This paper reports on experimental and theoretical investigations into the use of optical fiber sensors in the monitoring of civil engineering structures. For this purpose a highly accurate optical fiber deformation sensor based on low coherence interferometry has been developed. This system was conceived in order to monitor a test concrete slab over a period of years. It enabled the measurement of both concrete shrinkage and elastic coefficient in the whole slab with good reproducibility, in agreement with measurements performed on small concrete samples and with theoretical calculations. The thermal effects on the concrete structures are also presented.