GRD Journals- Global Research and Development Journal for Engineering | Volume 6 | Issue 1 | December 2020 ISSN- 2455-5703
M20 Grade Concrete Subjected to Elevated Temperature B Durga Vara Prasad Department of Civil Engineering Vishnu Institute of Technology, Bhimavaram, Andhra Pradesh K Suseela Department of Civil Engineering Vishnu Institute of Technology, Bhimavaram, Andhra Pradesh
B Mary Devika Department of Civil Engineering Vishnu Institute of Technology, Bhimavaram, Andhra Pradesh
Abstract The most widely used structural material in construction is concrete. Various natural disasters such as earthquakes, landslides, floods, cyclones, fire accidents, etc may occur in concrete structures. The major damage that a building may experience fire accidents. Concrete is used for controlling fireproofing. As concrete is exposed to elevated temperatures in a damaged building fire, the structural and non-structural elements of the building may undergo different changes. Depending on the intensity and duration of exposure, it may reach beyond 1000oC in an accidental fire. To replicate the fire exposure on the elements of the building, an experimental program took on in this study to analyse the effect of high temperatures on the concrete specimens of size 150mmx150mmx150mm. These specimens were exposed to temperatures ranging between room temperature to 1000oC for 3 hours duration at an interval of 10mins. M20 grade of 150mmx150mmx150mm concrete cubes are exposed from room temperature to 1000 ° C for 3 hours of fire exposure in every 100 ° C increment. After 3 hours duration cubes were air-cooled to room temperatures and its residual compressive strengths were found out by using Destructive and NDT tests (Rebound hammer and UPV). Thermal gradient variation in concrete from surface to the core at an every increment of 25mm depth was noted by placing thermocouples. The strength results from the destructive testing were substantiate through non-destructive i.e. Rebound hammer and Ultrasonic pulse velocity test. Keywords- Thermal Expansion, Elevated Temperature
I. INTRODUCTION Thermal gradient is rate of change of temperature with distance. Temperature stresses develop due to the change in temperature from surface to the bottom region of the concrete cube. Temperature along depth of the cube is to be recorded to determine thermal stresses. Thermocouples are used to record the temperature at the sufficient required depths. Thermocouples are available in various metals or calibration combinations. Because thermocouples measured in wide temperature ranges and it can be relatively uneven, they are very often used in industry. The scope of the project is to study the effect of elevated temperatures on Normal strength (M20) grade of concrete. To study the Non Destructive tests for the above grade of concrete before and after exposing the temperatures from 100°C to 1000°C at an interval of 100°C for the duration of 3 hours. The main objective is to study the behaviour of concrete during fire. The main parameters are residual compression strength, colour change, weight loss, crack width, and air voids. To find the residual compressive strength of the concrete exposed to elevated temperatures from 270C to 10000C for the normal strength (M20) grade of concrete at an interval of 1000C exposed to duration of 3 hours. To study the thermal gradient for the above grade of 150 mm X 150 mm X 150 mm concrete cubes that are exposed at an interval of 1000 C from 270C to 10000C from the surface to the core of the concrete cube at an interval of 25 mm, 50mm, 75mm. To check the quality of concrete by using crack width and Non-destructive tests like Rebound hammer and Ultrasonic pulse velocity.
II. LITERATURE REVIEW A. Omer Arioz Omer Arioz studied the effects of elevated temperatures on the physical and mechanical properties of different concrete mixtures formed by ordinary Portland cement, crushed limestone, and river gravel from 200 to 1200 ° C. The author cast the size of the cubes (70x70x70mm) and has a crushed limestone w/c ratio of 0.5. The w / c ratio is 0.4 for river gravel. In water, the specimens were cured for 28 days. The specimens were subjected to elevated temperatures ranging from 200 to 1200°C for 2 hours. When All rights reserved by www.grdjournals.com
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
exposed to elevated temperature they observed the chemical composition and physical structure of the concrete change considerably. Dehydration becomes significant above about 110 ° C, such as the release of chemically bound water from the calcium silicate hydrate (CSH). And from 300ºC micro-cracks are induced through the material. Calcium hydroxide [Ca (OH)2] which is the most important compound in cement paste, disappears at around 530°C resulting in the shrinkage of concrete. CSH gel, which is the strength giving compound of cement paste, decomposes above 600°C. They observed on 800°C, concrete is usually crumbled and above 1150°C feldspar melts and the other minerals of the cement paste turn into a glass phase. After exposure to 1200 ° C, where the spalling of the samples due to excessive cracking was observed, the specimens completely decomposed and lost their binding properties. B. Bahar Demirel Oguzhan Kelestemur Bahar Demirel Oguzhan Kelestemur studied the effect of elevated temperatures on the mechanical properties of finely ground pumice and silica fume concrete. By these, they investigated the mechanical and physical properties of the concrete such as compressive strength, porosity and high temperature resistance. The author coded 3 main groups of concrete were produced as C, P and PS. With no mineral admixture, the C series represents control concrete. In the P series, cement was replaced with finely grounded pumice at 4 proportions (5%, 10%, 15% and 20%) by weight. In the PS series, cement was replaced with silica fume at a constant ratio of 10% by weight in addition to pumice ( 5%, 10%, 15%, and 20% ).
III. EXPERIMENTAL INVESTIGATION In this present investigation various tests were conducted in laboratory on cement, fine aggregate, coarse aggregate. These are the materials used for the concrete in our thesis work. In this chapter the specifications and properties of these materials were presented as per the Indian standards. Table 1: Quantity of ingredients present in M20 grade of concrete Cement Fine aggregate Coarse aggregate Water 373 835.7 1055 186 1 2.26 2.85 0.5 Table 2: Trail mix of 6 cubes of 150 mm Ingridients Quantity 1.2% of extra Cement 7.53 9.05 Fine Aggregate 16.3 20.17 Coarse Aggregate 21.37 25.64 Water 3.78 4.52 Table 3: Workability of Ordinary Concrete Mix W/C Compaction Factor of mix Slump Degree of workability of mix Ordinary concrete mix 0.5 0.94 56mm Medium
A. Non Destructive Testing To determine strength without damaging the structure, it refers to a simple and safe process. The samples were tested by the required apparatus before and after exposed to elevated temperatures. 1) Ultrasonic Pulse Velocity Set reference: In order to check instrument zero, a reference bar is given. The bar's pulse time is engraved on it. Before placing on the opposite ends of the bar, add a smear of grease to the transducer faces. Up until the reference bar transit time is obtained on the instrument read-out, adjust the 'SET REF' control. Selection of range: For maximum accuracy, it is recommended that the 0.1 microsecond range be chosen for a path length of up to 400mm. Pulse velocity: Take careful measurement of the path length 'L' after determining the most suitable test points on the material to be tested. Apply the couplant to the transducer surfaces and press hard on the surface of the material. Do not move the transducers when taking a reading, as noise signals and measurement errors can be generated by this. Keeping the transducers until a clear reading appears on the display on the material surface, which is the time for the ultrasonic pulse to travel the 'L' distance in microseconds. When the digit unit hunts between two values, the mean value of the display readings should be taken. Pulse velocity = (Path length/Travel time) Separation of transducer leads: When taking transit time measurements, it is advisable to prevent the two transducer leads from coming into close contact with each other. If this is not done, the receiver lead will pick-up unwanted signals from the transmitter lead and this will result in an incorrect display of transit time. 2) Rebound Hammer In order to obtain reliable results for which the manufacturer of the rebound hammer indicates the range of readings on the anvil suitable for various types of rebound hammer, the rebound hammer should be tested against the test anvil prior to the start of the test. Apply light pressure to the plunger-the plunger is freed from the locked position and extended to the test ready position.
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
Press the plunger against the concrete surface, holding the instrument perpendicular to the surface of the test. Apply a gradual rise in pressure until it impacts the hammer. B. Residual Compression Strength After the exposure of cubes to a desired temperature, cubes were cooled down to room temperature then Residual compressive strengths are tested by using compression testing machine in our laboratory as per IS 516:1959. C. Crack Width Cracks occurred due to the internal pressure of evaporative moisture at elevated temperatures. The gap of width arrives in the form of crack is known as crack width. Cracks are visually observed by microscope. The scale of microscope is 10 divisions = 0.20mm. Heating the samples in the furnace and cools down properly in the room temperature. After it was observed by microscope. The cracks were arrived from 600°C. D. Weight Loss It refers to the reduction of total sample mass due to a mean loss of water content in the specimen. The weight percentage reduced by heat content present in bogie hearth furnace. Weight loss increased with increasing temperature of the furnace. Weight loss is calculated by weighing balance before and after heating of samples. E. Colour Change Colour change refers to the changing of colour from one to another. In elevated temperatures, colour change takes place from 600°C. At the time of heating the specimens turns into red from 600°C. After heating it turns gray colour into white. It was seen by visual observation. F. Elongation An expansion takes place to the original body that means change in length and volume. Elongation is calculated by Vernier callipers after heating of the specimens.
IV. RESULTS AND DISCUSSION A. Crack Width
Graph 1: Temperature vs Crack width
B. Colour Change
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
Graph 2: Temperature vs Elongation
Graph 3: Temperature vs Weight loss
Graph 4: Temperature vs Residual compression strength
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
Graph 5: Time vs Temperature at 200°C
Graph 6: Time vs Temperature at 600°C
Graph 7: Time vs Temperature at 800°C
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
Table 4: Distance vs Temperature Time(min) Depths 0 30 60 90 120 150 25mm 30 32 30 31 32 32 50 mm 30 31 31 32 32 32 75 mm 30 31 31 31 32 32
180 32 32 32
When the depth of the cube increases from surface to the core, the temperature present in the cube decreases from surface to the core. In below the temperature varies from 100°C to 800°C at an interval of 100°C with respect to the temperature and distance of the cube specimen.
Graph 8: Distance vs Temperature at 200°C
Graph 9: Distance vs Temperature at 600°C
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
Graph 10: Distance vs Temperature at 800°C
Graph 11: Temperature vs Rebound Hammer Table 5: Velocity of ultrasonic pulse velocity Temperature Velocity Efficiency Room Temperature 5.12 Excellent 100°C 5.05 Excellent 200°C 4.7 Excellent 300°C 4.47 Good 400°C 3.60 Good 500°C 3.11 Medium 600°C 2.83 Doubtful 700°C 1.07 Doubtful 800°C 0.58 Doubtful
V. CONCLUSION Above 200°C the specimens release chemically bound water from CSH gel. A type of water mist is formed near the entrance of the furnace before the temperature reached to 200°C. At 300°C CSH gel disappears and micro cracks are induced through the material. The shrinkage of the concrete was appeared from the temperature rises to 500°C. At 600°C the concrete started to crack and the colour became white. At 700°C the cracks became prominent and widely expanded. The colour of specimens became white and even red in some cases. At 800°C the spalling of concrete was appeared and concrete is crumbled. With increasing the temperature, the elongation of the cubes is also increasing simultaneously. The weight loss is increasing parallel to the temperature. The residual compression strength of concrete reduced with increase in exposure temperature. The recovered strength can be higher than that of control specimen. The normal weight concrete showed higher strength losses than light weight
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M20 Grade Concrete Subjected to Elevated Temperature (GRDJE/ Volume 6 / Issue 1 / 004)
concrete. When the time increases the frequency of the temperature is also increases. In thermal gradient, the distance of the cube from surface to the core the frequency of temperature decreases rapidly. Temperatures between 300°C and750°C may be regarded as critical to the strength loss of concrete in UPV and Rebound hammer.
VI. FURTHER EXTENSION OF THESIS WORK
Mineralogical and Morphological studies can also be done by X-RAY Diffraction, Scanning Electron Microscopy and Differential Thermal To determine flexural and split tensile strength. Curing periods can be extended to 56 and 90 days when replacement of concrete by cement and sand. To determine the water cooling method also in elevated temperatures.
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Omer Arioz “Effects of elevated temperatures on properties of concrete”sciencedirect, Fire Safety Journal 42 (2007) pp.516–522. Bahar Demirel n, O˘guzhan Keles-temur “Effect of elevated temperature on the mechanical properties of concrete produced with finely ground pumice and silica fume” sciencedirect, Fire Safety Journal 45 (2010) pp. 385–391. Bing Chen , ChunlingLi, LongzhuChen “Experimental study of mechanical properties of normal-strength concrete exposed to high temperatures at an early age” sciencedirect, Fire Safety Journal 44 (2009) pp.997–1002 Omar A. Abdulkareem , A.M. Mustafa Al Bakri , H. Kamarudin , I. Khairul Nizar , Ala’eddin A. Saif “Effects of elevated temperatures on the thermal behavior and Mechanical performance of fly ash geopolymer paste, mortar and lightweight concrete” sciencedirect, Construction and Building Materials 50 (2014) pp.377–387. Emre Sancak , Y. Dursun Sari , Osman Simsek “Effects of elevated temperature on compressive strength and weight loss of the light-weight concrete with silica fume and superplasticizer” sciencedirect, Cement & Concrete Composites 30 (2008) pp.715–721. SK.Mohammad Rafi, B.Ambalal , B.Krishna Rao and Mohd Abdul Baseer “Analytical Study on Special Concretes with M20 & M25 Grades for Construction” International Journal of Current Engineering and Technology ,E-ISSN 2277 – 4106, Pp.1-13. Prof Tanveer Asif Zerdi “Effect of Shahabad stone quarry dust on strength characteristics of M20 grade concrete” International Journal of Scientific Research, Volume : 5 , Issue : 1 , JANUARY 2016 , ISSN No 2277 – 8179,pp.1-21 K.D. Hertz “Limits of spalling of fire-exposedconcrete” Science direct, Fire Safety Journal 38 (2003) pp.103–116.
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