Concrete floor slab surveys

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

Why undertake a GPR floor slab survey?

Typically, GPR floor slab surveys are undertaken to determine or confirm the following:

• Floor slab construction detail
• Slab thickness
• Reinforcement distribution
• Adequate mesh overlap
• Detect variations in floor slab construction detail
• Determine the position of any ground beams and pile caps

A GPR floor slab may be required for several reasons:

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

Advantages of a GPR floor slab survey

GPR offers several clear advantages over more traditional survey methods. 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.

The GPR is non-intrusive and can be carried out in occupied premises with minimal disruption. It is suitable for scanning large or small local areas. The on-site scanning is quick and efficient. The data is saved electronically and processing and interpretation are typically carried out off-site.

Site survey

The GPR survey involves scanning the required area of the floor slab with a series of scan lines; typically, these are on a regular orthogonal grid but can be varied 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, while 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.

All site survey data is saved electronically. Typically, the data is then processed and interpreted off-site at our offices. This means data collection on site is quick and efficient, keeping any disruption of occupied premises to a minimum.

Deliverables

Typically, our GPR surveyors will scan the required area of the slab with scan lines at appropriate centres. All data is saved electronically and processed off-site. Our results and interpretation are presented in a clear report, including CAD drawings, sketches, photographs and annotated radargrams as required.