Canadian Parking Association - Fall 1997

Plaza Parkade (continued) - Repairs were undertaken recently to the Plaza Parkade parking structure in Prince George, B.C., using an innovative application of Advanced Composite Materials (ACM's) and conventional cast-in-place concrete repair techniques. The use of ACM's in the strengthening and rehabilitation of existing parking structures in North America is emerging as a practical, cost effective, and durable alternative to conventional demolition and reconstruction. In this case, the owner of the structure (the Prince George Downtown Parking Commission) saved many thousands of dollars by choosing to reinforce a deteriorated parking garage deck slab 'in-situ' with Carbon Fibre Reinforced Polymer (CFRP) strips and sophisticated epoxy adhesives.

Conventional deck surface repairs were undertaken in May and June of 1997 at the Plaza Parkade structure in Prince George, B.C. to correct chronic surface abrasion and delamination in the area of the ticket spitter, near the main level entrance.

These repairs involved milling the deck surface, filling local low spots with non-shrink cementitious grout, and installing a three component, abrasion resistant deck membrane system (TDM 1000) supplied by Sternson's Construction Products Ltd. of Vancouver. In the course of those repairs, a small walk-behind concrete milling machine broke through the deck slab in the area immediately above the ground level electrical room, exposing a significant zone of deteriorated concrete.

Examination of the 25 year old deck slab revealed improperly placed and significantly corroded reinforcing steel and evidence of previous, largely unsuccessful grout patch repairs. Leakage had likely been occurring through the slab for some time, aggravated by the deterioration of the deck surface and rupturing of the elastomeric waterproofing membrane at some time in the past. The deck slab was also found to be approximately 1 ½ inches thinner than the original design drawings specified, resulting in a 30% loss of thickness in the immediate area of the damage.

As an alternative to conventional demolition and reconstruction of the concrete slab (which would have involved extensive concrete removal, shoring and forming) the Prince George Downtown Parking Commission elected to use a system of Advanced Composite Materials (ACM's) to strengthen the slab in place.

In this case, Carbon Fibre Reinforced Polymer (CFRP) tow sheets were used in conjunction with epoxy resins to increase the strength of the slab by direct application to the deck soffit (underside). Surface preparation and application of the resins and tow sheets were in accordance with recently developed technical specifications for Advanced Composite Materials, provided by AutoCon Composites Inc. of Toronto.

Design of the repairs, supervision of the construction and certification of the final installation to the local Building Inspection Authority were provided by Scouten & Associates Engineering Ltd., of Prince George, B.C.

In this application, the following specific materials (as supplied by AutoCon Composites Inc.) were incorporated into the repairs:

• FTS C1 - 20 High Tensile Carbon Fibre Tow Sheet (505,000 psi tensile strength)
• FP - NS Standard Epoxy Primer
• FR - E3P Standard Epoxy Resin

After repairing the large hole conventionally with non-shrink grout, and preparing the slab soffit with simple hand tools (electric grinding wheels and wire brushes) the strength of the deck was restored by the EXTERNAL application of the carbon fibre sheets.

High modulus epoxy resin was used to impregnate the fibre sheets, and bond them securely to the slab soffit in the direction of principal flexural tension. The resulting rehabilitated deck slab has all the strength and durability required of a parking structure in a relatively aggressive, northern Canadian environment.

All site work was undertaken by Wayne Watson Construction Ltd. of Prince George, B.C., under a simple Extra Work Order to the original deck surface repair contract.

The applicators had no previous experience with in-place concrete restoration using Advanced Composite Materials, but were competent and enthusiastic throughout. In our opinion, additional repairs to facilities owned by the Prince George Downtown Parking Commission and other parking authorities could be undertaken in the same fashion by similarly qualified general contractors, with appropriate supervision provided by a qualified structural rehabilitation consultant.

Additional information on the practical use of Advanced Composite Materials in the strengthening and rehabilitation of existing parking structures may be obtained from: Scouten & Associates Engineering Ltd.