Experimental investigation into early age shrinkage of cement paste by using fibre Bragg gratings

A new technique based on fibre optics has been utilised for investigating early age shrinkage of cement paste. Fibre Bragg gratings are strain sensors within optical fibres which were embedded here in cement paste specimens. In this way, shrinkage strains could be measured starting from the beginning of the setting. Sufficient bond strength between the sensor fibre and the surrounding early age cement paste has been proved in pull-out tests. Influences of the w/c-ratio, the curing conditions as well as the specimen geometry were under investigation in the experiments. The significant influence of the drying conditions on the shrinkage strain during the first day after casting is demonstrated. Whereas the early age shrinkage appeared to result in a rather uniform deformation the subsequent drying shrinkage caused significant strain gradients in the specimens.