To develop a high-performance shrinkage reducing agent, this study investigated several shrinkage reducing materials and supplements for those materials. Fluidity and air content were satisfactory for the various shrinkage reducing materials. The decrease in viscosity was the lowest for glycol-based materials. The decrease in drying shrinkage was most prominent for mixtures containing glycol-based materials. In particular, mixtures containing G2 achieved a 40% decrease in the amount of drying shrinkage. Most shrinkage reducing materials had weaker level of compressive strength than that of the plain mixture. When 3% triethanolamine was used for early strength improvement, the strength was enhanced by 158% compared to that of the plain mixture on day 1; enhancement values were 135% on day 7 and 113% on day 28. To assess the performance of the developed high-performance shrinkage reducing agent and to determine the optimal amount, 2.0% shrinkage reducing agent was set as 40% of the value of the plain mixture. While the effect was more prominent at higher amounts, to prevent deterioration of the compressive strength and the other physical properties, the recommended amount is less than 2.0%.
Concrete is an outstanding construction material due to its outstanding strength and durability [
The causes of cracks in concrete can be largely divided into structural factors [
One effective method of reducing cracks caused by drying shrinkage is to reduce the unit content of water, but this achieves only a limited effect [
For this domestic production of shrinkage reducing agents, this study selected a total of seven materials: three alcohol-based materials (A1, A2, and A3), two glycol-based materials (G1, G2), animal fatty acids (AF), and vegetable fatty acids (VF). A Japanese shrinkage reducing agent (JP) was compared to the seven shrinkage reducing materials. In surface tension and mortar applications, three alcohol-based materials and two glycol-based materials were selected based on performance assessment in terms of flow, strength, and drying shrinkage. After applying the five shrinkage reducing materials to concrete, one material was eventually selected and processed into a high-performance shrinkage reducing agent for concrete. For performance assessment, the shrinkage reducing agent was applied to concrete and evaluated for various properties including slump, air content, compressive strength, and drying shrinkage length change.
This study performed concrete application tests on five shrinkage reducing materials, selected based on a literature review, theoretical examination, and surface tension and mortar applications. One shrinkage reducing material was eventually selected. Through performance enhancement, the selected material was used to produce a high-performance shrinkage reducing agent for concrete. The experimental plan is presented in Table
Experimental plan.
Experimental factors | Measurement | |||
---|---|---|---|---|
Mix | W/B (%) | 49.4 | (i) Fresh concrete: slump, air content | |
Binder (%/B) | FA 10 | |||
Slump (mm) | 180 ± 25 | |||
Air content (%) | 4.5 ± 1.5 | |||
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Concrete application | Shrinkage reducing (SR) materials | (i) Alcohol-based 1 (A1) |
0 (plain), 2.0 (%/B) | (i) Fresh concrete: slump, air content |
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Performance enhancement | Early strength materials | (i) NaNO3 (NN) |
0 (plain), 1.0, 3.0, 5.0 (%/SRA) | (i) Fresh concrete: slump, air content |
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Performance assessment | Shrinkage reducing (SR) materials | (i) Glycol-based (G) | 0 (plain), 0.5, 1.0, 2.0, 4.0 (%/B) | (i) Fresh concrete: slump, air content |
To develop a high-performance shrinkage reducing agent for concrete, a mortar test was used to select three alcohol-based and two glycol-based materials. The physical properties and the molecular structures of the selected shrinkage reducing materials are shown in Tables
Physical properties of shrinkage reducing materials in use.
Shrinkage reducing materials | Abbreviation | Density (g/ |
Color | State |
---|---|---|---|---|
Alcohol-based A | A1 | 0.78 | Colorless | Liquid |
Alcohol-based B | A2 | 0.82 | Colorless | |
Alcohol-based C | A3 | 0.79 | Colorless | |
Glycol-based A | G1 | 1.03 | Colorless | |
Glycol-based B | G2 | 0.86 | Colorless |
Molecular structures of shrinkage reducing materials in use.
Shrinkage reducing materials | Molecular structures |
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Alcohol-based A |
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Alcohol-based B |
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Alcohol-based C |
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Glycol-based A |
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Glycol-based B |
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The shrinkage reducing materials in Table
Physical properties of early strength materials.
Material | Abbreviation | Density (g/ |
pH | State |
---|---|---|---|---|
NaNO3 | NN | 1.29 | 7.48 | Liquid |
Triethanolamine | TEA | 1.48 | 5.23 | |
Calcium formate | CF | 1.91 | 7.2 |
A high-performance shrinkage reducing agent for concrete was developed by applying the early strength materials shown in Table
Physical/chemical properties of cement.
Density (g/ |
Blaine ( |
Setting time (min) | Compressive strength (MPa) | |||
---|---|---|---|---|---|---|
Initial | Final | 3 days | 7 days | 28 days | ||
3.15 | 3,265 | 210 | 300 | 22.0 | 28.9 | 38.9 |
Physical properties of fly ash.
Density (g/ |
Blaine ( |
LOI (%) |
|
Moisture (%) |
---|---|---|---|---|
2.20 | 3850 | 2.50 | 51.3 | 0.10 |
Physical properties of aggregates.
Aggregates | Density (g/ |
FM | Absorption (%) | Unit volume weight (kg/ |
0.08 mm sieve passing percentage (%) | |
---|---|---|---|---|---|---|
Fine agg. | River sand | 2.65 | 2.62 | 1.42 | 1,637 | 2.53 |
Crushed sand | 2.70 | 2.94 | 1.50 | 1,692 | 2.68 | |
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Coarse agg. | Granite stone | 2.83 | 6.55 | 0.58 | 1,684 | 0.40 |
Concrete tests were performed to analyze and assess the five shrinkage reducing materials. Aggregates and binders were mixed for 30 seconds using a shaft mixer. The shrinkage reducing materials, early strength materials, and admixtures were mixed for 90 seconds. Tests for slump and air content of fresh concrete employed the pressure method and were conducted in accordance with the KS F 2402 Method of testing for slump of concrete and the KS F 2421 Method of testing for air content of fresh concrete. To examine the effects of hardening on the concrete properties, compressive strength and drying shrinkage length change were measured. Compressive strength was measured using a Ø 100
To develop a high-performance shrinkage reducing agent for concrete, this study performed concrete application tests to analyze the properties of three alcohol-based and two glycol-based shrinkage reducing materials, selected through surface tension and mortar tests. To analyze the effects of the various shrinkage reducing materials on the slump and air content of concrete, the shrinkage unit powder content levels were set at 0 and 2%. The effects on compressive strength and drying shrinkage length change after hardening were analyzed, and the material exhibiting the best performance was selected to be developed into the shrinkage reducing agent.
In Figure
Relationship between the slump and the shrinkage reducing material.
The relationship between air content and shrinkage reducing material can be precisely seen in Figure
Relationship between air content and shrinkage reducing material.
Figure
Compressive strength by age for various shrinkage reducing materials.
Figure
Drying shrinkage length change by age for various shrinkage reducing materials.
As shown in Figure
Concrete application tests showed that the glycol-based G2 was the most outstanding shrinkage reducing material in terms of fluidity and drying shrinkage reduction. However, G2 also showed some decrease in initial strength, and certain ancillary materials had to be added to improve performance. The materials added were NN (NaNO3), TEA (triethanolamine), and CF (calcium formate); concrete properties were analyzed in relation to the type and amount of early strength material.
Figure
Slump of concrete in relation to the type and amount of early strength material.
The air content of concrete in relation to the type of early strength material is shown in Figure
Air content of concrete in relation to the type and amount of early strength material.
The compressive strength of concrete by age in relation to the type and amount of early strength material was shown in Figure
Compressive strength of concrete in relation to the type and amount of early strength material.
To assess the performance of the developed high-performance shrinkage reducing agent and to determine the optimal amount, the effects on concrete were analyzed at varying unit powder contents of 0, 0.5, 1.0, 2.0, and 4.0%.
Figure
Relationship between slump and amount of shrinkage reducing agent.
Figure
Relationship between air content and amount of shrinkage reducing agent.
Figure
Compressive strength by age for varying amounts of shrinkage reducing agent.
Some decrease in strength was observed with increasing amount of shrinkage reducing agent. On day 3, the strength values were 97, 95, 90, and 87% at 0.5, 1.0, 2.0, and 4.0%, respectively. The difference grew smaller as the days progressed. On day 28, the strength was 98, 98, 99, and 93% at 0.5, 1.0, 2.0, and 4.0%. When the amount of shrinkage reducing agent was 4.0%, there was a slight decrease in strength. The strength was 87% in the early days and rose to 90% in the long term. However, sufficient review is needed before using the shrinkage reducing agent at 4.0%. No special consideration is needed when the amount is less than 2.0%.
Figure
Drying shrinkage length change by age for varying amounts of shrinkage reducing agent.
To ensure domestic production of shrinkage reducing agents, this study performed concrete application tests using various shrinkage reducing materials and developed a high-performance shrinkage reducing agent based on the selected material. The following conclusions were derived. Fluidity and air content were satisfactory for the various shrinkage reducing materials. The decrease in viscosity was the lowest for glycol-based materials. The compressive strength was in the order of plain When 3% triethanolamine was used for early strength improvement, the strength was enhanced by 158% compared to that of the plain mixture on day 1, 135% on day 7, and 113% on day 28. The amount of shrinkage reduction for the 2.0% shrinkage reducing agent was 40% of the value of the plain mixture. While the effect was more prominent at higher amounts, to prevent deterioration of the compressive strength and the other physical properties, the recommended amount is less than 2.0%. Drying shrinkage can be reduced without affecting the compressive strength by using 3% triethanolamine for early strength improvement and a 2.0% glycol-based shrinkage reducing agent.
The authors declare that they have no competing interests.
This work was supported by the Power Generation & Electricity Delivery Department of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) through a grant funded by the Korean Government Ministry of Trade, Industry & Energy (no. 20131010501790).