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H=Hyatt Regency Dallas; U=Union Station

Open Topic Session, Part 2 of 2

Tuesday, October 25, 2022  4:00 PM - 6:00 PM, H-Reunion B

The purpose of this session is to offer authors/speakers an open forum for presentation of recent technical information that does not fit into other sessions scheduled for this convention.
Learning Objectives:
(1) Discuss bacterial cells for developing self-healing cement-based mortars;
(2) Investigate controlling parameters in design of FRP-slabs, and material specifications for FRP reinforcing bars;
(3) Analyze the fire resistance of hybrid fiber reinforced concrete;
(4) Explain the effects of fineness of harvested fly ash and ground glass pozzolans.

This session has been AIA/ICC approved for 2 CEU/PDH credits.


Non-Traditional Alumino-silicate Based Alkali-activated Mortars - Statistical Optimization of Solution Parameters and Processing Condition for Optimal Strength and Setting Time

Presented By: Roshan Muththa Arachchige
Affiliation: Clarkson University
Description: Fly ash and ground granulated blast furnace slag are the most widely researched precursors for producing alkali-activated binders. The recent shortage of good-quality fly ashes as supplementary cementitious material (SCM) prompted a rigorous search for alternative materials to replace the traditionally used SCM precursors for producing alkali-activated mortars. Three each calcined clays, ground bottom ashes, volcanic ashes, and two fluidzed combustion bed ashes, a total eleven materials, are evaluated as precursors for alkali-activated mortar. We identified several predictors of the properties like strength and flow, then adopted statistical tools like Design of Experiments (DoE), correlation analyses, and multiple linear regression analyses to build contour plots and regression models to predict the properties of the mortar. All the dominant variables that affect the properties of the alkaliactivated mortar are incorporated into statistical models so that the construction industry can efficiently utilize the knowledge about these new cementitious materials. Using the contour plots, the user can choose the solution parameters such as silica modulus, Na20 content, workability, the processing conditions such as heat cured vs. ambient cured, etc., for required strengths. The study also found that ten of eleven materials can be used as potential precursors for producing alkaliactivated binders that can produce a compressive strength of 4000 psi.


Meso-Scale Simulation of Chloride Penetration and Corrosion Induced Concrete Damage in Recycled Aggregate Concrete

Presented By: Jin Fan
Affiliation: New Jersey Institute of Technology
Description: Concrete made from recycled concrete aggregates is a multi-phases material made up of natural aggregate, an old interfacial transition zone (ITZ), an old mortar attached to the aggregates, a new ITZ, and a cementitious mortar. Recycled aggregate concrete (RAC) is a hetergeneous material that may contain varying levels of adhered mortar due to various processes associated with the production of recycled concrete aggregates. This study investigates the chloride penetration in RAC systems under five levels of adhered mortar content through meso-scale numerical simulations. In addition, the chloride introduced steel corrosion was modeled using a time-dependent multi-physics simulation framework, which considered the gradually increasing corroded area of the reinforcement. Finally, the corrosion product volume expansion was calculated and expansion induced concrete cracking was predicted through the meso-scale simulation. Simulation results showed that greater levels of adhered mortar led to faster chloride penetration and corrosion initiation. Non-uniform corrosion patterns were observed due to the impact of aggregate geometry. The local damage status of the concrete was also influenced by the individual mechanical properties of each phase of the material. Therefore, higher adhered mortar does not necessarily result in greater corrosion induced damage. This study using meso-scale modeling to predict time-dependent chloride induced concrete fracture provides a robust prediction method to understand the service life performance of reinforced RAC systems.


Understanding Metakaolin Pozzolanic Reactivity via Exfoliation & Dissolution

Presented By: Nishant Garg
Affiliation: University of Illinois at Urbana-Champaign
Description: Understanding and (potentially) enhancing the reactivity of calcined clays is a fundamental key to enable their widespread use as supplementary cementitious material (SCM). Considering that the pozzolanic reaction of these SCMs is essentially a dissolution-precipitation reaction, there has been a growing interest in measuring dissolution rates of calcined clays. While this reactivity has been studied in terms of dissolution kinetics, not much is known about the evolution of clay morphology upon dissolution. Here, we apply quantitiative imaging approaches to statistically quantify the extent of morphological changes that occur in dissolving kaolinite and metakaolin at multiple scales. Using in situ optical microscopy on clays undergoing dissolution, we find significant differences in the disintegration pattern for kaolinite and metakaolin. Moreover, using scanning electron microscopy, we report an evidence of layer thinning (of ~20nm) in metakaolin layers upon dissolution. Together, these new quantitative results on morphological changes in 1:1 clays upon dissolution could pave towards fundamental understanding of clay reactivity as well as widespread usage in cementitious systems.


A Comparative Study of Chemical and Physical Accelerators on Early Age Properties of Portland Cementitious Systems

Presented By: Abdul Peerzada
Affiliation: Clemson University
Description: The advancement in digital concrete technology, especially, additive manufacturing has changed the early-age requirements of cementitious systems. The cementitious system needs to have a very low stiffness (yield stress) in-line between the pump and the nozzle and on the other hand the printed matrix should gain stiffness rapidly for printing of subsequent layers. The control on the stiffness can be achieved through inline mixing of accelerators at the print head/nozzle. To choose the type and dosage of acceleartor which can give the desired stiffness control, a comprehensive study has been conducted. In this study, influence of two crystalline calcium silicate hydrate (C-S-H) nanoparticlebased accelerators, three tradition accelerators (chloride-based, two non-chloride) and shotcrete accelerators on early-age properties of Portland cementitious systems have been investigated through various techniques. The influence of rheology, hydration kinetics, setting time, phase evolution, compressive strength and restrained shrinkage have been studied for cement pastes and mortars with Binder fineness, water-binder ratio, accelerator type and dosage, sand-to-cement ratio, and temperature as variables. In addition to that, the study also investigates the efficacy of the chemical admixtures added inline. Results from the study show the effectiveness of the accelerators is a function of curing temperature, water-cement ratio, binder fineness etc. As the parameters are changed, the interaccelerator effectiveness changes.


Introducing New Biopolymers as Viscosity-Modifying Admixtures to Improve the Performance of Cement-Based Materials

Presented By: Jose Gonzalez-Avina
Affiliation: Universidad Autonoma de Nuevo Leon
Description: An experimental investigation was carried out to evaluate the performance of various biopolymers as viscosity-modifying admixtures (VMA) in cement-based suspensions. These include five natural gums, including tragacanth, almond, welan, guar, and locust bean, as well as one solution of a natural extract of brown seaweed. The effects of the preparation method, type, and dosage of the investigated biopolymers, as well as their interaction with superplasticizer admixtures on rheological behavior, hydration kinetics, stability, and compressive strength of the cement paste mixtures was evaluated. According to the experimental results, the pre-dispersion and pre-dispersion/pre-hydration methods showed more signifcant influences on the rheological performance of the investigated cement pastes compared to their use in a dry state. Moreover, the investigated bio-admixtures led to a shear-thinning response with a higher yield stress, apparent viscosity, and plastic viscosity, as well as higher rigidty and structural build-up than the reference mixture. On the other hand, the use of bio-admixtures resulted in higher stability, reflected by lower forced-bleeding values of the investigated cement paste mixtures. Furthermore, the investigated bio-admixtures mainly prolonged the dormant period and influenced the second and third hydration peaks. The use of bio-admixtures influenced the compressive strength at an early age. In addition, the performance of the bio-admixtures in combination with the superplasticizers was found dependent on their interaction and compatability.


Pore Solution in Concrete - Why it's Important and a New Way to Access it

Presented By: Atolo Tuinukuafe
Affiliation: Oregon State University
Description: The pore solution of concrete is an influential parameter for durability both in terms of performance and evaluation. Pore solution alkalinity effects concrete degradation mechanisms like reinforcement corrosion or alkali-aggregate reactions. The pore solution also plays a role in electrical measurements of concrete, which test methods for evaluating the transport properties often rely on. With increasing usage of supplementary cementitious materials and alternative cement chemstries, understanding the pore solution is more important than ever. A new method for determining the alkali concentrations of the pore solution through ex-situ leaching tests is presented and compared to existing methods.

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