Hot Weather Concrete ACI 305

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Hot Weather ConcreteACI 305

• Joseph E. Diedrich
• Technical Service Manager
• Southdown, Inc.

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What is Hot Weather Concreting?

• When concrete is mixed, transported, and place
  under conditions of high ambient temperature, low
  humidity, solar radiation, or wind, an
  understanding of the effects there environmental
  factors have on concrete properties and
  construction operations is required (ACI 305).

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Introduction

• Often specifiers establish a maximum as placed
  concrete temperature in an attempt to control
  strength, durability, plastic shrinkage, thermal,
  and drying shrinkage cracking.
• Concrete durability is a general term that is
  difficult to quantify, but it is perceived to
  mean resistance of the concrete to weathering.

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General

• Initial curing of concrete test specimens for
  checking adequacy of mix for strength or basis of
  acceptance are cured initially at 60 to 80F
  (16 to 27C), ASTM C31
• 24hr cure at 100F, 28 day may be 10 to 15
  percent lower than cured ASTM C31
• drying at early age, strengths will be reduced
  even further

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Definition of Hot Weather

• High ambient temperature
• High concrete temperature
• Low relative humidity
• Wind velocity
• Solar radiation
• Hot weather is any combination of the above which
  impair quality of fresh or hardened concrete
  and/or cause detrimental results

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Hot Weather

• Hot weather concrete problems generally occur
  during the summer season
• Thermal shrinkage is more severe in the spring
  and fall (temperature differential)
• When air temperatures are identical, a calm,
  humid day is less severe than a dry, windy, sunny
  day

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Potential Problems in Hot Weather - Plastic
Concrete

• Increased water demand
• Increased rate of slump loss, tendency to add
  water at the jobsite
• increased rate of setting, resulting in difficult
  handling, finishing, and risk of cold joint
• Increase for plastic shrinkage
• Increased difficulty in controlling entrained air
  content.

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Potential Problems in Hot Weather - Hardened
Concrete

• Decreased 28 day and later strengths, higher
  water demand, concrete temperatures
• Increase for drying shrinkage and thermal
  cracking
• Decreased durability from cracking
• Increased permeability
• Increased potential for reinforcing steel
  corrosion due to increased cracking

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Avoiding Potential Problems

• Use concrete materials and proportions with
  satisfactory records in hot weather
• Use cool concrete
• Use a concrete consistency that permits rapid
  placement and effective consolidation
• Transport, place, consolidate, and finish with
  least delay
• Protect concrete against moisture loss at all
  times, during placement and curing period

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Curing Temperature Relationship
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Water Vs. Temperature
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Temp, Slump, Water Demand
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Questions?

• Remember
• Use Common Sense
• Temperature effects on your body have very
  similar effects on concrete
• If you are not sure, ASK!!!