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.. The audience would be researchers, material suppliers, and practitioners.
Learning Objectives:
(1) Compare the performance of various chemical admixtures, grinding aids, and other additives in improving the workability of high-reactivity, high-surface-area binders;
(2) Discuss how modifications to water-to-cementitious materials ratio (w/cm) influence both fresh and hardened properties of low-carbon binder mixtures;
(3) Analyze case studies or experimental results demonstrating successful approaches to achieving adequate workability without compromising reactivity in low-carbon binder systems;
(4) Formulate guidelines for selecting and proportioning low-carbon binders in practical applications to meet both sustainability goals and performance requirements.
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.
Rheological Evolution of Alkali-Activated Low-Grade Metakaolin Pastes
Presented By: Sriramya Nair
Affiliation:
Description: The early age rheological behavior of low-grade metakaolin-based calcined clays (LCC) mined from different geographical locations in the US was studied. Small amplitude oscillatory shear (SAOS) was used to monitor the structural build-up of these alkali-activated pastes. Time sweeps of the storage modulus, loss modulus and the phase angle are used to understand their viscoelastic properties and determine their initial setting times. Four distinct rheological stages were identified with the end of stage III corresponding to the Vicat needle initial set time tests. Isothermal calorimetry links the rheological development of this cementitious system to its extent of reaction, while time-resolved FTIR captures its chemical evolution. Together, these chemical, mechanical, and rheological results provide a comprehensive understanding of the early-age behavior of these low grade metakaolin based calcined clays. The study also demonstrates that SAOS offers a material-efficient, low-variability alternative to traditional setting time methods, while simultaneously yielding deeper insights into the structural evolution of emerging low-carbon binder systems.
Balancing Workability and Reactivity of Low-carbon/Low-clinker Binders
Presented By: Apoorv Sinha
Affiliation:
Description: Achieving synergy between reactivity and water demand of SCMs
Low carbon or low clinker binders containing high volume fillers or SCMs are very useful in lowering the embodied energy of the concrete and valorizing waste or byproducts. However, most low-clinker binders require the fillers or SCMs to be modified both physically and chemically to enhance their reactivity so that they conform to the strength requirements of conventional high-clinker binders. These modifications usually involve pulverization to increase the specific surface area for more pozzolanic reaction sites and/or calcination for the dehydroxylation to increase the reactivity. Inadvertently, these procedures also increase the water demand of the binders, affecting the workability of concrete. To avoid this problem, carbon upcycling technologies process, CO2-assisted physical and mechanical modification of SCMs can help achieve high reactivity while not affecting or even improving the water demand of the binders. Basic oxygen furnace slags, electric arc furnace slags, clays, and shales are treated using the carbon upcycling technologies process and their paste and mortar properties are examined. These preliminary results show a possible solution to achieving synergy between reactivity and water demand.
Early Reactivity and Rheology of Low Clinker Materials - Impact of Specific Gravity and Absorption
Presented By: Fengyin Du
Affiliation:
Description: Supplementary cementitious materials (SCMs) are used to reduce the clinker content of concrete. Natural pozzolans (NPs) have been used for nearly a century and have recently gained renewed attention to response the decreasing traditional SCMs availability. The variability of natural pozzolan composition, reactivity, and specific gravity will be evaluated using pozzolanic reactivity, shear rheology and isothermal calorimetry.
Workability, Reactivity, and Strength of Mechanochemically Activated Supplementary Cementitious Material Systems
Presented By: Sofiane AMROUN
Affiliation: University of Miami
Description: Mechanochemical activation is a technique in which crystalline, inert materials can be transformed into amorphous, reactive supplementary cementitious materials. One of the interesting aspects of mechanochemical activation is that it results in a broad particle size distribution and in the creation of relatively spherical particles. Thus, while the specific surface area is high, the workability is not always negatively affected. We show results from the mechanochemical activation of a range of materials and discuss reactivity, strength, and workability in powder, paste, and mortar systems.
Development of UHPC with Low Carbon Cements - The Innovation Approach of Sincere Project
Presented By: Estefania Cuenca
Affiliation:
Description: A comprehensive experimental program has been developed in the framework of SINCERE project funded by EC HEurope (Grant agreement: 101123293) whose main objective is to develop more sustainable and energy efficient concretes without renouncing to the structural performance. To this purpose, several concretes have been produced replacing CEM I cement by low carbon cements (CEM IV, LC3) natural pozzolan as well as concretes using phase change materials for obtaining a better energy efficiency]. Challenges i guaranteeing workability have been first of all tackled. All the concretes herein produced were characterized in fresh state by means of the slump test and in hardened state by means of mechanical tests such as autogenous and drying shrinkage, compressive and flexural strength tests, the last one was particularly interesting for the mixes including amorphous fibres. For the mechanical characterization prismatic specimens (40x40x160mm) were produced, as well as thin specimens (500 x 100 x 30mm) for flexural strength characterization and self-healing assessment obtained from slabs (1000mm x 500mm x 30mm) in order to also evaluate the influence of the fibre orientation on the mechanical response as shown in [2]. The preliminary results of the experimental program showed that concretes with partial replacement of cement by natural pozzolan and concretes with phase change materials reached compressive and flexural strength values comparable to reference concrete, only a slight worse workability was observed compared to the reference one.