Construction and Building Materials 61 (2014) 10–17

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Construction and Building Materials

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X-ray computed tomography and fractal analysis for the evaluationof segregation resistance, strength response and accelerated corrosionbehaviour of self-compacting lightweight concrete

http://dx.doi.org/10.1016/j.conbuildmat.2014.02.0700950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Tel.: +90 (0) 212 473 00 00x17923.E-mail address: savas.erdem@istanbul.edu.tr

Savas� Erdem ⇑Department of Civil Engineering, University of Istanbul, Avcilar Campus, 34320 Avcilar-Istanbul, Turkey

h i g h l i g h t s

� Fractal characterisation and X-ray CT analysis of self-compacting lightweight concrete are carried out.� First study to analyse the segregation of concrete by means of 3D X-ray CT accompanied by image analysis.� Fractal dimension and fracture energy increase with the increase of the complexity of corrosion morphology.� Inherent void distribution is the dominant factor determining strength performance.

a r t i c l e i n f o

Article history:Received 2 November 2013Received in revised form 25 January 2014Accepted 26 February 2014

Keywords:Self-compacting concreteCorrosionFractureSurface analysisX-ray computed tomography

a b s t r a c t

In this study, fractal analysis and 3D X-ray computed tomography accompanied by digital image analysistechnique are used for the quantitative evaluation of segregation resistance, static strength andcorrosion-induced cracking in normal self-compacting concrete and self-compacting lightweightconcrete. From image analysis performed on the vertical sections of the specimens, it was observed thatself-compacting lightweight concrete had much higher resistance to segregation and the use of coarselightweight particles in self-compacting concrete did not contribute to extensive level of anisotropy.The results also indicate that self-compacting lightweight concrete was weaker in compression thannormal self-compacting concrete mainly due to less homogeneous internal structure. Finally, it was alsoshown that self-compacting lightweight concrete had lower susceptibility to corrosion in the early stageof exposure to the chloride environment than normal self-compacting concrete and greater fractal ener-gies were dissipated in self-compacting concrete made with less porous and stiffer conventionalaggregates.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Self consolidating concrete (SCC) is a new class of high perfor-mance concrete characterised by the high fluidity under its ownweight so that it can be placed without mechanical consolidation,easily fill small interstices of formwork and be pumped throughlong distances [1]. As a common practice, SCC contains a large vol-ume of powders apart from the traditional concrete constituents(such as sand, coarse aggregate, water and admixtures) and thusits density is much higher than that of conventional concrete [2]leading to an increase in the dimension of load-carrying elementsand consequent foundations loads. Ideally, employing lightweight

aggregates in SCC cannot only overcome the aforementionedproblem but also combine the favourable properties of light-weight concrete and SCC. Lightweight concrete can decrease thedead weight of structure which can result in reduced seismic forcein a structure building [3]. On other hand, SCC can prevent thesegregation of lightweight aggregates and produce a lightweightconcrete with enhanced quality and higher compressive strength[4].

As a practical concern, self-consolidating lightweight concrete(SCLC) is a possible candidate for use in long-span bridges andreinforced concrete constructions built in marine and coastalareas. Under such circumstances, the concrete are most likely tobe under the threat of chloride initiated corrosion [5,6]. Therefore,it is very important to assess the corrosion performance of suchconcretes apart from strength and workability. It would not be

S. Erdem / Construction and Building Materials 61 (2014) 10–17 11

an exaggeration to say that chloride-induced reinforcement corro-sion is today one of greatest challenges for scientists on concretetechnology. Considerable research activity is still going onto havea look behind the curtain. But this does not mean that our knowl-edge is scarce on that area. At that point, the beginning questionshould be what drives the corrosion damage of cementitiousmaterials when exposed to chloride solutions and how this in turnaffects the properties of concrete at the macro-scale. Corrosion ofsteel in reinforced concrete is essentially an electrochemical pro-cess that leads to the dissolution of iron to form a range of solidproducts, which are a complex mixture of iron oxides, hydroxidesand hydrated oxides [7]. The corrosion of steel takes place as a re-sult of either the reduction in alkalinity (pH) at the steel, due tocarbonation of concrete or leaching of alkalis, or the presence ofa significant amount of chloride ions in the concrete [8]. Rein-forcement corrosion reduces the cross-sectional area of the rebar,thereby, diminishing its load-bearing capacity and degrades theintegrity of the surrounding concrete [9] and thus triggers off acatastrophic failure.

One of the most important micro-structural characteristics ofconcrete is its distinctive pore structure associated with a largenumber of pores with different sizes, shapes and origins. Today theresearchers have accepted the common view that the pore structureof concrete controls its physical, mechanical and durability proper-ties. The permeability of concrete is strongly influenced by connec-tivity of pores, while the compressive strength is primarily affectedby the total volume of pores [10]. Similarly, durability to freezingand thawing and de-icer scaling are primarily governed by the vol-ume and spacing of entrained air voids [11]. Thus, the study of porestructure should assist in a more in-depth understanding of thematerial behaviour and development of long-life SCLC.

A review of the concrete literature indicates that in contrast toworkability, physical and mechanical properties of SCLC, no studyhas been conducted so far to investigate the combinedrheological-related properties and durability performance of SCLC.In this work, the rheological-related properties and segregationresistance, strength development, pore structure and acceleratedcorrosion resistance of SCLC is experimentally studied and com-pared with those of conventional self-compacting concrete. Inaddition, the technique of X-ray computed tomography (CT) coupledwith digital image software was used to visualise the micro-struc-tures of the mixes.

Fig. 1. A graphical presentation of the gradi

2. Materials and methodology

2.1. Properties of materials used in concrete production

Ordinary Portland cement CEM I 52.5N conforming to BS EN standards was usedto produce all concrete mixes. Fly ash was incorporated in the mix to supplementthe cementing property and to enhance the workability of concrete. Local river sandwith a specific gravity of 2.66 g/cm3 constituted the fine aggregates in all mixes.Natural gravel sourced from a local quarry with a nominal maximum size of14 mm and a specific gravity of 2.56 g/cm3 was used to produce a control (refer-ence) mix. The lightweight aggregate, kindly provided by Lytag Ltd., used was a sin-tered fly ash with a nominal maximum size of 14 mm. A graphical presentation ofthe gradings is displayed in Fig. 1. A polycarboxylate based superplasticizer with aspecific gravity of 1.08 was also employed to achieve the desired workability in allconcrete mixtures. The dosage of the superplasticizer was 1% by mass of powder.

2.2. Production of concrete mixtures

In all mixes, the volume fractions of cement, coarse aggregates, sand, superp-lasticizer and free water were the same. Thus, the same water–powder ratio of0.31 was used in all batches. The only difference was the type of coarse aggregateused in the mixtures. The mix proportions are given in Table 1. Before casting con-crete, lightweight aggregates were first immersed in water for 24 h until all parti-cles were fully saturated.

A mechanical pan mixer was used for the mixing of the concrete. The fine andcoarse aggregates were first introduced and mixed 1/3 of the water, which wasgradually added. The fly ash and cement were incorporated in the mix with a sub-stantial portion of the remaining water and mixed for 2 min. Finally, the superplast-icizer with the remaining was added in the mixture and mixing continued for3 min. From each mixture, cube and lollipop specimens were also cast withoutany compaction and vibration. 24 h after casting, they were de-moulded and curedat 20 ± 2 �C in a water tank until the day of testing.

2.3. Tests and analysis performed

2.3.1. X-ray diffraction analysisFinely ground aggregate particles were placed and levelled in the sample holder

and then positioned in the chamber of the Bruker –AXS D8 Advance XRD equipmentwhich has a Cu-anode X-ray tube, a Göbel mirror, a diffracted beam collimator witha 0.12� Soller slit, and a Sol-X energy-discriminating X-ray detector set to Cu Karadiation. The scanning was conducted between 5� and 70� at a speed of 2� per min-ute. The duration of the scan was about 60 min.

2.3.2. Accelerated corrosion resistanceLollipop samples, 65 mm in diameter and 120 mm high, were also cast with

6 mm diameter mild steel rods in the centre. The 150 mm long steel rods were pol-ished with SiC papers, cleaned with acetone and water respectively, and insulatedwith electrical tape to expose 30 mm of exposed steel at the bottom. A cover ofapproximately 32 mm was provided at the base of the concrete. The concrete lolli-pops were de-moulded after 24 h and were moist-cured for 27 days. At age 28 days,the specimens were placed in a cell with 10% NaCl solution.

ng of the lightweight fly ash aggregate.

Table 1Concrete mix properties.

MixID

Cement(kg/m3)

Fly ash(kg/m3)

Sand(kg/m3)

Coarse aggregate(kg/m3)

Water(kg/m3)

SCC 323 177 832 852 155SCLC 323 177 832 446 155

12 S. Erdem / Construction and Building Materials 61 (2014) 10–17

An electrochemical cell was set up as shown in Fig. 2 for the promotion of cor-rosion under a 30 V DC source. After 28 days the SCC samples were placed in a 10%NaCl solution and the current density was observed for 72 h at 24-h interval with apotentiostat/galvanostat ACM instrument. A scan rate of 0.1 mV/s was used todetermine the linear polar resistance (Rp) in the range of ±10 mV. The corrosion po-tential was determined by method set out in ASTM C 876 [12].

2.3.3. Fresh and mechanical testsAfter mixing, the slump flow and V-funnel tests were done to characterise the

consistency and passing ability of the two types of concrete with the Abrams coneand V-funnel respectively in accordance to EFNARC [13] guidelines. The compres-sive strengths were determined on 100 mm cubes in accordance with the BritishEuropean Standard. The average of three test specimens was reported.

2.3.4. X-ray computed tomographyAn X-ray CT system (Venlo H-350/225) with IMPS operating software was used

for scanning the specimens, as shown in Fig. 3. The 350 kV mini focus source has thenecessary power to penetrate the concrete specimens and the emitted ray whichoriginates from the light source is subsequently received by a detector. The processgives a profile of the structure of the concrete based on the intensity of the ray thatis received. The result is a 2D image with a reasonable resolution. In carrying out thetest, the specimens were fixed on the turn table to ensure that it does not movewhile the X-ray is scanning. The resolution of the X-ray CT images was0.083 mm/pixel. The captured images from the X-ray CT system were then analysed

Fig. 2. Photograph of the electrochemical cell set up.

Fig. 3. X-ray CT test set up and its component.

and converted to 3D images using the standard capabilities of an image analysissoftware package (Image J). Finally, the converted images were used to identifyand quantify air voids within the specimens.

2.3.5. Fractal analysisThe impressed voltage test resulted in the cracking of the lollipop samples dur-

ing the 3-day period. The profiles of the surface cracks of the specimens after cor-rosion were obtained using a digital camera and image software. Then, thecaptured images were digitized and converted into binary images to reveal thecrack path. Next, the fractal dimension of the surface cracks was determined usingthe same image software (box-counting method). Finally, for a rough measure offracture energy based on the surface- macro cracks, the formula suggested byGuo et al. [14] was adopted as follows: Ws=Gf ¼ a � ðd=aÞ1�D1�d where Ws is the totalenergy dissipated at the surface of the crack; Gf is the fracture energy at the scale ofobservation d (d is the maximum diameter of sand in concrete); a is the Euclideanlength, which is equal to the height of the cross-section and D1�d is the mean valueof the fractal dimension of surface cracks on the cracked specimen.

2.3.6. Segregation analysisImagine analysis was carried out on digital images obtained from CT scan of

concrete samples for the evaluation of segregation in the SCC. In this procedure,only the coarse aggregate was considered and the determination of the degree ofsegregation is based on method used by [15]. The scanning was done at 1 mm inter-val on 100 mm concrete cubes and so 100 slices were obtained. Using image soft-ware, the slices were stacked and two vertical sections were taken as shown in a3D representative sample (Fig. 4) to reveal the spatial identity of each particle inthe domain of the section which was defined in pixel units but which was later cal-ibrated to give metric units. Two horizontal sections were taken at one third andtwo thirds along the height of the cube and the sections were prepared in a similarway. It should also be mentioned that pixel thresholding was applied to help in theidentification of the course aggregates. Pixel thresholding the image produces a his-togram based on the intensity values (shades of gray) of the pixels which rangesfrom 0 to 255 to represent black to white respectively. After examination of 10slices for each type of concrete sample, it was shown that pixels with intensity val-ues between 0 and 70 identified the pores, 90 and 190 for the gravel and intensityvalues between 30 and 100 identified the mortar. This information, aided by visualexamination was used to differentiate the aggregate particles from the mortar andpores in the image. Filtering was carried out on each section to show particles 4 mmand greater and then a threshold was set to obtain a bitonal image, a process refersto binarization, which separates the concrete image into aggregate and mortar frac-tions. From the binary image of each vertical section, the volume of the aggregate inthe upper section was calculated based on the area of unit width that was obtainedafter setting the threshold. The volumes of the total aggregates in the upper half(Vvu) and that in the lower half (Vvl) of each vertical section were found separatelyand expressed as a ratio (Rvu and Rvl respectively) of the volumetric fraction ofaggregate in the concrete (Vaf) as shown in Eqs. (1) and (2). A similar procedurewas adopted on the upper and lower horizontal sections to obtain the ratio Rhu

and Rhl for the respective horizontal sections.

Rvu ¼Xin

i¼i1

Vvu � Vaf ð1Þ

Fig. 4. 3D X-ray CT representative image for the segregation analysis.

S. Erdem / Construction and Building Materials 61 (2014) 10–17 13

Rv l ¼Xjn

j¼j1

Vv l � Vaf ð2Þ

A qualitative assignment is given to the segregation of the section as follows:

TaFr

No segregation:

ble 2esh properties of SCC and SCLC specimens.

Mix ID Slump flow (mm)

SCC 750SCLC 780

Fig. 5. Compressive strength te

Fig. 6. Typical X-ray CT ima

Rvu = Rvl = 1Rhu = Rhl = 1

Moderate segregation:

1.0 > Rvu P 0.85 or 1.0 > Rvl 6 1.151.0 > Rhl P 0.85 or 1.0 > Rhl P 0.85

High segregation:

Rvu < 0.85 or Rvl > 1.15Rhl < 0.85 or Rhu > 1.15

3. Results and discussion

3.1. Rheological-related properties and image analysis

The results of the slump flow, V-funnel, segregation and J-ringtests are displayed in Table 2. The slump flow of the referenceSCC is 750 mm and that of the SCLC is 780 mm. The measurementsof the confined slump flow with the J-ring are 750 mm and

V-funnel (s) J-ring (mm)

8.7 75011.6 770

st results of the mixes.

ge of the SCLC mix.

770 mm respectively for the reference SCC and the SCLC. Measure-ments with the V-funnel on the other hand produced efflux timesof 8.7 s for the traditional concrete and 11.6 s for SCLC, resulting inthe latter having a lower flow rate even though it displayed higherfluidity.

This however, is typical of concrete with lightweight aggregate.The relatively low self weight of the recipient concrete automati-cally reduces flow rate of the material. Practically, this flow ratecan ultimately serve to reduce productivity on construction pro-jects where SCLC with light weight fly ash aggregates is used.

As seen in the test results, when the coarse aggregate of theconventional concrete was replaced with fly ash aggregate theslump spread is increased. There are two main features of thislightweight aggregate that can enhance the rheological perfor-mance of the fresh concrete.

Firstly, the improvement in the flow can be ascribed to the lowdensity of the artificial aggregate. Normal weight aggregatesabsorb a significant amount of energy that is required for theeffective flow of the cementitious material. The mechanism

Fig. 7. Typical X-ray CT image of the SCC mix.

Fig. 8. Air void distributions of the specimens.

Fig. 9. X-ray diffraction pattern of the fly ash lightweight aggregate.

14 S. Erdem / Construction and Building Materials 61 (2014) 10–17

involved is more evident around the juncture of obstacles wherethe expenditure of energy to overcome the increase of internalstress often leads to blockage [16]. The substitution of this typeof aggregate for lightweight fly ash particles can result in a reduc-tion in the energy that is required to transport the coarse particlesparticularly in constricted areas and hence can avail more energyfor better deformability. The benefit of this substitution is clearlydemonstrated in the higher level of unrestrained and restraintslump flow in fly ash SCLC.

Further, the improvement can also be attributed to the geomet-rical properties of the aggregates particles [17]. Unlike naturalaggregate, the fly ash particles are all roughly spherical withrelatively glassy surface texture. These inherent characteristics willlower the inter-particle friction and reduce the yield stress in thecementitious material; hence promoting better flow. Referring tothe results in Table 2, it can be seen that even with obstacles inits path, the flow of SCLC is higher than that of the traditionalSCC when unconfined. This enhancement is partly derived fromthe shape of the aggregate particles as the spherical shape removethe possibility of the particles interlocking in the vicinity of obsta-cles and therefore, compared to the gravel SCC, the internal stressis further reduced when there is restriction in space.

Fig. 10. The change in corrosion current density of the specimens with respect totime.

From image analysis performed on the vertical sections of thefly ash SCC cubes, the ratio for segregation (Rvu) from the uppervertical section was 1.07, while the corresponding ratio for thegravel SCC was 0.91. A similar analysis carried out on the horizon-tal sections gave Rhu values of 1.06 and 0.89 respectively for the flyash and gravel SCC and hence there was a strong correlation be-tween the ratios of aggregate found in the vertical and horizontalsections of the concrete cubes. The higher proportion of Lytag par-ticles in the upper half of the cube is expected as there is a propen-sity for the lightweight particles to float causing settlement in theupper section (cast end) of the cube. The segregation values for thefly ash and gravel samples indicate that, while both types of SCCunderwent moderate segregation, the fly ash SCC had a higher seg-

Fig. 11. Digitized fractal dimension curves a-) SCC mix and b-) SCLC mix.

Fig. 12. The view of the deteriorated specimens.

S. Erdem / Construction and Building Materials 61 (2014) 10–17 15

regation values and hence higher resistance to segregation. Theanalysis shows that lightweight fly ash particles when used willnot contribute extensive level of anisotropy, a condition that canresult in variability in the mechanical and transport properties.

3.2. Strength development and X-ray CT analysis

Fig. 5 gives a graphical representation of variation of compres-sive strength with age. The strength varied from 12 to 24 MPa at7 days and from 34 to 52 MPa at 28 days, respectively for SCCand SCLC. An examination of the development of the strength of

Fig. 13. Typical 3D plot and surface map

the mixtures indicates that the SCC samples gained the majority(85%) of its long-term strength in 7 days while the SCLC samplesattained only 60% over the same time. This means that there wasa much less gain in static strength in the reference SCC specimensthan in the SCLC sample after seven days.

Increase in interconnected void content and consequent the to-tal volume of pores (high porosity) could be the reason that causesthe reduction of quasi-static compressive strength with fly ashlightweight aggregate addition. It is generally accepted that thepore structure is of paramount importance in determining thestrength of hardened cement paste and concrete. Figs. 6 and 7show a typical image of the SCC and the SCLC mixes obtained byX-ray CT technique coupled with digital image analysis. The differ-ences in colours indicate the different material phases in themixture.

The analysis (Fig. 8) carried out clearly indicates that the inher-ent void distribution was not homogeneous for the mixes, and thevoid content in the SCLC was much higher than that in the SCC. Asreported and highlighted by Erdem et al. [18] and Yuan and Harri-son [19], such initial defects and heterogeneous micro-structurewould not only cause a dramatic increase in the concentrationsof the stresses around the pores but these features will also resultin destructive transverse tensile strains, providing a line of weak-ness for failure to take place.

Further from X-ray diffraction (XRD) results (Fig. 9), it is shownthat the lightweight aggregate is of an amorphous nature and pos-sesses pozzolanic characteristics. Hence, it can be assumed thatthere would be considerable influence on the kinetics of the hydra-tion process and further on the hydrating of the cement paste.However, it is concluded that the glassy surface texture of the flyash aggregate could possible reduce the inter-particle friction,

of the corroded surface in the SCC.

16 S. Erdem / Construction and Building Materials 61 (2014) 10–17

which mobilizes shear stresses in the material, and inter-particlecontacts and eventually weaken the resistance of SCLC to tensileplastic deformation resulting in a much lower static strength.

The reduction of compressive strength of concrete incorporat-ing lightweight fly ash aggregates could be also attributed to lowerimpact value-softness of these aggregates. Since the aggregates inthe lightweight concrete are usually the weakest part of the micro-structural system, it would be logical to expect signs of failureemanating from severe cracking and fragmentation of the weakash aggregates. A visual observation carried out on the fracturedsurfaces of the mixes shows that the ash aggregates in SCLC wereeasily split across their diameter under compression signifying thatthe load is mainly carried by the interfaces and transferred by theaggregate, which this in turn results with a lower ability ofre-disturbing stress accompanied by a lower energy dissipationin the mix and consequent a premature failure. The majority ofthe gravel particles in SCC, on the other hand, exhibited an oppo-site tendency for crack propagation. Here, the gravel particles weremostly pulled out from their cavities, indicating a poor adhesionbetween the matrix and the aggregates. Thus, in this case, stifferaggregate could effectively spread the loads and improve thecontact point interactions for the matrix materials that flow anddeform in the vicinity of the coarse aggregate.

3.3. Corrosion resistance and fractal analysis

The corrosion potential (Ecorr) of the sample was determinedafter 28 days and all the results were lower than �270 mV basedon a saturated calomel reference electrode (SCE), indicating thatcorrosion had not been initiated in any of the lollipop samples be-fore the commencement of impressed voltage used for acceleratedcorrosion.

Fig. 14. Typical 3D plot and surface map

For the corrosion current density, the reference point used forthe identification of the onset of corrosion in reinforced concreteis 3 � 10�4 mA/cm2 [20]. Examination of the current density (Icorr)results shows (Fig. 10) that the fly ash and gravel SCC samples hadvalues several orders of magnitude higher than 3 � 10�4 mA/cm2,an indication that both samples were experiencing active corrosionat this point. Interestingly however, the results revealed that thefly ash SCC showed lower susceptibility to corrosion than the grav-el SCC in the early stages of exposure to the chloride environment.

The resistivity of concrete plays an important role in the corro-sion process. Factors such as porosity and chemical compositionof the pore solution of the concrete have effects on its level of resis-tance to corrosion [21]. Both types of SCC were produced with flyash powder, but it was evident that the particulates from the flyash aggregates contributed to a slightly different mortar composi-tion in the SCLC. The resulting higher fly ash powder content musthave triggered additional reaction with the chloride ions thatresulted in more chloride binding than that experienced in the grav-el SCC and this further reduced the total free Cl� initially. However,as the concrete samples continued in the corrosive environmentand the counteraction of the chemical binding abated, the effectof the higher chloride diffusivity (stemming from the more porousLytag aggregate) became more dominant in the FA SCC.

As a contribution to the discussion on the corrosion damage in-volved in these concretes; a quantitative analysis of the crackedsurfaces was conducted to determine the fractal dimension values.Fig. 11 shows the digitized fractal dimension curves of the speci-mens. The calculated fractal dimensions of the surface cracks andthe fracture energies based on surface macro-crack measurementare also presented in Fig. 11.

The results obviously show that the fractal dimensionality andfracture energy of the SCC are much higher than those of the SCLC.

of the corroded surface in the SCLC.

S. Erdem / Construction and Building Materials 61 (2014) 10–17 17

In addition, the fractal parameters increase with the increase of thecomplexity of the corrosion morphology (Fig. 12), which is consis-tent with the findings of Xu et al. [22] and may reflect tensilestrength and effective surface area differences created under thecorrosion damage.

The greater fractal dimension and fracture energy may also beexplained by the change in the fracture plane. In the case of SCC,likely due to a combined reason of high particle stiffness and lessimpedance mismatches between the paste matrix and particle,secondary crack branches can be produced and crack deflectionscan take place, leading to a more tortuous crack profile (Figs. 13and 14). A further explanation is, unlike the SCC, the higher poros-ity of the fly ash helped the SCLC to accommodate the products ofcorrosion and this reduced the stress created by the dissolved Fe2+

from the steel. This helped in mitigating corrosion-induced cracksin the SCLC and hence its fractal dimension is less than that of SCC.

4. Concluding remarks

In the light of the findings obtained from this experimentalstudy, the following conclusions can be drawn:

� The substitution of the conventional aggregate for the light-weight fly ash particles in the self-compacting concrete pro-duction enhanced the rheological performance of the freshconcrete (confirmed from the X-ray CT accompanied byimage analysis).

� This finding is interesting as not only has it shown for the firsttime that analysis of segregation of concrete can be done withX-ray CT accompanied by image analysis but that this knowl-edge further confirms the importance in the careful selectionof aggregate when improved property such as high flow-abil-ity is needed in concrete structures (i.e. beam-columnconnections).

� Application of fractal theory on the macro-scale evolution ofcorrosion-induced damage was carried out for the first timein the concrete literature. The analysis revealed that the frac-tal dimension of the cracks positively correlated with thecomplexity of corrosion morphology. In addition, for the selfcompacting concrete with less porous and stronger particles,greater fractal energies are dissipated during the corrosiondamage.

� The SCLC had much lower current density values (lower sus-ceptibility to corrosion) than the SCC. This signifies that theeffect of the higher chloride diffusivity stemming from theporous nature of lightweight aggregate did not become dom-inant in the early stage of exposure to the chlorideenvironment.

� Self compacting concrete with lightweight fly ash particleshad a lower compressive strength than the concrete withgravel aggregate partly due to the strength characteristics

of the aggregate and partly due to less homogeneous internalstructure – higher void content (as confirmed by 3D X-ray CTand image analysis).

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