Pál Vásárhelyi Doctoral School of Civil Engineering and Earth Sciences 

Faculty of Civil Engineering, Department of Construction Materials and Technologies

Supervisor: Dr. NEMES Rita

Effects of Aggregate Type on Concrete Subjected to Elevated Temperatures

Introducing the research area

This research investigates the influence of different coarse aggregate types on the behavior of concrete under ambient and elevated temperatures, with a specific focus on fire resistance. By conducting experimental tests on ten concrete composites, including ordinary, lightweight, and recycled aggregates, this study aims to advance our understanding of concrete properties, enhance fire resistance capabilities, and promote sustainability in the construction industry. The findings from this research will contribute to informed material selection, improved design practices, and the development of more resilient and environmentally friendly concrete structures.

Brief introduction of the research place

The research takes place in a controlled laboratory environment, at the laboratory of the Department of Construction Materials and Technology, where various experiments are conducted to study the effects of aggregate type on concrete properties under elevated temperatures. The laboratory provides the necessary facilities and equipment (mixing machines, curing basins, ovens, and testing machines) for comprehensive tests and evaluations, ensuring accurate data collection and analysis for insightful findings.

History and context of the research

Over time, the human needs on the earth are changing due to the increase in population. Construction is one of the things that humanity has always needed (Curović, 2016). Today, at the beginning of the 21st century, it is undeniable that concrete was the primary construction material of the twentieth century and is likely to remain during the current century. Concrete is a worldwide building material that consumes large amounts of raw materials. Concrete structure raw materials can be found almost anywhere and can be molded easily. Nevertheless, the concrete industry produces a lot of waste, and the old concrete often goes to landfills (Moriconi et al., 2005; Naik, 2008).

During the structural design of buildings, fire resistance is an essential factor that must be considered (Kodur et al., 2020). Construction materials can maintain their intended load-bearing capabilities when subjected to fire. Material selection plays a significant role in fire resistance and can minimize structural failure and save lives (Rahla et al., 2021). The construction industry provides a wide range of materials whose structural behavior is affected by temperature to varying degrees. Concrete has recently become one of the most popular building materials for various structures. While information and research concerning concrete characteristics at ambient temperature are common, the behavior at elevated temperatures must be extensively researched (Fletcher et al., 2007).

The behavior of concrete under elevated temperatures is directly influenced by factors such as the temperature of exposure, mixture composition, moisture content, heat exposure duration, cooling methods, and the properties of its individual components (Neville, 2011; Rahla et al., 2021; Thomas et al., 2019). Aggregates compose around 70% of the concrete structure (Dehghan A. and Maher, 2023), which greatly influences the thermal response of concrete and its mechanical and physical properties. Therefore, aggregates have a crucial effect on the phenomena exhibited by concrete under elevated temperatures. Various observations clearly show aggregate effects on concrete behavior at elevated temperatures (Mindeguia et al., 2012), (Abdelalim et al., 2009).

For instance, (Khoury, 2000) observed that the stresses caused by the difference in the thermal expansion coefficients between the coarse aggregate and the hardened cement paste contribute to the appearance of micro-cracks in the cement paste, subsequently reducing the concrete's strength.

Understanding the relationship between aggregate type and concrete performance under elevated temperatures is essential for designing fire-resistant structures and developing strategies to mitigate potential failures. By studying different aggregate types and their effects on concrete properties, researchers aim to provide valuable insights for optimizing concrete mixtures and enhancing the fire resistance of structures.

This research builds upon the existing knowledge and seeks to contribute to a deeper understanding of the influence of aggregate type on concrete behavior under elevated temperatures, ultimately leading to the development of more resilient and durable construction materials and practices.

 

The research goals, open questions

The research goals of studying the effects of aggregate type on concrete subjected to elevated temperatures include investigating the fresh and characteristic properties of concrete with different aggregate types, evaluating their thermal properties, assessing the influence of micro-fiber content, which is used to increase the fire resistance of concrete, analyzing the impact of concrete age, and exploring the mechanical and thermal properties of concrete using different aggregates derived from the same base materials. Additionally, the research aims to utilize a Hungarian andesite (Kisnána) as a coarse aggregate for structural concrete and compare its performance with other aggregate types.

This research raises several open questions that require investigation. How do different aggregate types affect the fresh properties of concrete? What are the characteristic properties of concrete with different aggregates? How do aggregates impact the thermal properties of concrete? How does micro-fiber content influence the physical and mechanical properties of concrete? How does concrete age affect the properties of concrete with different aggregates? What are the mechanical properties of concrete after exposure to elevated temperatures with different aggregate types? How does the microfiber content influence concrete's physical and mechanical properties after exposure to elevated temperatures? What are the effects of using different aggregates derived from the same base materials on concrete's mechanical and thermal properties?

Addressing these research goals and answering these open questions will provide a comprehensive understanding of the interactions between aggregate type, fiber content, and concrete age in influencing the properties of concrete under elevated temperature conditions. The findings will contribute to developing more fire-resistant and durable concrete structures, enhancing their performance and longevity in real-world applications.

Methods

The research employs a combination of experimental methods to investigate the behavior of concrete with different aggregate types under elevated temperature conditions. The research methodology can be divided into several key steps.

·         Material selection: Various types of coarse aggregates representing different concrete categories, such as ordinary concrete, lightweight concrete, and recycled aggregate concrete, are carefully chosen. The selection is based on availability, relevance to the research objectives, and suitability for the experimental program. Cement type, fine aggregate, and fibers are also selected and tested carefully to create a range of concrete mixes.

·         Concrete mixing and specimen preparation: The selected materials are used to prepare concrete mixes according to predetermined proportions and mixing procedures. The concrete mixes are designed to ensure consistency and accuracy. Specimens, including cubic shapes, prisms, and cylinders, are cast using concrete mixes. The dimensions of the specimens are determined based on the required testing standards.

·         Experimental parameters: The research program considers various parameters to investigate their influence on the properties of concrete with different aggregate types. These parameters include the concrete specimens' age, elevated temperatures, and fiber contents. By controlling and varying these parameters, the research aims to identify the specific effects of aggregate type on concrete behavior.

 

 

 

·         Testing and evaluation: The prepared concrete specimens undergo a comprehensive range of tests to assess their mechanical, physical, and thermal properties. The mechanical tests include compressive strength, flexural tensile strength testing, shear strength, and microstructure analysis. The physical tests include moisture content, hardened density and weight loss. Thermal testing targets thermal conductivity. These tests are conducted at different stages, including ambient temperature and after exposure to elevated temperatures.

·         High-temperature exposure: Concrete specimens are subjected to elevated temperatures in a controlled environment. The temperature levels range from 200 ℃ to 1000 ℃, including ambient temperature as a reference. The exposure duration has been constant to 2 hours heating. The properties of the concrete specimens are measured and evaluated at each temperature level to understand the effects of aggregate type on concrete behavior under elevated temperatures.

·         Statistical analysis: The data collected from the experimental tests are subjected to statistical analysis. This analysis helps quantify the significance of observed differences in concrete behavior resulting from different aggregate types. Statistical methods enable the identification of patterns, trends, and correlations in the data, enhancing the reliability and robustness of the research findings.

 

By following these research methods, the study aims to generate reliable data, provide insights into the effects of aggregate type on concrete behavior, and contribute to the development of resilient and durable concrete structures. The research findings can be used to optimize material selection, enhance fire resistance, and improve the overall performance of concrete structures under elevated temperature conditions.

 

 

Results

In this section, we present the results of our study on the effects of aggregate type on concrete subjected to elevated temperatures. The experimental program was designed to investigate the influence of different aggregate types on the mechanical and physical properties of concrete, with a focus on its behavior under elevated temperature conditions. The results provide valuable insights into the performance and characteristics of concrete with various aggregate types.

To begin with, we evaluated the fresh properties of the concrete, including workability, air content and fresh density, to assess the impact of different aggregate types on the ease of construction. Subsequently, we examined the characteristic properties of the concrete, such as compressive strength, shear strength, and flexural tensile strength, at the 28-day curing stage as shown in Table 1 and Figure 1. These properties are crucial indicators of concrete's structural integrity and load-bearing capacity.

Table 1. Characteristic mechanical properties and fresh properties

 

Figure 1. Mechanical properties.

In addition to mechanical properties, we conducted microstructure analysis to gain a deeper understanding of the concrete's behavior as shown in Figure 2 to Figure 6. Microcracks formed within the cement paste were examined, providing insights into the influence of aggregate type on the occurrence of these microcracks and their potential impact on the concrete's strength.

 

 

 

 

 

Considering the ageing of the concrete, we evaluated its properties at 120 and 240 days of curing, both at ambient temperature and after exposure to elevated temperatures. This analysis enabled us to assess the long-term behavior and durability of the concrete as presented in Figure 7, as well as its response to elevated temperature conditions over time, as shown in Figure 8 to Figure 11.

 

Figure 7. Compressive strength rate at different ages.

Figure 8. Residual compressive strength at age 120 days.   Figure 9. Residual compressive strength at age 120 days

Figure 10. Residual compressive strength at age 240 days.   Figure 11. Residual compressive strength at age 240 days

 

 

Comparative analysis among different aggregate types derived from the same base materials highlighted mechanical and thermal properties variations. Aggregate types derived from different sources demonstrated different behaviours, emphasising the importance of carefully selecting and evaluating aggregates in the concrete mix design. Figures 12 and 13 show part of the thermal conductivity results.

 

 

 

Expected impact and further research

This research's expected impact on improving the understanding of fire-resistant concrete, sustainable solutions and the aggregate type's effects on concrete subjected to elevated temperatures is to provide valuable insights for the design and construction industry. The findings will contribute to optimizing material selection, enhancing fire resistance, and improving concrete structures' overall performance under elevated temperature conditions. The research outcomes can guide engineers and practitioners in making informed decisions regarding the selection of aggregate types and fiber content to ensure the durability and resilience of concrete structures.

Further research in this area can explore additional aggregate types, investigate the long-term effects of elevated temperatures on concrete properties, and explore the use of innovative materials and technologies to enhance the fire resistance of concrete structures. Additionally, studying the influence of different cooling methods and the development of predictive models for concrete behavior under elevated temperatures would be valuable avenues for future research.

Publications, references, links

List of corresponding own publications.

1. Effects of Polypropylene fibres on Ultra High Performance Concrete at elevated temperature, Ahmed M. Seyam, Samir Shihada, Rita Nemes, Concrete Structures journal, https://doi.org/10.32970/CS.2020.1.2.
2. Behaviour of structural lightweight concrete produced with expanded clay aggregate after exposure to high temperatures, Rita Nemes, Mohammed Abed, Ahmed Maher Seyam, Éva Lublóy, Journal of Thermal Analysis and Calorimetry. https://doi.org/10.1007/s10973-021-11167-6
3. A Review in Technologies, Definitions, Properties and Applications of Ultra High-performance Concrete (UHPC), Ahmed M Seyam, Balázs György László, Concrete Structures journal.
4. Using Hungarian andesite as a coarse aggregate for concrete, Ahmed M. Seyam, Rita Nemes, Építőanyag-Journal of Silicate Based & Composite Materials. https://doi.org/10.14382/epitoanyag-jsbcm.2023.06
5. Influence of Elevated Temperatures on the Compressive Strength of Concrete Made with Different Types of Aggregate, Ahmed M. Seyam, Rita Nemes, Construction and Building Materials Journal.
6. Comparing the European Standards and the American Standards for Testing Concrete Mechanical Properties. Ahmed M Seyam, Rita Nemes, Concrete Structures journal.
7. Age Influence on Compressive Strength For Concrete Made With Different Types Of Aggregates After Exposed To High Temperatures. Ahmed M Seyam, Rita Nemes, Materials Today journal
8. Effects of using polypropylene and steel fibres on Ultra High-Performance Concrete subjected to elevated temperatures. Ahmed M. Seyam, Samir Shihada, Rita Nemes; Proceedings of the 2020 Session of the 13th fib International PhD Symposium in Civil Engineering, (2020). pp. 25-32. 2.
9. Shear strength behaviour for lightweight aggregate concrete subjected to elevated temperature, Ahmed M. Seyam, Rita Nemes. fib International Congress 2022, Norway, 2022.
10. Impacts of aggregate type and elevated temperature on flexural tensile strength of concrete, Ahmed M. Seyam, Rita Nemes, 14th fib International PhD Symposium in Civil Engineering, Italy, 2022.
11. A Review in Technologies, definitions and Mechanical Properties of Ultra High Performance Concrete (UHPC), Ahmed M. Seyam, Balázs György László, 13th Central European Congress on Concrete Engineering, Poland, 2022.
12. Production of sustainable concrete using BME cladding wastes (Presentation) , Ahmed M. Seyam, Rita Nemes, BME a fenntarthatóságért Conference, Hungary, 2022.
13. Production of sustainable, fire-resistant concrete using demolition waste, (Presentation), Ahmed M. Seyam, Rita Nemes, 4th International Conference on Central European Critical Infrastructure Protection, Hungary, 2022.
14. Age Influence on Compressive Strength for Concrete Made with Different Types of Aggregates After Exposed To High Temperatures, Ahmed M. Seyam, Rita Nemes,  4^th International Congress on Materials & Structural Stability, Morroco, 2023.

 

List of references.

1        Abdelalim, A. M. K., Abdel-Aziz, G. E., El-Mohr, M. A. K., & Salama, G. A. (2009). Effect of aggregate type on the fire resistance of normal and self-compacting concretes. Engineering Research Journal, 122, 47–62. https://www.researchgate.net/publication/271767318

2         Amin M, Hakeem IY, Zeyad AM, Tayeh BA, Maglad AM, Agwa IS. Influence of recycled aggregates and carbon nanofibres on properties of ultra-high-performance concrete under elevated temperatures. Case Studies in Construction Materials 2022;16. https://doi.org/10.1016/j.cscm.2022.e01063.

3         Curović, N. (2016). Recycled concrete: Ecology and economic criteria. Istrazivanja i Projektovanja Za Privredu, 14(2), 271–274. https://doi.org/10.5937/jaes14-10964

4         Dehghan A. and Maher, M. L. J. and N. M. (2023). The Effects of Aggregate Properties on Concrete Mix Design and Behaviour. In M. and N. K. T. W. and S. M. and A. M. S. and el D. A. and L. G. Walbridge Scott and Nik-Bakht (Ed.), Proceedings of the Canadian Society of Civil Engineering Annual Conference 2021 (pp. 457–468). Springer Nature Singapore.

5         Fletcher, I. A., Welch, S., Torero, J. L., Carvel, R. O., & Usmani, A. (2007). Behaviour of concrete structures in fire. In Thermal Science (Vol. 11, Issue 2, pp. 37–52). Serbian Society of Heat Transfer Engineers. https://doi.org/10.2298/TSCI0702037F

6         Hlavička V, Hlavicka-Laczák LE, Lublóy É. Residual fracture mechanical properties of quartz and expanded clay aggregate concrete subjected to elevated temperature. Constr Build Mater 2022;328. https://doi.org/10.1016/j.conbuildmat.2022.126845.

7         Khoury, G. A. (2000). Effect of fire on concrete and concrete structures. Progress in Structural Engineering and Materials, 2(4), 429–447. https://doi.org/10.1002/pse.51

8         Kodur, V., Kumar, P., & Rafi, M. M. (2020). Fire hazard in buildings: review, assessment and strategies for improving fire safety. PSU Research Review, 4(1), 1–23. https://doi.org/10.1108/PRR-12-2018-0033

9         Mindeguia, J. C., Pimienta, P., Carré, H., & la Borderie, C. (2012). On the influence of aggregate nature on concrete behaviour at high temperature. European Journal of Environmental and Civil Engineering, 16(2), 236–253. https://doi.org/10.1080/19648189.2012.667682

10     Moriconi, G., Naik, T. R., & Moriconi, G. (2005). Environmental-friendly durable concrete made with recycled materials for sustainable concrete construction. https://www.researchgate.net/publication/238096274

11     Naik, T. R. (2008). Sustainability of Concrete Construction. Practice Periodical on Structural Design and Construction, 13(2), 98–103. https://doi.org/10.1061/(ASCE)1084-0680(2008)13:2(98)

12     Nemes R, Abed MA, Seyam AM, Lublóy É. Behavior of structural lightweight concrete produced with expanded clay aggregate and after exposure to high temperatures. J Therm Anal Calorim 2022;147:8111–8. https://doi.org/10.1007/s10973-021-11167-6.

13    Neville AM. Properties of concrete. 5th edition. Trans-Atlantic Publications, Inc.; 2012.

14     Rahla, K. M., Mateus, R., & Bragança, L. (2021). Selection Criteria for Building Materials and Components in Line with the Circular Economy Principles in the Built Environment—A Review of Current Trends. Infrastructures, 6(4), 49. https://doi.org/10.3390/infrastructures6040049

15     Thomas, C., Rico, J., Tamayo, P., Ballester, F., Setién, J., & Polanco, J. A. (2019). Effect of elevated temperature on the mechanical properties and microstructure of heavy-weight magnetite concrete with steel fibers. Cement and Concrete Composites, 103, 80–88. https://doi.org/10.1016/j.cemconcomp.2019.04.029