Cure for Thinning Concrete

by Michael Grodner, P.E., (M.ASCE), Asst. Resident Engr.; Parson Brinckerhoff Quade & Douglas, South Salt Lake City,
Gary McClellan, P.E., (M.ASCE), Supervising Struct. Engr.; Parsons Brinckerhoff Quade & Douglas, Boston, MA,
Len Beystrom, P.E., (M.ASCE), Field Engineer; Parsons Brinckerhoff Construction Services, San Juan, Puerto Rico,

Serial Information: Civil Engineering—ASCE, 1998, Vol. 68, Issue 12, Pg. 49-51

Document Type: Feature article

Abstract: After placing 75% of the concrete liner for twin 4.6 km transit tunnels in Portland, Ore., engineers discovered areas of concrete that were thinner than the prescribed 305 mm thickness. After probing the tunnel and investigating other examples of similar problems, designers chose to use nondestructive testing methods—impact echo (IE) and ground-penetrating radar (GPR)—to determine the extent of the problem. GPR was most effective due to the liner design. Remediation included a breakout and repair with a patch pour where thickness was significantly less than 305 mm, and a fill-void using neat cement grout where thinning was moderate and the area had not been previously grouted. Repairs were completed on an especially tight schedule that called for one of the tunnels to be turned over to subcontractors just after the July 4th holiday.

Subject Headings: Concrete | Linings | Nondestructive tests | Radar | Rehabilitation | Tunnels |

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