Luis Estenssoro
Senior restoration consultant, Walker Restoration Consultants, Greenwood Village
All buildings have plazas and walkways for pedestrian access. They come in all shapes and sizes, and they can be built with concrete, brick, stone, asphalt or a combination of many materials, including timber accents. Plazas and walkways can be set on the ground or on a structurally supported deck. Most have stairs and ramps and some even include heated snowmelt systems.
Of the many challenges facing building owners and managers, pedestrian access has to be at the top of the list. Pedestrian pathways have to be safe, clean and as aesthetically pleasing as possible. They are decorated, landscaped and exposed to the elements. They must meet Americans with Disabilities Act requirements, have non-slippery surfaces, drain well and be well lit. Plazas over occupied spaces must be waterproof. Architectural concepts and design details are available from many sources, such as Google “plaza design” and “plaza waterproofing,” but these sources do not address maintenance.
Ongoing maintenance and repair of these property elements are the responsibility of any organization, regardless of age and condition, in order to provide safety and ease of circulation under all operating periods, including emergency situations. The basic concepts of plaza design should be recognized to implement proper maintenance. Some plazas will require minimal to no maintenance, while some will require periodic care.
Plazas are inherently porous. Although most of the surface water is handled with surface slopes and area drains, water will infiltrate the top wear system whether it is concrete, stone, asphalt or brick. Basically, it is impractical to design and install a regular plaza that will not percolate water down to its subbase. And, based on their subbase, there are only two types of plaza and walkway systems – one plaza system is set on ground and the other is set on structural deck. They behave entirely differently.
Plazas on ground are more forgiving and flexible than plazas on deck. They are set on a drainable subbase to allow the seeping water to slowly continue to soak into the soils below.
Plazas on deck are more complicated. One must first assure that the structural deck is adequate to support the plaza and applied loads without significant deflections. A waterproofing membrane has to be present to prevent “percolated” water entering the building interior. The waterproofing membrane typically is installed on top of the structural deck and below the plaza system – hence a buried membrane. Placed on top of the waterproofing membrane, a drainage medium (drain mat or other system) delivers this water to specialty two-level floor drains.
The top and exposed surface (wearing surface) of a plaza is critical to its long-term performance. Poor-quality concrete, brick, stone and joint grout mortar will deteriorate with the increasing number of freeze-thaw cycles, the application of de-icing salts and, in some cases, the type of loading, such as hard wheels with impact-point loads.
Equally important to the long-term performance of plazas is the quality of the subbase. The subbase of plazas on ground needs to be competent, meaning it is properly prepared and compacted. The subbase of plazas on deck varies with the type of materials used and the design. Masonry plazas can be set on a bed of sand, dry or wet cementitious mortar or bitumen. Stone and precast concrete panels can be set on pedestals.
Many issues can arise with plazas and walkways but there are always solutions. The culprits to damage and problems with plazas include design, construction, vehicular and pedestrian damage, water, temperature changes and the construction materials themselves. Investigation is required to determine the root cause of the problems and determine a restoration protocol that will address the problem, maximize the useful service life of the plaza and ensure user safety. Some of the reoccurring problems that have been observed over several years of plaza investigations are tabulated in the accompanying chart.
The restoration methods to address these plaza issues vary in repair effort and cost. Some can be handled by the resident building engineer and an experienced contractor. Most restoration work, however, will require a large capital expenditure. At this stage, the best approach is to verify and determine the root cause of the problem following an investigative protocol. The findings then need to be translated into an asset management plan with restoration priorities, alternatives and recommendations, and associated costs, which subsequently is followed by construction documents.
During the renovation or restoration work, pedestrian accessibility must be provided and code requirements must be met. Most projects require the work to be phased or alternate pedestrian routes need to be provided. Flow restrictions can be difficult and disruptive to the building operation but the details must be ironed out between contractor, designer, building tenants and occupants, and owner.
This chart shows reoccurring maintenance problems and potential causes.
