THE COURSE OF THE ALKALI-AGGREGATE REACTION IN THE PRESENCE OF LITHIUM NITRATE

Lithium nitrate is recognized as a chemical compound capable of inhibiting the alkali-silica aggregate reaction. The extent to which the reaction is inhibited or limited is affected by the amount of the applied lithium compound and by the kind of reactive aggregate that has been used. In the case of the polymineral aggregate this process is particularly complex, as the alkali-silicate reaction may be accompanied by other alkali-aggregate reactions, i.a. the alkali-carbonate reaction. The paper presents the results of the investigation on the effect of lithium nitrate on the course of the alkali - reactive gravel aggregate reaction. The investigation was conducted in accordance with ASTM 1260 standard. The investigation results showed that lithium nitrate, when applied in appropriate amount, inhibits the process of mortar samples expansion. The appearance of spalls in the samples modified with a lithium compound indicates the occurrence of two reaction types: alkalisilica and alkali-carbonate

The role of lithium compounds in mitigating alkali-gravel aggregate reaction

AbstractAlkali reaction with reactive aggregates is an example of concrete internal corrosion. Cracks and damage to elements of a concrete structure are the result of the formation of an expansive alkali-silica gel. One of the ways to minimise the effects of this damaging reaction is to use lithium compounds as an admixture to concrete mixes. Lithium ions are believed to reduce the reaction between the alkalis and aggregate or minimise damaging expansivity by modifying chemical composition of the reaction products.This paper presents the results from the tests carried out on mortars from reactive polymineral gravel with lithium nitrate according to the modified ASTM C1260 standard and ASTM C227. The findings show that lithium ions decrease mortar expansion until it reaches the levels markedly lower than those set out in the standards. A considerable reduction in the number of microcracks may indicate either lower swelling capacity of the gels or reduced reactivity of the aggregate, leading to the reduction in the quantity of damaging expansive products

The studies of scale surface produced on outer diffusion layers

In this study at attempt was made to examine the scale formed on ferritic-austenitic duplex type steel subjected to previous thermochemical treatment. The treatment consisted in diffusion aluminising in a metallising mixture composed of Fe-Al powder. As an activator, ammonium chloride (NH4Cl) added in an amount of 2 wt.% was used. Then, both the base material and samples with the diffusiondeposited surface layers were oxidised at 1000°C in the air. Thus formed scales were identified by light microscopy, SEM and X-ray phase analysis. The aim of the oxidation tests carried out under isothermal conditions was to compare the scale morphology when obtained on untreated substrate material and on the surface layers rich in aluminium

The Alkaline Reactivity of Opal in Mortars Modified with Lithium Nitrate

AbstractPreventing the destructive reaction between reactive aggregate and sodium and potassium ions in concrete pore solution is vital for the maintenance of concrete durability. There are several methods of preventing this adverse reaction, such as the application of cement with pozzolanic additives. Several papers also indicate the high efficiency of lithium compounds in mitigating the alkali-aggregate reaction.The aim of this study was to determine the effect of lithium nitrate on the reaction between opal and alkali in mortar bars. The mortar samples contained alkalis of two different concentration levels.Lithium nitrate was applied at a fixed molar ratio of lithium to sodium and potassium ions. Expansion studies were conducted in accordance with the methodology included in the ASTM C1260 standard. The modification of samples with lithium nitrate contributes to the decrease of expansion both for the low alkali cement and high alkali cement. The microstructure of mortar samples, both modified and non-modified with lithium nitrate, was examined and X- ray microanalysis was performed

Effect of freezing on abrasion resistance of cast steel containing 1,1 % C, 16 % Cr, and 0,9 % Mo

The results of abrasion-resistance tests that were carried out on cast steel containing 1,1 % C, 16 % Cr, and 0,89 % Mo after several variants of heat treatment (including freeze hardening at -70 °C immediately before tempering at 200° and 550 °C) are presented in this paper. The wear-resistance tests were carried out with the ball-on-disc dryfriction method. In the samples that were tempered at 200 °C (with and without freezing), lower mass losses were obtained than in the samples that were tempered at 550 °C. Additionally, it was found that the applied freezing procedure significantly contributed to the reduction of mass losses in those samples that were tempered at both temperatures

Effect of freezing on abrasion resistance of cast steel containing 1,1 % C, 16 % Cr, and 0,9 % Mo

The results of abrasion-resistance tests that were carried out on cast steel containing 1,1 % C, 16 % Cr, and 0,89 % Mo after several variants of heat treatment (including freeze hardening at -70 °C immediately before tempering at 200° and 550 °C) are presented in this paper. The wear-resistance tests were carried out with the ball-on-disc dryfriction method. In the samples that were tempered at 200 °C (with and without freezing), lower mass losses were obtained than in the samples that were tempered at 550 °C. Additionally, it was found that the applied freezing procedure significantly contributed to the reduction of mass losses in those samples that were tempered at both temperatures

Negatywne aspekty oddziaływania bakterii na beton

This paper presents the most frequently occurring cases of cement paste corrosion caused by living organisms. Concrete is exposed to the effects of corrosive factors. One of the factors which cause corrosion are living organisms. The key role is played by bacteria, algae, fungi, lichen. The role of microorganisms is essential in the destructive processes. The enzymes and metabolites secreted by microorganisms contribute to the destruction of the material by dissolution, hydrolysis, crystallization of the products of corrosion. Also, the settlement of microorganisms on the surface of a material, the biofilm effect, may lead to the processes of destruction

Influence of modifier concentration on retention in hydrophilic interaction chromatography - preliminary investigations

Zbadano wpływ składu fazy ruchomej na retencję kilku wybranych substancji testowych w kolumnie Acclaim Mixed-Mode HILIC-1 z diolową fazą stacjonarną w układach z fazami ruchomymi złożonymi z metanolu i wody oraz acetonitrylu i wody (z dodatkiem 0,1 M octanu amonu, pH 5,2). Zaproponowano nową postać równania opisującego zależność współczynnika retencji od stężenia modyfikatora eluentu w chromatografii oddziaływań hydrofilowych oraz dokonano jego wstępnej, eksperymentalnej weryfikacji. Poprawność tego modelu w opisie wpływu stężenia modyfikatora na retencję porównano także z dwoma modelami retencji znanymi z literatury. Do oceny modeli zastosowano trzy kryteria statystyczne: sumę kwadratów różnic między danymi doświadczalnymi i teoretycznymi, odchylenie standardowe oraz test Fischera.The influence of mobile-phase composition on the retention of a few selected test analytes in alkyl diol Acclaim Mixed-Mode HILIC-1 column in systems with methanol - water and acetonitrile - water (with 0.1 M Ammonium Acetate, pH 5.2) mobile phases is studied. A novel equation for an accurate prediction of the chromatographed substance retention for hydrophilic liquid chromatography is proposed. On the basis of experimentally determined retention data, the performance of this equation was preliminary tested and compared with two retention models reported in literature. All tested models were verified using three criteria: the sum of squared differences between the experimental and theoretical data, the standard deviation and the Fisher test