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Article

Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder

by
Kazim Turk
1,
Ceren Kina
2 and
Moncef L. Nehdi
3,*
1
Department of Civil Engineering, Engineering Faculty, Inonu University, 44280 Malatya, Türkiye
2
Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Malatya Turgut Ozal University, 44210 Malatya, Türkiye
3
Department of Civil Engineering, McMaster University, Hamilton, ON L8S 4L8, Canada
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(16), 10388; https://doi.org/10.3390/su141610388
Submission received: 17 July 2022 / Revised: 12 August 2022 / Accepted: 17 August 2022 / Published: 20 August 2022
(This article belongs to the Special Issue Innovations in Durability of Sustainable Concrete Materials)
Browse Figures
Review Reports Versions Notes

Abstract

:
This study investigates the effects of using limestone powder (LSP) and high-volume fly ash (FA) as partial replacement for silica sand (SS) and portland cement (PC), respectively, on the durability properties of sustainable engineered cementitious composites (ECC). The mixture design of ECC included FA/PC ratio of 1.2, 2.2 and 3.2, while LSP was used at 0%, 50% and 100% of SS by mass for each FA/PC ratio. Freeze-thaw and rapid chloride ions penetrability (RCPT) tests were performed to assess the durability properties of ECC, while the compressive and flexural strength tests were carried out to appraise the mechanical properties. Moreover, mercury intrusion porosimetry (MIP) tests were performed to characterize the pore structure of ECC and to associate porosity with the relative dynamic modulus of elasticity, RCPT and mechanical strengths. It was found that using FA/PC ratio of more than 1.2 worsened both the mechanical and durability properties of ECC. Replacement of LSP for SS enhanced both mechanical strengths and durability characteristics of ECC, owing to refined pore size distribution caused by the microfiller effect. It can be further inferred from MIP test results that the total porosity had a vital effect on the resistance to freezing–thawing cycles and chloride ions penetration in sustainable ECC.

1. Introduction

Engineered cementitious composites (ECC) are a special class of fiber-reinforced high-performance cementitious composite with properties tailored as per fundamental principles of micromechanics and fracture mechanics [1]. ECCs exhibit excellent strain hardening behavior and ultimate tensile strain capacity that can attain several hundred times that of traditional concrete [2]. Most ECC mixtures reported in the open literature incorporate short randomly distributed polyvinyl alcohol (PVA) fibers, which ensure superior tensile strain hardening behavior under increasing tensile loading through formation of multiple cracks. The interfacial interactions between the cementitious matrix and PVA fibers have an important role in this tensile strain hardening behavior [3]. Generally, the crack width is controlled below 60 µm and the strain capacity can reach up to 8% at the peak strength [4,5]. Considering such increased ductility, narrow crack widths, as well as excellent tensile properties, ECC can overcome many durability problems in structures exposed to harsh environments [6,7,8].
Durability is a crucial parameter, which affects the service life performance of concrete structures. It is directly linked to the crack width that governs the permeability of concrete. To enhance the water-tightness and durability, the cementitious matrix needs to be densified and the crack width needs to be minimized. ECC is further endowed with self-healing ability of its micro-cracks, thus further mitigating transport mechanisms. Moreover, the crack bridging benefit of fibers in ECC [9] provides enhanced durability performance, including reduced permeability, and better resistance to freezing–thawing cycles, carbonization, chloride ions penetrability, sulfate attack and other degradation mechanisms [10,11,12] compared to that of ordinary concrete.
The production of ECC mixtures is facilitated via the incorporation of supplementary cementitious materials, such as fly ash (FA), silica fume and metakaolin as partial replacements for cement. Usually, the use of these mineral admixtures in concrete decreases and refines the permeable voids through the microfiller effect, pozzolanic reaction and densification of the cement paste-aggregate interfacial zone. This results in enhanced resistance to damage mechanisms such as chloride-ions or carbonation induced corrosion, damage by freezing–thawing cycles, sulfate attack, alkali-aggregate reactions, leaching etc., thus yielding overall superior durability properties of concrete [13,14,15,16]. FA has been the most widely used mineral admixture in typical ECC mixtures owing to its favorable properties including improved workability, mechanical strength and durability [17,18,19,20,21]. It was reported in the study of Yang et al. [22] that the reduction in the crack width of ECC incorporating FA was due to restricting the slippage of fibers through the effect of high interfacial frictional bond.
The inclusion of limestone powder (LSP) in cementitious systems is desirable considering its relatively low cost and reduction of CO2 emissions from cement production while maintaining adequate mechanical and durability properties. Turk and Demirhan [23] investigated the effect of using LSP instead of quartz sand on the permeability of ECC mixtures. They found that the carbonation resistance was improved via LSP addition. Likewise, Lecomte et al. [24] concluded that LSP fillers increased the sorptivity while porosity characteristics changed according to the grinding quality of LSP. Some researchers [25,26,27] found that an increase in the replacement rate of LSP for cement increased the carbonation depth in concrete.
In the production of ECC, special gradation silica sand (SS), which is relatively costly and difficult to source compared to other conventional sands, is used as aggregate in ECC in general. A novel aspect in this study is the use of LSP as aggregate owing to its low cost and advantageous properties. While there is significant work on the use of LSP in conventional concrete, there is currently a dearth of studies in the available literature on the effects of LSP on the mechanical and durability properties of ECC. The limited existing experimental works explored the inclusion of mineral admixtures, including FA, SF or slag in ECC. Within this scope, the goal of this study is to use LSP as aggregate with FA as binder for the partial replacement of SS and PC, respectively, to develop more sustainable ECC, which can help widespread usage of this promising material using local materials. Hence, in the present study, dedicated experimental research was designed to investigate the effects of using both LSP and high-volume of FA on the durability properties of ECC, as can be observed in Figure 1. LSP was used as aggregate at 0%, 50% and 100% mass replacement for silica sand to study the effectiveness of LSP as replacement for SS, while FA was used as a binder partial replacement for cement at FA/PC ratio of 1.2, 2.2 and 3.2. Additionally, in this study, to reveal the effects of using high-volume FA content, FA/PC ratios of 2.2 and 3.2 were selected in the design of ECC mixtures, while the FA/PC ratio used is 1.2 for standard ECC. To assess the durability properties of the sustainable ECC mixtures thus developed, mercury intrusion porosimetry (MIP), resistance to freezing–thawing (F-T) cycles, and rapid chloride ions penetrability (RCPT) tests were performed. Moreover, compressive and flexural strength tests were carried out to assess mechanical properties. The consistency between the mechanical and durability test results of ECC specimens was discussed. Given the importance of the pore size distribution and porosity for durability and mechanical properties, the correlation between MIP and mechanical/durability properties was examined.

2. Experimental Program

2.1. Materials

The binders used in the manufacturing of ECC mixtures included Type I ordinary portland cement (PC) and Class-C fly ash (FA) conforming to guidelines of ASTM C150 [28] and ASTM C618 [29], respectively. Table 1 shows the physical and chemical properties of the binders. Silica sand (SS) with a maximum particle size of 1.18 mm and limestone powder (LSP) with an average particle size of 425 µm were used as aggregate. The specific gravity of LSP and SS were 2.65 and 2.70, respectively, and their particle size distribution is depicted in Figure 2. To meet the strain-hardening performance requirements for ECC, PVA fibers with the properties presented in Table 2 were used. In order to improve the interfacial bond between the cementitious matrix and PVA fibers, a proprietary hydrophobic oiling matter was used to coat the surface of PVA fibers during the manufacturing process [30]. A high-range-water-reducing admixture (HRWR) with a specific gravity of 1.06 was added into ECC mixtures to enhance the fresh properties.

2.2. Mixture Design and Sample Preparation

In this study, three reference ECC mixtures incorporating SS and with a FA/PC ratio of 1.2, 2.2 and 3.2 were made as given in Table 3. In total, nine ECC mixtures were designed considering 0%, 50% and 100% LSP mass replacement for SS, whilst the FA/PC ratio was varied at 1.2, 2.2 and 3.2. All the mixtures had a water-to-cementitious materials ratio of 0.26, identical total mass of cementitious materials and identical PVA fiber dosage (2% by volume). To mitigate workability as a source of variability, the slump flow of sustainable fresh ECC mixtures was adjusted within the close range of 27–28 cm using a high-range water-reducing admixture (HRWR). All ingredients were kept constant, except the FA/PC ratio (1.2, 2.2, 3.2) and the content of SS and LSP.
A high-shear mixer with a twenty-liter capacity was used in the preparation of the ECC mixtures. The cementitious materials and sand were first dry mixed at 100 rpm for a minute. Then, water and HRWR were added, and mixed for additional 3 min at 300 rpm. Finally, PVA fibers were added, and mixing resumed for 3 min at 150 rpm. The specimens were cast via pouring the fresh mixtures into molds. Subsequently, the specimens were compacted using a vibrating table for 2 min. At 24 h after casting, all specimens were demolded and cured for 7 days in sealed plastic bags at 25 ± 2 °C to prevent moisture loss. Then, the specimens were stored in laboratory conditions at temperature of 25 ± 2 °C and relative humidity of 50 ± 5% until the testing age of 28 and 90 days. Similar curing process for ECC mixtures was adopted in previous studies [31,32,33]. Three replicate specimens were prepared for each designed mixtures and testing age.

2.3. Test Methods

2.3.1. Mechanical Properties

The mechanical properties of ECC mixtures were investigated in terms of compressive and flexural tensile strengths. For each test and curing age (28 and 90 days), three replicate specimens were tested for all designed mixtures and the average values were recorded as the experimental results. The compressive strength test was carried out using 50 × 50 × 50 mm3 cube specimens according to ASTM C39 [34]. Four-point bending test was performed to evaluate the flexural strength of ECC specimens with a cross section of 100 × 100 mm2 and a length of 380 mm as per the provisions of ASTM C78 [35]. The loading rate of the MTS testing machine with tri-axial cell testing capability was 0.003 mm/s. The mid-span deflection of ECC prisms was recorded via an LVDT placed at the middle of the span and the applied force was measured using a computerized data recording system.

2.3.2. Durability Properties

Mercury intrusion porosimetry (MIP) test was performed to characterize the pore size distribution of the sustainable ECC specimens. A Micrometrics AutoPore IV 9500 Series porosimeter capable of producing pressures up to 414 MPa was used for pore size distribution analysis based on the mercury intrusion method. The contact angle and assumed surface tension of mercury were 130° and 0.484 N/m (ASTM D4404 [36]), respectively. Cubic fragments with the size of 10 × 10 × 10 mm3 from all ECC specimens were first dried to constant weight at 50 °C and stored in a vacuum chamber prior to testing. The average of test results of three specimens was recorded as the MIP test result for each mixture.
The freezing and thawing (F-T) test was carried out and the pulse velocity test method was used to monitor the deterioration of specimens during F-T cycling; thus, the dynamic elastic modulus of ECC specimens was calculated at each interval of nominally 30 cycles of freezing and thawing. The resistance to F-T cycles of ECC specimens was assessed in accordance with ASTM C666 “Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing procedure (b)-rapid freezing in air and thawing in water” [37] using a freeze–thaw cabinet. The test was continued until 330 cycles. After each 30 cycles, the relative dynamic modulus of elasticity of ECC specimens was estimated as follows:
P i = f i 2 f 0 2 × 100
where f i and f 0 are the ultrasonic pulse velocity at ith cycle and before the start of freeze–thaw cycling, respectively.
The electrical conductivity of concrete was measured through the RCPT test, which is an indirect measure of chloride ions penetrability [38]. The resistance of concrete to chloride ions penetration is paramount for durability in chloride-laden environments and greatly depends on the pore structure characteristics. Cylindrical specimens with a diameter of 100 mm and thickness of 50 mm were tested as per the guidelines of ASTM C1202 [39] at the age of 28 curing days. The test specimens were put between parallel stainless steel plates, which provide electrical connection between the concrete and steel plates by conductive saturated sponges. The resistance was evaluated via the application of a known alternating current of about 250 μA across the specimen and acquiring the resulting voltage. The measured resistance was divided by the depth of the specimen and multiplied by its cross-sectional area to obtain the resistivity. The average values of three identical specimens were reported as test results for each mixture.

3. Results and Discussions

3.1. Compressive Strength and Flexural Tensile Strength

The compressive and flexural strengths of the sustainable ECC specimens incorporating FA as partial replacement for PC at ratios of 1.2, 2.2 and 3.2, and 0%, 50% and 100% LSP as aggregate instead of SS are shown in Figure 3. ECC specimens with FA/PC = 1.2 and 0%, 50% and 100% mass replacement of SS with LSP attained higher compressive and flexural strengths, while strength values were lowest when the FA/PC ratio was 3.2 (see Figure 3). It can be deduced that both the compressive and flexural strengths of ECC specimens decreased with the increase in FA/PC ratio, regardless of the LSP content. The lowest compressive strength was measured as 38.13 MPa for the ECC specimen FA3.2_LSP0.0 with a decrease of about 50.98% with regard to the corresponding value for specimen of FA1.2_LSP0.0. The ECC specimen of FA3.2_LSP0.5 had the lowest flexural strength of 6.75 MPa with a decrease of about 15.95% with regard to the corresponding value for specimen FA1.2_LSP0.0. This may be attributed to the reduction of the cement content resulting in less formation of hydration products and decreased availability of calcium hydroxide for the pozzolanic reaction of fly ash. Several studies (e.g., [40,41]) found that FA replacement for cement slowed down the hardening rate of specimens at the early hydration stage, but at later ages its contribution to mechanical strength may become more pronounced owing to the advancement of the pozzolanic reaction [42].
Using LSP substitution for SS as aggregate improved the compressive strength, except for ECC specimens made with FA/PC = 1.2. This may be ascribed to the filler effect of LSP considering its finer grain size distribution compared to that of SS. The enhancement in strength could also be related to the reduction in the total porosity caused by LSP acting as a microfiller, the formation of carbo-aluminates [43], and LSP providing preferential specific surface area for the nucleation and growth of hydration products [44]. The inclusion of 100% LSP instead of SS into ECC mixtures caused a slight increase in the flexural strength of ECC specimens with FA/PC = 2.2. Conversely, the content of LSP had no significant influence on the flexural strength of ECC specimens for all other FA/PC ratios likely because all ECC specimens included sufficient fine materials resulting in uniform distribution of PVA fibers.

3.2. Mercury Intrusion Porosimetry

The strength and durability of cementitious materials are generally related to microstructure features [45]. The evolution of the pore structure of ECC specimens was investigated via MIP testing in this study. Figure 4 shows the total porosity of ECC specimens with 1.2, 2.2 and 3.2 ratio of FA/PC and variable LSP mass replacement for SS at 0%, 50% and 100%. It can be observed that, regardless of the LSP content, an increase in the FA/PC ratio appears to be associated with increased porosity. For instance, the porosity of ECC specimens made with 3.2 ratio of FA/PC was 33.77% on average, while for the ECC specimens with 1.2 ratio of FA/PC, this value was 24.61% on average. This can be explained by the fact that the substitution of a higher amount of PC with FA diluted the cement, resulting in less formation of hydration products, which affected the compressive and tensile strength of the ECC specimens at 28 and 90 days (See Figure 3). Long et al. [41] also found that the increase in the content of FA/PC from 1.2 to 1.5 increased the porosity and negatively affected the microstructure. On the other hand, for ECC specimens with 1.2 and 3.2 ratio of FA/PC and 50% replacement of SS with LSP caused a reduction in porosity at a ratio of 0.51% and 4.27%, respectively, while 100% replacement of SS with LSP induced a 0.68% decrease in the porosity of ECC specimens made with FA/PC of 2.2%. Moreover, for FA/PC = 2.2, the replacement of LSP by SS in proportion of 100% by mass had an almost similar effect on the porosity compared to corresponding values for ECC specimens, including no LSP. The experimental results show that the replacement of SS with LSP can densify the internal pore structure and reduce the porosity of ECC, thus resulting in an enhancement in compressive strength, which conforms to the compressive strength test results performed in this study (see Figure 3).
Figure 5a,b illustrate the pore size distribution and pore volume fraction of ECC matrices, respectively. The pore structure can be grouped into three sizes: micropores (<2 nm), mesopores (2–50 nm) and the macropores (>50 nm) that cause a great effect on both strength and durability of concrete as per International Union of Pure and Applied Chemistry (IUPAC) [45]. The limitations of the MIP test allow the capture of a minimum pore size of 5.6 nm. Thus, in this study, the pore structure includes only mesopores and macropores. It can be observed in Figure 5a that the cumulative intrusion curves exhibited similar behavior at pore sizes below 0.8 µm. However, as the pore diameter decreased, the cumulative mercury intrusion volume for ECC specimens varied versus the FA/PC ratio. The cumulative mercury intrusion volume for the specimens with 3.2 ratio of FA/PC was highest. That is, FA2.2 and FA1.2 specimens had lower pore volume than that of FA3.2 specimens, regardless of the LSP content, and this is notable for the pore sizes below 0.8 µm. Moreover, the volume fraction of macro-pores of ECC specimens including 3.2 ratio of FA/PC was approximately 48.5%, on average, while it was 42.5% and 31.0% for ECC specimens, which have a FA/PC ratio of 2.2 and 1.2, respectively. It can be explained by the fact that the replacement of a higher amount of PC with FA led to coarsening the micro-pores of ECC matrix, which could be due to the formation of less hydration products due to insufficient dosage of PC. This detrimental effect also caused a reduction in the mechanical strength of specimens, which is consistent with the compressive strength test results at 28 and 90 days.
As illustrated in Figure 5b, for ECC specimens with a 1.2 ratio of FA/PC, 100% replacement of SS with LSP induced a positive effect on the formation of mesopores. It could be inferred that the substitution of SS with LSP caused a refinement of pore distribution of the ECC matrix owing to the filler effect and fineness of LSP, especially for FA/PC = 1.2. However, it was found that there was not a certain trend of the effect of LSP inclusion on the volume fraction and pore size of ECC specimens including FA/PC = 2.2 and 3.2. Even for FA/PC = 2.2 and 3.2, ECC specimens with only SS had similar pore structure and size compared to that of specimens with 50% and 100% LSP content. According to [46,47], the use of a proper amount of fine LSP did not only reduce the amount of large pores, but also led to the formation of a higher amount of small pores with a diameter smaller than 100 nm. Valcuende et al. [48] also found that the inclusion of LSP instead of normal aggregate to the cementitious matrix lowered the threshold pore diameter as well as the volume of large capillary pores.

3.3. Freezing–Thawing Resistance

The resistance of concrete to freezing–thawing (F-T) cycles is highly dependent on the internal pore distribution. Increasing the porosity generally compromises the resistance of concrete to F-T cycles [3]. As is known, the change in the value of relative dynamic modulus of elasticity (RDME) of concrete over the duration of F-T cycles gives prior knowledge about the strength. Hence, it can be informative in the assessment of the engineering properties of concrete [49]. Figure 6 depicts the RDME of ECC specimens with a 1.2, 2.2 and 3.2 ratio of FA/PC, as well as the replacement of SS with LSP in proportions of 0%, 50% and 100% by mass. It can be observed that the increase in FA/PC ratio caused a significant reduction in the F-T resistance of ECC, regardless of LSP content. That is, ECC specimens with a 1.2 ratio of FA/PC had the highest average RDEM values at 95.41%, followed by 88.88% and 82.38% for ECC specimens made with FA/PC of 2.2 and 3.2, respectively, after 330 F-T cycles. This can be explained by the fact that as FA content increased beyond a certain threshold, the matrix became more porous and mechanical strength decreased as discussed earlier (see Figure 3).
Referring to Figure 6, the RDEM of ECC specimens made with FA/PC = 1.2 remained almost the same during the F-T cycles. Since the RDEM is dependent on the internal compactness of matrix, the near linear trend of RDEM values of ECC specimens with FA/PC = 1.2 indicates that the addition of FA can densify the ECC matrix owing to its pozzolanic reaction with a sufficient amount of CH and resulting in maintaining the integrity after F-T cycles. Şahmaran et al. [50] also found that fly ash provided denser and more compact microstructure. On the other hand, the ECC specimens with a 2.2 ratio of FA/PC exhibited a slightly continuous downward trend, while those with FA/PC = 3.2 had a more apparent decreasing trend compared to that of ECC specimens with FA/PC = 1.2 ratio. Two reasons may be responsible for the reduction in RDEM when FA increased. First, the substitution of higher amount of PC with FA could result in fewer amount of calcium hydroxide to react with silica in FA. Second, from the aspect of pore size volume fraction, as it was found in the MIP test results (see Figure 6), the volume fraction of macro-pores of ECC specimens made with FA/PC = 3.2 was higher than that of the other ECC specimens, which could be detrimental in terms of F-T resistance, and this is consistent with previous study [51]. It was also concluded from this work that the F-T resistance of sample decreased when the pore size diameter increased from 40 nm to 2000 nm. On the other hand, it can be remarked that the RDEM values for ECC specimens with 2.2 and 3.2 ratio of FA/PC were high (88.88% and 82.38%, respectively) after 330 F-T cycles though they exhibited a downtrend. This may be attributed to the insufficient cement dosage and, thus, the filler effect of the unreacted FA particles.
As illustrated in Figure 6, for ECC specimens with a 3.2 ratio of FA/PC, the inclusion of LSP instead of SS into ECC mixtures increased the RDEM values. For instance, the RDEM of ECC specimens, which had a replacement of SS with LSP in proportions of 50% and 100% by mass were 83.17% and 83.79%, respectively, while it was 81.17% for the specimens with no LSP after 330 cycles. This can be explained by the fact that finer particles of LSP compared to SS and the associated filler effect could be more pronounced in the use of higher FA content in terms of inhibiting the interaction between the formed pores. On the other hand, for the ECC specimens having 1.2 and 2.2 ratio of FA/PC, there was no clear trend for the use of LSP, that is, RDEM of ECC specimens were comparable after 330 cycles, especially that in the microstructure of ECC specimens with 1.2 ratio of FA/PC, the pozzolanic reaction was dominant. However, the replacement of LSP with SS in the proportion of 100% by mass had positive influence on RDEM values of the specimens with 2.2 ratio of FA/PC until 120 F-T cycles.

3.4. Rapid Chloride Ion Penetrability

The RCPT test depends on the pore solution chemistry and pore structure characteristics of concrete. The presence of pores and cracks cause an aisle and, thus, the charge passed increases [38]. It was emphasized [52] that the chloride penetrability of specimens measured from RCPT was an important parameter to assess the quality of concrete. The migration of more chloride ions into the ECC specimens results in the passing more current through the specimens. An increase in the total charge passed shows that the ECC specimen is more penetrable. Figure 7 indicates the charge passed for ECC specimens with 1.2, 2.2 and 3.2 ratio of FA/PC, as well as the replacement of SS with LSP in proportions of 0%, 50% and 100% by mass. Based on ASTM C1202 [39], RCPT is categorized into five groups: high (>4000 coulombs), moderate (2000–4000 coulombs), low (1000–2000 coulombs), very low (100–1000 coulombs) and negligible (<100 coulombs). Referring to Figure 7, the chloride ion penetration of FA/PC = 1.2 specimens was the lowest, but the increase in FA/PC led to an increase in the charge passed, regardless of the LSP content. For instance, the ECC specimens with FA/PC = 1.2 achieved ‘low’ ion permeability rating, while it was ‘low’ to ‘moderate’ for the specimens with FA/PC = 2.2. However, the use of FA/PC = 3.2 caused higher value of total charge passed, yet the specimens remained below the ‘moderate’ permeability classification range except for ECC specimens with only SS. This may be explained by the fact that the inclusion of a higher amount of FA made ECC more porous, leading to the formation of more pore networks for charge to pass through. Therefore, the increased RCPT of ECC specimens with FA/PC = 3.2 could also be explained by having higher amounts of inert fly ash particles because of the replacement of PC with high ratio of FA and lack of CH for pozzolanic reaction. The highest RCPT test results obtained from the ECC specimens having 3.2 ratio of FA/PC may be attributed to slow initiation of the pozzolanic reactions because of the low CH content.
The curves in Figure 7 show that the replacement of LSP with SS caused a reduction in the chloride permeability of ECC specimens for all FA/PC ratios. The decrease in total charge passed was the highest for FA2.2_LSP1.0 with 54.86% followed by FA1.2_LSP1.0 with 37.88% compared to the ECC specimens with the same FA/PC content and no LSP. With the inclusion of LSP instead of SS into the mixtures, the ECC specimens with FA/PC = 2.2 and 3.2 were classified as ‘low’ and ‘moderate’ according to ASTM C1202, respectively. The lower charge passed through ECC specimens with LSP can be attributed to its filler effect and fineness compared to SS. Moreover, the calcium mono-carbo-aluminates formed by the addition of LSP can fill additional pores [53] and, thus, provide a denser matrix and past aggregate interfacial zone [54].

3.5. The Relationship between MIP and Mechanical/Durability Properties

As already mentioned, MIP is performed to determine the pore size distribution, porosity and average pore diameter of cementitious materials, which play an important role in their performance including strength and durability. Therefore, this study focused on developing a mathematical relation to calculate the compressive strength, flexural strength, chloride permeability and freeze–thaw resistance of ECC via the total porosity of ECC.
Observing Figure 8a, the exponential relationship between the compressive strength ( f c ) and porosity ( p ) yielded the equation: f c = 212.87 e − 0.049 p . The coefficient of determination value for this equation was estimated as 0.8824. On the other hand, the fitted second order equation for the flexural strength ( f f ) and porosity ( p ) was f f = 0.0155 p 2 − 1.048 p + 25.34 with an R2 value of 0.6515, which is a low value in terms of validity. Mohr et al. [55] and Armaghani et al. [56] also described the relationship between permeability and compressive strength of concrete by a power function.
As for the correlation between the total porosity and the durability properties of ECC (Figure 8b), there was a significant linear relationship between the RDEM and porosity of ECC in the form RDEM = − 1.1151 p + 120.37 and the R-squared value was 0.9116. It is worth noting that the effect of porosity on freeze–thaw resistance of ECC was prominent in this study. According to the correlation between RCPT and porosity of ECC, the fitted second order equation was found as RCPT = 23.636 p 2 − 983.84 p + 10740 with the R-squared value of 0.9747, which shows that the resistance of ECC to RCPT was strongly affected by the total porosity in its microstructure. Therefore, these empirical formulas showed that the total porosity was a parameter that had the closest relationship to RCPT. Finally, it can be emphasized that the correlation between the porosity and durability properties rendered better fitting results compared to those of the mechanical properties. Zhang and Li et al. [57] found a linear correlation between chloride permeability and pore structure of concretes with coefficient of determination of 0.93.

4. Conclusions

This work investigated the influences of high-volume FA along with LSP partial or total replacement for SS by weight on the durability properties of ECC. Within this scope, mercury intrusion porosimetry, rapid chloride ion penetrability and freezing–thawing tests were conducted. Moreover, the compressive and flexure strengths of ECC were assessed to appraise the hardened properties of ECC. The following conclusions can be listed according to the experimental results:
  • The compressive and flexural strengths of ECC specimens decreased with increase in FA/PC ratio, regardless of LSP content, while the addition of LSP as aggregate enhanced the compressive strength in general. As for flexural strength of ECC specimens, the use of LSP instead of SS caused slight improvement for ECC specimens with 2.2 ratio of FA/PC, whilst the full replacement of LSP for SS had no clear effect for all FA/PC ratios.
  • The MIP results showed that using higher ratio of FA/PC increased the total porosity of ECC specimens, resulting in higher volume fraction of macropores. On the other hand, in general, the partial replacement of LSP with SS caused a reduction in porosity and a refinement of pore distribution of ECC matrix. In particular, 100% replacement of LSP with SS for ECC specimens with FA/PC of 1.2 implied a positive influence on the formation of mesopores.
  • The freezing–thawing resistance of ECC specimens decreased when FA/PC ratio increased, whilst for ECC specimens with a 3.2 ratio of FA/PC the full replacement of LSP with SS caused an increase in RDEM of ECC. On the other hand, for 1.2 and 2.2 ratio of FA/PC, the ECC specimens with LSP exhibited almost the same resistance with the ECC specimens with 100% SS.
  • The charge passed increased as the ratio of FA/PC increased for ECC specimens, regardless of LSP content. However, the use of LSP induced a decrease in the chloride permeability of ECC specimens for all FA/PC ratios.
  • The correlation between the porosity and the test results was higher for freezing–thawing and chloride permeability tests with the R-square value of 0.9116 and 0.9747, respectively, compared to those of the compressive and flexure strengths.
  • According to the test results, the replacement of LSP with silica sand can be advised for the development of sustainable ECC due to causing an improvement in pore size distribution and cumulative porosity of matrices resulting in an increase in the freezing–thawing resistance and chloride permeability as well as strength.

Author Contributions

K.T.: conceptualization; formal analysis; investigation; writing—original draft. C.K.: data curation; formal analysis; methodology; writing—original draft. M.L.N.: project administration; resources; supervision; writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Scientific and Technological Research Council of Turkey, Grant Number: TUBITAK-BIDEB-2219 International Postdoctoral Research Scholarship Program (2012-2).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Schematic flow diagram of this study.
Figure 1. Schematic flow diagram of this study.
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Figure 2. Particle size distribution of LSP and SS.
Figure 2. Particle size distribution of LSP and SS.
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Figure 3. Compressive strength and flexural strength test results at 28 days for ECC specimens.
Figure 3. Compressive strength and flexural strength test results at 28 days for ECC specimens.
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Figure 4. Porosity of ECC specimens.
Figure 4. Porosity of ECC specimens.
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Figure 5. Pore structures in ECC matrix: (a) pore size distribution and (b) pore volume fraction.
Figure 5. Pore structures in ECC matrix: (a) pore size distribution and (b) pore volume fraction.
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Figure 6. Relative dynamic modulus of elasticity of ECC specimens after different freeze–thaw cycles.
Figure 6. Relative dynamic modulus of elasticity of ECC specimens after different freeze–thaw cycles.
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Figure 7. RCPT results of ECC specimens.
Figure 7. RCPT results of ECC specimens.
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Figure 8. Correlation between the total porosity and (a) mechanical, (b) durability properties of ECC.
Figure 8. Correlation between the total porosity and (a) mechanical, (b) durability properties of ECC.
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Table
Table 1. Chemical characteristics and physical properties of PC and FA.
Table 1. Chemical characteristics and physical properties of PC and FA.
Chemical Characteristics (Oxides and Phase)
CaO SiO2Al2O3Fe2O3MgO SO3K2O + 0.66 Na2OC3SC2SC3AC4AF
PC (%)61.519.64.83.333.50.75515710
FA (%)14.9241.7622.919.232.951.62.05----
Physical Properties
Loss of IgnitionInsoluble ResidueSiO2 + Al2O3 + Fe2O3Autoclave Expansion, %Specific gravitySurface area (m2/kg)Amount retained on 45 micron, %
PC (%)1.90.4427.70.093.153713
FA (%)0.8-73.902.4311519
Table
Table 2. Properties of PVA fiber.
Table 2. Properties of PVA fiber.
FiberLength (mm)Diameter (µm)Tensile Strength (MPa)Modulus of Elasticity (GPa)Density (kg/m3)Max. Elongation (%)Melting Temperature (°C)
PVA83616004013006.5225
Table
Table 3. Mixture proportions of ECC and mortar.
Table 3. Mixture proportions of ECC and mortar.
Mixture IDUnit Weight, (kg/m3)Slump-Flow (cm)
PCFAWaterSandHRWRPVA
SSLSP
FA1.2_LSP0.057068433243209.02627.1
FA1.2_LSP0.557068433221821810.12627.6
FA1.2_LSP1.0570684332044010.32627.5
FA2.2_LSP0.039286233140206.52627.0
FA2.2_LSP0.53928623312022027.22627.2
FA2.2_LSP1.039286233104087.32627.1
FA3.2_LSP0.029995532938606.52627.2
FA3.2_LSP0.52999553291941946.62627.9
FA3.2_LSP1.029995532903926.72627.7
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Turk, K.; Kina, C.; Nehdi, M.L. Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder. Sustainability 2022, 14, 10388. https://doi.org/10.3390/su141610388

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Turk K, Kina C, Nehdi ML. Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder. Sustainability. 2022; 14(16):10388. https://doi.org/10.3390/su141610388

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Turk, Kazim, Ceren Kina, and Moncef L. Nehdi. 2022. "Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder" Sustainability 14, no. 16: 10388. https://doi.org/10.3390/su141610388

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