Presentations will provide state-of-the-art information regarding workability and reactivity of low-carbon binders. Recently, many low-carbon binders have been developed from thermal, mechanochemical, leaching, and CO2 uptake processes. These can behave differently from conventional supplementary cementitious materials. High reactivity materials can result from such processes, but they often have high specific surface, and thus have high water demand. Thus, for engineered supplementary cementitious materials and other similar binders, balancing workability and reactivity is key. Presentations will address issues in designing mixtures containing low carbon binders in relation to balancing the requirements to achieve acceptable workability in one hand, and in the other hand, achieving the necessary reactivity. Blended materials, further processing, modifications of w/cm, use of specific admixtures, grinding aids, and other related strategies are of interest.
Learning Objectives:
(1) Identify the different types of low-carbon binders produced through thermal, mechanochemical, chemical leaching, and CO2 uptake processes and how they differ from conventional supplementary cementitious materials (SCMs);
(2) Explain the relationship between specific surface area, water demand, and workability in high-reactivity low-carbon binders;
(3) Evaluate strategies to optimize mixture proportions for balancing workability and reactivity in systems incorporating engineered SCMs and other low-carbon binders;
(4) Assess the effects of blended materials and further processing on the workability-reactivity balance of low-carbon binder systems.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Low-carbon Cement, High-impact Admixtures: Enabling the Balance Between Workability and Reactivity
Presented By: Cesar Constantino
Affiliation: Chryso
Description: Limestone Calcined-Clay Cement (LC3) represents a promising advancement in sustainable construction materials, offering significant reductions in clinker content and associated CO2 emissions. While LC3 formulations are gaining traction internationally, their development and implementation in the United States remain in early stages. One of the key enablers for successful adoption of LC3 cements lies in the formulation of admixtures tailored specifically to their unique chemical and physical characteristics to provide workability ranges that concrete producers and contractors expect with conventional cements.
This presentation will explore the current state of LC3 development in the U.S., with a particular focus on how next-generation admixtures are being designed to meet the demands of these novel cement systems. Attendees will gain insight into how these admixtures differ from conventional products used with traditional Portland cement, both in performance and in compatibility. Through comparative analysis and case studies, we’ll illustrate how optimized admixture solutions can not only improve workability and durability but also play a pivotal role in reducing the carbon footprint of concrete at scale.
Why Cements Incorporating Calcined Clays Exhibit a Shorter Open Time?
Presented By: Franco Zunino
Affiliation: UC Berkeley
Description: In cements that include calcined clays, such as LC3, a fast flow loss is observed. In general, this issue can be addressed by increasing the dosage of superplasticizers. However, this can lead to an unnecessarily high initial slump and, if the dosage is too high, a delay in early hydration and a consequent reduction in early age strength. Different theories have been proposed to explain this behavior, including a fast reactivity of the clay, flocculation, admixture intercalation, and absorption of water by clay particles. In this presentation, it will be shown that the flow loss observed can be explained by the fast increase in surface area in these cements. Moreover, evidence against a mechanism involving admixture intercalation in systems incorporating calcined kaolinite clays will be presented.
Enhancing Early-age Reactivity and Performance through Co-calcination of Limestone and Clay
Presented By: Narayanan Neithalath
Affiliation: Arizona State University
Description: The adoption of Limestone-calcined clay cements (LC³) represents a transformative shift in the cement and concrete industry, significantly reducing environmental impact while accelerating the transition toward carbon neutrality. While conventional LC³-50 systems achieve properties and strengths comparable to Portland cements (OPC), their early-age performance can be suboptimal. This study investigates the effect of co-calcining limestone (LS) and bulk clay containing kaolinite in varying mass proportions (1:1, 1:2, 1:3, 1:4) for a 50% clinker replacement. The co-calcination process follows a pre-defined thermal treatment condition, partially calcining LS to introduce an external metastable CaO source during hydration. A preliminary assessment of fresh-state workability guided the final mix design selection. The co-calcined binder systems exhibited enhanced in-situ portlandite (CH) formation at the early age, significantly accelerating pozzolanic reactions between LS and calcined clay to precipitate carboaluminates. The increased carboaluminate formation resulted in reduced critical pore size and a higher volume fraction of fine capillary pore, corroborating the observed early strength enhancement over conventionally processed LC³. Remarkably, this improvement was evident even in the system with lower calcined clay content.
Low-Clinker Binders with High Limestone Content with Optimized Workability and Reactivity: A Comparative Study of SCMs
Presented By: Kamal Khayat
Affiliation: Missouri S&T
Description: With the global cement industry under increasing pressure to reduce carbon emissions, the development of low clinker binder technologies has gained significant attention. This study investigates the performance of binder system blends containing 20% Portland Limestone Cement (PLC), 40%-50% limestone filler, and 30%-40% of different SCMs—specifically class C and F fly ash, bottom ash, ground granulated blast furnace slag (GGBFS), calcined clay, metakaolin, natural zeolite, pumice and so on. The primary objective of this study is to explore the interplay between early-age reactivity and fresh-state workability (particularly considering chemical admixture dosages) in these low-clinker systems depending on the SCM. Different superplasticizers and their rheological impact have been studied at water-to-binder ratio sensible compared to high clinker content binders. Comprehensive experimental testing was conducted, including slump flow, slump retention, rheological measurements, isothermal calorimetry, compressive strength development (at 1, 3, and 28 days), and phase composition analysis via XRD and TGA. The findings offer a comparative framework for optimizing limestone-rich systems that meet performance-based standard (e.g., ASTM C1157) and reduce carbon footprint, contributing to sustainable construction practices.
Overcoming Workability and Air Stability Issues in High Filler, Low Water (HFLW) Concrete Designs
Presented By: Denise Silva
Affiliation: Wr Grace
Description: High Filler, Low Water (HFLW) concrete is an alternative concrete technology that enables significant reduction (>50% weight reduction) of cement consumption by replacement with finely ground fillers, and water reduction that is achieved by using HRWR admixtures at saturation point. In these conditions, it is possible to achieve similar or even superior concrete mechanical performance, even at early ages. However, particle packing and concrete viscosity can lead to air instability and very low air content in the mixtures. This work describes design factors that contribute to air instability and workability issues in HFLW systems as well as measures taken to minimize the problem without significant impact on mechanical performance.
Blended Systems with OPC-Pozzolan-High Limestone Filler
Presented By: T Wattez
Affiliation:
Description: Even if LC3 binders enable a significant improvement regarding carbon footprint, it still contains a large amount of highly emitting OPC. Therefore, it is important to search for binders that provide an even more significant impact on carbon emissions, while maintaining sufficient mechanical properties and suitable rheology at concrete level. The approach proposed in this work consists in, still relying on ternary binders made of clinker-pozzolanic material-limestone filler, further reducing the clinker content of the binder and increasing the limestone filler content, compared to the classical LC3 composition. The pozzolanic material content was adapted to reach both adequate rheology and mechanical performance. Not only the raw materials were characterized in terms of chemistry and mineralogy but also by means of their specific surface (BET) and their intrinsic reactivity (ASTM C1897-20), as indication of their potential and impact in the ternary blends. So to ensure those low clinker – high filler blends develop adequate mechanical performance and concrete durability, a significant water content reduction is required (water-to-binder ratio decreased from 0.5 to 0.35) compared to classical concrete design, therefore posing a challenge from the rheology standpoint. For the three pozzolan sources tested, one calcined clay and two natural pozzolans, rotational rheometry was performed at concrete scale along with conventional ready-mix rheological measurements (slump and flow time) and mechanical performance evaluation. By reducing the clinker content from a LC3 scenario (50%) to low values (approximately 25%) and adjusting the pozzolan-to-clinker ratio so control rheology and long-term reactivity, we demonstrated that it is possible to produce concrete mixes displaying adequate levels of rheology for ready-mix applications and with significantly lower reactive binder (clinker plus pozzolan) content and therefore binder intensity.