Link to Latest Report: September 2023 Progress Report
Background:
Bridge deck cracking is a prevalent problem in the United States. While early-age cracking will not cause failure of the bridge deck system independently, the penetration of deleterious substances (e.g., deicing chemicals) through the cracks leads to costly serviceability issues. If left unchecked these issues could lead to severe distress and the loss of structural integrity of the deck and superstructure. Bridge deck deterioration, therefore, must be managed through preservation efforts that range in scope from patch repairs to full deck replacement, with bridge deck concrete overlays and overlay replacement falling somewhere in between. There is also a need to strengthen some bridges due to higher demands, including increasing deck thickness through a structural overlay. Regardless of the scope of the rehabilitation project, one of the continuing challenges in these efforts is selecting a suitable repair material that can achieve specified engineering and durability properties quickly while also being long-lasting. As traffic volumes continue to increase, long-term closures or lane restrictions are nearly impossible, and many of these preservation projects must be completed during overnight closure windows, often in congested and heavily trafficked urban transportation corridors.
Currently, there are a number of repair and overlay materials available for protecting bridge decks from additional deterioration and extending their service life (e.g., ultra high-performance concrete, latex modified concrete, low slump concrete, etc.) [1-5]. Many of these overlay systems have shown varying degrees of success but mobility and safety issues have caused state DOTs to truncate construction times as much as possible, leaving less time for these conventional strength-gaining materials to be used. This has led to instances of using expensive polymer-based concretes (e.g., polyester polymer concrete or PPC) instead of preferred or higher-performing cementitious materials due to rapid traffic turnaround; PPC overlays set up very fast, but they do not address decks in poor condition and are expensive. Consequently, there is an urgent need in identifying, characterizing, and implementing sustainable and advanced high-early strength concrete (HESC) overlays to support rapid concrete bridge deck rehabilitation. The proposed research project explores the use of a calcium sulfoaluminate (CSA) cement-based overlay as alternative option.
CSA is a preferred option for HESC because of its ability to set within a short time window (roughly 15 min) and easily surpass a compressive strength of 2,500 psi in under 3 hours. A primary reason for the rapid strength development in CSA is due to its finer particle size, when compared with ordinary Portland cement (OPC), and a chemistry that promotes rapid and significant ettringite formation in the first few hours [6]. This rapid ettringite formation often leads to an early-age expansion characteristics resulting in a lower or neutral long-term shrinkage stress development and thus, reducing cracking potential. While the main incentive for using CSA is the rapid strength gain, it is worth noting that its lower calcium composition leads to a 30-50% reduction in CO2 emission from calcination compared to OPC [7]. Furthermore, the lower temperature needed in the kiln to produce the CSA compounds can reduce the energy of manufacturing by up to 60% [8].
A survey done in 2017 reported that California is the only state DOT recommending the use of CSA for high early strength concrete [9]. However, another survey found that 9 other states, including Washington, have had success using CSA for repair applications [10]. While CSAs have the potential to be successfully used in producing HESC overlays, significantly more data is needed in order to develop appropriate guidance and specification documents for their use. The construction of concrete overlays presents a unique problem, where sufficient bonding and compatibility between the overlay material and the substrate is essential for a long-lasting rehabilitation. The use of HESC in this application presents several additional challenges, where conventional bridge overlay construction practice may not work for these materials. The ideal material should possess high early-age strength, good adhesion to existing concrete substrates, and superior short- and long-term durability. These properties will be evaluated in the proposed testing program to develop a suitable CSA based HESC overlay material specification for accelerated bridge construction and rehabilitation applications
Objective:
This research will investigate the use of alternative and innovative high-early strength cements for concrete bridge repair and overlays. Specifically, a calcium sulfoalumiante (CSA) based cement will be the primary focus of this study. The objective of this research project is to identify the obstacles to successfully and reliably use CSA cement for structural bridge deck overlays with a particular focus on evaluating bond properties and performance. CSAs are gaining the attention of many state agencies, owing to their rapid setting and high-early-age strength gain, which can be leveraged to accelerate project delivery and shorten the duration of in-situ concreting activities. These cements have great potential to be successfully used in repair and overlay applications, especially when minimal traffic disruption is crucial.
Scope:
The objective of each of the five tasks and how they will be achieved are detailed in the following sections.
Task 1 – Literature review:
A comprehensive review of past experimental research involving high-early strength (HESC) concrete with respect to bridge overlays will be completed, including lab and field trials. It is expected that this preliminary information gathering will be completed in the first quarter of the project. There are several states that have used a high early-age strength concrete in recent years with varying degree of success. There are several known issues with these types of materials including, but not limited to, high early-age modulus, lower creep capacity, higher drying shrinkage strains, and higher autogenous shrinkage. However, specific rapid setting cement-based systems, especially those based on early-age ettringite formation such as CSAs, can provide early-age expansion characteristics that reduce shrinkage-related cracking risk. In addition, shrinkage reducing admixtures and fibers may also be beneficial in this regard. Through the proposed research, feasibility, constructability, and key properties with regards to CSA based concrete repair and overlay materials will be documented and disseminated in a format that will be made valuable to state departments of transportation.
Task 2 – HESC Mixture Design and Materials Optimization
In Task 2, a laboratory program will be developed to initially screen potential HESC materials and mixture designs (e.g., CSA cements, mixture proportions, curing, construction, and placement techniques). It is anticipated that at least 2-3 CSA cements will be procured for characterization in consultation with the advisory panel members. This task will focus on mixture design development and material optimization on mortar mixes including workability, setting time, and early-age strength development (e.g., up to 24 hr). These tests will be used to optimize and identify 2-3 high potential overlay mixtures to undergo a more exhaustive series of performance tests in Task 3. By focusing on mortars, a more expedient investigation can take place while minimizing materials waste. Thereafter, small adjustments can be made for concrete-scale mixtures. The main technical criteria to optimize mixture proportions will be decided by the research team in consultation with the advisory panel members. The exact number of permutations is unknown at this time, but a rough estimate would about 3-5 permutations on each CSA cement. The variable to be investigated may include the following:
- Chemical admixtures that impact workability/working time
- W/CM and water content
- Role of aggregate type
Candidate mixtures will be ranked based on their ability to develop high-early age strength, workability and working time, cost/availability, and constructability. The optimized mixture designs will be evaluated in Task 3 to develop preliminary performance specifications. It should be noted that it may not be possible to investigate all permutations with all materials given the budget and time allotted for the project. The research team will consult with advisory panel members, to make a determination as to how much work is merited in this task.
Task 3 – HESC Material Characterization
In Task 3, the research team will take the findings from Task 2 to inform 2-3 CSA overlay mixtures. This experimental program will evaluate key material and structural properties affecting the performance of concrete overlays (e.g., modulus, mechanical strength gain, setting time, and volume change), focusing particularly on bond strength and subsurface characteristics as a performance indicator of CSA concrete overlays.
Table 2 shows a preliminary fresh and hardened property test matrix for the overall concrete evaluation. The majority of tests will be conducted in the first 24 hours after casting due to the requisite of speed of construction. All other test samples shall be stored in a curing room (73F and >95% relative humidity) until the time of testing.
Table 2: Testing of fresh and hardened concrete properties
| Property | Test Method | Age of Test |
| Concrete slump | ASTM C143 | Fresh |
| Concrete Air Content | ASTM C173 | Fresh |
| Time of Setting (Penetrometer) | ASTM C403 | Fresh |
| Compressive Strength | ASTM C39 | 1, 3 hr, & 1, 3, 7, and 28 days |
| Tensile Strength | ASTM C496 | 1 & 28 days |
| Elastic Modulus | ASTM C469 | 1 & 28 days |
| Drying Shrinkage | ASTM C157 | 90 days (drying time) |
| Coeff. Of Thermal Expansion (CoTE) | AASHTO T336 | 1 day |
For all of the mixtures, drying shrinkage specimens will be cast and monitored as per ASTM C157. To simulate actual field conditions, the specimens will receive little or no moist curing prior to exposure to standard, drying conditions (73 ºF, 50% relative humidity).
| Table 3: Testing matrix for bond strength of CSA overlay mixtures | |||
| No | Surface Prep | Primer/Admixture | Curing Duration |
| 1 | AB | LM | 1 day |
| 2 | AB | LM | 7 day |
| 3 | AB | LM | 1 day |
| 4 | AB | LM | 7 day |
| 5 | AB | SP | 1 day |
| 6 | AB | SP | 7 day |
| 7 | AB | SP | 1 day |
| 8 | AB | SP | 7 day |
| 9 | MC | LM | 1 day |
| 10 | MC | LM | 7 day |
| 11 | MC | LM | 1 day |
| 12 | MC | LM | 7 day |
| 13 | MC | SP | 1 day |
| 14 | MC | SP | 7 day |
| 15 | MC | SP | 1 day |
| 16 | MC | SP | 7 day |
| AB: Abrasive BlastingMC: Mechanical Chipping
LM: Latex Modifier SP: Surface Primer |
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The coefficient of thermal expansion for each of the mixtures will be measured on 1-day old cylinders by immersing the cylinders in a water bath, changing the bath temperature, and measuring the length change using a submersible LVDT. This data will be important as thermal compatibility between repair and base materials is essential to a long-lasting repair.
Table 3 provides a tentative test matrix for the substrate bond testing. To evaluate the bond strength between each CSA concrete overlay mixture and a standard concrete substrate, two methods will be used including the pull-off method (ASTM C1583) and slant-shear bond test (ASTM C884). For the pull-off method, several miniature concrete deck specimens (i.e. slabs), 4-6-inches in thickness, will be cast and prepared to replicate a conventional WSDOT bridge deck using a standard bridge deck concrete mixture design. These specimens will be cast at the beginning of Task 2 and stored outdoors at the research team’s facility to ensure they have gone through most of their shrinkage before the overlays are placed in Task 3. To simulate as close as possible to actual field conditions, surface preparation of the substrate will be prepared using two methods including abrasive blasting (e.g., sand blasting) and mechanical concrete removal (e.g., chipping tools), to obtain different surface roughness, texture, and depth. In addition, placement of the overlay including consolidation, finishing, and curing will be done as close as possible to current construction methods (e.g., surface finish, curing application, etc.). All final design and construction considerations will be reviewed with advisory panels prior to overlay application. Variables of interest in the study include CSA concrete mixture design, substrate preparation, curing duration, and the use of admixtures/primers to enhance substrate bonding. For each variable, two alternatives will be evaluated for each, leading to at least 16 deck specimens.
Task 4 – Development of HESC mixture design specifications
Based on the results of Task 1-3, suitable CSA materials and mixture designs will be identified, in consultation with the advisory panel members. All material properties, characteristics, and performance data will be used to provide preliminary performance specifications for a CSA-based HESC repair and overlay mixture designs. The Washington State Department of Transportation anticipates funding a follow-on project in Autumn 2023 (see list of funded project in Section 4 below) that will focus on further developing HESC performance specifications based on additional durability testing (e.g., freeze-thaw, salt scale, restrained shrinkage cracking, etc.). The key data generated on fresh, hardened, and bond performance testing in the proposed project will be used to inform additional testing required for future field-scale deployment of CSA-based HESC overlays.
Task 5 – Interim and final reporting
The research team will submit timely quarterly reports and present annually at the Research Days meeting. Throughout the testing, the PIs will keep an open communication with the advisory panel members to make sure that the investigation is going in a direction that will be useful to the profession and to ensure rapid implementation of the results.
A final report, ABC-UTC Guide, and a 5-min video presentation will be prepared that summarize the methods used and the findings reached during the project. In addition, it is anticipated that the proposed work will result in at least one journal publication.
Research Team:
Principal Investigator: Travis Thonstad, Assistant Professor
Co-Principal Investigator: Fred Aguayo
Research Assistant: TBD