The Examination of Hydrated Cement Paste Made of CEM III/A 42,5 N-LH/HSR/NA under the Influence of Urea Solution

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.