About the research
It is becoming increasingly apparent that it is necessary to explore alternative options for cement and concrete production used in public infrastructure to reduce carbon footprint. One possible process is to bubble CO2 in the fresh concrete during production to sequester CO2 and possibly to reduce cement content in the concrete without compromising system performance. Concrete with reduced cement content will exhibit reduced shrinkage reducing the risk of early age cracking. Other CO2 sequestration techniques such as dissolving it in batch water and manufacturing CO2enhanced aggregates also need to be assessed.
Confirming these benefits would be a breakthrough in simultaneously reducing the CO2 footprint while enhancing concrete performance.
Two questions are therefore raised – how much CO2 is sequestered, and what are the effects on the performance of the pavement? The goal of this research is to address these questions through testing, measurements, and the observation of concrete made with CarbonCure technology. The work will also include an assessment of the reduction of the CO2 footprint compared to control mixtures based on determining the amount of CO2 bound in the mixture as well as potential changes in maintenance needs of the pavement over the life of the pavement under traffic and environmental exposure.
About the research
The use of roundabouts in rural areas of the US is growing rapidly. For roundabouts constructed with concrete pavement, joint layout can be especially challenging. To reduce the need for sophisticated joint layouts, consideration is being given to constructing roundabouts without joints and instead using structural fiber-reinforced concrete (FRC) to bridge any cracks that might occur. In 2018, Minnesota’s first jointless FRC pavement roundabout was constructed at the intersection of Minnesota Trunk Highway 4 and County State Aid Highway 29.
The National Road Research Alliance (NRRA) sponsored a study to document the construction and performance of Minnesota’s first jointless FRC roundabout. One of the key objectives was to carry out a three-year performance monitoring regimen of the roundabout to better understand its in-situ performance when exposed to traffic loading and environmental conditions. This report documents the third-year performance of the roundabout as per the requirements of Task 3 of the work plan.
About the research
Mixture proportioning generally uses a recipe based on a previously produced concrete, rather than adjusting the proportions based on the needs of the mixture and the locally available materials. As budgets grow tighter and environmental regulations increase, an emphasis on lowering the carbon footprint, is focusing attention on making mixtures that are more efficient in their usage of materials yet do not compromise engineering performance. A means of reducing environmental impact is to reduce the amount of binder in the mixture.
MnROAD is planning to construct several cells using reduced cementitious content mixtures, with the aim of monitoring the constructability and longevity of the concrete. The proposed work has been designed to identify the behavior and performance of concrete paving mixes with low cementitious content, i.e., between 475 to 500 lb/CY, and lower cementitious content, i.e., 430 to 470 lb/CY.
The objectives of this study included:
- Investigate the early-age characteristics (i.e., placement issues, slow strength gain) of concrete paving mixes containing low and lower cementitious content
- Assess causes of, or potential for, durability issues with very low cementitious content
- Identify effect of reduced cementitious content on long term serviceability and economics of concrete pavements (i.e., benefits of reduced shrinkage)
- Develop recommended specifications, mixing, and placement practices for the use of very low cementitious content concrete paving mixes
About the research
This project was performed to evaluate the performance of recycled aggregates and large stones used in the aggregate base/subbase layers of pavement systems and provide recommendations regarding pavement design and material selection.
As part of this project, 11 test cells were built at MnROAD to evaluate the impact of recycled aggregates and large stones on the long-term pavement performance via a series of laboratory [permeability, soil-water characteristic curve (SWCC), stereophotography (image analysis), gyratory compaction, and resilient modulus (MR) tests] and field tests [intelligent compaction (IC), falling weight deflectometer tests (FWD), rutting measurements, international roughness index (IRI) measurements, light weight deflectometer (LWD) tests, and dynamic cone penetrometer (DCP) tests]. In addition, a pavement mechanistic-empirical (ME) design approach was used to provide recommendations for designs of pavement systems containing recycled aggregate base (RAB) and large stone subbase (LSSB) layers.
Overall, this project found that finer recycled concrete aggregate (RCA) material would be preferable to coarser RCA material and a blend of RCA and recycled asphalt pavement (RAP) materials would be preferable to natural aggregate for aggregate base layers. RCA materials provided better performance than the blend of RCA and RAP materials, indicating that RCA materials would be preferable to the blend. For LSSB layers, this project found that geosynthetics would be required to successfully construct thinner LSSB layers. Overall, thicker LSSB layers provided better structural support than thinner LSSB layers both in the short term and the long term.