The paper concerns the use of limit value of siliceous fly ash content in concrete structures, with the application of various types of cements - based on the current standards and taking into consideration the requirements concerning current exposure classes. The conclusions were based on a review of literature, the results of scientific research, conclusions from expert opinions and buildings and structures supervision reports. In summary, it has been concluded that the use of limit content of siliceous fly ashes may result in negative changes in the properties of composites, which should be ruled out or confirmed by appropriate tests, taking into account the precisely defined composition of concrete, cement and the applied additives and admixtures. It has been emphasised that the problem concerns composites with the increased and limit values of fly ash content, especially as regards cements with the lowered content of clinker and high content of additives and admixtures (affecting the physical and mechanical properties of cement composites). Attention has been drawn to the need to modify the exposure classes, to focus on the requirements concerning the properties of concrete and not the composition - in order to achieve the expected durability.