Effect of temp. ppt Amit Payal
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This document summarizes the effects of temperature on fresh and hardened concrete. It discusses how both high and low temperatures can impact concrete strength and cracking. For high temperatures, it recommends precautions like cooling materials, using retarders, and protecting from moisture loss. For low temperatures, it advises heating materials and protecting concrete to prevent freezing, which can stop hydration and cause cracking. Proper planning, curing, and temperature control of ingredients are essential to account for temperature effects on concrete properties and performance.
Effect of temp. ppt Amit Payal
- 1. 12.12.2018 Effect of Temperature in fresh & Hardened concrete Prepared By:- Krishna Reniwal Devanshu Souda
- 2. Introduction In the laboratory testing of concrete , All test are done in controlled situation but in actual at site, control in temperature is Difficult. According to IS code 7861 part I And II, the temperature of concrete is must in range of 25.6°C to 35°C. In this range of concrete the strength is much better and more economical and eco-friendly. When temperature gets different from the standard temperature then strength is also gets different. In Hot weather conditions it accelerates the cement hydration reaction & In cold weather conditions it Show the cement Hydration process.
- 4. Detrimental Conditions • High ambient temperature • High concrete temperature • Low relative humidity • Wind velocity • Solar radiation.
- 5. Difficulties in Hot Weather • Increased water demand. • Accelerated slump loss. • Increased rate of setting. • Increased tendency of plastic shrinkage cracking. • Critical need for prompt early curing.
- 6. Hot Weather Concreting • Certain precautions should be taken in order to reduce the difficulties in hot weather conditions. • Temperature ranging from 10 to 15˚C is desirable, but such temperatures are not always practical. • Many specifications require that concrete when placed should have a temperature of less than 29 to 32˚C.
- 7. Precautions Depends on • Type of construction. • Characteristics of the materials being used. • The experience of placing and finishing crew in dealing with the atmospheric conditions in the site.
- 8. Precautions • Use materials and mix proportions that have a good record in hot weather conditions. • Cool the concrete or one or more of its ingredients. • Use a concrete consistency that allows rapid placement and consolidation. • Reduce the time of transporting, placing, and finishing as possible. • Schedule concrete placements to avoid extreme weather, such as at night or during favorable weather conditions. • Consider the methods to limit moisture loss during placing and finishing such as sunshades, wind screens, fogging, and spraying.
- 10. Effect of High Concrete Temperature • increase the rate of setting and shorten the length of time within which the concrete can be transported, placed, and finished. • Setting time can be reduced by 2 or more hours with a 10°C increase in concrete temperature • There is an increased tendency for cracks to form both before and after hardening. • Rapid evaporation of water from freshly placed concrete can cause plastic-shrinkage cracks before the surface has hardened. • .
- 11. • Cracks may also develop in the hardened concrete because of increased drying shrinkage due to higher water contents or thermal volume changes as the concrete cools
- 13. Cooling Concrete Materials • Lower the temperature of concrete materials before mixing. • The contribution of each material is related to • Temperature. • Specific heat. • Quantity of each material.
- 14. Supplementary Cementious Materials • The use of supplementary materials (fly ash, ground granulated blast furnace slag) can help in hot weather conditions. • These material slow the rate of setting as well as the rate of slump loss.
- 15. Controls for Hot Weather • Using a concrete mixture that is properly proportioned for conditions • Consider the use of a set-retarding admixture to control set times. The use of fly ash can also reduce the effects of fast-setting concrete. • Have manpower and equipment • Add water only once—adjust the slump when the truck first arrives and follow through with prompt placement.(For drying shrinkage cracking) • To minimize plastic shrinkage cracking, keep the surface wet (not saturated) by applying moisture with a fog sprayer until the final curing method is ready to be applied.
- 16. Admixtures • A retarding admixtures can be very helpful in delaying the setting time, despite increased rate of slump loss resulting from their use. • A hydration control admixture can be used to stop cement hydration and setting. As a general rule a 5°C to 9°C temperature rise per 45 kg of Portland cement can be expected from the heat of hydration.
- 17. EFFECTS OF LOW TEMPERATURE What Happens When Concrete Freezes? • Pore water in concrete starts to freeze around -1°C (30°F) • As some water freezes the ion concentration in the unfrozen water goes up, further depressing the freezing point. • At around -3 to -4°C enough of the pore water will freeze so that hydration will completely stop. and depending on the extent of hydration, and thus the strength of the concrete, the forces generated by the expansion of ice may be detrimental to the long term integrity of the concrete.
- 18. COLD WEATHER CONCRETE Definition • A period when for more than 3 successive days, the following conditions exist: • The average daily air temperature is less than 40°F, and • The air temperature is not greater than 50°F for not more than one half of any 24 hour period.
- 19. Effects of cold weather on concrete • Delayed Setting • Freezing of Concrete at Early Ages • Repeated Freezing and Thawing of Concrete • Stresses Due to Temperature Differential
- 20. Cold weather can be divided into three catagorias The severity or the weather determines the precautions to be taken. For this purpose cold weather can be divided into three catagorias 1. When the temperature is below 5°0 but does not fall below freezing point, 2. When frost occun at night only and is not very severe, and 3. When there is severe frost day and night
- 21. TEMPERATURE CONTROL • The most direct approach to keeping concrete temperature up by controlling the temperature of ingredients. The contribution of each ingredient to the temperature of concrete is function of the temperature. specific heat, and quantity used of that ingredient. The aggregates and mixing water exert the most pronounced effect temperature of concrete. Thus. in cold weather, all available means shall be used for maintaining these materials at a high a temperature practicable.
- 22. Ingredients • Aggregates : When aggregates in stockpiles are heated by Iteam pipes, exposed surfaces of aggregate shall be covered with tarpaulins as much as practicable to maintain uniform distribution of heat and to prevent formation of frozen crusts. • Water: water is heated to a temperature in excess of 40’c. • Cement: for extreme weather use Rapid hardening cement. • If loss of effectiveness of air entraining admixtures is noticed due to hot water. the admixture may be added to the batch only after water temperature has been reduced.
- 23. Recommended Practices and Basic Principles • Planning • Curing and Protection • Temperature Records • Heated Enclosures • Exposure to Freezing and Thawing • Slump • Truck Travel Time • Hot Water • Hydration in Cold Weather • Acceleration of Concrete 1. Calcium Chloride as an Accelerator 2. Air entraining agents
- 24. References • BIS 7861 part I • BIS 7861 part II • A Cade study under IJARS – INTERNATION JOURNAL OF ADVANCE RESEARCH IN SCIENCE AND ENGINEERING BY PROFF. ASIF HUSSAIN.
- 25. THANK YOU