Effect of Dynamic Load on Value of Point Load of Mineral Wool Boards

Abstract

This paper presents the research on the effect of dynamic load on the point load value of mineral wool boards used for thermal insulation in low-slope roofs. Mineral wool boards for thermal insulation of low-slope roofs are described by the values of compressive stress (σ10) and point load (F5). For this work, three types of mineral wool boards normally used as thermal insulating layer and/or as basis for the waterproof roofing membranes were tested. Usually, during roof installation or regular maintenance, these boards are affected by reoccurring short-term loads acting on a small area which is due to “walking”. In order to simulate the effects of short-term dynamic loading, a JW fatigue machine with a special construction was used. The surface of a test specimen was compressed till its deformation would reach 5 mm, using a periodic load of 147 kPa repeated every 2 seconds – in the same way as the board would have been affected while by “walking” on it during its operation use. In order to determine how the short-term loads affect the strength of the test specimen, the initial values of density and point load were measured. After dynamic fatigue test the changes of these values were determined again. The results show that the surfaces of all types of mineral wool boards were damaged. Residual deformations appeared on the surface due to strain concentration and plastic deformations. The presented results show that the value of point load dynamic resistance σPL(DR) amounted to 63 % – 86 % of the point load value measured before the tests. Some test specimens showed an increased value of point load, compared to the value before the tests. This demonstrates the structural non-homogeneous of the mineral wool.