Capillary Water Absorption Characteristics of Steel Fiber-Reinforced Concrete
Abstract
1. Introduction
2. Materials and Methods
2.1. Raw Materials
2.2. Mix Proportions
2.3. Compressive Strength
2.4. Capillary Water Absorption
2.5. Calculation of Capillary Water Absorption Rate
2.6. Determination of Microstructural Characteristics by Scanning Electron Microscopy
2.7. Determination of Pore Structure by Mercury Intrusion Porosimetry
2.8. Determination of Internal Water Migration Using 1H Low-Field Nuclear Magnetic Resonance
3. Results
3.1. Cumulative Capillary Water Absorption
3.2. Capillary Water Absorption Rate in Concrete
3.2.1. The Initial Capillary Water Absorption Rate
3.2.2. The Secondary Capillary Water Absorption Rate
3.3. Pore Structure Characteristics
4. Discussions
4.1. Water Transport Process and Mechanism
4.2. Explanation of the Abnormal Water Absorption Phenomenon
4.3. Influence of Steel Fibers on the Capillary Water Absorption
5. Conclusions
- The capillary water absorption process in concrete occurs in two distinct stages. The initial stage (0 min to 6 h) is characterized by rapid water absorption, while the secondary stage (1 day to 12 days) involves a slower rate of water absorption. Over time, the cumulative capillary water absorption rate decreases and eventually stabilizes.
- Significant differences in capillary water absorption rates are observed among the various types of concrete, primarily due to differences in their compactness. Lower strength grades, like C30, exhibit higher porosity, including a greater proportion of harmful pores, which enhances water transmission pathways and pore connectivity. By reducing the water–binder ratio and optimizing the composition of cementitious materials, the compactness of concrete improves, leading to reduced porosity and a lower proportion of harmful pores, thereby decreasing capillary water absorption.
- 1H low-field NMR analysis reveals that external water initially enters larger capillary pores through capillary absorption, filling gel pores near these capillary pores. Over time, as larger capillary pores reach partial saturation, water begins to migrate into smaller capillary pores. Larger capillary pores continue to absorb water at a diminished rate until a dynamic equilibrium is achieved. For pores smaller than gel pores, water migrates predominantly in the form of water vapor.
- Over extended periods, the capillary water absorption rate deviates from a linear relationship. This phenomenon is mainly attributed to water entering the concrete and reacting with unhydrated cement particles, producing additional C-S-H. The formation of C-S-H fills smaller pores, altering the internal pore structure, reducing pore connectivity, and increasing pore tortuosity. This phenomenon, termed the “C-S-H blocking effect”, plays a key role in reducing water absorption rates.
- Steel fibers influence water migration in concrete primarily through the following two mechanisms: the interfacial effect between steel fibers and the matrix and the blocking effect of steel fibers. These effects collectively determine the extent to which steel fibers affect the capillary water absorption rate of concrete.
- This study systematically investigates the effects and mechanisms of varying steel fiber contents on the capillary water absorption behavior of concrete. However, the dynamic transport process of water within the material’s microstructure was not directly monitored in real time. Future research should aim to integrate advanced, non-destructive evaluation methods capable of providing sufficient spatio-temporal resolution to track water movement dynamically. Coupling such experimental approaches with refined theoretical modeling will be crucial for fully elucidating the kinetic mechanisms underlying the water absorption process.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Raw Material | SiO2 | CaO | Al2O3 | Fe2O3 | SO3 | MgO | K2O | TiO2 | Na2O |
---|---|---|---|---|---|---|---|---|---|
Cement | 17.00 | 65.05 | 4.95 | 3.72 | 2.93 | 0.96 | 0.69 | 0.28 | 0.11 |
Fly ash | 45.69 | 2.94 | 42.20 | 2.72 | 0.52 | 0.31 | 0.53 | 2.04 | 0.13 |
GGBFS | 29.98 | 44.40 | 14.50 | 0.50 | 2.18 | 6.20 | 0.25 | 0.80 | 0.34 |
Silica fume | 84.92 | 1.04 | 0.63 | 3.44 | 0.89 | 1.18 | 2.58 | 0 | 0.97 |
Mixtures | Cement | Fly Ash | GGBFS | Silica Fume | Fine Aggregate | Coarse Aggregate | PCE | Steel Fiber | Water |
---|---|---|---|---|---|---|---|---|---|
C30-0 | 350 | / | / | / | 800 | 1045 | 0.017 | 0 | 190 |
C30-1 | 350 | / | / | / | 800 | 1045 | 0.017 | 20 | 190 |
C30-2 | 350 | / | / | / | 800 | 1045 | 0.017 | 40 | 190 |
C30-3 | 350 | / | / | / | 800 | 1045 | 0.017 | 60 | 190 |
C60-0 | 350 | 60 | 100 | / | 730 | 1000 | 0.020 | 0 | 160 |
C60-1 | 350 | 60 | 100 | / | 730 | 1000 | 0.020 | 20 | 160 |
C60-2 | 350 | 60 | 100 | / | 730 | 1000 | 0.020 | 40 | 160 |
C60-3 | 350 | 60 | 100 | / | 730 | 1000 | 0.020 | 60 | 160 |
C80-0 | 380 | 70 | 120 | / | 720 | 992 | 0.022 | 0 | 148 |
C80-1 | 380 | 70 | 120 | / | 720 | 992 | 0.022 | 20 | 148 |
C80-2 | 380 | 70 | 120 | / | 720 | 992 | 0.022 | 40 | 148 |
C80-3 | 380 | 70 | 120 | / | 720 | 992 | 0.022 | 60 | 148 |
UHPC-0 | 700 | 100 | 100 | 100 | 1000 | / | 0.060 | 0 | 170 |
UHPC-1 | 700 | 100 | 100 | 100 | 1000 | / | 0.060 | 80 | 170 |
UHPC-2 | 700 | 100 | 100 | 100 | 1000 | / | 0.060 | 160 | 170 |
UHPC-3 | 700 | 100 | 100 | 100 | 1000 | / | 0.060 | 240 | 170 |
Concrete Strength Grade | Compressive Strength (MPa) | |||
---|---|---|---|---|
Concrete-0 | Concrete-1 | Concrete-2 | Concrete-3 | |
C30 | 32.5 | 35.3 | 39.1 | 40.8 |
C60 | 62.0 | 64.5 | 66.3 | 68.4 |
C80 | 84.1 | 86.3 | 88.6 | 92.2 |
UHPC | 108.7 | 115.5 | 122.7 | 128.3 |
Concrete Strength Grade | Specimen Number | The Initial Water Absorption (cm/s1/2) | The Secondary Water Absorption (cm/s1/2) |
---|---|---|---|
C30 | C30-0 | 9.82 × 10−4 | 6.77 × 10−4 |
C30-1 | 9.98 × 10−4 | 6.61 × 10−4 | |
C30-2 | 1.16 × 10−3 | 6.78 × 10−4 | |
C30-3 | 8.82 × 10−4 | 6.69 × 10−4 | |
C60 | C60-0 | 4.19 × 10−4 | 1.01 × 10−4 |
C60-1 | 4.12 × 10−4 | 1.05 × 10−4 | |
C60-2 | 4.08 × 10−4 | 1.29 × 10−4 | |
C60-3 | 4.59 × 10−4 | 1.19 × 10−4 | |
C80 | C80-0 | 2.36 × 10−4 | 4.78 × 10−5 |
C80-1 | 2.88 × 10−4 | 4.69 × 10−5 | |
C80-2 | 2.25 × 10−4 | 4.56 × 10−5 | |
C80-3 | 3.23 × 10−4 | 3.73 × 10−5 | |
UHPC | UHPC-0 | 7.17 × 10−5 | 2.95 × 10−5 |
UHPC-1 | 3.65 × 10−5 | 2.77 × 10−5 | |
UHPC-2 | 4.74 × 10−5 | 2.19 × 10−5 | |
UHPC-3 | 5.69 × 10−5 | 2.43 × 10−5 |
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Nan, F.; Shen, Q.; Zou, S.; Yang, H.; Sun, Z.; Yang, J. Capillary Water Absorption Characteristics of Steel Fiber-Reinforced Concrete. Buildings 2025, 15, 1542. https://doi.org/10.3390/buildings15091542
Nan F, Shen Q, Zou S, Yang H, Sun Z, Yang J. Capillary Water Absorption Characteristics of Steel Fiber-Reinforced Concrete. Buildings. 2025; 15(9):1542. https://doi.org/10.3390/buildings15091542
Chicago/Turabian StyleNan, Fang, Qing Shen, Shuang Zou, Haijing Yang, Zhenping Sun, and Jingbin Yang. 2025. "Capillary Water Absorption Characteristics of Steel Fiber-Reinforced Concrete" Buildings 15, no. 9: 1542. https://doi.org/10.3390/buildings15091542
APA StyleNan, F., Shen, Q., Zou, S., Yang, H., Sun, Z., & Yang, J. (2025). Capillary Water Absorption Characteristics of Steel Fiber-Reinforced Concrete. Buildings, 15(9), 1542. https://doi.org/10.3390/buildings15091542