Role of lithium compounds in mitigating alkali-gravel aggregate reaction

Significance Statement

The reaction between alkalis in cement and aggregates composed of reactive forms of silica is detrimental to concrete. Therefore, it is important to identify the factors that affect the gravel reactivity as well as how to minimize the effects of the reaction. Lithium compounds, especially lithium nitrate, which are neutral and soluble, have been found to be effective in reducing the detrimental effects of the alkali-aggregate reaction. The lithium salt does not increase the pH of the solution in the concrete pores, but incorrect amounts of lithium ions may lead to increased expansion which is harmful to concrete.

Polish researchers, Justyna Zapala Slaweta and Zdzisława Owsiak at Kielce University of Technology set out to investigate the role of the lithium ions in mitigating the alkali-aggregate reaction. Their work is now published in Construction and building Materials.

In their study gravel aggregates containing large amounts of quartz, calcite, plagioclase, and lower amounts of clay minerals were sampled. Portland cement containing 0.66% equivalent alkali content was used. Both the accelerated and the long-term methods were used in evaluating the potential reactivity of the aggregates. From the results of silica leachability, the gravel aggregates were classified as potentially reactive. The aggregate grain types were subjected to a petrographic analysis which showed that chalcedony, opal and strained quartz played a major role in the reactivity of the aggregates.

Preparation of grain composition was done and bar samples were made, with and without the lithium nitrate. The bars were then immersed in a solution containing lithium and alkali ions at a molar ratio of 0.74. Data was collected for fourteen days in the accelerated method and three hundred and sixty days for the long-term method. A microanalysis of the reaction was then studied.

For mortars without lithium nitrate, the authors observed that the expansion surpasses the reactivity threshold of the aggregate for both the short-term and long-term methods which confirmed the reactivity of the aggregates used.

For mortars containing lithium nitrate in the short-term method, there was a markedly reduced expansion by about ninety three percent which was limited to a safe level of 0.1% and half the value up to ninety days. In the long-term method, the expansion was reduced by about seventy three percent and was limited to a safe level of 0.1% after ninety days. Percentage expansion differences for the two methods is due to the changes in the immersion solution composition.

Microanalysis of samples not having lithium nitrate exhibited substantial amounts of microcracks. For samples with lithium nitrate the number of cracks was lower. It was also observed that the products of the reaction that filled the microcracks had little amounts of potassium and sodium.

From the research, the researchers found that compounds of lithium especially lithium nitrate are effective in controlling the expansion of mortars composed of reactive aggregates. Further research is important in order to properly understand the effects of lithium compounds because current analysis methods fall short in analyzing the distribution and content of lithium as a result of its light weight.

About The Author

Justyna Zapała-Sławeta is a Associate Professor in the Faculty of Civil Engineering and Architecture at Kielce University of Technology, Poland. She graduated from the Faculty of Chemistry of the Jagiellonian University in Cracow and the Faculty of Materials Science and Ceramics of the AGH University of Science and Technology in Cracow. She received her PhD degree from Kielce University of Technology based on the doctoral dissertation entitled: „The influence of lithium compounds on alkali aggregate reaction in concrete”.

Her research is in the field of durability of concrete, focusing on the study the effect of chemical admixtures and mineral additives on mitigating the alkali-silica reaction in concrete. She is the author or co-author of over 20 publications in science magazines in the area of internal corrosion in concrete.

About The Author

Professor Zdzisława Owsiak graduated from the Faculty of Materials Science and Ceramics of the AGH University of Science and Technology in Cracow and was granted the degree of Master of Science, Engineer in the specialty of the  binding construction materials and concretes technology. She was granted the degree of a Ph.D. of technical sciences by the decision of the Council of the Faculty of Civil Engineering of the Warsaw University of Technology based on the doctoral dissertation entitled: “The effect of the structure of extruded concretes with fine carbonate aggregate on their functional properties”, and the degree of associate professor was granted to her at the Faculty of Civil and Environmental Engineering of the Kielce University of Technology based on the dissertation entitled “The internal sulphate corrosion of concrete”.

Professor Zdzisława Owsiak’s main areas of interest in scientific activity concern the properties of carbonate aggregate concretes, concrete strength and the diagnosis of concrete in construction.

As far as the first area is concerned, the Professor examined the interactions between cement slurry and carbonate aggregate. Particular significance within this scientific field is given to the research of the effect of the structure of concretes on their functional properties. Further on in her research, she focused on the question of concrete strength. These papers explained the concrete dilapidation as a result of the reaction of the aggregate with the alkali in the cement and covered the use of   methods preventing the reaction of sodium and potassium hydroxide with the aggregate in the concrete from occurring. Zeolite, which occurs in nature, and the main component of which is clinoptilolite, was used as the component of the concrete, limiting the reaction of the alkali with silica. The influence of a chemical additive with lithium compounds on limiting the corrosion processes of concrete caused by the reaction of the alkali with the aggregate was also researched.

Professor Z. Owsiak’s scientific activity also concerned the internal sulphate corrosion of concrete (DEF), taking consideration a simultaneous occurrence of the reaction of the alkali with the aggregate and the influence of certain mineral additives on the carbonization and frost-resistance of self-compacting concretes.

Professor Zdzisława Owsiak is the author or co-author of over 130 publications in science magazines as well as three monographs and an academic textbook.

Reference

J. Zapala- Slaweta, Z. Owsiak. The role of lithium compounds in mitigating alkali-gravel aggregate reaction. Construction and Building Materials 115(2016) 299-303

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