Alkali-Activated Binders

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Clays and Engineered Mineral Materials".

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 6230

Special Issue Editors

Department of Civil, Environmental and Architectural Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
Interests: alkali-activated materials

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Guest Editor
Advanced Structures and Composites Center, University of Maine, Orono, ME 04469, USA
Interests: low-carbon cementitious materials

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Guest Editor
Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
Interests: composite materials; polymer encapsulation; polymer-reinforced concrete; thermal regulation
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Special Issue Information

Dear Colleagues,

Alkali-activated materials (AAMs) have been a focus area of research for the past few decades, and are attracting increasing attention from both academia and industry due to their relatively lower CO2 emissions compared to traditional ordinary Portland cement (OPC)-based binders. However, there are a few bottleneck problems which limit their wider applications, including a lack of standards applicable for direct comparisons among different results from various studies, greater drying shrinkage than that seen in OPC-based binders, and the high cost and embodied energy of alkaline activators. Thus, for the first problem, it is highly recommended to set up a platform where AAMs prepared using various precursors, such as metakaolin, red mud, incinerator bottom or fly ash, can be compared directly. To achieve this goal, effective Si/Al, Na/Al and Ca/Si ratios in AAM binding systems should be made clearer for comparison purposes, and related review papers are strongly favored for this Special Issue. For the second problem, it has been known that higher drying shrinkage of AAMs is closely associated with their intrinsic chemical compositions, finer and narrowed pores as well as possible creep deformation. However, there remain some uncertainties regarding the relationship between the final shrinkage values and these influential factors, especially when different raw materials (precursors) are utilized. Therefore, a deeper understanding about this should be obtained. For the last, different types of alkali activators, including single activators or their combinations, can be used, but what are their embodied energy and cost? How can one wisely select an alkaline activator considering that a large array of potential applications with different requirements is of critical importance? Are there any fundamental principles? This Special issue is organized into three sections:

  • Section 1: A shared platform for the direct comparison of different AAMs with specified Si/Al, Na/Al and Ca/Si ratios with the aim of better understanding the correlation between the properties of AAMs and their intrinsic characteristics, regardless of various precursors.
  • Section 2: More insights into the mechanisms regarding the effects of different influential factors on the shrinkage behavior of AAMs and related solutions.
  • Section 3: A more comprehensive analysis for a better selection of alkaline activators and addition methods (either one-part or traditional two-part) given different possible application requirements.

Dr. Jie Ren
Dr. Linfei Li
Dr. Zhenhua Wei
Guest Editors

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Keywords

  • alkali-activated materials
  • alkaline activators
  • drying shrinkage
  • Si/Al, Na/Al and Ca/Si ratios
  • no trial-and-error
  • application-oriented optimization or selection

Published Papers (4 papers)

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Research

18 pages, 8862 KiB  
Article
Strength Performance and Microstructures of Alkali-Activated Metakaolin and GGBFS-Based Mortars: Role of Waste Red Brick Powder Incorporation
by Hussam Alghamdi, Aref A. Abadel, Mohammad Khawaji, Mohammed Alamri and Abdullah Alabdulkarim
Minerals 2023, 13(7), 848; https://doi.org/10.3390/min13070848 - 23 Jun 2023
Cited by 1 | Viewed by 1104
Abstract
Excessive use of natural resources and environmental concerns are key issues motivating the recycling of waste materials in the construction industry to minimize landfill problems. Free cement binders such alkali-activated binders have emerged as a prospective alternative to ordinary Portland cement, wherein diverse [...] Read more.
Excessive use of natural resources and environmental concerns are key issues motivating the recycling of waste materials in the construction industry to minimize landfill problems. Free cement binders such alkali-activated binders have emerged as a prospective alternative to ordinary Portland cement, wherein diverse industrial, agriculture, and by-product waste materials have been converted as valuable spin-offs. Annually, tens of millions tons of red brick wastes are generated, which leads to several environmental problems. Thus, waste red brick powder (WRBP) was used as binder or a fine aggregate (silica sand) substitute to prepare some new types of alkali-activated mortars (AAMs). These mortars contained ground blast furnace slag (GGBFS) and metakaolin (MK) with various levels of WRBP (0, 15, 30, and 45%) as a substitute for silica sand. The prepared AAMs were cured at 300 °C, 600 °C, and ambient temperature. All the specimens were tested to determine the effects of various WRBP contents on the workability, strengths, and microstructures of the designed AAMs. The workability of the fresh AAMs was considerably dropped due to the incorporation of WRBP as binary binder or fine aggregate replacement. In addition, AAM containing 15% of WRBP as GGBFS and MK replacement displayed a significant improvement (by 30.7%) in the strength performance. However, the increasing content of WRBP to 30% and 45% significantly led to a decrease in compressive strength from 49.9 MPa to 44.7 and 34.2 MPa, respectively. Overall, the mortars’ strength was increased with the increase in WRBP contents from 0 to 45% as sand substitute. Conversely, the mortars strength was reduced with the increase in curing temperatures. The microstructure analyses of the studied mortars revealed an appreciable enhancement of the geopolymerization process, gels formulation, and surface morphology, leading to an improvement in their compressive and flexural strength characteristics. It was asserted that high-performance mortars with customized engineering properties can be designed via the inclusion of WRBP into alkali-activated MK-GGBFS mixes. Full article
(This article belongs to the Special Issue Alkali-Activated Binders)
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21 pages, 25115 KiB  
Article
Ceramic Aggregate Material Formulated with MSWI Fly Ash and Fuel Ash for Use as Filter Media
by Ning Lu, Hougang Chen, Jiao Chen and Yi-Fang Cao
Minerals 2023, 13(7), 845; https://doi.org/10.3390/min13070845 - 22 Jun 2023
Cited by 1 | Viewed by 955
Abstract
This study aimed to develop a novel filtering medium ceramic aggregate prepared using municipal solid waste incineration (MSWI) fly ash and the fuel ash from coal power plants, together with small amounts of silicon carbide foaming agent and magnesia flux as additives. For [...] Read more.
This study aimed to develop a novel filtering medium ceramic aggregate prepared using municipal solid waste incineration (MSWI) fly ash and the fuel ash from coal power plants, together with small amounts of silicon carbide foaming agent and magnesia flux as additives. For the manufacturing process, the dosage of MSWI fly ash and the sintering temperature were optimized to maximize the performance of the resulting materials. Leaching test results indicated that the heavy metal concentrations in the ceramic aggregate were significantly below the limits proposed by GB5085.3-2007, demonstrating its safety for wastewater treatment. The ammonia nitrogen removal efficiency was assessed, and the removal rate of the developed ceramic aggregate was found to be 16.4% higher than that of zeolite, making it comparable to commercial ceramic aggregate. Scanning electron microscopy and X-ray diffractometer analyses were conducted on the ceramic aggregates. The ammonia-nitrogen-removing mechanism, attributed to adsorption and ion exchange, is discussed based on the microstructural analysis results. Full article
(This article belongs to the Special Issue Alkali-Activated Binders)
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25 pages, 14344 KiB  
Article
Study the Mechanical Properties of Geopolymer under Different Curing Conditions
by Jinliang Liu, Xiaohui Shi, Guanhua Zhang and Linfei Li
Minerals 2023, 13(5), 690; https://doi.org/10.3390/min13050690 - 18 May 2023
Cited by 2 | Viewed by 1571
Abstract
The geopolymer is an environmentally friendly and high-performance material. Nowadays, how to improve the degree of the geopolymer’s reaction and enhance its mechanical properties has become a hot topic. This study used orthogonal tests to design the precursor mixing ratio, considering GGBS content [...] Read more.
The geopolymer is an environmentally friendly and high-performance material. Nowadays, how to improve the degree of the geopolymer’s reaction and enhance its mechanical properties has become a hot topic. This study used orthogonal tests to design the precursor mixing ratio, considering GGBS content (A), water/binder ratio (B), and alkaline activator modulus (C). The fly ash (FA) ground granulated blast furnace slag (GGBS)-based geopolymers were cured under two standard curing conditions: 40 °C under water and 40 °C in the oven. Then, the influence of these factors on the mechanical properties of geopolymers under different curing conditions was summarized. The contribution of each factor was ranked, which was used to find out the most sensitive factors affecting the mechanical properties. Taking the 7 days and 28 days of compressive strength and flexural strength of the geopolymer specimens as the evaluation criteria, the optimum ratio method for preparing geopolymers was obtained. Then, the prediction model of compressive strength under different curing conditions was established. SEM and XRD were used to analyze the microstructure and hydration products of the samples. The test results showed that the optimum ratio of FA-based geopolymers varied under different curing conditions. The GGBS content was the key factor in determining the mechanical properties. The heat curing condition was the best curing condition, the 28-day compressive strength could reach 76.3 MPa, and the 28-day flexural strength could reach 7.4 MPa. The prediction models established for compressive strength under different curing conditions had high accuracy. The specimens under the best curing conditions exhibited a dense internal microstructure and the presence of C-S-H gels, C-A-S-H gels, and N-A-S-H gels. Full article
(This article belongs to the Special Issue Alkali-Activated Binders)
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16 pages, 3452 KiB  
Article
Stabilization of Aeolian Sand for Pavement Subbase Applications Using Alkali-Activated Fly Ash and Slag
by Likang Bai, Zhenjia Yang, Yang Wu, Mohadeseh Anbarlouie and Zhu Pan
Minerals 2023, 13(3), 453; https://doi.org/10.3390/min13030453 - 22 Mar 2023
Cited by 1 | Viewed by 1509
Abstract
Using local materials to construct building elements as well as transport road facilities, including highways, intercity roads, and roads, in remote areas is a top topic of scholarly research all over the world. The main reason for that is the fact that these [...] Read more.
Using local materials to construct building elements as well as transport road facilities, including highways, intercity roads, and roads, in remote areas is a top topic of scholarly research all over the world. The main reason for that is the fact that these kinds of materials not only ease the intensity of material transportation but are also cost-efficient. In desert areas, aeolian sand is a commonly used local material and it has been investigated in unbound and cement-stabilized pavement base/subbase applications. However, the production of cement is associated with a high carbon footprint, leading this research to seek alternative low-carbon binders. This research investigated the strength properties and the carbon footprint of fly ash (FA) and a ground-granulated blast-furnace slag (S)-based geopolymer-stabilized aeolian sand. Setting time, compressive strength, California bearing ratio (CBR), and temperature shrinkage measurements of the stabilized aeolian sand were carried out in this research. The maximum strength of the stabilized aeolian sand was found at the optimal ratio of Si/Al ratio of 2.5 and Na/Al ratio of 1.0. The compressive strength increased as the geopolymer stabilizer content increased. A stabilizer content ranging between 8% and 20% is recommended in practice. The carbon footprint of the geopolymer-stabilized aeolian sand was lower than that of cement-stabilized aeolian sand. This tendency became more evident in the samples with higher strength, indicating the effectiveness of geopolymer as an alternative green soil stabilizer to traditional Portland cement. Full article
(This article belongs to the Special Issue Alkali-Activated Binders)
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