Tuesday, March 31, 2026 4:00 PM - 6:00 PM, LAX
Reducing clinker in concrete by paste volume reduction and increase in SCM replacement can lead to significant changes in plastic properties of concrete such as bleed rate, viscosity and set time. If not properly addressed, these changes can increase the risk of early age cracking, especially in slab applications. This session discusses these potential changes and how to mitigate the risk of cracking.
Learning Objectives:
(1) Understand how reducing clinker in mixtures can potentially affect plastic properties of concrete mixtures;
(2) Understand how changes in plastic properties can lead to early age distresses, if not accounted for;
(3) Review best practices on how to modify concrete mixtures to mitigate the risk of early-age distresses;
(4) Review best construction practices to further mitigate the risk of early onset of distresses, especially in SOG applications.
Plastic Shrinkage Cracking: A Race Between Shrinkage Stress and Tensile Strength
Presented By: Kenneth Hover
Affiliation: Cornell University
Description: Although we distinguish between plastic shrinkage and drying shrinkage cracking, they both occur when stress induced by restrained shrinkage exceeds the time-dependent development of concrete’s tensile strength. Early-age concrete is easily deformed (or “plastic”) and has a low tensile strength, with resulting “cracks” resembling tearing or pulling taffy. If we cure the concrete effectively enough and long enough to delay shrinkage through and beyond the “plastic” stage and promote greater tensile strength at the surface, the hardened concrete is more resistant to tension, yet more brittle, allowing sharper cracks to form at higher values of shrinkage stress. Although “autogenous” shrinkage starts in the readymix truck, shrinkage at the concrete surface begins when the rate of surface evaporation exceeds the rate at which bleeding brings water to that surface. That apparently simple concept (now 72 years old) is complicated by: 1.) Concrete surface texture and variable microclimate, resulting in highly variable evaporation within the same job site during the same placing and finishing operation. 2) Our inability to accurately measure or predict evaporation, and 3.) Variability of bleeding rate and its duration (all concrete eventually has a bleed-rate of zero) depending on cementitious materials, mixture proportions, depth of concrete, and consolidation.
How to Evaluate Cementitious Materials Quickly
Presented By: Tarek Khan
Affiliation:
Description: In an effort to quickly assess multiple raw materials and their effects on concrete properties, especially early-age properties, Master Builders refined a testing protocol to use mortar mixes to screen materials. The properties developed in these mortar tests compare well when compared to concretes made with the same materials as will be shown in case studies.
Stiffening, Setting and Bleeding in Low Clinker Materials
Presented By: Jason Weiss
Affiliation: Oregon State University
Description: This presentation will re-examine early works on settlement, stiffening and bleeding in fresh cement pastes. The work will be extended to discuss how these works can be reinterpreted during the movement to lower clinker mixtures. The work will provide both a theoretical and practical background to plastic shrinkage in modern cementitious systems. Research needs will be identified.
Placing PLC Concrete
Presented By: Kyle Kammer
Affiliation: CONCRETE STRATEGIES
Description: PLC has presented many challenges to the industry in recent years. Along with the change of materials, many things have shifted and necessitated change in the way concrete is placed. This presentation will include, some of the preconstruction items to look at and consider will be highlighted, several changes to processes of placement will be discussed as well as the importance of trial batches and adequate test placements.
Experiences Placing and Finishing PLC
Presented By: Robert Young
Affiliation: Lithko Contracting
Description: This presentation will discuss the adverse effects technicians have noticed in the field and discuss the adjustments in products and processes to overcome these when placing PLC. Specifically discuss mix designs and additives with their effects at the time of placement and move specifically to finishing flat work containing PLC. Directives given on techniques, timing and products post placement.