Concrete floor slab surveys

Our GPR surveys provide a fast and efficient NDT means of surveying large or small areas of concrete floor slab. They can determine construction detail and help identify possible defects. Suitable for warehouses, offices, car parks, etc.

Why undertake a GPR floor slab survey?

A GPR floor slab survey may be required for several reasons:

• Determine construction detail.
• Verify construction drawings.
• Identify the reason for slab failure.

We typically undertake GPR floor slab surveys to determine or confirm the following:

• Floor slab construction detail (e.g. reinforced concrete, mass concrete, clay-pot, precast planks, etc.).
• Slab thickness.
• Reinforcement distribution.
• Adequate mesh overlap.
• Detect variations in floor slab construction detail.
• Determine the position of any ground beams and pile caps.

Advantages of a GPR floor slab survey

GPR offers several clear advantages over more traditional survey methods. Notably, as it detects changes in the sub-surface, it will detect not only reinforcement but also any voiding beneath the slab, the slab thickness, construction layers, variations in construction, services (including plastic), etc.

GPR is non-intrusive and can be carried out in occupied premises with minimal disruption. It is suitable for scanning large or small areas. Furthermore, on-site scanning is quick and efficient. This is because typically, we save the data electronically and undertake processing and interpretation off-site. Consequently, this keeps the time spent on-site to a minimum.

Site survey

The GPR survey involves scanning the required area of the floor slab with a series of scan lines. Usually, these are on a regular orthogonal grid, but this can be flexible to accommodate obstructions.

For office, warehouse or any other floor slab survey, we use a GSSI SIR-3000/4000, dual-frequency or a multi-channel GPR system. The dual-frequency scans provide a greater depth range with a better resolution than a single frequency antenna. Multi-channel systems use an array of antennas, providing rapid scanning of large open areas.

Antenna central frequency is typically in the range 1.5GHz to 300MHz. We frequently scan using several different frequencies to obtain a range of depths and resolutions. The 1.5GHz antenna would typically penetrate to a depth of 400mm in concrete and is best for detecting shallow features such as layers of reinforcement. The 300MHz antenna can penetrate to a depth of 2m or more (conditions permitting), thus resolving deeper features, albeit with a loss in resolution in the data.

We save the site survey data electronically and process it at our offices using specialist Radan software. This has two main advantages. Firstly, it means data collection on site is quick and efficient, keeping any disruption of occupied premises to a minimum. Secondly, the results are more accurate because data processing such as surface position correction, gain adjustment and migration make interpretation easier.

Deliverables

Our results and interpretation are presented in a clear report. They including CAD drawings, sketches, photographs and annotated radargrams as required.