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Fundaments & Innovations for Hot Weather Concreting in Colorado

Presented by: Kevin Kane

Technical Services EngineerHolcim (US) Inc.

a member of LafargeHolcim

Necessary Components for Good Concrete Construction

Good Design Good Specifications Good Materials Good Construction Good Inspection Good Testing Good Maintenance & Repair Matching Expectations

Today’s presentation goals:

Introduce the ACI 305-10 Guide to Hot Weather Concreting

Understand the effects of hot weather on concrete mixtures, concrete construction, and concrete testing

Learn what key steps can be taken to ensure successful hot weather concreting

Resources: ACI 305-10 Guide to Hot Weather Concreting PCA Design and Control of Concrete Mixtures ASTM C94-14 Standard Specification for Ready-Mixed Concrete

ACI 305-10 Guide to Hot Weather Concreting

American Concrete Institute

concrete.org

Non-member price: $59.50

Member price: $36.00

ACI 305-10 Guide to Hot Weather Concreting

Detrimental Hot Weather Conditions

Higher ambient temperature Higher concrete temperature Lower relative humidity Wind Solar radiation

Effects of Hot Weather on Plastic Concrete

Higher concrete temperature Increased water demand Increased difficulty in controlling air content Increased rate of slump loss Increased difficulty in placing, handling, and finishing Faster setting time Increased evaporation rate of surface water Increased tendency for plastic shrinkage cracking Increased importance of prompt and proper curing

Effects of Hot Weather on Hardened Concrete

Increased rate of drying shrinkage Increased importance in proper timing of sawcutting

Increased importance on proper initial curing of strength specimens

Increased chances of scaling Concrete rate of strength gain is altered Higher early strength Lower late strength

Effects of Hot Weather on Concrete Materials

Wt. Temp. o F BTUs / 1oF Total BTUs

Cement 564 50 124.08 6204.00Fly Ash 0 0 0.00 0.00Coarse Aggregate 1750 40 385.00 15400.00Fine Aggregate 1275 40 280.50 11220.00Water 285 130 285.00 37050.00

Concrete Temp. = 65 1074.58 69874.00

Concrete Temperature Calculator

Typical Cold Weather Material Temperatures


Typical Hot Weather Material Temperatures



Concrete Temp. = 82 1074.58 87711.20



Extreme Hot Weather Material Temperatures



Concrete Temp. = 88 1074.58 94945.30


To reduce concrete temperature by 1 °F:• Cement temp reduced by 9 °F• Water temp reduced by 4 °F• Aggregate temp reduced by 1.6 °F

Effect of Concrete Temperature on Water Demand

Is it okay to add water on job to increase slump?

Rule-of-thumb on effect of 1 gal/yd3 : 200 psi lower

Unless specifications prohibit adding water, ASTM C94 allows for a one-time addition of water to increase slump if:

Slump of delivered concrete is less than specified Does not exceed the maximum water content for the batch as

established by the designed mixture proportions A “one-time addition of water” …….. Discharge shall be completed within 1-1/2 hrs ……..

Relevance of overdesign calculations Importance of observation

Effect of Concrete Temperature on Time of Set

Effect of Curing Temperature on Strength Development


ACI 305-10 Figure 4.1, Verbeck and Helmuth 1968)


Adapted from ACI 305-10 Figure 4.1, Verbeck and Helmuth 1968)

Effect of Initial Curing of Test Specimens on Strength Development

Data Source: CRMCA Test Fest, Grand Junction, CO. 8/29/13

Effect of Initial Curing of Test Specimens on Strength Development

Executive SummaryInitially curing PCC test cylinders in saturated lime water provides more consistent surrounding temperature, a record of the surrounding temperature and rigidly conforms to T-23-93 section 9.2.1, preventing moisture loss. This is a practical curing method that leads to more consistent 28-day compressive strength. More consistent results will reduce costs associated with unnecessary over-design of PCC mixes, further testing of in-place PCC, and the time consuming claims process.

Ways to Lessen the Effect of Hot Weather on Concrete

Supplementary cementitious materials Cool aggregates Chemical admixtures Water chillers and/or ice Time of placement Reduce the time of transport or placing Use sunshades and/or windscreens Prompt curing of concrete during the placement Finishing Aids


Supplementary cementitious materials Class C or Class F fly ash Plastic concrete benefits

Slower time of set Better workability / response to internal vibration

Hardened concrete benefits Lower heat of hydration Slower rate of strength gain Higher later age strength Consumes Calcium Hydroxide Creates more Calcium Silicate Hydrate



Colloidal-silica Finishing Aids NOT evaporation retarders “Better Concrete Starting at the Finish: Long-term

benefits of colloidal silica-based finishing” Jon Belkowitz, David Loe, Steven Miller


Colloidal-silica Finishing Aids

Colloidal silica is a liquid dispersion of very small, spherical particles of pure silica. The particles used in the finishing aid are about 5 nm (less than 2 ten millionths of an inch)—so small it is difficult to image them even with an electron microscope. (The particles seen here are under electron microscopy are much larger at about 115 nm.) This gives them a vast surface area proportional to their weight, and makes them highly reactive.







Necessary Components for Good Concrete Construction Good Design Good Specifications Good Materials Good Construction Good Inspection Good Testing Good Maintenance & Repair Matching Expectations


CURING CONCRETE


www.concrete.org

Definition of Curing

ACI 308 Guide to Curing Concrete1. The process by which concrete matures and develops hardened concrete

properties over time as a result of continued hydration of the cement in the presence of sufficient water and temperature.

2. The action taken to maintain moisture and temperature conditions in a freshly placed cementitious mixture to allow hydraulic-cement hydration and, if applicable, pozzolanic reactions to occur so that potential properties of the concrete develop.

3. The curing period is defined as the time period beginning at placing, through consolidation and finishing, and extending until desired concrete properties have developed

MOISTURE, TEMPERATURE, TIME


ACI 308 Guide to Curing Concrete• Initial Curing: action taken after placing to prevent loss of moisture

from the concrete surface

– Fogging

– Liquid-applied evaporation reducers

– Windscreens / sunshades

Fogging

Fogging

Fogging: for smaller jobs……

Originally designed for dust suppression, these Buffalo Turbine Air Misters are suited for evaporative of cooling small, localized work areas.

Liquid-applied evaporation reducers

Plastic Shrinkage Cracking Potential

Max Evaporation Rate:

Common: > 0.2 lb/ft2/hr

w/ Fly Ash: > 0.1 lb/ft2/hr

w/ Silica Fume: > 0.05 lb/ft2/hr

Air Temperature Relative Humidity Concrete Temperature Wind Speed


Bridge Deck placement, Albuquerque, New Mexico


Portable Weather Station on bridge deck




Holcim weatherAPP



ACI 308 Guide to Curing Concrete

• Final Curing: actions taken after final finishing to prevent the loss of moisture and to maintain proper temperature in order to foster normal strength development

– External source of water (fogging, ponding)

– Burlap (poly-coated burlap)

– Plastic film

– Liquid membrane-forming compounds

Effect of Proper Curing on Hardened Concrete

Increased Strength Increased Watertightness Increased Abrasion resistance Increased Freeze-thaw resistance Increased Volume stability

Effect of Moist Curing on Strength


Increased oxygen permeability at the surface of concrete can be accompanied by increased carbonation, which weakens the paste.

Which part of the concrete seems to be most vulnerable to scaling???

Extending the Service Life of Concrete Pavements


Phenolphthalein is used by petrographers as a pH indicator. Lower pH is an indication that the surface has carbonated, often prematurely.

Curing Methods

Saturated Wet Coverings

Curing Methods

Liquid membrane-forming compounds

Curing Methods


Curing Methods


Curing Methods

Is this an adequate application of liquid membrane-forming compound?

Type of liquid membrane-forming compounds

Curing Compounds - ASTM C309 Type I – Clear without fugitive dye Type ID – Clear with fugitive dye Type 2 – White pigmented Class A – wax based Class B – resin based

Shall not allow concrete to lose more than 0.55 kg/m2 of water in 72 hours

White pigment shall exhibit a reflectance of at least 60%

Type of liquid membrane-forming compounds

Cure & Seal Compounds - ASTM C1315 Type I – Clear Type 2 – White pigmented Class A – non yellowing Class B – moderate yellowing Class C – may undergo severe darkening and has no

requirement relative to yellowing

Shall not allow concrete to lose more than 0.40 kg/m2 of water in 72 hours

Cure & Seals last long and serve to prevent ingress of water


Importance of Inspection

To ensure compliance To observe and document (with respect to concrete)

Ambient air temperature Relative humidity Wind speed Clear or cloudy Concrete batch ticket information Water added to concrete Concrete temperature Location where each load was deposited Observations on appearance of concrete Compliance to testing standards Methods of initial and final curing

Key Steps to Ensure Successful Hot Weather Concreting

Good planning better than last minute improvisations CRMCA Concrete Quality Pre-Construction Checklist NRMCA / ASCC Pre-Construction Checklist Understand the construction application Understand the construction requirements Ask about the characteristics of the concrete mix

design Anticipate the implications of weather Document the construction activities

“Don’t feed the dog”

Today’s presentation goals:

Introduce the ACI 305-10 Guide to Hot Weather Concreting

Understand the effects of hot weather on concrete mixtures, concrete construction, and concrete testing

Learn what key steps can be taken to ensure successful hot weather concreting

Resources: ACI 305-10 Guide to Hot Weather Concreting PCA Design and Control of Concrete Mixtures ASTM C94-14 Standard Specification for Ready-Mixed Concrete

Fundamentals & Innovations for Hot Weather Concreting in Colorado

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Fundaments & Innovations for Hot Weather Concreting …colorado.apwa.net/Content/Chapters/colorado.apwa.net/File... · Fundaments & Innovations for Hot Weather Concreting in Colorado