Polyurethane materials can be used for nondestructive maintenance of infrastructure, such as slab lifting through injection in a road or railway. Understanding the mechanical behavior and microstructure characteristics of this material is critical to ensure safe service of the infrastructure. This study investigates stress-strain behavior, microstructure characteristics, fatigue behavior, and failure mode of rigid polyurethane grout materials subject to both static and cyclic compressive loads. The densities of the investigated polyurethanes range from 80 to $500\mathrm{kg}/{\mathrm{m}}^3$ , which are normally used in grouting. The yielding stress corresponding to 5% strain is measured and predicted based on the microstructure characteristics. The fatigue process of polyurethane can be divided into elastic, incubation, and failure stages. The failure threshold is identified for polyurethanes with different densities and at different stress levels. The failure mode is described based on the microstructure observation.

Tensile stress develops in concrete when shrinkage deformations and restraints (internal or external) exist. Utilization of appropriate creep or relaxation functions is crucial for assessing stress and the associated cracking potential in concrete, especially at early ages when chemical and physical properties change rapidly. The existing models, developed either from compressive creep tests or conventional tensile creep tests with constant loads applied at certain ages, were found to be unsuitable for such stress evaluation. This study was performed to investigate the restrained strain-stress development and tensile creep behavior of concrete subject to constant restraint starting at very early ages, which well represents field conditions of actual structures. Restrained stresses were measured using a specially designed frame. The concretes were cured and tested at two different temperatures (23°C versus 33°C) and ground granulated blast furnace slag contents (0% versus 30% of the total cementitious materials by mass). A modified tensile creep model is proposed to account for the high viscosity of concrete under constantly restrained conditions, allowing more accurate assessments of stress and cracking potential in structures such as slabs or pavements on the ground.