.1. Maturity methods for cold-mix bituminous materials

Cold bituminous mixtures gain strength with the expulsion of

moisture from the mix [1,4] and the reduction of moisture content

is accelerated with increased temperature. Therefore a function of

time and temperature was considered an appropriate method for

describing cold-mix bituminous materials. Previous work by Doyle

et al. [18] considered the use of a maturity approach as a means to

correlate various conditioning regimes for cold-mix materials and

to overcome the lack of consensus on conditioning methods. A

modified version of the Nurse–Saul maturity function was used

and a strong correlation between the stiffness modulus and speci-

men maturity was observed. There were however some significantshortcomings, most notably with the inability of the method to

deal with changes in temperature for specified discrete time inter-

vals. This was due to the use of a logarithmic function to character-

ise maturity; when applied over intervals the nature of the

logarithmic function was to over-estimate maturity by repeatedly

measuring the initial higher rate of maturity gain. Consequently

the function was unsuitable for assessing the effect of conditioning

intervals at different temperatures. This represented a major chal-

lenge as it meant that the function could not be used for assessing

performance when in service.

One of the features of the Nurse–Saul Maturity Function is that

it allows for the summation of discrete intervals of material curing

thus allowing it to account for the natural fluctuations in temper-

ature. The objective of this research was to develop a robust matu-rity function suitable for the assessment of in situ performance of

cold-mix materials and is therefore required to account for the ef-

fects of temperature fluctuations.

4.2. Influence of time intervals

As explained above, logarithmic based maturity functions were

found to be unsuitable for assessing the influence of a varying tem-

perature on strength development of cold-mix materials. An alter-

native approach that accounted for the diminishing effect of time

was required. To achieve this, the stiffness modulus results pre-

sented in Fig. 1 were used to develop a maturity function for

cold-mix materials. The revised equation is presented in Eq. (2).

A datum temperature of 0 C was adopted due to the influence of moisture evaporation on the strength development of the material.

R² = 0.994

R² = 0.987

R² = 0.999

0

1

2

3

4

5

6

0 50 100 150 200

S t i f f n e s s m

o d u l u s ( x 1 0 3 M P a )

Conditioning time (days)

20°C

40°C

60°C

Fig. 1. Results for stiffness tests at different conditioning temperatures.

526 T.A. Doyle et al. / Construction and Building Materials 38 (2013) 524–529

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M ¼Xt

0

ðT T 0ÞDt e ð2Þ

where t e is the equivalent age (days) and other symbols are as de-

scribed earlier. The introduction of the equivalent age term to the

maturity function significantly improves the sensitivity to temper-

ature fluctuations. The equivalent age, defined in Eq. (3), is based

on time at a reference temperature and is used to translate thematurity acquired for any given time and temperature combination.

t e ¼ t eBðT T r Þ ð3Þ

where t e is the equivalent age (days); T r is the reference tempera-

ture (20 C) and B is a material dependent temperature sensitivity

parameter. This was determined by performing a regression analy-

sis of the expected logarithmic relation between stiffness and matu-

rity index. For this particular mix, B was found to take a value of

0.08. The equivalent age was determined using the method de-

scribed by Carino and Lew [21] for determining a maturity index

for concrete materials. It can be seen that the equivalent age will

be less than the real time for conditioning periods at temperatures

below the reference temperature, and vice versa.

The correlation between maturity calculated using Eq. (2) andthe stiffness of the material tested in the laboratory is illustrated

in Fig. 2. There is clearly a strong correlation between the two,

but with the advantage that the maturity function can allow for

temperature fluctuations.

4.3. Testing the maturity hypothesis

The second and third phases of laboratory conditioning were

used to assess the suitability of the maturity function presented

in Eq. (2) to describe the effect of varying conditioning tempera-

tures. Samples were initially conditioned at 20 C and 40 C before

being moved to an environment at 60 C. The samples were tested

periodically using the ITSM and the results are illustrated in Fig. 3.

These are accompanied by predicted values for the stiffness mod-ulus that are calculated using the correlation identified in Fig. 2.

As expected, the results clearly illustrate an increase in the rate

of stiffness gain when the conditioning temperature is increased

to 60 C. The correlation between the test data and the predicted

values suggest that the maturity approach provides a good basis

for determining the stiffness of the material. While there is some

underestimation of stiffness acquired when the temperature is in-

creased to 60 C, this would also be in agreement with concerns

raised [6,19] over the use of specimen conditioning at 60 C due

to the proximity to the softening point of the binder, the loss of

volatile components and the oxidation of the binder. Consequently

it is expected that the prolonged exposure of the specimens to the

elevated temperature may contribute to the test results’ deviation

from the predicted values.

5. Practical applications

The use of a maturity approach presents an opportunity to bet-

ter characterise the strength development of cold-mix materials. In

particular, where in situ temperature data is available the maturity

method can be employed to predict the stiffness gain of the mate-

rial in service. Consequently, the effect of using cold-mix materials

at different times in the laying season can be assessed.

The maturity function demonstrates the significance of the

ambient temperature on the rate of stiffness gain for cold-mix

materials. In Ireland a distinct laying season is enforced by wet

winters; this has the practical effect of restricting the use of

cold-mix materials from late spring to autumn. However, the risk

of rainfall is not the only seasonal climatic pattern affecting theuse of cold-mix materials. The reduced temperatures at the end

of the laying season can potentially lead to a significant reduction

in the rate of stiffness gain. Assessment of the effect of seasonal

temperature on early age performance of cold-mixes is a useful

analytical tool due to the heightened risk of failure in early life.

5.1. Seasonal effects

Ambient temperature data can be used to analyse the typical ef-

fect of in situ conditioning on cold-mix materials. Temperature

data is readily available across Europe and one such source is the

European Climate Assessment project [27]. This provides a high-

quality dataset containing summaries of temporal variations in

precipitation and daily mean, minimum and maximum tempera-tures for several hundred sites across Europe. To assess the influ-

ence of ambient temperature on cold-mix development, mean

daily temperature data was taken for a site in the Dublin region

for the years 2009, 1999 and 1990. Using Eq. (3) the equivalent

time associated with each day of ambient conditioning was deter-

mined; Eq. (2) was then used to determine the cumulative matu-

rity developed on a monthly basis. The correlation determined in

Fig. 2 was then used to calculate the stiffness developed after

1 month and this data is presented in Fig. 4.

The figure highlights the influence of ambient temperature and

it can be seen that material laid during the warmest summer

months can result in a 1 month stiffness modulus that is almost

double that obtained for material laid in winter months. Using this

maturity approach it is possible to scientifically identify appropri-ate times of the year for using cold-mix materials. Fig. 4 suggests

y = 0.1812x0.294

R² = 0.97

0

1

2

3

4

1 10 100 1000 10000 100000

S t i f f n e s s m o d u l u s ( x 1 0 3 M p a )

Maturity (ºC.day)

Fig. 2. Relationship between maturity and stiffness.

0

1

2

3

4

5

6

7

0 200 400 600 800

S t i f f n e s s m

o d u l u s ( x 1 0 3 M P a )

Time (days)

40°C - storage - 60°C

20°C - storage - 60°C

Maturity prediction

Fig. 3. Influence of temperature change on stiffness – experimental and calculated.


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development in cold-mix materials. The introduction of an equiv-

alent time function has resulted in a strong correlation between

maturity and stiffness of laboratory-tested specimens for time

intervals with differing conditioning temperatures.

The application of the maturity method to the assessment of

cold-mix pavements in service identified the significant impact of

ambient conditions. This also allowed for this impact to be quanti-

fied, offering a more scientific basis for engineers to decide on theuse of cold-mix materials.

Acknowledgements

The authors would like to acknowledge the National Roads

Authority of Ireland for their financial support, and the assistance

of Tom Webster in the UCD Transport Laboratory.

References

[1] Jenkins KJ. Mix design considerations for cold and half-warm bituminousmixes with emphasis on foamed bitumen. PhD thesis. South Africa: Universityof Stellenbosch; 2000.

[2] Thanaya INA, Zoorob SE, Forth JP. A laboratory study on cold-mix, cold-lay

emulsion mixtures. Proc Inst Civil Eng: Transport 2009;162 (TR1):47–55.[3] Serfass JP, Poirier JE, Henrat JP, Carbonneau X. Influence of curing on cold mix

mechanical performance. Mater Struct 2004;37(5):365–8.[4] Bowering RH. Upgrading marginal road building materials with foamed

asphalt. Melbourne South: Highway Engineering in Australia, Mobil Oil of Australia; 1970.

[5] Leech D. Cold mix bituminous materials for use in structural layers of roads. Crowthorne (Berkshire, UK): Transport Research Laboratory (TRL); 1994.ISSN 0968-4093.

[6] Muthen KM. Foamed asphalt mixes-mix design procedure. Report No. CR-98/077. South Africa: Sabita Ltd. and CSIR Transportek; 1998.

[7] Kekwick SV. Best practice. Bitumen emulsion and foamed bitumen materialslaboratory processing. In: Proceedings of the 24th Southern African transportconference, SATC, South Africa; 2005. ISBN No. 1-920-01712-7.

[8] O’Prey, DP. Sustainable use of foamix in Ireland. PhD thesis. Northern Ireland:University of Ulster; 2007.

[9] Ruckel PJ, Acott SM, Bowering RH. Foamed-asphalt paving mixtures:preparation of design mixes and treatment of test specimens. TransportationResearch Record. USA: Transportation Research Board; 1983. p. 88–95.

[10] Bowering RH, Martin CL. Foamed bitumen production and application of mixtures evaluation and performance of pavements. In: Proceedings of

association of Asphalt paving technologists. New Orleans, Louisiana. vol. 45.1976. p. 453–77.

[11] Maccarrone S. Cold asphalt systems as an alternative to hot mix. In:Proceedings of the 9th AAPA international Asphalt conference. Australia:AAPA; 1994.

[12] Ramanujam JM, Jones JD. Characterization of foamed-bitumen stabilisation.Int J Pavement Eng 2007;8(2):111–22.

[13] South African Bitumen Association. ETB – the design and use of emulsion-treated bases. Sabita Manual 21, Cape Town. South Africa; 1999.

[14] Kishore Kumar C, Amar Kumar DSNV, Amarantha Reddy M, Sudhakar Reddy K.

Investigation of cold in-place recycled mixes in India. Int J Pavement Eng2008;9(4):265–74.

[15] Yan J, Ni F, Yang M, Li J. An experimental study on fatigue properties of e mulsion a nd foam c old rec yc led mixe s. Constr Build Ma ter2010;24(11):2151–6.

[16] Kim Y, Lee HD. Development of mix design procedure for cold in-placerecycling with foamed asphalt. J Mater Civ Eng 2006;18(1):116–24.

[17] National Roads Authority. NRA Interim Advice Note 01/11 on Low EnergyPavements. NRA, Dublin; 2011.

[18] Doyle T, Gibney A, McNally C, Tabaković A. Development of maturity methodsfor predicting performance of cold-mix pavement materials. In: Proceedings of 9th international conference, sustainable construction materials andtechnology in ASPHALT pavement engineering and highway maintenance.Liverpool; 2010

[19] Brown SF, Needham D. A study of cement modified bitumen emulsionmixtures. In: Proceedings of the annual meeting of the association of AsphaltPaving Technologists, AAPT; 2000.

[20] Ozsahin TS, Oruc S. Neural network model for resilient modulus of emulsifiedasphalt mixtures. Constr Build Mater 2007;22(7):1436–45.

[21] Carino NJ, Lew HS. The maturity method: from theory to application. Maryland(USA): National Institute of Standards and Technology; 2001.

[22] Carino NJ. Handbook on non-destructive testing of concrete. In: Malhotra VM,Carino NJ, editors. The maturity method. Florida (USA): CRC Press Inc.; 2004[chapter 5].

[23] Neville AM. Properties of concrete, Chapter 6 – Strength of concrete, Chapter 8– Temperature effects in concrete. 4th ed. Essex (UK): Longman Group; 1995.

[24] De Schutter G. Applicability of degree of hydration concept and maturitymethod for thermo–visco-elastic behaviour of early age concrete. CementConcr Compos 2004;26(5):437–43.

[25] National Roads Authority. Manual of contract documents for road works.Series 800 Road Pavements – Unbound Materials. vol. 1. Dublin: NRA; 2004.

[26] National Standards Authority of Ireland. IS EN 12697: Part 26. Bituminousmixtures – test methods for hot mix Asphalt – stiffness. Dublin (Ireland):NSAI; 2004.

[27] Klein Tank AMG, Wijngaard JB, Können GP, Böhm R, Demarée G, Gocheva A,et al. Daily dataset of 20th-century surface air temperature and precipitationobservations for European climate assessment. Int J Climatol

2002;22(12):1441–53.[28] Worldclimate.com. Mean monthly temperature data; 6th June 2011.


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