Temperature rise and initial shrinkage of alkali-activated fly ash cement pastes

Shekhovtsova, Julia; Kovtun, Maxim; Kearsley, Elsabé P.

doi:10.1680/jadcr.14.00079

Cited by 5 publications

(7 citation statements)

References 21 publications

(24 reference statements)

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“…Portland cement accounts for approximately 7-8% of the total CO2 emitted globally (approximately 0.8 tonnes of CO2 is released per tonne of clinker manufactured) (Duchesne et al, 2010;Garcia-Lodeiro et al, 2016c;Olivier et al, 2015;Palomo et al, 2007). The inherent advantage of hybrid alkaline cements, over their alkali activated counterparts is that they do not require the addition of highly alkaline (and usually expensive) chemicals, but rely on a safe source of alkali formed in situ to facilitate both the dissolution of any amorphous (glassy) phases present in the source materials, as well as hydration at ambient temperature (Donatello et al, 2013;Donatello et al, 2014b;Kovtun et al, 2015;Shekhovtsova et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Chemical and mechanical activation of hybrid fly ash cement

Toit

Kearsley

Donald³

et al. 2018

Advances in Cement Research

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Hybrid fly ash cement is a binder with a composition between that of pozzolanic fly ash cement and alkali-activated fly ash cement. Its production requires less cement clinker than ordinary Portland cement, facilitating a much-needed reduction in the carbon dioxide footprint related to the production of high-clinker-containing cement. Research on activation methods is required to overcome the low early age strength and slow strength development in hybrid fly ash cements. In this study the activation of a South African siliceous fly ash (70%) for use along with Portland cement (30%) in a hybrid alkaline binder was investigated. Both chemical (the addition of sodium sulfate) and mechanical (milling) activation of fly ash was studied. The aim of this work was to develop a better understanding of the characteristics of compressive strength development of hybrid fly ash cement mortars over an extended curing period of up to a year. The results indicated that the combination of mechanical and chemical activation (sodium sulfate) can be considered a viable solution to improving early strength and slow strength development, so that hybrid cements are able to comply with the strength requirements of the BS EN 197 cement specification.

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Section: Introductionmentioning

confidence: 99%

Chemical and mechanical activation of hybrid fly ash cement

Toit

Kearsley

Donald³

et al. 2018

Advances in Cement Research

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“…Alkali-activator should not, however, be used in excess. First of all, too much OH − will break the charge balance of the system, lowering the overall strength of GSP [45,46]. Secondly, under high alkalinity, hydration reactions will continue to occur, generating excessive silicate hydration products, mainly composed of ettringite.…”

Section: Discussionmentioning

confidence: 99%

Factors Affecting the Strength Formation Mechanism and Water Stability of Geopolymer Stabilized Phosphogypsum in Road Construction

Wu,

Zhang,

Lin

et al. 2023

Coatings

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By adjusting the content of geopolymer in geopolymer stabilized phosphogypsum (GSP) as roadbed filler, along with the mixing ratio, this paper mainly explores tendencies in the mechanical properties and water stability of GSP. This research is based on macro-mechanical properties such as unconfined compressive strength, resilience modulus, California bearing ratio and shear strength. It is also based on water stability tests, such as the water soaking test, dry and wet cycle test and expansion test, to explore changes in water stability. As for the durability of GSP, this paper is mainly based on the realization of a long time observation of mechanical properties and water stability. In the existing research, most of the stabilized phosphogypsum (PG) base material or roadbed filler consists of cement, lime, etc. In this paper, a new exploration is carried out on the composition of stabilized PG material, realized without the participation of cement. The 28 d compressive strength of GSP reaches 2.5 MPa, and over time this strength grows, which prevents the phenomenon of strength inversion that may occur in conventional cement-stabilized PG. In addition, a long-term soaking experiment was designed in this study based on the material after the strength was stabilized for up to 90 d. After the strength was steady, the GSP with the best water stability still had a softening coefficient of 80% after experiencing water immersion for 7 d. After determining the feasibility of the mechanical properties and water stability of GSP as roadbed filler, we further explored the strength formation mechanism of GSP by microscopic tests (XRD and SEM). This shows that geopolymer can stabilize PG in two main ways: one is the hydration reaction with PG to generate C-S-H gel and ettringite, and the other is to connect PG not involved in the chemical reaction to form a dense whole through generated hydration products. Geopolymer, stabilizing a high amount of PG, not only provides a new method for the consumption of PG, but also has more stable performance than cement, and has certain advantages in economy. In addition, the advantage of this study is that good performance can be achieved by simply sieving PG and adjusting the geopolymer ratio in practical engineering projects.

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“…The type of aluminosilicates also affects the temperature formation during the polymerization reaction of geopolymer compositions. Thus, it has been determined that geopolymer concrete based on metakaolin binder actively releases heat in direct proportion to strength gain, while geopolymer concrete based on FA begins to release heat only after 25 h from the start of the reaction, which is due to the difference in the polymerization processes of these compositions [ 150 ].…”

Section: Physical and Mechanical Properties Of Geopolymer Concretesmentioning

confidence: 99%

Analytical Review of Geopolymer Concrete: Retrospective and Current Issues

Meskhi,

Beskopylny,

Stel’makh

et al. 2023

Materials

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The concept of sustainable development provides for the search for environmentally friendly alternatives to traditional materials and technologies that would reduce the amount of CO2 emissions into the atmosphere, do not pollute the environment, and reduce energy costs and the cost of production processes. These technologies include the production of geopolymer concretes. The purpose of the study was a detailed in-depth analytical review of studies of the processes of structure formation and properties of geopolymer concretes in retrospect and the current state of the issue. Geopolymer concrete is a suitable, environmentally friendly and sustainable alternative to concrete based on ordinary Portland cement (OPC) with higher strength and deformation properties due to its more stable and denser aluminosilicate spatial microstructure. The properties and durability of geopolymer concretes depend on the composition of the mixture and the proportions of its components. A review of the mechanisms of structure formation, the main directions for the selection of compositions and processes of polymerization of geopolymer concretes has been made. The technologies of combined selection of the composition of geopolymer concrete, production of nanomodified geopolymer concrete, 3D printing of building structures from geopolymer concrete, and monitoring the state of structures using self-sensitive geopolymer concrete are considered. Geopolymer concrete with the optimal ratio of activator and binder has the best properties. Geopolymer concretes with partial replacement of OPC with aluminosilicate binder have a denser and more compact microstructure due to the formation of a large amount of calcium silicate hydrate, which provides improved strength, durability, less shrinkage, porosity and water absorption. An assessment of the potential reduction in greenhouse gas emissions from the production of geopolymer concrete compared to the production of OPC has been made. The potential of using geopolymer concretes in construction practice is assessed in detail.

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Temperature rise and initial shrinkage of alkali-activated fly ash cement pastes

Cited by 5 publications

References 21 publications

Chemical and mechanical activation of hybrid fly ash cement

Chemical and mechanical activation of hybrid fly ash cement

Factors Affecting the Strength Formation Mechanism and Water Stability of Geopolymer Stabilized Phosphogypsum in Road Construction

Analytical Review of Geopolymer Concrete: Retrospective and Current Issues

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