Construction and Building Materials 101 (2015) 596–601

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Construction and Building Materials

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Evaluation of the early-age-shrinkage of Fiber Reinforced Concrete (FRC)using image analysis methods

http://dx.doi.org/10.1016/j.conbuildmat.2015.10.0900950-0618/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: Department of ‘‘Sciences and Engineering of Matter,Environment and Urban Planning (SIMAU)”, Faculty of Engineering, UniversitàPolitecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy.

E-mail address: a.mazzoli@univpm.it (A. Mazzoli).

Alida Mazzoli ⇑, Saveria Monosi, Eleonora Stella PlesciaDepartment of ‘‘Sciences and Engineering of Matter, Environment and Urban Planning (SIMAU)”, Università Politecnica delle Marche, Ancona, Italy

h i g h l i g h t s

� Cracking of concrete due to early-age shrinkage leads to several problems.� Fibers in concrete try to reduce the propagation of the early-age-shrinkage cracking.� The effectiveness in preventing the growth of the cracks is analyzed using image analysis.� The addition of PP and PE macro fibers exhibits the best performance.

a r t i c l e i n f o

Article history:Received 28 October 2014Received in revised form 31 August 2015Accepted 15 October 2015

Keywords:Early-age shrinkageConcrete structuresMacro fibersMicro fibersImage analysisImageJ

a b s t r a c t

Cracking of concrete due to early-age shrinkage is a common problem that generally leads to severalproblems experienced by concrete structures, mainly influencing and reducing durability and lifetime.This is of particular relevance in the case of slabs type structures such as pavements, industrial floors,bridge decks, tunnel lining and precast elements, that show much larger surface areas compared withother kinds of structural components, such as beams and columns. In addition, the cracks allow waterand other chemical agents to penetrate into concrete and get in touch with steel reinforcements, leadingto reinforcement corrosion, even to breakage. Consequently, curing is the unique traditional method toavoid such problems. However, in certain applications, due to the severe environmental conditionsand/or due to the actual dimensions of structural elements, curing does not fit the purpose in the preven-tion of cracks. For the above said, fibers have been incorporated in concrete to reduce and/or prevent thepropagation of the early-age-shrinkage cracking. In fact, the utilization of fibers has increased progres-sively over the past years in structural applications. The present paper focuses on early-age shrinkagecracking with a special attention given to new concretes aiming at reduced shrinkage phenomenathrough the addition of different types of macro fibers within the cement matrix. In order to estimatethe effectiveness in preventing the growth of the cracks, an easy methodology, based on image analysis(IA), has been developed. The results show different considerations regarding distinct materials: in termsof the effectiveness of fibers, the addition of polypropylene and polyethylene macro fibers exhibits thebest performance and leads to a certain delay and a wide decreasing in cracking formation. The use offibers has been found to be very effective in the width reduction of the cracks and, even if not so signif-icantly, in the length reduction.

� 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Once it has stiffened, set and hardened, concrete is a relativelybrittle material that shrinks over time. Cracking will occur if theconcrete is restrained against the movement that results from this

shrinkage. While long-term (drying) shrinkage has been the focusof diverse researchers [1–3], recent studies have shown that theearly loss of moisture from fresh concrete can produce large tensilestresses in the concrete at a very early age, leading to early-ageshrinkage cracking. Early-age cracking can occur when volumetricchanges caused by temperature reduction, chemical reaction, andmoisture loss are prevented. The prevention of volume reductionresults in the development of tensile stress in the concrete. If thesetensile stresses exceed the tensile strength of the concrete, a visiblecrack can be expected to occur. In addition to free shrinkage and

A. Mazzoli et al. / Construction and Building Materials 101 (2015) 596–601 597

tensile strength, several other factors can also influence the poten-tial for early-age cracking including the magnitude and rate ofshrinkage, degree of restraint, stress relaxation, time-dependentmaterial property development, geometry of the structure, andfracture resistance of the material [4]. Early age shrinkage canresult in cracks that form in the same manner as at later ages. Evenif the early resulting cracks are internal and microscopic, furthershrinkage at later ages may merely open the existing cracks andcause problems [5]. Early-age cracking is problematic because itis responsible for the increase in the water penetration, de-icingchemicals, sulfates, and other corrosive or aggressive agents intoconcrete, thereby accelerating the corrosion of reinforcing steel.The structures that are particularly sensitive to the abovedescribed phenomenon include pavements, industrial floors,bridge decks, walls and tunnel linings. The above is due to thelow volume/surface ratio and to the fact that such structures typ-ically have a high rate of shrinkage and, moreover, they are fre-quently exposed to high concentrations of corrosive agents. Dueto the high impact associated with the repair of a damaged struc-ture, significant interest exists for the improvement of the durabil-ity of the structural elements given that concrete restoration isexpensive. The durability improving has typically resulted in theuse of higher strength and lower permeability that may be moresusceptible to early-age cracking, especially if they are insuffi-ciently cured. In order to better control cracking and its adverseeffects on durability, specifications have been developed to limitearly-age cracking [6,7]. Accordingly, there is an urgent need toreduce the extent of this cracking and thereby prevent the prema-ture deterioration. Although the concrete materials, concrete mixdesigns, design specifications and construction technologies havechanged a lot over the years, shrinkage cracking still remains a sig-nificant problem and is prevalent in construction. For the abovereason, concrete structures are equipped with secondary reinforce-ment, for example welded wire mesh [8] or closely spaced bars ofsmall diameter [9], that allow the width containment of the cracksassociated with the shock loadings and the contractions producedby the thermo-hygrometric phenomena. Unfortunately, no benefi-cial effect exists against cracks that occur during the first hoursafter the casting of the structures without formwork, when thetensile strength of the concrete is still very low. A more effectiveway to limit the phenomenon of the first cracking is the introduc-tion in concrete mixture of discrete fibers of different types, usuallylength from 10 to 80 mm and having diameter from some tens oflm to about 1 mm [10]. The fibers dispersed in the cement matriximplement a three-dimensional reinforcement and are able toabsorb tensile stresses acting in any direction. Moreover, by ensur-ing stitching of lesions, the fibers prevent their rapid spread andespecially limit their opening [11]. Therefore, fiber-reinforced con-crete shows also a higher capacity to dissipate energy associated toimpulsive loads (e.g. shocks and impacts) if compared to a tradi-tional conglomerate. For the above said, the study of shrinkage isimportant to avoid surface cracking that leads to a durability con-cern and not only to prevent esthetic defects of concrete. Moreover,the complex phenomena involved in the early-age shrinkage ofconcrete makes difficult a clear cracking potential quantification,given that concrete has not yet hardened completely when sucha phenomenon occurs, being the concrete itself in the state of tran-sition during the first 24 h. Diverse methods for the simulation andstudy of cracking induced by plastic shrinkage have been proposed,such as for example plates and rings, in order to test the effective-ness of the introduction of fibers in concrete in order to limitshrinkage phenomena. Banthia and Gupta have worked on theeffect of diameter, length and geometry of polypropylene fiberson the plastic shrinkage in concrete, by prismatic specimens con-sisting of a substrate with protuberances and an overlay on top.[12,13]. Lura et al. used a stress riser to create cracking in slabs

by means of a steel insert plate [14]. Such a testing methodadopted, several years ago as ASTM standard (ASTM C 1579: Stan-dard Test Method for Evaluating Plastic Shrinkage Cracking of Res-trained Fiber Reinforced Concrete using a Steel Form Insert). Thesedifferent test techniques produce cracks of different width and pat-tern that cannot be comparable. In fact, the reduction of the uncer-tainty associated with the prediction of mechanical performanceand mass transport, requires a more reliable approach in order toquantify the physical aspects of the developing cracks. For theabove reason the purpose of the present paper was to investigatethe effectiveness of different types of macro fibers, against thedevelopment of cracks in concrete, during the first 24 h, that is tosay during the plastic shrinkage, the autogenous shrinkage andthe first drying shrinkage. As a matter of fact the present paperfocuses on early-age shrinkage cracking with a special attentiongiven to new concretes aiming at reduced shrinkage phenomenathrough the addition of different types of macro and micro fiberswithin the cement matrix. In order to estimate the effectivenessin preventing the growth of the cracks, an easy methodology, basedon image analysis (IA), has been developed. The proposed methodis helpful in the objective comparison between different materials.In fact, most of the techniques used to estimate the shrinkagecracking patterns are subjective and labor-intensive given thatthey are based on visual and manual measurement with a conse-quent low precision of the results.

2. Materials and methods

2.1. Mix design

The used mix design was the same in all the Fiber Reinforced Concrete (FRC)mixtures. In particular, water–cement ratio (0.5) and aggregate–cement ratio(5.5) have been maintained constant. The only variables were the type and quantity(as percentage to volume) of the fibers added to the basic concrete mixture. In thisway, any difference in the performances could be solely due to the fibers containedin the mixture. The concrete chosen as a reference meets the criteria for strengthand durability widely used in industrial flooring, slabs, precast, tunnel linings anddecks bridge. The used mix design was the most suitable to achieve the requiredproperties for such a material. Therefore, a reference concrete with a strength classP30 MPa has been selected. The percentage of fibers was determined according tothe range recommended from suppliers and in accordance with the purposes of thepresent research. As known, the dosage of superplasticizer depends on the desiredconsistency (fluid-S4 or superfluid-S5) of the final product. In the present paper, therate of superplasticizer, in order to ensure a suitable workability to the referenceconcrete and to each FRC, has been maintained constant for all the mixtures. Thefollowing table shows the composition of the reference concrete (Table 1).

The manufactured concretes were produced using blended type CEM II/B-LL32,5R, superplasticizer admixture based on polycarboxylate ethers (0.76% byweight of cement), gravel (Dmax = 16 mm), gravel (Dmax = 8 mm) and sand(Dmax = 4 mm).

The fibers, consisting of different materials, have been selected and added to themixture at dosage of 0.3% by the volume. For a quick classification of the specimens,the following acronyms have been used:

– PP for polypropylene,– PVA for polyvinyl alcohol,– PET for polyethylene,– STL for steel.

Shape, size, physical andmechanical properties of the fibers are shown in Tables2 and 3 respectively.

2.2. Experimental procedure

The test has been performed in a short period of time (24 h) in order to focus onthe cracking related solely to the early age shrinkage. A method that ensures effec-tive constraints and a considerable loss of moisture has been selected. The experi-mental setup consisted of plate-type specimens held by anchors. In this way it hasbeen possible to simulate the real conditions of an in situ manufactured pavementbound to the base and sides. The upper surface of each slab, after casting and finish-ing, has been exposed to adverse environmental conditions such as: low relativehumidity (50 ± 2%), high wind speed (2.2 m/s) and a temperature between25 ± 1 �C in order to assure shrinkage and consequent cracking phenomena. Theabove cited conditions have been obtained in a small environment that will be iden-

Table 1Composition of the reference concrete.

Cement (kg/m3) Mixing water (kg/m3) Superplasticizer (Glenium Sky527)

Sand (kg/m3) Gravel (kg/m3)

Dosage (lt/m3) Cement (%) P0350 Media Coarse P1 8/12 P2 12/20

350 193 2.67 0.76 300 260 380 570 400

Table 2Composition and size of the fibers.

Identification Composition

PP2 Polypropylene Ondulated smoothPP3 Straight embossedPP4 Straight smoothPVA Polyvinyl alcohol Straight smoothPET Polyethylene Straight embossedSTL Steel (low carbon) Hooked ended

Fig. 1. Set-up to maintain environmental conditions (courtesy BASF Italy SpA).

Fig. 2. Pre-classification of the cracks using colored paths (a) and range crack width(b).

598 A. Mazzoli et al. / Construction and Building Materials 101 (2015) 596–601

tified as ‘‘environmental tunnel”. Recently, image analysis has become a powerfultool that can be used in order to study cementitious materials at different scales[15] (Fig. 1).

Image analysis has been used in order to better understand the development ofthe cracks and the microstructure of the cement-based systems [16,17], determinethe orientation and dispersion of the reinforcing fibers [18] and characterize thefracture process in concrete [19,20]. Using the above cited technique, diverse sizesof cracks have been identified, from about 10 lm to several millimeters, dependingon the field of interest [21]. In the present study the detection of cracks and theevaluation of their size in terms of opening on the surface of the slabs has been car-ried out 24 ± 2 h after casting. First of all the cracks have been located using a mag-nifying glass, then measured by an optical hand-held microscope in order toaccurately evaluate their width. A pre-classification of the cracks, according to theirwidth, has been carried out using different colored paths as shown in Fig. 2. A col-ored code has been used in order to highlight the width of the crack. In particularfour ranges, showing an increasing level of hazard, have been selected as follows:

– width 0–0.3 mm identified by green color;– width 0.3–0.6 mm identified by blue color;– width 0.6–1 mm identified by red color;– width 1–1.6 mm identified by black color.

The above grouping of cracks has been made in order to facilitate, during thenext phase, the identification of those cracks showing the same range of widths.The next step of the process considers the acquisition and processing of the imagesusing three different software such as: AutoStitch [22], ImageJ [23] and Adobe Pho-toshop (Adobe Systems Incorporated, San Jose, California, USA). AutoStitch creates apanorama from single images. This software needs images acquired by the samecamera, same exposure and showing enough overlapping area in order to performa proper stitching. The panorama created by AutoStitch is the composition of theoriginal images with the correction of any defect. The next phase consists in theremoving of the unnecessary parts of the ‘‘view image” in order to focus the patternof the crack and start the following analysis using ImageJ. ImageJ developed at theNational Institutes of Health (USA) is a Java-based public domain image processingand analysis program, which is freely available, open source, multithreaded, andplatform independent that can be utilized to develop user-coded plugins to suitthe specific requirements of any conceived application. In the present paper usingImageJ it is possible to analyze the acquired images and evaluate the size of thecrack assigning measures, based on the pixels, in order to identify the different col-ors on the sample that point out cracks showing different sizes. In this way it is pos-sible to obtain a path for each range of the width of the cracks. Thereafter thedifferent paths have been connected in order to achieve a unique frame (pattern).At the end of such a process, the software is able to provide the following fourkey parameters in order to characterize the crack from a dimensional point of view:

Table 3Properties of the fibers (UTS stands for ultimate tensile strength and E modulus ofelasticity).

ID Length(mm)

Equivalentdiameter (mm)

Aspectratio (l/d)

q (g/cm3)

UTS(MPa)

E(MPa)

PP2 40 0.75 53.3 0.91 338 4.8PP3 54 0.82 66 0.91 481 5.4PP4 40 0.43 93 0.92 620 9.5PVA 50 0.66 76 1.3 800 29PET 52 0.64 81 1.35 238 5.5STL 50 1.05 48 7.8 1000 210

– area of the crack relating to the extent of the flat surface comprised within theperimeter of the crack;

– length of the crack intended as the sum of the distances between end-to-end ofeach crack;

– width of the crack defined as the distance from one side to the other of thecrack, measured among all those cracks that form the pattern of the crack.

A width of the crack equal or greater than 0.3 mm is considered particularlydangerous in terms of durability of the material [24]. For the above said the follow-ing three parameters have been identified in order to establish the effectiveness ofthe added fibers in concrete.

– ARR (Area Reduction Rate): is accountable to the effectiveness of the fibersadded to the mixture in order to reduce the cracked area due to the shrinkage

Table 4Workability of the reference concrete (PLN) and FRC.

Type Fibers (% by volume) Slump (mm) Reduction in slump (mm)

PLN 0 228 (S5) 0PP2 0.3 212 (S5) 7PP3 0.3 215 (S5) 6PP4 0.3 170 (S4) 34PVA 0.3 170 (S4) 14PET 0.3 215 (S5) 6STL 0.3 210 (S4) 8

Fig. 3. Cumulative evaporation.

R2 = 0,9144

40

50

60

70

80

90

40 60 80 100aspect ratio

AR

R%

Fig. 4. Correlation between aspect ratio and ARR.

R² = 0.8637

20

40

60

80

100

120

40 60 80 100

WR

Raspect ratio

Fig. 5. Correlation between aspect ratio and WRR.

R2 = 0,7531

10

20

30

40

50

60

40 60 80 100aspect ratio

LRR

%

Fig. 6. Correlation between aspect ratio and LRR.

A. Mazzoli et al. / Construction and Building Materials 101 (2015) 596–601 599

ARR ¼ 1� Cracked area of FRCCracked area of reference concrete

� �� 100

- LRR (Length Reduction Rate): denotes the effectiveness of the fibers added tothe mixture in order to reduce the length of the crack

RR ¼ 1� Cracked length of FRCCracked length of reference concrete

� �� 100

- WRR (Width Reduction Rate): showing the effectiveness of the fibers added tothe mixture in order to reduce the width of the crack

WRR ¼ 1� FRC crack width > 0:3Reference concrete crack width > 0:3

� �� 100

The width of the crack has been calculated as the ratio between the area of thesingle crack and its length.

3. Results and discussion

The aim of the present paper is to study mixtures of fiber-reinforced concrete showing a suitable class of consistency. Therequired values of consistency (UNI EN 206-1: 2006 standard)should be not lower than S4. In order to achieve such a result thereference concrete has been realized at a consistency of S5(slump > 210), given that the addition of fibers generally decreases

Table 5Aspect ratio, number of the fibers and performances of FRC.

Identification Aspect ratio (l/d) Fibers/m3 Cracks area (mm2) ARR (%)

PLN – 1670 –PP2 53.3 1.55E + 05 758 55PP3 66 1.00E + 05 574 66PP4 93 4.75E + 05 305 82PVA 76 1.46E + 05 532 68PET 81 1.55E + 05 308 82STL 48 0.56E + 04 767 54

the workability of the mixture. As can be observed in Table 4 theaspect ratio of the fibers has a remarkable effect on the workabilityof the concrete and, consequently, on the maximum quantity offibers that can be added. In fact, the higher the aspect ratio, theworse is the workability of the FRC.

The results concerning the air content are not shown becausethey are very similar and, however, all under the 3% in agreementwith the performance requirements for an ordinary concrete. As

Cracks length (mm) LRR (%) Area cracks wide >0.3 mm (mm2) WRR (%)

3375 – 1196 –2880 15 344 382051 39 174 581668 51 0 1002221 34 157 571675 50 0 1002452 27 381 30

0

20

40

60

80

100

120

PP2 PP3 PP4 PVA PET STL

ARR%LRR%WRR%

Fig. 7. Parameters characterizing the fibers.

Table 6Correlation between aspect ratio and ARR.

Identification Aspect ratio (l/d) ARR (%)

PP4 93 82PET 81 82PVA 76 68PP3 66 66PP2 53 55STL 48 54

Table 7Correlation between aspect ratio and WRR.

Identification Aspect ratio (l/d) WRR (%)

PP4 93 100PET 81 100PVA 76 57PP3 66 53PP2 53 38STL 48 30

Table 8Correlation between aspect ratio and LRR.

Identification Aspect ratio (l/d) LRR (%)

PP4 93 51PET 81 50PVA 76 34PP3 66 39PP2 53 15STL 48 27

Table 9Parameters characterizing the fibers.

Identification Fibers/m3

PP2 1.55E + 05PP3 1.00E + 05PP4 4.75E + 05PVA 1.46E + 05PET 1.55E + 05STL 0.56E + 04

600 A. Mazzoli et al. / Construction and Building Materials 101 (2015) 596–601

for regard the compressive strength achieved by all the concretes itis 10 ± 1 MPa at 1 day, 24 ± 1 MPa at 7 days and 37 ± 1 MPa at28 days. As for regards the evaporation rate of the water, this isof primary relevance on the shrinkage at early age. For the abovesaid, the impact of the ‘‘tunnel environment”, on concrete drying,results to be very important and should be determined. In order

to quantify such a parameter, the weight loss of the pan was mea-sured every hour. The cumulative evaporation is described in Fig. 3.

As can be observed the evaporation trend shows a higher rateoverture followed by a lower rate, approximately after 6 h. Thechange of the slope corresponds to the decrease of the bleedingwater conveyed into the surface by the capillary action. Further-more, it can be observed that the curves show comparable trendsafter 6–7 h, when the evaporation rate seems to take similar valuesindependently of the type and quantity of fibers added to the plainconcrete. It can be noticed that the first cracking phenomenaappear at about two or three hours after the beginning of the test,with the exception of the concretes that contains respectively themicrofibers PP4 and PET. On these samples, the cracking phenom-ena start after 4 and 5 h respectively. As expected, the referenceconcrete (PLN) shows cracking before any of the proposed FRC thatgets benefit from the presence of fibers. All the samples exhibitregular and wide cracks at a very early age. The further cracksspread in irregular patterns and are thinner. It can be noticed thatusually the cracks appear in the middle of the sample and developtoward the outer edges. In addition the cracking pattern show anhigh degree of symmetry confirming the effectiveness of thetwo-dimensional restraint that induces a stress concentrationexactly in the center of the slab. As previously stated, three param-eters can be used in order to summarize the performance of theFRC with respect to the reference concrete. The above cited param-eters show the effectiveness of the fibers in the reduction of thearea, length and width of the cracks in FRC. All the obtained resultsare shown in Table 5.

The same results, related to each of the above cited threeparameters, are showed separately in the following figures. Ascan be seen the aspect ratio plays a basic role in terms of the per-formances of the FRC (Figs. 4–6).

As can be noticed, the reduction of the ARR affects the width ofthe crack. As a matter of fact the percentage of cracks wider than0.3 mm it is strongly reduced. Two kinds of fibers (PP4 and PET)completely prevent the development of cracks wider than0.3 mm. The correlation between the length of the crack and theaspect ratio of the fibers it is more complicated. In fact, as can beobserved, the higher the aspect ratio does not correspond to alower extension of the cracks. The number of the added fibersseems to be a less significant parameter as long as the differencestays under a certain level, as this is the case, as showed inFig. 7. As a matter of fact, it can be observed marked differencesin ARR or WRR in those concretes that contain the same numberof fibers (PP2–PET) but different aspect ratio, or in reverse thesame values of ARR and WRR corresponding to a different numberof added fibers (PP4–PET or PP2-STL) but about the same aspectratio (Tables 6–9).

4. Conclusions

� The use of fibers confirmed to be very effective in the widthreduction of the cracks and, even if not so significantly, in thelength reduction.

� The addition of polypropylene and polyethylene macro fibersexhibits the best performance: a certain delay in cracking for-mation and a wide decreasing were exhibited. In particularthe crack width has never exceeded the threshold value of0.3 mm.

� The most important parameter is confirmed to be the aspectratio, assuming that the number of fibers is about of the sameorder of magnitude.

� The software Image J has proven effective not only in measuringthe width of the cracks, but also the length by following thepath, tight curves and right angles included.

A. Mazzoli et al. / Construction and Building Materials 101 (2015) 596–601 601

Acknowledgements

A special tribute to the company BASF Italy SpA for the givencontribution in the development and execution of the presentresearch.

References

[1] M. Mazloom, Estimating long-term creep and shrinkage of high-strengthconcrete, Cement Concr. Compos. 30 (2008) 316–326.

[2] R.I. Gilbert, M.A. Bradford, A. Gholamhoseini, Z.T. Chang, Effects of shrinkage onthe long-term stresses and deformations of composite concrete slabs, Eng.Struct. 40 (2012) 9–19.

[3] J. Saliba, E. Rozière, F. Grondin, A. Loukili, Influence of shrinkage-reducingadmixtures on plastic and long-term shrinkage, Cement Concr. Compos. 33(2011) 209–217.

[4] H.R. Shah, J. Weiss, Quantifying shrinkage cracking in fiber reinforced concreteusing the ring test, Mater. Struct. 39 (2006) 887–899.

[5] E. Holt, M. Leivo, Cracking risks associated with early age shrinkage, CementConcr. Compos. 26 (2004) 521–530.

[6] American Concrete Institute (ACI). Early-age cracking: Causes, measurements,and mitigation. ‘‘State-of-the-Art Rep. of ACI Committee 231”, 2008.

[7] ACI 224 1R–93. Causes, evaluation and repair of cracks in concrete structures.Reapproved 1998. In Specifications for Structural Concrete, ACI 301–05, withSelected ACI References: Field Reference Manual, 2005.

[8] ASTM A185/A185M-07 Standard Specification for Steel Welded WireReinforcement, Plain, for Concrete (Withdrawn 2013).

[9] J.R. Deluce, F.J. Vecchio, Cracking behavior of steel fiber-reinforced concretemembers containing conventional reinforcement, ACI Struct. J. 110 (3) (2013)481–490.

[10] National Research Council Advisory Committee on TechnicalRecommendations for Constructions. Guide for the design and constructionof fiber-reinforced concrete structures. CNR-DT 204/2006.

[11] R.N. Swamy, H. Stavrides, Influence of fiber reinforcement on restrainedshrinkage and cracking, ACI J. Procd. 76 (3) (1979) 443–460.

[12] N. Banthia, R. Gupta, Influence of polypropylene fiber geometry on plasticshrinkage cracking in concrete, Cem. Concr. Res. 36 (7) (2006) 1263–1267.

[13] N. Banthia, R. Gupta, Test method for evaluation of plastic shrinkage crackingin fiber-reinforced cementitious materials, Exp. Tech. 31 (6) (2007) 44–48.

[14] P. Lura, B. Pease, G.B. Mazzotta, F. Rajabipour, J. Weiss, Influence of shrinkage-reducing admixtures on development of plastic shrinkage cracks, ACI Mater. J.104 (2) (2007) 187–194.

[15] J.L. Chermant, L. Chermant, M. Coster, A.S. Dequiedt, C. Redon, Some fields ofapplications of automatic image analysis in civil engineering, Cement Concr.Compos. 23 (2001) 157–169.

[16] A. Ammouche, D. Breysse, A new image analysis technique for the quantitativeassessment of micro-cracks in cement-based materials, Cement Concr. 30 (1)(2000) 25–35.

[17] J. Valenca, D. Dias de Costa, Characterisation of concrete cracking duringlaboratorial tests using image processing, Constr. Build. Mater. 28 (1) (2012)607–615.

[18] N. Ozyurt, L.Y. Woo, T.O. Mason, S.P. Shah, Monitoring fiber dispersion in fiber-reinforced cementitious materials: comparison of AC-impedance spectroscopyand image analysis, ACI Mater. J. 103 (5) (2006) 340–347.

[19] S. Choi, S.P. Shah, Measurement of deformations on concrete subjected tocompression using image correlation, Exp. Mech. 37 (3) (1997) 307–313.

[20] J.S. Lawler, D.T. Keane, S.P. Shah, Measuring three-dimensional damage inconcrete under compression, ACI Mater. J. 98 (6) (2001) 465–475.

[21] A. Ammouche, J. Riss, D. Breyss, Image analysis for the automated study ofmicro-cracks in concrete, Cement Concr. Compos. 23 (2001) 267–278.

[22] M. Brown, D.G. Lowe, Automatic panoramic image stitching using invariantfeatures, Int. J. Comput. Vision 74 (2006) 59.

[23] W.S. Rasband, J. Image, U.S. National Institutes of Health, Bethesda, Maryland,USA, <http://imagej.nih.gov/ij/>, 1997 (accessed July 2014).

[24] R.I. Gilbert, Shrinkage, cracking and deflection of concrete structures, Electron.J. Struct. Eng. 1 (1) (2001) 2–14.