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Article

Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber

by
Pochpagee Markpiban
* and
Raktipong Sahamitmongkol
*
Department of Civil Engineering, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand
*
Authors to whom correspondence should be addressed.
Buildings 2023, 13(10), 2514; https://doi.org/10.3390/buildings13102514
Submission received: 27 August 2023 / Revised: 25 September 2023 / Accepted: 27 September 2023 / Published: 4 October 2023
(This article belongs to the Section Building Materials, and Repair & Renovation)
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Abstract

:
Recycled tire steel fiber (RTSF) is added to mortar with pre-wetted bottom ash (BA) to enhance the mechanical properties of the mortar, in addition to providing an internal curing effect. This work investigated the mechanical properties of BA mortar, such as the compressive strength, splitting tensile strength, and flexural strength, including the heat of reactions and the total shrinkage, considering different contents of BA (i.e., 10%, 20%, and 30% replacements by volume of fine aggregate) and recycled steel fiber (RSF, i.e., 0.5% and 1.0% by volume). The results showed that BA reduced all mechanical properties; however, it increased the degree of hydration by raising the heat peak of hydration in the first 7 days, increasing the amount of calcium hydroxide at 28 days, and significantly refining the pore structure during the curing period. Regarding the effects of RTSF, the bridging effect positively affected the compressive strength, splitting tensile strength, and flexural strength of the mortar with 30% BA when 1% RTSF was added, increasing them by 25%, 46%, and 40%, respectively. Moreover, adding 1% RTSF reduced the total porosity of the mortar with 30% BA from 17.2% to 14.8%.

1. Introduction

Bottom ash (BA) is a municipal solid waste (MSW) from power plants that use coal to generate electricity. About 20% of non-combustion zone coal falls to the bottom of the furnace, where it sinters to become BA. In 2020, the World Bank reported that around 2.24 billion tons of MSW is generated worldwide and that this will increase to 3.88 billion tons by 2050, raising concerns regarding the environmental impact, especially in terms of the disposal area [1]. Recently, many countries, including the U.S., have attempted to use and develop MSW incineration to reduce the amount of MSW [2]. For example, in 2021, nearly 41%, or 3.6 million tons, of the remaining BA (around 8.7 million tons) was utilized in various applications, with a significant presence in the construction industry. The top three applications include structural fills, concrete grout, and blended cement. The incorporation of industrial waste into construction materials provides a solution for its disposal. The inclusion of waste materials in concrete mixtures has become increasingly essential in both modern research and the concrete industry. Therefore, the use of BA represents an alternative construction material that not only reduces building material costs but also decreases the carbon footprint. It is evident that focusing on environmentally friendly and sustainable construction materials is vital for both concrete production and the construction industry.
BA can potentially be used to provide an internal curing effect considering its two main properties, namely, high water absorption and high water desorption, resulting in an increasing degree of hydration and a reduction in autogenous shrinkage at an early age. The internal curing (IC) method was introduced over a decade ago with pre-wetted lightweight aggregates (LWAs) for low-permeability concrete that is inadequate for external curing, such as water curing. Generally, proper curing provides early benefits for cement hydration, strength development, and, finally, long-term properties like durability. Therefore, the good distribution of internal water in pre-wetted LWAs is designed to solve the issue of external curing, especially at the center of a concrete member. BA is widely used as a fine aggregate, and several studies have reported the effect of internal curing with BA on concrete, alkali-activated concrete, and geopolymers [3,4,5,6,7,8,9,10,11,12,13,14,15,16]. However, all the studies agreed that BA reduced the compressive strength due to its low density compared to sand and its high porosity, which increases the total porosity of concrete and negatively affects mechanical properties (i.e., compressive strength, splitting strength, and flexural strength). To date, several studies have attempted to use BA as a cement replacement material with the use of grinding as a pre-treatment to reduce porosity and increase BA density; the pozzolanic reaction can be activated during the curing period. For example, Chindasiriphan et al. (2023) [10] studied the effect of BA as a fine aggregate on the strength and heat evolution of high-strength concrete. They indicated that BA reduced the compressive strength and elastic modulus due to it having a lower strength than sand. Compared to ground BA (GBA) used for cement replacement, the combination of GBA and BA was more effective in reducing heat evolution and autogenous shrinkage due to the pozzolanic reaction of GBA. Ahmad Mousa (2023) [17] claimed that coal BA can provide pozzolanic reactivity with grinding and that using up to 50% of ground BA to replace cement can produce a compressive strength of up to 51 MPa. Bheel et al. (2022) [18] investigated the workability density, water absorption, compressive strength, and splitting tensile strength of concrete made from BA and sugarcane bagasse ash (SCBA) used as cement- and sand-replacing materials. They found that the compressive strength and splitting tensile strength increased in the concrete made from BA and SCBA due to their pozzolanic reaction. Moreover, mixing greater amounts of BA and SCBA into the concrete resulted in the total embodied carbon being lower than that of the reference concrete (400 kgCO2/m3), which should be minimized in the construction industry. It can be seen that recent studies have attempted to use BA as a cement replacement material with additional processes like grinding and that they have only focused on the compressive strength and pozzolanic reaction of BA; however, the advantage of BA as an internal curing agent has been ignored. In recent years, most studies have been devoted to incorporating high-strength materials in cementitious materials, such as steel bars and various types of fibers. For instance, Aghaee and Khayat (2023) [19] investigated the properties of a mortar containing internal curing materials reinforced with straight steel fiber. They found a stronger interfacial transition zone (ITZ) and higher fiber–matrix bonding in the area close to the fiber in the mortar containing internal curing materials. Chimeremeze et al. (2022) [20] studied the mechanical properties of concrete made from a lightweight aggregate reinforced with a basalt fiber and found that the basalt fiber improved the strength and delayed crack formation. Akinyemi and Dai (2020) [21] explored the effect of natural fiber in mortar containing BA. They found that the ductility and toughness of the cement mortar were improved due to the good compactness between the fiber and interface of the hydration product, resulting in an enhanced splitting strength and flexural strength. Recently, Michalik et al. (2023) [22] examined the properties of a cement matrix reinforced with recycled tire steel fiber (RTSF), and their results showed that using RTSF improved fracture strength and fracture toughness due to the fiber crack-bridging effect, which is an effect afforded by using fiber reinforcement in a cement matrix. Interestingly, works in the literature have investigated the effect of RTSF on properties of the cementitious matrix. For example, Caggiano et al. (2017) [23] claimed that RTSF could be used to replace industrial steel fiber (ISF) in concrete considering its positive effect on the mechanical properties of concrete, such as increasing the compressive strength by 5–10% compared to concrete with ISF, improving flexural behavior, especially toughness and ductility at post-peak cracking, and providing a small crack opening from the bridging effect. These findings align with those of another study [24], which measured the effect of using 30 kg/m3 of RTSF on the compressive strength and flexural properties of concrete, indicating that the compressive strength and magnitude of the post-crack opening of the concrete containing RTSF were 20% and 103% greater than those of the concrete containing ISF, respectively [25,26]. This occurred because the geometrical characteristics of the RTSF provided an improved bridging effect across the crack openings, as mentioned in several studies. Moreover, researchers concluded that using RTSF increased the mechanical interlocking of reinforced concrete during frictional pull-out behavior compared to reinforced concrete without RTSF [27,28,29]. Apart from that, the effects of the RTSF on the drying shrinkage and mechanical properties (i.e., tensile strength) of concrete were investigated, and it was reported that the addition of 1% RTSF by mix volume mitigated drying shrinkage by 18.8% compared to a plain mix [30]. Thus, the evidence from previous studies points out that the inclusion of RTSF can enhance the mechanical properties of a cementitious matrix, as well as being more environmentally friendly and producing fewer greenhouse gas emissions that are associated with the construction industry. In particular, RTSF could potentially be applied to improve the mechanical properties of mortar containing BA and maintain the internal curing effect, which is the main factor for maximizing the hydration reaction and mitigating the autogenous shrinkage of mortar with a low water-to-cement (w/c) ratio.
This study, therefore, investigated the effects of BA and RTSF on the engineering properties of mortar specimens by conducting two series of experimental tests. The first series evaluated the effects of the BA contents of various sand replacement ratios (that is, 0%, 10%, 20%, and 30% by volume) on the flow, setting time, total shrinkage, compressive strength, splitting tensile strength, and flexural strength of the mortar. The second series evaluated the effects of incorporating the RTSF contents of 0.5% and 1.0% by mix volume on the same properties of a mortar specimen with a BA content of 30%. Moreover, the evolution of the mortar containing BA was examined through its microstructure and pore structure to verify the degree of hydration during the curing period using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), a thermogravimetric analysis (TGA), and mercury intrusion porosimetry (MIP).

2. Materials and Methods

2.1. Materials

Three materials were used to prepare the mortar with w/c = 0.35. The first was ordinary Portland cement (OPC) as the only binder following the specification of ASTM C150-2020 [31], and the two fine aggregates were river sand and BA. The river sand’s water absorption was 1.15% and its specific gravity was 2.58, following the standard cone test ASTM C128-2015 [32]. In Figure 1, the particle size distributions of the river sand, BA, and their combination are displayed. BA’s particles followed the aggregate standard requirement, namely, ASTM C33-2003 [33].
For the internal curing effect, BA was soaked in water for 72 h, known as the material preparation step, before mixing with the other mortar ingredients. The 72 h water absorption was 19.19% with a specific gravity of 2.09 using the paper towel method following ASTM C1761-2015 [34]. Regarding the high water absorption, the pore structure was determined using the mercury intrusion porosimetry (MIP) test. An AutoPore V 9620 series (Micrometrics instrument Ltd., Norcross, GA, USA) was used with an increasing pressure from atmosphere pressure to 30,000 psia. In Figure 2, the pore size distributions are displayed, and most of them were large pores in the range of 50–90 μm. BA’s pores were irregular, as shown in Figure 3, and most of them were in the range of 200–300 μm, which was in good agreement with their fineness modulus of 2.93.
Moreover, the chemical composition of the BA used is presented in Table 1. As mentioned in the Introduction section, RTSF enhances mechanical properties. The properties of the RTSF are presented in Table 2.
For the mix proportions, six different mixtures were prepared for two different series. The first series investigated the properties of the mixtures containing BA. The mix proportions were designed based on a previous study [5] using a volumetric ratio of cement paste to aggregate of 60:40 with a w/c ratio of 0.35. At the same time, the other series investigated the properties of the mixture containing BA reinforced with RTSF. Based on previous results [35], 1% RTSF can be added to produce a mortar compressive strength of at least 35 MPa. The second series was thus designed to have an RTSF content up to 1%. Two different RTSF contents (i.e., 0.5% and 1.0%) were added to mortar containing 30% BA to observe the effect of the RTSF content on the properties of the mortar, especially on the mechanical properties (i.e., compressive strength, splitting strength, and flexural strength). More details can be found in Table 3.

2.2. Methods

2.2.1. Flow Table Test

A flow table test was conducted, following ASTM C1437-2015 [36], immediately after mixing to determine the workability of the fresh mortar. The diameter of the fresh mortar was measured using a vernier caliper along four directions. The experimental value is the summation of the four diameters.

2.2.2. Setting Time Test

The transition stage of the mortar was observed by inserting a modified Vicat needle with a diameter of 2 mm into the mortar following ASTM C807-2013 [37]. Thirty minutes after mixing, the initial penetration of the modified Vicat needle was performed, and the penetration depth was recorded every 10 min until the needle did not pass through the surface of the mortar. The setting time of the mortar was determined at a penetration depth of 10 mm.

2.2.3. Length Change Test

A length measurement was performed following ASTM C157-2014 [38] on three prism specimens with a cross-section of 75 mm and a length of 285. Twenty-four hours after mixing, the mortar specimens were demolded and their initial length was recorded; then, they were stored in a chamber with a controlled temperature of 23 ± 1 °C and a relative humidity of 50 ± 5%. The length measurement was obtained for each specimen for 28 d. The total shrinkage was defined as the decrease in the length of the mortar specimen. This total shrinkage included autogenous shrinkage and drying shrinkage.

2.2.4. Compressive Strength Test

A compression test was performed on three cubic specimens with a size of 100 × 100 × 100 mm3 following ASTM C109-2016 [39] at ages of 1, 7, and 28 d. Twenty-four hours after mixing, the mortar specimens were demolded and stored in a moist room. The presented results are the average value taken from three testing values.

2.2.5. Splitting Test

A splitting test was performed at 28 d on three cylindrical specimens with a diameter of 100 mm and a length of 200 mm following ASTM C496-2017 [40]. Twenty-four hours after mixing, the mortar specimens were demolded and stored in a moist room. The presented results are the average value taken from three testing values.

2.2.6. Flexural Test

A flexural test was performed at 28 d on three prismatic specimens with a diameter of 100 mm and a length of 200 mm following ASTM C496-2017 [41]. Twenty-four hours after mixing, the mortar specimens were demolded and stored in a moist room. The presented results are the average value taken from three testing values.

2.2.7. Microstructural Analysis

Three different testing methods were used to study the physical and chemical properties of the mortar containing BA for 28 d. The microstructure evolution, used to examine physical properties, was observed using scanning electron microscope (SEM) image and pore structure data, including the total porosity and pore size distribution. The progress of hydration, used to examine chemical properties, was observed via energy-dispersive spectroscopy (EDX) equipment and a thermogravimetric test through the Ca(OH)2 content.
  • SEM equipped with EDX.
    The mortar specimens were prepared with a diameter of 25 mm and a height of 10 mm at 1, 7, and 28 d to observe their microstructures at different curing ages and compare their microstructure evolution. Based on a previous study [42], the prepared specimens were soaked in an acetone solution for 2 d and then placed in a vacuum dryer for 3 d to stop hydration and avoid carbonation. The surface of the samples was polished with silicon carbide no. 400, no. 800, and no. 1200, followed by a diamond powder with sizes of no. 9, no. 3, and, finally, no. 1, respectively. Before capturing the samples’ microstructures, a gold coating was applied to the surface of the samples to attract electrons and increase the samples’ conductivity. To examine the physical appearance, back-scattered electron (BSE) images were obtained at 20 kV and a magnification of 100×. The EDX was used to examine the chemical appearance to identify the key elements of hydration products, such as Ca, Si, Na, and Fe, under “spot scanning mode” and “map scanning mode”, presenting the atomic percentage and weight percentage, respectively.
  • TGA
    TGA was carried out to examine the decomposition of the plain mortar and mortar containing 30% BA at different curing ages of 1 and 28 d. The mortar specimens were prepared with a size of 5 × 5 mm2, placed in an acetone solution for 2 d, stored in a vacuum dryer for 3 d to stop hydration, and then ground until they became a powder with a weight not more than 100 mg. The TGA test was started at room temperature under a fixed heating rate of 10 C/min until the final temperature reached 1000 °C. The percent mass loss at different testing temperatures, known as the TG curve, can be used to identify the decomposition of a hydration product. The decomposition temperature ranges of hydration products were summarized in a previous study [43]. For example, CSH is associated with a range of 150–400 °C, and Ca(OH)2 is associated with a range of 400–550 °C. Moreover, the mass loss content of the hydration products of interest like Ca(OH)2 can be calculated from the TG curve using a previous study’s equation [10].
  • MIP
    As mentioned in Section 2.1 Materials, pore structures were examined using the MIP technique. The plain mortar and mortar containing 30% BA were prepared with a size of 15 × 15 × 15 mm3 at different curing ages of 1 and 28 d to observe the pore evolution, such as the total porosity and pore size distribution. The prepared specimens were soaked in an acetone solution for 2 d and then stored in a vacuum dryer for 3 d to stop hydration. For the MIP procedure, mercury under high pressure was penetrated into the sample to fill the space between each pore; the volume of used mercury is known as “intrusion”. Then, the mercury was taken from the filled pores, known as “extrusion”. At this stage, some of the mercury remained in the pores, resulting in a difference between the intrusion volume and the extrusion volume, which is caused by ink-bottle pores, as explained in a previous study [44].

3. Results

3.1. Flow Value

The flow value is used to describe the workability of fresh mortar. As shown in Figure 4, the flow value of the plain mortar (B0) was 97%, while the flow value of the mortar with BA was higher. For example, the flow values of B10, B20, and B30 were 101.50%, 104.75%, and 108%, respectively. The workability of the mortar improved with BA, which is in agreement with a previous work [45]. This may be due to the lubricating water on the surface of pre-wetted BA, which reduces friction along fresh mortar. The pre-wetted BA did not reduce the workability of the fresh mortar, although BA has an irregular shape and a rough texture. However, adding the RTSF reduced the workability of the mortar. The flow values of the mortar containing 30% BA were reduced to 99% and 73% when increasing the RTSF content from 0.5% to 1%. This was mainly due to increased friction, which is in good agreement with a previous work [35]. It should be noted that the workability of the mortar containing BA reinforced with RTSF was higher than that of the plain mortar (B0). This may be due to the high volume of paste to aggregate. In the future development of internal curing with BA for concrete, the mix proportion needs to be adjusted with a superplasticizer and batch trials to produce the final concrete.

3.2. Setting Time

The setting time of mortar is another property that can be used to describe the desorption behavior of BA along with the hydration reaction. The setting time of the mortar was determined when the penetration depth of the modified Vicat reached 10 mm, as mentioned in ASTM C807-2013 [37]. The setting times of all the mortars are shown in Figure 5. It could be seen that the setting time of the plain mortar (B0) was 89 min, while the setting times of the mortar with BA slightly increased to 90, 95, and 99 min when sand was replaced with 10%, 20%, and 30% BA, respectively. The delay in the setting time was due to BA’s desorption behavior. Thus, with a higher BA content, the setting time was longer due to more water being released from BA in the mortar. In contrast, using the RTSF slightly shortened the setting time of the mortar. With 0.5% and 1% RTSF, the setting times were around 86 and 69 min, respectively. This may be due to there being more voids in the fresh mortar created with RTSF, thereby affecting the feasibility of fresh mixes, which is in agreement with a previous work [46].

3.3. Total Shrinkage

The length change of mortar owing to a chemical reaction and moisture loss is defined as the total shrinkage. The total shrinkages of all the mixtures are presented in Figure 6, indicating that using BA caused a slight change in the total shrinkage compared to the plain mix (B0). In a testing condition, a mortar specimen is subjected to both types of shrinkages, autogenous shrinkage and drying shrinkage. For mix proportions, more autogenous shrinkage can be expected, while less severe drying shrinkage can be expected. Since autogenous shrinkage is mainly governed by the internal curing effect of pre-wetted BA, a small change in the shrinkage might be related to moisture transfer corresponding to the volume-to-surface (v/s) ratios of the specimens. At the same time, adding the RTSF mitigated the total shrinkage. This occurred because the RTSF is effective in restraining the drying shrinkage, as indicated by a previous study on RTSF [30]. Moreover, Atis and Karahan (2009) [47] reported that fibers are randomly distributed in concrete, with only a few of them running parallel to the shrinkage strain in any particular direction; thus, these fibers effectively reduced concrete shrinkage throughout the specimen.

3.4. Compressive Strength

The compressive strengths of all the mixtures are presented in Figure 7. The 1 d compressive strengths of B0, B10, B20, and B30 were 37.0, 34.5, 33.8, and 33.2 MPa, respectively; the 7 d compressive strengths of B0, B10, B20, and B30 were 44.8, 41.7, 40.8, and 39.5 MPa, respectively; and, finally, the 28 d compressive strengths of B0, B10, B20, and B30 were 47.7, 44.5, 46.6, and 49.0 MPa, respectively. Notably, the compressive strengths measured after 1 and 7 d exhibited similar slightly increasing trends with an increasing BA content, but only B30 exhibited a higher compressive strength than B0 after 28 d of curing. The increase in compressive strength from 1 to 28 d of curing was approximately 38.2% for B0 and 56.3% for B30. The use of 30% BA likely increased the compressive strength because of an increase in the degree of hydration at 28 d, which can be explained by the results from the TGA test (see Section 3.7.1). Furthermore, adding 0.5% and 1% RTSF increased the compressive strengths by 9% and 25%, respectively. The strength enhancement was due to the fiber bridging effect; this controls crack development and leads to an increase in the load-carrying capacity under compression, which is in agreement with the findings of a previous study [26].

3.5. Splitting Strength

Figure 8 shows the splitting tensile strengths of all mixtures at 28 d, indicating that the splitting tensile strengths of B0, B10, B20, and B30 were 4.5, 3.6, 3.4, and 3.3 MPa, respectively; thus, the splitting tensile strength decreased overall when compared to that of the plain mortar (B0). As mentioned in a previous study [5], this was due to the high porosity of BA, as the total porosity of the mortar containing BA increased compared to that of the mortar without BA (B0). Meanwhile, adding 0.5% and 1% RTSF increased the splitting strength by 21% and 39% compared to that of the mortar without the RTSF, which was due to the fiber bridging effect, as mentioned above in Section 3.4. Compared to the mortar containing 30% BA (B30), the splitting strength significantly improved by 63% (5.5 MPa) and 91% (6.3 MPa) when adding RTSF at 0.5% and 1%. Similarly, Mastali et al. (2019) [28] found that the splitting strength of a concrete specimen with 1.5% RTSF was 25% higher than that of a specimen without fibers.

3.6. Flexural Strength

The 28 d flexural strengths of all mixtures were obtained from a four-point bending test. As shown in Figure 9, BA lowered the flexural strength compared to that of the plain mortar (B0); however, the flexural strength of the mortar was increased by approximately 20% when the BA content was increased from 10% to 30%. This could be associated with the internal curing effect of BA, as this increases the hydration of mortar, which can be proved by the increase in the Ca(OH)2 content from 1 d to 28 d (see the results in Section 3.7.1).
For the effect of the RTSF content on the flexural strength of the mortar, adding 0.5% and 1% RTSF steeply increased the flexural strength by 11% and 40% compared to that of the mortar containing 30% BA. This was due to the fiber bridging effect, as mentioned in Section 3.4.

3.7. Microstructure Characteristics

The microstructures of three different mortars, namely, the plain mortar (B0), mortar containing 30% BA (B30), and mortar containing 30% BA reinforced with 1% RTSF, were characterized using SEM equipped with EDX, TGA, and the MIP technique to verify the hydration enhancement from BA acting as an internal curing material.

3.7.1. Microstructure Using SEM Equipped with EDX

As shown in Figure 10 and Figure 11, more compact and denser microstructures were formed in both the B0 and B30 mixes, respectively. This agrees with the results in Section 3.4. Moreover, the distributions of key elements (Al, Si, Ca, Fe, and Na) in Figure 12 indicated a trend of increasing uniformity during the curing period.

3.7.2. TG Curve and Ca(OH)2 Content Using TGA

Figure 13 and Figure 14 show the TG curves and DTA curves of B0 and B30 used to determine the chemical reactions that occurred during the curing period. The products of these reactions were identified as calcium silicate hydrate (C-S-H) in the 150–220 °C range by a previous work [48], calcium aluminate hydrate C-A-H and calcium hydroxide (CH) in the 350–400 °C range and 430–530 °C range, respectively, by a previous work [46], and calcium carbonate (CaCO3) in the 650–800 °C range by a previous work [49]. Finally, the Ca(OH)2 content was estimated following the calculation in a previous work [43] to verify the hydration reaction. Figure 15 shows that the Ca(OH)2 in B30 increased from 1 d to 28 d, which was the same trend as the B0 mix. This indicated that the enhancement of the hydration of B30 was more significant than the enhancement of that of the plain mortar (B0).

3.7.3. Pore Structure Using MIP

The pore size distribution and total porosity of the plain mortar (B0) and the mortar containing 30% BA (B30) are presented in Figure 16 and Figure 17. As shown in Figure 16a, most of the pores at 1 d had a pore size of 100,000 nm on average, with a volume fraction of almost 25%, while the volume fractions of the pore size in the range of 100–1000 were around 5% and 7% in B0 and B30, respectively. The pore size distribution at 28 d (see Figure 16b) was found to be smaller, and the average pore size became smaller, indicating pore evolution. The total porosity at 1 and 28 d is presented in Figure 17. The total porosity of B0 was around 25%, while the total porosity of B30 was higher. As expected, the high porosity of BA increased the total porosity of the mortar. At an age of 28 d, the total porosity was reduced due to hydration enhancement for both B0 and B30. However, the average pore size of B30 was smaller than that of B0. This may be due to the higher hydration enhancement of BA, which is consistent with the TGA results in this study. Moreover, the total porosity of B30F1.0 was investigated and compared with that of B30, and it was found that the total porosity was lower than that of B30; however, the average pore size was larger. However, this is inconsistent with a previous study of a fiber-reinforced system, which stated an increase in porosity in all mixtures. This might be due to the good combination of 30% BA and 1% RTSF resulting in a total porosity reduction. Further studies varying the BA and RTSF contents are needed to study their combination and to verify this phenomenon.

4. Discussion

BA acts as an internal curing agent very well considering the development of a higher compressive strength of about 10%, compared to that of plain mortar, and the more compact and refined pore structure due to the continued hydration reaction resulting from an increase in the Ca(OH)2 content from 1 d to 28 d.
Moreover, using BA in mortar is more applicable with the addition of RTSF. The positive performance was well exhibited, such as the increase in the compressive strength of 35%, the increase in the splitting tensile strength of 46%, and the increase in the flexural strength of 40%, when adding 1% RTSF to mortar containing 30% BA; furthermore, there was a reduction in total shrinkage due to fiber restraining caused by the bridging effect and a more compact and denser microstructure with a lower total porosity than the mortar containing only 30% BA.
BA acts as an internal curing agent well and is more practical when reinforcing with RTSF, considering the improved mechanical properties.

5. Conclusions

Based on the experimental results of mortars containing bottom ash (BA) and recycled tire steel fiber (RTSF), the main conclusions of this study can be summarized as follows:
  • The addition of BA improved the workability of fresh mortar.
  • As the percentage of BA in the mixture increased, the setting time also increased, primarily due to BA’s desorption properties.
  • Mortar containing 30% BA exhibited a significant increase in compressive strength, particularly after 28 days of curing. This enhancement amounted to a 56.3% increase in strength compared to that of plain mortar.
  • A microstructural analysis revealed that the mortar with BA exhibited a denser microstructure, which contributed to the development of higher strength. The increased hydration and refinement of pores from 1 day to 28 days supported this observation.
  • The addition of recycled tire steel fiber (RTSF) further improved the mechanical properties of the mortar. The RTSF acted as a reinforcement, increasing the compressive, splitting tensile, and flexural strengths by 25%, 46%, and 40%, respectively, when added at 1%.
  • The combination of BA and RTSF effectively reduced the total shrinkage by nearly 30%.
Overall, the mortar made from 30% BA and 1% RTSF demonstrated a 28-day compressive strength exceeding 50 MPa, making it more durable and capable of bearing heavier loads. This combination is particularly suitable for the structural bonding of fiber composites and the strengthening of building concrete members. Future investigations should focus on durability, compatibility, tensile behavior, and shrinkage due to long-term exposure to old concrete substrates when using bottom ash mortar reinforced with recycled tire steel fiber.

Author Contributions

Conceptualization, P.M.; methodology, P.M.; validation, P.M.; formal analysis, P.M.; investigation, P.M.; resources, P.M.; data curation, P.M.; writing—original draft preparation, P.M.; writing—review and editing, P.M.; visualization, P.M.; supervision, R.S.; project administration, P.M.; funding acquisition, P.M. and R.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Royal Golden Jubilee, Ph.D. Program (RGJ-Ph.D. Program) grant number PHD58K0109.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Solid Waste Management. Available online: https://www.worldbank.org/en/topic/urbandevelopment/brief/solid-waste-management (accessed on 14 August 2023).
  2. News Release Coal Ash Production and Use 2021. Available online: https://acaa-usa.org/wp-content/uploads/2022/12/2021-Production-and-Use-Survey-Results-FINAL.pdf (accessed on 14 August 2023).
  3. Rodríguez-Álvaro, R.; Seara-Paz, S.; González-Fonteboa, B.; Ferrándiz-Mas, V.; Paine, K. Waste-Based porous materials as water reservoirs for the internal curing of Concrete: A review. Constr. Build. Mater. 2021, 299, 124244. [Google Scholar] [CrossRef]
  4. Rodríguez-Álvaro, R.; Seara-Paz, S.; González-Fonteboa, B.; Etxeberria, M. Study of different granular by-products as internal curing water reservoirs in concrete. J. Build. Eng. 2022, 45, 103623. [Google Scholar] [CrossRef]
  5. Kim, H.K.; Lee, H.K. Hydration kinetics of high-strength concrete with untreated coal bottom ash for internal curing. Cem. Concr. Compos. 2018, 91, 67–75. [Google Scholar] [CrossRef]
  6. Maldonado-Alameda, A.; Giro-Paloma, J.; Svobodova-Sedlackova, A.; Formosa, J.; Chimenos, J.M. Municipal solid waste incineration bottom ash as alkali-activated cement precursor depending on particle size. J. Clean. Prod. 2020, 242, 118443. [Google Scholar] [CrossRef]
  7. Hamada, H.; Alattar, A.; Tayeh, B.; Yahaya, F.; Adesina, A. Sustainable application of coal bottom ash as fine aggregates in concrete: A comprehensive review. Case Stud. Constr. Mater. 2022, 16, e01109. [Google Scholar] [CrossRef]
  8. Gao, X.; Yuan, B.; Yu, Q.L.; Brouwers, H.J.H. Characterization and application of municipal solid waste incineration (MSWI) bottom ash and waste granite powder in alkali activated slag. J. Clean. Prod. 2017, 164, 410–419. [Google Scholar] [CrossRef]
  9. Nakararoj, N.; Nhat Ho Tran, T.; Sukontasukkul, P.; Attachaiyawuth, A.; Tangchirapat, W.; Chee Ban, C.; Rattanachu, P.; Jaturapitakkul, C. Effects of High-Volume bottom ash on Strength, Shrinkage, and creep of High-Strength recycled concrete aggregate. Constr. Build. Mater. 2022, 356, 129233. [Google Scholar] [CrossRef]
  10. Chindasiriphan, P.; Meenyut, B.; Orasutthikul, S.; Jongvivatsakul, P.; Tangchirapat, W. Influences of high-volume coal bottom ash as cement and fine aggregate replacements on strength and heat evolution of eco-friendly high-strength concrete. J. Build. Eng. 2023, 65, 105791. [Google Scholar] [CrossRef]
  11. Balapour, M.; Zhao, W.; Garboczi, E.J.; Oo, N.Y.; Spatari, S.; Hsuan, Y.G.; Billen, P.; Farnam, Y. Potential use of lightweight aggregate (LWA) produced from bottom coal ash for internal curing of concrete systems. Cem. Concr. Compos. 2020, 105, 103428. [Google Scholar] [CrossRef]
  12. Promsaeng, A.; Krammart, P.; Sancharoen, P.; Tangtermsirikul, S. Effect of Using Bottom Ash as Internal Curing Material on Compressive Strength of Concrete. In Proceedings of the 10th Annual Concrete Conference, Dusit Island, Chiang Rai, Thailand, 20–22 October 2014. [Google Scholar]
  13. Bai, Y.; Darcy, F.; Basheer, P.A.M. Strength and drying shrinkage properties of concrete containing furnace bottom ash as fine aggregate. Constr. Build. Mater. 2005, 19, 691–697. [Google Scholar] [CrossRef]
  14. Kim, H.K.; Jang, J.G.; Choi, Y.C.; Lee, H.K. Improved chloride resistance of high-strength concrete amended with coal bottom ash for internal curing. Comput. Chem. Eng. 2014, 71, 334–343. [Google Scholar] [CrossRef]
  15. Lee, H.K.; Kim, H.K.; Hwang, E.A. Utilization of power plant bottom ash as aggregates in fiber-reinforced cellular concrete. Waste Manag. 2010, 30, 274–284. [Google Scholar] [CrossRef] [PubMed]
  16. Wyrzykowski, M.; Ghourchian, S.; Sinthupinyo, S.; Chitvoranund, N.; Chintana, T.; Lura, P. Internal curing of high performance mortars with bottom ash. Cem. Concr. Compos. 2016, 71, 1–9. [Google Scholar] [CrossRef]
  17. Mousa, A. Utilization of coal bottom ash from thermal power plants as a cement replacement for building: A promising sustainable practice. J. Build. Eng. 2023, 74, 106885. [Google Scholar] [CrossRef]
  18. Bheel, N.; Khoso, S.; Baloch, M.H.; Benjeddou, O.; Alwetaishi, M. Use of waste recycling coal bottom ash and sugarcane bagasse ash as cement and sand replacement material to produce sustainable concrete. Environ. Sci. Pollut. Res. 2022, 29, 52399–52411. [Google Scholar] [CrossRef]
  19. Aghaee, K.; Khayat, K.H. Effect of internal curing and shrinkage-mitigating materials on microstructural characteristics of fiber-reinforced mortar. Constr. Build. Mater. 2023, 386, 131527. [Google Scholar] [CrossRef]
  20. Chimeremeze, P.; Adegoke, A.; Abu, I.; Mohamed, M.; Abd, A.A.; Mayowa, E.; Milad, A. Case Studies in Construction Materials Mechanical characteristics of hardened basalt fiber expanded clay concrete cylinders. Case Stud. Constr. Mater. 2022, 17, e01368. [Google Scholar] [CrossRef]
  21. Akinyemi, B.A.; Dai, C. Development of banana fibers and wood bottom ash modified cement mortars. Constr. Build. Mater. 2020, 241, 118041. [Google Scholar] [CrossRef]
  22. Michalik, A.; Chyliński, F.; Piekarczuk, A.; Pichór, W. Evaluation of recycled tyre steel fibres adhesion to cement matrix. J. Build. Eng. 2023, 68, 106146. [Google Scholar] [CrossRef]
  23. 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. Constr. Build. Mater. 2017, 147, 286–295. [Google Scholar] [CrossRef]
  24. Hu, H.; Papastergiou, P.; Angelakopoulos, H.; Guadagnini, M.; Pilakoutas, K. Mechanical properties of SFRC using blended manufactured and recycled tyre steel fibres. Constr. Build. Mater. 2018, 163, 376–389. [Google Scholar] [CrossRef]
  25. Al-Kamyani, Z.; Figueiredo, F.P.; Hu, H.; Guadagnini, M.; Pilakoutas, K. Shrinkage and flexural behaviour of free and restrained hybrid steel fibre reinforced concrete. Constr. Build. Mater. 2018, 189, 1007–1018. [Google Scholar] [CrossRef]
  26. Hu, H.; Papastergiou, P.; Angelakopoulos, H.; Guadagnini, M.; Pilakoutas, K. Mechanical properties of SFRC using blended Recycled Tyre Steel Cords (RTSC) and Recycled Tyre Steel Fibres (RTSF). Constr. Build. Mater. 2018, 187, 553–564. [Google Scholar] [CrossRef]
  27. Alsaif, A.; Bernal, S.A.; Guadagnini, M.; Pilakoutas, K. Freeze-thaw resistance of steel fibre reinforced rubberised concrete. Constr. Build. Mater. 2019, 195, 450–458. [Google Scholar] [CrossRef]
  28. Mastali, M.; Dalvand, A.; Sattarifard, A.R.; Abdollahnejad, Z.; Nematollahi, B.; Sanjayan, J.G.; Illikainen, M. A comparison of the effects of pozzolanic binders on the hardened-state properties of high-strength cementitious composites reinforced with waste tire fibers. Compos. Part B Eng. 2019, 162, 134–153. [Google Scholar] [CrossRef]
  29. Mastali, M.; Dalvand, A. Fresh and hardened properties of self-compacting concrete reinforced with hybrid recycled steel-polypropylene fiber. J. Mater. Civ. Eng. 2017, 29, 1–15. [Google Scholar] [CrossRef]
  30. Zhong, H.; Zhang, M. Experimental study on engineering properties of concrete reinforced with hybrid recycled tyre steel and polypropylene fibres. J. Clean. Prod. 2020, 259, 120914. [Google Scholar] [CrossRef]
  31. ASTM C150/C150M-20; Standard Specification for Portland Cement. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2020; pp. 1–9. [CrossRef]
  32. ASTM C128-15; Standard Test Method for Rlative Density (Specific Gravity) and Absorption of Fine Aggregate. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2015; pp. 1–6.
  33. ASTM C33-03; Standard Specification for Concrete Aggregates. ASTM International: West Conshohocken, PA, USA, 2003.
  34. ASTM C1761/C1761M-15: ASTM C1761-15; Standard Specification for Lightweight Aggregate for Internal Curing of Concrete. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2015; pp. 1–8.
  35. Zhong, H.; Poon, E.W.; Chen, K.; Zhang, M. Engineering properties of crumb rubber alkali-activated mortar reinforced with recycled steel fibres. J. Clean. Prod. 2019, 238, 117950. [Google Scholar] [CrossRef]
  36. ASTM C1437-15; Standard Test Method for Flow of Hydraulic Cement MOrtar. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2015; pp. 1–2.
  37. ASTM C807-13; Standard Test Method for Time of Setting of Hydraulic Cement Mortar by Modified Vicat Needle. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2013; pp. 1–3.
  38. ASTM C157/C157M-14; Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and concrete. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2014; Volume 08, pp. 1–7.
  39. ASTM C109/C109M-16; Standard Test Method for Compressive Strength of Hydraulic Cement. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2016; pp. 1–10.
  40. ASTM C496/C496M-17; Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2017; p. 5.
  41. ASTM C1609-19: C 1609/C 1609M-05; Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading) 1. American Society for Testing and Materials International: West Conshohocken, PA, USA, 2019; pp. 1–9. [CrossRef]
  42. Tu, W.; Zhu, Y.; Fang, G.; Wang, X.; Zhang, M. Internal curing of alkali-activated fly ash-slag pastes using superabsorbent polymer. Cem. Concr. Res. 2019, 116, 179–190. [Google Scholar] [CrossRef]
  43. Chindasiriphan, P.; Yokota, H.; Kawabata, Y.; Pimpakan, P. Combined effect of rice husk ash and superabsorbent polymer on self-healing capability of mortar. Constr. Build. Mater. 2022, 338, 127588. [Google Scholar] [CrossRef]
  44. Ghourchian, S.; Wyrzykowski, M.; Lura, P.; Shekarchi, M.; Ahmadi, B. An investigation on the use of zeolite aggregates for internal curing of concrete. Constr. Build. Mater. 2013, 40, 135–144. [Google Scholar] [CrossRef]
  45. Kim, H.K.; Ha, K.A.; Lee, H.K. Internal-curing efficiency of cold-bonded coal bottom ash aggregate for high-strength mortar. Constr. Build. Mater. 2016, 126, 1–8. [Google Scholar] [CrossRef]
  46. Wang, Y.; Chan, C.L.; Leong, S.H.; Zhang, M. Engineering properties of strain hardening geopolymer composites with hybrid polyvinyl alcohol and recycled steel fibres. Constr. Build. Mater. 2020, 261, 120585. [Google Scholar] [CrossRef]
  47. Atiş, C.D.; Karahan, O. Properties of steel fiber reinforced fly ash concrete. Constr. Build. Mater. 2009, 23, 392–399. [Google Scholar] [CrossRef]
  48. Lasseuguette, E.; Burns, S.; Simmons, D.; Francis, E.; Chai, H.K.; Koutsos, V.; Huang, Y. Chemical, microstructural and mechanical properties of ceramic waste blended cementitious systems. J. Clean. Prod. 2019, 211, 1228–1238. [Google Scholar] [CrossRef]
  49. Flores-Alés, V.; Martín-del-Río, J.J.; Alducin-Ochoa, J.M.; Torres-González, M. Rehydration on high temperature-mortars based on recycled glass as aggregate. J. Clean. Prod. 2020, 275, 124139. [Google Scholar] [CrossRef]
Buildings 13 02514 g001
Figure 1. Particle distributions of river sand and bottom ash.
Figure 1. Particle distributions of river sand and bottom ash.
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Figure 2. Pore size distribution of bottom ash.
Figure 2. Pore size distribution of bottom ash.
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Figure 3. Scanning electron microscope image of bottom ash.
Figure 3. Scanning electron microscope image of bottom ash.
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Figure 4. Effects of BA and RTSF contents on flow values of all mixtures.
Figure 4. Effects of BA and RTSF contents on flow values of all mixtures.
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Figure 5. Effects of BA and RTSF contents on setting times of all mixtures.
Figure 5. Effects of BA and RTSF contents on setting times of all mixtures.
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Figure 6. Effects of BA and RTSF contents on total shrinkages of all mixtures.
Figure 6. Effects of BA and RTSF contents on total shrinkages of all mixtures.
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Figure 7. Effects of BA and RTSF contents on compressive strengths of all mixtures.
Figure 7. Effects of BA and RTSF contents on compressive strengths of all mixtures.
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Figure 8. Effects of BA and RTSF contents on splitting tensile strengths of all mixtures.
Figure 8. Effects of BA and RTSF contents on splitting tensile strengths of all mixtures.
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Figure 9. Effects of BA and RTSF contents on the flexural strengths of all mixtures.
Figure 9. Effects of BA and RTSF contents on the flexural strengths of all mixtures.
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Figure 10. Development of B0 microstructure at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d with magnification 100×.
Figure 10. Development of B0 microstructure at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d with magnification 100×.
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Figure 11. Development of B30 mortar microstructure at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d.
Figure 11. Development of B30 mortar microstructure at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d.
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Figure 12. Effects of BA contents on microstructure development and EDX spectra at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d.
Figure 12. Effects of BA contents on microstructure development and EDX spectra at curing ages of (a) 1 d, (b) 7 d, and (c) 28 d.
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Figure 13. TG curves of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
Figure 13. TG curves of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
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Figure 14. DTA curves of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
Figure 14. DTA curves of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
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Figure 15. Ca(OH)2 content in plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
Figure 15. Ca(OH)2 content in plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
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Figure 16. Pore size distributions of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of (a)1 d and (b) 28 d.
Figure 16. Pore size distributions of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of (a)1 d and (b) 28 d.
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Figure 17. Total porosity of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
Figure 17. Total porosity of plain mortar (B0) and mortar containing 30% BA (B30) at curing ages of 1 d and 28 d.
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Table 1. Chemical composition of bottom ash (%).
Table 1. Chemical composition of bottom ash (%).
SiO2Al2O3Fe2O3CaOK2OTiO2Na2OSO3Others
27.0014.0023.2025.802.970.660.693.031.51
Table 2. Properties of recycled tire steel fiber.
Table 2. Properties of recycled tire steel fiber.
Length, L
(mm)		Nominal Diameter, D
(μm)		Aspect Ratio
(L/D)		Density
(g/m3)		Tensile Strength
(MPa)		Young’s Modulus
(GPa)
201507.828500.69200
Table 3. Mix proportions of all mixtures.
Table 3. Mix proportions of all mixtures.
MixOPC
(kg/m3)		w/c RatioSand
(kg/m3)		BA
(kg/m3)		RTSF
(kg/m3)
B0898.90.351038.0--
B10898.90.35934.270.4-
B20898.90.35830.4140.8-
B30898.90.35726.6211.2-
B30F0.5898.90.35726.6211.239.0
B30F1.0898.90.35726.6211.278.0
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Markpiban, P.; Sahamitmongkol, R. Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber. Buildings 2023, 13, 2514. https://doi.org/10.3390/buildings13102514

AMA Style

Markpiban P, Sahamitmongkol R. Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber. Buildings. 2023; 13(10):2514. https://doi.org/10.3390/buildings13102514

Chicago/Turabian Style

Markpiban, Pochpagee, and Raktipong Sahamitmongkol. 2023. "Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber" Buildings 13, no. 10: 2514. https://doi.org/10.3390/buildings13102514

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