An Innovative Material with Strong Frost Resistance—Concrete Containing Dolomite Powder

The effects of dolomite powder on the freeze–thaw resistance of C30 and C45 concrete were investigated in this manuscript. Scanning electron microscopy (SEM), the electric flux method, and a freeze–thaw cycle testing machine were used to determine the morphology, chloride penetration resistance, mass loss rate, and relative dynamic elastic modulus (Er) of concrete incorporating dolomite powder. Concrete’s freeze–thaw resistance improved as the dosage of dolomite powder was increased. After 300 cycles, the mass loss rates of reference specimens of C30 and C45 concrete were 6.71% and 0.14%, respectively, whereas the mass loss rates of C30 and C45 concrete in the presence of dolomite powder at a 50% replacement level were 5.81% and 0.13%, respectively. After 225 cycles, the Er of C30 concrete was 42.57% and 48.56% in the case of dolomite powder at 0 and 50% replacement levels, respectively. Meanwhile, after 300 cycles, the Er of C45 concrete was 67.54% and 71.50% in the case of dolomite powder at 0 and 50% replacement levels, respectively. Accordingly, the structure of dolomite-containing cement-based materials became more compact. Based on the Weibull distribution, a damage model for concrete containing dolomite powder was proposed. It established that concrete treated with dolomite powder had a lower degree of damage than reference specimens when subjected to the same freeze–thaw conditions.


Introduction
Dolomite is an essential carbonate rock, a compound composed of calcium, magnesium, and carbonate ions with the formula CaMg(CO 3 ) 2 that can act as a source of carbon dioxide and magnesium [1][2][3]. Dolomite was discovered to be widely distributed throughout the world, with over 4 billion tons discovered in China [4,5]. Previously, dolomite was considered an inert material and was calcined at high temperatures to be used as a building material. Magnesium cement was made by combining dolomite and magnesite that had been calcined [6]. Xie et al. discovered that cementitious materials containing lightburned dolomite had a higher strength than cement blended with dolomite [7]. Numerous correlations between aggregate minerals and concrete specimens have been reported by some researchers [8,9]. When dolomite was used as coarse aggregate in concrete, it was demonstrated that an alkali-aggregate reaction could occur [10]. Thus, some researchers ground dolomite into powder and then added it as a mineral admixture to cement-based materials [11]. The substitution of dolomite powder for cement clinker facilitated energy savings and environmental protection.
Recently, more attention has been paid to the research of dolomite powder as a mineral admixture for cement-based materials. Numerous studies established that dolomite powder influenced the working properties, cement hydration process, and mechanical properties of concrete [12,13]. Yan et al. discovered that as the specific surface area of dolomite powder increased, the fluidity and dry shrinkage of mortar increased as well [14]. Gali  Table 3. Chemical composition of fly ash (wt.%). prepared. Superplasticizer was used to maintain a stable fluidity due to the high fineness of dolomite powder.

SEM Test
To examine the microstructure of the specimen, the accelerating voltage was set as 15 KV. Slices of the hydrated cement paste were cut. The immersion time of the slices in ethanol absolute lasted for one week. Subsequently, the slices were dried overnight at 40 °C and then stored in a vacuum desiccator. Eventually, a piece of slice was examined with the SEM (TM4000, Hitachi Limited, Tokyo, Japan).

Test Design of Chloride-Penetration Resistance
The chloride-penetration resistance of concretes mixed with dolomite powder was performed using the electric flux method. Specimens of cylinders with a diameter of 100 mm were cast. The specimens were taken out from the standard curing room after 28 days of curing, then the specimens were saturated with water in vacuum before the measurement. The measurement was repeated at three times for reproducibility by concrete electric flux meter (TR-SDL, Shanghai Tongrui Instrument Equipment Co., Ltd, Shanghai, China). The electric flux value of each specimen was calculated according to GB/T50082-2009 [31].

Test Design of Frost Resistance Durability
Concretes were made according to a quick freezing method following the standards (GB/T50082-2009) [31]. Three prism specimens of 400 × 100 × 100 mm 3 were cast. The measurement was repeated at three times for reproducibility by concrete rapid freezing and thawing testing machine (TR-TDRF-28, Shanghai Tongrui Instrument Equipment Co., Ltd, Shanghai, China). The specimens were taken out from the standard curing room after 24 days of curing, and then the specimens were immersed in water for 4 days, i.e., the freezethaw test of the specimens was performed after 28 days of curing. The temperature of the specimen center ranged from (−18 ± 2) °C to (5 ± 2) °C. During every 25 cycles, the damage shapes, mass loss rate and relative dynamic elastic modulus of concretes with different compositions under the freeze-thaw cycles were tested.

Mass Loss Rate Test
The mass loss rate test was performed in accordance with GB/T50082-2009 [31]. Before placing the specimens into the freeze-thaw test box, the initial mass of the specimens was weighed. During every 25 cycles, the mass of the specimens was measured. The mass loss rate was calculated using the Equations (1) and (2) as given below: The cement pastes were made for SEM measurement (TM4000, Hitachi Limited, Tokyo, Japan). C30 and C45 concretes were cast for the mass loss rate and relative dynamic elastic modulus tests under the freeze-thaw cycles. The water-to-binder ratio in cement paste was 0.36. It was noted that binder materials in this work included cement and fly ash. C30 and C45 concretes with two water to binder ratios (0.55 and 0.36) were prepared. Superplasticizer was used to maintain a stable fluidity due to the high fineness of dolomite powder.

SEM Test
To examine the microstructure of the specimen, the accelerating voltage was set as 15 KV. Slices of the hydrated cement paste were cut. The immersion time of the slices in ethanol absolute lasted for one week. Subsequently, the slices were dried overnight at 40 • C and then stored in a vacuum desiccator. Eventually, a piece of slice was examined with the SEM (TM4000, Hitachi Limited, Tokyo, Japan).

Test Design of Chloride-Penetration Resistance
The chloride-penetration resistance of concretes mixed with dolomite powder was performed using the electric flux method. Specimens of cylinders with a diameter of 100 mm were cast. The specimens were taken out from the standard curing room after 28 days of curing, then the specimens were saturated with water in vacuum before the measurement. The measurement was repeated at three times for reproducibility by concrete electric flux meter (TR-SDL, Shanghai Tongrui Instrument Equipment Co., Ltd., Shanghai, China). The electric flux value of each specimen was calculated according to GB/T50082-2009 [31].

Test Design of Frost Resistance Durability
Concretes were made according to a quick freezing method following the standards (GB/T50082-2009) [31]. Three prism specimens of 400 × 100 × 100 mm 3 were cast. The measurement was repeated at three times for reproducibility by concrete rapid freezing and thawing testing machine (TR-TDRF-28, Shanghai Tongrui Instrument Equipment Co., Ltd., Shanghai, China). The specimens were taken out from the standard curing room after 24 days of curing, and then the specimens were immersed in water for 4 days, i.e., the freeze-thaw test of the specimens was performed after 28 days of curing. The temperature of the specimen center ranged from (−18 ± 2) • C to (5 ± 2) • C. During every 25 cycles, the damage shapes, mass loss rate and relative dynamic elastic modulus of concretes with different compositions under the freeze-thaw cycles were tested.

Mass Loss Rate Test
The mass loss rate test was performed in accordance with GB/T50082-2009 [31]. Before placing the specimens into the freeze-thaw test box, the initial mass of the specimens was weighed. During every 25 cycles, the mass of the specimens was measured. The mass loss rate was calculated using the Equations (1) and (2) as given below: In which ∆W ni : Mass loss rate of specimen i after n freeze-thaw cycles, %; W oi : Mass of specimen i before the freeze-thaw test, g; W ni : Mass of specimen i after n freeze-thaw cycles, g.
In which ∆W n : Average mass loss rate of a group of specimens (three parallel specimens) after n freeze-thaw cycles, %.

Relative Dynamic Elastic Modulus Test
The relative dynamic elastic modulus test was performed based on GB/T50082-2009 [31]. The size of specimens was 400 × 100 × 100 mm 3 . During every 25 cycles, the relative dynamic elastic modulus of the specimens was measured by dynamic elastic modulus testing machine (DT-20, Jinan Langrui Testing Technology Co., Ltd., Jinan, China). The relative dynamic elastic modulus was calculated using the Equation (3) as given below: In which E i : The relative dynamic elastic modulus of specimen i after n freeze-thaw cycles, %; f ni : Transverse fundamental frequency of specimen i after n freeze-thaw cycles, Hz; f n0 : Transverse fundamental frequency of specimen i before the freeze-thaw test, Hz.

Establishment of Damage Model of Concretes Incorporating Dolomite Powder Based on Two-Parameter Weibull Distribution
The freeze-thaw damage of the concretes resulted in declines of the relative dynamic elastic modulus, which reflected the structure changes inside the concrete. Thus, the E r was selected to describe the degradation rules of concretes blended with dolomite powder. Combined with damage mechanics, the degree of the freeze-thaw damage could be expressed as [32]: In which D N : The freeze-thaw damage degree; E i : The relative dynamic elastic modulus of specimen i after n freeze-thaw cycles. The Weibull distribution had an increasing hazard function with time and was commonly used for describing the process of material failure [33]. In this manuscript, the Weibull distribution was used to study the damage model of concretes incorporating dolomite powder. The equation of two-parameter Weibull distribution was defined as: In which When the Weibull distribution was suitable to describe the service life of concretes incorporating dolomite powder under the freeze-thaw cycles, the freeze-thaw damage degree was equivalent to the distribution function. The equation was expressed as: Taking the logarithm twice of both sides of Equation (6): To simplify the calculation, mathematical transformation was made: Equation (8) could be written in the following form: Figure 2a depicts the morphology of dolomite powder. The shape of dolomite powder was identified as a trigonal system in Figure 2a. The PDF0 specimen's morphology after 90 days is depicted in Figure 2b. The reference specimen developed some microcracks and micropores. In other words, the PDF0 specimen's structure was relatively loose. Additionally, a few spherical hollow particles precipitated in the vicinity of the micro-pore. According to the morphology analysis, the spherical hollow particles could be identified as fly ash. After 90 days, the morphology of cement pastes containing 50% dolomite powder was observed in Figure 2c. Cement paste containing dolomite powder exhibited a more compact structure than the PDF0 specimen. Cuboidal hydrate phases (shown in blue circles in Figure 2c) precipitated in the vicinity of the micro-pore. In conjunction with Figure 2a, this implied that the cuboidal hydrate phases should be composed of dolomite powder. Thus, dolomite powder was used to fill micro-cracks and micro-pores in cement paste, resulting in the refinement of the cement paste structure.

SEM Test
Materials 2022, 15, x FOR PEER REVIEW When the Weibull distribution was suitable to describe the service l incorporating dolomite powder under the freeze-thaw cycles, the freeze degree was equivalent to the distribution function. The equation was expr Taking the logarithm twice of both sides of Equation (6): To simplify the calculation, mathematical transformation was made: Equation (8) could be written in the following form: Figure 2a depicts the morphology of dolomite powder. The shape of der was identified as a trigonal system in Figure 2a. The PDF0 specimen after 90 days is depicted in Figure 2b. The reference specimen develo crocracks and micropores. In other words, the PDF0 specimen's structure loose. Additionally, a few spherical hollow particles precipitated in the vic cro-pore. According to the morphology analysis, the spherical hollow pa identified as fly ash. After 90 days, the morphology of cement pastes cont lomite powder was observed in Figure 2c. Cement paste containing dolom hibited a more compact structure than the PDF0 specimen. Cuboidal h (shown in blue circles in Figure 2c) precipitated in the vicinity of the micr junction with Figure 2a, this implied that the cuboidal hydrate phases s posed of dolomite powder. Thus, dolomite powder was used to fill microcro-pores in cement paste, resulting in the refinement of the cement paste (a)  Figure 3 depicts the relationship between the electric flux of C30 and C45 concrete and the dosage of dolomite powder. The results indicate that by adding dolomite powder to C30 and C45 concrete, the electric flux was decreased. Electric flux values for CD0-L, CD3-L, and CD5-L specimens of C30 concrete were 3691C, 2808C, and 2615C, respectively. Electric flux values for CD0-H, CD3-H, and CD5-H specimens of C45 concrete were 1991C, 1803C, and 1462C, respectively. It was obvious that resistance to chloride penetration increased. This was because the addition of dolomite powder increased the density of the concrete structure. Thus, by adding dolomite powder, the chloride ion penetration was inhibited, and the impermeability of concrete was increased. This analysis corroborated the SEM test results.

Damage Shapes of Different Freeze-Thaw Cycles
The damage shapes of C30 and C45 concrete with varying compositions at various stages of the freeze-thaw cycle are depicted in Figures 4 and 5. As illustrated in Figure 4, the increased frequency of freeze-thaw cycles accelerated the deterioration of C30 concrete. Concrete had a smooth surface prior to the freeze-thaw cycles. After 50 freeze-thaw cycles, the concrete began to peel away from the surface, and a small pit formed. When the freeze-thaw cycles reached 150, a significant amount of mortar fell off the concrete surface, enlarging the pit area, particularly in the left area of the CD0-L specimen's surface. After 200 cycles, the coarse aggregate within the reference specimen was gradually exposed to the surface, whereas the coarse aggregate had not yet appeared on the surface  The results indicate that by adding dolomite powder to C30 and C45 concrete, the electric flux was decreased. Electric flux values for CD0-L, CD3-L, and CD5-L specimens of C30 concrete were 3691C, 2808C, and 2615C, respectively. Electric flux values for CD0-H, CD3-H, and CD5-H specimens of C45 concrete were 1991C, 1803C, and 1462C, respectively. It was obvious that resistance to chloride penetration increased. This was because the addition of dolomite powder increased the density of the concrete structure. Thus, by adding dolomite powder, the chloride ion penetration was inhibited, and the impermeability of concrete was increased. This analysis corroborated the SEM test results.  Figure 3 depicts the relationship between the electric flux of C30 and C45 concrete and the dosage of dolomite powder. The results indicate that by adding dolomite powder to C30 and C45 concrete, the electric flux was decreased. Electric flux values for CD0-L, CD3-L, and CD5-L specimens of C30 concrete were 3691C, 2808C, and 2615C, respectively. Electric flux values for CD0-H, CD3-H, and CD5-H specimens of C45 concrete were 1991C, 1803C, and 1462C, respectively. It was obvious that resistance to chloride penetration increased. This was because the addition of dolomite powder increased the density of the concrete structure. Thus, by adding dolomite powder, the chloride ion penetration was inhibited, and the impermeability of concrete was increased. This analysis corroborated the SEM test results.

Damage Shapes of Different Freeze-Thaw Cycles
The damage shapes of C30 and C45 concrete with varying compositions at various stages of the freeze-thaw cycle are depicted in Figures 4 and 5. As illustrated in Figure 4, the increased frequency of freeze-thaw cycles accelerated the deterioration of C30 concrete. Concrete had a smooth surface prior to the freeze-thaw cycles. After 50 freeze-thaw cycles, the concrete began to peel away from the surface, and a small pit formed. When the freeze-thaw cycles reached 150, a significant amount of mortar fell off the concrete surface, enlarging the pit area, particularly in the left area of the CD0-L specimen's surface. After 200 cycles, the coarse aggregate within the reference specimen was gradually exposed to the surface, whereas the coarse aggregate had not yet appeared on the surface

Damage Shapes of Different Freeze-Thaw Cycles
The damage shapes of C30 and C45 concrete with varying compositions at various stages of the freeze-thaw cycle are depicted in Figures 4 and 5. As illustrated in Figure 4, the increased frequency of freeze-thaw cycles accelerated the deterioration of C30 concrete. Concrete had a smooth surface prior to the freeze-thaw cycles. After 50 freeze-thaw cycles, the concrete began to peel away from the surface, and a small pit formed. When the freeze-thaw cycles reached 150, a significant amount of mortar fell off the concrete surface, enlarging the pit area, particularly in the left area of the CD0-L specimen's surface. After 200 cycles, the coarse aggregate within the reference specimen was gradually exposed to the surface, whereas the coarse aggregate had not yet appeared on the surface of dolomitepowder-infused concrete. When the freeze-thaw cycle was repeated 225 times, a large amount of coarse aggregate was exposed on the reference specimen's surface, and numerous small pits were connected to form large pits. The CD3-L specimen sustained relatively minor damage compared to the CD0-L specimen, and a small amount of coarse aggregate was exposed on the surface of the CD5-L specimen following 225 cycles. After 300 freezethaw cycles, the mortar spalling area spread to the entire surface of the concrete. Meanwhile, the mortar on the concrete surface was nearly imperceptible, and the specimens' edges had been damaged. In general, increasing the dosage of dolomite powder reduced the degree of damage to concrete caused by freeze-thaw cycles. The surface of C45 concrete was relatively intact and smooth, and the mortar on the concrete surface did not peel off evidently before 250 cycles, as illustrated in Figure 5a-c. After 300 freeze-thaw cycles, a small amount of mortar began to peel away from the reference specimen's surface, whereas there was no apparent mortar peeling away from the dolomite powder-infused concrete. C45 concrete has a lower damage degree than C30 concrete when subjected to the same freeze-thaw condition. of dolomite-powder-infused concrete. When the freeze-thaw cycle was repeated 225 times, a large amount of coarse aggregate was exposed on the reference specimen's surface, and numerous small pits were connected to form large pits. The CD3-L specimen sustained relatively minor damage compared to the CD0-L specimen, and a small amount of coarse aggregate was exposed on the surface of the CD5-L specimen following 225 cycles. After 300 freeze-thaw cycles, the mortar spalling area spread to the entire surface of the concrete. Meanwhile, the mortar on the concrete surface was nearly imperceptible, and the specimens' edges had been damaged. In general, increasing the dosage of dolomite powder reduced the degree of damage to concrete caused by freeze-thaw cycles. The surface of C45 concrete was relatively intact and smooth, and the mortar on the concrete surface did not peel off evidently before 250 cycles, as illustrated in Figure 5a-c. After 300 freeze-thaw cycles, a small amount of mortar began to peel away from the reference specimen's surface, whereas there was no apparent mortar peeling away from the dolomite powder-infused concrete. C45 concrete has a lower damage degree than C30 concrete when subjected to the same freeze-thaw condition.   Figure 6 depicts the mass loss rate of concrete due to freeze-thaw cycles. The mass loss rate of C30 concrete is depicted in Figure 6a. As illustrated in Figure 6a, the rate of mass loss from C30 concrete increased as the number of freeze-thaw cycles increased. When the number of freeze-thaw cycles was low, the rate of mass loss was gradual. After 150 freeze-thaw cycles, the mass loss rate of C30 concrete increased significantly. When freeze-thaw cycles were repeated 25 times, the mass loss rates of C30 concrete with various dolomite powder dosages ranged from 0.39% to 0.44%. After 150 cycles, the mass loss rates were determined to be 2.65-2.89%. Meanwhile, the mass loss rates of C30 concrete decreased as dolomite powder dosage was increased. After 25 cycles, the mass loss rates were 0.44%, 0.41%, and 0.39% for CD0-L, CD3-L, and CD5-L specimens, respectively. When the freeze-thaw cycle was repeated 300 times, the mass loss rates of concrete increased to 6.71%, 6.33%, and 5.81% for dolomite powder at 0%, 30%, and 50% replacement levels, respectively. The mass loss rate experiment indicated that the reference specimen of C30 concrete was close to failing after 225 freeze-thaw cycles, whereas concrete blended with dolomite powder failed after 250 freeze-thaw cycles [31]. This result was determined by the damage shapes associated with various freeze-thaw cycles depicted in Figure 4. It demonstrated that dolomite power slowed the mass loss rate of C30 concrete. The mass loss rate of C45 concrete is depicted in Figure 6b. As a result, the development of the concrete's mass loss rate due to freeze-thaw cycles varied between C30 and C45. Prior to 150 cycles, the mass loss rate grew at a negative rate, but increased to a positive rate after 150 cycles. Due to the low water-to-cement ratio in C45 concrete, the structure was relatively dense. When the number of freeze-thaw cycles was low, C45 concrete suffered minor damage. The concrete contained gel holes, pores, and bubbles. During freeze-thaw cycles, the water and ice in the concrete pores were constantly transformed, resulting in volume expansion [34][35][36]. As a result, the porosity of C45 concrete increased. Water molecules migrated continuously into the concrete's interior, increasing the moisture content. Thus, when the number of cycles was low, the mass of C45 concrete increased. The freeze-thaw cycles severely damaged the concrete after 150 cycles. Increased concrete mass was insufficient to compensate for the loss. The mass loss rates of CD0-H, CD3-H, and CD5-H specimens were 0.09%, 0.07%, and −0.04%, respectively, when 200 freeze-thaw cycles were performed. After 300 cycles, the mass loss rate of C45 concrete was 0.14%, while concrete incorporating dolomite powder lost mass at a rate of 0.13%. These results demonstrate  Figure 6 depicts the mass loss rate of concrete due to freeze-thaw cycles. The mass loss rate of C30 concrete is depicted in Figure 6a. As illustrated in Figure 6a, the rate of mass loss from C30 concrete increased as the number of freeze-thaw cycles increased. When the number of freeze-thaw cycles was low, the rate of mass loss was gradual. After 150 freezethaw cycles, the mass loss rate of C30 concrete increased significantly. When freeze-thaw cycles were repeated 25 times, the mass loss rates of C30 concrete with various dolomite powder dosages ranged from 0.39% to 0.44%. After 150 cycles, the mass loss rates were determined to be 2.65-2.89%. Meanwhile, the mass loss rates of C30 concrete decreased as dolomite powder dosage was increased. After 25 cycles, the mass loss rates were 0.44%, 0.41%, and 0.39% for CD0-L, CD3-L, and CD5-L specimens, respectively. When the freezethaw cycle was repeated 300 times, the mass loss rates of concrete increased to 6.71%, 6.33%, and 5.81% for dolomite powder at 0%, 30%, and 50% replacement levels, respectively. The mass loss rate experiment indicated that the reference specimen of C30 concrete was close to failing after 225 freeze-thaw cycles, whereas concrete blended with dolomite powder failed after 250 freeze-thaw cycles [31]. This result was determined by the damage shapes associated with various freeze-thaw cycles depicted in Figure 4. It demonstrated that dolomite power slowed the mass loss rate of C30 concrete. The mass loss rate of C45 concrete is depicted in Figure 6b. As a result, the development of the concrete's mass loss rate due to freeze-thaw cycles varied between C30 and C45. Prior to 150 cycles, the mass loss rate grew at a negative rate, but increased to a positive rate after 150 cycles. Due to the low water-to-cement ratio in C45 concrete, the structure was relatively dense. When the number of freeze-thaw cycles was low, C45 concrete suffered minor damage. The concrete contained gel holes, pores, and bubbles. During freeze-thaw cycles, the water and ice in the concrete pores were constantly transformed, resulting in volume expansion [34][35][36]. As a result, the porosity of C45 concrete increased. Water molecules migrated continuously into the concrete's interior, increasing the moisture content. Thus, when the number of cycles was low, the mass of C45 concrete increased. The freeze-thaw cycles severely damaged the concrete after 150 cycles. Increased concrete mass was insufficient to compensate for the loss. The mass loss rates of CD0-H, CD3-H, and CD5-H specimens were 0.09%, 0.07%, and −0.04%, respectively, when 200 freeze-thaw cycles were performed. After 300 cycles, the mass loss rate of C45 concrete was 0.14%, while concrete incorporating dolomite powder lost mass at a rate of 0.13%. These results demonstrate that the addition of dolomite powder reduced the degree of damage to C45 concrete during freeze-thaw cycles. that the addition of dolomite powder reduced the degree of damage to C45 concrete during freeze-thaw cycles.

Relative Dynamic Elastic Modulus of Different Freeze-Thaw Cycles
The relationship between the and the number of freeze-thaw cycles of the concrete is depicted in Figure 7. The is a critical parameter in the study of freeze-thaw cycles because it can be used to characterize the degree of damage within the concrete [37]. In general, the of concrete decreased steadily as the number of cycles increased. As illustrated in Figure 7a, the of C30 concrete after 50 cycles was approximately 90.45-98.36%. It indicated that the internal damage to C30 concrete was relatively minor after 50 cycles. After 125 cycles, the decreased to 68.08-76.58%, indicating that the decreased significantly and the concrete's internal structure was severely damaged. After 225 freeze-thaw cycles, the mortar peeled away from the concrete's surface, exposing many coarse aggregates. Meanwhile, after 225 cycles, the could not be accurately measured. The CD0-L specimen approached the failure standard after 150 cycles, whereas the CD3-L and CD5-L specimens reached the failure standard after 175 cycles.
Combining the results of the mass loss rate test in Figure 6 implied that the mass loss rate test for concrete had a lower sensitivity than the relative dynamic elastic modulus test. When the freeze-thaw cycle was 25, values for CD0-L, CD3-L, and CD5-L specimens were 95.79%, 95.95%, and 99.74%, respectively. After 225 cycles, the values of CD0-L, CD3-L, and CD5-L specimens reached 42.57%, 44.72%, and 48.56%, respectively. It was discovered that the values increased as the dosage of dolomite powder was increased. Figure 7b depicts the relationship between the relative dynamic elastic modulus and the number of freeze-thaw cycles of C45 concrete with various mix proportions. The freeze-thaw damage to C45 concrete was slowed by increasing the dolomite powder dosage. After 25 freeze-thaw cycles, the values of CD0-H, CD3-H, and CD5-H specimens were 96.82%, 98.05%, and 98.72%, respectively. The values of specimens containing 0%, 30% and 50% dolomite powder were 67.54%, 68.62% and 71.50%, respectively, after 300 cycles. The results of mass loss rate and relative dynamic elastic modulus experiments in Figures 6 and 7 indicate that C45 concrete did not meet the failure standard after 300 freeze-thaw cycles. This phenomenon occurred due to the compact nature of the structure of C45 concrete with a lower water-binder ratio.

Relative Dynamic Elastic Modulus of Different Freeze-Thaw Cycles
The relationship between the E r and the number of freeze-thaw cycles of the concrete is depicted in Figure 7. The E r is a critical parameter in the study of freeze-thaw cycles because it can be used to characterize the degree of damage within the concrete [37]. In general, the E r of concrete decreased steadily as the number of cycles increased. As illustrated in Figure 7a, the E r of C30 concrete after 50 cycles was approximately 90.45-98.36%. It indicated that the internal damage to C30 concrete was relatively minor after 50 cycles. After 125 cycles, the E r decreased to 68.08-76.58%, indicating that the E r decreased significantly and the concrete's internal structure was severely damaged. After 225 freeze-thaw cycles, the mortar peeled away from the concrete's surface, exposing many coarse aggregates. Meanwhile, after 225 cycles, the E r could not be accurately measured. The CD0-L specimen approached the failure standard after 150 cycles, whereas the CD3-L and CD5-L specimens reached the failure standard after 175 cycles.

The Influence Mechanism of Water-to-Binder Ratio and Dolomite Powder on the Concrete Properties
The volume of the pore solution of concrete increased during freeze-thaw cycles due to the phase change of the bound water caused by the alternate action of positive and negative temperatures. Volume expansion forced the pore solution into unfrozen pores, resulting in the formation of hydrostatic pressure. Hydrostatic pressure annihilated the internal structure of the concrete. Increased freeze-thaw cycles accelerated the growth of cracks and pores, resulting in the superficial degradation of the concrete [38,39]. As illustrated in Figures 4 and 5, the spalling area of mortar spread to the entire surface of C30 concrete after 300 cycles, whereas no visible mortar peeling off occurred with C45 concrete, indicating that the damage degree of C45 concrete was less than that of C30 concrete under the same freeze-thaw condition. It was consistent with the mass loss rate and relative dynamic elastic modulus values obtained from various freeze-thaw cycles. As illus- Combining the results of the mass loss rate test in Figure 6 implied that the mass loss rate test for concrete had a lower sensitivity than the relative dynamic elastic modulus test. When the freeze-thaw cycle was 25, E r values for CD0-L, CD3-L, and CD5-L specimens were 95.79%, 95.95%, and 99.74%, respectively. After 225 cycles, the E r values of CD0-L, CD3-L, and CD5-L specimens reached 42.57%, 44.72%, and 48.56%, respectively. It was discovered that the E r values increased as the dosage of dolomite powder was increased. Figure 7b depicts the relationship between the relative dynamic elastic modulus and the number of freeze-thaw cycles of C45 concrete with various mix proportions. The freeze-thaw damage to C45 concrete was slowed by increasing the dolomite powder dosage. After 25 freeze-thaw cycles, the E r values of CD0-H, CD3-H, and CD5-H specimens were 96.82%, 98.05%, and 98.72%, respectively. The E r values of specimens containing 0%, 30% and 50% dolomite powder were 67.54%, 68.62% and 71.50%, respectively, after 300 cycles. The results of mass loss rate and relative dynamic elastic modulus experiments in Figures 6 and 7 indicate that C45 concrete did not meet the failure standard after 300 freeze-thaw cycles. This phenomenon occurred due to the compact nature of the structure of C45 concrete with a lower water-binder ratio.

The Influence Mechanism of Water-to-Binder Ratio and Dolomite Powder on the Concrete Properties
The volume of the pore solution of concrete increased during freeze-thaw cycles due to the phase change of the bound water caused by the alternate action of positive and negative temperatures. Volume expansion forced the pore solution into unfrozen pores, resulting in the formation of hydrostatic pressure. Hydrostatic pressure annihilated the internal structure of the concrete. Increased freeze-thaw cycles accelerated the growth of cracks and pores, resulting in the superficial degradation of the concrete [38,39]. As illustrated in Figures 4 and 5, the spalling area of mortar spread to the entire surface of C30 concrete after 300 cycles, whereas no visible mortar peeling off occurred with C45 concrete, indicating that the damage degree of C45 concrete was less than that of C30 concrete under the same freeze-thaw condition. It was consistent with the mass loss rate and relative dynamic elastic modulus values obtained from various freeze-thaw cycles. As illustrated in Figure 6, after 300 cycles, the mass loss rates of CD0-L, CD3-L, and CD5-L specimens could increase to 6.71%, 6.33%, and 5.81%, respectively. Meanwhile, the mass loss rates of CD0-H, CD3-H, and CD5-H specimens were 0.14%, 0.13%, and 0.13%, respectively. Figure 7 showed that after 200 cycles, the E r values of CD0-L, CD3-L, and CD5-L specimens reached 50.61%, 51.79%, and 54.09%, respectively. On the other hand, the E r values of CD0-H, CD3-H, and CD5-H specimens were 79.86%, 82.87%, and 83.24%, respectively. In conclusion, the degree of freeze-thaw damage to concrete decreased as the water-to-binder ratio increased. A lower water-binder ratio enhanced mechanical properties and pore refinement, resulting in increased impermeability and decreased water absorption. As a result, there was less freezing water inside the specimen, and the concrete demonstrated increased freeze-thaw resistance [37,40,41]. As illustrated in Figures 4 and 5, the degree of damage to C30 and C45 concrete blended with dolomite powder was relatively low in comparison to reference specimens. The SEM and chloride-penetration resistance tests revealed that the addition of dolomite powder refined the pore structure of concrete and increased its impermeability. Additionally, the concrete containing dolomite powder peeled slightly away from the surface during freeze-thaw cycles, as the formation of pores and cracks in concrete was inhibited. Thus, the degree of damage caused by hydrostatic pressure on concrete blended with dolomite powder was limited during freeze-thaw cycles. This analysis corroborated the mass loss rate and relative dynamic elastic modulus results. Dolomite powder slowed the mass loss rate of C30 and C45 concrete, while increasing the E r of the concrete. All of these findings indicate that increasing the dosage of dolomite powder improved the freeze-thaw resistance of concrete. Figure 8 depicts a graphical analysis of concrete's freeze-thaw damage. The parameters of Equation (9) were determined using linear regression analysis between In(In 1 1−D N ) and InN. Table 6 summarizes the Weibull distribution's characteristic parameters. As illustrated in Figure 8 and Table 6, the damage degree of concrete blended with dolomite powder was found to follow the two-parameter Weibull probability function during freezethaw cycles. As illustrated in Figure 9, an evolution model of concrete damage for various dolomite powder replacement levels was developed using Table 6 and Equation (6). As a result, the curves of C30 and C45 concrete with dolomite powder were generally lower than those of the reference concrete. Under the same freeze-thaw conditions, the damage degree of concrete treated with dolomite powder was less than that of reference specimens. It demonstrated that increasing the dosage of dolomite powder resulted in increased freezethaw resistance. Equations (10)- (15) show the evolution model formula for the damage degree of CD0-L, CD3-L, CD5-L, CD0-H, CD3-H, and CD5-H specimens, respectively. eters of Equation (9) were determined using linear regression analysis between In(In ) and In . Table 6 summarizes the Weibull distribution's characteristic parameters. As illustrated in Figure 8 and Table 6, the damage degree of concrete blended with dolomite powder was found to follow the two-parameter Weibull probability function during freeze-thaw cycles. As illustrated in Figure 9, an evolution model of concrete damage for various dolomite powder replacement levels was developed using Table 6 and Equation (6). As a result, the curves of C30 and C45 concrete with dolomite powder were generally lower than those of the reference concrete. Under the same freeze-thaw conditions, the damage degree of concrete treated with dolomite powder was less than that of reference specimens. It demonstrated that increasing the dosage of dolomite powder resulted in increased freeze-thaw resistance. Equations (10)- (15) show the evolution model formula for the damage degree of CD0-L, CD3-L, CD5-L, CD0-H, CD3-H, and CD5-H specimens, respectively.

Damage Model of Concrete Incorporating Dolomite Powder Based on Weibull Distribution
According to material science, the damage degree of concrete was reduced to 40% after several freeze-thaw cycles, which could be considered a material failure [42]. Table  7 shows the number of rapid freeze-thaw concrete cycles with material failure when the of concrete is 40% based on Equations (10)- (15). As shown in Table 7, the number of rapid freeze-thaw cycles performed on CD0-L, CD3-L, and CD5-L specimens with material failure was 161, 171, and 180, respectively. Meanwhile, the number of rapid freezethaw cycles performed on CD0-L, CD3-L, and CD5-L specimens with material failure was 150, 175 and 175, respectively. The calculated value for C30 concrete was induced to be close to the experimental value. As a result, a damage model for concrete incorporating dolomite powder based on the Weibull distribution could accurately reflect the degree of damage sustained by the concrete during rapid freeze-thaw cycles. The number of rapid According to material science, the damage degree of concrete was reduced to 40% after several freeze-thaw cycles, which could be considered a material failure [42]. Table 7 shows the number of rapid freeze-thaw concrete cycles with material failure when the D N of concrete is 40% based on Equations (10)- (15). As shown in Table 7, the number of rapid freeze-thaw cycles performed on CD0-L, CD3-L, and CD5-L specimens with material failure was 161, 171, and 180, respectively. Meanwhile, the number of rapid freeze-thaw cycles performed on CD0-L, CD3-L, and CD5-L specimens with material failure was 150, 175 and 175, respectively. The calculated value for C30 concrete was induced to be close to the experimental value. As a result, a damage model for concrete incorporating dolomite powder based on the Weibull distribution could accurately reflect the degree of damage sustained by the concrete during rapid freeze-thaw cycles. The number of rapid freezethaw cycles performed on CD0-H, CD3-H, and CD5-H specimens with material failure was 326, 377 and 389, respectively, according to the Weibull distribution. The service life of C30 and C45 concrete can be calculated using the average annual number of actual field freeze-thaw cycles, the number of rapid freeze-thaw cycles, and their equivalent relationship [43]. As a result, the service life of concrete incorporating dolomite powder was sufficient to be evaluated using a damage model based on the Weibull distribution (as seen in Equations (10)-(15)).

Conclusions
In this work, the freeze-thaw resistance and damage model of C30 and C45 concretes with different dolomite powder dosages were investigated. The following conclusions could be drawn: Under the freeze-thaw cycles, the damage degree of C30 and C45 concretes blended with dolomite powder was restrained due to the refinement of the cement paste structure with the addition of dolomite powder. The evolution model of the damage degree based on the two-parameter Weibull probability function showed that the damage degree of concretes decreased with the addition of dolomite powder under the same freeze-thaw conditions. The evolution model of the damage degree of concretes was proposed, which was expressed in terms of the number of the freeze-thaw cycles. The comparison between experimental and calculated values indicated that the evolution model of the damage degree of concretes based on the two-parameter Weibull probability function could be used to forecast and evaluate the service life of concretes blended with dolomite powder. This manuscript provides a new path to improve the service life of concretes from the perspective of freeze-thaw resistance for readers. Therefore, researchers can improve the service life by designing an evolution model of the damage degree of concretes based on the two-parameter Weibull probability function in future work. It is worth noting that deep studies on slight differences in service life between experimental and calculated values have rarely been reported up to now. It is necessary to further optimize the evolution model of the damage degree of concretes based on the two-parameter Weibull probability function at a later stage, especially for building materials with high durability requirements.