Current State of the Discussion on Pyrrhotite in Concrete
Presented By: Jamison Langdon
Affiliation: Braun Intertec Corporation
Description: Recent legislative efforts to mitigate pyrrhotite in concrete are beginning to take shape in the form of limits on sulfide in the aggregates being used. A quick overview of some of those efforts will be presented as well as provide a bit of technical guidance on how and where pyrrhotite naturally occurs.
Evaluating Damage Generation and Propagation of ASR Affected RCA Concrete
Presented By: Cassandra Trottier
Affiliation: University of Ottawa
Description: The use of recycled concrete aggregates (RCA) is gaining interest in the industry due to the pressure to adopt more sustainable practices; yet, concerns regarding the potential for further ASR damage in concrete made with RCA remain. In the current literature, the original extent of the ASR damage is often unknown when the concrete is crushed into RCA particles, therefore, inconsistencies regarding the potential for further ASR in concrete made with affected RCA are observed in the literature. RCA is a multi-phase material consisting of the original virgin aggregate (OVA) and residual mortar (RM), which is further divided into residual sand and cement paste. ASR may, therefore, originate from the reactive OVA or residual sand, and its extension into the cement paste depends on the extent of reaction/damage. This work evaluated the secondary damage generation and propagation in concrete made with RCA presenting two levels of initial damage (i.e., 0.05% and 0.30% of expansion, representing a concrete returned to the plant and demolished concrete, respectively) induced by either reactive coarse OVA or residual sand. A microscopic tool (i.e., Damage Rating Index - DRI) was used for the analysis, while distress features (i.e., cracks) were measured in counts per 100 cm2, length, width, and types of propagation to characterize the distinct damage patterns induced by various types of RCA affected by ASR.
Influence of Coarse Aggregates Mineralogy on Long–Term Durability Properties of Optimized Concrete Mixes
Presented By: Shuyah Tani Ouoba
Affiliation: University of Arkansas
Description: As aggregates constitute more than 60% of concrete volume, their impact on concrete durability is significant. However, the aggregate component of concrete is generally thought of as inert filler. This study examines the influence of coarse aggregate mineralogy on long-term concrete properties such as drying shrinkage and bulk resistivity. Concrete mixtures were prepared according to the Arkansas Department of Transportation specifications using Type 1L cement; the cement content was progressively reduced, and fly ash was used. Aggregate gradation methods were employed to optimize mix proportions with reduced cement contents. Additionally, a new test procedure for assessing the potential for Alkali-Silica Reaction of Aggregates is compared to traditional test methods for the different species of aggregates considered.
Alkali-Aggregate Reaction in Concrete (AAR): Current Challenges and Research Needs
Presented By: Leandro Sanchez
Affiliation: University of Ottawa,
Description: In 2024, the International Conference on Alkali-Aggregate Reaction in concrete (ICAAR) was held in Ottawa, ON, Canada. ICAAR-2024 was the 17th international conference on the topic; this conference normally takes place every 4 years and in 2024, the 50th anniversary of the event was celebrated. After so many years of in-depth research, numerous protocols, guidelines, and standards have been produced to help avoiding, mitigating, assessing, rehabilitating, and managing concrete infrastructure affected by AAR. However, there are still plenty of doubts and unknowns on both scientific aspects and practical procedures. The purpose of this work is to highlight my personal impressions after the 17th ICAAR, pointing out some of the current challenges and research needs and opportunities on the topic.