Study On The Evolution Of Concrete Performance Based On Hydration Properties At Macro-meso Scale

Thermal stresses and temperature controlling measures to prevent cracking are key concerns for mass concrete structures.In most cases,proper materials may be selected to satisfy the strength requirements;reasonable construction and cooling schedules may also be established according to regular calculations.However,due to the conventional calculation process simplifies the hydration process,concrete mechanical properties,such as elastic modulus,are not predictied precisely,finally,the actual process of mass concrete pouring in still often crack unpredictable,which affect the durability and performance of structure.Therefore,it is necessary to take the direct relationship among the internal temperature,the rate of hydration heat generation and the rate of increase of strength into account,and to simulate the temperature and stress characteristics of mass concrete structures in a more reasonable way.At present,numerous efforts have been made to develop a general model for evaluating the hydration heat of hardening concrete.this work employs a finite element analysis of a chemo-thermal-coupled concrete model that is clearly distinguishable from other models in the existing literature.Simulations are run on concrete samples with various water cement ratios,and the outcomes are compared to experimental temperature curves,which show that the hydration model provides a relatively high accuracy.Finite-element simulations are performed on mesoscale,with a mesoscopic mesh of random polygons generated by a Monte Carlo method.In order to link the two scales(macro and meso scale)and identify their differences,a multi-scale framework based on a homogenization scheme is adopted in the parameter studies.Mesoscopic thermo-chemical behaviors are accurately predicted for concrete samples with various volume fractions and aggregate compositions.The results show that the cooling conditions and the aggregate volume fraction and composition play a significant role in the chemo-physical process.The inhomogeneous distribution of hydration degree caused by the coarse aggregates in the concrete may lead to the presence of temperature gradients and slow the growth of cement strength,particularly in the areas where aggregates are concentrated.Moreover,this work conduct a contrastive investigation of numerical simulations to improve the comprehension of thermo-structural coupled phenomena of mass concrete structures during construction.Simulations are run on a concrete dam section with a conventional method and a chemo-thermo-mechanical coupled method.Both tempature and stress field simulation results show a difference within the dam setion,by means of the conventional method and coupled method.Based on engineering facts,the prediction results of thermo-chemical-mechanical model conform with the engineering practice.Then,combined with the random aggregate model in mesomechanics,the properties evolution model is introduced to study damage characteristics of concrete specimens.The thermal and mechanical parameters of numerical specimens are calibrated by a coupled thermo-chemo-mechanical model that can directly reflect the evolution of the material parameters along with the hydration process of early-age concrete.A hydration damage model is adopted,in which the damage parameters can be related with the development of chemical reaction inside the concrete.The simulation results show that:the stress-strain curves and cracking state of different early-age concrete specimens are variant because of the diversity of mesoscopic structure;the whole developing process of crack can be visually exhibited by this hydration damage mode,which supplied a powerful numerical tool to the analysis of early-age concrete tensile failure.At last,the finite element analysis of thermo-structural behaviors is used to investigate the applicability of supersulfated cement(SSC)in mass concrete structures.Based on the experimental data of hydration heat evolution rate and quantity of SSC and ordinary Portland cement,the hydration properties of various cements are studied.The results show that SSC is more suitable for mass concrete structures from the standpoint of temperature control and crack prevention.The research of this paper can provide reference for material design from the viewpoint of numerical calculation.