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This Week's Featured Presentation

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Concrete Modulus of Elasticity—How High is High (ACI Spring 2018 Convention, Salt Lake City, UT)
The number of high-rise projects requiring high modulus of elasticity has increased substantially over the past two years in the Chicago construction market. With a number of jobs completed or underway, VC Prairie Material has extensive experience producing and delivering high modulus of elasticity concrete to meet specifications and contractor requirements. However, achieving modulus of elasticity specifications, while maintaining expected workability and pumpability of concrete, has forced VC Prairie Material to evaluate common production practices. Material selection, mix proportioning, batching procedures, and even internal testing procedures were adapted to better control new mix designs and consistently achieve required specifications. The collective experiences and challenges that arose throughout the different projects with modulus of elasticity specifications including interactions with contractors will be presented.

Upcoming Presentation

September 16 – 22

Mechanical Tools to Assess Damage in Concrete Affected by AAR and Combined Mechanisms
by Leandro Sanchez, University of Ottawa

Session details

Hot Topic Session: Durability of Concrete: Aggregate Matters and Alternative Test Methods (ACI Spring 2019 Convention, Québec City, QC, Canada) Deleterious chemical reactions of aggregates in concrete are among the various mechanisms that can conduct to regular or recurring repairs or eventually the replacement of the affected elements/structures. Assessing concrete degradations in structures starts with a reliable diagnosis process performed by a concrete professional. Alkali-aggregate reaction (AAR) or any other aggregate degradation mechanism is a gradual process and determining the current condition and the potential for further damage is rather complex. Testing methods for accurate condition assessment and determination of reaction stage are limited and a deep understanding of the reactions involved and of their impact on the mechanical properties of the affected concrete are crucial in this process. Testing methods for prognosis are generally performed under accelerated laboratory conditions and their correlation with field exposure is often not very accurate. Relatively “new” reactions in concrete such as internal sulfate attack associated with sulfide-bearing aggregates need better understanding and also methods to detect reliably and accurately reactive aggregates. Therefrom, relatively new/upgraded test methods (petrographic and mechanical) for diagnosis of current level of damage due to AAR or other aggregate reactions are presented in this session. Results on the correlation between field exposed concrete blocks and laboratory results for the prevention of AAR are also presented accompanied by new information on the challenges of evaluating the deleterious potential of sulfide-bearing aggregates.

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