EXPERIMENTAL STUDIES ON EFFECT OF ELEVATED TEMPERATURE ON FIBRE REINFORCED GEOPOLYMER CONCRETE

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EXPERIMENTAL STUDIES ON EFFECT OF ELEVATED TEMPERATURE ON FIBRE REINFORCED GEOPOLYMER CONCRETE Rakshith D R1, Dr. Sadath Ali Khan Zai2, Akash Babu L A3, Mohiyuddhin C S4 1,3,4 Department of Civil Engineering 2professor, Department of Civil Engineering 1,2,3,4UVCE, Bengaluru, Karnataka, India

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Abstract - The present studies involves a comparative

service environments. Understanding the behavior of hardened concrete under elevated temperatures is essential for evaluating structural safety, residual strength, and durability. Exposure to high temperatures significantly influences the physical, mechanical, and microstructural properties of concrete. In some cases, slight strength improvement may occur due to further hydration of unhydrated cement particles. When concrete is exposed to temperatures between 100°C and 200°C and 300°C to 600°C, significant degradation occurs, Calcium hydroxide decomposes around 450°C –550°C, causing loss of cohesion in the cement matrix.

experimental investigation on the strength characteristics of M40 grade Conventional Concrete (CC) and Geopolymer Concrete (GPC) of having compressive strength 40 N/mm2 with 10 Molarity to which incorporating glass fibre and steel fibre. A total of eight concrete matrix were considered for detail experimental work, viz: M40 Conventional Concrete (control mix), M40 + GF, M40 + SF, M40 + GF + SF, Geopolymer Concrete GPC+10M, GPC+10M+GF, GPC +10M + SF, and GPC +10M + GF +SF. It is evident from the Experimental Study on Effect of Elevated Temperature on Mechanical Properties of Fibre Reinforced Geopolymer Concrete results obtained at 28,56 days and 90 days, the mix containing GPC +10M + GF +SF. has sustained maximum compressive strength, and flexural strength even at 100°C, 200°C and however, it is noticed that strength reduction at elevated temperature 300°C.

2. EXPERIMENTAL INVESTIGATION Experimental investigation of the elevated temperature mechanical properties of concrete focuses on evaluating its behavior under high thermal exposure, particularly in compression and flexure. This research is essential for assessing structural safety during fire incidents and hightemperature industrial applications. In a typical study, concrete specimens such as cubes (for compression tests) and prisms or beams (for flexural tests) are cast using standardized mix designs and cured for 28,56 and 90 days.

After curing, specimens are exposed to elevated temperatures commonly 100°C, 200°C and 300° in an electric furnace. The heating rate is carefully controlled to prevent thermal shock, and specimens are maintained at the target temperature for a specified duration to ensure uniform heat distribution. After exposure, samples are allowed to cool either naturally (air cooling) depending on the experimental objective.

Key Words: GPC, Fly Ash GGBS, Steel fibre, Glass fibre, Alkaline activators and Elevated temperature,

1. INTRODUCTION Concrete is one of the most widely used construction materials in the world and plays a vital role in the development of modern infrastructure. From residential buildings and bridges to highways, dams, and industrial structures, concrete forms the backbone of civil engineering projects. Its popularity arises from a combination of factors such as high compressive strength, durability, versatility in form, and the availability of raw materials at relatively low cost. Over the years, concrete technology has evolved significantly, responding to the growing demand for safer, more durable, and sustainable structures.

Compressive strength is determined using a compression testing machine, where axial load is applied until failure.

Results typically show a gradual reduction in compressive strength with increasing temperature due to moisture loss, microcracking, and decomposition of hydration products such as calcium silicate hydrate (C–S–H). Flexural strength is evaluated using a three-point or four-point bending test.

Flexural performance generally deteriorates more significantly than compressive strength because tensile zones are highly sensitive to thermal cracking.

Geopolymer concrete has gained significant attention as a sustainable alternative to conventional cement-based concrete due to increasing concerns over environmental pollution and climate change. The production of ordinary Portland cement is highly energy-intensive and is responsible for approximately 7–8% of global carbon dioxide (CO₂) emissions. This substantial environmental impact has encouraged the construction industry and researchers to explore eco-friendly materials that can reduce carbon emissions without compromising structural performance. Hardened concrete structures are often exposed to elevated temperatures due to fire accidents, industrial processes, nuclear facilities, or high-temperature

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3. MATERIALS AND MIXES

28, 56, and 90 days to evaluate the strength development over time. The compressive strength values obtained for each mix at these intervals are summarized in the table below.

Geopolymer concrete (GPC) is produced by activating aluminosilicate-rich industrial by-products using alkaline solutions. The primary binders used are Fly ash (FA), especially Class F, and Ground Granulated Blast Furnace Slag (GGBS), both known for their high silica (SiO₂) and alumina (Al₂O₃) content. The alkaline activator typically consists of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃).

Aggregates (fine and coarse) are used similarly to conventional concrete, often constituting about 75– 80% of the total mix. The water-to-binder ratio is kept low, while 8M molarity of NaOH solution is used while mixing, it helps to significantly influences strength.

Residual Compressive Strength at 28 days Table 2: Compressive strength of all mixes cured for 28 days at elevated temperature

Table 1: Concrete mix designation MIXES M40 M40+GF

DETAILS M40 Grade of concrete (control mix) Glass fiber combined with M40 Grade of concrete M40+SF Steel fiber combined with M40 Grade of concrete M40+GF+SF Glass fiber and steel fiber combined with M40 Grade of concrete GPC+10M Geopolymer concrete with 10M molarity GPC+10M+GF Geopolymer concrete with 10M combined with Glass fiber GPC+10M+SF Geopolymer concrete with 10M combined with Steel fiber GPC+10M+GF Geopolymer concrete with 10M combined +SF with Glass fiber and Steel fiber

Type of mixes

Compressive strength in N/mm2

M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

Temperatures 100°C 200°C 300°C 51.54 54.23 35.57 52.68 55.20 36.44 54.36 57.05 37.67 56.66 59.35 39.30 52.14 54.82 36.09 55.48 57.86 38.40 57.93 60.72 40.27 59.67 62.38 41.75

4. INSTRUMENTATION The sample exposed to elevated temperature to find out the residual strength of concrete. The elevated temperature test was carried out using thermo controlled oven using electric furnace installed by Max Heat Furnaces, Bengaluru at Structural Engineering Laboratory, Civil Engineering Department, UVCE, Bangalore University, Bengaluru-56.

Concrete testing oven equipment is an essential laboratory apparatus used to study the thermal behavior of concrete under elevated temperature conditions. In this research, an electrically operated laboratory oven is employed to expose concrete specimens to controlled temperatures of 100°C, 200°C, and 300°C, simulating fire exposure and hightemperature service environments.

Figure 1: Comparison of Compressive Strength of concrete of all mixes cured for 28 days at elevated temperature

5. RESULTS AND DISCUSSIONS 1) Residual Compressive Strength of Concrete on Elevated Temperature at 100°C, 200°C and 300°C For 28, 56 and 90 Days Compressive strength tests were performed on standard cube specimens of size 150 × 150 × 150 mm for all mix variations. The specimens were tested after curing periods of

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Residual Compressive Strength at 56 days Table 3: Compressive strength of all mixes cured for 56 days at elevated temperature

Type of mixes M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

Compressive strength in N/mm2 Temperatures 100°C 200°C 300°C 54.43 57.18 37.59 55.99 58.69 38.68 58.11 60.89 40.25 60.71 63.55 42.18 55.51 58.19 38.32 60.09 62.90 41.64 61.30 64.14 42.79 63.72 66.67 44.89

Figure 3: Comparison of Compressive Strength of concrete of all mixes cured for 90 days at elevated temperature 2) Residual Flexural Strength of Concrete on Elevated Temperature At 100°C, 200°C and 300°C For 28, 56 and 90 Days Flexural strength tests were conducted on beam specimens with dimensions of 100 × 100 × 500 mm. The specimens were tested after curing periods of 28, 56, and 90 days to evaluate the strength development over time. During testing, the maximum load at failure was recorded for each specimen. Using this data, the flexural strength was calculated in accordance with standard procedures. The flexural strength values obtained for all concrete mixes are summarized in the below table.

Residual Flexural Strength at 28 days

Figure 2: Comparison of Compressive Strength of concrete of all mixes cured for 56 days at elevated temperature

Table 5: Flexural strength of all mixes cured for 28 days at elevated temperature

Residual Compressive Strength at 90days

Type of mixes

Table 4: Compressive strength of all mixes cured for 90 days at elevated temperature

Type of mixes M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

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M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

Compressive strength in N/mm2 Temperatures 100°C 200°C 300°C 55.88 58.66 39.03 57.25 60.04 39.94 59.33 62.17 41.52 61.89 64.82 43.33 56.85 59.55 39.61 61.07 63.96 42.70 62.37 65.41 44.00 64.32 67.41 45.72

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Flexural strength in N/mm2 Temperatures 100°C 200°C 300°C 5.29 5.55 3.58 5.54 6.64 3.76 5.64 6.97 3.84 5.99 7.29 4.08 5.47 6.40 3.71 5.93 7.12 4.03 6.41 7.81 4.32 6.72 7.92 4.59

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Residual Flexural Strength at 90 days Table 7: Flexural strength of all mixes cured for 90 days at elevated temperature

Type of mixes M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

Figure 4: Comparison of Flexural Strength of concrete of all mixes cured for 28 days at elevated temperature Residual Flexural Strength at 56 days

Flexural strength in N/mm2 Temperatures 100°C 200°C 300°C 5.90 6.18 4.00 6.06 6.35 4.12 6.25 6.54 4.28 6.74 7.04 4.62 5.97 6.26 4.06 6.41 6.71 4.40 6.79 7.10 4.67 7.01 7.34 4.82

Table 6: Flexural strength of all mixes cured for 56 days at elevated temperature Flexural strength in N/mm2 Temperatures 100°C 200°C 300°C 5.75 6.03 3.98 5.91 6.18 4.10 6.12 6.41 4.25 6.38 6.68 4.44 5.84 6.12 4.05 6.26 6.55 4.35 6.65 6.96 4.65 6.86 7.18 4.79

Type of mixes M40 M40+GF M40+SF M40+GF+SF GPC+10M GPC+10M+GF GPC+10M+SF GPC+10M+GF+SF

Figure 6: Comparison of Flexural Strength of concrete of all mixes cured for 90 days at elevated temperature

6. CONCLUSION

Figure 5: Comparison of Flexural Strength of concrete of all mixes cured for 56 days at elevated temperature

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1.

It is noticed that for the 28 days the increase in elevated Compressive strength of test specimen from 200°C is 15.03% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in Compressive strength at 300°C is GPC+10M+GF+SF than M40 respectively.

2.

It is noticed that for the 56 days the increase in elevated Compressive strength of test specimen from 200°C is 16.60% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in Compressive strength at 300°C is GPC+10M+GF+SF than M40 respectively.

3.

It is noticed that for the 90 days the increase in elevated Compressive strength of test specimen from 200°C is 14.92% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in

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Compressive strength at 300°C is GPC+10M+GF+SF than M40 respectively.

4.

5.

6.

It is noticed that for the 28 days the increase in elevated Flexural strength of test specimen from 200°C is 16.98% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in Flexural strength at 300°C is GPC+10M+GF+SF than M40 respectively.

It is noticed that for the 56 days the increase in elevated Flexural strength of test specimen from 200°C is 19.07% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in Flexural strength at 300°C is GPC+10M+GF+SF than M40 respectively.

It is noticed that for the 90 days the increase in elevated Flexural strength of test specimen from 200°C is 18.77% for GPC+10M+GF+SF than M40 respectively. It also found that less reduction in Flexural strength at 300°C is GPC+10M+GF+SF than M40 respectively.

6.

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7.

J. Ahmad et al., “Glass fibers reinforced concrete: Overview on mechanical, durability and microstructure analysis,” Materials, vol. 15, no. 15, 2022.

8.

J. Asanammal Saral and A. M. Uzair, “A comprehensive review on fiber reinforced geopolymer concrete: Mechanical performance, mix design, and durability,” International Journal of Civil Engineering and Technology (IJCIET), vol. 10, no. 2, 2019.

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