Mesoscale model for thermal conductivity of concrete

e thermal model and the relevant parameters of concrete are the most important issues to study the space-time characteristics of temperature field, which are also the theoretical foundation of temperature control and crack prevention for the mass concrete structures. In this research, the improved adiabatic temperature rise test is carried out, and the temperature variation of fly ash concrete is analyzed. Furthermore, a thermal model of concrete considering the hydration degree is established based on the existing achievements. Meanwhile, the thermal conductivity and specific heat of concrete are measured via three approaches: by treating the parameters as constant values, by computing the parameters as variables of the degree of hydration, and by backanalyzing the parameters through BP neural network. Finally, the thermal parameters determined by different methodologies are substituted into the thermal model, respectively, and the finite element analysis of the concrete specimen is performed. By comparing simulated temperatures with various measured results, it can be found that the numerical analysis results of parameters calculated by BP neural network are closest to the measured values in the whole curing ages. erefore, BP neural network method is an effective way to calculate the thermal parameters, and BP inversion algorithm provides a new way for accurately study the temperature profile of mass concrete structures.

Section: Ermal Conductivity Coe Cientmentioning

confidence: 99%

Study on Adiabatic Temperature Rise Reflecting Hydration Degree of Concrete

Wang

et al. 2018

“…To confirm the validity of mesoscopic numerical method for the ETC of concrete with arbitrary gradation, four specimens (L-RC1, L-RC5, L-RC6, and L-RC7) were selected from Zhang's experiment [10], and the mix proportions of four specimens are listed in Table 1 e other four specimens (basalt concrete, limestone concrete, siltstone concrete, and quartzite concrete) were from Khan's experiment [8]; then, the ETC of each specimen was calculated and compared with the experimental results. In Khan's experiment, four different rocks (basalt, limestone, siltstone, and quartzite) were chosen as coarse aggregates for four concrete specimens with dimensions of 120 × 120 × 40 mm, and the natural river sand was used as fine aggregates.…”

Section: Parameters Of the Test Modelmentioning

confidence: 99%

“…Khan [8] measured the thermal conductivity of concrete at various moisture contents, and developed a relationship between the ETC of concrete and the thermal conductivity of aggregate at different saturations. Kim et al [9] and Zhang et al [10] investigated quantitatively the influence factors on the ETC of concrete and proposed different prediction equations for the ETC of concrete. Experimental investigation on the ETC of concrete is the most direct and effective method, but it can be timeconsuming, costly, and labor intensive for investigating plentiful concrete specimens.…”

Section: Introductionmentioning

confidence: 99%

“…erefore, the 2D PNCDF of coarse aggregates is modified by changing the particle size range to (2, D max ). L-RC2 specimen (the crushed limestone with particle sizes of 5-16 mm) was selected from Zhang's experiment [10], in order to illustrate the implementation of 2D random polygonal aggregate model. e 2D random polygonal aggregate model of a slice-cut was conducted by the method described above.…”

mentioning

confidence: 99%

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Mesoscopic Finite Element Method of the Effective Thermal Conductivity of Concrete with Arbitrary Gradation

Huang

Zhao

Niu

et al. 2018

e effective thermal conductivity (ETC) of concrete is the most important parameter in determining the temperature field and thermal stresses. A 2D random polygonal aggregate model and its modified model considering porosity were established in this paper in order to partially replace the experiment for parametric analysis on the ETC of concrete and to save the experiment cost. A mesoscopic finite element method for the ETC of concrete with arbitrary gradation was also proposed. In addition, the influence factors (thermal conductivity of coarse aggregate, cement mortar, and volume fraction of coarse aggregate) of the effective thermal conductivity of concrete were analyzed. e results show that the 2D gradation curve of coarse aggregates is proved to exist, and there is a corresponding relationship between the 2D and 3D gradation curves of coarse aggregates. e effective thermal conductivity of concrete has a positive exponential relationship with the volume fraction of coarse aggregates, a positive logarithm relationship with the thermal conductivity of coarse aggregates, and a positive linear correlation with the thermal conductivity of cement mortar. e most practical way to improve the effective thermal conductivity of concrete is to increase the ETC of the cement mortar, but the most effective way is to replace the aggregate with a material with a high thermal conductivity.

“…Previous studies have shown that water-cement ratio, pH value, type and proportion of cement, coarse aggregate content, mineral admixture, and other factors have important effects on the sulfuric acid corrosion mechanism for concrete [6][7][8][9][10][11][12][13]. In fact, these factors will affect the pore structures of concrete, and the change of pore structures will significantly affect the transport performance of concrete [14][15][16][17], which results in a decline in concrete resistance to sulfuric acid corrosion. Being different from the mechanism of sulfate attack on concrete [11,12,18,19], the sulfuric acid corrosion mechanism for concrete is the result of a combined action of dissolved corrosion caused by hydrogen ion (H + ) and expanded corrosion caused by SO 4 2− (sulfate ion) [20].…”

Section: Introductionmentioning

confidence: 99%

Investigation on the Sulfuric Acid Corrosion Mechanism for Concrete in Soaking Environment

Min

Zhang

2018

Self Cite

is paper chooses the apparent diffusion coefficient for OH − (hydroxyl ion) for concrete as an index to evaluate the corrosion degree of concrete subjected to sulfuric acid. Based on the reaction boundary layer theory, a sulfuric acid corrosion model for concrete was established and verified through experiments. e experiment design and data processing of sulfuric acid corrosion tests for concrete were carried out using uniform test design and nonparametric regression. Effects of water-cement ratio and pH value are presented on the sulfuric acid corrosion mechanism for concrete. Test results show that when the pH value was 2.50, the sulfuric acid corrosion degree of concrete was the most serious. e boundary layer effect always existed in the sulfuric acid corrosion for concrete, and the corrosion process included rapid and stable corrosion stages. e apparent diffusion coefficient for OH − for concrete increased with the decrease of pH value and the increase of water-cement ratio and cement proportion.