Early-Age Hydration of Low Carbon Cements, Part 2 of 2

Tuesday, November 5, 2024  1:30 PM - 3:30 PM, Grand BR Salon D

To fulfill the decarbonization roadmap established for the concrete industry, the average substitution levels of clinker by SCMs need to increase from about 25% currently to above 50%. This poses practical challenges in terms of early-age strength development and flowability properties of fresh concrete. This session will cover aspects of the early age reactivity, rheology, hydration and development of strength. It is aimed for professionalsand scientists working with different types od low-carbon cements. At the end of the sessions, the attendees will be able to identify strategies to tackle the outstanding challenges related to early age performance of these systems.

CO2 Uptake and Reactivity of Supplementary Cementitious Materials

Presented By: Prannoy Suraneni
Affiliation: University of Miami
Description: Abstract: Several supplementary cementitious materials (SCMs) with a range of calcium contents were exposed to CO2 to quantify their CO2 uptake. The uptake was studied at different moisture contents, temperature, and chamber RH. Thermogravimetric analysis (TGA) run before and after the CO2 chamber exposure was used to quantify uptake by original mass of material. The modified R3 test run before and after exposure was used to quantify reactivity. Some effect of the environmental conditions on the CO2 uptake was found but the order of the uptake did not change significantly. Steel slags and recycled cement materials showed the highest uptake, 10 – 25%. A significant change of the reactivity post-uptake was not noticed for most materials. Post uptake morphology was studied using advanced characterization techniques and linked to uptake and reactivity.

Carboaluminates: The Overlooked Key to High Performance, Low-Carbon LC3 Cements

Presented By: Franco Zunino
Affiliation: UC Berkeley
Description: Limestone calcined clay cements (LC3) represent a ternary blend that combines limestone and calcined kaolinitic clay, effectively replacing 50% or more of the traditional PC. With a 50% replacement level, LC3 achieves strength development comparable to that of conventional PC within 7 days of hydration. The LC3 technology offers the potential to reduce CO2 emissions by 30% to 40% per ton of cement produced compared to PC. During the first 72 hours of hydration, an enhanced precipitation of hemi and monocarboaluminate (AFm phases) is observed in these systems, associated with the high amount of alumina sourced from calcined clay, in contrast to other pozzolanic materials. Carboaluminates precipitate in large pores that remain after clinker hydration, filling space and contributing significantly to strength gain at early age. Approaches to enhanced the precipitation of carboaluminate appear then as a key strategy to offset the reduction of early-age performance seen in low-clinker binders.

Understanding Defect Chemistry of Alite Particles at Single-Atom Level

Presented By: Qi Zheng
Affiliation: UC Berkeley
Description: Crystallographic defects significantly impact cement hydration, especially in the initial dissolution stage where etch pit formation is influenced by surface defect intersections. Despite their importance, the precise nature of defects in cement particles has been elusive due to limited atomic-scale observations. Utilizing scanning transmission electron microscopy, this study elucidates defects in alite particles at the single-atom level. Identified defects include vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering within the alite crystal was analyzed using a single-atom recognition method. Our findings indicate that defects in cement particles serve as reactive sites during early hydration, facilitating initial dissolution and providing nucleation sites for hydration products. This research provides insights into cement defect formation at the single-atom level, offering opportunities for tuning the hydration process through defect engineering.

Accelerating Early Age Hydration with Low Clinker Cements

Presented By: Jason Weiss
Affiliation: Oregon State University
Description: A major objective for the concrete construction industry is to achieve carbon neutrality over the next two to three decades. Reducing clinker contents using fillers or SCMs represents one method that can be readily implemented. One drawback that can arise with these approaches however is slow reaction at early ages that can lead to strength issues in some applications. This package will review methods to accelerate reactions, examine what we mean by w/cm, and review a case where specification review could lead to more sustainable mixtures.

Industrial Production of Calcined Clays in the US: Experiences and Perspectives of IP/IT Cements

Presented By: Chengqing Qi
Affiliation: Ash Grove Cement Co
Description: Calcined clays are increasingly recognized as a viable substitute for fly ash and slags, which are anticipated to become less accessible in the coming years. Ash Grove has established an industrial facility for producing calcined clays in the United States, introducing this innovative material to the market. This allows contractors and project owners to explore formulations utilizing Type IP or Type IT cements. This presentation showcases insights, experiences, and perspectives drawn from a company actively engaged in calcined clay production. It also provides a critical assessment of ongoing challenges, emphasizing the necessity of industrial-academic collaborations to address them effectively.