Resistance to Sulfuric Acid Corrosion of Geopolymer Concrete Based on Different Binding Materials and Alkali Concentrations

Geopolymer binder is expected to be an optimum alternative to Portland cement due to its excellent engineering properties of high strength, acid corrosion resistance, low permeability, good chemical resistance, and excellent fire resistance. To study the sulfuric acid corrosion resistance of geopolymer concrete (GPC) with different binding materials and concentrations of sodium hydroxide solution (NaOH), metakaolin, high-calcium fly ash, and low-calcium fly ash were chosen as binding materials of GPC for the geopolymerization process. A mixture of sodium silicate solution (Na2SiO3) and NaOH solution with different concentrations (8 M and 12 M) was selected as the alkaline activator with a ratio (Na2SiO3/NaOH) of 1.5. GPC specimens were immersed in the sulfuric acid solution with the pH value of 1 for 6 days and then naturally dried for 1 day until 98 days. The macroscopic properties of GPC were characterized by visual appearance, compressive strength, mass loss, and neutralization depth. The materials were characterized by SEM, XRD, and FTIR. The results indicated that at the immersion time of 28 d, the compressive strength of two types of fly ash-based GPC increased to some extent due to the presence of gypsum, but this phenomenon was not observed in metakaolin-based GPC. After 98 d of immersion, the residual strength of fly ash based GPC was still higher, which reached more than 25 MPa, while the metakaolin-based GPC failed. Furthermore, due to the rigid 3D networks of aluminosilicate in fly ash-based GPC, the mass of all GPC decreased slightly during the immersion period, and then tended to be stable in the later period. On the contrary, in metakaolin-based GPC, the incomplete geopolymerization led to the compressive strength being too low to meet the application of practical engineering. In addition, the compressive strength of GPC activated by 12 M NaOH was higher than the GPC activated by 8 M NaOH, which is owing to the formation of gel depended on the concentration of alkali OH ion, low NaOH concentration weakened chemical reaction, and reduced compressive strength. Additionally, according to the testing results of neutralization depth, the neutralization depth of high-calcium fly ash-based GPC activated by 12 M NaOH suffered acid attack for 98 d was only 6.9 mm, which is the minimum value. Therefore, the best performance was observed in GPC prepared with high-calcium fly ash and 12 M NaOH solution, which is attributed to gypsum crystals that block the pores of the specimen and improve the microstructure of GPC, inhibiting further corrosion of sulfuric acid.

Mechanical Properties and Resistance to Acid Corrosion of Polymer Concrete Incorporating Ceramsite, Fly Ash and Glass Fibers

A novel polymer concrete (PC) using an aggregate of ceramsite, fly ash and glass fiber was created. Specimens were used in experiments to investigate its anticorrosion properties to determine the viability of its use in flue gas desulfurization (FGD) stacks. The inclusion of ceramsite reduces both the weight and the cost of the material. The effects of ceramsite and glass fiber on the flexural strength and compressive strength of the concrete were investigated. The experimental results showed that ceramsite reduces the flexural strength and the compressive strength of the concrete, but that the glass fiber increases both. Surface resistance to sulfuric acid corrosion and the microstructure of the corroded concrete were investigated. Specimens of the novel PC and the control PC strongly resisted acid corrosion. Although the specimen surfaces deteriorated, the interior structure of the PC was unaffected after 50 days of acid immersion. Processes by which sulfuric acid corrodes PC surfaces were determined.

Experiment Study on Degradation Laws of Sulfuric Acid Corrosion Reinforcements

The corrosion of concrete structures is serious in sulfuric acid environments. Corrosion damage of reinforcements caused sulfuric acid corrosion is very serious. The rapid experiments of sulfuric acid corrosion steel bars were carried out, and the apparent morphology and mechanical properties of sulfuric acid corrosion steel bars were studied. The results show that the corrosion of steel bars is uniform corrosion. With the increase of corrosion rate, the yield platforms and the yield strengths and ultimate strengths are reduced. Based on the experimental datas, the relationship models between yield strengths and ultimate strengths and corrosion rates were obtained. The constitutive models of corrosion steel bars were established. The stress - strain relationship model is in good agreement with the experimental data.

Investigation on the Sulfuric Acid Corrosion Mechanism for Concrete in Soaking Environment

This paper chooses the apparent diffusion coefficient for OH− (hydroxyl ion) for concrete as an index to evaluate the corrosion degree of concrete subjected to sulfuric acid. Based on the reaction boundary layer theory, a sulfuric acid corrosion model for concrete was established and verified through experiments. The experiment design and data processing of sulfuric acid corrosion tests for concrete were carried out using uniform test design and nonparametric regression. Effects of water-cement ratio and pH value are presented on the sulfuric acid corrosion mechanism for concrete. Test results show that when the pH value was 2.50, the sulfuric acid corrosion degree of concrete was the most serious. The boundary layer effect always existed in the sulfuric acid corrosion for concrete, and the corrosion process included rapid and stable corrosion stages. The apparent diffusion coefficient for OH− for concrete increased with the decrease of pH value and the increase of water-cement ratio and cement proportion.

Development of Compressive Strength of Slag Based Cement Mortars Exposed to an Aggressive Sulphate Environment

Sulfuric acid corrosion can cause severe damage to concrete and cement composites. There are a variety of approaches to enhancing the sustainability of concrete and mortar one of which is to enhance the durability of concrete using different cement replacement. Granulated blast furnace slag is used in mortar and concrete, as a partial replacement of Portland cement, and this use has resulted in significant savings in the cost of production of concrete. Moreover the use of conventional concrete is notoriously subject to durability and corrosion issues. Laboratory experiments were conducted to investigate the compressive strength of cement mortars samples with cement partially replaced by blast furnace slag. The samples with different share of slag (65, 75, 85 and 95 wt.%) were exposed to a bacterial sulphate environment for 90 days. A decrease in compressive strengths of reference samples by 8% as well as an increase in compressive strengths of all slag-based sampless up to 95 % have been observed. Surface structure and chemical com-positions of cement mortars´ leachates confirmed a deterioration process under the microbial exposure of Acidithioba-cillus thiooxidans.