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HotWeather Concreting

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Hot-Weather and Hardened Concrete. Decrease strength from higher water-to ... Use materials and mix proportions that have a history in hot-weather conditions ... – PowerPoint PPT presentation

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Title: HotWeather Concreting


1
Chapter 13
  • Hot-Weather Concreting

2
Detrimental Hot-Weather Conditions
  • Accelerate the rate of moisture loss and rate of
    cement hydration that occur at high temperatures.
  • High ambient temperature (85 -90F)
  • High concrete temperature
  • FDOT 95F
  • Low relative humidity

3
Hot-Weather and Fresh Concrete
  • Increase water demand
  • Accelerate slump loss (leading to adding water at
    the job site)
  • Increase rate of setting resulting in placing and
    finishing problems
  • Increase tendency for plastic shrinkage cracking
  • Critical need for early curing
  • Control entrained air content
  • Long-term strength loss
  • Increase potential for thermal cracking

4
Hot-Weather and Hardened Concrete
  • Decrease strength from higher water-to-cement
    ratio
  • Decreased durability due to cracking
  • Increased permeability
  • Non-uniform surface appearance
  • Increased tendency for drying shrinkage cracking
  • Reduced abrasion resistance from adding water too
    soon

5
Precautions to Avoid Problems
  • Use materials and mix proportions that have a
    history in hot-weather conditions
  • Cool the concrete or its ingredients
  • Use concrete consistency that allows rapid
    placement and consolidation
  • Reduce the time of transport, placing and
    finishing

6
Cont
  • Schedule concrete placements to limit exposure to
    hot-weather conditions?
  • Consider methods to limit moisture loss during
    placing and finishing?
  • Apply temporary moisture-retaining films after
    screeding
  • Organize a preconstruction conference to discuss
    the precautions required

7
Examples
  • Temp of fresh concrete increases from 50 to 100F
  • 33 pcy of water required to maintain a 3-inch
    slump
  • results in a 12 to 15 reduction in compressive
    strength
  • durability?????????

8
Examples
  • Setting time can be reduced by 2 or more hours
    with an 18F increase in fresh concrete
    temperature
  • Placing???
  • Finishing??
  • Cold Joints???
  • Admixture - Which one?

9
Examples
  • Rapid evaporation of water before sufficient
    hardening and after hardening
  • plastic shrinkage cracking
  • drying shrinkage cracking
  • humidity
  • Thermal cracking as concrete cools

10
Examples
  • Air-entrainment in fresh concrete
  • more AEA is required to produce the same amount
    of entrained air in hot weather

11
Examples
  • Effect of high temperatures of fresh concrete on
    compressive strength.
  • Figure 13-4
  • higher temperatures lead to higher short term
    strengths but lower long term strengths

12
Cooling Concrete Materials
  • Lower the temperature of concrete materials
    before mixing
  • Water
  • Easiest to cool
  • Cooling water 4F lowers concrete temperature by
    1F
  • Usually concrete temp lowered only by about 8F by
    cooling water.
  • Using ice lowers the concrete temperature by 20F
  • Vol. of ice should not replace more than 75 of
    mix water.
  • Aggregates
  • lower the temperature of the fresh concrete 1F
  • coarse aggregate temperature needs to be reduced
    by only 2F
  • Liquid nitrogen injected into the mixer reduce
    the concrete temperature by 40F or more.

13
Hot Weather Concrete Checklist
  • Page 236 and 237 of your workbook
  • 8 Recommended Items
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