AbstractFiber‐optic strain sensors to be used in materials research and for long‐term monitoring the state of chemically stressed concrete, e. g. sewer pipes, cooling towers, have to be intimately embedded in cement matrices. They should be coated with very thin alkaline‐resistant coatings. This is necessary to achieve a reliable strain transfer from the matrix to the fiber sensor.In order to clarify possible ways to replace thick coatings, which are unstable in cement environment, optical fibers have been modified and investigated with regard to their chemical compatibility, their strength behavior after alkaline attacks and their adhesion behavior to the matrix. The surface state of differently treated optical fibers intended for embedding has been characterized; additional strength estimation of alkaline attacked fibers was carried out. All estimations have been compared with those of bare alkaline attacked fibers.The real adhesion behavior was determined using the fiber push‐in test technique (indentation). Recent results suggest that fibers coated with very thin organic layers have remarkable adhesion properties. However, the fiber strength after exposing to alkaline pore solution (pH = 13.9) is worse than that of bare fibers. Optimum fiber/cement bond strength showed fibers, which were coated with a crosslinked polymer, produced in gas