Construction materials testing

What does a construction materials testing regime on a live site actually involve?

It's a planned sequence of tests carried out as the works proceed, so each material and each layer is checked before it is covered up or built on. In practice that means ground and formation testing before construction starts, compaction and material checks through the earthworks and subbase, and concrete testing at the pour. The methods, frequencies and acceptance criteria come from the project specification rather than from us.

How is testing frequency decided, per load, per area or per volume?

The specification sets it, and the basis changes with the material. Earthworks and subbase testing is usually expressed per area or per volume of each layer placed, aggregate testing per tonnage or per delivery, and concrete testing per volume poured or per number of loads. Highway schemes normally take earthworks requirements from Series 600 of the Specification for Highway Works and subbase from Series 800. Where a specification is silent, the frequency is agreed with the engineer before work starts.

Who holds the testing schedule on a project, and who calls off each test?

On most jobs the main contractor or their quality manager holds the schedule and calls tests off as the works reach each stage. The schedule itself usually originates with the designer or is written into the contract, and the engineer or clerk of works may witness testing or be copied into results. We work to whoever is named as our point of contact, and reports can be copied to the engineer, client or a shared project address by agreement.

How does testing fit around the main contractor's programme and quality plan?

Testing is planned against the construction sequence, so a test happens when the layer is ready rather than when the diary allows. That normally means agreeing the methods, frequencies and hold points once, then calling visits off against the weekly programme. The testing schedule usually sits inside the contractor's inspection and test plan, so results feed the quality records directly. A change of sequence on site then means moving a visit rather than rewriting the schedule.

Can the client instruct testing independently of the contractor's own testing?

Yes, and it is a common arrangement where a client wants their own check on material the contractor has already tested. The testing itself is the same; what changes is who instructs it, who receives the report and how the positions are chosen. Independent check testing is most useful when the positions are agreed in advance and are genuinely separate from the contractor's, otherwise the two sets of results are difficult to compare.

Will the report say whether the material passes the specification?

A report states the measured result and the method used, and will compare it against a specified limit where that limit has been given to us in writing. It does not decide whether the material is accepted: that judgement sits with the engineer, clerk of works or whoever carries the responsibility under the contract. If you want results reported against particular criteria, send the relevant clause or schedule with the instruction so the comparison is made against the right figure.

What happens if a test fails during the works?

We tell you the result straight away rather than waiting for the report to be issued. What follows is set by the specification and the contractor's own procedures, commonly a check test nearby to establish whether the result is local or general, then reworking, drying back, further compaction or removal and replacement, followed by a retest. Some specifications also increase the testing frequency for a period after a failure.

Can you test materials in existing construction rather than new work?

Yes. Construction materials testing covers investigation of what is already there as well as control of what is being built, which is often how a defect, a settlement problem or a change of use gets looked at. That can mean coring existing concrete or surfacing, assessing the layers beneath with DCP or plate bearing testing, or sampling and testing made ground and old fill. The scope is normally agreed with whoever is writing the investigation report.

Do you need to be on site full time, or do you attend for each test?

Most projects are covered by scheduled visits, with a technician attending for the day or half day a set of tests needs. Where testing becomes frequent enough that visits run into each other, a resident technician or a site laboratory usually works out better than repeated mobilisation. The deciding factors are how many tests a week the programme generates, how far the site is from a laboratory and how quickly results have to come back.

How are results recorded and tracked across a long programme?

Each test is reported individually and we can also keep a running register against the schedule, so it is clear at any point what has been done and what is outstanding. Reports are normally issued as PDFs by email and geotechnical results can also be supplied in AGS data format. Agree the reference system at the outset, including how positions, layers and chainages are named, because retrofitting references across hundreds of tests is painful.

Does UKAS accreditation apply across a whole testing programme?

Not automatically, because accreditation is granted method by method rather than for a service or a project. Hixtra holds UKAS accreditation to ISO/IEC 17025 for the tests listed in its schedule of accreditation, number 8996. Accreditation is specific to the listed methods and scope, and site and laboratory activities can carry different entries. Ask us to confirm whether the tests you need are covered before the programme is set up.

What should we send for a quotation for a testing programme?

Send the site postcode, the testing schedule or specification, the construction programme and the approximate number of tests by type, along with your preferred start date. Across a programme the cost is driven more by the number of visits than the number of tests, so travel, standby time, out-of-hours or weekend working and any reinstatement matter as much as the test count. Call 01908 505833 if the works are already under way.