Kunal Kupwade-Patil

Impact of Alkali Silica Reaction on Fly Ash-Based Geopolymer Concrete

This study reports the findings of an experimental investigation for alkali silica reaction (ASR) between reactive aggregates and the geopolymer matrix. Specimens were prepared using one Class C and two Class F fly ash stockpiles. Mechanical testing included potential reactivity of the aggregates via length change and compression test measurements, as per ASTM standards. Results suggest that the extent of ASR reaction due to the presence of reactive aggregates in fly ash-based geopolymer concretes is substantially lower than in the case of ordinary portland cement-based concrete, and well below the ASTM specified threshold. Furthermore, geopolymer concrete specimens appeared to undergo a densification process in the presence of alkali solutions, resulting in reduced permeability and increased mechanical strength. Utilizing ASR-vulnerable aggregates in the production of geopolymer concrete products could contribute to the economic appeal and sustainability of geopolymer binders in regions that suffer from insufficient local supply of high quality aggregates.

Toxicity mitigation and solidification of municipal solid waste incinerator fly ash using alkaline activated coal ash

Municipal solid waste (MSW) incineration is a common and effective practice to reduce the volume of solid waste in urban areas. However, the byproduct of this process is a fly ash (IFA), which contains large quantities of toxic contaminants. The purpose of this research study was to analyze the chemical, physical and mechanical behaviors resulting from the gradual introduction of IFA to an alkaline activated coal fly ash (CFA) matrix, as a mean of stabilizing the incinerator ash for use in industrial construction applications, where human exposure potential is limited. IFA and CFA were analyzed via X-ray fluorescence (XRF), X-ray diffraction (XRD) and Inductive coupled plasma (ICP) to obtain a full chemical analysis of the samples, its crystallographic characteristics and a detailed count of the eight heavy metals contemplated in US Title 40 of the Code of Federal Regulations (40 CFR). The particle size distribution of IFA and CFA was also recorded. EPAs Toxicity Characteristic Leaching Procedure (TCLP) was followed to monitor the leachability of the contaminants before and after the activation. Also images obtained via Scanning Electron Microscopy (SEM), before and after the activation, are presented. Concrete made from IFA, CFA and IFA-CFA mixes was subjected to a full mechanical characterization; tests include compressive strength, flexural strength, elastic modulus, Poissons ratio and setting time. The leachable heavy metal contents (except for Se) were below the maximum allowable limits and in many cases even below the reporting limit. The leachable Chromium was reduced from 0.153 down to 0.0045 mg/L, Arsenic from 0.256 down to 0.132 mg/L, Selenium from 1.05 down to 0.29 mg/L, Silver from 0.011 down to .001 mg/L, Barium from 2.06 down to 0.314 mg/L and Mercury from 0.007 down to 0.001 mg/L. Although the leachable Cd exhibited an increase from 0.49 up to 0.805 mg/L and Pd from 0.002 up to 0.029 mg/L, these were well below the maximum limits of 1.00 and 5.00 mg/L, respectively.

Examination of Chloride-Induced Corrosion in Reinforced Geopolymer Concretes

The durability of steel reinforced-concrete specimens made from three alkali-activated fly ash (FA) stockpiles and ordinary portland cement (OPC) in cyclic wet-dry chloride environment was evaluated over a period of 12 months. Testing methods included electrochemical methods, chloride diffusion and contents analysis, chemical and mechanical analyses, and visual examination. Geopolymer concrete (GPC) specimens made from Class F FA exhibited lower diffusion coefficients, chloride contents, and porosity compared with their GPC Class C FA and OPC counterparts. Overall, GPC specimens displayed limited signs of leaching and corrosion product formation, whereas OPC specimens exhibited the formation of multiple corrosion products along with significant leaching.

Corrosion Mitigation in Mature Reinforced Concrete Using Nanoscale Pozzolan Deposition

Electrokinetic nanoparticle (EN) treatments were employed to mitigate corrosion in reinforced concrete. In this approach an electric field was used to drive pozzolanic nanoparticles through the capillary pores of concrete and directly to the reinforcement. The intent was to use the nanoparticles as pore-blocking agents to prevent the ingress of chlorides. Treatment effectiveness was examined for both freshly batched and relatively mature concrete. Cylindrical reinforced concrete specimens were subjected to EN treatment immediately after batching and then exposed to chlorides for a period of two years. The EN-treated specimens exhibited a reduction in corrosion rates by a factor of 74 as compared to the untreated controls. Another set of specimens was subjected to chlorides for a period of two years prior to EN treatment application. Electrochemical chloride extraction and EN treatments were performed on these mature specimens for one week. These specimens were placed back into saltwater exposure for an ad...

Corrosion Mitigation in Reinforced Concrete Beams via Nanoparticle Treatment

Reinforcement corrosion in concrete is a major cause of damage in the civil infrastructure. This study evaluates the corrosion behavior of reinforced concrete beams when subjected to electrokinetic nanoparticle (EN) treatment. The EN treatment used an electric field to transport 24 nm nanoparticles directly to the steel reinforcement via capillary pores. Each beam was subjected to saltwater exposure followed by electrochemical chloride extraction (ECE) in concurrence with EN treatment. The specimens were re-exposed to saltwater following treatment. The results from this test indicate significantly lower corrosion current density among the EN-treated specimens (0.014 mA/cm2 [0.09 mA/in.2]) compared to the untreated control specimens (2.12 mA/cm2 [13.67 mA/in.2]). Mercury intrusion porosimetry (MIP) was used to examine the microstructural impact of the treatment process. A reduction in the porosity (adjacent to the steel) of as much as 74% was observed due to EN treatment. During treatment application, the electric field also caused chlorides to be drawn away from the reinforcement and extracted from the concrete beam. After the chloride was extracted, the nanoparticles appeared to form a physical barrier against chloride repenetration.

Hydration kinetics and morphology of Cement Pastes with Pozzolanic Volcanic Ash studied via Synchrotron based Techniques

AbstractThis study investigates the early ages of hydration behavior when basaltic volcanic ash was used as a partial substitute to ordinary Portland cement using ultra-small-angle X-ray scattering and wide-angle X-ray scattering (WAXS). The mix design consisted of 10, 30 and 50% substitution of Portland cement with two different-sized volcanic ashes. The data showed that substitution of volcanic ash above 30% results in excess unreacted volcanic ash, rather than additional pozzolanic reactions along longer length scales. WAXS studies revealed that addition of finely ground volcanic ash facilitated calcium-silicate-hydrate related phases, whereas inclusion of coarser volcanic ash caused domination by calcium-aluminum-silicate-hydrate and unreacted MgO phases, suggesting some volcanic ash remained unreacted throughout the hydration process. Addition of more than 30% volcanic ash leads to coarser morphology along with decreased surface area and higher intensity of scattering at early-age hydration. This suggests an abrupt dissolution indicated by changes in surface area due to the retarding gel formation that can have implication on early-age setting influencing the mechanical properties of the resulting cementitious matrix. The findings from this work show that the concentration of volcanic ash influences the specific surface area and morphology of hydration products during the early age of hydration. Hence, natural pozzolanic volcanic ashes can be a viable substitute to Portland cement by providing environmental benefits in terms of lower-carbon footprint along with long-term durability.

Encapsulation of Solid Waste Incinerator Ash in Geopolymer Concretes and Its Applications

The current study examines chemical and mechanical behaviors resulting from the gradual incorporation of incinerator fly ash (IFA) into an alkaline-activated coal fly ash (CFA) matrix, such as: 1) the incinerator ash is chemically stabilized; and 2) the resulting mixture provides fresh and hardened properties adequate for the production of commercially viable precast components. This paper presents the results of an extensive chemical characterization of IFA and CFA, including particle size distribution (PSD), X-ray fluorescence (XRF), and inductive coupled plasma (ICP) methods. Geopolymer concretes and grouts made from IFA, CFA, and four IFA-CFA blends were subjected to leachability tests, as well as extensive mechanical and rheological testing, including compressive strength, elastic modulus, Poisson’s ratio, and setting time. Preliminary results are encouraging, suggesting that toxicity levels of the leachate can be reduced by up to two orders of magnitude. Reduction in leaching levels of heavy metals was observed for Al, Cr, Ni, Zn, Se, Mo, Ba, Tl, Pb, and Th in geopolymer samples. Furthermore, the resulting mixture is workable and yields a mechanical strength of up to 41 MPa (6000 psi). PSD analysis showed CFA was 8% smaller than IFA. PSD plays a vital role in contributing to geopolymerization, as finer particle sizes involved in geopolymerization lead to a dense microstructure. This indicates that while geopolymerization could be viewed as an effective approach for treating IFA, immobilization of heavy metals by forming stable zeolites provides an additional mechanism for encapsulation of heavy metals. The use of IFA in beneficiation applications is expected to result in significant cost reduction to operators of municipal waste incinerators, eliminating costly transportation and landfill expenditures.

Diffusion Analysis of Chloride in Concrete Following Electrokinetic Nanoparticle Treatment

Concrete is a highly porous material which is susceptible to the migration of highly deleterious species such as chlorides and sulfates. Various external sources including sea salt spray, direct sea water wetting, deicing salts and brine tanks harbor chlorides that can enter reinforced concrete. Chlorides diffuse into the capillary pores of concrete and come into contact with the rebar. When chloride concentration at the rebar exceeds a threshold level it breaks down the passive layer of oxide, leading to chloride induced corrosion. Application of electrokinetics using positively charged nanoparticles for corrosion protection in reinforced concrete structures is an emerging technology. This technique involves the principle of electrophoretic migration of nanoparticles to hinder chloride diffusion in the concrete. The re-entry of the chlorides is inhibited by the electrodeposited assembly of the nanoparticles at the rebar interface. In this work electrochemical impedance spectroscopy (EIS) combined with equivalent circuit analysis was used to predict chloride diffusion coefficients as influenced by nanoparticle treatments. Untreated controls exhibited a diffusion coefficient of 3.59 × 10−12 m2 /s which is slightly higher than the corrosion initiation benchmark value of 1.63 × 10−12 m2 /s that is noted in the literature for mature concrete with a 0.5 water/cement mass ratio. The electrokinetic nanoparticle (EN) treated specimens exhibited a diffusion coefficient of 1.41 × 10−13 m2 /s which was 25 times lower than the untreated controls. Following an exposure period of three years the mature EN treated specimens exhibited lower chloride content by a factor of 27. These findings indicate that the EN treatment can significantly lower diffusion coefficients thereby delaying the initiation of corrosion.Copyright

Irradiated recycled plastic as a concrete additive for improved chemo-mechanical properties and lower carbon footprint

Concrete production contributes heavily to greenhouse gas emissions, thus a need exists for the development of durable and sustainable concrete with a lower carbon footprint. This can be achieved when cement is partially replaced with another material, such as waste plastic, though normally with a tradeoff in compressive strength. This study discusses progress toward a high/medium strength concrete with a dense, cementitious matrix that contains an irradiated plastic additive, recovering the compressive strength while displacing concrete with waste materials to reduce greenhouse gas generation. Compressive strength tests showed that the addition of high dose (100kGy) irradiated plastic in multiple concretes resulted in increased compressive strength as compared to samples containing regular, non-irradiated plastic. This suggests that irradiating plastic at a high dose is a viable potential solution for regaining some of the strength that is lost when plastic is added to cement paste. X-ray Diffraction (XRD), Backscattered Electron Microscopy (BSE), and X-ray microtomography explain the mechanisms for strength retention when using irradiated plastic as a filler for cement paste. By partially replacing Portland cement with a recycled waste plastic, this design may have a potential to contribute to reduced carbon emissions when scaled to the level of mass concrete production.

Galvanically assisted crevicing of electroplated chrome press cylinders

Abstract Printing press cylinders release ink that is stored in a surface pattern of micro-indentations. The cylinder consists of a steel substrate electroplated with a layer of copper. A micro-indentation pattern is applied followed by a 10 μm top layer of electroplated chrome. This layer generally contains microcracks at a rate if 1000 cracks/2·5 cm. Chrome flaking was common during the warm summer months, leading to costly shutdowns. Corroded cylinders were examined using optical and scanning electron microscopy, energy dispersive spectroscopy, corrosion potential measurement and chemical analysis. It was found that rapid crevicing was taking place in the microcracks. At the chrome/copper interface, galvanically assisted crevicing further accelerated the flaking process. It was also found that the percentage of micro-indentations found to exhibit corrosion spots correlated well with measured corrosion potentials. Polymeric storage covers were recommended to limit atmospheric sources of moisture, oxygen, chlorides and sulphates.