Testing - Concrete Mix Design, Quality Control and Specification - page 156

authorities. Unconservative assessment is one aspect of the risk and unre-
liability of the equipment is another. Either of the EA and TTF methods
can be made to give satisfactory results by a knowledgeable operator using
any of the available equipment. However, some equipment requires greater
skill, care, and understanding than others and this can be involved/pro-
vided in different ways and at different stages. Decades ago, Day achieved
satisfactory results by personally making and installing thermocouples
and assessing results. Any faulty readings were recognised as such and dis-
carded. Judgments on readiness for stressing and so on were made in a full
knowledge of current test results and circumstances and past performance
and with appropriate safety margins. This does not mean that the methods
used would be satisfactory if applied by the average site worker or an
inexperienced young engineer.
It is difficult to generalise on the economics of alternatives.
1. In most cases the savings made from the information gained far
outweigh the cost of the testing. To this extent whatever it takes to
satisfy authorities is worthwhile.
2. Also, in many cases the results reveal a substantial margin between
the strength developed and that necessary for the purposes envisaged.
In such cases a large margin can be allowed for inaccuracy.
3. The cost of personnel is often a major factor. They may be involved in
preassembly, calibration, installation, reading, evaluating results, and
equipment recovery. The level of skill and ability required varies sig-
nificantly between different equipment and different work scenarios.
4. The number of probes installed may be influenced both by their
perceived reliability and the consequences of an occasional failure.
5. The risk of damage or theft of external equipment will vary consid-
erably between different working scenarios (e.g., site or precasting
factory), and even different countries and locations.
6. The curing situation, varying from in situ slabs in winter to steam
cured precast units, may be an overriding factor.
There is clearly a need for one or more kinds of certification, but this
also may not be easy to arrange. One kind is the training and certification
of operators by equipment providers. Another is the certification of equip-
ment providers (as opposed to particular equipment). However, it is not
clear who would be sufficiently competent and independent to provide such
certification. It would be important not to introduce regulation that could
rule out satisfactory solutions.
Chapter 10 gives details of the use of early age data in the ConAd QC and
other programs. While these programs can display the graphs described
earlier, it is not necessary to use them in the normal course of events,
except for checking purposes. Entry of a strength and its associated EA in