Direct causality between film formation and water-retaining effect of surfactant-based film-forming curing compound for concrete

Surfactant-based film-forming curing compounds (SFCCs) are widely used to retain water on fresh concrete by forming multilayered films. However, the water-retaining mechanism is not yet fully understood; therefore, we aimed to clarify this mechanism, thereby potentially aiding in evaluating the effect of SFCC or to develop more effective SFCCs. It was confirmed that SFCC does not hinder the setting and hardening properties or strength development. Thus, we examined water evaporation from cement pastes on which SFCC was sprayed. Consequently, the water-retaining effect lasted up to 8 h, which indicating that 8 h after spraying SFCC is enough time for suppression of plastic cracking. We then observed the water surface on which SFCC was spread under a Brewster angle microscope and discovered that SFCC on the water surface forms continuous thin film and agglomerates. The water-retaining effect was higher when a continuous thin film was formed; thus, the observation of this thin film facilitated the evaluation of the effect of SFCC.