TEMPERATURE CONTROLLED MASS CONCRETE

K. K. PATHAK Corporate QAC

MASS CONCRETEACI 116.R

ANY VOLUME OF CONCRETE WITH DIAMENSIONS ARE SO LARGE THAT ADDITIONAL MEASURES WILL REQUIRED TO BE TAKEN TO COPE UP HEAT OF HYDRATION AND VOLUME CHANGE TO ELEMINATE THERMAL CRACKING.

ACI 301

ANY MEMBER WITH MINIMUM LATERAL DIAMENSION OF MORE THAN 1.3 M SHOULD BE CONSIDERED AS MASS CONCRETE

EFFECTS OF HIGH TEMPERATURE OF PLACING AND CORE

• INCREASED HEAT OF HYDRATION• FLOW OF HEAT TOWARDS THE SURFACE• VOLUME CHANGE• THERMAL CRACKING ( MICRO AND MAJOR )• REDUCED CONCRETE STRENGTH AT CORE.• DELAYED ETRINGITE FORMATION.• HIGH PERMEABILITY• REDUCED DURABILITY.

Codal References

• ACI-207-1R/2R/3R/4R• ACI-301• SP-23-HOT WEATHER CONCRETING.

BRIEF HISTORY OF TEMP.CONTROL

• CONTROLLING OF TEMPERATURE BY POST COOLING WAS ADAPTED FIRST IN THE YEAR 1930 FOR CONSTRUCTION OF HOOVER DAM.

• IN 1945, PRE COOLING BY CHILLED WATER STARTED.• IN 1955, USING OF INSULATION MATERIALS STARTED• IN 1960, TEMPERATURE MONITORING STARTED • IN INDIA PRE COOLING AND POST COOLING WAS

ADAPTED FOR CONSTRUCTION OF NUCLEAR POWER PLANTS/ TG FOUNDATIONS SINCE SEVETIES.

• DUE TO TRENDS IN CONSTRUCTION OF TALLER BUILDINGS AS WELL AS THICKER FOUNDATIONS, TEMPERATURE CONTROLLED CONCRTE IS BECOMING VERY CUMMON FOR ENSURED STRUCTURAL ABILITY .

FACTORS INFLUENCING TEMPERATURE.

• 1.OPC Contents.• 2.Grade of OPC.• 3.Inclusion of Puzzolanas/GGBS. • 4.Maximum size Aggregate. Quality Of Agg.• 5. Admixture.• 6.Size of Member• 7. High placing temperature.• 8.Ambient Temperature• 9.Mechanical and frictional gain of heat.

Permissible Parameters

• Concrete placing temperature should not be more than 35 C.

• Core temperature should not be more than 70 C

• Differential Concrete Temperature between surface and core should not be more than 20 c

• Ref : ACI-207.2R/Thronton Tomasetti/NRCMA.

Actions Adaptable• Mix. With minimum OPC content. By using good quality of

aggregates,GGBS, puzzolanas, Hyper plasticizers,• GGBS is more effective for temperature reduction as it can replace

OPC even by 70 %. ( as per IS-456- 70%).

• Placing Concrete with at low temperature.• Placing Insulation materials to reduce temperature differential.• Post Cooling by using chilled water cycling by network of thin pipe

lines inside the concrete.• Pre cooling of aggregates.• Wrapping of transit mixers by hessian cloth and sprinkling of water as

it cools down due to latent heat.

Most effective method of reduction of temperature is liquid nitrogen injection( -196 c) in feeding water but it is not very commercially feasible.

A very effective technology for mass concrete, is roller compacted concrete, used for dam construction with high volume fly ash.

Temperature Monitoring

• Temperature is monitored during placing up to 7-14 days.

• Probes are fixed to collect temperature data at surface , core and corners. Data stored continuously, even may be displayed digitally.

• In Normal Concrete temperature start decreasing after 3 days.

INSIDE AND SURFACE TEMP. DATA

Control of Concrete Placing Temperature

Involves • Theoretical calculations and determining

temperature to be maintained at various stages.• Determining temperature to be maintained for

various materials.• Logistics, measures to minimize mechanical loss.• Precautions to store ingredients under shed. • Full scale trial of manufacturing, placing and

monitoring.

Determining Temp. Limits • Max. Temp. of core specified. Say ,70 c• Calculate Max. Temp. rise for your mix.

From table-2.2, ACI 207.4R-5 ,

• For a 3 m depth raft for a mix of 200 kg OPC and 300 kg. other cementicious Materials , temp rise will be 45 C

• Then The temperature at placing should not be more than =(70-45)=25 C

ACI-207.4R,Table-2.2

Slab thk M

0.9 1.5 3.0 4.6 6.1 7.6 Above

Deg. C 5.6 8.7 13.1 15.0 16.7 17.2 17.7

Temp. Rise deg C per 100 kg of cement per cum of concrete

• 50 % of total Puzzolonic materials should be considered for calculation of temp. rise.

• Then The temperature at placing should not be more than =(70-45)=25 C.

• Considering 5 C as cooling loss due to mechanical and frictional heat generation.

• Concrete should be manufactured at =25-5=20 C

• Cooling water or replacing by ice flakes is more effective to lower concrete temperature rather than chilling of other materials

• For very effective and further reduction of concrete temperature ice flakes to be used as during melting of ice flakes it draws latent heat from other materials,

• 1 kg of ice absorbs 334 KJ of Heat.

• Popular Rules of Cooling

1.For every 0.5 C reduction of concrete temperature , reduction of 2 C of water temperature required.

2. For every 0.5 C reduction of Concrete temperature ,required ice flakes replacement will be 2 %.

Calculation of chilled water temperature/% age of Ice Flakes Required

• Considering Materials Temperature , 35 C.• Temperature of feeding water to be

maintained.• (35-20) x 2/0.50= 35-60= -25 C.• Hence its not possible to make such

concrete with only chilled water.• Hence we have to partially replace chilled

water by ice flakes

• Considering use of water of 35 C. • Replacement % of ice flakes = 60 %

OPTION-2, Use Chilled water and Ice Flakes Both.• If we use chilled water of 6 C and ice flakes

both:• The concrete temp. may be achieved with 6 c

water=35-(35-6)x0.5/2=35-7=28 C.• Hence Replacement of Ice flakes required:• For further reduction of (28-20)= 8 C=32 %

• Up to 75 % of water can be replaced by ice flakes, ( Ref-ACI-207-4R)

• Full scale mock up of same depth required to be conducted for temperature monitoring.

• Temperature of chilled water or % age of ice flakes required, may also be calculated PERFECTLY from the formulae of

• ACI-207.4 R -93• SP-23(Hot Weather concreting)

Thickness and Quality of insulation like thermocol(EPS Board) required is calculated to cope up with the requirement that it will be able to maintain the temperature at 70-20= 50 c , when , ambient temperature is 30-35 C. Thermal conductivity of thermocol varies from 0.30 -0.40 kcal/ m/deg C.

Normally 50 /75 mm thk. thermocol is provided all around and above the concrete.

Water curing is not done at it lowers the surface temperature. Polythene sheet may be used with EPS Board to reduce evaporation loss.

FULL SCALE MOCK UP

• FULL SCALE MOCK UP SHOULD BE DONE FOR A DEPTH EQUAL TO THE ACTUAL MEMBER.

• TEMPERATURE RISE OF CONCRETE INSIDE THE TRANSIT MIXERS FOR MAXIMUM DESIGNED PERIOD OF RETENTION SHOULD ALSO BE CHECKED.

• TEMPERATURE SHOULD BE MONITORED FOR 7 DAYS.

DELAYED ETTRINGITE FORMATION

• MOST ALLARMING AND DEGEROUS EFFECT OF HIGH TEMPERATURE CONCRETE.

• IDENTIFIED IN LAST 10-15 YRS.• CAUSE VOLUME EXPANSION AFTER HARDENING

OF THE MEMBER.• AS ETTRINGITE FORMATION DOES NOT TAKES

PLACE ABOVE TEMP-70 C.• SO FAR CAUSES FAILURE OR DETORIATION OF

MANY BRIDGES/STRUCTURES WORLD WIDE.

Conclusion• Construction industry always prefers cement with

accelerated early strength development without realizing the consequences of such cement. Because of the demand for such cements, cement manufactures adjusted their technologies to fulfil the market requirement. This was achieved by

• changing the composition of cement (increased• amounts of C3S and C3A, increased amounts of• sulphate and increased proportion of alkali• sulphates) and increasing the fineness to accelerate

early strength development (Aitcin, 2008). This has resulted in high temperature rise,

CONCLUSION

This has resulted in high temperature rise, leading to modification of microstructure and hydration chemistry which can affect mechanical properties and durability of concrete. Therefore it is important to control temperature rise of concrete with modern day cement, especially in construction of large structures.

Thank You