An experimental investigation on freezing and thawing durability of high performance fiber reinforced concrete (HPFRC)

Journal Pre-proofs An experimental investigation on Freezing and Thawing Durability of High Performance Fiber Reinforced Concrete (HPFRC) L. Feo, F. Ascione, R. Penna, D. Lau, M. Lamberti PII: DOI: Reference:

S0263-8223(19)33894-2 https://doi.org/10.1016/j.compstruct.2019.111673 COST 111673

To appear in:

Composite Structures

Received Date: Accepted Date:

14 October 2019 3 November 2019

Please cite this article as: Feo, L., Ascione, F., Penna, R., Lau, D., Lamberti, M., An experimental investigation on Freezing and Thawing Durability of High Performance Fiber Reinforced Concrete (HPFRC), Composite Structures (2019), doi: https://doi.org/10.1016/j.compstruct.2019.111673

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier Ltd.

An experimental investigation on Freezing and Thawing Durability of High Performance Fiber Reinforced Concrete (HPFRC) L. Feo (1), F. Ascione (2), R. Penna (3,*) , D. Lau (4), M. Lamberti (5) Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Civil Engineering, University of Salerno, Italy, [email protected] (3) Department of Civil Engineering, University of Salerno, Italy, [email protected] (4) Department of Architecture and Civil Engineering, City University of Hong Kong, Hong Kong, China, [email protected] (5) College of Environmental Science and Engineering, Nankai University, Tianjin, China, [email protected] (*) Corresponding author: [email protected] (1) (2)

ABSTRACT This study presents the preliminary results of an experimental study of the durability of a commercial High Performance Fiber Reinforced Concrete (HPFRC) subjected to rapid freeze/thaw cycle. High-performance fiber reinforced concrete (HPFRC) is currently being used in the construction industry both for strengthening existing members and for controlling opening cracks in new ones. In literature there are many studies focused on the evaluation of the HPFRC mechanical properties varying the matrix composition and/or the type and quantity of the fibers but a lack of knowledge exists for what concerns its durability. Durability of concrete may be defined as the ability of concrete to resist weathering conditions, chemical attack and abrasion while maintaining its desired engineering properties. In particular, durability can be defined by the percentage ratio of the dynamic modulus of elasticity after a number of freeze and thaw cycles to the corresponding value before the freeze and thaw cycles. In this paper, three different concrete mixtures with various fiber volume fraction, i.e. 0%, 1.25% and 2.50%, were examined. Seventy-five freeze-thaw cycles were performed according to UNI 7087-2017 on five prismatic specimens per each concrete mixture while other three specimens were selected as reference samples. The durability evaluation was determined adopting the Impact Resonance Method (IRM) provided by the ASTM C215 for the evaluation of above mentioned dynamic moduli.

KEYWORDS Fiber Reinforced Concrete, Steel fibers, Freezing and Thawing Durability, Mechanical properties, Mechanical testing

1. INTRODUCTION The use of concrete dates back to the ancient time. Even though the actual design mix of ancient concrete is not the same as that of modern concrete, the history of concrete has indicated that this material is durable. Nowadays, concrete has become one of the most consumed substances in the world, only second to water, due to our ever-increasing social and economic needs for new civil infrastructures. However, concrete production involves lots of carbon footprint which violates the concept of sustainable development. In order to circumvent this problem, one effective and feasible solution is to extend the life of civil infrastructures. Hence, there is an urgent need to understand the degradation mechanisms that can affect the durability of cementbased structures. Understanding this issue will provide the basis to the development of

innovative construction materials that are more durable and economically appealing [1-3]. Similar to normal strength concrete, the strength of high performance fiber reinforced concrete (HPFRC) comes from the structural formation of calcium-silicate-hydrate (C-S-H) product, which enables load transfer between different components therein. During the hydration process, lots of voids (which can be filled with liquid or gas) can be formed, and hence concrete is porous in nature. This makes concrete susceptible to penetration of various chemicals, for which the extent of degradation can be correlated with the permeability of concrete. In evaluating durability, various environmental conditions and processes must be considered [4,5]. These include pH value (i.e. degree of acidity/alkalinity), temperature fluctuations, moisture ingress, stress history, wet-dry cycles, and freeze-thaw actions. Among these, the freeze-thaw damage is believed to be the most critical in places where there is snow in winter [6-9]. The presence of pore water in concrete leads to possible freeze-thaw damage during winter season. The mechanism of freeze-thaw damage is quite complicated and several explanations have been proposed. If concrete is saturated to a certain level, freeze-thaw damage will be resulted. When water freezes, it causes an expansive pressure on the pores in concrete due to the volume increase from water to ice. If the magnitude of this pressure (i.e. stress) exceeds the tensile strength of concrete, micro-cracks will occur. When temperature increase, the deformation of concrete becomes complicated because the coefficient of thermal expansion of ice is higher than that of water, which results in a differential expansion between concrete pore and ice as the temperature is rising during the thawing process. A loss of strength and stiffness due to extensive cracks will be resulted if concrete suffers a repetition of freeze-thaw cycle. Nowadays, high performance fiber reinforced concrete is currently being used in the construction industry both for strengthening existing members [10-19] and for controlling opening cracks in new ones [20-23]. In literature there are many studies focused on the evaluation of the HPFRC mechanical properties varying the matrix composition and/or the type and quantity of fibers [24-37], but a lack of knowledge exists for what concerns its durability. The authors of this paper are developing a multi-phase research program in which the main objective is to study the applications of HPFRC for the strengthening of existing civil structures. This work describes the first phase of an experimental investigation carried out at the Structural Engineering Testing Hall (STRENGTH) of the Department of Civil Engineering of the University of Salerno (Italy), as a part of a collaborative research program with City University of Hong Kong (China), on freezing and thawing durability of HPFRC reinforced with steel

Commented [DL1]: Please consider to include two more references coming from my previous work: Ao Zhou, Oral Buyukozturk and Denvid Lau (2017), "Debonding of concrete-epoxy interface under the coupled effect of moisture and sustained loading", Cement and Concrete Composites, 80:287-297. Denvid Lau and Oral Buyukozturk (2010), "Fracture characterization of concrete/epoxy interface affected by moisture", Mechanics of Materials, 42(12):1031-1042.

fibers, varying the fiber volume fraction Vf : 0%, 1.25% and 2.50%. Seventy-five freeze-thaw cycles have been performed according to UNI 7087-2017 [38] on five prismatic specimens per each concrete mixture and other three specimens have been selected as reference samples. In order to evaluate the durability factor of the three mixture, the resonant frequencies (i.e. transversal, longitudinal and torsional) and the dynamic moduli of elasticity were measured using the Impact Resonance Method (IRM) provided by the ASTM C215 [39]. Moreover, the prismatic specimens were tested under four-point bending setup to evaluate the influence of the freeze/thaw cycles on the flexural behavior of mixtures under investigation according to UNI 11039-2 [40,41]. 2. MATERIALS AND METHODS 2.1

Materials

The materials used in HPFRC include a high performance concrete (HPC) produced by Kerakoll [42] (GeoLite® Magma) and steel fibers produced by Bekaert [43] (Dramix OL 13/.20). Table 1a reports some technical data of HPC for the manufacturing of one cubic meter of the HPC abovementioned, while the geometrical and mechanical properties of the steel fibers (Figure 1) are summarized in Table 1b. In particular, l is the fiber length, de is the equivalent diameter of fibers and l/de is the aspect ratio. The preparation of the HPFRC mix consisted of slowly mixing the dry mixture and 75% amount of the water for about fifteen minutes; then, the steel fibers and the remaining quantity of water (25%) were added and mixed until a homogeneous mixture (HPFRC) was obtained. The mixing procedure was conducted at room temperature (20 ± 2 °C). In particular, the following three concrete mixture proportions were considered varying the steel fibers dosage V f

 as summarized in Table 2.

Table 1a. Geolite® Magma. Table 1b. Dramix OL 13/.20. Table 2. Concrete Mixture.

Figure 1. Steel fibers (type Dramix® OL 13/.20).

2.2

Preparation of Specimens

A total of twenty-four HPFRC prismatic specimens (PS), with dimensions of

150×150×600mm, and fifteen cubes samples (CS), with dimensions of 150×150×150mm, were prepared to carry out the overall experimental program of this research. In particular, for each type of HPFRC mixture, CM0, CM1 and CM2, eight prismatic samples (PS1-PS8) and five cubic specimens (CS1-CS5) were casted. During preparation, specimens were vibrated until the frequency of the emerging air bubbles decreased significantly. Then, they were covered with plastic sheets and, after for 24 hours, they were removed from their formworks and completely immersed in a tank filled with water for 27 days at a temperature of 20°C ± 2°C. The dimensions and the weight of all prismatic specimens measured at the twenty-eighth day are tabulated in Table 3, where the values of the width, w, and height, h, represent the average ones obtained by three different measurements (at mid-span and at ends cross sections, respectively. Furthermore, l represent the value of the length of the specimen measured at mid-span longitudinal cross-section. The prismatic specimens were subjected to rapid freeze/thaw cycles to evaluate the durability of mixtures. Thus, they were tested using a four point bending setup to characterize the tensile strength of HPFRC. The cubic samples were only tested in compression to evaluate the variation of their mechanical properties with the variation in the percentage of fibers. Table 4 reports the values of dimensions of all cubic specimens as well as the compression failure load  Fu  and strength

 f  evaluated according to EN 12390-4 [44]. Moreover, for each concrete mix, the average c , avg

compression strength is also shown. As it can be seen, the addition of fibers in mixtures CM1 and CM2 leads to a sensible increase of the average value of the compressive strength, with respect to CM0: 25.00% and 29.39%, respectively.

Table 3. Prismatic specimens (PS): measurements. Table 4. Cubic specimens (CS): measurements and compressive strength.

2.3

Test Methods

As already mentioned, after completion of the curing period, all prismatic specimens were subjected to freeze and thaw cycles according to UNI 7087-2017 “Determination of the resistance to the degrade due to freeze- thaw cycles” [38]. Hence, in order to evaluate freezing and thawing durability of HPFRC, four-point bending tests were performed according to UNI 11039-1 [40] and UNI 11039-2 [41]. 2.3.1 Freeze-thaw cycles Five prismatic specimens for each concrete mixture were subjected to 75 freeze-thaw cycles while the other three prismatic samples were stored in the water of a thermostatic tank at constant temperature of 20°C (±2°C). The freeze-thaw cycles were preceded by a phase of thermal stabilization of the samples by immersion in water at temperature of 5°C (±2°C) with an hydraulic head no less than 30 mm. Then, no more than ten samples were put in the cell testing machine (Figure 2). Figure 2. Freeze/thaw testing machine.

Each cycle had a duration of 12 hours (±30 minutes). It consists of the following three phases, as shown in Figure 3: i) a cooling phase, in which the temperature inside the testing machine moves from 5°C (± 2°C) to -20°C (± 2°C) at a constant rate of 5°C/h (±0.5°C/h); ii) a constant phase in which the temperature is kept constant for two hours; iii) a heating phase in which the temperature returns to 5°C (±2°C) at the same velocity as step i). Figure 3. Schematization of a freeze-thaw cycle.

The values of the dimensions and weight of all prismatic specimens, evaluated before freezethaw cycles (Table 3), were measured again at 25, 50 and 75 cycles and no significant reductions were observed. However, at the end of freeze-thaw cycles, looking into the cross section of the specimens, the corrosion of steel fibers in the concrete mix has been observed (Figures 4a and 4b). The corrosion of the fibers not only reduce their sectional area, but it also

affects the durability of the material which depends on the performance of the bridging capacity of the fibers embedded in the concrete (Figure 4c), which will be discussed in the following. Figure 4a-c. Corrosion of steel fibers in the concrete mixture of a CM2 specimen.

2.3.2 Impact Resonance Method Setup In order to evaluate the durability factor of the three mixture, the resonant frequencies (transversal, longitudinal and torsional) and the dynamic moduli of elasticity were measured using the Impact Resonance Method (IRM) provided by the ASTM C215 [40]. The setup for the Impact Resonance Test is composed of a waveform analyzer, an amplifier, an impactor, an accelerometer and steel supports of the specimen (Figure 5). The IRM consists in exiting the supported specimen to vibrate with a small impactor; the specimen response, in terms of fundamental frequency, is measured by a lightweight accelerometer positioned on the specimen. In particular, three different testing modes for the determination of the transversal

 f ,

longitudinal  f '  , and torsional frequencies  f ''  were considered by changing the position of the impactor, of the accelerometer, and of the supports and recording the highest peak in the amplitude spectrums with a digital waveform analyzer: -

For the transverse mode (Figure 6), the supports were placed at 0.224 l from the edge of the specimen, the impactor at the middle of the upper surface, and the accelerometer at the middle of the width, w, near the specimen edge;

-

For the longitudinal mode (Figure 7), the supports were placed in the middle of the specimen, the impactor at the centre of the end cross section, and the accelerometer at specimen’s top sensing along the direction of the vibrations;

-

For the torsional mode (Figure 8), the supports were placed in the middle of the specimen, the impactor at 0.132 l from its edge, and the accelerometer at 0.224 l from the edge of the sample.

Figure 5a,b. Apparatus for Impact Resonance Test (ASTM C215-02: a) Schematic Apparatus (ASTM C215-02); b) Photo of the apparatus. Figure 6. Location of impactor and accelerometer in the Transverse Mode. Figure 7. Location of impactor and accelerometer in the Longitudinal Mode. Figure 8. Location of impactor and accelerometer in the Torsional Mode.

2.3.3 Four-point bending tests The prismatic specimens were tested under four-point bending setup in order to evaluate the influence of the freeze/thaw cycles on the flexural behavior of the mixtures under investigation, as shown in Figure 9. The four-point bending tests were carried out according to UNI 110392 [41] after 75 cycles in displacement control at a constant rate of 0.005 mm/min. In particular, three displacement transducers were placed inside the notch (about 45 mm in depth). In particular, two transducers were positioned in parallel on the vertical sides of the specimens to evaluate the so-called “Crack Tip Opening Displacement” (CTODm, where m stands for average value). Figure 9. Experimental set-up of the four-point bending test.

3. EXPERIMENTAL RESULTS 3.1

Fundamental frequencies '

''

The values of the three fundamental frequencies, f , f and f , evaluated before freeze-thaw cycles (0 cycles), at 25, 50 and 75 cycles are summarized in Tables 5-7, respectively. The D dynamic moduli of elasticity for transversal mode  ETra  , longitudinal mode

E  D Lon

and

D torsional mode  GTor  , corresponding to the three above mentioned fundamental resonant

'

''

frequencies, f , f and f , were evaluated according to ASTM C215 method, using the following equations: D ETra  C  m ( f )2 ,

(1)

D ELon  D m ( f ' )2 ,

(2)

G  B m ( f ) ,

(3)

D Tor

'' 2

where the constants C, D and B assume the following meanings:

C=

0.9464  l 3  T w  h3

,

(4)

4l , w h 4l  R B= . w h D=

(5) (6)

In eqns (4-6), T represents a correction factor depending on the ratio of the radius of gyration (the radius of gyration for a prism is h/3.464), on the length of the specimen, l, and on Poisson’s ratio, and whose values are given in Table 1 of ASTM C215. Finally, R is a shape factor, equal to 1.183. The freezing and thawing durability of HPFRC was measured by the Durability Factor (DF), whose values are given by the following expression: 2   's s  mn fn  s F =  Fd ,0 2 'r  r  n  r mn fn  r   

   

s d ,n

s

,

(7)

s

where mn and fn represent the mass and the longitudinal fundamental resonant frequency of the r

s-th specimen subjected to freeze-thaw cycles (FT) after n cycles, respectively; while, mn and

fnr are relative to the r-th reference specimen (NFT) after n cycles. Finally, Fds,0 is the normalization factor evaluated (eqn.8) according to the following expression, which is formally the same as eqn. 7, but relative to reference specimens only: 2   m0s f0' s   F = . 2 'r  r   r m0 f0 nr       s d ,0

   

(8)

s Results in terms of durability factor, Fd ,n , of all prismatic specimens are reported in Table 8

at 25, 50 and 75 cycles, respectively.As it can be seen, the durability factor decreases from an average percentage value of 96.41 (at 25 cycles) to 88.27 (at 75 cycles) passing through the value of 95.08 (at 50 cycles) for the case of concrete mixture without steel fibers. The decrement of the durability factor is quite negligible for the other two concrete mixtures. More in details, for concrete mixture CM1, the aforementioned factor decreases from an average

value of 97.08 (at 25 cycles) to 94.93 (at 75 cycles), while in the case of CM2, no decrements were observed. Table 5. Frequencies and elastic moduli before freeze-thaw cycles. s), NFT; ** specimen subjected to freeze-thaw cycles, FT Table 6. Fundamental transverse, longitudinal and torsional frequencies at 25th, 50th and 75th cycles. Table 7. Elastic moduli: transversal, longitudinal and torsional at 25th, 50th and 75th cycles. Table 8. Freeze-Thaw durability factor evaluated at 25th, 50th and 75th cycles.

3.2

Four-point bending experimental results

The flexural behaviour of the three concrete mixtures under investigation, CM0, CM1 and CM2, has been derived from the results of the four-point bending experimental tests. Specifically, Figure 10 plots the vertical load versus crack-tip opening displacement (CTODm) experimental curves referred to each sample of the unreinforced “plain” mixture (CM0), while, for completeness, Figure 11 summarizes the experimental results of the four-point bending tests performed on both the unconditioned (NFT) and the conditioned (FT) sample of the “plain” mixture (CM0). Moreover, Figure 12 plots the experimental curves referred to each sample of the concrete mixture CM1 ( Vf =1.25%), and Figure 13 reports the CTODm versus vertical load curves of all CM1 samples. Similarly Figure 14 plots the curves referred to each specimen of CM2 mixture ( Vf =2.5%), and Figure 15 presents the experimental response of all CM2 samples. Finally, in Figure16a and Figure16b the flexural behaviour curves of the three concrete mixtures under investigation are compared before and after the freeze-thaw-cycles. Figure 10a-g. CTODm - vertical load for each specimen of CM0 concrete mixture. Figure 11. CTODm - vertical load (CM0). Figure 12a-e CTODm - vertical load for each specimen of CM1 concrete mixture. Figure 13. CTODm - vertical load (CM1). Figure 14a-f. CTODm - vertical load for each specimen of CM2 concrete mixture. Figure 15. CTODm - vertical load (CM2). Figure 16a,b. CTODm - vertical load (NFT and FT).

A more exhaustive analysis can be developed following the UNI-11039 – 2 procedure which starts from the evaluation of the average value (CTOD0,avg) of the crack-tip opening displacements (CTOD0), corresponding to the maximum vertical loads  Pmax  , of the HPC samples (CM0). Table 9 summarizes the values of CTOD0 and CTOD0,avg for both the unconditioned (NFT) and the conditioned (FT) specimens of the “plain” concrete, as well as the values of the maximum load Pmax. The second step of the procedure is to evaluate the representative parameters of the HPFRC concrete mixture, which are the first crack load the first crack strength

P , lf

 f  , the work capacity indices, U and U (energy absorption values), lf

1

2

the equivalent post-cracking strengths, f eq (00.6) and f eq (0.63) and the ductility indices, D0 and

D1 . The first crack load was evaluated according to [41] in function of CTOD0,avg per each

tests. The expressions of the first crack strength, flf , and those of the two ductility indices, D0 and D1 , are given in the following equations:

flf =

D0 =

Plf  l h   b  a0 

feq(00.6) flf

, D1=

2

(9)

,

feq(0.63) feq(00.6)

,

(10)

where, symbols Plf , l, h and b, represent the first crack load (in Newton), the length (in mm), the heigth (in mm) and the width (in mm) of the tested prismatic specimen, respectively. Furthermore, a0 is the notch depth (in mm). More in details, the parameters U1 and U2 represent, respectively, the areas under the curves of Figures 9-11 in a representative range for the Serviceability Limit State (SLS), with CTOD ranging between CTOD0,avg and CTOD0,avg + 0.6 mm, and for the Ultimate Limit State (ULS), with CTOD ranging between CTOD0,avg + 0.6 mm and CTOD0,avg + 3.0 mm. The values of the above mentioned parameters for CM1 and CM2 samples are summarized in Table 10 and Table 11, respectively. Table 9. Crack-tip opening displacement (CTOD0) and the corresponding load Pmax . Table 10. Post-cracking toughness and representative parameters (CM1). Table 11. Post-cracking toughness and representative parameters (CM2).

3.3 Observations 3.3.1 Effect of fiber volume content As it can be observed from the curves of Figure 11, specimens without steel fiber exhibited a linear-elastic behavior up to the maximum load  Pmax  , corresponding to the initial cracking, followed by a brittle failure. On the contrary, as numerous previous studies have already confirmed [29], the behaviour of HPFRC specimens can be divided into three different branches, as shown in Figure 13 and Figure 15: (i) a pre-cracking stage, in which the applied load is supported by a joint action of the concrete and steel fibers, in which the concrete plays the main role and, therefore, the bonding stress between fibers and concrete is relatively weak, (ii) a post-cracking stage, characterized by the formation of many micro-cracks in the HPFRC mix, the bonding stress between steel fibers and concrete increases as the micro-cracks expand and the load is mainly supported by the fibers which serve as a "bridge" over cracks (bridging action of the fibers), (iii)a descending phase where there is a decrease in the applied load, since the fibers that are lost in the fracture plane, due to the pull-out failure, are higher than those that are activated over micro-cracks. As it can be seen from the curves in Figure 16a, the bending response of the un-conditioned HPFRC concrete mixtures is highly influenced by the fiber contribution: in fact, compared to the plain mixture, specimens with steel fiber exhibited a higher first-crack strength and a postcracking behaviour with a high energy absorption capacity (toughness). In particular, the average increments of HPFRC specimens first-crack loads, with respect to plain concrete, were equal to 22.61% (CM1_NFT) and 39.69% (CM2_NFT), respectively [Tables 9-11]. Moreover, doubling the fiber volume percentages, increments of the residual strength values, f eq (00.6) and f eq (0.63) , equal to 38.3% and 43.6, respectively, have been observed. Finally, according to UNI-11039, and based on the values of the ductility indices, D0 and D1 , which are both greater than 1.1, the post-cracking response of the two HPFRC examined can be defined as “hardening” [Tables 10-11].

3.3.2 Effect of freeze and thaw cycles As it can be seen from the curves plotted in Figure 16b, the qualitative response of the conditioned specimens is similar to that exhibited by the un-conditioned samples: in fact, the CM0_FT specimens have presented a linear-elastic behavior up to the maximum load, followed by a brittle failure, and the experimental curves of CM1_FT and CM2_FT samples present the same three different segments already observed for the NFT specimens (Figure 16a). Quantitatively, the behavior of the conditioned specimens is significantly influenced by freeze and thaw cycles. In details [Table 12], after 75 cycles, the average value of the first crack strengths of the three concrete mixture under investigation, CM0, CM1 and CM2, have presented percentage decreases equal to 23.1%, 15.5% and 16.9%, respectively. Regarding the concerns of equivalent post-cracking strengths, i.e. f eq (00.6) and f eq (0.63) , decrements equal to 21.7% and 16.7% for concrete mixture CM1 and equal to 21.4% and 23.9% for the CM2 mixture, respectively, have been obtained. These reductions are attributable to the degradation due to the freeze-thaw cycles of the concrete/fiber interface that progressively reduces the anchorage capacity. Despite the observed reductions, the post-cracking response of the two HPFRC can still be defined as “hardening” being the values of the ductility indices, D0 and D1 , are both greater than 1.1 [Tables 10-11]. Table 12. Comparison between the average values of the first crack strength and the equivalent post-cracking strengths before and after the freeze-thaw cycles.

4. CONCLUSIONS This paper presents the results of a first phase of a multi-phase comprehensive joint research program between University of Salerno (Italy) and City University of Hong Kong (China), on investigating one of the major structural issues concerning the mechanical response of high performance fiber reinforced concrete (HPFRC). Specifically, the freezing and thawing durability of HPFRC reinforced with steel fibers, varying the fiber volume fraction ( Vf ): 0% (CM0), 1.25% (CM1) and 2.50% (CM2). Based on the obtained experimental results, the following conclusions can be drawn: - Dimension and weight: dimensions and weight of all prismatic specimens were measured before the freeze/thaw cycling and at 25, 50 and 75 cycles. The results have revealed no significant differences in dimensions and in weight due to the freeze and thaw cycling; - Compressive strength: the compression tests indicated that the addition of fibers in mixtures CM1 and CM2 leads to a sensible increase of the average value of compressive strength, with respect to CM0, equal to 25.00% and 29.39%, respectively; - Durability factor: the freeze and thaw tests results indicated that the durability factor of the HPFRC prismatic specimens decreases from an average percentage value of 96.41 (at 25 cycles) to 88.27 (at 75 cycles) passing through the value of 95.08 (at 50 cycles) for the case of concrete mixture without steel fibers (CM0). The decrement of the durability factor is quite negligible for the other two concrete mixtures. In fact, for concrete mixture CM1, the aforementioned factor decreases from an average value of 97.08 (at 25 cycles) to 94.93 (at 75 cycles), while in the case of CM2, no decrements were observed, showing a good freeze-thaw resistance; - Flexural strength: the prismatic specimens have been tested under four-point bending to evaluate the influence of both fiber volume content and freeze/thaw cycles on the flexural behavior of mixtures under investigation. Firstly, it has been observed that the bending response of the HPFRC concrete mixtures is highly influenced by the fiber contribution: in fact, compared to the plain mixture, specimens with steel fiber exhibited a higher first-crack strength and a post-cracking behaviour with a high energy absorption capacity (toughness). Moreover, the experimental results have shown that the flexural behavior is significantly influenced by freeze and thaw cycles. In fact, after 75 cycles, decreases of the average value of the first crack strength, equal to 23.1%, 15.5% and 16.9%, have been obtained for the three concrete mixture under investigation, CM0, CM1 and CM2, respectively.

Finally, the degrade due to the freeze-thaw cycles also results in reductions of the equivalent post-cracking strengths, f eq (00.6) and f eq (0.63) , equal to 21.7% and 16,7%, for concrete mixture CM1, and equal to 21.4% and 23.9 for the CM2 mixture, respectively. These differences are attributable to the progressive degrade of the anchorage capacity of the concrete/fiber interface due to the freeze-thaw cycles. To sum up, the experimental results gathered from the first phase of this joint research program between University of Salerno and City University of Hong Kong (China) provided important information on freezing and thawing durability of HPFRC reinforced with steel fibers and can be used by structural engineers in designing an optimum concrete mixture to achieve the maximum benefits of high performance fiber reinforced concrete. The second part of this study on the freezing and thawing durability of HPFRC, varying the matrix composition and/or the type and quantity of fibers, will be investigated in near future. ACKNOWLEDGEMENTS The authors are grateful to ‘‘Kerakoll S.p.A.” (Sassuolo, Italy) for their important support to the experimental investigation. Moreover, it should be highlighted that this study is part of the activities carried out by the authors within the ‘‘ReLUIS-Italian Department of Civil Protection’s Executive Project 2018”, funded by ReLUIS/DPC (www.reluis.it). REFERENCES [1] Lau D, Jian W, Yu Z, Hui D. Nano-engineering of construction materials using molecular dynamics simulations: Prospects and challenges. Compos Part B 2018, 143: 282-291. [2] Pakravan H R, Latifi M, Jamshidi M. Hybrid short fiber reinforcement system in concrete: A review. Construct Build Mater 2017, 142: 280-294. [3] Choi W C, Yun H D, Cho C G, Feo L. Attempts to apply high performance fiber-reinforced cement composite (HPFRCC) to infrastructures in South Korea. Compos Struct 2014, 109: 211-223. [4] Lau D, Qiu Q, Zhou A, Chow L C. Long term performance and fire safety aspect of FRP composites used in building structures. Construct Build Mater 2016, 126: 573-585. [5] Escoffres P, Desmettre C, Charron J P. Effect of a crystalline admixture on the self-healing capability of high-performance fiber reinforced concretes in service conditions. Construct Build Mater 2018, 173, 763-774.

[6] Ma H, Yu H, Li C, Tan Y, Cao W, Da B. Freeze–thaw damage to high-performance concrete with synthetic fibre and fly ash due to ethylene glycol deicer. Construct Build Mater 2018, 187, 197-204. [7] Hamoush S, Picornell-Darder M, Abu-Lebdeh T, Mohamed A. Freezing and Thawing Durability of Very High Strength Concrete. AJEAS 2011, 4: 42-51. [8] Ao Zhou, Oral Buyukozturk and Denvid Lau (2017), "Debonding of concrete-epoxy interface under the coupled effect of moisture and sustained loading", Cement and Concrete Composites, 80:287-297. [9] Denvid Lau and Oral Buyukozturk (2010), "Fracture characterization of concrete/epoxy interface affected by moisture", Mechanics of Materials, 42(12):1031-1042. [10] Hung C C, Hu F Y. Behavior of high-strength concrete slender columns strengthened with steel fibers under concentric axial loading. Construct Build Mater 2018, 175: 422-433. [11] Jang S J, Jeong G Y, Yun H D. Use of steel fibers as transverse reinforcement in diagonally reinforced coupling beams with normal- and high-strength concrete. Construct Build Mater 2018, 187: 1020-1030. [12] Pansuk W, Nguyen T N, Sato Y, Den Uijl J A, Walraven J C. Shear capacity of high performance fiber reinforced concrete I-beams. Construct Build Mater 2017, 157, 182-193. [13] Martinola G, Meda A, Plizzari G A, Rinaldi Z. Strengthening and repair of RC beams with fiber reinforced concrete”. Cem Concr Compos 2010, 32: 731-739. [14] Chang-Geun Cho, Byung-Chan Han, Seung-Chan Lim, Noharu Morii, Jae-Whan Kim, Strengthening of reinforced concrete columns by High-Performance Fiber-Reinforced Cementitious Composite (HPFRC) sprayed mortar with strengthening bars, Compos Struct 2018, 202: 1078-1086. [15] Muhammad Irfan Khan, Mohammed Ali Al-Osta, Shamsad Ahmad, Muhammad Kalimur Rahman, Seismic behavior of beam-column joints strengthened with ultra-high performance fiber reinforced concrete, Compos Struct 2018, 200: 103-119. [16] Javier Pereiro-Barceló, José L. Bonet, Beatriz Cabañero-Escudero, Begoña MartínezJaén, Cyclic behavior of hybrid RC columns using High-Performance Fiber-Reinforced Concrete and Ni-Ti SMA bars in critical regions, Compos Struct 2019, 212: 207-219. [17] G. Metelli, E. Marchina, G. A. Plizzari, Experimental study on staggered lapped bars in fiber reinforced concrete beams, Compos Struct 2017, 179: 655-664. [18] Di Carlo F, Meda A, Rinaldi Z. Numerical cyclic behaviour of un-corroded and corroded RC columns reinforced with HPFRC jacket. Compos Struct 2017, 163: 432-443. [19] Cho C G, Kim Y Y, Feo L, Hui D. Cyclic responses of reinforced concrete composite columns strengthened in the plastic hinge region by HPFRC mortar. Compos Struct 2012, 94: 2246-2253.

[20] Martinello Carlesso D, de la Fuente A, Pialarissi Cavalaro S H. Fatigue of cracked high performance fiber reinforced concrete subjected to bending. Construct Build Mater 2019, 220: 444-455. [21] Foglar M, Hajek R, Fladr J, Pachman J, Stoller J. Full-scale experimental testing of the blast resistance of HPFRC and UHPFRC bridge decks. Construct Build Mater 2017, 145: 588601. [22] Tufekci M M, Gokce A. Development of heavyweight high performance fiber reinforced cementitious composites (HPFRCC) – Part II: X-ray and gamma radiation shielding properties. Construct Build Mater 2018, 163: 326-336. [23] Tiberti G, Minelli F, Plizzari G A, Vecchio F J. Influence of concrete strength on crack development in SFRC members. Cem Concr Compos 2014, 45: 176-185. [24] Xu L, Wu F, Chi Y, Cheng P, Zeng Y, Chen Q. Effects of coarse aggregate and steel fibre contents on mechanical properties of high performance concrete. Construct Build Mater 2019, 206: 97-110. [25] Benaicha M, Jalbaud O, Alaoui A H, Burtschell Y. Correlation between the mechanical behavior and the ultrasonic velocity of fiber-reinforced concrete. Construct Build Mater 2015, 101: 702-709. [26] Kim J, Kwon M, Seo H, Lim J. Experimental study of torsional strength of RC beams constructed with HPFRC composite mortar. Construct Build Mater 2015, 91: 9-16. [27] Caggiano A, Folino P, Lima C, Martinelli E, Pepe M. On the mechanical response of Hybrid Fiber Reinforced Concrete with Recycled and Industrial Steel Fibers. Construct Build Mater 2017, 147: 286–295. [28] Caggiano A, Gambardelli S, Martinelli E, Nisticò N, Pepe M. Experimental characterization of the post-cracking response in Hybrid Steel/Polypropylene Fiber-Reinforced Concrete. Construct Build Mater 2016, 125: 1035–1043. [29] Babanajad S K, Farnam Y, Shekarchi M. Failure criteria and triaxial behaviour of HPFRC containing high reactivity metakaolin and silica fume. Construct Build Mater 2012, 29: 215229. [30] Li Q, Ansari F. High-strength concrete in triaxial compression by different sizes of specimens. ACI Mater J 2000, 97: 684–9. [31] Caratelli A, Imperatore S, Meda A, Rinaldi Z. Punching shear behavior of light weight fiber reinforced concrete slabs. Compos Part B 2016, 99: 257–65. [32] Choi Won-Chang, Jang Seok-Joon, Yun Hyun-Do. Bond and cracking behavior of lapspliced reinforcing bars embedded in hybrid fiber reinforced strain-hardening cementitious composite (SHCC). Compos Part B 2017, 108: 35–44.

[33] Gesoglu M, GÃüneyisi E, Muhyaddin GF, Asaad DS. Strain hardening ultra-high performance fiber reinforced cementitious composites: effect of fiber type and concentration. Compos Part B 2016, 103: 74–83. [34] Hannawi K, Bian H, Prince-Agbodjan W, Raghavan B. Effect of different types of fibers on the microstructure and the mechanical behavior of Ultra-High Performance FiberReinforced Concretes. Compos Part B 2016, 86: 215–20. [35] Jiang L, Niu D T, Bai M. Experiment study on the frost resistance of steel fiber reinforced concrete. Adv Mater Res 2010, 243:150–1. [36] Savino V, Lanzoni L, Tarantino AM, Viviani M. An extended model to predict the compressive, tensile and flexural strengths of HPFRCs and UHPFRCs: Definition and experimental validation. Compos Part B 2019, 163: 681-689. [37] Savino V, Lanzoni L, Tarantino AM, Viviani M. Simple and effective models to predict the compressive and tensile strength of HPFRC as the steel fiber content and type changes. Compos Part B 2018, 137: 153-162. [38] UNI 7087-2017 Concrete – Determination of the resistance to the degrade due to freezethaw cycles, 2017. [39] ASTM C215, Standard Test Method for Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of Concrete Specimens, 2002. [40] UNI 11039–1. Steel fibre reinforced concrete definitions, classification and designation, 2003. [41] UNI 11039–2. Steel fibre reinforced concrete – test method for determination of first crack strength and ductility indexes, 2003. [42] Kerakoll S.p.A. – web site: . [43] Bekaert S.p.A. – web site: . [44] UNI EN 12390-4. Testing hardened concrete. Part 4: Compressive strength - Specification for testing machines, 2000.

An experimental investigation on Freezing and Thawing Durability of High Performance Fiber Reinforced Concrete (HPFRC) L. Feo (1), F. Ascione (2), R. Penna (3,*) , D. Lau (4), M. Lamberti (5) Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Civil Engineering, University of Salerno, Italy, [email protected] (9) Department of Architecture and Civil Engineering, City University of Hong Kong, Hong Kong, China, [email protected] (10) College of Environmental Science and Engineering, Nankai University, Tianjin, China, [email protected] (*) Corresponding author: [email protected] (6) (7) (8)

Commented [D2]: I have removed Kowloon in my affiliation.

LIST OF FIGURES Figure 1. Steel fibers (type Dramix® OL 13/.20). Figure 2. Freeze/thaw testing machine. Figure 3. Schematization of a freeze-thaw cycle. Figure 4. Corrosion of steel fibers in the concrete mixture of a CM2 specimen. Figure 5. Apparatus for Impact Resonance Test (ASTM C215-02: a) Schematic Apparatus (ASTM C215-02); b) Photo of the apparatus. Figure 6. Location of impactor and accelerometer in the Transverse Mode. Figure 7. Location of impactor and accelerometer in the Longitudinal Mode. Figure 8. Location of impactor and accelerometer in the Torsional Mode. Figure 9. Experimental set-up of the four-point bending test. Figure 10. CTODm - vertical load for each specimen of CM0 concrete mixture. Figure 11. CTODm - vertical load (CM0). Figure 12 CTODm - vertical load for each specimen of CM1 concrete mixture. Figure 13. CTODm - vertical load (CM1). Figure 14. CTODm - vertical load for each specimen of CM2 concrete mixture. Figure 15. CTODm - vertical load (CM2). Figure 16. CTODm - vertical load (NFT and FT).

Figure 1. Steel fibers (type Dramix® OL 13/.20).

Figure 2. Freeze/thaw testing machine.

Figure 3. Schematization of a freeze-thaw cycle.

(a) Conditioned specimen.

(b) Corrosion of steel fibers in the concrete mix.

(c) Bridging action of fibers embedded in the concrete. Figure 4a-c. Corrosion of steel fibers in the concrete mixture of a CM2 specimen.

a) b) Figure 5a,b. Apparatus for Impact Resonance Test (ASTM C215-02: a) Schematic Apparatus (ASTM C215-02); b) Photo of the apparatus.

Figure 6. Location of impactor and accelerometer in the Transverse Mode.

Figure 7. Location of impactor and accelerometer in the Longitudinal Mode.

Figure 8. Location of impactor and accelerometer in the Torsional Mode.

Figure 9. Experimental set-up of the four-point bending test.

a)

b)

c)

d)

e)

f)

g) Figure 10a-g. CTODm - vertical load for each specimen of CM0 concrete mixture.

Figure 11. CTODm - vertical load (CM0).

a)

b)

c)

d)

e) Figure 12a-e. CTODm - vertical load for each specimen of CM1 concrete mixture.

Figure 13. CTODm - vertical load (CM1).

a)

b)

c)

d)

e)

f) Figure 14a-f. CTODm - vertical load for each specimen of CM2 concrete mixture.

Figure 15. CTODm - vertical load (CM2).

a)

b) Figure 16a,b. CTODm - vertical load (NFT and FT).

An experimental investigation on Freezing and Thawing Durability of High Performance Fiber Reinforced Concrete (HPFRC) L. Feo (1), F. Ascione (2), R. Penna (3,*) , D. Lau (4), M. Lamberti (5) (11) (12) (13) (14) (15)

Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Civil Engineering, University of Salerno, Italy, [email protected] Department of Architecture and Civil Engineering, City University of Hong Kong, Hong Kong, China, [email protected] College of Environmental Science and Engineering, Nankai University, Tianjin, China, [email protected]

Commented [D3]: I have removed Kowloon in my affiliation.

(*) Corresponding

author: [email protected] LIST OF TABLES

Table 1a. Geolite® Magma. Table 1b. Dramix OL 13/.20. Table 2. Concrete Mixture. Table 3. Prismatic specimens (PS): measurements. Table 4. Cubic specimens (CS): measurements and compressive strength. Table 5. Frequencies and elastic moduli before freeze-thaw cycles. Table 6. Fundamental transverse, longitudinal and torsional frequencies at 25th, 50th and 75th cycles. Table 7. Elastic moduli: transversal, longitudinal and torsional at 25th, 50th and 75th cycles. Table 8. Freeze-Thaw durability factor evaluated at 25th, 50th and 75th cycles. Table 9. Crack-tip opening displacement (CTOD0) and the corresponding load Pmax Table 10. Post-cracking toughness and representative parameters (CM1). Table 11. Post-cracking toughness and representative parameters (CM2). Table 12. Comparison between the average values of the first crack strength and the equivalent post-cracking strengths before and after the freeze-thaw cycles.

Commented [D4]: Why do we highlight the last two columns in red? I cannot find the explanation in the main text.

Table 1a. Geolite® Magma. Components [-] Dry Mixture Water

Density [daN/m3] 2200 290

Table 1b. Dramix OL 13/.20. Type

l [mm]

de [mm]

l/de [-]

Density [daN/m3]

Weight [daN]

Tensile strength [MPa]

13.0

0.2

65

7850

3.18 x 10-6

2600

Table 2. Concrete Mixture. Concrete mixture identification

Steel fibers dosage, V f

Concrete type

CM0 CM1 CM2

0.0 % 1.25 % 2.50 %

HPC HPFRC HPFRC

Table 3. Prismatic specimens (PS): measurements. Sample PS1_CM0_NFT* PS2_ CM0_NFT PS3_ CM0_NFT PS4_ CM0_FT** PS5_ CM0_FT PS6_ CM0_FT PS7_ CM0_FT PS8_ CM0_FT PS1_ CM1_NFT PS2_ CM1_NFT PS3_ CM1_NFT PS4_ CM1_FT PS5_ CM1_FT PS6_ CM1_FT PS7_ CM1_FT PS8_ CM1_FT PS1_ CM2_NFT PS2_ CM2_NFT PS3_ CM2_FT PS4_ CM2_NFT PS5_ CM2_FT PS6_ CM2_FT PS7_ CM2_FT PS8_ CM2_FT

width w [mm] 150.90 150.35 150.19 150.66 150.60 150.50 150.31 151.07 150.47 151.25 150.35 151.48 150.40 150.36 150.19 151.02 149.17 150.13 150.32 150.46 150.40 150.70 150.07 150.55

length l [mm] 603.00 603.00 603.00 602.00 602.00 602.50 602.00 603.00 603.00 603.00 600.50 603.00 603.00 602.50 602.50 603.00 603.00 605.00 604.00 604.00 602.00 605.00 605.00 603.00

height h [mm] 140.66 146.86 148.98 148.31 145.59 145.29 149.03 148.46 142.60 146.56 147.44 149.82 147.34 145.01 147.41 149.56 147.95 150.42 144.71 142.78 149.86 147.80 144.24 150.62

weight m [daN] 28.54 29.36 29.96 29.71 29.38 29.15 30.00 29.83 29.86 30.82 30.81 30.88 30.76 30.33 30.81 31.29 31.47 31.77 31.18 30.74 32.33 31.67 30.91 32.43

* reference specimen (not subjected to freeze-thaw cycles), NFT; ** specimen subjected to freeze-thaw cycles, FT

Table 4. Cubic specimens (CS): measurements and compressive strength. Sample CS1_CM0 CS2_CM0 CS3_CM0 CS4_CM0 CS5_CM0 CS1_CM1 CS2_CM1 CS3_CM1 CS4_CM1 CS5_CM1 CS1_CM2 CS2_CM2 CS3_CM2 CS4_CM2 CS5_CM2

width w [mm] 147.50 150.00 150.00 149.00 149.00 147.00 149.00 150.00 150.00 150.00 150.00 150.00 149.00 150.00 149.00

length l [mm] 150.00 143.00 149.00 148.00 149.00 149.00 145.00 148.00 149.00 149.00 147.00 149.00 149.00 150.20 149.00

height h [mm] 149.50 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00 150.00

Fu

fc

fc,avg

[kN] 1519.28 1487.10 1403.11 1228.16 1424.26 1847.49 1859.28 1841.00 1840.00 2052.14 1996.33 1959.03 1993.30 2111.30 2050.33

[MPa] 68.67 69.33 62.78 55.69 64.15 84.35 86.06 82.93 82.33 91.82 90.54 87.65 89.78 93.71 92.35

[MPa]

64.12

85.50

90.81

Table 5. Frequencies and elastic moduli before freeze-thaw cycles. Sample

f0

'

f0

''

f0

D

ETra,0

D

E Lon ,0

D GTor ,0

[kHz] [kHz] [kHz] [MPa] [MPa] [MPa] PS1_CM0_NFT* 1.417 3.308 1.912 39077.72 35497.70 14021.38 PS2_CM0_NFT 1.421 3.297 1.910 35667.22 34856.70 13841.65 PS3_CM0_NFT 1.417 3.285 1.908 34689.75 34853.01 13914.34 PS4_CM0_FT** 1.418 3.298 1.915 34615.88 34831.34 13890.04 1.422 3.293 1.913 36408.34 34997.18 13974.22 PS5_CM0_FT 1.421 3.272 1.898 36426.52 34389.91 13696.91 PS6_CM0_FT 1.417 3.305 1.917 34496.56 35225.65 14015.03 PS7_CM0_FT 1.421 3.282 1.908 34908.78 34547.95 13820.59 PS8_CM0_FT PS1_CM1_NFT 1.417 3.293 1.887 39346.48 36390.89 14144.22 PS2_CM1_NFT 1.418 3.247 1.900 37252.42 35349.56 14321.90 PS3_CM1_NFT 1.422 3.225 1.875 36544.42 34721.28 13884.29 1.421 3.245 1.880 35049.15 34558.05 13722.09 PS4_CM1_FT 1.415 3.317 1.920 36675.01 36828.92 14600.66 PS5_CM1_FT 1.417 3.299 1.904 37943.80 36494.01 14377.65 PS6_CM1_FT 1.410 3.322 1.920 36369.14 37004.36 14626.08 PS7_CM1_FT 1.421 3.303 1.910 35814.37 36463.39 14439.71 PS8_CM1_FT PS1_CM2_NFT 1.377 3.207 1.863 35356.78 35367.53 14127.42 PS2_CM2_NFT 1.373 3.200 1.863 33919.02 34864.12 13984.43 1.327 3.203 1.850 34670.62 35536.25 14021.54 PS3_CM2_FT PS4_CM2_NFT 1.320 3.190 1.853 35195.99 35179.83 14047.67 1.407 3.280 1.890 36013.47 37161.70 14596.75 PS5_CM2_FT 1.387 3.227 1.870 36195.60 35824.80 14234.54 PS6_CM2_FT 1.340 3.210 1.860 35644.06 35608.57 14143.44 PS7_CM2_FT 1.423 3.250 1.883 36571.84 36436.54 14474.70 PS8_CM2_FT * reference specimen (not subjected to freeze-thaw cycles), NFT; ** specimen subjected to freeze-thaw cycles, FT

Table 6. Fundamental transverse, longitudinal and torsional frequencies at 25th, 50th and 75th cycles. Sample

f25

f 25

f 25

f50

f50

f50

f75

f75

f75

PS1_CM0_NFT PS2_CM0_NFT PS3_CM0_NFT PS4_CM0_FT PS5_CM0_FT PS6_CM0_FT PS7_CM0_FT PS8_CM0_FT PS1_CM1_NFT PS2_CM1_NFT PS3_CM1_NFT PS4_CM1_FT PS5_CM1_FT PS6_CM1_FT PS7_CM1_FT PS8_CM1_FT PS1_CM2_NFT PS2_CM2_NFT PS3_CM2_FT PS4_CM2_NFT PS5_CM2_FT PS6_CM2_FT PS7_CM2_FT PS8_CM2_FT

[kHz] 1.417 1.421 1.417 1.393 1.395 1.397 1.395 1.390 1.417 1.418 1.422 1.399 1.403 1.393 1.395 1.390 1.377 1.373 1.310 1.320 1.400 1.383 1.340 1.400

[kHz] 3.310 3.303 3.303 3.300 3.267 3.260 3.270 3.260 3.300 3.290 3.310 3.243 3.317 3.290 3.283 3.267 3.207 3.200 3.207 3.190 3.280 3.227 3.210 3.250

[kHz] 1.920 1.910 1.910 1.917 1.900 1.900 1.897 1.900 1.900 1.920 1.910 1.880 1.920 1.883 1.900 1.887 1.863 1.863 1.850 1.853 1.890 1.870 1.860 1.883

[kHz] 1.417 1.421 1.417 1.380 1.390 1.380 1.373 1.403 1.417 1.418 1.422 1.387 1.403 1.390 1.395 1.413 1.377 1.373 1.333 1.320 1.400 1.390 1.350 1.410

[kHz] 3.310 3.303 3.303 3.230 3.280 3.260 3.193 3.263 3.300 3.290 3.310 3.250 3.297 3.290 3.310 3.270 3.207 3.200 3.207 3.190 3.290 3.240 3.227 3.260

[kHz] 1.920 1.910 1.910 1.413 1.467 1.440 1.357 1.457 1.900 1.920 1.910 1.427 1.443 1.443 1.463 1.423 1.863 1.863 1.860 1.853 1.890 1.890 1.873 1.890

[kHz] 1.417 1.421 1.417 1.350 1.340 1.303 1.340 1.340 1.417 1.418 1.422 1.370 1.400 1.367 1.380 1.387 1.377 1.373 1.333 1.320 1.400 1.390 1.350 1.410

[kHz] 3.310 3.303 3.303 3.227 3.233 3.193 3.227 3.223 3.300 3.290 3.310 3.273 3.303 3.313 3.310 3.297 3.207 3.200 3.207 3.190 3.290 3.240 3.227 3.260

[kHz] 1.920 1.910 1.910 1.330 1.423 1.390 1.387 1.420 1.900 1.920 1.910 1.450 1.467 1.467 1.460 1.450 1.863 1.863 1.860 1.853 1.890 1.890 1.873 1.890

'

''

'

''

'

''

Table 7. Elastic moduli: transversal, longitudinal and torsional at 25th, 50th and 75th cycles. D

Sample

ETra ,25

D

ELon,25

D GTor ,25

D

D

ELon,50

ETra ,50

D GTor ,50

D

ETra ,75

D

ELon,75

D GTor ,75

[MPa]

[MPa]

[MPa]

[MPa]

[MPa]

[MPa]

[MPa]

[MPa]

[MPa]

PS1_CM0_NFT PS2_CM0_NFT PS3_CM0_NFT PS4_CM0_FT PS5_CM0_FT PS6_CM0_FT PS7_CM0_FT PS8_CM0_FT

39255.34 35768.01 35158.03 33971.73 35198.39 35377.50 33958.29 33865.93

35647.63 35025.07 35450.84 35065.14 34495.69 34242.15 34644.10 34322.31

14189.33 13852.42 14020.81 13993.48 13805.34 13759.98 13787.98 13792.19

39255.34 35768.01 35158.03 33268.58 34915.63 34467.11 32841.07 34507.18

35647.63 35025.07 35450.84 33536.77 34730.51 34171.66 32983.58 34381.00

14189.33 13852.42 14020.81 7596.09 8215.07 7887.52 7042.72 8104.03

39255.34 35768.01 35158.03 31837.85 32448.89 30743.81 31266.19 31462.80

35647.63 35025.07 35450.84 33467.58 33749.28 32788.34 33675.77 33543.33

14189.33 13852.42 14020.81 6726.73 7736.80 7349.29 7357.64 7701.18

PS1_CM1_NFT PS2_ CM1_NFT PS3_CM1_NFT PS4_ CM1_FT PS5_CM1_FT PS6_CM1_FT PS7_ CM1_FT PS8_ CM1_FT

37386.71 37956.74 37225.93 35513.67 36467.33 36404.42 36050.95 35059.49

35927.96 36588.14 36835.94 35088.37 36973.44 36353.12 36322.87 35977.18

14089.53 14741.30 14510.00 13946.99 14657.96 14092.53 14389.38 14265.29

37386.71 37956.74 37225.93 34906.89 36467.33 36206.56 36050.95 36234.84

35927.96 36588.14 36835.94 35232.76 36493.25 36329.15 36915.28 36039.12

14089.53 14741.30 14510.00 8031.74 8275.24 8271.45 8535.35 8166.37

37386.71 37956.74 37225.93 34072.83 36258.90 35001.19 35296.70 34880.39

35927.96 36588.14 36835.94 35740.49 36641.00 36846.28 36915.28 36629.31

14089.53 14741.30 14510.00 8296.61 8544.96 8541.04 8496.51 8396.40

PS1_CM2_NFT PS2_CM2_NFT PS3_CM2_FT PS4_CM2_NFT PS5_ CM2_FT PS6_ CM2_FT PS7_ CM2_FT PS8_ CM2_FT

35356.78 33919.02 33674.87 35195.99 35551.55 35896.68 35517.21 35273.49

35367.53 34864.12 35473.20 35179.83 37035.26 35700.37 35481.85 36324.19

14127.42 13984.43 13967.57 14047.67 14547.09 14185.10 14093.11 14430.07

35356.78 33919.02 34885.17 35195.99 35551.55 36243.51 36049.30 35779.20

35367.53 34864.12 35473.20 35179.83 37261.43 35996.02 35851.25 36548.07

14127.42 13984.43 14118.98 14047.67 14547.09 14490.15 14295.88 14532.41

35356.78 33919.02 34885.17 35195.99 35551.55 36243.51 36049.30 35779.20

35367.53 34864.12 35473.20 35179.83 37261.43 35996.02 35851.25 36548.07

14127.42 13984.43 14118.98 14047.67 14547.09 14490.15 14295.88 14532.41

Table 8. Freeze-Thaw durability factor evaluated at 25th, 50th and 75th cycles. s

Fd ,25

s

Sample

Fd ,50

Fd ,75

s

PS4_CM0_FT PS5_CM0_FT PS6_CM0_FT PS7_CM0_FT PS8_CM0_FT PS4_ CM1_FT PS5_CM1_FT PS6_CM1_FT PS7_ CM1_FT PS8_ CM1_FT PS3_CM2_FT PS5_CM2_FT PS6_CM2_FT PS7_CM2_FT PS8_CM2_FT

[%] 96.60 96.24 96.60 96.97 95.64 96.88 98.31 96.69 97.84 95.68 99.99 99.99 99.99 99.99 99.99

[%] 94.60 95.46 94.12 93.78 97.45 95.23 98.31 96.16 97.84 98.89 99.99 99.99 99.99 99.99 99.99

[%] 90.53 88.72 83.95 89.28 88.85 92.95 97.75 92.96 95.79 95.20 99.99 99.99 99.99 99.99 99.99

Table 9. Crack-tip opening displacement (CTOD0) and the corresponding load Pmax Sample

CTOD0

CTOD0,avg

Pmax

Pmax,avg

fmax

f max,avg

[mm]

[kN] 11.043 11.387 11.209 9.800 8.292 8.590 9.740

[kN]

[MPa]

[MPa]

PS1_CM0_NFT PS2_CM0_NFT PS3 CM0_NFT PS4_CM0_FT PS5_CM0_FT PS6_CM0_FT PS7_CM0_FT

[mm] 0.0719 0.0611 0.0522 0.0602 0.0765 0.0636 0.0515

0.0617

0.0629

11.213

9.105

3.003 3.097 3.049 2.665 2.255 2.336 2.649

3.050

2.477

Table 10. Post-cracking toughness and representative parameters (CM1). Sample

Plf

flf

U1

U2

feq(00.6)

feq(0.63)

[kN] 15.117 14.026 14.324 11.110 13.966

[MPa] 4.29 3.81 3.94 3.10 3.85

[kNmm] 14419.30 14100.00 14331.00 10529.80 12955.00

[kNmm] 71044.20 68068.00 68568.00 55612.70 62737.60

[MPa] 6.89 6.39 6.57 4.91 5.96

[MPa]

[-]

[-]

PS1_CM1_NFT PS2_CM1_NFT PS3_CM1_NFT PS6_CM1_FT PS7_CM1_FT

8.40 7.71 7.86 6.48 7.21

1.59 1.68 1.67 1.58 1.55

1.23 1.21 1.20 1.32 1.21

D0

D1

Table 11. Post-cracking toughness and representative parameters (CM2). Sample

Plf

flf

U1

U2

feq(00.6)

feq(0.63)

D0

D1

[MPa] 4.76 5.06 5.10 4.30 4.00 4.68

[kNmm] 20550.20 20033.20 20942.00 17509.60 16731.90 16446.00

[kNmm] 104844.10 103169.10 100620.60 89234.60 76749.40

[MPa] 9.17 8.94 9.34 7.81 7.46 7.34

[MPa]

[-]

[-]

PS1_CM2_NFT PS2_CM2_NFT PS4_CM2_NFT PS3_CM2_FT PS6_CM2_FT PS8_CM2_FT

[kN] 17.795 18.926 19.065 16.089 14.958 17.478

11.69 11.51 11.22 9.95 8.56

1.92 1.76 1.83 1.81 1.86 1.57

1.28 1.29 1.20 1.33 1.17

Commented [D5]: Why do we highlight the last two columns in red? I cannot find the explanation in the main text.

Table 12. Comparison between the average values of the first crack strength and the equivalent post-cracking strengths before and after the freeze-thaw cycles. Mix.

flf ,avg

NFT

flf ,avg

FT

NFT

FT

NFT

FT

%

feq (0  0.6),avg

feq (0  0.6),avg

%

feq (0.6 3),avg

feq (0.6 3),avg

%

[MPa]

[MPa]

-

[MPa]

[MPa]

-

[MPa]

[MPa]

-

CM0

3.050

2.477

-23.1

-

-

-

-

-

-

CM1

4,013

3,475

-15.5

6,617

5,435

-21.7

7,990

6,845

-16.7

CM2

5,060

4,327

-16.9

9,150

7,537

-21.4

11,473

9,255

-23.9

Commented [D6]: After knowing the effect of freeze-thaw cycles, how can the public be benefited? A paragraph to wrap up is suggested to be added so that we can emphasize the research significance of this paper.