A unified solidification model of hardening concrete composite for predicting the young age behavior of concrete R. Mabrouk * , T. Ishida, K. Maekawa Department of Civil Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8556, Japan Abstract The prediction of hardening young concrete behaviors is proposed using a solidification model based on the microphysical information of temperature, hydration ratio, porosity, saturation, isotherm and others. The solid model deals with cement paste as the solidified finite fictitious clusters having each creep property. Aggregates are idealized as suspended continuum media of perfect elasticity. The combination of both phases may create the overall features of concrete composite under the unstable transient conditions at early age. The micro-scale surface tension is treated as the driving force for the shrinkage associated with and without water migration. The solidification model is expected to offer the deformability of hardening concrete under the combined effect of external loads and the capillary stress estimated by the thermo-dynamic computation. Verification of the proposed model is con- ducted through comparison with some experimental data available in the literature. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Young age concrete; Shrinkage; Creep; Multiphase material; Microphysics; Solidification; Constitutive modeling; Elasticity; Plasticity; Viscosity 1. Introduction The early stage of concrete life is known to have a significant control on the overall performance of con- cretestructures.Infact,itcanbesaidthatthefutureofa reinforced concrete structure may be decided based upon the information obtained from this period. Due to this, several models dealing with concrete at the early age have been proposed. These models can generally be divided into two groups. The first uses a parametersuchasmaturity[1]ordegreeofhydration[2] to represent the aging process. While the other group is based on some form of curve fitting using the mathe- matical formulation of Maxwell or Kelvin chains [3]. The aforementioned models have many shortcomings and could only give a narrow range of predictability. Recently,somemodelsthatarebasedontheassumptive physical phenomena in concrete such as moisture transport or microstructure of cement paste are being studied. These types of models show a better under- standing of the young concrete behavior and thus are better suited for establishing more reasonable formula- tions. Some of the models that have shown good po- tential are the solidification theory [4], the model by Anders Boe Hauggaard-Nielsen [5,6] and the Lokhorst creep estimation model [7,8]. In this research, a model based on the solidification theory will be proposed. 2. Basic concept of the proposed model The basic concept of this method is to predict the behavior of concrete based on the actual thermo-hygro- physical information of the microstructure. The input data is the concrete information like mix proportions, type of cement and environmental conditions of tem- perature and relative humidity, structure information like size, shape, reinforcement and loading conditions. Microphysical information of temperature, hydration ratio, pore structure and moisture transport are calcu- lated using the computational framework DuCOM [9,10]. Where, a dynamic coupling of cement hydration, microstructure formation and moisture transport mod- elsisincorporated.Thisinformationisthenalsousedas input data in the proposed model. This input data of microphysical information are linked to the structural * Corresponding author. Tel.: +81-3-5841-7498; fax: +81-3-5841- 6010. E-mail address: rasha@concrete.t.u-tokyo.ac.jp (R. Mabrouk). 0958-9465/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0958-9465(03)00073-8 Cement & Concrete Composites 26 (2004) 453–461 www.elsevier.com/locate/cemconcomp