CALCULATION OF SELF-INDUCED STRESS IN EARLY-AGE CONCRETE USING CREEP AND RELAXATION MODEL

High-Performance concretes, characterized by low water-binder ratio, are particularly sensitive to self-desiccation of the cement paste during the hydration process, which is a principal cause of autogenous shrinkage. If an external restraint is present, autogenous shrinkage, added to temperature-induced deformations, may lead to high self-induced stresses, possibly causing surface and even through cracks. These cracks may cause leakage of water [1], and penetration of chloride and carbon dioxide with possible decay of the reinforcement [2]. In order to estimate the cracking risk, it is of vital importance to accurately calculate the self-induced stresses. In this calculation the early-age creep behavior of the concrete plays a prominent role, since the self-induced stresses will be substantially reduced due to relaxation. An underestimation of early-age creep would lead to unnecessary precautions in order to reduce the stresses. Even worse, an overestimation would lead to underestimate the cracking risk of the concrete member, causing damage to the structure. In this contribution, two recent models describing early-age creep and relaxation in concrete, namely Lokhorst’s model (based on the degree of hydration concept) and Westmann’s model (based on the early-age development of the mechanical properties), are discussed. The potential of the two models to predict the development of self-induced stresses in early-age concrete is evaluated by comparison with the experimental results obtained with a Thermal Stress Testing Machine (TSTM).