Enhancement of Compressive Strength and Durability of Sulfate-Attacked Concrete
1
Department of Architecture and Civil Engineering, Lyuliang University, Lvliang 033001, China
2
Department of Civil Engineering, Shanxi Institute of Technology, Yangquan 045000, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(7), 2187; https://doi.org/10.3390/buildings14072187 (registering DOI)
Submission received: 21 May 2024
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Revised: 30 June 2024
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Accepted: 13 July 2024
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Published: 16 July 2024
(This article belongs to the Section Building Materials, and Repair & Renovation)
Abstract
:This experimental study is carried out in order to improve the properties of sulfate-attacked concrete. The concrete specimens were immersed in 15% Na2SO4 solution before being protected with a concrete repairing agent (CRA). The effects of sulfate corrosion time, the curing time after being attacked, and the concrete repairing agent on concrete were investigated. The experimental results indicate that the properties slightly increased after being attacked by sulfate for 60 days than for 30 days. However, they decreased after being attacked by sulfate for 90 days. CRA could effectively improve the properties of sulfate-attacked concrete. After being re-cured for 7 days, the properties of the sulfate-attacked concrete were significantly improved in comparison with those of the specimens taken out from the sulfate solution immediately. When the specimens were attacked for three months, the compressive strength of specimens coated with CRA was increased by 6.1%, 6.4%, and 6.4% compared to that of the specimens without CRA after being cured for 7 to 56 days, respectively. The carbonation depth of concrete specimens with CRA was reduced by 4.6%, 8.3%, and 4.9%, respectively. However, the chloride ion permeation coefficient of concrete with CRA decreased by 20.3%, 28.5%, and 28.7%, respectively, for the concrete immersed in sulfate for one month.
1. Introduction
Sulfate corrosion has become an unneglectable reason that decreases the mechanical properties and durability of concrete. Sulfates penetrate into the concrete and cause gypsum corrosion or ettringite corrosion, resulting in cracks and destruction in concrete structures [1,2,3]. In the coastal or inland salt area, the concrete structures are suffering from the penetration of SO42−, Cl− and so on. These would lead to degradation in concrete, which seriously impacts the performance of concrete elements [4,5]. It has been pointed out that chloride slowly affects the corrosion of sodium sulfate, and the presence of chloride could affect the degradation caused by sulfates [6]. The degeneration of concrete subjected to sulfates was caused by the generation of AFt and gupse due to the chemical reactions of SO42− and CSH. The main features of sulfate-attacked concrete specimens are the destructive cracks and soft and powdery concrete structures. The surface hardness was significantly influenced by the water/cement ratio and the concentration of sulfate solution [7]. When the freeze–thawing and sulfate attack interact with mutual coupling in the process of concrete deterioration, the freeze–thaw cycle slows the deterioration of sulfate-attacked concrete. Meanwhile, sulfate corrosion accelerated the development of micro-cracks in concrete, resulting in more serious deterioration due to the freeze-thawing circle [8,9]. Concrete degraded more seriously in Na2SO4 solution than in other sulfate solutions. The limestone cement concrete showed a more serious degree of damage in the sulfate corrosion than the siliceous cement concrete [10]. The resistance to sulfate corrosion was enhanced by using fly ash, blast-furnace clinker, or metakaolin mineral admixture [11]. Degradation of concrete due to sulfate corrosion could be slowed down by partially replacing cement with mineral admixtures [12].
CRA is a reaction accelerator that activates the unhydrated cement in concrete to hydrate fully. It can penetrate into the concrete and take part in hydration with the unhydrated cement. Newly generated hydrated calcium silicate filled the pores and cracks, which enhanced the compactibility, compressive strength, carbonation resistance, and resistance to chloride ion permeation of concrete [13]. The improvement of load-bearing performance of concrete applied with crack repair materials was significant after about three months of immersing in hydrochloric acid and sulfate liquor [14]. The clay nanocomposite material clogged the pores in the concrete. The capillary suction was reduced, which produced a positive influence on the sulfate-corrosion resistance of the specimen [15]. The nanoclay obviously enhanced the sulfate-corrosion resistance of concrete. The porosity of concrete without coating varied from 21.0% to 17.7%, but the concrete specimens with coating produced an obvious reduction of 11.0%. The urea hydrolysis-based bacterial carbonate precipitation surface treatment technology reduced the degradation of concrete in sulfate surroundings and increased the durability of attacked specimens [16]. Suleiman et al. [17] measured the durability of sulfate-attacked concrete after being treated with different kinds of coating materials. They found that the surface flaking and mass loss of concrete coated with epoxy, silane and bituminous materials were significantly reduced. A decrease in the durability of non-coated concrete cylinders was observed. However, almost no reduction was observed for the specimens with coating. The durability of the sulfate-attacked concrete was improved with calcifying bacteria. The concrete specimens with coating were enhanced by 35% more than the reference specimen [18].
The experimental studies above mainly focus on measuring the strength and permeability of concrete, which was first protected with a coating. Then, the coated concrete specimens were immersed in sulfates. In practice, the sulfate-attacked concrete needs to be protected and treated. However, research on improving the mechanical properties and durability of sulfate-attacked concrete is seldom published. Therefore, the performance of concrete subjected to sulfate corrosion was studied. The sulfate corrosion time, the curing time after being attacked, and the influences of CRA on the strength, the carbonation resistance, and the Cl− permeation coefficient of concrete were investigated.
2. Experimental Details
Ordinary Portland cement produced by Xuzhou Zhonglian Cement Co., Ltd. (Xuzhou, China) was used in concrete as a binder. The chemistry and physical characteristics of the binder are summarized in Table 1. Gravel and natural river sand were used as aggregates. The specific gravity of the binder of the coarse and fine aggregates were 3.14, 2.72, and 2.6, respectively. The dimension ranges of coarse aggregate were 5.0–16.0 mm. The fineness modulus of the gravel and the sand were 6.62 and 2.57, respectively. The water absorption of crushed stone and sand were 0.40 and 1.65, respectively. The sodium sulfate solution was mixed as a mass fraction of 15%. CRA, produced by Jiangsu Huike New Building Materials Co., Ltd. (Lianyungang, China), is an inorganic infiltration solution. The alkali metal sodium silicate is the main component of CRA. The main components and properties of CRA are presented in Table 2.
The concrete mixture proportion is shown in Table 3. Cubic specimens with a side length of 100 mm were prepared. The cube specimens were used to measure the compression strength. Concrete prisms with sizes of 100 × 100 × 300 mm were prepared for measuring the carbonization depth, and the specimens with a thickness of 5 cm and diameter of 10 cm were used to test the chloride ion permeation coefficient. The concrete blocks were cured in stable water at the temperature of 20 ± 2 °C for 28 days. The 28th-day strength was 29.1 MPa. The concrete specimens were immersed for three kinds of sulfate attack periods 1 month, 2 months, and 3 months. Then, the specimens were re-cured for three re-curing times of 7 to 56 days after being attacked. The specimens were placed in a chamber at 20 ± 2 °C and 60 ± 5% relative humidity. To compare with the specimens attacked by sulfate, the concrete specimens that were not attacked by sulfate were placed in water and cured for the same time as the sulfate-attacked specimens. Some sulfate-attacked specimens were coated with CRA. CRA was brushed on the surface of concrete specimens. The test conditions of the concrete are listed in Table 4.
The test specimens were soaked in 15% Na2SO4 solution for 30 days, 60 days and 90 days, respectively. The solution was changed with a new solution once a month to keep the concentration of the sulfate solution stable. After being kept in the solution for a specified time, the CRA was coated onto the face of the specimens.
To enhance the properties of the sulfate-attacked concrete, the outside of some concrete specimens were brushed with CRA. The total dosage of CRA applied onto the outside of sulfate-attacked concrete specimens was approximately 0.6 kg/m2. Afterward, the concrete specimens were re-cured in an ambient environment for 56 days at most. The mechanical properties of concrete with CRA were measured after being cured for 7 to 56 days. Meanwhile, the durability of sulfate-attacked concrete was also tested.
The strength experiments were performed on the basis of ‘Standard for test methods of concrete physical and mechanical properties’ [19]. The loading rate was set at 0.5 MPa/s. The experiment for determining the carbonation depth was carried out according to standard [19]. The specimens were put into a carbonized tank at the corresponding time, where the carbon dioxide concentration was maintained at 20 ± 3%. The R.H. was controlled at 70 ± 5%, and the temperature was controlled at 20 ± 2 °C. The average carbonation depth of specimens after being accelerated carbonated for 14 days was measured.
The relative chloride diffusivity coefficient experiment was detected according to the standard [20]. This test measures the relative chloride diffusivity coefficient of sulfate-attacked specimens. The equipment for the experiment was the chloride ion permeation coefficient tester and the supporting automatic vacuum water machine.
SEM images and XRD analysis of sulfate corrosion concrete were obtained to compare the differences in the microstructure and phases of concrete. Furthermore, the impact of CRA on the microstructure of the specimens attacked in sulfate solution was also tested.
3. Experiment Results and Discussion
3.1. The Compressive Strength
The strength results of the sulfate corrosion tests are listed in Table 5.
3.1.1. Effect of Sulfate Corrosion Time on the Strength
As presented in Table 5 and Figure 1, the strength was greater for specimens subjected to sulfate corrosion than that of the concrete without sulfate corrosion. The strength of concrete soaked in sulfate solution for 30 days is 17.5% bigger than that of the concrete without sulfate corrosion. The strength of sulfate-corroded concrete rose at the initial stage and subsequently declined after extending the corrosion time in the sulfate solution. When the sulfate corrosion period was extended to 60 days, the strength rose slightly by 0.3%. When the sulfate corrosion time was increased to 90 days, the strength of the concrete specimen was reduced by 3.8%.
At the initial stage, the sulfate ions entered the concrete’s surface pores and reacted with the cementitious material to form ettringite and gypsum [21]. These products expanded and filled the original micro-cracks. These products led to the internal structure of concrete denser [22]. Thus, the compressive strength of concrete soaked in solution for 60 days was slightly higher than that of concrete immersed in the sulfate for 30 days. It was much greater than that of the concrete, which was not subjected to sulfate attack. However, when the concrete was attacked in sulfate for 90 days, the expansion resulted from the continuous generation of AFt and gupse exceeded a certain extent. This caused an increase in internal cracks and reduced the compactness of concrete. Additional sulfate ions permeated into the concrete and participated in the reaction, which aggravated the damage to the concrete and reduced its strength.
3.1.2. Effect of CRA on the Strength
Table 5 and Figure 2 show that the strength of the specimens coated with CRA is higher than that of the specimens without CRA. The use of CRA can effectively raise the strength of concrete after being attacked by sulfate solution.
In Figure 2a, for the 30 days corrosion case, when the sulfate-attacked concrete specimens coated with CRA were re-cured for 7 to 56 days, the strength of concrete increased by 3.0%, 3.7%, and 3.6% than that of the specimens without CRA, respectively. In Figure 2b, for the 60-day corrosion case, when the sulfate-attacked concrete specimens coated with CRA were re-cured for 7 to 56 days, the strength of concrete increased by 0.5%, 3.5%, and 6.0%, respectively. In Figure 2c, when the concrete was attacked for three months, the compressive strength of concrete specimens coated with CRA was enhanced respectively by 6.1%, 6.4%, and 6.4% than that of the specimens without CRA after being re-cured for 7 to 56 days, respectively.
This was mainly because the CRA penetrated the concrete through the surface pores and cracks. CRA promoted the unhydrated cement particles to continue the hydration reaction and form a stable, hydrated calcium silicate gel. Moreover, the silicide in the CRA reacted with the calcium hydroxide in concrete to generate calcium silicate hydrate [12]. The calcium silicate hydrate filled the holes and microcracks in the concrete and improved its compactness. Therefore, the strength was improved obviously. If the concrete is attacked by sulfate, the CRA can also be used as a protective film between the concrete and sulfate solution. CRA could lessen the permeation of sulfate into concrete. Thereby, the strength of the specimen was enhanced.
3.1.3. Effect of Curing Time after Being Attacked in Sulfate
Table 5 and Figure 3 show that the strength of concrete exhibits similar change regularity with the extension of the re-curing time of concrete after being attacked.
As illustrated in Figure 3a, the compressive strength of concrete attacked in sulfate for 30 days increased lightly after being re-cured for 7 days in a room environment and continued to decline after 28 and 56 days, respectively. For the concrete without CRA, the strength of the sulphate-attacked specimen re-curing for 7 days was 15.8% higher than that of the concrete curing for 0 days. When the curing time was increased to 28 and 56 days, the strength decreased by 4.3% and 4.5%, respectively. For the concrete specimens coated with CRA, the strength of sulfate-attacked concrete after being re-cured for 7 days was 19.3% higher than that of the concrete re-cured for 0 days. When the concrete coated with CRA was re-cured for 28 and 56 days, the strength decreased by 3.7% and 4.6%, respectively.
As shown in Figure 3b, after being attacked in sulfate solution for 60 days, the strength of concrete showed the same tendency as Figure 3a with the increase in re-curing time. For concrete specimens without CRA, after being re-cured for 7 to 56 days following the sulfate corrosion, the strength of the concrete increased by 12.0% firstly, then decreased by 3.6% and 5.9%, respectively. For concrete specimens with CRA, after being re-cured for 7 to 56 days following the sulfate corrosion, the strength increased by 12.5% first and then decreased by 0.8% and 3.7%, respectively.
As shown in Figure 3c, after being attacked in sulfate solution for three months, the variation of the strength for the concrete without CRA is illustrated. After being re-cured for 7 to 56 days following the sulfate corrosion, the compressive strength increased by 3.6% first and then decreased by 3.8% and 0.9%, respectively. For concrete specimens with CRA, after being re-cured for 7 to 56 days following the sulfate corrosion, the strength increased by 10.0% and then dropped by 3.6% and 0.9%, respectively.
The compressive strength of concrete after being attacked in sulfate solution for 7 days is obviously higher than that of the concrete just removed from sodium sulfate solution. They decreased when the re-curing time increased to 28 days and 56 days, respectively. In addition, for the concrete coated with CRA, after being re-cured for 7 to 56 days, the strength of attacked concrete was obviously greater than that of the concrete re-cured for 0 days.
After being removed from the sulfate solution, the specimens were no longer directly affected by the sulfate solution. The number of sulfate anions immersed in concrete and the reaction rate significantly slowed. The AFt and gupse filled the fractures and pores in the concrete, which enhanced the compactness of the concrete. Accordingly, the strength of the attacked concrete after being re-cured for 7 days was improved. However, the residual sulfate anion in the concrete continued to react with concrete, and the generation of AFt and gupse expanded to a certain extent and destroyed the internal structure of concrete. This resulted in more micro-cracks and lower compactness in concrete. Therefore, the strength declined when the attacked concrete specimens were re-cured for 28 and 56 days. The degeneration of sulfate-attacked concrete was caused by the generation of AFt and gupse produced by the chemical process of sulfate anion and calcium silicate hydrates [22,26,27]. It can be found that the strength was also reduced even after being removed from the sulfate environment. The strength increased in the first week but decreased after being re-cured for 28 and 56 days. Therefore, even if the concrete structures are isolated from the sulfate environment at the site, protective measures should be taken to prevent further reduction in the mechanical properties of concrete.
3.2. Anti-Carbonization Performance of Concrete
The anti-carbonization performances of sulfate-attacked concrete are shown in Table 6. The effects of CRA and re-curing time after being attacked on the carbonization depth are presented and compared in Table 6.
3.2.1. Effect of Sulfate Corrosion Time on Carbonation Resistance of Concrete
According to Table 6, the carbonization depth of sulfate-attacked concrete first decreased and then increased along with the extension of the sulfate corrosion period. Figure 4 shows that the carbonization depth of the specimen subjected to sulfate attack for 60 days is 2.9% lower than that of concrete attacked for 30 days. The carbonization depth of concrete specimens attacked for 90 days was 2.1% higher than those attacked for 60 days. The carbonization resistance of concrete increased lightly after being attacked for 30 days. It declined along with the extension of sulfate corrosion time to 60 days.
The changes in the carbonization depth of concrete subjected to sulfate corrosion also confirmed the reason for the changes in the compressive strength of sulfate-attacked concrete. The carbonization value of the calcium silicate hydrate was an important factor that influenced the carbonation resistance under corrosion conditions [28]. At the beginning stage of the corrosion, the sulfate ion reacted with cementitious slurry to generate AFt and gupse. The expansion of the new product increased the compactness of the interior of the concrete. Similar to the mechanical properties, the carbonation resistance was also improved, and the carbonation depth was reduced. With the extension of the corrosion period, the generation of AFt and gupse increased. When the expansion exceeded a certain degree, micro-cracks appeared inside the concrete. This intensified the internal breakage and reduced the concrete compactness. Therefore, the compressive strength was reduced, and the anti-carbonation performance was weakened. Under the interaction of multiple erosion environments, the permeation of CO2 represented the harsh working environment for concrete, promoting a decrease in carbonization resistance [29].
3.2.2. Effect of CRA on Carbonation Resistance of Concrete
Table 6 and Figure 5 illustrate that even though the sulfate attack time and the re-curing time were different, the carbonization value of concrete specimens without CRA was deeper than that of concrete specimens with CRA. CRA can increase the carbonization resistance of concrete.
In Figure 5a, for the concrete attacked by sulfate corrosion for 30 days, after being re-cured for 1, 4, and 8 weeks, respectively, the carbonation depth of concrete specimens with CRA reduced respectively by 18.2%, 3.3%, and 3.1% than that of concrete specimens without CRA. In Figure 5b, for the concrete specimens subjected to sulfate corrosion for 60 days, after being re-cured for 1, 4, and 8 weeks, the carbonation depth of concrete specimens with CRA were reduced, respectively, by 6.3%, 8.2%, and 7.4% than that of reference samples without CRA. In Figure 5c, for the concrete immersed in sulfate solution for 90 days, after being re-cured for 1, 4, and 8 weeks, the carbonation depth of concrete specimens with CRA was reduced, respectively, by 4.6%, 8.3%, and 4.9% than that of concrete specimens without CRA.
CRA is a strongly alkaline liquid, and it easily penetrates the cracks and pores of the concrete. CRA mainly reacts with H2O and Ca(OH)2 in concrete to form hydrated calcium silicate. The cracks and pores of concrete are filled with new materials, thereby improving the compactness of concrete.
The reason is that the CRA permeated the concrete by the surface pores and micro-cracks and reacted with the incompletely hydrated cement and calcium hydroxide to form calcium silicate hydrate gel [13,14]. The internal pore and fracture were filled, and the compactness of the concrete was increased. Therefore, the carbonization resistance performance of concrete was improved. The carbonization depth was effectively reduced. At the same time, CRA can also act as a protective film for concrete. The entry of CO2 was hindered, carbonation speed slowed, and carbonization resistance enhanced.
3.3. Chloride Ion Permeation Resistance of Concrete
The data of the tests on chloride ion permeation resistance of concrete attacked by sulfate corrosion are listed in Table 7.
3.3.1. Effect of Sulfate Corrosion Time on Chloride Ion Permeation Resistance
In Table 7, compared with the chloride ion permeation coefficient of concrete without sulfate attack, they illustrate that the sulfate-attacked concrete’s relative chloride ion permeation coefficient decreased after being attacked in sulfate solution for 30 days. In Figure 6, the relative chloride ion permeation coefficient decreased by increasing the sulfate corrosion time to 60 days and 90 days. The relative chloride ion permeation coefficient of concrete immersed in sulfate solution for 60 days decreased by 19.7% than that of concrete attacked for 30 days. The relative chloride ion permeation coefficient of concrete attacked for 90 days increased by 22.4% than that of concrete attacked for 60 days.
The reason is similar to the reason for the changes in carbonation resistance of sulfate-attacked concrete. When the concrete attacked for 30 days and 60 days, the chemical reaction of sulfate ions resulted in the formation of AFt and gupse. The expansion of the two products enhanced the denseness of concrete. The relative chloride ion permeation coefficient of concrete decreased, and the Cl- permeation resistance of concrete was enhanced. For 90 days, the expansion of AFt and gupse led to many micro-cracks in the concrete. The sulfate corrosion reduced the compactness of concrete and exacerbated the damage. The Cl− coefficient of impermeability of concrete decreased.
3.3.2. Effect of CRA on Chloride Ion Permeation Resistance
The influence of CRA on the chloride ion permeation resistance of concrete attacked by sulfate corrosion is shown in Figure 7.
In Figure 7a, after being re-cured for 1, 4, and 8 weeks, respectively, for the specimens subjected to sulfate attack for 30 days, the relative chloride ion permeation coefficient of concrete with CRA was less than that of the concrete without CRA. The concrete specimen with CRA had better chloride ion permeation resistance than those without CRA. The relative chloride permeation coefficient of attacked concrete with CRA was reduced by 20.3%, 28.5%, and 28.7%, respectively. In Figure 7b, after being re-cured for 1, 4, and 8 weeks, followed by being attacked for 60 days, the relative chloride ion permeation coefficient of concrete with CRA decreased by 19.3%, 14.7%, and 15.8%, respectively, than that of the concrete specimens without CRA. The chloride ion impermeability of concrete specimens with CRA was obviously improved. In Figure 7c, after being re-cured for 1, 4, and 8 weeks, the concrete was immersed in sulfate solution for 60 days, and the relative permeation coefficient of concrete with CRA decreased by 17.0%, 14.0%, and 16.8%, respectively, than that of the concrete without CRA.
Table 7 and Figure 7 illustrate that the concrete specimens with CRA significantly decreased the relative chloride permeation coefficient compared with the concrete without CRA. CRA can effectively reduce the relative chloride permeation coefficient of the concrete, enhancing the Cl− permeation resistance of concrete.
The reason is that CRA cannot only act as a protective film on the skin layer of the concrete specimens. CRA prevented sulfate entry and reduced capillary water’s rising and crystallization on the concrete surface [30,31]. In addition, CRA reacted with calcium hydroxide in concrete to generate hydrated silicon calcium chloride gel to promote the non-hydrated cement to continue the reaction to produce a gel to fill the micro-cracks [14]. Therefore, the compactness of sulfate-attacked concrete increased. Its permeability was reduced. Thus, the chloride impermeability of concrete was improved, and the relative chloride permeation coefficient was reduced.
Its disadvantage is that it can only penetrate the surface of concrete to enhance its compactness. The penetration depth is only about 1 cm. The price is about USD 22 per kilogram.
3.4. SEM Analysis
Take the concrete attacked in sulfate solution for 30 days, for example; the SEM images of concrete are shown in Figure 8.
The reference concrete with a 58-day re-curing age, the concrete attacked in sulfate solution for 30 days at the 28th day were selected for SEM test. From Figure 8a, it can be seen that there are sheets of calcium hydroxide and C-S-H flocculent deposits with loose surfaces and more voids. The concrete had a complete appearance and rich hydration products. The products produced in concrete were mainly hydrated calcium silicate, ettringite aft and calcium hydroxide Ca(OH)2. A large number of flocs, which is CSH, can be seen in the figure. In the figure, a slender rod, which is AFt, can be seen. Although calcium hydroxide was deposited in hydrated calcium silicate, the flake deposition of calcium hydroxide can still be seen in the figure.
After being attacked in sulfate solution for 30 days, Figure 8b shows that the compactness of the attacked concrete is much higher than the control concrete. Sulfate reacted with C3A and CH in concrete to generate the expansive product AFt and part of gupse. It also can be seen that the scattering of gypsum crystals is in the form of rosettes. Similar morphology was found by [32,33] in mortar mixtures subjected to sodium sulfate. Compared with the image of concrete without CRA in Figure 8c, after being re-cured for 4 weeks with CRA in Figure 8d, there was more vermicular calcium silicate hydrate in the concrete, and the pores were small. It can be seen from the figure that concrete with a repair agent produces a large number of leafy hydration products, such as calcium silicate hydrate, which is the main component of concrete strength. In addition, some flake deposits of calcium hydroxide can be seen among the leafy hydration products.
The pore structures were filled due to the formation of additional calcium silicate hydrate through the reaction between the silicate of CRA and portlandite [13]. A similar phenomenon was reported, which was that the reduced void and reduction in porosity in concrete resulted in higher sulfate resistance [34,35].
3.5. XRD Analysis
XRD analysis for the concrete with and without CRA was carried out using the XRD instrument produced by Bruker, Germany. The phases of concrete were detected by the XRD instrument for samples with CRA and without CRA after the sulfate attack, as shown in Figure 9. Take the concrete specimens attacked in sulfate solution for 90 days as an example; the XRD analyses are given in Figure 9. The XRD analysis for the sulfate-attacked concrete attacked for 90 days was given in Figure 9b. The XRD analysis for the sulfate-attacked concrete re-cured for 28 days without CRA was given in Figure 9c. The XRD analysis for the sulfate-attacked concrete re-cured for 28 days with CRA was given in Figure 9d.
It can be observed that the notable phases of concrete attacked by sulfate are CaCO3, CaSiO4, C-S-H, SiO2, and Aft. CSH gel and calcium zeolite were observed in the concrete samples. In Figure 9c,d, when the concrete was attacked by sulfate, the peak values were clearly decreased after being attacked in sulfate; because of that, the ion of SO42− reacted with CSH to form gupse. In Figure 9d, when the newly formed gupse met CRA, it disappeared because of the higher pH value of the CRA.
4. Conclusions
The compressive strength, carbonation depth, and chloride diffusion factor of the sulfate-attacked concrete were investigated. The performance of concrete subjected to sulfate corrosion was improved with CRA. The following conclusions can be drawn:
- (1)
- The strength and durability of concrete attacked for 60 days were higher than that of the concrete attacked for 30 days. While the sulfate corrosion time increased to 90 days, the strength of sulfate-attacked concrete decreased significantly.
- (2)
- CRA could effectively improve the compressive strength, enhance the carbonation resistance, and reduce the chloride diffusion coefficient of sulfate-attacked concrete.
- (3)
- The strength of attacked concrete coated with CRA increased by 6.1% more than that of the concrete without CRA.
- (4)
- The carbonation depth of concrete specimens with CRA decreased by 4.6% compared to concrete specimens without CRA.
- (5)
- The relative chloride ion permeation coefficient of concrete with CRA decreased by 14.0% more than that of the concrete without CRA.
- (6)
- Even if the concrete was removed from the sulfate environment, the compressive strength and durability of sulfate-attacked concrete were still affected by sulfate ions and continued to decrease along with the increase in re-curing time.
Author Contributions
Conceptualization, data curation, investigation, writing—original draft M.H.; writing—review and editing, methodology, funding acquisition, resources J.L. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Special Fund of Shanxi Provincial Department of Science and Technology (Grant No. 202104010910031).
Data Availability Statement
The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.
Conflicts of Interest
Author Meiqin Han was employed by Lyuliang University. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
References
- Ali, B.; Gulzar, M.A.; Raza, A. Effect of sulfate activation of fly ash on mechanical and durability properties of recycled aggregate concrete. Constr. Build. Mater. 2021, 277, 122329. [Google Scholar] [CrossRef]
- Stroh, J.; Schlegel, M.-C.; Irassar, E.; Meng, B.; Emmerling, F. Applying high resolution SyXRD analysis on sulfate attacked concrete field samples. Cem. Concr. Res. 2014, 66, 19–26. [Google Scholar] [CrossRef]
- Campos, A.; López, C.M.; Aguado, A. Diffusion–reaction model for the internal sulfate attack in concrete. Constr. Build. Mater. 2016, 102, 531–540. [Google Scholar] [CrossRef]
- Yuan, J.; Liu, Y.; Tan, Z.; Zhang, B. Investigating the failure process of concrete under the coupled actions between sulfate attack and drying–wetting cycles by using X-ray CT. Constr. Build. Mater. 2016, 108, 129–138. [Google Scholar] [CrossRef]
- Martins, M.C.; Langaro, E.A.; Macioski, G.; Medeiros, M.H.F. External ammonium sulfate attack in concrete: Analysis of the current methodology. Constr. Build. Mater. 2021, 277, 122252. [Google Scholar] [CrossRef]
- Maes, M.; Belie, N.D. Resistance of concrete and mortar against combined attack of chloride and sodium sulphate. Cem. Concr. Compos. 2014, 53, 59–72. [Google Scholar] [CrossRef]
- Ouyang, W.Y.; Chen, J.K.; Jiang, M.Q. Evolution of surface hardness of concrete under sulfate attack. Constr. Build. Mater. 2014, 53, 419–424. [Google Scholar] [CrossRef]
- Jiang, L.; Niu, D.T. Study of deterioration of concrete exposed to different types of sulfate solutions under drying-wetting cycles. Constr. Build. Mater. 2016, 117, 88–98. [Google Scholar] [CrossRef]
- Jiang, L.; Niu, D.; Yuan, L.; Fei, Q. Durability of concrete under sulfate attack exposed to freeze–thaw cycles. Cold Reg. Sci. Technol. 2015, 112, 112–117. [Google Scholar] [CrossRef]
- Sotiriadis, K.; Nikolopoulou, E.; Tsivilis, S. Sulfate resistance of limestone cement concrete exposed to combined chloride and sulfate environment at low temperature. Cem. Concr. Compos. 2012, 34, 903–910. [Google Scholar] [CrossRef]
- Skaropoulou, A.; Sotiriadis, K.; Kakali, G.; Tsivilis, S. Use of mineral admixtures to improve the resistance of limestone cement concrete against thaumasite form of sulfate attack. Cem. Concr. Compos. 2013, 37, 267–275. [Google Scholar] [CrossRef]
- Sotiriadis, K.; Nikolopoulou, E.; Tsivilis, S.; Pavlou, A.; Chaniotakis, E.; Swamy, R.N. The effect of chlorides on the thaumasite form of sulfate attack of limestone cement concrete containing mineral admixtures at low temperature. Constr. Build. Mater. 2013, 43, 156–164. [Google Scholar] [CrossRef]
- Li, Q.; Li, Z.; Yuan, G.; Shu, Q. The effect of a proprietary inorganic coating on compressive strength and carbonation depth of simulated fire-damaged concrete. Mag. Concr. Res. 2013, 65, 651–659. [Google Scholar] [CrossRef]
- Li, Q.T.; Liu, L.; Yuan, G. Improvement of bond behaviour between steel bar and concrete subjected to elevated temperature at early age. Mag. Concr. Res. 2018, 70, 885–893. [Google Scholar] [CrossRef]
- Scarfato, P.; Di Maio, L.; Fariello, M.L.; Russo, P.; Incarnato, L. Preparation and evaluation of polymer/clay nanocomposite surface treatments for concrete durability enhancement. Cem. Concr. Compos. 2012, 34, 297–305. [Google Scholar] [CrossRef]
- Nosouhian, F.; Mostofinejad, D.; Hasheminejad, H. Influence of biodeposition treatment on concrete durability in a sulphate environment. Biosyst. Eng. 2015, 133, 141–152. [Google Scholar] [CrossRef]
- Suleiman, A.R.; Soliman, A.M.; Nehdi, M.L. Effect of surface treatment on durability of concrete exposed to physical sulfate attack. Constr. Build. Mater. 2014, 73, 674–681. [Google Scholar] [CrossRef]
- Joshi, S.; Goyal, S.; Mukherjee, A.; Sudhakara Reddy, M. Protection of concrete structures under sulfate environments by using calcifying bacteria. Constr. Build. Mater. 2019, 209, 156–166. [Google Scholar] [CrossRef]
- GB/T 50081-2019; Standard for Test Methods of Concrete Physical and Mechanical Properties. MOC: Beijing, China, 2019.
- GB/T 50082-2009; Standard for Test Method of Long-Term Performance and Furability of Ordinary Concrete. MOC: Beijing, China, 2009.
- Haufe, J.; Vollpracht, A. Tensile strength of concrete exposed to sulfate attack. Cem. Concr. Res. 2019, 116, 81–88. [Google Scholar] [CrossRef]
- Ragoug, R.; Metalssi, O.O.; Barberon, F.; Torrenti, J.M.; Roussel, N.; Divet, L.; Lacaillerie, J.B.E. Durability of cement pastes exposed to external sulfate attack and leaching: Physical and chemical aspects. Cem. Concr. Res. 2019, 116, 134–145. [Google Scholar] [CrossRef]
- Cheng, H.; Liu, T.; Zou, D.; Zhou, A. Compressive strength assessment of sulfate-attacked concrete by using sulfate ions distributions. Constr. Build. Mater. 2021, 293, 123550. [Google Scholar] [CrossRef]
- Burgos, D.M.; Guzmán, Á; Delvasto, S. Assessment of the performance of SCC incorporating volcanic materials in a sodium sulfate environment. Constr. Build. Mater. 2019, 195, 52–65. [Google Scholar] [CrossRef]
- Boudali, S.; Kerdal, D.; Ayed, K.; Abdulsalam, B.; Soliman, A. Performance of self-compacting concrete incorporating recycled concrete fines and aggregate exposed to sulphate attack. Constr. Build. Mater. 2016, 124, 705–713. [Google Scholar] [CrossRef]
- Schmidt, T.; Lothenbach, B.; Romer, M.; Neuenschwander, J.; Scrivener, K. Physical and microstructural aspects of sulfate attack on ordinary and limestone blended Portland cements. Cem. Concr. Res. 2009, 39, 1111–1121. [Google Scholar] [CrossRef]
- Wei, L.; Guang, J.X.; Ya, Z. Triaxial test on concrete material containing accelerators under physical sulphate attack. Constr. Build. Mater. 2019, 206, 641–654. [Google Scholar] [CrossRef]
- Liu, Z.; Heede, P.V.; Zhang, C.; Shi, X.; Wang, L.; Li, J.; Yao, Y.; Lothenbach, B.; Belie, N.D. Carbonation of blast furnace slag concrete at different CO2 concentrations: Carbonation rate, phase assemblage, microstructure and thermodynamic modelling. Cem. Concr. Res. 2023, 169, 107161. [Google Scholar] [CrossRef]
- Oliveira, R.L.N.; Bragança, M.O.G.; Junior, R.A.M. Effect of coarse aggregate size on corrosion of reinforced concrete exposed to carbonation and chloride ingress by electrochemical measurements. Constr. Build. Mater. 2022, 361, 129665. [Google Scholar] [CrossRef]
- Liu, Q.; Liao, Z.; Xiong, Y.; Liu, Z.; Zhang, W. Effect of imitation fair-faced curing and protective coating on the durability of concrete. J. Build. Eng. 2023, 63, 10554. [Google Scholar] [CrossRef]
- Zhang, M.; Xu, H.; Zeze, A.L.P.; Liu, X.; Tao, M. Coating performance, durability and anti-corrosion mechanism of organic modified geopolymer composite for marine concrete protection. Cem. Concr. Compos. 2022, 129, 104495. [Google Scholar] [CrossRef]
- Huang, Q.; Wang, C.; Zeng, Q.; Yang, C.; Luo, C.; Yang, K. Deterioration of mortars exposed to sulfate attack under electrical field. Constr. Build. Mater. 2016, 117, 121–128. [Google Scholar] [CrossRef]
- Brekailo, F.; Pereira, E.; Medeiros-Junior, R.A. Migration test as an accelerated methodology in concrete for evaluating sulfate attack by Na2SO4 and MgSO4. Constr. Build. Mater. 2023, 388, 131681. [Google Scholar] [CrossRef]
- Gurumoorthy, N.; Arunachalam, K. Micro and mechanical behaviour of treated used foundry sand. Constr. Build. Mater. 2016, 123, 184–190. [Google Scholar] [CrossRef]
- Gurumoorthy, N.; Arunachalam, K. Durability studies on concrete containing treated used foundry sand. Constr. Build. Mater. 2019, 201, 651–661. [Google Scholar] [CrossRef]
Figure 1.
Effect of corrosion time on the compressive strength.
Figure 2.
Effect of CRA on the strength of concrete attacked for different periods.
Figure 3.
Effect of re-curing time on the strength of sulfate-attacked concrete.
Figure 4.
Effect of corrosion time on the carbonization depth of the attacked concrete.
Figure 5.
Effect of CRA on the carbonation depth of attacked concrete.
Figure 6.
Influence of corrosion time on the chloride ion permeation coefficient of concrete.
Figure 7.
Effect of CRA on the chloride ion permeation coefficient of attacked concrete.
Figure 8.
SEM images of concrete attacked in sulfate solution for 30 days.
Figure 9.
The XRD spectra of sulfate-attacked concrete with CRA and without CRA. 1 = Aft, 2 = Quartz, 3 = Calcium silicate, 4 = Calcium hydroxide, 5 = calcium carbonate, 6 = scolecite, 7 = Calcium Silicate Hydrate, 8 = gypsum.
Figure 9.
The XRD spectra of sulfate-attacked concrete with CRA and without CRA. 1 = Aft, 2 = Quartz, 3 = Calcium silicate, 4 = Calcium hydroxide, 5 = calcium carbonate, 6 = scolecite, 7 = Calcium Silicate Hydrate, 8 = gypsum.
Table 1.
Main components of cement.
| Components/Property | Value |
|---|---|
| SiO2 | 22.86% |
| Al2O3 | 7.34% |
| Fe2O3 | 3.24% |
| CaO | 58.64% |
| MgO | 1.94% |
| SO3 | 2.02% |
| Na2O | 0.86% |
| K2O | 0.76% |
| MnO | 0.07% |
| P2O5 | 0.06% |
| Cl | 0.029% |
| Ignition loss | 2.14% |
| Specific gravity | 3.14 |
| Specific surface (cm2/g) | 3280 |
Table 2.
Main components and properties of CRA.
| Content | Property |
|---|---|
| Main components | Propylene glycol (1.0%) Aluminate solution (0.3%) Na2O·nSiO2 (30%) Water (68%) |
| Appearance | Clear transparent liquid |
| Odors | Inodorous |
| Specific gravity | 1.23 |
| Solid content | 31.1% |
| pH | 11.27 |
| Kinematic viscosity | <5.70 cSt |
Table 3.
Proportions of concrete mixtures.
| w/c Ratio | Mixture Proportion (kg/m3) | ||||
|---|---|---|---|---|---|
| Water | Cement | Sand | Crushed Stone | Superplasticizer | |
| 0.593 | 172 | 290 | 735 | 1102 | 2.65 |
Table 4.
Test conditions for concrete specimens.
| Sulfate Corrosion Time (Day) | Dosage of CRA (kg/m2) | Curing Time after Being Coated CRA (Day) |
|---|---|---|
| 30 | 0 | 0 |
| 30 | 0 | 7 |
| 30 | 0 | 28 |
| 30 | 0 | 56 |
| 30 | 0.6 | 7 |
| 30 | 0.6 | 28 |
| 30 | 0.6 | 56 |
| 60 | 0 | 0 |
| 60 | 0 | 7 |
| 60 | 0 | 28 |
| 60 | 0 | 56 |
| 60 | 0.6 | 7 |
| 60 | 0.6 | 28 |
| 60 | 0.6 | 56 |
| 90 | 0 | 0 |
| 90 | 0 | 7 |
| 90 | 0 | 28 |
| 90 | 0 | 56 |
| 90 | 0.6 | 7 |
| 90 | 0.6 | 28 |
| 90 | 0.6 | 56 |
Table 5.
Compressive strength of sulfate-attacked concrete.
| Corrosion Time (Day) | Dosage of CRA (kg/m2) | Compressive Strength (MPa) | ||||
|---|---|---|---|---|---|---|
| Without Sulfate | Curing Time after Being Attacked (Day) | |||||
| 0 | 7 | 28 | 56 | |||
| 30 | 0 | 33.2 | 34.2 | 39.6 | 37.9 | 36.2 |
| 60 | 33.8 | 34.3 | 38.4 | 37.0 | 34.8 | |
| 90 | 34.2 | 33.0 | 34.2 | 32.9 | 32.6 | |
| 30 | 0.6 | 33.2 | 34.2 | 40.8 | 39.3 | 37.5 |
| 60 | 33.8 | 34.3 | 38.6 | 38.3 | 36.9 | |
| 90 | 34.2 | 33.0 | 36.3 | 35.0 | 34.7 | |
Table 6.
Carbonization depth of sulfated attacked concrete.
| Corrosion Time (Day) | Dosage of CRA (kg/m2) | Carbonization Depth (mm) | ||||
|---|---|---|---|---|---|---|
| Without Sulfate | Curing Time after Being Attacked (Day) | |||||
| 0 | 7 | 28 | 56 | |||
| 30 | 0 | 10.02 | 8.31 | 6.88 | 8.09 | 8.46 |
| 60 | 9.74 | 8.07 | 7.19 | 7.55 | 8.23 | |
| 90 | 9.37 | 8.24 | 7.77 | 7.79 | 7.94 | |
| 30 | 0.6 | 10.02 | 8.31 | 5.63 | 7.82 | 8.20 |
| 60 | 9.74 | 8.07 | 6.74 | 6.93 | 7.62 | |
| 90 | 9.37 | 8.24 | 7.41 | 7.14 | 7.55 | |
Table 7.
The chloride ion diffusion coefficient of concrete after being attacked.
| Corrosion Time (Day) | Dosage of CRA (kg/m2) | Chloride Ion Permeation Coefficient (10–12 m2/s) | ||||
|---|---|---|---|---|---|---|
| Without Sulfate | Curing Time after Being Attacked (Day) | |||||
| 0 | 7 | 28 | 56 | |||
| 30 | 0 | 4.75 | 4.06 | 3.74 | 4.46 | 4.63 |
| 60 | 3.82 | 3.26 | 3.00 | 3.19 | 3.41 | |
| 90 | 3.49 | 3.99 | 4.71 | 4.99 | 5.17 | |
| 30 | 0.6 | 4.75 | 4.06 | 2.98 | 3.19 | 3.30 |
| 60 | 3.82 | 3.26 | 2.42 | 2.72 | 2.87 | |
| 90 | 3.49 | 3.99 | 3.91 | 4.29 | 4.30 | |
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Han, M.; Li, J. Enhancement of Compressive Strength and Durability of Sulfate-Attacked Concrete. Buildings 2024, 14, 2187. https://doi.org/10.3390/buildings14072187
AMA Style
Han M, Li J. Enhancement of Compressive Strength and Durability of Sulfate-Attacked Concrete. Buildings. 2024; 14(7):2187. https://doi.org/10.3390/buildings14072187
Chicago/Turabian StyleHan, Meiqin, and Jianguo Li. 2024. "Enhancement of Compressive Strength and Durability of Sulfate-Attacked Concrete" Buildings 14, no. 7: 2187. https://doi.org/10.3390/buildings14072187
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