A simple model for the characterization of concrete creep and shrinkage in design of concrete structures is proposed. It represents a shortened form of model B3 which was presented in [2] (as and improvement of the original version [3]) and appears in this volume, and an update of a previous short form [4]. The main simplification compared to model B3 comes from the use of the log-double-power law as the basic creep compliance function. The B3 formulae for predicting material parameters in the model are simplified by dropping the dependence of these parameters on the composition of concrete mix, leaving only dependence on the strength and the specific water content of the concrete mix. The model is justified by statistical comparisons with all the data in the internationally accepted RILEM data bank. The differences be-tween the present short-form and model B3 are discussed and limitations of the short form are compared to model B3 are noted. The model is suitable for design of concrete structures with the exception of highly creep-sensitive struc-tures for which the full model B3 is necessary

The present paper presents in chapter 1 a model for the characterization of concrete creep and shrinkage in design of concrete structures (Model B3), which is simpler, agrees better with the experimental data and is better theo-retically justified than the previous models. The model complies with the gen-eral guidelines recently formulated by RILEM TC- 107. Justifications of various aspects of the model and diverse refinements are given in Chapter 2, and many simple explanations are appended in the commentary at the end of Chap-ter 1 (these parts are not to be read by those who merely apply the model). The prediction model B3 is calibrated by a computerized databank comprising practically all the relevant test data obtained in various laboratories throughout the world. The coefficients of variation of the deviations of the model from the data are distinctly smaller than those of the latest CEB model (1990), and much smaller than those for the previous model in ACI209 (which was devel-oped in the mid- 1960s). The model is simpler than the previous models (BP and BP-KX) developed at Northwestern University, yet it has comparable accuracy and is more rational. The effect of concrete composition and design strength on the model parameters is the main source of error of the model. A method to reduce this error by updating one or two model parameters on the basis of short-time creep tests is given. The updating of model parameters is particularly important for high-strength concretes and other special concretes containing various admixtures, superplasticizers, water-reducing agents and pozzolanic materials. For the updating of shrinkage prediction, a new method in which the shrinkage half-time is calibrated by simultaneous measurements of water loss is presented. This approach circumvents the large sensitivity of the shrinkage extrapolation problem to small changes in the material param-eters. The new model allows a more realistic assessment of the creep and shrinkage effects in concrete structures, which significantly affect the durability and long-time serviceability of civil engineering infrastructure.

This paper summarizes most of the aspects and details related to testing for creep and shrinkage in concrete. The experimental determination of con-crete creep and shrinkage is discussed in detail, analyzing each of the condi-tions likely to be encountered during planning, testing and reporting test data. The subjects discussed are: objectives of test programs, test concept, as-sumptions, designing a test program, standard test methods for creep and shrinkage, test specimens, equipment for measuring deformations, concrete-mixing, batching and preparation of test specimens, testing environments, tem-perature and humidity tolerances, deformation measurement schedule, docu-mentation and interpretation of test results. Test programs are presented in detail. Field studies are discussed and correlated to laboratory test programs for three types structures sensitive in varying degrees to effects of creep and shrinkage. That is, field studies of reinforced and prestressed concrete nuclear containments, the uneven long-term shortening of columns with respect to the shear walls in reinforced concrete high rise buildings with shear walls, and the determination of prestressing forces, cambers, deflections and prestress loss in prestressed members.

This paper presents a comparison between laboratory creep and shririkage data and the performance of a long-span box-girder bridge structure. As part of a long-term instrumentation and monitoring program on the North Halawa Valley Viaduct, a number of laboratory creep and shrinkage tests were performed on the concrete used in the viaduct. The data are compared with current theoretical models for the prediction of creep and shrinkage. These models all underestimate the long-term effects on the concrete used in this structure. This is attributed in part to the nature of the basalt aggregates available on the Hawaiian Islands. It is shown that with as little as 28 days of data from creep and shrinkage tests, the prediction models can be modified to provide a far more accurate prediction of the long-term performance of the structure.

The effect of ambient temperature and humidity to which concrete is exposed prior to or during loading should be taken into account; when creep and shrinkage are predicted. The purpose of this study is to clarify the effect of ambient temperature and humidity on the creep and shrinkage of concrete. In this study, we carried out creep and shrinkage tests under constant and varying histories of temperature and humidity. Creep and shrinkage tests sub-jected to ambient temperature and humidity were also carried out in the room where the effect of rain and wind were negligible. The effect of temperature on shrinkage is much bigger than that of changes in humidity. The shrinkage strain on concrete subjected to increase in temperature is much bigger than that measured under constant temperature. The magnitude of creep and shrinkage is highly influenced by the difference of the season in which concrete is cast. The effect or variance of humidity on creep seems to be small. The temperature of curing water before application of load significantly influenced creep of concrete.