During the past decade, the science of concrete behavior has made much progress and many useful results are now incorporated in technical codes such as those governing mix design, quality of mix and post pouring verification. The stage of Very Early Age (VEA) concrete begins with pouring and ends with hardening. Behavior at this stage influences safety and durability of structures. Concrete is a cast-in-place hardening material. Other hardening materials, such as epoxy mortars have recently raised interest. Techniques used for concrete can potentially be applied to these new composite materials. The overall objective of this thesis is to develop a methodology for predicting mechanical properties and for separating important phenomenon in hardening materials, such as commercial concrete and mortar, to be ultimately applied in real time and in situ. A literature survey has shown a lack of knowledge in the areas of measurement techniques at VEA, prediction of compressive strength, separation of the autogenous deformation and values for the thermal expansion coefficient. This lack of knowledge is especially clear for cement-based materials hardening at varying temperatures. Few VEA data are available and few tools are capable of monitoring VEA parameters. A new device has been constructed to monitor deformations and help identify phenomenological contributions to the total deformation. The design of this device takes into account aspects such as usability in the field and reliability in practice. More than 80 embedded fiber optic sensors and 100 specimens were used for development and testing. Several special sensors have been designed and tested so that their features are adapted to the characteristics of the hardening material at VEA. An important part of this work has been the development of procedures where VEA data are interpreted and reduced in order to determine the parameters that describe the evolution of the degree of reaction, as well as mechanical properties, and allow for the decoupling of values for the total deformation into parts that are related to different physical phenomena. Concluding, this methodology allows accurate prediction of the compressive strength evolution in term of degree of reaction using VEA data carried out within the first 72 hours of the hardening material life. The methodology also leads to straightforward determination of values for the thermal expansion coefficient and the separation of values for autogenous and drying deformation. Furthermore, pilot testing on epoxy mortar demonstrates that the methodology is not limited to cement-based materials Finally, the results of this thesis have the potential to make further contributions to scientific research and to strategies for quality control and safety during construction.