From the observation of site, plant and works concrete, it is understood that people rarely follow specified procedures to the letter of the specification and the test samples (cubes/cylinders) that are tested are not the true representative of the concrete actually used at the site (Realcrete). It is remarkable how frequently data from cube or cylinder tests are emphasized with little concentration on any part of the manufacture, cure or testing of these items to get the desired results satisfying the required standard, but the compliance of these results with the standard does not necessarily mean that it will produce the target performance in realcrete.
From the foregoing discussion, it may be concluded that the value of a test result is exclusively dependent on potential compressive strength. The test cannot cater for realcrete factors such as:
a) How well the concrete has been compacted,
b) How well the concrete has been cured (thermal and/or moisture),
c) The effect of segregation, honeycombing etc.,
d) The likelihood of specifying strength when strength is an unnecessary specification requirement.
The problem regarding the concrete strength occurs in two parts:
· The laboratory data and
· The strength that the concrete has in the construction.
The first part give the results that are complying with the standards. The second part of the problem is much more common, and is encountered when a site dispute arises over aspects such as compaction, curing or materials in general.
In the case of steel, the results are not so much varying however in some cases the contractors order for the whole amount of steel needed in construction in lump sum and it remain at the site as long the project is going on. Meanwhile, it is subjected to rusting, corrosion etc. that causes the reduction in strength and when it comes to the testing, the test samples are brought from the portion that is safe from rusting or somewhere from the middle of the steel bar to get the desired results, which is again not the true representation of the steel actually used at site.
Recommendations
For a project to be accomplished complying with the standards, it must be monitored at every stage of its execution otherwise it can give rise to many problems. The concrete is expected to perform as a function of cube or cylinder test data. The performance requirement has been either unrelated or only somewhat related to strength. The problem arising from the reliance on test sample strength data is aggravated by having to wait for several days for the strength value to arrive on site, by that time the construction would have probably been advanced by several stages. As far as waiting for strength data to arrive on site is concerned, there are a number of non-destructive and semi-non-destructive tests that could be agreed as criteria, the use of a non-destructive test such as the rebound hammer could be considered, cores should be tested, or the concrete should be examined for surface hardness. The authorities that are concerned with the technical requirements need to agree what performance characteristics are relevant, how these are to be assessed, and with what limits (standards).
BIBLIOGRAPHY
Choo, Newman and. Concrete Technology.
Concrete Basics published by Cement Concrete & Aggregates Australia (CCAA)
Gambhir, M. L. Concrete Technology.
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