Hot Weather Concrete (Presentation)
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This document discusses the effects of temperature on concrete. It finds that higher temperatures can cause problems in both fresh and hardened concrete, such as increased water demand, faster setting and slump loss, and decreased long term strength. An experiment tested concrete strengths at 3, 7, and 28 days for temperatures of 25, 29, and 41.5 degrees Celsius and found higher early strengths but lower long term strengths with increased temperature. It recommends methods to lower the temperature of fresh concrete such as cooling mix water, aggregates, and using chilled materials.
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Hot Weather Concrete (Presentation)
- 5. What is HotWeather Concreting ? Problems Due in HotWeather Concreting Major Effects ofTemperature on Concrete Experiment's Program & Results Conclusion & Recommendation
- 6. What is Hot Weather Concreting ? Hot weather is any combination of the following conditions that tends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration or otherwise causing detrimental results: 1. High ambient temperature. 2. High concrete temperature. 3. Low relative humidity. 4. Wind speed. 5. Solar radiation.
- 7. How to Use Graphs To know the Rate of Evaporation
- 8. PROBLEMS DUE IN HOT WEATHER CONCRETE: A. Increased water demand. B. Increased rate of slump loss C. Increased rate of setting, resulting in greater difficulty with handling, compacting, and finishing. D. Increased tendency for plastic- shrinkage cracking. E. Increased difficulty in controlling entrained air content. In the Wet state
- 9. A. Decreased 28-day strengths. B. Increased tendency for drying shrinkage and differential thermal cracking. C. Decreased durability resulting from cracking. D. Greater variability of surface appearance, such as cold joints or color difference. E. Increased potential for reinforcing steel F. Increased permeability. in the hardened state PROBLEMS DUE IN HOT WEATHER CONCRETE:
- 10. Influence of early temperature on strength of concrete Hydration process Capillary pores formation the overall structure of the hydrated cement paste becomes established very early. Rapid initial hydration appears to form products of a poorer physical structure, probably more porous. A proportion of these pores will always remain unfilled. This will lead to a lower strength
- 11. Hydration process A higher temperature during placing and setting increases the very early strength, it may adversely affect the strength from about 7 days to 28 days. Influence of early temperature on strength of concrete
- 12. Hydration process Delayed Ettringite formation: Also, at higher temperatures, the solubility of gypsum is decreased so that some of it might not react with C3A and do so only later, Which is known as Delayed Ettringite Formation (DEF). (DEF) is an internal sulphate attack that eventually leads to cracking. The principle methods of eliminating the risk of DEF are: ▫ Limit curing temperature to 70°C. ▫ Exclude water access. ▫ Include a minimum additives of 20% FA or 50% GGPFS in the mix. Influence of early temperature on strength of concrete
- 13. Setting and cooling process: In hot weather a mix will set 25% quicker for each 5°C rise in concrete temperature. • . This leads to: 1. cold joints formation. 2. poor surface finishing. • Rapid rate of surface setting or stiffening due to high rate of evaporation (above 1kg/m2/hr ) that is exceeding water loss of bleed , causes volumetric contraction to occur . Which leads to irregular cracks existence . • This normally occurs within a few days after casting. • They can be from few centimeters to just less than 1 m long. The crack spacing varies from a few centimeters to 0.6 m apart. Influence of early temperature on strength of concrete
- 14. • At later ages, after the peak temperature has been reached and the internal concrete enters the cooling phase, the increased stiffness of the surface zone now acts as a restraint to the thermal shrinkage of the internal concrete. Internal sections are, therefore, subjected to tensile stresses and significant internal cracking is possible. drying shrinkage and thermal cracking
- 15. • Some of the preventive measures that can be taken to reduce the mix temperature are reducing the cement content or precooling one or more of the ingredients of the mix. • A placing temperature of concrete as low as 10°C (50 °F) is desirable but may well be impractical. • However the maximum temperature differential between the interior and exterior concrete should not exceed 20°C to avoid crack development. • The temperature T of the freshly mixed concrete can be calculated from that of the ingredients, using the expression • Limitations of fresh mix temperature :
- 16. Experimental Program This report aims to compare three different temperatures of concrete (hot , moderate and cold) and their affect to strength at 3, 7, and 28 days , with the aid of the equation used to get the temperature of fresh concrete in respect to temperature of ingredients and environment. to verify the criteria The variable focused on was the concrete temperature and the proceeding steps have been followed :
- 17. Materials Cement Coarse aggregate Fine aggregate The fine aggregates were a blend of natural silica sand, named kangar. Collected from valley downstream beds around Khartoum area. Bearing in mind the sample was chosen after trials. Rejected fine samples due to high fineness percentage (samples from Omdurman quarries) Were a blend of 20 mm and 10 mm uncrushed silica obtained from quarries around Khartoum. It is a normal Portland cement type 1 manufactured by Atbara cement factory with fineness properties collected from ordinary Portland cement properties done in faculty lab. Mix design of 30 N/mm2 has been designed and the necessary constituents cement ratio, coarse aggregate, water content &fine aggregate were calculated according to constituent material properties.
- 18. Temperature Variation In order to make proper judgment, the temperature is room temperature, left the same conditions for every trial and water, coarse and fine aggregate temperatures were recorded together with the final mix at pouring, In order to follow the effect of temperature on concrete strength The following arrangements were done :
- 19. The tests were carried in an overall condition in a room of measured temperature, mild condition with a mechanical mixing device having all relative temperature of constituents and product measured. Results of test were recorded for 3,7and 28 day were recorded. The process was done having the same curing temperature in an open basin in the lab room for the whole duration up to 28 day.
- 28. Result (Consistency) Temperature(°c) Slump(cm) 25 10.7 29 10.525 41.5 9.98 10.7 10.525 9.98 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Effect of Temprature on Fresh Mix Slump Effect of Temp on Slump
- 29. Results - Effect of temperature on the development of the strengths at different ages for 3 Days 3 25 degree stress(Mpa) load(kN) area(mm^2) 22.4 506.3 22590 24.5 554.4 22590 25.2 570.4 22590 29 degree stress(Mpa) load(kN) area(mm^2) 19 430.7 22590 20 452.8 22590 21.6 489.1 22590 41.5 degree stress(Mpa) load(kN) area(mm^2) 24.6 557 22590 26 589.4 22590 26.3 594.3 22590 for 7 Days 7 25 degree stress(Mpa) load(kN) area(mm^2) 23.5 531.7 22590 29.7 671 22590 30.2 683.9 22590 29 degree stress(Mpa) load(kN) area(mm^2) 22.9 518 22590 24.5 553.7 22590 28.9 653.6 22590 41.5 degree stress(Mpa) load(kN) area(mm^2) 26.2 594 22590 27.4 621.1 22590 28.1 636 22590 for 28 Days 28 25 degree stress(Mpa) load(kN) area(mm^2) 33.4 754.9 22590 34.6 782.8 22590 32.9 743.6 22590 29 degree stress(Mpa) load(kN) area(mm^2) 31.5 713 22590 30.3 686.1 22590 28.8 651.5 22590 41.5 degree stress(Mpa) load(kN) area(mm^2) 32.8 741 22590 32.6 735.8 22590 36.3 821.9 22590
- 30. 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 for 25 Degree for 29 Degree for 41.5 Degree Stress (Mpa) Age (Days)
- 31. Conclusion Temperature inside the cast concrete is increased as result of rising the temperature of mix proportion that mean when casting concrete in hot weather without using retarders of hydration, it will gain strength more quickly than a similar concrete kept at lower temperature . If the temperature reach a critical value this will lead to destroy the formation of ettringitte and will react later increasing the tend of sulphate attack
- 32. Recommendation In order to lower the temperature of the fresh mix concrete we recommend this guidance to be followed: 1) It’s preferable not to use cement at temperature above 75c , however if hot cement is damped by small amount of water before it well dispersed with other solids it may set quickly and form cement balls. 2) Coarse aggregate can be cooled by spraying with chilled water 3) Fine aggregate can also be cooled by air freezing by liquid nitrogen 4) Mix water can also be cooled or partially replaced by crushed or flaked ice . 5) Paint the mixer and storage bins white to minimise absorption of heat from the sun. 6) Programme concreting for the cooler parts of the day, or even schedule night- time placement if possible. 7) Specify the maximum acceptable delivery temperature of the concrete so that the supplier can plan to cool the materials as needed. 8) Avoid delays at all stages.
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- Beginning course details and/or books/materials needed for a class/project.
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- Objectives for instruction and expected results and/or skills developed from learning.
- Objectives for instruction and expected results and/or skills developed from learning.
- Objectives for instruction and expected results and/or skills developed from learning.
- Objectives for instruction and expected results and/or skills developed from learning.
- Relative vocabulary list.
- A list of procedures and steps, or a lecture slide with media.
- Relative vocabulary list.
- Marquee with 3-D perspective rotation (Intermediate) To reproduce the effects on this slide, do the following: On the Home tab, in the Slides group, click Layout, and then click Blank. On the Home tab, in the Drawing group, click Shapes, and then under Rectangles click Rectangle (first option from the left). On the slide, drag to draw a rectangle. Under Drawing Tools, on the Format tab, in the Size group, do the following: In the Shape Height box, enter 3.12”. In the Shape Width box, enter 7.67”. On the Home tab, in the Drawing group, click the arrow next to Shape Fill, and then click No Fill. On the Home tab, in the Drawing group, click the arrow next to Shape Outline, and then click No Outline. Right-click the rectangle, and then click Edit Text. Enter text in the text box, and then select the text. On the Home tab, in the Font group, select Franklin Gothic Medium from the Font list, enter 50 in the Font Size box, and then click Bold. On the Home tab, in the Paragraph group, click Center to center the text in the text box. Under Drawing Tools, on the Format tab, in the WordArt Styles group, click the arrow next to Text Fill, point to Gradient, and then click More Gradients. In the Format Text Effects dialog box, click Text Fill in the left pane, select Gradient fill in the Text Fill pane, and then do the following: In the Type list, select Linear. Click the button next to Direction, and then click Linear Down (first row, second option from the left). In the Angle box, enter 90°. Under Gradient stops, click Add gradient stop or Remove gradient stop until three stops appear in the drop-down list. Also under Gradient stops, customize the gradient stops that you added as follows: Select the first stop in the slider, and then do the following: In the Position box, enter 0%. Click the button next to Color, click More Colors, and then in the Colors dialog box, on the Custom tab, enter values for Red: 80, Green: 80, Blue: 80. Select the next stop in the slider, and then do the following: In the Position box, enter 49%. Click the button next to Color, click More Colors, and then in the Colors dialog box, on the Custom tab, enter values for Red: 89, Green: 89, Blue: 89. Select the last stop in the slider, and then do the following: In the Position box, enter 50%. Click the button next to Color, and then under Theme Colors click Black, Text 1 (first row, second option from the left). Also in the Format Text Effects dialog box, click Shadow in the left pane. In the Shadow pane, click the button next to Presets, and then under Outer click Offset Center (second row, second option from the left). On the Home tab, in the Drawing group, click Shapes, and then under Rectangles click Rounded Rectangle (second option from the left). On the slide, drag to draw a rounded rectangle. Select the rounded rectangle. Under Drawing Tools, on the Format tab, in the Size group, do the following: In the Shape Height box, enter 3.12”. In the Shape Width box, enter 7.67”. Drag the yellow diamond adjustment handle at the top of the rounded rectangle to adjust the amount of rounding on the corners. Under Drawing Tools, on the Format tab, in the Shape Styles group, click the arrow next to Shape Fill, point to Gradient, and then click More Gradients. In the Format Shape dialog box, click Fill in the left pane, select Gradient fill in the Fill pane, and then do the following: In the Type list, select Linear. Click the button next to Direction, and then click Linear Right (first row, fourth option from the left). In the Angle box, enter 0°. Under Gradient stops, click Add gradient stop or Remove gradient stop until two stops appear in the slider. Also under Gradient stops, customize the gradient stops that you added as follows: Select the first stop in the slider, and then do the following: In the Position box, enter 0%. Click the button next to Color, and then under Theme Colors click White, Background 1 (first row, first option from the left). Select the last stop in the slider, and then do the following: In the Position box, enter 100%. Click the button next to Color, and then under Theme Colors click White, Background 1, Darker 25% (fourth row, first option from the left). Also in the Format Shape Effects dialog box, click Line Color in the left pane. In the Line Color pane, select No line. Select the rounded rectangle. On the Home tab, in the Clipboard group, click the arrow to the right of Copy, and then click Duplicate. Select the duplicate rounded rectangle. On the Home tab, in the Drawing group, click the arrow next to Shape Fill, and then click No Fill. On the Home tab, in the Drawing group, click the arrow next to Shape Outline, and then under Theme Colors click White, Background 1 (first row, first option from the left). On the Home tab, in the Drawing group, click the arrow next to Shape Outline, point to Weight, and then click More Lines. In the Format Shape dialog box, click Line Style in the left pane, and then do the following in the Line Style pane: In the Width box enter 10 pt. Click the button next to Dash type, and then click Round Dot (second option from the top). In the Cap type list, select Round. On the Home tab, in the Drawing group, click Shape Effects, point to Glow, and then do the following: Under Glow Variations, click Accent color 1, 11 pt glow (third row, first option from the left). Point to More Glow Colors, and then click More Colors. In the Colors dialog box, on the Custom tab, enter values for Red: 255, Green: 233, Blue: 33. Under Drawing Tools, on the Format tab, in the Size group, do the following: In the Shape Height box, enter 3.53”. In the Shape Width box, enter 8.05”. On the Home tab, in the Drawing group, click Shapes, and then under Lines click Line (first option from the left). Press and hold SHIFT to constrain to a straight, horizontal line, and then drag to draw a horizontal line on the slide. Select the line. Under Drawing Tools, on the Format tab, in the Size group, in the Shape Width box, enter 7.67”. On the Home tab, in the Drawing group, click the arrow next to Shape Outline, and then do the following: Under Theme Colors, click Black, Text 1, Lighter 50% (second row, second option from the left). Point to Weight, and then click 1 1/2 pt. Select the line. On the Home tab, in the Clipboard group, click the arrow to the right of Copy, and then click Duplicate. Repeat the process for a total of eight straight lines. On the Home tab, in the Editing group, click Select, and then click Selection Pane. In the Selection and Visibility pane, select the first rectangle that contains text. On the Home tab, in the Drawing group, click Arrange, and then click Bring to Front. Also in the Selection and Visibility pane, press and hold CTRL and select all three rectangle objects. On the Home tab, in the Drawing group, click Arrange, point to Align, and then do the following: Click Align to Slide. Click Align Center. Click Align Middle. Drag each of the straight lines onto the gradient-filled rectangle, spacing them vertically as evenly as possible. In the Selection and Visibility pane, press and hold CTRL and select all eight straight connector objects (the lines). On the Home tab, in the Drawing group, click Arrange, point to Align, and then do the following: Click Align Selected Objects. Click Distribute Vertically. Click Align Center. Press CTRL+A to select all of the objects on the slide. On the Home tab, in the Drawing group, click Arrange, and then click Group. Select the group. On the Home tab, in the Drawing group, click Shape Effects, point to 3-D Rotation, and then under Perspective click Perspective Right (first row, third option from the left). Drag the group slightly to the right on the slide to position it in the center. To reproduce the background effects on this slide, do the following: Right-click the slide background area, and then click Format Background. In the Format Background dialog box, click Fill in the left pane, select Gradient fill in the Fill pane, and then do the following: In the Type list, select Linear. Click the button next to Direction, and then click Linear Down (first row, second option from the left). Under Gradient stops, click Add gradient stop or Remove gradient stop until four stops appear in the slider. Also under Gradient stops, customize the gradient stops that you added as follows: Select the first stop in the slider, and then do the following: In the Position box, enter 0%. Click the button next to Color, and then under Theme Colors click Dark Blue, Text 2 (first row, fourth option from the left). Select the next stop in the slider, and then do the following: In the Position box, enter 15%. Click the button next to Color, and then under Theme Colors click Black, Text 1, Lighter 5% (sixth row, second option from the left). Select the next stop in the slider, and then do the following: In the Position box, enter 85%. Click the button next to Color, and then under Theme Colors click Black, Text 1, Lighter 5% (sixth row, second option from the left). Select the last stop in the slider, and then do the following: In the Position box, enter 100%. Click the button next to Color, and then under Theme Colors click Dark Blue, Text 2 (first row, fourth option from the left).
- Example graph/chart.
- Example graph/chart.
- Conclusion to course, lecture, et al.
- Relative vocabulary list.
- Relative vocabulary list.