Parking structures require routine maintenance and inspection, and neglecting to follow a prescribed maintenance schedule can lead to a reduced service life and accelerated deterioration of the structure.  What methods do you typically employ for effectively evaluating the condition of parking structures?

In the December 2023 SEU Session, D. Matthew Stuart, PE, SE, P.Eng., from Partner Engineering & Science, and Sharat Menon, from Structural Technologies, presented Understanding and Avoiding Costly Repairs of Precast Prestressed Thin Slab Parking Structures.  In this session, Matt and Sharat discussed methods of investigating a parking structure, the benefits of regular maintenance, and methods of repairing precast, prestressed thin slab members.

Matt noted that there are several available methods of on-site condition assessment and investigation.  Visual examination is necessary to identify and quantify surface defects such as cracking and spalling.  However areas with deterioration may not always have visible signs at the surface.

Chain dragging is an inexpensive method to detect subsurface delaminations within the slab.   Often the corrosion has not yet revealed itself on the surface as cracking or spalling; however, the rust layer has caused delamination or voids within the concrete.  The sound caused by chain dragging over delaminations is significantly different than dragging over solid concrete.  Chain dragging cannot be used on vertical or overhead surfaces, however a small hammer can be used effectively. The procedures for chain dragging can be found in ASTM D458.

Matt emphasized the importance of core samples which can enable petrographic analysis and chloride and carbonation testing.  To hear Matt explain the usefulness of petrographic analysis of core samples, watch this short two minute video:

Matt noted that a proper petrographic analysis can include the following services:

The procedures for petrographic analysis are found in ASTM C856.  Matt noted the requirements for the core samples should adhere to section 8 of the specification which include the location and orientation of the cores, the age of the structure, and the reason for the request for analysis.

Correctly identifying the cause of the deterioration is crucial in selecting the appropriate repair approach.  Using these methods, the engineer can establish the extent of the deterioration of the reinforcement and concrete and establish the next steps in the investigation and repair of the structure.  Regular evaluations of parking structure are necessary to identify these tell-tale signs of distress when proper investigation methods are used.