DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

CEL 774 CONSTRUCTION PRACTISESCONSTRUCTION PRACTISES

Hot & Cold weather Concreting

B. Bhattacharjee

CIVIL ENGINEERING DEPARTMENTIIT DELHI

General Outline

• Hot Weather problems• Concreting • Mass Concrete• Cold weather problem• Concreting in cold weather

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

Hot Weather problems

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

Rapid Hydration → accelerated setting→ Lower long term strength dueto less uniform frame work of gelRapid evaporation in lower humiditycauses loss of water → Plastic shrinkage& crazingIn mass concrete cracks due to thermalgradient is also experiencedAir entrainment is more difficult at highertemperature.

Affect of 28 days on strength of concrete

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

w/c=0.41Air content 4.5%

Hot Weather problems

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

Curing at high temperature posesadditional problem due to rapidevaporation → slower hydration

→ Inadequate development of strength &→may be cracking due to shrinkage

Hot weather concreting

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

Lower temperature of aggregate by sprinklingwater , shading, retarders tom prevent loss ofslump; Lower temperature of cement & water;May use iceHeat balance equation

T temperature of the mixtureSWW(T-TW)+SCC(T-TC)+SA(CA+FA)(T-TA)+SWWWA (T-TA)=0

Hot weather concreting

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

T=WTW+SCCTC/SW+SA(CA+FA)TA/SW+WWATA)/[W+SCC/SW+SA(CA+FA)+ WWA ]

T=WTW+0.22{CTC+(CA+FA)TA}+WWATA)/[W+0.22{C+(CA+FA)}+ WWA ]

When ice is added: all ice must melt beforemixingT=WTW+0.22{CTC+(CA+FA)TA}+WWATA-LWi)/[W+0.22{C+(CA+FA)}+ WWA +Wi]

Evaporation loss prevention

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

ACI 305.RLoss > 0.5 kg/m2

is to be avoided

Hot Weather problems

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

Temperature differentials cause thermalcracking

Creep relieves the stressWhen interior cools it would tend to contractstress in the exterior is relieved but furthercontraction may result in compression ofexterior and tensile stresses in interior, creepis now less, can result in crackingInsulation may reduce this effect whenwhole mass is not restrained

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

SummaryHot

Insitu testing

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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