Processing of Inorganic Silicates for Arduous Environments

The work herein discusses a variety of processing techniques for silicates utilized in the development of infrastructure. The first half of the work is focused on the chloride durability of silicious alkali activated cementitious binders, focusing on the chloride binding potential of zeolitic phases (i.e., chabazite and faujasite) and the use of chemical admixtures to direct their formation. It is shown that these zeolites can uptake chlorides, and their formation can be successfully promoted. The second half of the dissertation is focused on in-situ resource utilization for exploration and habitat building. The work pertains to the development of ceramic and glass materials, their characterization and manufacture. Sintered ceramics and glasses are produced via additive manufacturing and conventional sintering and melting methodologies with properties suitable for construction.</p

Zeolite Adsorption of Chloride from a Synthetic Alkali-Activated Cement Pore Solution

This work presents experimental evidence that confirms the potential for two specific zeolites, namely chabazite and faujasite (with a cage size ~2&ndash;13 &Aring;), to adsorb small amounts of chloride from a synthetic alkali-activated cement (AAC) pore solution. Four synthetic zeolites were first exposed to a chlorinated AAC pore solution, two faujasite zeolites (i.e., FAU, X-13), chabazite (i.e., SSZ-13), and sodium-stabilized mordenite (i.e., Na-Mordenite). The mineralogy and chemical composition were subsequently investigated via X-ray diffraction (XRD) and both energy- and wavelength-dispersive X-ray spectroscopy (WDS), respectively. Upon exposure to a chlorinated AAC pore solution, FAU and SSZ-13 displayed changes to their diffraction patterns (i.e., peak shifting and broadening), characteristic of ion entrapment within zeolitic aluminosilicate frameworks. Elemental mapping with WDS confirmed the presence of small amounts of elemental chlorine. Results indicate that the chloride-bearing capacity of zeolites is likely dependent on both microstructural features (e.g., cage sizes) and chemical composition.</p

A Review of chloride transport in alkali-activated cement paste, mortar, and concrete

In this review, we present a meta-analysis of experimental data concerning chloride transport in alkali-activated cement (AAC) paste, mortar, and concrete. Sixty-six (66) studies were reviewed with a primary focus on measurement methodology, mixture design, and process-structure-property relationships related to microstructural development (i.e., porosity, pore size distribution), chloride diffusion, and chloride binding. In general, this review elucidates that aluminosilicate precursors with high amorphous contents and increased fineness that are activated with solutions of high alkalinity (Na:Al ≥ 0.75) and silica content (Si:Al ≥ 1.5) in combination with heat-curing (>40 °C) lead to microstructural characteristics (e.g., binder gel chemistries) that improve chloride durability, even though interactions between these factors are not well understood. Descriptive statistics of reported AAC paste porosities and AAC concrete chloride diffusion coefficients by aluminosilicate precursor (i.e., fly ash, slag, calcined clay, natural clay, binary blends) are presented, along with a summative discussion regarding new opportunities for advancing current scientific understanding of chloride transport in AACs

Thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel particles improve workability loss and autogenous shrinkage in cement paste

In this work, we show that non-superabsorbent, thermo-responsive poly(N-isopropyl acrylamide) (PNIPAM) hydrogel particles (&lt; 250&nbsp;&mu;m) can reduce autogenous shrinkage in cement paste and improve early-age stiffening that can be caused by traditional superabsorbent polymers (SAPs). Swelling measurements in DI water and cement filtrate solution suggest that SAP-induced early-age stiffening is caused by its super-absorbency in low-ionic solutions &ndash; a behavior not exhibited by non-superabsorbent PNIPAM. Addition of PNIPAM resulted in a 29% and 60% reduction in autogenous shrinkage strain at 14 days when used alone (0.3&nbsp;wt% PNIPAM) and in combination with SAP (0.15% PNIPAM, 0.15% SAP), respectively, compared to a Control with no polymer addition. Furthermore, an addition of 0.3 wt.% PNIPAM exhibited a &sim;29% and &sim;37% decrease in static yield stress compared to a Control and 0.3&nbsp;wt% SAP-modified cement pastes, respectively. Taken together, the results provide initial evidence to suggest that the use of hydrogels as internal curing agents may not necessarily require super-absorbency to reduce autogenous shrinkage. Non-superabsorbent hydrogels, like PNIPAM, may help reduce autogenous shrinkage while alleviating the effects of SAP-induced early-age stiffening. &nbsp;</p

Carrageenan-based superabsorbent biopolymers mitigate autogenous shrinkage in ordinary portland cement

We report the synthesis and characterization of biobased superabsorbent copolymers from κ-carrageenan and poly(acrylic acid) that mitigate autogenous shrinkage in ordinary portland cement paste. Synthesized via free radical graft polymerization, the biobased superabsorbent polymers (SAPs) were characterized with regard to their thermochemical properties and swelling behavior in both aqueous and ionic solutions. The biobased SAPs were incorporated into cement paste to investigate their ability to mitigate autogenous shrinkage cracking in high-performance concrete. Results demonstrate that the biobased SAPs absorb up to 438 and 94 [g/g] (by mass) in aqueous and ionic solutions, respectively, after 24 h. Furthermore, the biobased SAPs were successful in mitigating shrinkage in low water-to-cement ratio pastes. While the control paste exhibited negative strain and ultimate shrinkage cracking, the samples containing biobased SAP experienced net-positive expansion during cement hydration

Influence of Powder Type on Aerosol Emissions in Powder- Binder Jetting with Emphasis on Lunar Regolith for In-Situ Space Applications

Powder-binder jetting is an additive process with applications for manufacturing complex geometric structures, such as lightweighting, mold making, and in-situ resource utilization (ISRU) for space applications. With this technique, a powder feedstock is spread across a bed during which aerosol may be released leading to human health implications. This study characterizes airborne powder emissions for three powders of varying particle diameters and composition: Hydroperm® gypsum plaster, Lunar Highland Simulant regolith (LHS-1, a lunar soil simulant), and Zeolite 13X (a molecu- lar sieve). Bulk powder D50 values were 22 μm for Hydroperm®, 304 μm for LHS-1, and 3.85 μm for Zeolite. Total particle emission rates were (5.4 ± 0.96) × 105 min−1 for Hydroperm®, (1.0 ± 0.28) × 106 min−1 for Zeolite, and (2.2 ± 0.82) × 107 min−1 for LHS-1. An emission factor was developed normalized to the volume of powder spread resulting in emission factors of 2.8 ±0.85 min−1mm−3 for Hydroperm®, 220 ±72 min−1mm−3 for LHS-1, and 5.0 ±0.24 min−1mm−3 for Zeolite. This indicates that particle emissions from powder-binder jetting machines with a constant spreading mechanism can vary widely depending solely on powder type. In the In the experimental enclosure where testing took place, LHS-1 PM10 concentrations exceeded 8-hour TWA PEL OSHA standards for crystalline silica by 6-fold indicating that air quality should be a strong design consideration for 3D printing for lunar ISRU. With lower gravitational settling effects, Lunar particulate concentrations 20 m away from the printer were modeled to be 330% higher than on Earth. This study suggests that powder size, morphology, and powder chemistry should be considered holistically when determining emission concerns for new powders in powder-binder jetting. This study also suggests particular attention should be paid to aerosol emissions in a Lunar environment

Recent progress in low-carbon binders

The development of low-carbon binders has been recognized as a means of reducing the carbon footprint of the Portland cement industry, in response to growing global concerns over CO2 emissions from the construction sector. This paper reviews recent progress in the three most attractive low-carbon binders: alkali-activated, carbonate, and belite-ye'elimite-based binders. Alkali-activated binders/materials were reviewed at the past two ICCC congresses, so this paper focuses on some key developments of alkali-activated binders/materials since the last keynote paper was published in 2015. Recent progress on carbonate and belite-ye'elimite-based binders are also reviewed and discussed, as they are attracting more and more attention as essential alternative low-carbon cementitious materials. These classes of binders have a clear role to play in providing a sustainable future for global construction, as part of the available toolkit of cements

Utility of genetic algorithms for solving large scale construction time/cost trade-off problems

The Time/Cost Trade-off (TCT) problem has long been a popular optimization question for construction engineering and management researchers. The problem manifests itself as the opti- mization of total costs of construction projects that consist of indirect project costs and individual activity costs. The trade-off occurs as project duration and, as a result, indirect project costs de- crease with reduced individual activity duration. This reduction in individual activity duration is achieved by increasing resource allocation to individual activities, which increases their costs to completion. Historically, metaheuristic solutions have been applied to small scale problems due to computational complexities and requirements of larger networks. In this paper, we demonstrate that the metaheuristic approach is highly effective for solving large scale construction TCT problems. A custom Genetic Algorithm (GA) is developed and used to solve large benchmark networks of up to 630 variables with high levels of accuracy (<3% deviation) consistently using computational power of a personal computer in under ten minutes. The same method can also be used to solve larger net- works of up to 6,300 variables with reasonable accuracy (∼7% deviation) at the expense of longerprocessing times. A number of simple, yet effective, techniques that improve GA performance for TCT problems are demonstrated; the most effective of which is a novel problem encoding, based on weighted graphs, that enables the critical path problem to be partially solved for all candidate solutions a priori, thus significantly increasing fitness evaluation. Other improvements include parallel fitness evaluations, optimal algorithm parameters, and the addition of a stagnation criteria. We also present some guidelines of optimal algorithm parameter selection through a comprehensive parameter sweep and a computational demand profile analysis. Moreover, the methods proposed in this article are based on open source development projects that enable scalable solutions without significant development efforts. This information will be beneficial for other researchers in improving computational efficiency of their solution in addressing TCT problems

A conceptual framework for incorporating competitiveness into network-level transit quality metrics

In today’s mobility context, people have more mode choices than in the past, and many of those new choices are auto-based. This has led to a resurgence of transit agencies rethinking their networks and how well they connect people to opportunities. This paper proposes a new theoretical framework, Competitive Access, for transportation researchers and practitioners to use in describing and measuring regional transit access. The Competitive Access framework incorporates the concept of competitiveness between auto-based modes and transit, and is flexible enough to capture the varying contexts in which accessibility can change between and within regions. Using this framework, we propose two measures that describe the trip coverage and regional access provided by a transit network. These measures better reflect the realities experienced by riders in comparison to traditional access measures. Additionally, this paper includes a guide for practitioners to implement the framework and its associated measures in a network redesign context