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State-of-the-Art Practices of Mass Concrete A Literature Review

October 23, 2013

Mass Concrete Overview

ACI Definition: Any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking 1. Cement hydration is a very exothermic process. 2. Placement of large amounts of concrete results in storing heat

within the core, resulting in Adiabatic Temperature Rise (ATR). 3. Mass concrete is considered for a structure where the least

dimension is 3-ft (1-m) or greater. 4. Controlling both maximum core temperature and surface/core

temperature differential are critical to preserving quality.

Mass Concrete - Overview

Cement (C3S, C2S, C3A, C3AF) + Water --> C-S-H + CaOH + heat • Proper cement compound proportions in a cement mix is

required to control the heat of hydration in the reaction • Cement mixes with reduced tricalcium silicates and calcium

aluminates effectively control heat during hydration

Cement Hydration

Cement Compound Specific Heat of Hydration (cal/g)

C3S 120

C2S 62

C3A + CŜH2(Gypsum) 320

C3AF 100

Values courtesy of Cannon (1986)

• Cement blends have been developed to control temperatures in hydrating concrete.

Heat of Hydration in Cements

Image courtesy of ACI 207.1R

• SCMs offer a means of reducing heat of hydration through cement replacement.

• FLDOT study indicates peak temperature reductions of 0.1% to 26.1% compared to Ordinary Portland Cement (OPC) concrete

Supplementary Cementitious Materials (SCMs)

Cement Source Placing Temperature

% Reduction in Peak Temperature after 14 days

25% Fly Ash 35% Fly Ash 50% Slag 70% Slag

A 73oF 12.7 17.2 8.2 21.2

B 73oF 8.5 26.1 14.1 24.1

Average for Cements A & B 10.6 21.7 11.2 22.7

A 95oF 1.9 8.0 0.1 23.4

B 95oF 9.7 18.6 4.6 7.0

Average for Cements A & B 5.8 13.3 2.4 15.2

Chini & Parham, 2005

No. Cement Type Heat of Hydration at 100% Hydration (cal/g)

1 Type I Cement 114

2 Type I Cement + 15% Class C Fly Ash 113

3 Type I Cement + 25% Class C Fly Ash 112

4 Type I Cement + 35% Class C Fly Ash 111

5 Type I Cement + 45% Class C Fly Ash 110

6 Type I Cement + 15% Class F Fly Ash 106

7 Type I Cement + 25% Class F Fly Ash 101

8 Type I Cement + 35% Class F Fly Ash 95

9 Type I Cement + 45% Class F Fly Ash 88

10 Type I Cement + 30% Ground Granulated Blast Furnace Slag

113

11 Type I Cement + 50% Ground Granulated Blast Furnace Slag

112

Mix Design: SCMs

ACI Materials Journal, “Heat of Hydration Models for Cementitious Materials”, Title no. 102-M04

Aggregates in mass concrete

Image courtesy of FHWA

Coefficient of Thermal Expansion 10-6/°C 10-6/°F

Aggregate Granite 7-9 4-5 Basalt 6-8 3.3-4.4

Limestone 6 3.3 Dolomite 7-10 4-5.5

Sandstone 11-12 6.1-6.7 Quartzite 11-13 6.1-7.2 Marble 4-7 2.2-4

• Lower thermal expansion protects concrete from thermally induced volume changes that can lead to cracking

• Lower thermal conductivity also protects concrete from thermal gradients that can lead to cracking

Issue 1: Thermal Cracking

• Cement hydration causes a rise in internal concrete temperature. • Temperature differentials may result in surface tension. • “Shocking” the surface with cold water/air can lead to cracks.

Adiabatic Temperature Rise (ATR)

Trapped heat from Cement reaction Thermal cracking

Restrained concrete

Reducing Thermal Cracking

• Surface tension is typically discouraged in concrete design • Typically ~10%f’c – can be lower during curing stages • Concrete elements designed with large (Volume) : (Surface Area)

ratio are more susceptible to thermal cracking • Tabulating temperature differentials as a function of curing time

is recommended • Current specifications call for ∆T < 35°F • ACI 207.1R-96 - ft = 1.7 fc

2/3 (psi) • Controlling initial temperature and using cements with low heat

of hydration also help reduce potential for thermal cracking

Issue 2: Delayed Ettringite Formation

Delayed Ettringite Formation (DEF)

• High initial placement temperatures and poor temperature control can lead to entrapped sulfates and aluminates.

• Once temperatures recede, sulfates/aluminates precipitate and react with monosulfate hydrates to form Ettringite

Trapped heat from Cement reaction causes monosulfates to remain unreacted in aggregate

Ettringite - C3A·3CaSO4·32H2O Naturally forming Expansive material

Image Courtesy of Rob Lavinsky (commons.wikimedia.org)

ATR and Delayed Ettringite Formation (DEF)

• DEF is a long term adverse effect resulting from high internal curing temperatures

• Threshold internal peak temperature of 160°F widely accepted • Ettringite is a naturally forming EXPANDING material within

concrete. • When concrete is properly cured, ettringite can easily be found

intertwined within the concrete matrix. • When ettringite forms as a result of entrapped sulfates and

aluminates, it causes internal stresses that have deleterious effects on concrete durability

Delayed Ettringite Formation (DEF)

Images courtesy of Yang et. al (1999)

DEF 90 days after curing DEF 255 days after curing

DEF 365 days after curing

Delayed Ettringite Formation (DEF)

Images courtesy of CMC, Inc. - http://www.cmc-concrete.com/delayed%20ettringite.htm

Reducing or Eliminating potential for DEF

• Proper mix, placement and temperature control design is critical • Mixes should consider low Heat of Hydration cements, low

cementitious content, use of SCMs, cooled aggregates, cold water (or ice chips)

• Formwork should be insulated to prevent excessive heat loss (differential temperatures)

• Thermal Control plan should outline methods to mitigate peak temperature and temperature differentials

• Maintain peak temperature below 160°F

Summary of Recommendations

1. ACI recommends cements that consist of a max 58% C3S + C3A or limiting heat of hydration to 70 cal/g

2. Use Type II Cements to reduce heat of hydration. This results in slower heat buildup and lower peak Temperature

3. Select proportioning of cementing material used in design mix no greater than that needed to satisfy design strength.

4. ACI states that using ASTM option for Type II cement (70 cal/g), and limit content to 235 LB/CY, temperature rise can be limited to 35oF (ACI 207.1R-13 Subsection 2.8.2)

Recommendations - Cements

1. Use SCMs, mainly Class F Fly Ash or Ground Granulated Blast Furnace slag to further reduce heat of hydration.

2. Silica Fume is not recommended, as it increases heat of hydration.

3. NJDOT currently does not allow use of Grade 80 slag. It’s low activity index is ideal to retard reaction and reduce heat generation in concrete. Re-adoption of Grade 80 slag for Mass Concrete application only, could provide another option.

Recommendations - SCMs

1. Use aggregates with low thermal conductivity (10-6/oF) • Granite – 4.3 • Basalt – 4.4 to 4.6 • Limestone – 4.0

2. Shading and/or chilling/cooling aggregates helps control the temperature gradient and minimizes volumetric changes in the concrete.

Recommendations - Aggregates

1. Each concrete component must be accounted for in terms of heat of hydration

2. Timing of forms/insulation must coincide with modeled time to thermal normalization.

3. Thermal modeling can be used to predict the element’s behavior,

4. Including cooling pipes, insulation or other means to maintain thermal control can be determined via modeling

5. Monitoring the element should also include concrete maturation. Tables can be developed to provide a more stringent control over thermal differentials

Recommendations – Thermal Control Plan

6. Temperature differentials cause surface tensions (leading to cracks). Controlling core temperatures during curing is critical to prevent cracking.

7. It is critical to maintain core temperatures below 160°F and control thermal differentials below 35°F – Corrective actions:

• For thermal induced cracks • Sealants • Coatings • More comprehensive repairs

• DEF • May not be visible for months or years after construction • Generally pervasive • May require replacement

Recommendations – Thermal Control Plan

8. Duration of temperature control should be considered. • 15 days may not be sufficient to allow temperature to

normalize • Modeling should guide removal of insulation or other

protective measures (cooling pipes) to ensure temperatures achieve ambient balance

9. Consider developing tables for differential temperature thresholds based on concrete maturation. Modeling can assist in developing tables

10. Place concretes at temperatures ranging between 50°F (preferred) and 70°F (Max)

Recommendations – Thermal Control Plan

Andrés M. Roda, P.E. Research Manager Center for Advanced Infrastructure and Transportation (CAIT) Rutgers, The State University of New Jersey 100 Brett Road • Piscataway NJ 08854-8058 848-445-2915 aroda@rci.rutgers.edu http://cait.rutgers.edu List of literature references provided at the end of this presentation.

Thank you!

1. ACI Code 207.1R-13 – Mass Concrete

2. ACI Code 207.2R-02 – Effect of Restraint, Volume Change, and Reinforcement on Cracking of Mass Concrete

3. ASTM C150 – Standard specification for Portland Cement

4. Gajda, J., “Mass Concrete: How do you handle the heat?”, PCA

5. Kurtis, K, “Portland Cement Hydration”, Georgia Institute of Technology

6. Folliard, K., et al., “Preventing ASR/DEF in New Concrete: Final Report”, FHWA/TX-06/0-4085-5, June 2006

7. ACI 207.1R-96, November 1996

8. Chini, A., Parham, A., “Adiabatic Temperature Rise of Mass Concrete in Florida”, BD 529, February 2005

References (1 of 3)

9. Breitenbücher, R. (1990). Investigation of thermal cracking within the cracking frame. Materials and Structures, (23), 172-177

10. Chini, A. R., Muszynski, L. C., Acquaye, L., & Tarkhan, S. (2003, February). Determination of the maximum placement and curing temperatures in mass concrete to avoid durability problems and DEF

11. Siler, P., Kratky, J., & De Belie, N. (2011). Isothermal and solution calorimetry to assess the effect of superplasticizers and mineral admixtures on cement hydration. Journal of Thermal Analysis and Calorimetry.

12. Ramlochan, T., Zacarias, P., Thomas, M. D., & Hooton, R. D. (2003). The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature Part I: Expansive behaviour. Cement and Concrete Research, 33(6), 807-814.

References (2 of 3)

13. Pongsak Choktaweekarn; Somnuk, T. (2010) Effect of aggregate type, casting, thickness and curing condition on restrained strain of mass concrete. Songklanakarin Journal Of Science & Technology, 32(4), 391.

14. Quality Assurance Sample, Essroc Cement Co. Plant #1 – Nazareth, PA, dated October 18, 2011

15. PCA, Concrete Technology Today, Vol. 18/Number 2, July 1997

16. Diamond, S. (1996). Delayed ettringite formation — Processes and problems. Cement and Concrete Composites, 18(3), 205-215. doi: 10.1016/0958-9465(96)00017-0

17. Riding, K. A., Poole, J. L., & Schindler, A. K. (2008). Quantification of effects of fly ash type on concrete early-age cracking. ACI Materials Journal, 105(2), 149-155.

References (3 of 3)