Abstract
The production of urea, used inter alia in agriculture, is increasing. Therefore, urea hydrolysis products are expected in groundwater. Due to lack of new research on the influence of urea on the technical condition of concrete structures, the changes that this compound may cause to hardened cement paste were initially check. After 11 months of immersion of hardened cement paste in 20% CO(NH2)2 solution, tests were conducted at different depths of penetration. A pH of 11.97 was recorded in the first layer with a thickness of 0.5 mm, and the pH of the innermost layer was 12.48. The decalcification process and the formation of predominantly secondary calcite in the edge layers were confirmed using XRD, SEM, and analytical methods. No nitrogen phase was formed, but the deeper was the layer, more wollastonite was present. Moreover, up to a depth of about 20 mm, the sample was mechanically weak-breakable by the force of the hands. The examination of the filtrate’s conductivity, leachable calcium content, and pH along the way of urea diffusion confirmed changes in the examined material. When analyzing the technical condition of concrete treated with urea, pH could be an indicator due to the possibility of buffer reactions.
Highlights
Urea whose systematic IUPAC name is carbonyl diamide, is an organic compound [1]
The experimental results of this paper showed that urea fertilizer used in 0.2%, 0.5%, and 1% concentrations is an effective inhibitor and gives good corrosion inhibition for concrete-reinforced steel immersed in simulated concrete pore solutions
This article returns to the issues of concrete corrosion caused by urea, because in recent years this problem has been to some extent forgotten
Summary
Urea whose systematic IUPAC name is carbonyl diamide, is an organic compound [1]. Urea is a natural product of nitrogen and protein metabolism and predominantly found in urine and animal waste. Biodegradation of urea is common, releasing carbon dioxide and ammonia. Increasing temperatures, alkalinity, and the presence of the biological enzyme urease can catalyze chemical hydrolysis of urea [2]. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use; more than 90% of the world’s industrial production of urea is used as nitrogen-release fertilizer, and which is expected to increase by 50% towards 2050 to feed a growing global population [3,4,5]. Urea has a large potential market of 180 Mt per year [6]
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