You are here:

Civil Engineering/Class 30 Cement content

Advertisement

Expert: - 10/12/2011


Question
QUESTION: I have been having this argument with my seniors regarding the cement content of a class 30 concrete. Could you please confirm the minimum cement content requirement, and also the maximum cement content requirement for this class.

Cheers.

ANSWER: Hi Vishal,

This depends a lot on how well you do your aggregate grading and what water cement ratio you use, as well as on the type of cement (OPC or pozolanna)and any additives. The usual amount is around 275 kg/m3, but with really good mix design you can get it down to 250 or with poor mix design you may need over 300 kg/m3 to achieve the same 30 N/mm2 cube strength at 28 days.

Of course if durability is an issue, you will need higher proportion of cement than just for strength.

---------- FOLLOW-UP ----------

QUESTION: Thank you,

Regarding the aggregate we are using 19mm, and the water cement ratio is 0.45 up to 0.5 w/c. And the type of cement is 32.5 ppc. Please advice, because at the moment I am using 12bags 50 kg each and I've still got complaints from the site engineer.

Regards,

Vishal Patel.

Answer
Hi Vishal,

I am not sure what 32.5 ppc is, but you are using far too much cement for 1m3 of concrete!

When I said that aggregate grading is important, I did not mean maximum or nominal size of aggregate- it is what proportion the aggregate has of 19mm, 12mm and 8mm sieve sizes (or equivalent). This mix proportion is vital in order to minimise cement content. The same applies for the sand- the grading needs to be within a certain envelope, to ensure a good concerte mix.

Civil Engineering

All Answers

Answers by Expert:

Ask Experts

Volunteer

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: 36 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

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 date)

©2012 About.com, a part of The New York Times Company. All rights reserved.