# Modeling of Hydration, Compressive Strength, and Carbonation of Portland-Limestone Cement (PLC) Concrete

## Abstract

**:**

## 1. Introduction

_{2}and NO

_{x}emissions from cement manufacturing, can be obtained by using PLC concrete [1,2].

^{3}of concrete), limestone is added as filler material in quantities of 200 to 300 kg/m

^{3}for producing self-consolidating concrete. This study focuses on PLC concrete rather than limestone-blended self-consolidating concrete. In this study, water-to-binder ratio (W/B) means the mass ratio of water to Portland cement plus limestone, and water-to-cement ratio (W/C) means the mass ratio of water to Portland cement.

_{2}diffusivity and the carbonation depth of PLC concrete are evaluated, considering material properties and environmental conditions.

## 2. Hydration Model

#### 2.1. Hydration Model for Cement

#### 2.2. Dilution Effect, Nucleation Effect, and Chemical Effect of Limestone Particles

## 3. Gel–Space Ratio and Compressive Strength

## 4. Carbonation Model of Concrete

_{2}weight in C-S-H [26,27].

_{2}. The carbonation depth of concrete can be determined as follows [17]:

_{2}diffusivity, ${[C{O}_{2}]}_{0}$ is CO

_{2}molar concentration at the concrete surface, $[\mathrm{CH}]$ is molar concentration of calcium hydroxide, $[\mathrm{CSH}]$ is molar concentration of calcium silicate hydrate, A and a are carbonation reaction parameters, and RH is the environmental relative humidity. $[\mathrm{CH}]+3[\mathrm{CSH}]$ in the denominator of Equation (26) is the content of carbonatable material [26,27]. The dependence of CO

_{2}diffusivity on temperature can be considered by using Arrhenius’s Law [28,29,30].

## 5. Verification of the Proposed Model

#### 5.1. Degree of Cement Hydration in Cement-Limestone Blends

#### 5.2. Compressive Strength of Concrete

^{3}. Limestone replaced cement at two levels: 15% and 25%. The concrete specimens were sealed and cured at 20 °C. At the ages of one day, three days, 28 days, and 18 months, the compressive strength of concrete was measured. The ages of one day and three days represent the early ages of concrete, and the age of 18 months represents the long-term age of concrete. Using the hydration model that considers the limestone dilution effect and the physical effect, the reaction degree of cement, and the gel–space ratio of concrete were calculated. Furthermore, the coefficients of ${\sigma}_{0}$ and $n$ were set as 157 and 2.74, respectively, based on the experimental results [6]. Bentz et al. [5] proposed that the strength exponent, $n$, was between 2 and 3. The calibrated value of $n$ in this study generally agrees with that value. As shown in Figure 5, the calculation results generally agree with the experimental results. However, the predicted long-term compressive strength deviates from the experimental results. This is because the formation of a monocarboaluminate phase at late ages was not considered in the proposed model.

#### 5.3. Carbonation of PLC Concrete

^{−5}and a = 4.7). With increasing water-to-binder ratios or decreasing cure periods, the carbonation depth of concrete increases. When the curing period increases from one day to three days, the concrete carbonation depth decreases by approximately 25%. While the curing period increases from three days to 28 days, the concrete carbonation depth decreases by approximately 25%–30%. This is because the rate of cement hydration at early ages (before three days) is much quicker than that at late ages (28 days). Hence, early age curing is effective for reducing the carbonation depth of concrete.

_{2}diffusivity on local relative humidity requires additional examination. Second, the change in carbonation depth may also be related to the changes in the pore solution and the composition of the cement hydrates with limestone present (and reacting) in the cement paste. This point was not considered.

## 6. Conclusions

_{2}diffusivity and carbonation depth of PLC concrete are evaluated by considering concrete material properties and environmental conditions. With increasing water-to-binder ratios and limestone content or reductions in curing period, the carbonation depth of concrete increases. The carbonation resistance of PLC concrete is related to both increasing factors (limestone replacements can increase the reaction degree of cement) and deceasing factors (limestone replacements decrease cement contents in mixing proportions).

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**Degree of hydration in plain cement paste [3].

**Figure 3.**Dilution effect of limestone replacements: (

**a**) 9% limestone powder; and (

**b**) 18% limestone powder [3].

**Figure 4.**Dilution effect and nucleation effect of limestone replacements: (

**a**) 9% limestone powder; and (

**b**) 18% limestone powder [3].

**Figure 5.**Compressive strength of PLC concrete: (

**a**) the relation between strength and gel–space ratio; and (

**b**) the predicted compressive strength [6].

**Figure 6.**Effects of limestone replacements on the ratio of degree of hydration: (

**a**) water-to-binder ratio of 0.4; (

**b**) water-to-binder ratio of 0.25.

**Figure 7.**Effects of limestone replacements on compressive strength development: (

**a**) water-to-binder ratio of 0.4; (

**b**) water-to-binder ratio of 0.25.

**Figure 8.**Effects of limestone replacements on the compressive strength ratio: (

**a**) water-to-binder ratio of 0.4; (

**b**) water-to-binder ratio of 0.25.

**Figure 9.**Carbonation depth of PLC concrete. The water-to-binder ratio (

**a**) 0.65; (

**b**) 0.61; (

**c**) 0.53; and (

**d**) 0.48 [7].

**Figure 10.**Effects of limestone replacements on carbonation: (

**a**) three-day cure before carbonation; (

**b**) 28-day cure before carbonation.

Binder (kg/m ^{3}) | Water-to-Binder Ratio | Gravel/Sand | 28 Days Compressive Strength (MPa) |
---|---|---|---|

300 | 0.65 | 1 | 25.1 |

340 | 0.61 | 1.13 | 32.6 |

380 | 0.53 | 1.13 | 37.8 |

420 | 0.48 | 1.15 | 43.5 |

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**MDPI and ACS Style**

Wang, X.-Y.
Modeling of Hydration, Compressive Strength, and Carbonation of Portland-Limestone Cement (PLC) Concrete. *Materials* **2017**, *10*, 115.
https://doi.org/10.3390/ma10020115

**AMA Style**

Wang X-Y.
Modeling of Hydration, Compressive Strength, and Carbonation of Portland-Limestone Cement (PLC) Concrete. *Materials*. 2017; 10(2):115.
https://doi.org/10.3390/ma10020115

**Chicago/Turabian Style**

Wang, Xiao-Yong.
2017. "Modeling of Hydration, Compressive Strength, and Carbonation of Portland-Limestone Cement (PLC) Concrete" *Materials* 10, no. 2: 115.
https://doi.org/10.3390/ma10020115