SUMMARY

Evaluation of Ultra-High Performance Concrete Connections

This report presents findings from an evaluation study TRB conducted to assess (1) the potential socioeconomic impact of the use of ultra-high performance concrete (UHPC) for bridge connections in the United States and (2) the work the FHWA Turner-Fairbank Highway Research Center (TFHRC) has conducted since 2002 to encourage deployment of the technology. The UHPC Research and Development Program at TFHRC has conducted research and produced reports, technical briefs, and guidelines for the use of UHPC, leading to its use in multiple bridge applications, predominantly for prefabricated bridge element (PBE) deck-level connections.

UHPC is a cementitious composite material with higher compressive, tensile, and flexural strength; lower permeability; and better durability than conventional concrete. Because of the relative benefits and costs of UHPC compared with conventional concrete, as described in this report, TFHRC has focused mostly on encouraging the adoption of UHPC connections (UHPC-C). TFHRC has focused on expanding the use of UHPC-C through research and publication efforts, including disseminating information through workshops and “consulting” informally with state and local transportation departments. TFHRC labs are among the few in the United States with the tools to conduct large-scale concrete structural testing and to characterize materials.

S.1 Evaluation Approach

The evaluation focused primarily on the impacts of UHPC-C compared with conventional concrete connections (CC-C) for deck-level prefabricated bridge elements and had three core objectives:

1. Review the process by which TFHRC selected UHPC-C as a research focus, assess the effectiveness of its activities in promoting UHPC-C adoption, and document program accomplishments and UHPC-C deployment milestones.
2. Assess the technical and business cases for using UHPC-C, the barriers to adoption for construction stakeholders, and the potential role for TFHRC in addressing those barriers.
3. Quantitatively estimate the benefits and costs of UHPC-C to determine the socioeconomic return from adoption.

The evaluation team reviewed existing literature on the use and benefits of UHPC-C and aggregated publicly available bridge data to quantify the socioeconomic impact of UHPC-C use. The team also conducted 16 interviews with subject matter experts from organizations within six stakeholder groups associated with bridge delivery. The interviews were used to collect information on the process by which TFHRC UHPC research was developed and promoted and to corroborate findings from the reviews.

Figure S-1 summarizes the methods the team used to quantify the socioeconomic impacts of UHPC-C adoption. Net benefits were calculated by estimating the benefits and costs per square foot associated with adopting UHPC-C compared with CC-C in a typical accelerated bridge construction (ABC) project. To estimate national benefits, net benefits were expressed in dollars per square foot of bridge and then scaled to the aggregate square footage of existing and potential future bridge projects that use UHPC-C. The proportion of these benefits attributable to TFHRC activities was compared with TFHRC UHPC-C research costs to determine the national-level return on TFHRC investment.

S.2 Findings

The evaluation results suggest substantial benefits of UHPC-C use and strong positive national-level returns to TFHRC UHPC-C research activities. The hypothesis was that the main outcome of TFHRC activities and outputs is the increased adoption of UHPC-C, contributing to the increased adoption of prefabricated deck slabs (mostly for ABC applications). On the basis of a review of cost estimates from a subset of bridges in Florida International University’s ABC Project Database, the average onetime net benefit of using UHPC-C for construction is estimated to be $8 to $18 per square foot of bridge. Data on average annual rehabilitation costs per square foot of bridge from Kentucky and New York imply an added annual benefit of $1 to $4 per square foot per year.

Figure S-2 shows the number of U.S. bridges built per year using UHPC-C, from 2011 through 2018. UHPC-C benefits were applied per square foot of bridge to the total square footage of these bridges, generating an aggregate present value of realized UHPC-C benefits of $20.8 million to $56.3 million.

To estimate the number of bridge projects using UHPC-C to be completed between 2019 and 2028, observed trends in UHPC-C adoption were applied to FHWA National Bridge Inventory data on bridge conditions, along with the aggregate square footage of these bridges. UHPC-C benefits per square foot of bridge were then applied to the projected square

footage of the bridges to be built using UHPC-C to generate a future present value of UHPC-C benefits of $89.1 million to $249.6 million.

Interviews with industry stakeholders indicated that TFHRC research and outreach activities offered high value and greatly influenced the adoption of UHPC-C in the United States. A high percentage of the benefits could be attributed to TFHRC initiatives to promote UHPC-C use: most respondents attributed virtually all U.S. UHPC-C deployments to TFHRC technology transfer efforts in the form of either research or dissemination. To remain conservative, the evaluation attributed 60% to 75% of UHPC-C adoption to TFHRC.

Table S-1 shows the realized and potential present value of benefits reasonably attributable to the efforts of TFHRC. Results indicate total UHPC-C benefits attributable to TFHRC of $66.0 million to $229.4 million.

From the perspective of FHWA, the return on the TFHRC investment is substantial. TFHRC’s estimate of expenditures specific to UHPC-C was $2,545,000 total between 2009 and 2017. The present value of these costs, assuming an even distribution of costs over time, is $3.1 million.

Table S-2 summarizes the net present value and the benefit–cost ratio of TFHRC’s research activities. Comparing TFHRC UHPC-C research costs with the realized and future benefits of UHPC-C attributable to TFHRC, the analysis suggests a net present value of $62.9 million to $226.3 million and a benefit–cost ratio of 21.2 to 73.8.

Table S-1. Present value of realized and potential UHPC-C benefits attributable to TFHRC, 2011–2028.

NOTE:: FHWATFHRC = FHWA Turner-Fairbank Highway Research Center; UHPC-C = ultra-high performance concrete connections.

Table S-2. Net present value and benefit–cost ratio of TFHRC UHPC-C research.

NOTE: BCR = benefit–cost ratio; NPV = net present value; TFHRC = FHWA Turner-Fairbank Highway Research Center; UHPC-C = ultra-high performance concrete connections.

S.3 Uncertainties

Interviews suggested that the net benefits of UHPC-C depend on bridge project characteristics, including traffic, climate, and exposure to water. To reflect the diversity among projects, the evaluation modeled UHPC-C adoption by region and crossing feature. However, the bridge construction and maintenance cost estimates in this report were derived from the limited data available in public bridge databases and existing literature and thus were assumed to be constant across bridge applications throughout the United States. Furthermore, materials and labor costs can vary greatly by contractor, even in bids for the same project. More representative and diverse data on bridge construction costs and benefits, both with and without UHPC-C, would allow for more specificity in these estimates.

The monetary disincentives owner agencies sometimes attach to construction contracts were used as a lower-bound proxy for the impacts of traffic congestion. Disincentives are stipulated by hour or by day, using FHWA guidance, to encourage contractors to complete construction on schedule. As such, they reflect the owner agencies’ perception of the value of each day of traffic disruption. The evaluation team concluded that these disincentives are reasonable lower bounds for the impacts of field construction time, because FHWA focuses on road user costs and excludes impacts on neighboring businesses, the value of reduced risk of traffic or worker accidents, and the value of reduced emissions.

Finally, the evaluation team advises caution in the use of the benefits and costs of UHPC-C estimated in this report for other applications of UHPC. Net benefits of using UHPC versus conventional concrete may vary on the basis of the quantity of material needed and the expected performance benefits for each application.

S.4 Significance and Promoting Adoption

Stakeholder interviews indicated strong agreement that TFHRC’s UHPC-C technology transfer efforts are highly effective. Across multiple stakeholder groups, interviewees described how helpful TFHRC has been in promoting and supporting the adoption of UHPC-C. Several interviewees felt the current U.S. adoption of UHPC-C could be attributed almost entirely to TFHRC’s efforts. Stakeholders did note that proprietary UHPC suppliers carry out their own stakeholder outreach efforts but indicated that FHWA, as a highly respected and unbiased source of information, likely had the most influence

on UHPC-C adoption in the United States. Many researchers and owner agencies recognized TFHRC as both their preliminary and their primary source of information about UHPC-C, initiating their engagement with the material and continually serving as a guide for best practices through workshops, Every Day Counts initiatives, research publications, and technical reports.

The key remaining barriers to adoption of UHPC-C are the high costs of the material itself and of the needed equipment and labor required to apply the material. Interviewees suggested that additional TFHRC standards for producing and testing generic UHPC mixes could help decrease materials costs. Interviewees also suggested that additional demonstration projects could help contractors increase their familiarity with UHPC-C application best practices in varying field conditions. Such demonstration projects would also allow owner agencies to observe performance benefits. Increasing and synthesizing data on bridge costs and benefits would better allow owners and industry to observe the results of UHPC-C applications throughout the United States.