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Civil Engineering/Measurement of max differential temperature

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Question
Dear Sir;  I installed 15 thermocouples in raft of 30m by 15m by 3m. After three days of cast, thermocouples' readings showed drop. Kindly guide me to calculate the max differential temperature. Thanks

Answer
Hi Mahmood,

Thermocouples are usually located in pairs, so that one is in the core of the casting (middle depth, middle width, or at least 3m away from the side, and the other within 100mm of the side edge. Then you measure the two pairs of temperatures every 1-2 hours and see the differential between the pairs. At first the differential will increase, probably for the first 2-3 days, then the differential will start dropping. These are the rules for tempertures and differentials:

*The Contractor shall employ effective means such as shading the aggregates, pre-cooling mixing water and adding flaked ice to ensure the temperature of concrete prior to and including the time at which it is placed shall not exceed 25 deg C.

*After the concrete has been placed, its peak temperature in any part of the structure shall not be permitted to rise above 70 deg C.

*After the concrete has been placed, the maximum temperature difference between a point at the centre of a concrete section and the adjacent surface shall not be greater than 20 deg C times the shortest distance, in metres, between the concrete section centre and the surface.
Therefore for 1m wall, maximum differential should be 10 deg C and for 2.5m wall, maximum differential should be 25 deg C.

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Arshad Khan

Expertise

I can answer any questions to do with civil and structural engineering consultancy and construction industry in East Africa and the Middle East, and specifically with the analysis and design of reinforced concrete structures. My particular expertise is in the aseismic design and optimisation of tall buildings.

Experience

Employment history: 40 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Zambia, Austria, Bahrain, Kuwait, Doha and the U.A.E.

Organizations
.Fellow of Institution of Structural Engineers (UK) .Fellow of Institution of Civil Engineers(UK) .Member of the Institution of Engineers, Kenya .Registered Engineer, ERB, Kenya .Member of the Architectural Association of Kenya (Engineers Chapter) .Chartered Engineer (UK)

Publications
•1984: International Conference on the Art and Practice of Structural Design, London •1994: 3rd Int. Kerensky Conference in Structural Engineering, Singapore •2008: International Conference on High-Rise Towers, Abu Dhabi •2013: IEK International Conference, Kisumu, Kenya

Education/Credentials
BSc, 1st Class Hons, in Building Engineering, University of Bath, UK MSc in Concrete Structures and Technology, University of London. Diploma of Imperial College, UK.

Awards and Honors
•Science Congress Special Award (for 2-seater Hovercraft - 1968) •Institution of Civil Engineers Award for outstanding performance at Bath University (1975) •Concrete Society Postgraduate study Bursary Award (1976) •Consular Representative for British High Commission, Nairobi. (1995 to 1998) •Examiner for Institution of Civil Engineers Professional Interviews, Nairobi. (1997 to 1998) •Branch Representative in Vienna for PI assessment for Inst. of Struct. Engrs. (1999 to 2010)

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