Next Article in Journal
Electromigration of Chloride Ions in Cementitious Material: Extension of Nernst–Planck Theory
Previous Article in Journal
Cognition–Paradigm Misalignment in Heritage Conservation: Applying a Correspondence Framework to Traditional Chinese Villages
Previous Article in Special Issue
Settlement Characteristics and Control Parameters for the Integrated Construction of Large-Section Underground Structures and Airport Terminals: A Case Study
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Buildings
Volume 15
Issue 18
10.3390/buildings15183428
buildings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles

by
Fan Xu
1,*,
Zhijun Li
1,*,
Honghao Ying
2 and
Bin Du
1
1
School of Civil Engineering, Xi’an Technological University, Xi’an 710021, China
2
School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
*
Authors to whom correspondence should be addressed.
Buildings 2025, 15(18), 3428; https://doi.org/10.3390/buildings15183428
Submission received: 14 July 2025 / Revised: 29 August 2025 / Accepted: 8 September 2025 / Published: 22 September 2025
(This article belongs to the Special Issue Research on Durability, Resilience and Stability of Building Structures)
Browse Figures
Versions Notes

Abstract

To improve the mechanical properties and durability of concrete made with recycled fiber-reinforced tailings aggregate, the influence of metakaolin (MK) content on its properties was studied. Freeze–thaw cycle tests and sulfate freeze–thaw cycle tests were performed. Moreover, the service life of concrete under freeze–thaw cycles was predicted using the grey system theory. The findings showed that even a small quantity of MK can significantly enhance the compressive strength of concrete, with the highest strength observed at 10% MK content. Concrete’s ability to withstand freeze–thaw and sulfate freeze–thaw conditions was improved by MK, with effectiveness increasing alongside MK content. The grey system theory effectively predicts the relative compressive strength of concrete in freeze–thaw environments. The prediction results demonstrated that MK significantly extends the service life of concrete. This research investigates the properties of concrete made from MK and industrial waste and provides a theoretical basis for engineering applications in cold climates, saline soils, and marine areas in Northwest China. The findings provide a reference for promoting a circular economy and environmental protection.

1. Introduction

China’s swift urban growth has resulted in a significant rise in construction waste, threatening sustainable development. Developed countries employ advanced construction waste disposal methods and have a resource utilization rate of over 90% [1]. In contrast, landfill or stacking remains the predominant method in China, yielding a resource utilization rate of less than 10%, far lower than in developed areas such as Europe and the United States [2,3,4]. On the one hand, the accumulated concrete waste occupies valuable land resources. On the other hand, the depletion of natural resources has emerged as a major global development problem [5].
Utilizing waste concrete to produce recycled coarse aggregate (RCA) represents an effective method to promote the rational utilization of waste resources. However, RCA has lower strength and a higher porosity compared to natural coarse aggregate (NCA). Hence, RCA cannot completely replace NCA, which limits its use in various engineering applications [6,7]. To enhance the mechanical properties, iron tailings (IOTs) were incorporated into recycled aggregate concrete (RAC). IOTs are solid waste products discharged from the beneficiation process during the mining of non-ferrous metals and are primarily composed of minerals and rocks that cannot be economically utilized [8,9]. However, our previous research revealed that integrating IOTs in RAC can markedly increase the mechanical strength of concrete, but it also lessened its ductility [10]. Therefore, waste polypropylene (PP) fibers were introduced to modify the iron tailings concrete. These fibers bridge the cracks within the concrete and alleviate stress concentration at the crack tips, thereby improving the ductility [11]. However, using IOTs and waste PP fibers to improve concrete durability has limitations.
In addition, the cement industry faces numerous challenges, including high energy consumption and toxic substance emissions. Contributing to both acid rain and the greenhouse effect, these air pollutants have a significant impact [12]. Metakaolin (MK) can partially replace cement in concrete to mitigate the cement industry’s negative environmental impacts. MK is a clay mineral created by calcining kaolin [13,14]. China is rich in kaolin resources, which are mainly distributed in the northern regions. Rare high-quality kaolin deposits are found in the Inner Mongolia Zunger Banner region, with reserves of up to 810 million tons [15]. Kaolin is a hydrous aluminosilicate with a layered structure. Calcination at 600–880 °C dehydrates the layered structure of kaolin and produces MK with high pozzolanic reactivity. MK is composed mainly of SiO2 and Al2O3, which react with Ca(OH)2 in concrete, increasing its density and improving durability [16,17,18].
Two key environmental factors impacting concrete durability are sulfate attacks and freeze–thaw cycles [19]. Concrete deterioration due to exposure to environmental factors typically progresses from the exterior surface inward. The gradual spalling of the concrete surface further exacerbates the erosion, which accelerates degradation. In addition, environmental factors also play a crucial role. For example, large temperature differences are observed in Northwest China over the year, and some lakes contain a large amount of sulfate. Such environmental conditions increase concrete exposure to freeze–thaw cycles and sulfate erosion, collectively degrading the concrete. Compared with freeze–thaw damage alone, the damage caused by sulfate attacks combined with freeze–thaw cycles involves complex interactions. Under such conditions, the deterioration of concrete is not merely the additive result of both mechanisms, as they may mutually enhance or inhibit deterioration. Consequently, a thorough comparative study was carried out to explore how freeze–thaw cycles and sulfate attack affect concrete.
Researchers have earlier investigated how freeze–thaw cycles and sulfate attack together impact concrete [20,21,22,23]. The study by Bao et al. [24] examined how high-performance eco geopolymer concrete (HPEGPC) deteriorated under low-pressure salt erosion and freeze–thaw cycles, using indicators such as mass loss, RDEM and compressive strength. HPEGPC was significantly more resistant to freezing and salt erosion than OPCC in both standard and hypobaric settings. Ayano et al. [25] added blast furnace slag to mortar and concrete, revealing that calcium hydroxide precipitated around the aggregate reacted with cement slurry and blast furnace slag sand, thus changing the transition zone. Therefore, blast furnace slag can improve the freeze–thaw resistance of concrete in saline environments. Gregory et al. [26] studied the freeze–thaw resistance of concrete reinforced with self-shrinking chitosan-based fibers. The 2 wt% shrinking fiber-reinforced concrete exhibited a 219% increase in durability compared to non-shrinking fiber-reinforced concrete. These studies [27,28,29,30] provide evidence on freeze–thaw damage and salt corrosion of concrete.
However, few studies have investigated the properties of concrete produced by combining MK and industrial waste (hereinafter MK concrete), including RCA, IOTs, and waste PP fiber [31,32,33,34,35,36]. Furthermore, the susceptibility of the MK concrete to sulfate freeze–thaw damage remains unknown. Consequently, this investigation employed IOTs as an alternative to natural sand, with waste PP fiber as a supplementary material. The study investigated how different MK contents affected the compressive and axial compressive strength of concrete. Different MK contents (0, 5%, 10%, 15%, 20%) in concrete were tested under freeze–thaw and sulfate freeze–thaw cycles. The weight loss rate, relative compressive strength, and RDEM of each concrete were tested after 0, 25, 50, 75, and 100 cycles. Furthermore, the impact of MK content on concrete’s resistance to deterioration was examined. A model for freeze–thaw damage in concrete was developed, and the lifespan of concrete under freeze–thaw cycles was predicted. The study findings offer a theoretical foundation for engineering construction in cold, saline soil and marine areas in Northwest China and provide a reference for promoting a circular economy and environmental protection.

2. Materials and Methods

2.1. Materials

2.1.1. Cement

Qinling Portland (PO 42.5) cement, adhering to the Chinese Standard GB175 [37], was employed in this survey. The cement had a specific surface area of 354 square meters per kilogram and a fineness modulus of 2.8.

2.1.2. Coarse Aggregate

In this research, NAC and RCA were acquired from Xi’an in Shaanxi Province. Both materials had particle sizes between 5 and 20 mm, the RCA comprising 32% brick material. To enhance the quality and purity of RCA, impurities such as wood, plastic, and iron wire were manually removed. Subsequently, a high-pressure water jet was used to reduce the slurry content of RCA. The aggregate was then sun-dried to eliminate fine particles from the crushing process. Despite these measures, the recycled coarse aggregate did not meet the standard requirements for continuous grading. Hence, the RCA was sieved to the appropriate particle size range and then recombined according to particle size. Figure 1a depicts the particle size distribution of the recombined RCA and NCA, while Figure 2a and Figure 2b display the appearances of NCA and treated RCA, respectively.

2.1.3. Fine Aggregate

Sand was gathered from the Weihe River in Xi’an, Shaanxi Province, while IOTs were sourced from the YAOGOU tailings pond in Shangluo City, Shaanxi Province. Figure 2c,d illustrate the appearance of IOTs sand and natural sand. Both types of sand complied with the Chinese Standard for Technical Requirements and Test Method of Sand and Crushed Stone (or Gravel) for Ordinary Concrete (JGJ 52-2006) [38]. The particle size distribution is depicted in Figure 1b. Specifically, D10, D30, and D60 were 2.31 mm, 1.14 mm, and 0.58 mm, respectively, where D10, D30, and D60 represented the particle sizes when the cumulative particle size distribution reached 10%, 30%, and 60%, respectively. The nonuniformity coefficient (D60/D10) for natural sand was 0.25, and the curvature coefficient (D302/(D10D60)) was 0.97. Compared to natural sand, the surface of IOTs sand was rough and exhibited more angular particles with numerous edges and corners, thereby reducing the fluidity of the test specimen. Therefore, a water-reducing agent was added.

2.1.4. Water Reducer

In this study, a polycarboxylate high-performance water reducer was utilized. Its primary physical characteristics are detailed in Table 1.

2.1.5. Fiber

The fiber employed in this test was sourced from waste cement woven bags, composed of PP fiber, which was machine-cut into sections, bleached, and dyed. The fiber length was approximately 22 mm, with a diameter of 0.08 mm. Table 2 provides details on the waste PP fiber’s characteristics.

2.1.6. Metakaolin

The MK used in this study was manufactured by Shanxi Jufeng Co., Ltd. (Jinzhong, China). It possessed a specific surface area of 2800 m2/kg, an average particle size of 10 μm, and a specific gravity of 2.53. According to Table 3, the primary chemical compounds of MK are SiO2 and Al2O3, which together comprise 94.59% of the total.

2.2. Mix Proportions

Listed in Table 4 are the concrete mix proportions, with the water–cement ratio being 0.4. Studies conducted previously found that an RCA content of 30% or less by weight did not have a significant effect on the mechanical properties of concrete. Consequently, the replacement rate of RCA for NCA was set to 30%. The experiment was divided into three stages. Our prior research indicated that in the first phase, RAC with 30% IOTs performed the best [10,23]. In the second phase, TRAC-PP with 0.6% PP fiber yielded the most favorable results [11]. Consequently, RAC containing 30% IOTs and 0.6% PP fiber was selected as the control group, and the optimal content of MK was then explored.

2.3. Specimen Preparation

Based on the formula in Table 4, the coarse and fine aggregates were initially weighed and placed in a horizontal twin-shaft mixer for a minute of dry mixing. Subsequently, PP fibers were introduced and mixed for an additional minute to achieve uniform distribution. Finally, cement, water, and a water reducer were incorporated, and the mixture was stirred for three minutes. The obtained mixture was poured into 100 mm × 100 mm × 100 mm and 100 mm × 100 mm × 300 mm molds, and the air from the concrete mixture was removed by using a vibration table. After a 24 h period, the specimens were taken out of the mold and subsequently subjected to curing under standard conditions for durations of 7, 14, 28, and 90 days. Upon completion of the curing process, subsequent performance tests encompassing compressive strength, freeze–thaw resistance, sulfate freeze–thaw resistance, among others, were conducted to assess the various properties of the composite foam concrete. The ultimate results of each test were derived from the average of three samples.

2.4. Test Methods

2.4.1. Freeze–Thaw Cycle Test Method

As shown in Figure 3, the rapid freeze–thaw test was performed using a TDR-28 concrete rapid freeze–thaw test machine from Tianjin Gangyuan Testing Machine Co., Ltd., based in Tianjin, China.
Concrete with a curing age of 28 days and a size of 100 mm × 100 mm × 300 mm was used for the test. The concrete specimen was placed into a rubber test piece box with the dimensions 115 mm × 115 mm × 500 mm, as illustrated in Figure 4. A 20 mm gap was maintained between the specimen boxes to ensure an unobstructed flow of antifreeze within the tank. Distilled water was added to the specimen box until the water level was approximately 20 mm above the top surface of the concrete specimen. A temperature sensor placed at the center controlled the temperature of the concrete specimen. Throughout each freeze–thaw cycle, the specimen was cooled from 5 °C to −20 °C over a period of 3 h. Then, the concrete specimen was thawed to 5 °C within 1 h, with a temperature error of ±2 °C.

2.4.2. Sulfate Freeze–Thaw Cycle Test Method

Except for using a 5% Na2SO4 solution in the specimen box, the test process was identical to the freeze–thaw cycle test outlined in Section 2.4.1. During erosion, sulfate ions reacted with hydrated calcium silicate in the concrete, reducing sulfate ion levels in the solution. To maintain a consistent erosion environment, the Na2SO4 solution was replaced every 30 days.

3. Results and Discussion

3.1. Cubic Compressive Strength

It can be seen from Figure 5 that MK addition markedly increased the compressive strength of concrete, which rose with age, similar to NAC. At equivalent curing ages, concrete with MK replacement achieved higher compressive strength compared to the control specimen (TRAC-PP). Specifically, the 28-day compressive strength of specimens with MK replacements of 5%, 10%, 15%, and 20%—identified as M5, M10, M15, and M20, respectively—showed significant improvements. Compared to TRAC-PP, their strengths increased by 38.7%, 66.2%, 63.2%, and 59.4%, respectively.
Notably, the replacement ratio of MK did not lead to a linear enhancement in compressive strength but revealed a segmented connection. For instance, without MK, the 90-day compressive strength of concrete was 31.33 MPa. Adding 10% MK boosted it to 53.40 MPa, but increasing MK to 20% reduced the strength to 50.84 MPa. The compressive strength was at its highest with 10% MK content. MK enhanced the compressive strength of concrete through physical and chemical effects. Physically, it acts as a filler, reducing gaps in the matrix. Chemically, it reacts with volcanic ash to influence hydration kinetics, forming CSH, CAH, and CSAH; these compounds increased the density of the pore structure, particularly in the interfacial transition zone (ITZ) [39]. Nežerka et al. [40] revealed that replacing cement with 10% and 20% MK reduced ITZ thickness by 48% and 15%, respectively. In contrast, 30% MK replacement had adverse effects. Thus, a 10% MK replacement is recommended, aligning with the conclusion of the test results in this article.
Figure 6 displays the effect of curing time on the compressive strength of concrete cubes. MK concrete exhibited a rapid early strength development, with the 7-day cubic compressive strength reaching over 78% of the 28-day strength. Beyond 28 days, the rate of strength development decelerated. Notably, as the MK content increased, the strength growth rate of the concrete between day 7 and day 14 diminished. This reduction was attributed to the interaction between MK and the previously formed C-S-H gel during cement hydration, resulting in the formation of additional hydration products. These hydration products enveloped the unhydrated cement particles, thereby impeding further hydration.

3.2. Axial Compressive Strength

It can be seen from Figure 7 that the strength of concrete shows an obvious upward trend with the increase in MK content. As the content of MK increased, the strength of the concrete was significantly enhanced. The axial compressive strength of MK concrete consistently surpassed that of TRAC-PP. Notably, the 7-day strength of concrete containing 5% MK was equivalent to the 90-day strength of TRAC-PP. Furthermore, the 7-day strength of concrete incorporating 10%, 15%, and 20% MK was greater than that of concrete without MK. These results indicated that MK significantly influenced early strength development, primarily through its rapid pozzolanic reaction, which accelerated the early strength gain of concrete. Additionally, the finer particle size of MK compared to cement and sand contributed to improved internal porosity.
Additionally, with the increase in curing age, the axial compressive strength of the concrete generally enhanced, reflecting the development trend observed in cubic compressive strength. Nonetheless, at a 15% MK content, the concrete’s axial compressive strength fluctuated at various curing ages. To illustrate, the axial compressive strength of MK-20 was 2.5% and 6.4% lower than MK-15 after curing for 14 and 90 days, respectively. Conversely, MK-20 exhibited a 3.3% and 7.3% higher axial compressive strength than MK-15 after 7 and 28 days of curing. The overall change stayed relatively insignificant despite these fluctuations. The observed fluctuation might be explained by the hydration products generated from the cement and MK reaction, which encapsulated MK particles. These hydration products functioned as barriers that impeded the migration of water molecules, thereby causing a slight variation in strength. Moreover, the agglomeration of MK particles resulted in an uneven dispersion within cement-based materials. This uneven dispersion led to the formation of diverse hydration products from the cement–MK reaction, consequently causing strength fluctuations.

3.3. Freeze–Thaw Cycle Test

3.3.1. Weight Loss Rate

According to Figure 8, the rate of weight loss in concrete after freeze–thaw cycles is shown. The test revealed that freeze–thaw cycles resulted in a reduction in concrete weight. The incorporation of MK enhanced the durability of concrete. Moreover, the weight loss rate in concrete due to freeze–thaw cycles decreased as the MK content increased. After 25 freeze–thaw cycles, TRAC-PP showed a weight loss of 0.23%, while the maximum weight loss for MK concrete was 0.17%, with MK-20 exhibiting the lowest weight loss. After 100 cycles, the weight loss rate of MK-20 was only 43.4% of that of TRAC-PP. These results indicated that MK addition significantly improved concrete’s frost resistance, with the 20% MK content demonstrating the highest resistance against freeze–thaw damage.
The weight variation observed during the freeze–thaw cycle was attributed to the migration of solution across the specimen’s surface and within microcracks. The dense microstructure of MK concrete enhanced the adhesion of surrounding fibers, thereby improving the bond between fibers and the matrix. PP fibers effectively mitigated crack formation through a bridging mechanism [39]. Concurrently, the fine particles of MK occupied the interstitial spaces between cement particles, increasing the concrete’s density. This increased density impeded the ingress of water molecules, reducing the osmotic pressure associated with water transport, and improving the concrete’s frost resistance.
Compared to other concretes analyzed in this study, MK-20 showed the lowest rate of weight loss. This result aligns with the findings of Hassan et al. [41], who demonstrated that a high proportion of MK (with an optimal substitution rate of approximately 20%) can greatly improve the durability of self-compacting concrete. Moreover, self-compacting concrete with a high MK content demonstrated greater durability than that containing silica fume.
The results of this study were compared with the existing literature. A study by Meddah et al. [42] indicated that incorporating MK into concrete resulted in enhanced durability, compared to ordinary concrete, such as superior freeze–thaw resistance. Their findings indicated that substituting ordinary Portland cement with up to 20% MK resulted in increased durability. However, substitution rates exceeding 20% did not yield further improvements. Similarly, Mardani-Aghabaglou et al. [43] observed that incorporating 10% MK reduced the weight loss rate of mortar mixtures subjected to freeze–thaw cycles. In the aforementioned studies, the incorporation of MK enhanced the freeze–thaw resistance of concrete. Still, slight variations were found among the results, which may be attributable to differences in testing methodologies.

3.3.2. Relative Compressive Strength

Figure 9 illustrates the change in relative compressive strength of concrete following freeze–thaw cycles. After undergoing 25, 50, 75, and 100 cycles, TRAC-PP’s relative compressive strength was recorded at 93.1%, 89.2%, 84%, and 77.1%, respectively. After 25 cycles, the relative compressive strengths of MK-5, MK-10, MK-15, and MK-20 were 95%, 97.6%, 98.2%, and 98%, respectively. After 100 cycles, these values decreased to 83%, 86.3%, 88.5%, and 90.1%, respectively. As the substitution rate of MK increased, the loss in relative compressive strength decreased, with 20% MK replacement demonstrating the best results. The notable enhancement in freeze–thaw resistance may be ascribed to the supplementary C-S-H generated by the pozzolanic reaction of MK. Additionally, the ultrafine particles of MK increased the density of the concrete matrix, thereby augmenting its strength under freeze–thaw cycles.

3.3.3. Relative Dynamic Modulus of Elasticity

The RDEM serves as a metric for assessing the uniformity and quality of materials. Figure 10 illustrates the variations in RDEM for each concrete sample exposed to freeze–thaw cycles. In general, the RDEM of the samples diminished with an increase in the number of cycles. TRAC-PP underwent freeze–thaw cycles, leading to a reduction in RDEM ranging from 2.9% to 12%. For MK concrete, the reduction rate of RDEM ranged from 1.3% to 9.4%. Therefore, concrete with varying MK content exhibited an enhanced resistance to freeze–thaw cycles than the control concrete TRAC-PP.
The test specimens’ RDEM gradually decreased at the start of the freeze–thaw cycle. However, after 100 cycles, a larger reduction in RDEM was observed. In the early stages, the overall structure of concrete remained relatively dense, and the matrix demonstrated strong resistance to osmotic pressure, resulting in slower crack development. Following repeated freeze–thaw cycles, a higher number of microcracks were observed, showing larger widths and progressive coalescence. Consequently, the RDEM reduction rate accelerated during the later phases of the freeze–thaw test.

3.4. Sulfate Freeze–Thaw Cycle Test

3.4.1. Weight Loss Rate

Figure 11 depicts the weight loss rate of concrete due to sulfate freeze–thaw cycles. As the number of cycles increased, the weight loss rate also progressively rose. During the initial 0–25 cycles, the average weight loss rate for each concrete specimen was 0.19%. In the subsequent stages of 25–50 cycles, 50–75 cycles, and 75–100 cycles, the average weight loss rates were 0.27%, 0.36%, and 0.56%, respectively. The results indicated a faster rate of concrete weight loss during the later phases of the combined sulfate and freeze–thaw cycle erosion test.
Notably, the rate of weight loss increased more rapidly in the absence of MK, as illustrated in Figure 11. Incorporation of MK resulted in a significantly lower weight loss rate. For instance, upon reaching 100 cycles, TRAC-PP’s weight loss rate was 1.92%, in contrast to MK-5, MK-10, MK-15, and MK-20, which had rates of 1.46%, 1.24%, 1.14%, and 1.13%, respectively. These findings indicated that increasing MK content led to a reduction in the weight loss rate. Specifically, the reduction ratio of the MK-20 specimen reached as high as 41.4%. The addition of MK to TRAC-PP enhanced its resistance to freeze–thaw cycle erosion in the sodium sulfate solution.
MK is primarily composed of SiO2 and Al2O3 and facilitates the formation of additional gel materials when used as a partial cement substitute. This results in a denser microstructure, thereby reducing the penetration of sulfate solution into the concrete’s pores. Consequently, the incorporation of MK in concrete enhanced its density and improved its resistance to corrosion under sulfate freeze–thaw cycles.

3.4.2. Relative Compressive Strength

Figure 12 depicts the relative compressive strength of concrete. All concrete specimens exhibited a reduction in relative compressive strength following sulfate freeze–thaw cycles. Following 100 freeze–thaw cycles in water, the decrease in relative compressive strength ranged from 9.9% to 22.9%. In contrast, after 100 freeze–thaw cycles in a 5% sodium sulfate solution, the reduction in relative compressive strength ranged from 22.3% to 31.8%. Freeze–thaw cycles in the 5% sodium sulfate solution caused a significantly higher reduction in relative compressive strength compared to freeze–thaw cycles in the water solution. The results showed that the sodium sulfate solution negatively impacted the freeze–thaw resistance of concrete.
MK substitution in cement resulted in similar changes in relative compressive strength during sulfate freeze–thaw cycles compared to freeze–thaw cycles in water. Among the tested specimens, MK-20 exhibited the highest relative compressive strength, followed sequentially by MK-15, MK-10, and MK-5. When compared to TRAC-PP, the relative compressive strengths of MK-5, MK-10, MK-15, and MK-20 after 100 cycles increased by 4.1%, 7.3%, 10.7%, and 13.9%, respectively. All concrete incorporating MK outperformed those with TRAC-PP.

3.4.3. Relative Dynamic Modulus of Elasticity

Figure 13 illustrates the RDEM of concrete subjected to freeze–thaw cycles in 5% sodium sulfate solution. Under identical cyclic conditions, the RDEM of concrete increased with the MK content. The control concrete (TRAC-PP) exhibited the largest reduction in RDEM, which decreased to 74.8% after 100 cycles. In contrast, the RDEM of concrete with MK content of 5%, 10%, 15%, and 20% decreased to 76.5%, 79%, 80.8%, and 82.8%, respectively. This improvement was attributed to the high reactivity of MK, which interacted with the calcium hydroxide produced during cement hydration, thereby enhancing the microstructure. Cheng et al. [44] further characterized the Ca/Si ratio of the interfacial transition zone (ITZ) in MK-based lightweight aggregate concrete using energy dispersive spectroscopy (EDS). The results indicated that the pozzolanic reaction between MK and calcium hydroxide, produced through cement hydration, contributed to a denser microstructure in the concrete. This higher density was likely responsible for the observed increase in durability under sulfate freeze–thaw cycle conditions.

3.5. SEM Analysis

Figure 14a,b illustrates the SEM images comparing the microstructures of TRAC-PP and MK-20 after compressive strength tests. TRAC-PP shows a loose, porous structure, while MK-20 exhibits a flat and dense structure, indicating that MK reduces porosity. Figure 14c,d displays the SEM images of MK-10 and MK-20 after 100 freeze–thaw cycles in sulfate solution. MK-10 shows needle-like clusters and hexagonal Ca(OH)2 crystals, leading to a loose structure. In contrast, MK-20 shows reduced Ca(OH)2 content and fewer pores, enhancing compactness and resistance to freeze–thaw and sulfate erosion, aligning with previous durability findings.
The optimal MK content for compressive strength is 10%, as it best matches the Ca(OH)2 from cement hydration, forming a strong C-S-H gel that bonds aggregates effectively. A higher MK content, like 20%, may not react fully early on, increasing water demand and potentially reducing strength benefits. The optimal 20% MK dosage enhances durability by effectively consuming Ca(OH)2, a weak phase prone to sulfate attack and freeze–thaw damage. This conversion into C-S-H gels improves chemical stability and refines pore size, increasing capillary tension and frost resistance. Additionally, 20% MK offers a longer lasting pozzolanic reaction due to ample active SiO2 and Al2O3, continuously repairing microcracks and refining pores, unlike the 10% MK dosage.
Thus, 10% MK is ideal for projects needing quick early strength, while 20% MK is better for long-term durability in harsh environments.

3.6. Freeze–Thaw Damage Model and Life Prediction

Freeze–thaw damage refers to the progressive accumulation and development of micro-damage within the concrete due to repeated freeze–thaw cycles during its service life, ultimately leading to the gradual degradation of the concrete’s mechanical properties. The relative compressive strength of the concrete can serve as an indirect measure of its internal compactness. This provides a useful metric for analyzing the evolution process of freeze–thaw damage.
The Grey System Model, GM (1,1), provides a scientific and quantitative approach for predicting uncertain objective phenomena. The fundamental principle of GM (1,1) involves accumulated generation and discrete data to formulate compatible equations that adhere to differential and difference laws. By utilizing a limited set of known data, the model facilitates quantitative predictions of future developmental trends.
Based on the theoretical analysis, the relative compressive strength values at 25, 50, 75, and 100 cycles were utilized as the initial dataset to forecast the damage sustained by concrete under freeze–thaw cycles. Concrete was deemed to have reached the erosion limit when the relative compressive strength fell below 75%.
The Grey System Model was employed to predict the relative compressive strength. The parameters a and b, along with the time response formula of the Grey System Model for the relative compressive strength of five groups of test specimens, are presented in Table 5.
By calculating the variance ratio and the small error probability, the variance ratio for the five groups of test specimens was determined to be less than 0.35, while the small probability error exceeded 0.95. Consequently, the prediction grade was classified as Grade I, indicating very high model accuracy. The predicted values for the relative compressive strength of concrete were derived using the time response formula presented in Table 5, with the results displayed in Table 6.
To ascertain the service life of concrete in natural environments, the service life of concrete was estimated based on the correlation between indoor and outdoor freeze–thaw cycle erosion of concrete in Northwest China, as reported in the previous literature [45]. A past study [45] conducted both natural environment erosion tests and laboratory rapid freeze–thaw cycle tests in Northwest China. The results revealed that one day of freeze–thaw cycling in the laboratory was equivalent to 592.8 days of damage in outdoor conditions.
The ratio of the strength value of concrete in this test to that in the previous study [45,46,47] was utilized as a conversion factor to adjust the test results reported in the aforementioned literature. Based on the predictive data derived from the Grey System Model, the service life of concrete subjected to freeze–thaw conditions in Northwest China was determined, as illustrated in Figure 15.
Figure 15 illustrates the remarkable impact of MK on enhancing the service life of concrete. Specifically, concrete with 20% MK content exhibited optimal durability against freeze–thaw cycle erosion. Compared to the control group TRAC-PP, the MK-20 concrete showed a service life that was 2.50 times longer. According to the experimental results, a well-designed fiber-reinforced tailings recycled aggregate concrete incorporating MK can achieve superior macro-mechanical properties and long-term durability.

4. Conclusions

This research leads to the following conclusions:
(1)
MK exerts high pozzolanic activity, and even a small quantity can substantially increase concrete strength. The cubic and axial compressive strengths of the concrete initially increased with the MK content but subsequently decreased. Concrete achieved its highest strength with a 10% MK content. Overall, the addition of MK can improve these properties by up to 70.4%.
(2)
The durability test results demonstrated that concrete’s performance was compromised by freeze–thaw cycles, but incorporating MK improved its durability. The concrete’s ability to resist freeze–thaw cycles improved as the MK content increased, with 20% being the most effective proportion.
(3)
Damage from freeze–thaw cycles was worsened by exposure to sulfate solutions. The addition of MK to concrete significantly enhanced its resistance to freeze–thaw cycles and mitigated the erosive effects when exposed to both sulfate and freeze–thaw cycles.
(4)
The grey system theory was employed to predict the relative compressive strength of concrete in corrosive environments. The validity of the model was assessed by calculating the variance ratio and small probability error, revealing that the prediction results had high accuracy. The existing literature was comprehensively reviewed. In addition, the relationship between the service life of concrete exposed to the natural environment of Northwest China and that observed under laboratory-accelerated testing was analyzed. MK was found to significantly enhance the durability of concrete. The addition of MK has been shown to increase the service life of concrete subjected to freeze–thaw cycles by a factor of 2.50, thereby substantially contributing to sustainable development.
(5)
Using 5–20% metakaolin enhanced MK concrete’s mechanical properties and durability. For projects needing quick early strength, like early form removal or factory strength, 10% MK is ideal and economically sustainable. For long-term durability, 20% MK is best, maximizing chemical stability and impermeability, suitable for structures in harsh environments like freeze–thaw zones and sulfate soils.

Author Contributions

F.X.: Conceptualization, Experimental design, Formal analysis, Writing-Original Draft Resources, Z.L.: Investigation. H.Y.: Investigation. B.D.: Project administration. All authors have read and agreed to the published version of the manuscript.

Funding

Financial assistance for this study was granted by the Natural Science Foundation of Shaanxi Province (2023-JC-QN-0553) and the Basic Research Program of the Shaanxi Science and Technology Department (2024JC-YBMS-317).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the corresponding authors on request.

Conflicts of Interest

The authors report no conflicts of interest in relation to the publication of this article.

References

  1. Guo, F.; Wang, J.; Song, Y. How to promote sustainable development of construction and demolition waste recycling systems: Production subsidies or consumption subsidies. Sustain. Prod. Consum. 2022, 32, 407–423. [Google Scholar] [CrossRef]
  2. Wang, Z.; Hu, T.; Liu, J. Decoupling economic growth from construction waste generation: Comparative analysis between the EU and China. J. Environ. Manag. 2024, 353, 120144. [Google Scholar] [CrossRef]
  3. Ma, W.; Hao, J.L. Enhancing a circular economy for construction and demolition waste management in China: A stakeholder engagement and key strategy approach. J. Clean. Prod. 2024, 450, 141763. [Google Scholar] [CrossRef]
  4. Bao, Z. Developing circularity of construction waste for a sustainable built environment in emerging economies: New insights from China. Dev. Built Environ. 2023, 13, 100107. [Google Scholar] [CrossRef]
  5. Basaran, B.; Kalkan, I.; Aksoylu, C.; Ozkilic, Y.O.; Sabri, M.M.S. Effects of Waste Powder, Fine and Coarse Marble Aggregates on Concrete Compressive Strength. Sustainability 2022, 14, 14388. [Google Scholar] [CrossRef]
  6. Salgado, F.; Silva, F.D.A. Recycled aggregates from construction and demolition waste towards an application on structural concrete: A review. J. Build. Eng. 2022, 52, 104452. [Google Scholar] [CrossRef]
  7. Ashraf, M.J.; Idrees, M.; Akbar, A. Performance of silica fume slurry treated recycled aggregate concrete reinforced with carbon fibers. J. Build. Eng. 2023, 66, 105892. [Google Scholar] [CrossRef]
  8. Long, H.; Zhu, D.; Pan, J.; Li, S.; Yang, C.; Guo, Z.; Xu, X. A critical review on metallurgical recovery of iron from iron ore tailings. J. Environ. Chem. Eng. 2024, 12, 112140. [Google Scholar] [CrossRef]
  9. Ghasemi, S.; Behnamfard, A.; Arjmand, R. Iron ore tailings valorization through separate characterization and upgradation of different tailings streams of an Iranian iron ore processing plant. Environ. Sci. Pollut. Res. 2023, 30, 115448–115460. [Google Scholar] [CrossRef]
  10. Xu, F.; Wang, S.; Li, T.; Liu, B.; Li, B.; Zhou, Y. The mechanical properties of tailing recycled aggregate concrete and its resistance to the coupled deterioration of sulfate attack and wetting-drying cycles. Structures 2020, 27, 2208–2216. [Google Scholar] [CrossRef]
  11. Xu, F.; Wang, S.; Li, T.; Liu, B.; Li, B.; Zhou, Y. Mechanical properties and pore structure of recycled aggregate concrete made with iron ore tailings and polypropylene fibers. J. Build. Eng. 2021, 33, 1015772. [Google Scholar] [CrossRef]
  12. Guo, Z.; Bai, X.; Liu, S.; Luo, L.; Hao, Y.; Lv, Y.; Xiao, Y.; Yang, J.; Tian, H. Heterogeneous Variations on Historical and Future Trends of CO2 and Multiple Air Pollutants from the Cement Production Process in China: Emission Inventory, Spatial-Temporal Characteristics, and Scenario Projections. Environ. Sci. Technol. 2022, 56, 14306–14314. [Google Scholar] [CrossRef]
  13. Khalid, S.M.; Shobha, M.S. Effect of Ternary Blends on Mechanical Strength, Durability and Microstructural Properties of Geopolymer Concrete. Iran. J. Sci. Technol. Trans. Civ. Eng. 2023, 48, 1395–1411. [Google Scholar] [CrossRef]
  14. Asghari, Y.; Mohammadyan-Yasouj, S.E.; Koloor, S.S.R. Utilization of metakaolin on the properties of self-consolidating concrete: A review. Constr. Build. Mater. 2023, 389, 131605. [Google Scholar] [CrossRef]
  15. Hao, R.; Li, X.; Xu, P.; Liu, Q. Thermal activation and structural transformation mechanism of kaolinitic coal gangue from Jungar coalfield, Inner Mongolia, China. Appl. Clay Sci. 2022, 223, 106508. [Google Scholar] [CrossRef]
  16. Philip, N.; Jedrzejewska, A.; Varughese, A.E.; James, J. Influence of pore structure on corrosion resistance of high performance concrete containing metakaolin. Cem. Wapno Beton 2022, 27, 302–319. [Google Scholar] [CrossRef]
  17. Kumar, K.N.; Divahar, R.; Sangeetha, S.P.; Singh, R.; Akash, M. Enhancing alkaline resistance of concrete using alccofine and metakaolin in mineral admixtures of sustainable development. Eur. J. Environ. Civ. Eng. 2024, 28, 3749–3769. [Google Scholar] [CrossRef]
  18. Jindal, B.B.; Alomayri, T.; Hasan, A.; Kaze, C.R. Geopolymer concrete with metakaolin for sustainability: A comprehensive review on raw material’s properties, synthesis, performance, and potential application. Environ. Sci. Pollut. Res. 2023, 30, 25299–25324. [Google Scholar] [CrossRef] [PubMed]
  19. Zheng, C.; Wan, S.; Zong, Z. Durability evaluation and lifetime prediction of recycled coarse aggregate self-compacting concrete after freeze–thaw and sulfate erosion coupling. Mater. Today Commun. 2024, 39, 109115. [Google Scholar] [CrossRef]
  20. Ziada, M.; Tanyildizi, H.; Uysal, M. Bacterial healing of geopolymer concrete exposed to combined sulfate and freeze–thaw effects. Constr. Build. Mater. 2023, 369, 130517. [Google Scholar] [CrossRef]
  21. Tanyildizi, H. Durability of concrete exposed to combined freeze–thaw, sulfate, and acid attacks after two years. Rev. Constr. 2023, 22, 102–121. [Google Scholar] [CrossRef]
  22. Farhan, K.Z.; Megat, A.M.J.; Demirboga, R. Performance of polypropylene fiber reinforced GGBFS-based alkali activated composites under sulfate and freeze–thaw conditions. Mater. Struct. 2023, 56, 44. [Google Scholar] [CrossRef]
  23. Xu, F.; Wang, S.; Li, T.; Liu, B.; Zhao, N.; Liu, K. The mechanical properties and resistance against the coupled deterioration of sulfate attack and freeze–thaw cycles of tailing recycled aggregate concrete. Constr. Build. Mater. 2021, 269, 121273. [Google Scholar]
  24. Bao, W.; Yin, Y.; Mi, W.; Chen, R.; Lin, X. Durability and microstructural evolution of high-performance ecological geopolymer concrete under low-pressure-salt-erosion-freeze–thaw cycling conditions. Constr. Build. Mater. 2024, 426, 136197. [Google Scholar] [CrossRef]
  25. Ayano, T.; Fujii, T.; Okazaki, K. freeze–thaw Resistance of Concrete using Ground Granulated Blast-furnace Slag and Blast-furnace Slag Sand in Salt Water. J. Adv. Concr. Technol. 2024, 22, 253–266. [Google Scholar] [CrossRef]
  26. Gregory, D.Z. Chitosan-Based Shrinking Fibers for Post-Cure Stressing to Increase Durability of Concrete. Master’s Thesis, University of Vermont, Burlington, VT, USA, 2022. [Google Scholar]
  27. Majhi, R.K.; Nayak, A.N.; Mukharjee, B.B. Development of sustainable concrete using recycled coarse aggregate and ground granulated blast furnace slag. Constr. Build. Mater. 2018, 159, 417–430. [Google Scholar] [CrossRef]
  28. Rao, M.C.; Bhattacharyya, S.K.; Barai, S.V. Influence of field recycled coarse aggregate on properties of concrete. Mater. Struct. 2011, 44, 205–220. [Google Scholar]
  29. Ceia, F.; Raposo, J.; Guerra, M.; Julio, E.; de Brito, J. Shear strength of recycled aggregate concrete to natural aggregate concrete interfaces. Constr. Build. Mater. 2016, 109, 139–145. [Google Scholar] [CrossRef]
  30. Pereira-de-Oliveira, L.A.; Nepomuceno, M.C.S.; Castro-Gomes, J.P.; Vila, M.F.C. Permeability properties of self-compacting concrete with coarse recycled aggregates. Constr. Build. Mater. 2014, 51, 113–120. [Google Scholar] [CrossRef]
  31. Ulucan, M.; Alyamac, K.E. A holistic assessment of the use of emerging recycled concrete aggregates after a destructive earthquake: Mechanical, economic and environmental. Waste Manag. 2022, 146, 53–65. [Google Scholar] [CrossRef]
  32. Tang, Y.; Xiao, J.; Zhang, H.; Duan, Z.; Xia, B. Mechanical properties and uniaxial compressive stress-strain behavior of fully recycled aggregate concrete. Constr. Build. Mater. 2022, 323, 126546. [Google Scholar] [CrossRef]
  33. Tabsh, S.W.; Alhoubi, Y. Experimental Investigation of Recycled Fine Aggregate from Demolition Waste in Concrete. Sustainability 2022, 14, 10787. [Google Scholar] [CrossRef]
  34. Kim, J.; Grabiec, A.M.; Ubysz, A. An Experimental Study on Structural Concrete Containing Recycled Aggregates and Powder from Construction and Demolition Waste. Materials 2022, 15, 2458. [Google Scholar] [CrossRef]
  35. Kang, X.; Tong, X.-Y.; Chen, R.-P.; Chen, Y.-Q. Effect of ITZ on chloride ion transport in recycled aggregate concrete: Analytical and numerical studies. J. Build. Eng. 2024, 83, 108443. [Google Scholar] [CrossRef]
  36. Joseph, A.M.; Matthys, S.; De Belie, N. Properties of Concrete with Recycled Aggregates Giving a Second Life to Municipal Solid Waste Incineration Bottom Ash Concrete. Sustainability 2022, 14, 4679. [Google Scholar] [CrossRef]
  37. JG 175-2007; Common Portland Cement. Ministry of Housing and Urban-Rural Construction of the People’s Republic of China: Beijing, China, 2007.
  38. JGJ 52-2006; Standard for Technical Requirements and Test Method of Sand and Crushed Stone (or Gravel) for Ordinary Concrete. Ministry of Housing and Urban-Rural Construction of the People’s Republic of China: Beijing, China, 2006.
  39. Homayoonmehr, R.; Ramezanianpour, A.A.; Mirdarsoltany, M. Influence of metakaolin on fresh properties, mechanical properties and corrosion resistance of concrete and its sustainability issues: A review. J. Build. Eng. 2021, 44, 103011. [Google Scholar] [CrossRef]
  40. Nežerka, V.; Bílý, P.; Hrbek, V.; Fládr, J. Impact of silica fume, fly ash, and metakaolin on the thickness and strength of the ITZ in concrete. Cem. Concr. Compos. 2019, 103, 252–262. [Google Scholar] [CrossRef]
  41. Hassan, A.A.A.; Lachemi, M.; Hossain, K.M.A. Effect of metakaolin and silica fume on the durability of self-consolidating concrete. Cem. Concr. Compos. 2012, 34, 801–807. [Google Scholar] [CrossRef]
  42. Meddah, M.S.; Ismail, M.A.; El-Gamal, S.; Fitriani, H. Performances evaluation of binary concrete designed with silica fume and metakaolin. Constr. Build. Mater. 2018, 166, 400–412. [Google Scholar] [CrossRef]
  43. Mardani-Aghabaglou, A.; Sezer, G.I.; Ramyar, K. Comparison of fly ash, silica fume and metakaolin from mechanical properties and durability performance of mortar mixtures view point. Constr. Build. Mater. 2014, 70, 17–25. [Google Scholar] [CrossRef]
  44. Cheng, S.; Shui, Z.; Li, Q.; Sun, T.; Yang, R. Properties, microstructure and hydration products of lightweight aggregate concrete with metakaolin and slag addition. Constr. Build. Mater. 2016, 127, 59–67. [Google Scholar] [CrossRef]
  45. Qiao, H.X.; Guo, F.; Lu, C.G.; He, H.J. Exposure environment ordinary concrete durability test and life prediction research based on the acceleration coefficient K method. Concrete 2020, 4, 148–152+156. [Google Scholar]
  46. Liu, Y.; Wu, H.; Gao, Y.; Wang, W.; Wang, Z. Influence of macadamia nutshell particles on the apparent density and mechanical behavior of cement-based mortars. Constr. Build. Mater. 2024, 411, 134600. [Google Scholar] [CrossRef]
  47. Liu, Y.; He, J.; Liang, J.; Wang, W.; Wang, Z. A new improved particle swarm algorithm for optimization of anchor lattice beam support structures. Nat. Hazards 2024, 121, 225–243. [Google Scholar] [CrossRef]
Buildings 15 03428 g001
Figure 1. Particle size distribution diagram.
Figure 1. Particle size distribution diagram.
Buildings 15 03428 g001
Buildings 15 03428 g002
Figure 2. Surface topography of the materials.
Figure 2. Surface topography of the materials.
Buildings 15 03428 g002
Buildings 15 03428 g003
Figure 3. Rapid freeze–thaw test machine.
Figure 3. Rapid freeze–thaw test machine.
Buildings 15 03428 g003
Buildings 15 03428 g004
Figure 4. Rubber test piece box.
Figure 4. Rubber test piece box.
Buildings 15 03428 g004
Buildings 15 03428 g005
Figure 5. Cubic compressive strength of the concrete.
Figure 5. Cubic compressive strength of the concrete.
Buildings 15 03428 g005
Buildings 15 03428 g006
Figure 6. Impact of curing time on the compressive strength of concrete.
Figure 6. Impact of curing time on the compressive strength of concrete.
Buildings 15 03428 g006
Buildings 15 03428 g007
Figure 7. Axial compressive strength of the concrete.
Figure 7. Axial compressive strength of the concrete.
Buildings 15 03428 g007
Buildings 15 03428 g008
Figure 8. Weight loss rate of concrete after freeze–thaw cycle.
Figure 8. Weight loss rate of concrete after freeze–thaw cycle.
Buildings 15 03428 g008
Buildings 15 03428 g009
Figure 9. Relative compressive strength of concrete after freeze–thaw cycle.
Figure 9. Relative compressive strength of concrete after freeze–thaw cycle.
Buildings 15 03428 g009
Buildings 15 03428 g010
Figure 10. RDEM of concrete after freeze–thaw cycle.
Figure 10. RDEM of concrete after freeze–thaw cycle.
Buildings 15 03428 g010
Buildings 15 03428 g011
Figure 11. Weight loss rate of concrete after sulfate freeze–thaw cycles.
Figure 11. Weight loss rate of concrete after sulfate freeze–thaw cycles.
Buildings 15 03428 g011
Buildings 15 03428 g012
Figure 12. Relative compressive strength of concrete after sulfate freeze–thaw cycles.
Figure 12. Relative compressive strength of concrete after sulfate freeze–thaw cycles.
Buildings 15 03428 g012
Buildings 15 03428 g013
Figure 13. RDEM of concrete after sulfate freeze–thaw cycles.
Figure 13. RDEM of concrete after sulfate freeze–thaw cycles.
Buildings 15 03428 g013
Buildings 15 03428 g014aBuildings 15 03428 g014b
Figure 14. SEM images.
Figure 14. SEM images.
Buildings 15 03428 g014aBuildings 15 03428 g014b
Buildings 15 03428 g015
Figure 15. Service life of concrete subjected to freeze–thaw conditions (year).
Figure 15. Service life of concrete subjected to freeze–thaw conditions (year).
Buildings 15 03428 g015
Table 1. Primary physical characteristics of the water reducer.
Table 1. Primary physical characteristics of the water reducer.
Density (g/m3)pH ValuesWater
Solubility		CL—Content (%)Na2SO4 Content (%)R2O Content (%)
1.05 ± 0.26∼7Immiscible≤1.0≤2.0≤5.0
Table 2. Characteristics of waste PP fibers.
Table 2. Characteristics of waste PP fibers.
Length
(mm)		Tensile Strength
(MPa)		Specific Gravity (kg/cm3)Elongation
at Break (%)		Elastic Modulus (MPa)Retention Rate of Alkali Resistance (%)
22>3501.1212–40>4000>94.4
Table 3. Chemical composition of MK.
Table 3. Chemical composition of MK.
Chemical CompositionAl2O3SiO2K2OFe2O3Na2OCaO
Content/%44.5450.050.100.3660.060.14
Table 4. Mix proportions.
Table 4. Mix proportions.
Specimen
Number		MK (kg/m3)Cement (kg/m3)NCA
(kg/m3)		IOTs
(kg/m3)		Natural Sand
(kg/m3)		PP Fibers (%)RCA
(kg/m3)		Water
(kg/m3)
TRAC-PP05377441724000.6319215
MK-526.85510.157441724000.6319215
MK-1053.7483.37441724000.6319215
MK-1580.55456.457441724000.6319215
MK-20107.4429.67441724000.6319215
Table 5. Parameters a, b, and the time response formula of the Grey System Model.
Table 5. Parameters a, b, and the time response formula of the Grey System Model.
SpecimenabTime Response Formula
TRAC-PP0.60.0611.030 X 1 ∧ ( k + 1 ) = − 15.745 e − 0.062 k + 16.745
MK-50.0451.027 X 1 ∧ ( k + 1 ) = − 21.633 e − 0.045 k + 22.633
MK-100.0411.042 X 1 ∧ ( k + 1 ) = − 24.424 e − 0.041 k + 25.424
MK-150.0341.035 X 1 ∧ ( k + 1 ) = − 29.207 e − 0.034 k + 30.207
MK-200.0281.028 X 1 ∧ ( k + 1 ) = − 35.279 e − 0.028 k + 36.279
Table 6. The predicted values of the relative compressive strength.
Table 6. The predicted values of the relative compressive strength.
SpecimenNumber of Freeze–Thaw Cycles
0255075100125150175200225250
TRAC-PP0.610.9390.8830.8300.781--
MK-510.9590.9170.8760.8370.8000.765----
MK-1010.9810.9420.9040.8670.8330.7990.767---
MK-1510.9840.9510.9190.8880.8580.8290.8010.7740.748-
MK-2010.9860.9580.9310.9050.8800.8560.8320.8080.7860.764
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Xu, F.; Li, Z.; Ying, H.; Du, B. Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles. Buildings 2025, 15, 3428. https://doi.org/10.3390/buildings15183428

AMA Style

Xu F, Li Z, Ying H, Du B. Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles. Buildings. 2025; 15(18):3428. https://doi.org/10.3390/buildings15183428

Chicago/Turabian Style

Xu, Fan, Zhijun Li, Honghao Ying, and Bin Du. 2025. "Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles" Buildings 15, no. 18: 3428. https://doi.org/10.3390/buildings15183428

APA Style

Xu, F., Li, Z., Ying, H., & Du, B. (2025). Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles. Buildings, 15(18), 3428. https://doi.org/10.3390/buildings15183428

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop