Composition Of Concrete Mix Research Articles

Improved prediction model for time-dependent deformations of concrete: Part 2—Basic creep

The second part of this series presents the formulae for the prediction of basic creep of concrete, i.e. creep at no moisture exchange. The formulae give the secant uniaxial compliance function which depends on the stress level, and, as a special case, the compliance function for linear structural analysis according to the principle of superposition. The formulae are based on the recently developed solidification theory for concrete creep which takes into account simultaneous ageing, satisfies all the basic thermodynamic requirements, and avoids divergence of creep curves. The formulae, which describe both creep and elastic properties, involve only four free material parameters. All four appear linearly, so that optimum data fits can be obtained by linear regression. For the frequent situations where no test data for the particular concrete to be used are available, empirical formulae for predicting these four parameters from the concrete mix composition and the standard compressive strength are given. These formulae, however, involve considerable error. To avoid it, one should, whenever possible, carry out measurements of the elastic modulus and, if possible, also the short-time creep of 7 to 28 days duration. With such measurements, greatly improved predictions can be achieved. The predictions are compared with 17 extensive data sets taken from the literature, and the coefficients of variation of the deviations are found to be smaller than with previous models.

Practical prediction model for shrinkage of steel fibre reinforced concrete

A practical prediction model is proposed for predicting the shrinkage of steel fibre reinforced concrete (SFRC) from the composition of concrete mix, strength, age when drying begins, conditions of environment, size and shape of structures, fibre volume, aspect ratio of fibre, etc. The formulas were developed according to an extension of the well-recognized BP prediction model for the shrinkage of plain concrete (OPC). All important features of the BP prediction model, such as the diffusion-type size dependence of humidity effects and the square-root hyperbolic law for shrinkage, are automatically adopted for SFRC. In order to supplement the insufficient test data collected from the literature, a recently finished experimental series was used to expand the databank and hence the authors have a better command of the prediction formulas. Results of shrinkage from the literature and from the test series are reported, together with comparisons with predictions using the proposed model.

Practical prediction of time-dependent deformations of concrete

Proposed is a practical model for predicting creep and shrinkage of concrete from the composition of concrete mix, strength, age at loading, conditions of environment, size and shape, etc. The main features are: double power law for basic creep, square-root hyperbolic law for shrinkage, diffusion-type size dependence of humidity effects, additive drying creep term related to shrinkage, and activation energy treatment of thermal effects. Optimization techniques are used to fit numerous test data available in the literature. The work is a continuation of previous investigations and consists of several parts. This first part deals with shrinkage.

Practical prediction of time-dependent deformations of concrete

Proposed is a practical model for predicting creep and shrinkage of concrete from the composition of concrete mix, strength, age at loading, conditions of environment, size and shape, etc. The main features are: double power law for basic creep, square-root hyperbolic law for shrinkage, diffusion-type size dependence of humidity effects, additive drying creep term related to shrinkage, and activation energy treatment of thermal effects. Optimization techniques are used to fit numerous test data available in the literature. The work is a continuation of previous investigations and consists of several parts. This first part deals with shrinkage.