UNSATISFACTORY CONCRETE TEST RESULTS CAUSES BASIC AND TUTORIALS

UNSATISFACTORY CONCRETE TEST RESULTS CAUSES BASIC INFORMATION
What Are Some Causes Of Unsatisfactory Concrete Test Results


The two most common kinds of failure are:
• failure to get the required strength, the concrete being otherwise apparently good;
• structural failures, such as honeycombing, sandy patches, and cracking.

Failure to get the right strength in cubes taken from a concrete pour can sometimes have a very simple cause. Among such causes are the following:
• the cube was not compacted properly;
• it was left out all night in hard frost or dried out in hot sun;
• there was a mix-up of cubes and a 7-day old cube was tested on the assumption it was 28 days old;
• the cube was taken from the wrong mix.

Such simple errors are not unusual and must be guarded against because they cause much perplexity and waste of time trying to discover the cause of a bad test result.

The concrete must be fully compacted in the mould, which is kept under damp sacking until the next day when the mould can be removed and the cube marked for identity.

It is then best stored in water at ‘room temperature’ for curing until sent to the test laboratory. If poor cube test results appear on consecutive batches, an error in the cement content of batches may be suspected, or else the quality of the cement itself.

Honeycombing is most usually caused by inadequate vibration or rodding of the concrete adjacent to the face of formwork.

Sometimes too harsh a mix is used so there are insufficient fines to fill the trapped interstices between coarse aggregate and formwork, or the larger stones cause local arching.

Sand runs – patches of sandy concrete on a wall surface which can be scraped away with a knife – can be due to over-vibration near a leaking joint in the formwork which allows cement and water to pass out of the mix.

One simple, and not infrequent, cause of poor concrete is use of the wrong mix due to a ‘failure of communication’ with the batching plant operator or ready-mix supplier. An experienced concreting foreman should be able to detect a ‘wrong mix’ the moment it is discharged.

ICE (UK) CONDITIONS OF CONTRACT FOR WORKS OF CIVIL ENGINEERING CONSTRUCTION

UNITED KINGDOM INSTITUTE OF CIVIL ENGINEERING CONTRACTS
ICE Conditions of Contract for Works of Civil Engineering Construction


These are generally known as the ICE conditions and have for many years been the most widely used conditions for UK civil engineering works. They have a long history of satisfactory usage and have been tested in the courts and in arbitration so that the parties to a contract can be confident as to the meaning and interpretation to be placed on these conditions.

The latest edition is the 7th, published in 1999 together with guidance notes, reprinted with amendments in 2003. This edition is known as the Measurement Version to distinguish it from other ICE types of contract based on this established standard.

The principal provisions of the Measurement Version are as follows:
• The contractor constructs the works according to the designs and details given in drawings and specifications provided by the employer.

• The contractor does not design any major permanent works, but may be required to design special items (such as bearing piles whose choice may depend on the equipment he owns) and building services systems, etc.

• An independent engineer, designated ‘the Engineer’ is appointed by the employer to supervise construction, ensure compliance with the contract, authorize variations, and decide payments due; but his decisions can be taken by the employer or contractor to conciliation procedures, adjudication and/or arbitration.

• The contractor can claim extra payment and/or extension of time for overcoming unforeseen physical conditions, other than weather, which ‘could not…reasonably have been foreseen by an experienced contractor’ (Clause 12) and for other delays for which the employer is responsible.

• Payment is normally made by re-measurement of work done at rates tendered against items listed in bills of quantities, which can also include lump sums.

A particular advantage of the ICE conditions is that interpretation of the provisions of the contract lies in the hands of an independent Engineer, who is not a party to the contract, but is required to ‘act impartially within the terms of the contract having regard to all the circumstances’ (Clause 2(7)).

This gives assurance to both employer and contractor that their interests and obligations under the contract will be fairly dealt with. Also the contractor is paid for overcoming difficulties he could not reasonably have foreseen.

Both these matters reduce the contractor’s risks, making it possible for him to bid his lowest economic price. This benefits the employer, since the initial price is low and he does not pay out to cover risks which may not occur.

The ICE conditions contain many other provisions that have stood the test of time. These include requirements for early notice of potential delays and problems such as adverse ground conditions and provisions for submission and assessment of claims and valuation of variations.

Properly drawn up and administered, a contract under these conditions appears fair to both parties, and the percentage of contracts ending in a dispute which goes to arbitration is very small.