Effect of air entraining admixture on thixotropy in Portland cement with urea: step change and loop test analysis

The European Green Deal emphasizes reducing global warming through sustainable approaches in all sectors, including building materials. Beyond lowering CO2 emissions and production costs, extending the service life of structures minimizes maintenance needs and supports sustainability goals. This study investigates the effect of air-entraining admixture (AEA) dosage on the thixotropic properties of urea-containing cementitious systems. Urea has been reported to enhance workability and flowability, while AEAs mitigate freeze-thaw damage. Despite their combined potential, no studies have explored their interaction on thixotropy. For this purpose, two series of cement paste mixtures, control and 3% urea-modified, were prepared. Results showed that urea improved flowability, whereas AEA reduced it. Both urea and AEA increased time-dependent rheological parameters. These findings provide insight into the fresh-state behavior of urea-modified systems and contribute to developing more durable and sustainable cementitious materials aligned with the objectives of the European Green Deal.