Improvement of the mechanical properties of a glass multifilament yarn reinforced ettringitic matrix using an innovative pre-impregnation process

Fiber reinforced mineral matrix composites have been used increasingly, through the last few decades, to build lightweight and thin structures, and to repair or strengthen old and damaged buildings. However, the reinforcing efficiency of these composites is limited by the low penetrability of cement particles into the space between the inner filaments, leading to a decrease in the composite's mechanical performance due to the low yarn-matrix bond. To improve this bond, multifilament yarns are usually subjected to wet-process pre-impregnation using mineral or organic powders. However, this method is long, poorly controlled, and can be used only in the prefabrication field. The objective of this work is to compare this conventional pre-impregnation method with an alternative method called dry-process pre-impregnation which allows the production of large-size building elements in site. It is based on an alternating electrostatic field used to impregnate yarns with powder. Classical tensile tests were used to characterize glass yarn/ettringitic matrix composites, and completed by microstructure observations. Three configurations were tested: a dry yarn (D), a yarn pre-impregnated using the wet process (PIW) with ettringitic matrix particles, and a yarn pre-impregnated using the dry process (PID) with three different types of powders. Two composite reinforcement rates are investigated and their effect on the result is discussed. Mechanical and microscopic characterizations shed light on the effect of the pre-impregnation processes. It was found that the tensile behavior of the composite depends on the pre-impregnation method, pre-impregnation powder and reinforcement rate.