Leaching of calcium and silicon from cement composites in the aggressive environment

Deterioration of concrete materials exposed to an aggressive solution is often characterized by the leaching of calcium and silicon compounds from the cement matrix. This paper presents the results of the study of concrete composites exposed to the various sulphate environments (sulphuric acid and magnesium sulphate solutions) under laboratory model conditions. The leaching of the calcium and silicon from concrete specimens has been studied during 180 days using X-ray fluorescence method for leachate analysis. As expected, sulphuric acid of pH3 was confirmed to have the most significant effect on the studied ions releasing. The released amounts of analysed ions were 192.2 and 9.6 times higher for calcium and silicon ions, respectively in H2SO4 with pH=3 when compared to fresh water. The concentration of released calcium was 2.6 times highe

Impact of calcium ions leaching caused by biogenic acid attack on durability of cement composites

Leaching of calcium ions increases the porosity of cement-based materials, consequently resulting in a negative effect on durability since it provides an entry for aggressive harmful ions, causing corrosion of concrete. Sulphuric acid corrosion of concrete can be caused due to attack of aggressive media naturally existing in the environment. Another possibility of corrosion formation is biogenic acid effect through the agency of microorganisms. The paper is focused on the investigation of the influence of biogenic acid attack on the cement composites affected with bacteria Acidithiobacillus thiooxidans. The concrete specimens with 95% wt. addition of antimicrobial activated granulated blast furnace slag as durability increasing factor as well as without any addition were studied. The experiments proceeded during the nine 7-day cycles. The pH values and chemical composition of leachates were measured and evaluated after each cycle. The higher resistance of concrete samples with the addition of 95% wt. of antimicrobial activated granulated blast furnace slag to the aggressive environment was confirmed. The leaching of calcium ions of concrete sample affected with bacteria Acidithiobacillus thiooxidans was 1.13 times lower (736.6 mg/L of leachate) for concrete sample with antimicrobial activated granulated blast furnace slag addition comparing to concrete sample of ordinary CEM I Portland cement without any additives (832.0 mg/L of leachate)

Leachability of chromium and barium from concrete samples with blast furnace slag addition

The paper presents the results of leachability testing of selected heavy metals from the concrete composites of various compositions in order to assess the degree of a contamination risk of the environment. Tested concrete samples contained various amounts of special ingredients based on the blast furnace slag (65%, 75%, 85% and 95% of Portland cement replacement). Leaching tests have been performed by using distilled water. The concentrations of chromium and barium ions in the leachates were measured after period of 30 and 240 days. Changes in pH and conductivity values in leachates have been also observed

Investigation of the Precipitates on the Concrete Surface due to Sulphate Exposure

The aim of this study is to investigate the durability of cement-based materials subjected to the effects of sulphuric acid in terms of surface deterioration. Damaged concrete surfaces and the samples’ mass changes were studied during 270-day simulation of both chemical and biological attacks. Chemical corrosion was simulated by sulphuric acid with pH of 3.0 and 4.0, respectively, while biological corrosion was simulated by activity of bacteria Acidithiobacillus thiooxidans. XRD and SEM analyses confirmed a massive sulphate precipitate formation on the concrete surface due to chemical and biological sulphate corrosion