Impact of high volume E.M.D. residue on the corrosion resistance and mechanical properties of construction materials in sulfate environment

This study examines the potential use of Electrolytic Manganese Dioxide (EMD) residue as a replacement of cement (20%wt by cement weight) in construction materials to provide anticorrosion protection on reinforcing steel and improve the strength of cementitious materials under sulfate attack. To assess the corrosion parameters, the constructed building materials were immersed in a 5%wt sulfate salt (Na2SO4), while concrete samples incorporating 20%wt EMD were prepared and subjected to mechanical, porosity and thermal tests. Moreover, SEM images were obtained in order to examine the microstructure of concrete and the extent of damage caused by sulfate ions. The results demonstrate that the inclusion of EMD caused a notable rise in the corrosion of steel bars within cement mortars, as well as a decrease in the mechanical strength of the building materials. Overall, the experimental outcomes of the study suggest that the incorporation of high volume (20%wt) EMD residue leads to the degradation of all measured properties.


Introduction
Concrete is a widely used building material with several benefits over other commonly used materials in construction such as wood, steel, and masonry. The versatility and durability of concrete make it an excellent choice for a variety of construction projects, including residential and commercial buildings, bridges, dams, and highways [1][2][3]. Concrete structures are resistant to weathering, corrosion, and fire, while can last for a long period without requiring maintenance [4][5][6]. Furthermore, concrete exhibits a significant compressive strength, rendering it a suitable option for the structures capable of withstanding substantial loads. Concrete is also considered a sustainable building material, prepared from locally sourced materials and has a low carbon footprint compared to other materials [7,8]. Despite the fact that concrete has many benefits as a building material, it has some drawbacks compared to other commonly used materials. Over time, concrete may develop cracks, shrinkage, and corrosion of steel rebars, which could potentially weaken the building's structural stability and lead to costly repairs [9][10][11]; thus, the enhancement of cementitious material quality poses a challenge for engineers worldwide.
The problem of sulfate attack in concrete has become more prevalent in recent times, and it has the potential to cause significant harm to its durability and service life; this issue can ultimately result in the deterioration of concrete structures [12][13][14]. Upon contact with concrete, sulfates can react with the C 3 A in the cement to form ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O). This compound cause expansion, cracking, and loss of strength in the cementitious material [15]. The formation of calcium sulfate (CaSO 4 ) also results in the expansion of the cement paste, leading to cracking and eventual mechanical deterioration [16,17]. According to Nielsen's research [18], ettringite crystals were observed to form after the occurrence of cracks. The predominant reaction product was believed to be gypsum, with ettringite being a less commonly formed product. However, the concentration of sulfates in the pore solution of the concrete is an important parameter that affects the rate of sulfate attack [19,20]; when the concentration of sulfates in the pore solution exceeds a certain threshold, it can cause significant damage to the concrete, leading to cracking, spalling, and loss of structural integrity. Based on the above, it is crucial for the engineers to protect concrete structures from sulfate attack by using appropriate construction materials, such as low-sulfate cement [21,22], and by taking measures to prevent the penetration of sulfates into the concrete, such as the use of additives during concreting, which results in the reduction of concrete porosity and affect the hydration process [23,24].
In recent years, various methods for protecting reinforcement steel in cement mortars have been investigated, including the use of additives such as fly ash, silica fume, and metakaolin [25][26][27][28]. One such additive that has received less attention is Electrolytic Manganese Dioxide (EMD). Electrolytic manganese dioxide (EMD) is a type of manganese dioxide that is commonly used as a cathode material in batteries [29][30][31], in which, the chemical composition of electrolytic manganese dioxide (EMD) is primarily manganese dioxide (MnO 2 ) in the form of pyrolusite [32]; in the production of EMD, small amounts of ferrous oxides, silicon dioxide, calcium oxide and traces of metals (Al 2 O 3 and alkali oxides) may also be present [33,34]. Electrolytic Manganese Dioxide (EMD), typically has a dark black or dark gray appearance and a density of approximately 5.0 g cm −3 .
In concrete, EMD residue (EMDR) is added as a coloring agent to provide a grayish-black color to the end product. Due to the presence of pyrolusite and iron oxides, adding a small amount of EMDR can also improve the compressive strength of the concrete and make it less porous, making it more resistant to water and other environmental factors. It can also improves the durability of concrete in corrosive environments by improving its resistance to chloride ion penetration, which can cause corrosion of steel reinforcement in concrete structures [35][36][37][38] . EMD residue react with the calcium hydroxide (Ca(OH) 2 ) in the cement paste, forming a compound called calcium manganite hydrate (Ca 2 Mn 3 O 8 ·H 2 O) which fills some of the pore spaces in the concrete. This reaction can reduce the concrete's permeability and improve its resistance to water and other substances that can cause damage. However, the use of EMDR in concrete can also have some drawbacks. EMD waste can potentially react with other components in the concrete mixture, such as the cement or aggregates (alkali-silica reaction-ASR), leading to a reduction in the concrete's strength and durability over time [39]. Additionally, EMD waste is a fine-grained material and can lead to a higher water demand, which can result in a weaker and more porous end product. Finally, it should be noted that EMDR contains gypsum, which can lead to expansion, resulting in cracking and weakening of the material.
The supplementary cementitious materials (SCMs) such as EMDR also play a siglificant role in controlling sulfate diffusion in concrete. Zhang et al [40] examined the influence of Na 2 SO 4 concentration on the diffusion rate of sulfate ions in concrete. The researchers found that as the concentration and duration of exposure increased, there was a significant rise in compressive strength and relative dynamic elastic modulus, accompanied by a shift from larger pores to medium and small ones. Wang et al [41] investigated how the addition of fly ash (FA) and silica fume (SF) to concrete affected its resistance to sulfate attack. Their results showed that both FA and SF improved the concrete's ability to resist sulfate diffusion when exposed to a 5% sodium sulfate solution, with SF providing better protection than FA. Additionally, Yan et al [42,43] investigated the impact of slag content on the sulfate resistance of concrete under different curing conditions. The researchers found that while a 50% slag content was beneficial for standard curing, the optimal slag content for steam curing was 70%. Low slag content resulted in the diffusion of sulfate ions from the exterior into the concrete matrix, leading to physicochemical reactions that degraded its cementitious material.
In the present experimental research, high volume of EMDR was utilized to provide anticorrosion protection on steel bars and enhance the strength of construction materials. The challenge and innovation of this work is to prepare sustainable building materials containing a harmful waste material enriched in gypsum with acceptable mechanical properties and better anticorrosion behavior than the conventional OPC concrete.
The objective of this study is to investigate the impact of incorporating 20%wt EMD residue in construction materials on their quality and the corrosion of reinforcing steel when exposed to sulfate ions. For the experiments, several tests were conducted on mortars and concrete (with or without reinforcing steel) specimens prepared in the laboratories.

Raw materials
For the preparation of the test samples, we used Cement I 42.5 N, water from the Athens supply network, and crushed calcareous aggregates. We replaced 20 wt%. of the cement, with Electrolytic Manganese Dioxide residue (EMDR) during the production of the specimens. For reinforcement, we utilized weldable steel rebars of type B500C Tempcore, which conformed to both EN-10080 and ELOT 1421-3 standards. Table 1 summarizes the quantities for the preparation of the concrete and mortar specimens.
EMD residue (EMDR) utilized in the present study typically include filter cake, sludge, and other residues that are generated during the process of purifying manganese sulfate solutions [51]. EMD waste materials are highly acidic, due to the presence of sulfuric acid (H 2 SO 4 ) used in the production of EMD [52]. Furthermore, these wastes may contain residual solvents or carbonaceous materials, contributing to their overall toxicity, while also containing heavy metals, such as Cr, Ni, and Cd, which can be harmful to human health and the environment [53,54]. Due to their hazardous nature, EMD wastes require proper handling and disposal to prevent environmental pollution and health hazards. An effective approach to minimize waste and avert environmental harm is to recycle and reuse waste materials from EMD.
The waste material generated from EMD manufacturing when used in small quantities, it may improve the concrete's strength and decrease its permeability; the latter is attributed to the presence of MnO 2 and Fe 2 O 3 in the chemical composition of EMD waste [35]. In fact, small amounts of EMD waste addition may increase the concrete's compressive strength and reduce its permeability due to the presence of pyrolusite (MnO 2 ) and hematite in its chemical composition [55][56][57]. Previous experimental studies have demonstrated that iron oxides (Fe 2 O 3 ) can have a positive impact on the resistance of cement mortars against chloride penetration [58,59]. EMD waste is an ultrafine substance that can result in reduced concrete porosity, potentially enhancing its durability and making it more resistant to water and other substances. Despite the potential benefits of utilizing EMD waste in concrete, its inclusion may lead to a reduction in the concrete's strength and durability; the presence of impurities and gypsum may have detrimental effects on the material's overall characteristics (figure 1). Moreover, the primary chemical reaction that occurs during the sulfate attack on concrete is the formation of ettringite through the reaction of and C 3 A via monosulfate.

Preparation of specimens
To assess the anticorrosive properties of EMDR, reinforced cement mortars were created with dimensions of H = 100 mm and d = 50 mm (as depicted in figure 2). Steel rebars that meet the EN-10080 standard and were supplied by Sidenor Steel Industry S.A. were utilized to reinforce the samples. The rebars, measuring 10 mm in diameter and 100 mm in length, were cleansed with water, distilled water, and acetone to eliminate oils and oxides from their surfaces before being embedded into the cement mortars. An epoxy resin was applied to the top surface of the mortars and the protruding part of the steel, with a 15-mm space between the steel rebar and the bottom surface of the specimen. The water-to-cement (w/c) ratio was kept constant at 0.55 for all mixtures.
To conduct physic-mechanical measurements, two sets of samples were produced: one group containing 20%wt EMDR additive (referred to as MC1), and another group (referred to as RC1) constructed without any additive for comparative purposes. To conduct the compression test, steel molds (as shown in figure 3) were used to create cubic samples that measured 150 × 150 × 150 mm 3 . The splitting strength tests, on the other hand, were carried out on cylinders with a diameter of 150 mm and a length of 300 mm. The fresh concrete was compacted on a vibrating table operating at 3000 Hz for 15 s. After 24 h of casting, the specimens were demolded and fully immersed in a water tank for 7 days before being partially submerged in a 5%wt Na 2 SO 4 salt until testing.

Tests and experiments 2.3.1. Mechanical strength and MIP measurements
In accordance with EN 12390-3, mechanical strength tests and ultrasonic pulse velocity (UPV) measurements were done on the concrete samples using 150 × 150 × 150 mm 3 cubes. The mechanical test was conducted at 28, 56 and 90 days after casting (average of three samples at each age); a total of 12 specimens were tested, with a loading rate of 0.05 MPa s −1 and 0.5 MPa/s for splitting and compressive strength, respectively.
The determination ofpore size distribution was performed utilizing a Mercury intrusion porosimeter (MIP) that features a pressure up to 228 MPa. From the tests, representative fragments weighing approximately 1-1.5 g were extracted from the samples.

Ulrasonic pulse velocity
The quality of 100-mm cubic concrete specimens was assessed using ultrasonic pulse velocity (UPV) based on the guidelines provided in BS EN 12504-4. This method is effective in detecting cracks and voids within concrete. The UPV waves were measured using the Pundit Plus 6, a portable ultrasonic non-destructive tester manufactured by CNS Farnell. To ensure good contact between the transducers and specimens, a thin layer of  lubricant was applied at their interface and were placed on opposite faces of the cubes. Prior to the test, the specimens were partially submerged in 5%wt Na 2 SO 4 and then dried in an oven for 24 h. The tests were performed at three ages (28, 56, and 90) after casting.

Thermal properties
The diffusion of temperature within mortar is a crucial factor in moisture transfer, resistance to sulfate attack, and the corrosion of reinforcement steel, all of which contribute to the degradation of reinforced concrete's durability. The chemical composition, characteristics of the concrete mix, curing conditions, and age of the concrete can affect the measured thermal properties. Therefore, it is essential to determine the thermal characteristics of concrete. In the framework of the present study, thermal coefficients were assessed on cubic specimens with dimensions of 150 × 150 × 150 mm 3 . Prion toeach measurement, certain specimens were removed from a sulfate solution and then dried in an oven at a temperature of 105°C for 24 h.

Electrochemical measurements
To investigate the corrosion of reinforcing steel, we utilized cylindrical mortar specimens with a diameter of 5 cm and a height of 10 cm during the testing process. Throughout the corrosion testing process, multiple measurements were recorded, including the half-cell potential (HCP), corrosion current, and corrosion rate of the reinforcement steel. The HCP is an essential parameter that provides information on the condition of embedded reinforcement steel in concrete, specifically with regard to corrosion caused by sulfate attack. In general, a HCP value above −126 mV suggests the absence of corrosion in steel rebars, while a potential of −276 mV indicates a failure in the protective layer surrounding the steel; typically, a potential value lower than −426 mV signifies active corrosion of steel [60]. The measurements were conducted in accordance with the ASTM C876/87 standard, utilizing a saturating calorimeter electrode (SCE) as the reference.
To evaluate the corrosion current (i) of steel rebars embedded in cement mortars, the LPR (Linear Polarization Resistance) technique, according to the ASTM G59-97 standard, was employed for a total period of 24 months. Data analysis was performed using a potentiostat/galvanostat model 263 A from EG&G Princeton Applied Research along with associated software. The steel rebars served as the working electrode, while a calomel (SCE) reference electrode and a graphite bar counter electrode were used. The potential scan range was 15 mV from the open-circuit potential (OCP), and the scan rate was 0.1 mV s −1 .

Corrosion rate measurements
The mass loss of reinforcement steel was determined by removing the steel rebars from the mortar specimens and measuring their final weight after 24 months of partial immersion in a 5%wt Na 2 SO 4 solution. The corrosion rate of steel rebars was calculated using equation (1); this formula assumes a linear corrosion rate over the exposure period and is commonly used in gravimetric corrosion measurements to determine the corrosion rate of reinforcing steel in concrete. 10 1 7 Where W is the mass loss of the specimen in milligrams (mg), ρ is the density of the steel in g/cm 3 , A is the exposed area of the steel in cm 2 and t is the duration of exposure in hours.

Carbonation test
The depth of carbonation in mortars that were subjected to sulfate salt for 24 months, with or without EMDR, was determined using the phenolphthalein spray test. The chemical solution was prepared by dissolving 1.0% of the weight of phenolphthalein in a solution of 70% ethyl alcohol and 30% distilled water. The solution was sprayed on a fresh fractured surface of the samples, and the carbonated area was measured using a digital caliper.
To obtain an average value, the depth of carbonation was measured three times for each sample. This process was conducted on both the composite blends and the control mixture.

Microstructural analysis
Scanning electron microscopy (SEM) is a useful tool for investigating the impact of a sulfate attack on concrete.
In the present study, using a Philips XL, Scanning Electron Microscope (SEM) with a maximum resolution of 2.0 nm at 30 kV (in the high vacuum mode) and a magnification of 20-1.000.000x, the mortars were subjected to microstructural analysis. Secondary Electron Images (SEI) were utilized to perform the observations. To make the surface conductive, the samples were sputter coated with gold before the analysis. The observation involved the examination of crystal size, shape, and morphology, as well as investigating the structure of the mortars. Figure 4 provides the mechanical strength values of two different mixtures, MC1 and RC1, exposed to sulfate solution over a period of 90 days, while figure 5 shows the specimens after testing. MC1 contains EMD waste material, while RC1 is a reference mixture without additives.  compressive strength was affected by the presence of sulfate ions in the additive, which have an adverse effect on the mechanical properties of concrete [63]. Additionally, the duration of salt immersion plays a crucial role in the advancement of damage caused by sulfate attack (figure 6) [64]. Figure 4 also illustrates the splitting strength ( f t ) of two different mixes, MC1 and RC1, when exposed to sulfate solution at three different ages (28, 56, and 90 days after concreting). At 28 days, the splitting strength of MC1 was 2.41 MPa, while that of RC1 was slightly higher at 2.64 MPa. At 56 days, the equal f t values of both mixtures decreased, while at 90 days, the splitting strength of both mixtures decreased further, with the composite mix showing a more significant reduction than RC1. Overall, figure 4 indicates that both mixes demonstrate a decrease in splitting strength over time when exposed to Na 2 SO 4 salt. However, the mixture incorporating EMD waste material (MC1) exhibited lower f t values compared to the reference mixture (RC1) at all measurements.

Results
Mercury intrusion porosimetry (MIP) was used to figure out the average size of the pores in MC1 and RC1.In figure 7, the relationship between the total number of pores and the average size of mortars that were exposed to sulfates is shown. Analysis of the graph indicates that the mean pore diameter decreases as the cumulative pore volume increases. The findings reveal that MC1 had a slightly higher mean pore diameter than RC1, which suggests that the addition of EMD may have resulted in a slightly more porous mortar. It is widely accepted that concrete pores can be categorized based on their diameter, such as gel pores (<10 nm), capillary pores (10 nm − 0.1 μm), and macropores (>0.1 μm). Hence, the addition of EMDR can have a significant impact on the durability and strength of the mortar.   Table 2 compares the thermal properties of two types of concrete constructed in the lab. The thermal properties measured are the thermal conductivity (λ), the specific heat capacity (C p ), and the thermal diffusivity (a). The measurements were conducted on both dry and moist specimens. Table 2 shows that the wet concrete containing EMDR has higher thermal conductivity, specific heat capacity and thermal diffusivity compared to the concrete without any additive. Overall, these results suggest that incorporating EMD into concrete can improve its thermal properties, which may be beneficial in applications where efficient heat transfer is required, such as in building envelopes, nuclear power plants, or industrial processes. On the other hand, dry concrete with 20% EMD waste gave values around 22.0%, 2.0%, and 20.0% lower than those of the reference concrete for all thermal coefficients, which may have potential benefits for thermal insulation applications. However, it should be noted that the specific heat capacity of the concrete with EMD waste material is higher, which may have implications for its overall thermal performance. Figure 8 displays the corrosion current (i corr ) values of mortars, MC1 and RC1, with and without EMDR addition, respectively, for a time period of 24 months. The corrosion current value of MC1 was initially 34.5% higher than that of RC1, suggesting that both types of mortars were corroded to some extent. Over the first 4 months, there was a rise in the i corr values for both batches of mortars, but -RC1 showed a higher value than MC1. However, after this period, the corrosion current value for RC1 remained relatively stable, whereas for MC1, it continued to increase at a faster rate compared to RC1, indicating that the EMD waste material was not providing adequate protection against corrosion. Although the i corr values for both groups of mortars increased over time, the values for MC1 were consistently higher than for RC1, suggesting that the EMD waste material may have contributed to the increased corrosion rate in MC1. Upon completion of 24 months, the corrosion current value for MC1 continued to be considerably higher than that of RC1. Thus, as indicated by the data presented in figure 8, the incorporation of EMDR was not successful in providing effective corrosion protection, and both mortar types demonstrated a growing trend in corrosion over time when exposed to SO 4 2− ions. Figure 9 shows the half-cell potentials (HCP) of steel rebars embedded in mortars and exposed to sulfates for two different mixtures, RC1 (the reference mixture) and MC1 (the mixture with EMD waste). The mortars remained in the sulfate salt for a total period of 11 months. The potential difference indicates the tendency of the steel reinforcement to corrode, with more negative potentials indicating a higher risk of corrosion. The data suggests that the steel reinforcement in the MC1 mixture with EMD waste has a more negative half-cell potential than in the RC1 reference mixture, indicating a higher risk of corrosion. The difference in potential between the two mixtures varies over time, with some values showing greater differences than others. Initially, the difference  Table 2. Thermal coefficients for dry and moist mortars after exposure to a 5%wt Na 2 SO 4 solution.

Moist specimens
Dry specimens between RC1 and MC1 is −14 mV, while at 28 days, it changes to −51 mV. This suggests that the effect of EMD waste on the corrosion potential of steel reinforcement in mortar may be time-dependent. It is also worth noting that there is significant variation in the potential values within each mixture; the half-cell potential of the MC1 mixture ranges from −349 mV to −658 mV, indicating that there may be some variability in the quality of the mixture or the exposure conditions. To sum up, the HCP measurements suggest that the use of EMD waste in mortar may increase the risk of corrosion of steel reinforcement, particularly over time. Figure 10 illustrates the corrosion rate of steel barsembedded in mortars and exposed to a sulfate solution for a period of 24 months. It can be seen that when the duration of immersion increases, the corrosion rate of both mixtures also increases, which is consistent with the findings of other researchers [65]. However, the corrosion rate of MC1 is consistently higher than that of RC1 at all time intervals, indicating that the addition of EMD waste material may have contributed to an increase in the rate of corrosion. At the 4-month point, MC1 exhibited a 50% higher corrosion ratethan that of RC1.The results indicate that the presence of EMD waste material in the mortar specimens may accelerate the corrosion process of steel bars in the presence of sulfate solution. One possible explanation for this is that EMD waste contains sulfuric acid and traces of metals [66,67]; these impurities may elevate the electrochemical activity of steel bars and facilitate the formation of aggressive corrosion products. Tian and Cohen [68] examined whether the formation of gypsum could result in expansion; following exposure to a 5% Na 2 SO 4 solution, the test samples exhibited significant expansion. Further experimental studies have confirmed that sulfate attack leads to damage to the microstructure of concrete, decomposition of hydration products, and deterioration in macro-performance [69][70][71].  In figure 11, the ultrasonic pulse velocities (UPV) of RC1 and MC1 mortar mixes subjected to sulfates are presented. The UPV test is commonly used to evaluate the quality of a material by measuring the speed of sound waves that propagate through it. It is well known that, a decrease in ultrasonic pulse velocity can be an indication of deterioration due to sulfate attack, which causes expansion and cracking of the material. According to the findings, there is a correlation between the variation in ultrasonic velocities of the samples and their compressive strength. Figure 11 indicates that the ultrasonic waves of the MC1 mixture are generally lower than those of the RC1 reference group. The results demonstrate that the use of EMD waste may lead to a decrease in the compressive strength and durability of the mortar, potentially due to the presence of metallic impurities that influence the microstructure of the mortar. The data also shows that the difference in pulse velocity between the two mixtures varies over time. In particular, at 28 days, the difference between RC1 and MC1 is 4.6 km h −1 , while at 100 days, it is 2.7 km h −1 . This suggests that the effect of EMD waste on the ultrasonic pulse velocity of mortar may be time-dependent, and that the deterioration of the material may accelerate over time. In general, using EMD waste in mortars exposed to sulfate salt can lead to a reduction in the material's quality, which can cause cracking and the formation of voids.
The carbonation depths estimated by phenolofthalein test are presented in figure 12. The results show that the carbonation depth of both MC1 and RC1 increased with an increase in exposure to SO 4 2− . Comparing the data for RC1 and MC1, it can be seen that the mortars with EMD (MC1) generally show a higher depth of carbonation than the mortars without EMD (RC1). Furthermore, the data also suggest that the effect of EMD on  carbonation is more pronounced at late ages. At 8 weeks, the depth of carbonation is similar for both mixtures, but at 16 and 24 months, the depth of carbonation in MC1 is significantly higher than that in the RC1 group. This indicates that the addition of EMDR to the mixture may have a negative effect on its durability by increasing its porosity and accelerating the carbonation process.
This result is expected since EMD waste has a unique mineralogical and chemical composition. The addition of EMD to mortar can increase the total amount of sulfate ions present in its microstructure, leading to the formation of ettringite needles and gypsum [72]; these needles can consume calcium hydroxide, making it less available for reaction with CO 2 , ultimately reducing the carbonation depth at early ages (4 and 8 months). However, at 16 and 24 months, the expansion caused by ettringite can lead to micro-cracking, which can increase the permeability of mortar and the diffusion of CO 2 and thereby increasing the carbonation depth [73,74].
Scanning Electron microscopy applied to concrete exposed to sulfate attack can provide valuable information about the microstructure of the material, including pore structure and the presence of expansive products. In our study, SEM images (figure 13) were taken of selected fragments in order to examine their microstructure following a sulfate attack. Microscopic analysis confirmed that the sulfate attack led to both mechanical deterioration of the concrete and corrosion of the steel. Figure 13 indicates the presence of ettringite, Ca(OH) 2 and gypsum crystals in the structure of the sample, which is consistent with the results obtained by other researchers [75,76]. The presence of needle-like ettringite can be reduced by lowering the C 3 A content in the cement, which affects the cement's hydration. It was previously mentioned that EMD waste contributes to the overall sulfate content in concrete; hence, the abundance of ettringite needles is attributed to the primary reaction between CaSO 4 and C 3 A via monosulfate. The accumulation of these products leads to the development of cracks in the structure, ultimately resulting in the destruction of the concrete.
Microscopic analysis also revealed that the incorporation of EMD waste material in concrete can lead to a degradation in its mechanical strength. The mechanical properties of concrete are affected by the presence of EMDR, resulting in the formation of pores and cracks in the matrix; the formation of voids in the matrix can allow water and other aggressive agents to penetrate the concrete, leading to further degradation of its strength and durability. The above-mentioned defects reduce the density of the concrete and weaken its overall strength. Moreover, the chemical composition of the EMD waste material also contributes to the degradation of strength under compression. The high levels of pyrolusite and gypsum in the waste material can react with the cement hydration products, leading to the formation of sulphate minerals (ettringite) and other chemical compounds that cause deterioration of the end-material. In addition, the incorporation of EMD waste material in concrete can also affect its durability.

Conclussions
Based on the findings of the experimental investigation, the substitution of EMDR for cement resulted in the degradation of all the properties examined. Specifically, replacing cement with EMDR at a level of 20%wt led to a Figure 12. Carbonation test measurements for cylindrical mortars after exposure to sulfate attack. reduction in both compressive and tensile strengths. Additionally, the electrochemical measurements revealed a substantial rise in the corrosion of the reinforced MC1 mixture when compared to the reference (RC1) group. The conclusions of the study can be summarized as follows: • EMDR addition doesn't improve concrete's compressive strength in sulfate solution, and may decrease splitting strength further.
• The addition of 20% EMDR to concrete, enhances its thermal properties in moist conditions, making it suitable for applications that demand efficient heat transfer. However, the higher specific heat capacity of EMD waste material may affect the overall thermal performance of the concrete.
• The addition of EMD waste material to mixtures may increase the risk of corrosion to steel reinforcement over time, as indicated by the more negative half-cell potentials and higher corrosion rate of MC1 compared to RC1 mixture. The higher rate of corrosion could be caused by the higher electrochemical activity of steel bars in the presence of gypsum and metallic impurities in EMDR.
• Exposure of EMDR specimens to SO 4 2− ions leads to an overall increase in carbonation over time. Although EMD residue can initially reduce carbonation depth, it can ultimately lead to a higher carbonation depth due to the growth of ettringite needles. The presence of ettringite can lead to the development of expansive products and the cracking of concrete over time.

Acknowledgments
The study was supported by both the State Scholarships Foundation (IKY) and the National Technical University (NTUA) of Athens, and the authors express their appreciation. Additionally, the authors acknowledge TITAN Cement Industry for their help in preparing the specimens and conducting the concrete's mechanical tests.