Materials

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22 pages, 4314 KiB

Open AccessArticle

The Effect of the Addition of Coal Fly Ash (CFA) on the Control of Water Movement within the Structure of the Concrete

by Grzegorz Ludwik Golewski

Materials 2023, 16(15), 5218; https://doi.org/10.3390/ma16155218 - 25 Jul 2023

Cited by 64 | Viewed by 2910

Studies were carried out to find a relation between the important physical property, i.e., water absorption and the main mechanical parameter, i.e., compressive strength (f_cm), of concretes containing coal fly ash (CFA) in the amounts of 0% (CFA-00), 20% (CFA-20%), [...] Read more.

Studies were carried out to find a relation between the important physical property, i.e., water absorption and the main mechanical parameter, i.e., compressive strength (f_cm), of concretes containing coal fly ash (CFA) in the amounts of 0% (CFA-00), 20% (CFA-20%), and 30% (CFA-30). The methodology of the water absorption tests reflected the conditions prevailing in the case of reinforced concrete structures operating below the water table. The microstructure of all materials was also assessed. Based on the conducted studies, it was found that both the f_cm of concretes with the addition of CFA and its water absorption depended on the percentage of waste used, whereas both analyzed parameters were closely related to the structure of the cement matrix and interfacial transition zone area between the coarse aggregates and the paste. It should be stated that at the content of 20% CFA in the binder composition, an increase in the f_cm of the material is observed, with a simultaneous increase in its water absorption. On the other hand, the addition of 30% CFA results in a significant decrease in both the strength of the composite and its water absorption. Thus, it was found that in the case of concretes with the addition of CFA, the strength of the material is directly proportional to the level of its water absorption. Moreover, the concrete including 30% CFA may increase the durability of reinforced concrete structures subjected to immersion conditions. From an application point of view, the obtained research results may be helpful in understanding the impact of the CFA additive on the level of water absorption in cement concretes with this waste. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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10 pages, 2028 KiB

Open AccessArticle

Effect of Stray Current on Corrosion and Calcium Ion Corrosion of Concrete Reinforcement

by Weijun Yang, Xin Ye, Rongjun Li and Jianyu Yang

Materials 2022, 15(20), 7287; https://doi.org/10.3390/ma15207287 - 18 Oct 2022

Cited by 7 | Viewed by 1733

Abstract

The construction of subways, hydroelectric stations and water substations is exposed to stray currents, which can accelerate concrete corrosion. The influence of stray currents on reinforced concrete structures is unclear. In this paper, the influence of concrete strength grade, reinforcement diameter and stray [...] Read more.

The construction of subways, hydroelectric stations and water substations is exposed to stray currents, which can accelerate concrete corrosion. The influence of stray currents on reinforced concrete structures is unclear. In this paper, the influence of concrete strength grade, reinforcement diameter and stray current intensity on the extent of reinforcement corrosion and calcium ion dissolution were investigated, and the damage of reinforcement and calcium ion corrosion to concrete strength was investigated by simulating a stray current environment and conducting an electrified acceleration test. The test results show that the higher the strength grade of concrete, the lower the stray current intensity and the smaller the corrosion rate and calcium ion dissolution rate of reinforcement; with the increase in the diameter of reinforcement the corrosion rate decreases, but the calcium ion dissolution rate is not affected by reinforcement diameter. The damage effect of reinforcement corrosion on concrete compressive strength is more obvious than that of calcium ion corrosion. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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19 pages, 4374 KiB

Open AccessArticle

Prediction of Concrete Compressive Strength in Saline Soil Environments

by Deqiang Yang, Changwang Yan, Shuguang Liu, Zhirong Jia and Chunguang Wang

Materials 2022, 15(13), 4663; https://doi.org/10.3390/ma15134663 - 2 Jul 2022

Cited by 11 | Viewed by 1827

Abstract

Saline soil in Western China contains high concentrations of chloride ions, sulfate ions, and other corrosive ions, and the performance of concrete will substantially deteriorate from exposure to this environment. Therefore, it is of great significance to study and predict the concrete compressive [...] Read more.

Saline soil in Western China contains high concentrations of chloride ions, sulfate ions, and other corrosive ions, and the performance of concrete will substantially deteriorate from exposure to this environment. Therefore, it is of great significance to study and predict the concrete compressive strength in saline soil environments. In this paper, the effects of corrosion on concrete were analyzed from the aspects of surface damage, damage depth, and X-ray diffraction (XRD) of the corrosion products. The effects of corrosion were quantified by damage depth and corrosion depth. Then, considering the corrosion effects combined with Fick’s diffusion law, a time-dependent model of concrete compressive strength and a time-dependent model of damage depth were established. The results show that the deterioration of concrete gradually developed from the surface to the interior, and that the interface of the concrete specimen was equivalent to three parts: a failure zone, a filling zone, and an undisturbed zone. The results also showed that the time-varying model of concrete compressive strength proposed by the author was fully applicable, with an error of less than five percent. The service life of concrete predicted by the damage depth was found to be about 253 months (21.1 years), and the service life predicted by the time-varying compressive strength model was about 187 months (15.6 years). Both prediction results were far less than the normal concrete service life of 50 years. In addition, the long-term compressive strength of the corroded concrete was about 90% of that of the noncorroded concrete, which did not deteriorate with the corrosion time. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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15 pages, 4821 KiB

Open AccessArticle

The Effect of Stray Current on Calcium Leaching of Cement-Based Materials

by Fang Liu, Yuanrui Zou, Baomin Wang and Xiaosa Yuan

Materials 2022, 15(6), 2279; https://doi.org/10.3390/ma15062279 - 19 Mar 2022

Cited by 9 | Viewed by 1967

Abstract

The metro engineering is in an environment rich in stray current and groundwater, which will accelerate concrete corrosion. In this study, the corrosion of cement-based materials, under stray current, consisting of direct current, was investigated, and the effects of stray current magnitude, water-binder [...] Read more.

The metro engineering is in an environment rich in stray current and groundwater, which will accelerate concrete corrosion. In this study, the corrosion of cement-based materials, under stray current, consisting of direct current, was investigated, and the effects of stray current magnitude, water-binder ratio, fly ash, and silica fume on its corrosion were analyzed. The results show that, as the energisation duration of the stray current increases, the mass of the cathode side leachables increases, and the compressive strength of the cement-based materials decreases overall; at 120 d of stray current, the water-binder ratio of 0.50 shows the least reduction in strength, compared to the others; the mass of cathode side leachables decrease significantly with the increase in fly ash content; when fly ash content is 15%, the mass of cathode side leachables is the least, and the decrease in the compressive strength at 120 d of stray current is the smallest. At 10% silica fume content, the mass of the cathode side leachables is the least, and the decrease in the compressive strength of the cement-based materials at 120 d of stray current is the smallest. In general, the corrosion resistance is relatively good at 15% fly ash content and 10% silica fume content under stray current. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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16 pages, 24906 KiB

Open AccessArticle

Hydration and Mechanical Properties of Calcium Sulphoaluminate Cement Containing Calcium Carbonate and Gypsum under NaCl Solutions

by Jianzheng Wang, Shilin Song, Yu Zhang, Tao Xing, Ying Ma and Haiyan Qian

Materials 2022, 15(3), 816; https://doi.org/10.3390/ma15030816 - 21 Jan 2022

Cited by 6 | Viewed by 2287

Abstract

Hydration characteristics and mechanical properties of calcium sulphoaluminate (CSA) cement with different contents of CaCO₃ and gypsum under NaCl solutions were studied, using the testing methods of isothermal calorimetry, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), linear shrinkage, and compressive strength. Results [...] Read more.

Hydration characteristics and mechanical properties of calcium sulphoaluminate (CSA) cement with different contents of CaCO₃ and gypsum under NaCl solutions were studied, using the testing methods of isothermal calorimetry, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), linear shrinkage, and compressive strength. Results show that CaCO₃ can promote hydration and reduce the hydration heat of CSA cement. The reaction between gypsum and C₄A₃

\bar{S}

releases a large quantity of heat in the initial hydration period; however, over 3 days of accumulation, the level of hydration heat is reduced. Under NaCl solutions, the aluminate phase has difficulty reacting with CaCO₃ to form carbonate phase but combines with chloride ions to form Friedel’s salt. On the contrary, gypsum reduces aluminate phase, and the content of Friedel’s salt is also reduced. Furthermore, CaCO₃ and gypsum both increase the total porosity of the CSA cement paste under NaCl solutions during the early curing phase, and over the long-term, pore structure is also optimized. CaCO₃ and gypsum reduce the linear shrinkage of CSA cement paste under NaCl solutions. Overall, the compressive strength of CSA cement is reduced with the addition of CaCO₃, and the trend will be sharper with the increase in CaCO₃. However, when it comes to gypsum, the compressive strength is almost the same during early curing, but in the long-term, compressive strength improves. Essentially, the compressive strength of CSA cement mortar with CaCO₃ and gypsum will improve under NaCl solutions. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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24 pages, 8643 KiB

Open AccessArticle

Assessment of Corrosion Performance of Steel Rebar in Snail Shell Ash Blended Cements under Marine Environments

by Muralidharan Raghav, Subbiah Karthick, Taejoon Park and Han-Seung Lee

Materials 2021, 14(23), 7286; https://doi.org/10.3390/ma14237286 - 28 Nov 2021

Cited by 9 | Viewed by 2886

Abstract

An attempt has been made on a constructive approach to evaluate the performance of snail shell ash (SSA) for its corrosion performance under marine environments. Corrosion performance of steel rebar in chloride-contaminated SSA with (0% to 50%) replacement levels of cement extract medium [...] Read more.

An attempt has been made on a constructive approach to evaluate the performance of snail shell ash (SSA) for its corrosion performance under marine environments. Corrosion performance of steel rebar in chloride-contaminated SSA with (0% to 50%) replacement levels of cement extract medium was examined through electrochemical and weight loss techniques. Initially, snail shell powder (SSP) is made by pulverizing and subsequently SSA is by thermal decomposition methods. Both SSP and SSA were characterized by X-ray diffraction, Fourier transforms infrared spectroscopy, scanning electron microscopy, and energy dispersion X-ray spectroscopy. Concrete cubes with 0% to 50% replacement levels of cement by SSA were evaluated for their mechanical properties. A critical level of 20 to 30% SSA improved both corrosion resistance and strength of concrete. Extrapolation modeling for the strength and corrosion rate with respect to later age were made. SSA is a suitable replacement material for natural limestone in cement productions. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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14 pages, 4324 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study on Chloride Ion Diffusion in Concrete under Uniaxial and Biaxial Sustained Stress

by Xiaokang Cheng, Jianxin Peng, C.S. Cai and Jianren Zhang

Materials 2020, 13(24), 5717; https://doi.org/10.3390/ma13245717 - 15 Dec 2020

Cited by 10 | Viewed by 2160

Abstract

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride [...] Read more.

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride solution erosion. The influence of different sustained compressive stress states on chloride ion diffusivity is evaluated by testing chloride concentration in concrete. The experiment results show that the existence of sustained compressive stress does not always inhibit the diffusion of chloride ions in concrete, and the numerical value of sustained compressive stress level can affect the diffusion law of chloride ions in concrete. It is found that the chloride concentration decreases most when the lateral compressive stress level is close to 0.15 times the compressive strength of concrete. In addition, the sustained compressive stress has a significant effect on chloride ion diffusion of concrete with high water/cement ratio. Then, the chloride diffusion coefficient model under uniaxial and biaxial sustained compressive stress is established based on the apparent chloride diffusion coefficient. Finally, the results demonstrate that the chloride diffusion coefficient model is reasonable and feasible by comparing the experimental data in the opening literature with the calculated values from the developed model. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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15 pages, 7079 KiB

Open AccessArticle

Effect of a Boric Acid Corrosive Environment on the Microstructure and Properties of Concrete

by Yu Wang, Bei Huang, Zhongyang Mao, Min Deng and Huan Cao

Materials 2020, 13(21), 5036; https://doi.org/10.3390/ma13215036 - 8 Nov 2020

Cited by 8 | Viewed by 3285

Abstract

Boric acid, a weak acid, is often used to shield neutrons in water cooling systems in nuclear power stations. The leakage of boric acid in water cooling systems damages the concrete structure and affects the safety of nuclear power engineering. In this experiment, [...] Read more.

Boric acid, a weak acid, is often used to shield neutrons in water cooling systems in nuclear power stations. The leakage of boric acid in water cooling systems damages the concrete structure and affects the safety of nuclear power engineering. In this experiment, concrete specimens were cured with boric acid at 20, 40, and 70 °C to study the effect of boric acid on the microstructure and properties of concrete. X-ray diffraction (XRD) and thermogravimetry and differential scanning calorimetry (TG-DSC) were used to analyze the change in mineral composition. The microstructure was examined by scanning electron microscope (SEM). The porosity of the concrete was examined by mercury intrusion porosimetry (MIP). The results show that the performance of specimens was stable under the curing conditions of 20 and 40 °C. Under the curing environment of 70 °C, the performance of concrete cured with 0, 2000, and 7000 ppm concentrations was stable, but the compressive strength of the 180,000 ppm specimen was reduced by 27.8% and suffered the most serious loss of mass and surface corrosion, with the most harmful pores. The high concentration of boric acid seriously damaged the surface structure of concrete, which is the main reason for its loss of properties. This situation is extremely dangerous in nuclear power engineering, so the effect of boric acid leakage cannot be ignored. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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