Martina Kovalcikova

Testing Silica Fume-Based Concrete Composites under Chemical and Microbiological Sulfate Attacks

Current design practices based on descriptive approaches to concrete specification may not be appropriate for the management of aggressive environments. In this study, the durability of cement-based materials with and without the addition of silica fume, subjected to conditions that leach calcium and silicon, were investigated. Chemical corrosion was simulated by employing various H2SO4 and MgSO4 solutions, and biological corrosion was simulated using Acidithiobacillus sp. bacterial inoculation, leading to disrupted and damaged surfaces; the samples’ mass changes were studied following both chemical and biological attacks. Different leaching trends were observed via X-ray fluorescence when comparing chemical with biological leaching. Lower leaching rates were found for concrete samples fortified with silica fume than those without silica fume. X-ray diffraction and scanning electron microscopy confirmed a massive sulfate precipitate formation on the concrete surface due to bacterial exposure.

Application of Granulated Blast Furnace Slag in Cement Composites Exposed to Biogenic Acid Attack

The deterioration of cement-based materials used for the civil infrastructure has led to the realization that cement-based materials, such as concrete, must be improved in terms of their properties and durability. 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. The use supplementary cementing composite materials have been reported to improve the resistance of concrete to deterioration by aggressive chemicals. The paper is focused on the investigation of the influence of biogenic acid attack on the cement composites affected by bacteria Acidithiobacillus thiooxidans. The concrete specimens with 65 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 150 days under model laboratory conditions. The pH values and chemical composition of leachates were measured after each 30- day cycle. The calcium and silicon contents in leachates were evaluated using X - ray fluorescence method (XRF). Summarizing the results, the 65% wt. addition of antimicrobial activated granulated blast furnace slag was not confirmed to be more resistant.

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

Abstract 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.

Deterioration of Cement Composites with Silica Fume Addition due to Chemical and Biogenic Corrosion Processes

The paper is aimed at comparative study of resistance of Portland cement composites with addition of silica fume as durability increasing factor in various aggressive environments (sulphuric acid with pH 4, the medium of activated bacteria and the cultivating medium without bacteria) during 150 days under model laboratory conditions. Experimental studies confirmed: the leaching of silicon ions calculated to 1 g of concrete sample affected with bacteria Acidithiobacillusthiooxidans was 2.5 times lower (31.78 mg/g of sample) for concrete sample with silica fume addition comparing to concrete sample of ordinary CEM I Portland cement without any additives (82.98 mg/g of sample). The highest concentration of calcium ions released (60.808 mg/g of sample) was observed for reference sample without silica fume addition placed in the cultivating medium. Silica fume based concrete samples were found to have better performance in terms of calcium ions leaching for all environments and silicon ions leaching.

Leaching of Ca, Si, Fe and Al from concretes, based on sulphate resistant cement, due to bacterial attack - a correlation study

Investigation of biological corrosion of concrete requires that composition of material, surface and aggressive environment have to be taken into account. Sulphate resisting cement, as one of the resistivity improving factors, was used for preparation of concrete samples studied in this experiment. Dependences of leached-out quantities of selected ions regarding bacterial versus non-bacterial environments were investigated and evaluated using correlation analysis. Leaching trends of calcium, silicon and aluminium strongly depends on the aggressiveness of medium which are the samples exposed to. A weak correlation was found for the leaching trends of aluminium and iron in both bacterial and non-bacterial media.

Biodeterioration of the Cement Composites

The destruction of natural and synthetic materials is the spontaneous and irreversible process of the elements cycling in nature. It can by accelerated or decelerated by physical, chemical and biological influences. Biological influences are represented by the influence of the vegetation and microorganisms (MO). The destruction of cement composites by different MO through the diverse mechanisms is entitled as the concrete biodeterioration. Several sulphur compounds and species of MO are involved in this complex process. Heterotrophic and chemolithotrophic bacteria together with fungi have all been found in samples of corroding cement composites. The MO involved in the process metabolise the presented sulphur compounds (hydrogen sulphide, elemental sulphur etc.) to sulphuric acid reacting with concrete. When sulphuric acid reacts with a concrete matrix, the first step involves a reaction between the acid and the calcium hydroxide forming calcium sulphate. This is subsequently hydrated to form gypsum, the appearance of which on the surface of concrete pipes takes the form of a white, mushy substance which has no cohesive properties. In the continuing attack, the gypsum would react with the calcium aluminate hydrate to form ettringite, an expansive product. The use supplementary cementing composite materials have been reported to improve the resistance of concrete to biodeterioration. The aim of this work was the study of the cement composites biodeterioration by the bacteria Acidithiobacillus thiooxidans. Experimental works were focused on the comparison of special cement composites and its resistance affected by the activities of used sulphur-oxidising

The Ability of Slag-Portland Cement Composites to Withstand Aggressive Environment

The use of separately ground blast-furnace slag, added at the mixer as a replacement for a portion of the Portland cement, has gained increasing acceptance in recent years. The effects of partial replacement of Portland cement with ground slag on the properties of hardened concrete have been extensively investigated and reported. Both laboratory testing and field experience have shown that properly proportioned slag-Portland cement concretes have the improved resistance to sulfates and seawater compared to regular Portland mixes. The paper is focused on the effects of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans on concrete mixtures with addition of ground granulated blast furnace slag compared to mixture without any additives. The concrete specimens with 65 and 75 % wt. addition of antimicrobial activated granulated blast furnace slag as durability increasing factor as well as without any addition were investigated in laboratory during the nine 7-day cycles. A laboratory study was conducted to comparison the performance of concrete samples in terms of a concrete deterioration influenced by the leaching of calcium and silicon compounds from the cement matrix. The changes in the elemental concentrations of calcium and silicon ions in leachates were measured by using X – ray fluorescence method. The pH values were measured and evaluated after each cycle. The concrete specimen with 65 % wt. addition of antimicrobial activated granulated blast furnace slag was found to have the best leaching performance of calcium ions than other samples. The final concentration of Si ions in leachate of concrete specimen with 75 % wt. addition of antimicrobial activated granulated blast furnace slag affected with bacteria Acidithiobacillus thiooxidans (4.614 mg/g of concrete sample) was observed to be 1.263 times lower than reference sample without any additives. The higher resistance of concrete samples with the addition of antimicrobial activated granulated blast furnace slag to the aggressive environment was confirmed.

Bio-Corrosion of Fibrous Cement Boards and Cement Composites

The paper deals with the comparative study of bio-corrosion of fibrous cement boards and Portland cement composites. Fibre-cement flat boards are widely used materials in the Slovak Republic for exterior and interior cladding, as fibre-cement slates for roofing and cladding and as fibre-cement corrugated sheets for roofing and cladding. Bio-corrosion of studied materials has been simulated in laboratory conditions during 80 days. Effect of sulphur-oxidizing bacteria Acidithiobacillusthiooxidans on the specimens was investigated. The bio-deterioration processes have been manifested by leaching of main cement components as well as by surface changes. The calcium and silicon contents in leachates were evaluated during the experiments using X – ray fluorescence method (XRF). Concluding the results of the concrete’s biodeteriogens influence on the analyzed samples (fiber boards and cement composites) more extensive leaching of calcium ions from the cement matrix was confirmed as assumed by bacteria influence when compared to the abiotic environment. Mixture of white compounds on the samples surface was identified by SEM microscopy and XRD analysis as sulphate products (ettringite, thaumasite, gypsum). Shift of pH of liquid media to alkaline region up to 7.2 due to alkaline products leaching were noticed for all studied samples.

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.