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Limestone powder is increasingly used in producing high-performance concrete in the modern concrete industry. Limestone powder blended concrete has many advantages, such as increasing the early-age strength, reducing the setting time, improving the workability, and reducing the heat of hydration. This study presents a kinetic model for modeling the hydration heat of limestone blended concrete. First, an improved hydration model is proposed which considers the dilution effect and nucleation effect due to limestone powder addition. A degree of hydration is calculated using this improved hydration model. Second, hydration heat is calculated using the degree of hydration. The effects of water to binder ratio and limestone replacement ratio on hydration heat are clarified. Third, the temperature history and temperature distribution of hardening limestone blended concrete are calculated by combining hydration model with finite element method. The analysis results generally agree with experimental results of high-performance concrete with various mixing proportions.

The use of limestone powder blended cement is a common practice in the modern concrete industry. The benefits from technical, economic, and ecological aspects can be achieved by using limestone blended concrete [

Many studies in experimental or theoretical aspects have been done about early-age properties and durability of limestone blended concrete. Bonavetti et al. [_{2} emission about 25% in comparison with average cement with the same performance.

Compared with abundant experimental studies, the theoretical models for limestone blended concrete are relatively limited. Lothenbach et al. [

To overcome the shortcomings in current models [

Wang and Lee [

The determinations of reaction coefficients

Equation (

Equation (

The influences of temperature on reaction coefficients can be described by using Arrhenius’s law [

Based on the degree of hydration of concrete with various types of Portland cement and various curing temperatures, Wang [

Summarily, the kinetic hydration model is composed of four rate determining coefficients, that is, the rate of formation of the initial impermeable layer (

Wang [

On the other hand, because the reactivity of limestone is very weak compared with other supplementary cementitious materials, limestone can be approximately regarded as chemical inert filler [

The dilution effect of limestone powder can be considered by using (

In (

In (

Summarily, for a cement-limestone blend, the dilution effect is considered through capillary water concentration. The nucleation effect is considered by nucleation effect indicator which considers binder proportions and surface area of binders. Furthermore, by using updated reaction coefficients, the reaction degree of cement in cement-limestone blends can be determined.

Hydrate heat of hydrating concrete is dependent on both cement content and degree of hydration. The relation heat from hydration of concrete can be determined as follows [

For hardening concrete, the temperature distribution is in a dynamic heat balance between the hydration heat generation inside the concrete and heat loss to the ambient. The heat generation comes from hydration reactions of the cement. The temperature distribution of hardening concrete is determined as follows [

For hardening concrete in construction sites, the boundary condition can be described as follows:

Equation (

The numerical procedure consists of a kinetic hydration model and a finite element model. The kinetic hydration model considers the dilution effect and nucleation effect from limestone additions. The heat of hydration of hydrating concrete is calculated by using the degree of hydration and cement content. The calculation results of the heat of hydration are used as a source term in finite element model. By using Galerkin method, the parabolic partial differential equation about temperature distribution of hardening concrete is solved. Temperature history of semiadiabatic temperature rise is calculated considering both concrete materials properties and ambient conditions. The proposed numerical procedure is valuable for thermal cracking analysis of hardening concrete and construction plan design and materials design of concrete structures.

Experimental results about isothermal heat evolution shown in [^{2}/g to 8900 cm^{2}/g. The curing temperature is 20°C. The used cement is moderate heat Portland cement. By using Portland cement hydration model shown in Section

Mixing proportions of paste for isothermal heat evolution.

Water (g) | Cement (g) | Limestone (g) | Blaine of limestone (cm^{2}/g) |
Limestone/(cement + limestone) | Water/cement | |
---|---|---|---|---|---|---|

M100 | 5 | 10 | 0 | — | 0 | 0.5 |

M90L10-35 | 5 | 10 | 1.11 | 3500 | 0.1 | 0.5 |

M70L30-35 | 5 | 10 | 4.29 | 3500 | 0.3 | 0.5 |

M70L30-89 | 5 | 10 | 4.29 | 8900 | 0.3 | 0.5 |

Rate of hydration heat.

100% Portland cement

90% Portland cement + 10% limestone

70% Portland cement + 30% limestone

70% Portland cement + 30% limestone with high Blaine surface

Effect of limestone powder on the rate of hydration heat

Furthermore, based on experimental results about hydration heat of limestone blended cement paste, the enhanced coefficients

Parameter studies are carried out to analyze the degree of hydration and hydration heat of hardening concrete with different limestone replacement ratios and water to binder ratios. The water to binder ratio ranges from 0.3 to 0.5, and limestone content ranges from 15% to 30%. The curing temperature is assumed as 20°C.

The calculated degree of hydration is shown in Figure

Degree of hydration.

Water to binder ratio 0.5

Water to binder ratio 0.3

The relative degree of hydration means the ratio of the degree of hydration of limestone blended concrete to that of control concrete. Figure

Relative degree of hydration.

Water to binder ratio 0.5

Water to binder ratio 0.3

As shown in (

Relative heat of hydration.

Water to binder ratio 0.5

Water to binder ratio 0.3

Experimental results about semiadiabatic temperature rise shown in [^{2}/day/k, respectively.

Mixing proportions of concrete.

Water/(cement + limestone) | Water^{3}) |
Cement^{3}) |
Limestone^{3}) |
Sand^{3}) |
Gravel^{3}) |
Superplasticizer^{3}) |
Initial temperature (°C) | Ambient temperature (°C) | |
---|---|---|---|---|---|---|---|---|---|

OPC | 30.3 | 171 | 565 | — | 820 | 915 | 1.0 | 30 | 23 |

Limestone 30% | 32.7 | 177 | 396 | 146 | 820 | 915 | 0.7 | 28 | 23 |

Limestone 55% | 32.6 | 168 | 226 | 291 | 820 | 916 | 0.7 | 28 | 23 |

Limestone 70% | 32.0. | 165 | 155 | 362 | 820 | 915 | 0.7 | 28 | 28 |

Compound compositions of cement.

C_{3}S |
C_{2}S |
C_{3}A |
C_{4}AF |
Gypsum |
Blaine^{2}/g) | |
---|---|---|---|---|---|---|

Cement | 53.9 | 18.8 | 11.0 | 10.4 | 5.83 | 3350 |

Because of symmetries of geometry condition and boundary condition of the specimen, a one-eighth specimen is adopted to represent the full specimen. The 8-node brick isoparametric element is used to mesh the specimen in three-dimensional spaces. Total 125 elements (

OPC concrete.

Temperature history

Temperature distribution

Limestone 30% concrete.

Temperature history

Temperature distribution

Limestone 55% concrete.

Temperature history

Temperature distribution

Limestone 70% concrete.

Temperature history

Temperature distribution

This study proposes a numerical procedure for predicting temperature history of hardening limestone blended concrete. The numerical procedure combines a kinetic limestone blended cement hydration model with a finite element method.

First, the hydration model analyzes the dilution effect and nucleation effect due to limestone additions. For concrete with a lower water to binder ratio, the dilution effect due to limestone addition becomes obvious, and the degree of hydration is significantly improved compared with control concrete without limestone.

Second, the released heat of concrete relates to both cement content and degree of hydration. Limestone additions increase the degree of hydration but reduce cement content. The total hydration heat depends on the combined action of cement content and degree of hydration. The results of parameter analysis show that limestone additions can reduce the heat of hydration.

Third, the calculation results of hydration heat from hydration model are used as input parameters of finite element model. The combined hydration and finite element model can be used to evaluate temperature history and temperature distribution of semiadiabatic hardening concrete. The analysis results show that, with the increasing of limestone content, the maximum temperature rise of concrete decreases.

The author declares that they have no conflicts of interest.

This research was supported by a grant from Smart Civil Infrastructure Research Program (13SCIPA02) funded by Ministry of Land, Infrastructure and Transport (MOLIT) of Korean Government and Korea Agency for Infrastructure Technology Advancement (KAIA).