Pre-applied bonded membranes are used to waterproof concrete basements and are installed before reinforcement works, e.g., in a formwork. The membranes form a bond with the subsequently poured fresh concrete and often use nonwovens as a bonding layer, which must be filled with cement paste during concrete placement. However, due to limited studies, the cement paste separation process and paste properties in the nonwoven are unknown. Also, no recommendations for optimized nonwovens are possible, and advice for practice is limited. This thesis aims to optimize the membrane products and understand processes during concrete placement. It first examines currently used pre-applied membranes for their essential nonwoven and fiber properties using thickness measurements, infrared spectrometry (FTIR), and microscopic analysis. In the second part of the thesis, the nonwoven deformation behavior during concrete placement is studied by measuring the thickness change of nonwovens using microsections and an incident light microscope. Also, porosity is analyzed via micro-computed tomography scans (micro-CT scans). During concrete placement, the nonwoven is initially compressed due to the fresh concrete load and relaxes again during vibration compaction as cement paste increasingly fills the nonwoven. The cement paste transfers the fresh concrete load, enabling the nonwoven to recover due to the residual stress in the nonwoven fibers. The separation of cement paste from fresh concrete and its properties in the nonwoven are investigated in the third part of the thesis using a customized filtration test stand, 'loose' nonwovens, and a practice-oriented concrete placement. The separated cement paste is analyzed for water content, solid density, and particle size. Video recordings supplement the tests and show that nonwovens are characterized by water movements during concrete placement. Similar to Controlled Permeable Formworks, excess water separates from the fresh concrete during concrete placement, filling the nonwoven pores in a short time. Simultaneously, a limited amount of fine solids enter the nonwoven, while unseparated particles on the nonwoven surface form a filter cake and stop the separation of solids, resulting in a water-rich cement paste within the nonwoven. It is upon vibration compaction that the filter cake is loosened and more solids enter the nonwoven. Water is displaced, the water-solid ratio in the nonwoven is reduced and is low for small nonwoven pore volumes, high compaction energies in the vicinity of the nonwoven, and high fresh concrete spreads. In order to identify overall good nonwoven properties, the fourth part of the thesis focuses on the bond strength between nonwoven and concrete by performing pull-off tests according to DIN EN 1542. The bond strength develops proportionally to the concrete tensile splitting strength and is influenced by the mortar strength in the bonding zone, which in turn is affected by the water content in the nonwoven. High bond strengths are achieved for nonwovens with low basis weights and concretes with high tensile splitting strengths. Vibration compaction displaces water accumulations and thus increases the bond strength, e.g., at formwork corners. This thesis provides an in-depth understanding of the time-dependent processes within nonwovens of pre-applied membranes during concrete placement and the impact of various boundary conditions. Based on the results, advantageous nonwoven properties for pre-applied bonded membranes and favorable installation conditions for the construction site are formulated.    «

Pre-applied bonded membranes are used to waterproof concrete basements and are installed before reinforcement works, e.g., in a formwork. The membranes form a bond with the subsequently poured fresh concrete and often use nonwovens as a bonding layer, which must be filled with cement paste during concrete placement. However, due to limited studies, the cement paste separation process and paste properties in the nonwoven are unknown. Also, no recommendations for optimized nonwovens are possible,...    »