Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85911
Photo courtesy of: Hossain and Ozyildirim Precast concrete panel installation on Virginia's I-66: (a) slab alignment; (b) temporary post-tensioning of threaded bars; (c) permanent post-tensioning; and (d) grouting operation "Both the PCP and PPCP systems are performing satisfactorily after one year of traffic, and the contractor was also satisfied with the constructability." The cementitious materials for the PCP system contained 25-percent slag cement and had a low w/cm, leading to low permeability values that averaged 1,493 coulombs, they write. The com- pressive strengths were higher than the 4,000 psi design strength at both seven and 28 days. Compressive strength requirements for PPCP systems were 3,500 psi for detensioning and 5,000 psi at 28 days. Strengths were higher than the specified values. One set of two cylinders was tested for permeability and exhibited a very low average value of 601 coulombs. CIP patches were placed 9 inches deep, while both PPCP and PCP slabs were 8-3/4 inches deep. A total of four lanes on I-66, including shoulder, were replaced using PPCP panels, each 10 feet long. The inside two 12-foot lanes were installed first, then the outer lane along with the shoulder was repaired using one 27-foot-wide slab. The whole sys- tem consisted of several types of panels: joint panels, anchor panels, base panels and closure pours. Several PPCP panels were post-tensioned together, creating 100- to 160-foot sections. Each sec- tion was tied to another with a doweled expansion joint. At both ends of each section were joint slabs containing five block-out slots for longitudinal post- tensioning. "Both the PCP and PPCP systems are performing satisfactorily after one year of traffic, and the contractor was also satisfied with the constructability," Hossain and Ozyildirim say. "One of the major concerns is the potential for wide expansion joints in the PPCP and eventual loss of support there. There were very few cracks in the PPCP section, mainly originating from grouting holes, cracks in the block-out patches, cracks and loss of epoxy at lifting hook holes, and corner breaks. PCP slabs showed some mid-slab cracks immediately after opening to traffic, but they are still tight and stable after 1.5 years of traffic." v Write Towmaster_BR0312pg27.indd 1 on Reader Service Card Better Roads Better Roads March 2012 27 2/21/12 9:36 AM