System Definition and Model Parameters

Given the potential of ECC to significantly enhance the characteristics of a

bridge/overpass, a bridge deck was selected as the application for this study. The design specifications and properties for the bridge deck were provided by a Michigan

construction company and results from a pilot study with the Michigan Department of Transportation; MDOT has sponsored a study to research the use of ECC in bridge decks.58

The bridge design analyzed in this study is based on a steel reinforced concrete overpass located outside of Ann Arbor, Michigan, on U.S.-23. The overpass is assumed to already be in place; this analysis does not include initial construction. The useful life of the bridge deck is assumed to be 30 years when constructed with CC and 60 years when ECC is used. The bridge deck for both systems will be replaced at the start of the analysis and will degrade over the analysis period, which is 60 years. Bridge deck dimensions are as follows:

• Length: 0.1 mile (160 meters)

• Width: 12 meters (includes two lanes in each direction) • Depth: 10 inches

Based on average annual daily traffic flow rates (AADT) provided by MDOT for U.S.-23 near Ann Arbor, the overpass maintained a traffic flow rate of 35,000 cars per day in each direction59; this rate is assumed to remain constant throughout the useful life of the bridge deck. The proportion of cars, trucks, and other transportation vehicles comprising the traffic flow is based on national average data, as per the Environmental Protection Agency’s MOBILE6.2 vehicle emission factor model.60

The four main bridge deck construction activities used in this study are outlined in Table 3.1 on the following page. The most material- and time-intensive construction activity is the deck replacement. A deck replacement involves replacement of the surface and subsurface concrete of the bridge deck. A deck resurfacing involves replacing the top two inches of concrete with new concrete. Repair and maintenance refers to fixing

58 _{Li, V.C.; Fischer, G.; Kim, Y.; Lepech, M.; Qian, S.; Weimann, M.; Wang, S. "Durable link slabs for}

jointless bridge decks based on strain-hardening cementitious composites." Project Report to MDOT. 2003.

59 _{Michigan Department of Transportation. “1997 University Region Level of Service E or F.” U.S.-23}

between Geddes Road and Plymouth Road. http://www.michigan.gov/documents/univr_16645_7.pdf. Date accessed: February 4, 2004.

60 _{U.S. Environmental Protection Agency. "MOBILE6.2." U.S. EPA, Ann Arbor, MI, 2002.}

MOBILE6.2 is a “vehicle emission factor model for predicting gram per mile emissions of HC, CO, NOx, CO2, PM, and toxics from cars, trucks, and motorcycles under various conditions”

potholes. Joint replacements apply to CC bridge decks and require the removal of one half meter of CC on each side of a joint (the point located directly above a supporting pier). This concrete is replaced with new CC and a steel joint is inserted. For an ECC bridge deck, rather than inserting CC, ECC is placed above the piers (three meters in road length). This is referred to as an ECC link slab and does not include a steel joint.

Table 3.1 Overview of Construction Activities Conventional Concrete Bridge Deck

Construction

Activity Frequency Description Dimensions

Deck replacement Every 30 years Replacing the full depth of the deck and re-pouring new concrete

Length: 160 meters Width: 12 meters Depth: 10 inches Joint replacement Every 15 years Extracting 0.5 meters worth

of concrete on each side of joint and replacing with new concrete

Length: 1 meters Width: 12 meters Depth: 11 inches Deck resurfacing Every 15 years –

when a joint replacement occurs

Removing top 2 inches of concrete along the entire deck and re-pouring new concrete Length: 160 meters Width: 12 meters Depth: 2 inches Bridge patching and repair Every 5 years following a deck resurfacing Chipping out a

square/rectangle shape and re-pouring with concrete

Depth: 2 inches

ECC Bridge Deck

Construction

Activity Frequency Description Dimensions

Deck replacement Every 60 years – when a link-slab replacement occurs

Replacing the full depth of the deck and re-pouring new concrete

Length: 160 meters Width: 12 meters Depth: 10 inches Link slab

replacement Every 60 years – when a deck replacement occurs

Extracting 1.5 meters worth of concrete on each side of joint and replacing with new concrete

Length: 1 meters Width: 12 meters Depth: 11 inches Deck resurfacing Every 20 years Removing top 2 inches of

concrete along the entire deck and re-pouring new concrete

Length: 160 meters Width: 12 meters Depth: 2 inches Bridge patching

and repair Every 7 years following a deck resurfacing

Chipping out a

square/rectangle shape and re-pouring with concrete

Depth: 2 inches

The key difference between the two systems is that the ECC is expected to extend the life of the bridge deck from 30 years to 60 years. By using a link slab made of ECC, rather than a concrete joint made of CC, the bridge deck is better able to withstand the stress of loads as well as the deterioration that occurs with weathering. Other than the joint area, both systems require the use of CC in deck resurfacings, bridge maintenance/repairs, and deck replacements, as well as epoxy-coated steel to reinforce the concrete in deck

replacements. Other model parameters, such as material densities, emissions factors, and fuel efficiencies are discussed throughout this study where appropriate.