Concrete Laboratory Capabilities

Banner of Portland Limestone Cement — Portland Limestone Cement: This project provides background, anecdotal implementation challenges, best practices, variability, reactivity, and the implications of characterization regarding Portland Limestone Cements. Click the title for more information.

Portland limestone cement (PLC) has been increasingly adopted in the United States since 2021 in effort to reduce the environmental impact of cement. To help facilitate the adoption of PLC, we have developed a PLC TechNote that describes the background, history, engineering principles, case studies, anecdotal challenges, and best practices. This PLC TechNote can be found at: https://highways.dot.gov/research/publications/infrastructure/FHWA-HRT-23-104.

Given that large-scale, widespread production of PLC in the United States began recently, we are investigating the variability of PLCs in terms of physical characteristics, microstructural characteristics, and reactivity. This work will also be correlated with PLC-concrete performance to provide indications of what performance, or differences in performance compared to what was expected from concretes with Type I/II cement, can be expected from the PLC-concrete depending on PLC characteristics.

Repair Materials

High-early strength (HES) concrete mixtures are used as (typically full-depth) repair materials in concrete infrastructure applications. HES is desired in effort to minimize closure times and therefore reduce effects on traffic. However, these mixtures are frequently designed only based on strength gain rate criteria, which results in poor durability characteristics and, eventually, premature failures that require additional repairs.

During this study, we investigated the impact of accelerating admixtures on the electrical properties of ordinary portland cements. By understanding potential impacts of admixtures on electrical properties, we can inform interpretation of durability test results such as resistivity that help us characterize the concrete mixture. The study details, results, and conclusions for which can be found at: https://www.sciencedirect.com/science/article/pii/S095894652200244X.

Maturity concepts were used to estimate the strength development of HES concrete mixtures using isothermal calorimetry. The heat released during cement hydration leads to increased rates of strength gain. Therefore, neglecting to account for heat of hydration within a repaired concrete section can severely underestimate the strength of the repair and contribute to overdesign of concrete mixture cementitious contents that increase susceptibility to material degradation mechanisms.

HES concrete mixtures were evaluated using AASHTO R 101 concepts to improve resistance to freeze-thaw damage. The risk of freeze-thaw damage can be reduced in HES concrete mixtures by reducing paste volume and partially replacing cement with reactive supplementary cementitious materials (SCMs). These strategies may work best with lower opening strength requirements.

Further, mortar mixtures incorporated portland limestone cement and set accelerators were evaluated for their early-age strength and porosity to investigate the use of PLC in HES mixtures. PLC when combined with an accelerator and mixed with a low water content was able to generate high early strength compatible with select state highway agency requirements.

Embodied carbon emissions of HES mixtures have been estimated to evaluate the effects of increased cementitious and admixture contents on the estimated A1-A3 global warming potentials.

Evaluation of Novel Cementitious Materials and Test Methods

A banner of Cementitious Materials with a graphic to the left and activities on the right separated by a vertical line — Evaluation of Novel Cementitious Materials and Test Methods: This project involves evaluating novel materials, characterizing their properties, and developing and modifying test methods to enhance testing as needed when existing methods do not apply.

Our team along with the FHWA Mobile Concrete Technology Center (MCTC) assisted with testing the innovative materials placed during the MNROADs high-volume road reconstruction summer of 2022 (https://www.dot.state.mn.us/mnroad/). The MCTC performed fresh material properties’ characterization testing including slump, box test, volumetric air content, super air meter, unit weight, Phoenix testing, and microwave testing, as well as semi-adiabatic calorimetry, compressive strength, and resistivity testing. In the Concrete Lab, we performed resistivity testing, formation factor testing, autogenous shrinkage testing, isothermal calorimetry, thermogravimetric analysis, and reactivity testing.

In addition to working with the innovative MNROADs materials, we are additionally studying freeze-thaw of concretes incorporating natural pozzolans, shrinkage and durability of concretes with colloidal silicas, and reactivity and durability of carbon-enriched supplementary cementitious materials. Coming work will investigate other novel commercially available admixtures and their effects on concrete performance.

Thorough investigations of the physical and microstructural characteristics, as well as mechanical and durability performance of calcined clay blended cements are underway. Data science and experimental techniques will be applied to estimate optimal proportioning of calcined clay blends.

Sustainability Assessment of Concrete Materials

A banner — Sustainability Assessment of Concrete Materials: This project uses research to advance the understanding, data collection, and implementation of sustainability for cement and concrete. Click the title for more information.

The FHWA Mobile Concrete Technology Center (MCTC) provides performance data, including workability, compressive strength, and resistivity metrics, for various field-implementable concrete mixtures. Our team at the Concrete Laboratory assists with these measurements and conducts a preliminary assessment of the A1-A3 global warming potentials that may be associated with the concrete mixtures. The sustainability and performance metrics are then correlated, as described at: https://onlinelibrary.wiley.com/doi/abs/10.1002/suco.202200634. The 28-day and 56-day compressive strengths of the concrete mixtures show no visible correlation with their estimated A1-A3 global warming potential. The durability, by proxy of resistivity, tends show improvement for concrete mixtures with associated reduced carbon emissions compared to those with higher global warming potentials, typically because of supplementary cementitious materials inclusions.

In addition, a member of our team is involved in the development of product category rules that apply to cements and concretes and provides guidance on reducing concrete carbon emissions.

Ultra-High Performance Concrete (UHPC)

The Concrete Laboratory works with the TFHRC Structures Laboratory to perform materials research on UHPC. We are involved in evaluating test methods for their application to UHPC materials, assisting with guidance development for testing and constructing UHPC. Some of our research on UHPC-class materials thus far includes:

Properties and Behavior of UHPC-class materials: