Study of Fine-Grained Composites Exposed to Sulfuric Acid and Sodium Sulfate

2016 ◽  
Vol 827 ◽  
pp. 275-278
Author(s):  
Martin Vyšvařil ◽  
Markéta Rovnaníková
Keyword(s):  
Waste Water ◽  
Sulfuric Acid ◽  
Sodium Sulfate ◽  
Sulfate Attack ◽  
Sewer Pipes ◽  
Sulfate Ions ◽  
Fine Grained ◽  
One Year ◽  
Corrosion Of Steel ◽  
Loss Of Strength

The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions, especially in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water and from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to sulfate interaction can result in the cracking and softening, with loss of strength of concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of one-year contact of 0.5% H2SO4, and 5% Na2SO4 on changes of pH and content of sulfates in 7 types of concrete has been analyzed. It was found that after one year of sulfate attack on concrete, significant growth of content of sulfates is observed in the lowermost layer of the samples. Samples treated by 5% Na2SO4 contain slightly more sulfates in the upper layers than samples treated by sulfuric acid. The reduction in pH of aqueous leaches occurred in all layers of the samples. However, even in the lower layers of the samples, the reduction of pH below 9.5 did not turn up (except for SRS sample), and thus the conditions for the depassivation of reinforcement were not met.

Sulfate Attack on Different Types of Concrete in Media Simulating Sewer System

2016 ◽  
Vol 714 ◽  
pp. 122-127
Author(s):  
Martin Vyšvařil ◽  
Markéta Rovnaníková ◽  
Patrik Bayer
Keyword(s):  
Waste Water ◽  
Sulfuric Acid ◽  
Sewage Water ◽  
Sulfate Attack ◽  
Acid Attack ◽  
Bottom Part ◽  
Sewer Pipes ◽  
Fine Grained ◽  
Different Types ◽  
One Year

The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions. Microbiologically induced concrete corrosion (MICC) damages especially sewage collection systems. The most rapid cases of deterioration always occur in areas with elevated H2S concentrations, moisture, and oxygen in the atmosphere. During the MICC, the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to a sulfate interaction can result in a cracking and softening, with a loss of strength of concrete. The formation of ettringite (AFt) from gypsum (forming by reaction of sulfate anion with calcium hydroxide) and C3A via monosulfate (AFm) is the main chemical reaction of sulfate attack on concrete. Ettringite and gypsum have considerably larger volume than initial compounds, which leads to increased pressure in concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of 0.5% sulfuric acid, simulating MICC, and a solution simulating sewage water has been investigated on changes of the pH, content of sulfates and the porosity in various types of concrete. The aim of this study is to compare the changes in different types of concrete during the sulfate attack in two kinds of medium represented the bottom part of pipelines (waste water) and the sewer crown (0.5% H2SO4). It was found, that after 1 year in 0.5% H2SO4, a visible degradation of surface occurs in all investigated types of concrete. Samples over the year in waste water became dark. Concentration of sulfates in all studied types of concrete increased six times at least after one year sulfuric acid attack and also the reduction of the pH of their aqueous leaches was determined. The solution simulating sewage water did not cause such changes.

Sulfuric Acid Attack on Various Types of Fine Grained Concrete

2015 ◽  
Vol 1100 ◽  
pp. 101-105
Author(s):  
Martin Vyšvařil ◽  
Markéta Rovnaníková
Keyword(s):  
Sulfuric Acid ◽  
Acid Corrosion ◽  
Sulfate Attack ◽  
Steel Reinforcement ◽  
Acid Attack ◽  
Sewer Pipes ◽  
Sulfate Ions ◽  
Fine Grained ◽  
Ph Values ◽  
Sulfuric Acid Corrosion

Sulfate corrosion is one of the major threats for durability of concrete constructions and it becomes a major destructor in sewage collection systems where the concrete sewer pipes are exposed to sulfates from wastewater as well as from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to steel depassivation and results in the corrosion of this steel reinforcement. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid, simulating biogenic sulfuric acid corrosion, on changes of pH and content of sulfates in various types of concrete has been investigated. After 3 and 6 months of the corrosive treatment, the content of sulfate ions and pH values in several layers of specimens were determined. It was found that the sulfate ions penetrate into concrete to the maximum depth of 20 mm and the pH of the aqueous leaches of particular layers of the samples was reduced to 11.4 at the most. Thus, the conditions for the depassivation of reinforcement were not met. The GL and GBFS concrete samples showed the least changes of their pH and therefore they had the best resistivity to the six months sulfate attack.

scholarly journals Deterioration Process of Concrete Exposed to Internal Sulfate Attack

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1336 ◽  
Author(s):  
Weifeng Chen ◽  
Bei Huang ◽  
Yuexue Yuan ◽  
Min Deng
Keyword(s):  
Compressive Strength ◽  
Sulfate Attack ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Great Loss ◽  
Sulfate Ions ◽  
Coarse Aggregates ◽  
Deterioration Process ◽  
One Year ◽  
Internal Sulfate Attack

Damage to concrete structures with gypsum-contaminated aggregate occurs frequently. Aggregates in much of the southern part of China are contaminated with gypsum. Therefore, in this study, the effects of using different quantities of gypsum-contaminated aggregate on the expansion and compressive strength of concrete were investigated over a period of one year. Two groups of concrete were designed with the gypsum-contaminated aggregate containing different parts of fine and coarse aggregate, respectively. The SO3 contents were 0%, 0.5%, 1%, 1.5%, 3%, 5%, and 7% by weight of aggregate. X-ray diffraction (XRD), thermogravimetry (TG), and differential scanning calorimetry (DSC) were used to analyze the change in mineral composition over time. The microstructure was also studied by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that significant expansion and great loss in compressive strength did not occur in concrete if the content of SO3 lay below 1.5% and 3% in fine and coarse aggregates, respectively. The concentration of sulfate ions in concrete was not enough to form new a phase of gypsum. During the process of internal sulfate attack, the content of gypsum decreased and the content of ettringite increased. Ettringite was the main reason for the expansion damage of concrete. Additionally, the fracture mode of internal sulfate attack on concrete was the crack extension from gypsum to paste; finally, the aggregate separated from the paste.

Behaviors of Long-Term Exposure Concrete to Sulfate Solution

2011 ◽  
Vol 368-373 ◽  
pp. 790-794
Author(s):  
Shun Bo Zhao ◽  
Thomas C.K. Molyneaux ◽  
David W. Law ◽  
Yong Li ◽  
Li Yun Pan
Keyword(s):  
Compressive Strength ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Sulfate Ions ◽  
Sulfate Solutions ◽  
Collaborative Studies ◽  
Diffusion Depth ◽  
One Year ◽  
The Uk

As a part of the collaborative studies between China, Australia and the UK, examing sulfate attack on concrete, this paper reports the experimental results obtained from the Chinese laboratory. Specimens were immersed in sodium and magnesium sulfate solutions with concentrations of 500mg/L, 5000mg/L and 50000mg/L. Investigations were conducted over approximately a one year period. Susceptibility to sulfate attack was assessed in terms of changes in the mass and length of specimens, the compressive strength of the concrete, as well as the diffusion depth of sulfate-ions into the concrete at fixed intervals. Several differences were observed between these results and those reported in studies from the UK laboratory.

One-Year Sulfate Attack on Various Types of Fine Grained Concrete

2015 ◽  
Vol 1124 ◽  
pp. 313-318
Author(s):  
Martin Vyšvařil ◽  
Markéta Rovnaníková
Keyword(s):  
Sulfuric Acid ◽  
Acid Corrosion ◽  
Surrounding Medium ◽  
Mineralogical Composition ◽  
Sulfate Solution ◽  
Xrd Analysis ◽  
Sewage Water ◽  
Sulfate Attack ◽  
Fine Grained ◽  
Ph Decrease

Concrete shows extensive degradation when exposed to the external sulfate attack, characterized by ingress of sulfate ions from surrounding medium. This process leads to gradual pH decrease, to expansion, cracking, spalling of concrete, and finally to the complete disintegration of the material. Sulfate attack becomes a major destructor in sewage collection systems where the concrete sewer pipes are exposed to sulfates from wastewater as well as from biogenic activity of bacteria. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid, simulating biogenic sulfuric acid corrosion, 5% sodium sulfate solution and solution simulating sewage water on various types of concrete has been investigated. The concrete specimens were characterized after exposition to corroding media by their mechanical parameters, microstructure and in the case of H2SO4 as the most aggressive corroding solution, the mineralogical composition was also determined by XRD analysis. It was found that the exposition to Na2SO4 solution twofold improved flexural strengths of concrete mixes based on Portland and sulfate-resisting cements. Contrary, the exposition to H2SO4 solution significantly decreased compressive strengths of all types of concrete.

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