Natural and accelerated carbonation behaviour of high-volume fly ash (HVFA) mortar: Effects on internal moisture, microstructure and carbonated phase proportioning

Heede, Philip Van den; Thiel, Charlotte; Belie, Nele De

doi:10.1016/j.cemconcomp.2020.103713

Cited by 11 publications

(6 citation statements)

References 13 publications

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“…The HVFA mortar prisms were not used for intermittent assessment of the carbonation front using phenolphthalein color indicator to determine the carbonation rate by plotting the as such observed carbonation front as a function of the square-root of the exposure time. This was already done in earlier research by the authors [12]. For each of the three considered exposure conditions (natural vs. slightly accelerated vs. highly accelerated carbonation) the obtained carbonation rates are summarized in Section 3.1.…”

Section: Colorimetric Carbonation Assessmentmentioning

confidence: 99%

“…This then implies exposing the binder system to elevated CO 2 levels. As already pointed out in earlier work by the authors, one should be careful when using results from accelerated carbonation experiments to predict natural carbonation rates [11,12]. Excessive production of the H 2 O reactant during carbonation at highly elevated CO 2 levels (i.e., 10% CO 2 ) may have a pore blocking effect hindering further carbonation [13,14].…”

Section: Introductionmentioning

confidence: 95%

“…The latter exposure conditions correspond with the temperature and RH prescribed during subsequent natural/accelerated carbonation tests. This way of sample preconditioning was similar to the one used in earlier carbonation related research by the authors [12]. After preconditioning the mortar prisms were equally divided in three groups for carbonation at 0.04%, 1% and 10% CO 2 .…”

Section: Sample Conditioning Prior and During Natural And Accelerated...mentioning

confidence: 99%

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Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Heede

Belie

2021

Applied Sciences

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Carbonation of cementitious binders implies gradual capture of CO2 and significant compensation for the abundant cement-related CO2 emissions. Therefore, one should always look at the CO2-sequestration-to-emission ratio (CO2SP/EM). Here, this was done for High-Volume Fly Ash (HVFA) mortar (versus two commercial cement mortars). Regarding their CO2 sequestration potential, effects of accelerated testing (at 1–10% CO2) on as such estimated natural carbonation degrees and rates were studied. Production related CO2 emissions were evaluated using life cycle assessment with no/economic allocation for fly ash. Natural carbonation rates estimated from accelerated tests significantly underestimate actual natural carbonation rates (with 29–59% for HVFA mortar) while corresponding carbonation degrees are significantly overestimated (67–74% as opposed to the actual 58% for HVFA mortar). It is advised to stick with the more time-consuming natural tests. Even then, CO2SP/EM values can vary considerably depending on whether economic allocation coefficients (Ce) were considered. This approach imposes significant portions of the CO2 emissions of coal-fired electricity production onto fly ash originating from Germany, China, UK, US and Canada. Ce values of ≥0.50% lower the potential CO2SP/EM values up to a point that it seems no longer environmentally worthwhile to aim at high-volume replacement of Portland cement/clinker by fly ash.

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Section: Colorimetric Carbonation Assessmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Section: Sample Conditioning Prior and During Natural And Accelerated...mentioning

confidence: 99%

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Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Heede

Belie

2021

Applied Sciences

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“…Efflorescence deposits are rapidly formed on the surface of geopolymer products when the other sides are in contact with water [4]. The wetting or drying conditions used for curing the geopolymers play dominant roles in controlling the moisture absorption/desorption isotherms in the matrix [10]. In addition, the pore structure also correlates well with the moisture transportation, which significantly influences the movement of free alkalis in the pore network [11,12].…”

Section: Introductionmentioning

confidence: 99%

Relationship between Moisture Transportation, Efflorescence and Structure Degradation in Fly Ash/Slag Geopolymer

Zhou

Zhang

et al. 2020

Materials

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The relationship between moisture transportation and efflorescence in sodium hydroxide- or sodium silicate-activated fly ash/slag geopolymers was investigated. The results show that the efflorescence products are sodium carbonate hydrates, mainly composed of natron, heptahydrate, trona and sodium carbonate. The efflorescence induces compressive strength loss, water absorption increases and pore structure degradation in the geopolymer. When the curved surface of a geopolymer cylinder is covered with plastic film, the moisture transportation drives the free alkalis to the top surface to initiate efflorescence. In comparison, the efflorescence occurring on the curved surface of an uncovered geopolymer cylinder results in a more intensive alkalinity loss. For the uncovered geopolymers prepared with sodium hydroxide activator, efflorescence deposits are formed on the lower half of cylinder. A low capillary absorption capacity developed in the pore structure can only drive the moisture to the middle of cylinder, which is confronted with the drying front. More efflorescence products are formed on the upper half of the uncovered geopolymer cylinder prepared with sodium silicate activator. A relatively higher capillary absorption capacity, developed in the more compact pore structure, transports the moisture from the bottom to the top of cylinder, so no drying line is observed in the cylinder.

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“…Therefore, the presence of fly ash in the fresh state of cement mixture and the final hydrating state can improve the microstructure of capillary pore in concrete through its physical manner, chemical revolution, and pozzolanic reaction [137]. As observed from the analysis, the chloride ion concentration at the top surface section (0-5 mm) cannot be measured for all samples owing to the evaporation of water in chloride salt solution from the exposed surface and the higher porosity and pore diameter [138]. Therefore, the chloride ion concentration at the 0-5 mm section is not used to calculate the Da value.…”

Section: Heat Flow and Heat Release Of Fly Ash-cement Pastesmentioning

confidence: 96%

Effect of fly ash in Southeast Asia on the properties of concrete

Win¹

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A wide use of fly ash (FA) as a supplementary cementitious material (SCM) can result in an enhancement in its durability performance in our civil engineering applications. Although FA is either agricultural or industrial by‑product and is abundant for use in cement and concrete works for many decades now, the utilization of FA still has a practical challenge. The challenge is due to variability and their heterogeneity. In Southeast Asia, fly ash is used in concrete production replacing cement as a pozzolanic material. However, there are few standard guidelines for using fly ash across the region. This study evaluates the durability of cementitious materials after the including of five types of fly ash in different mix proportions from three countries, Myanmar, Thailand, and Indonesia. For the mathematical model, each type is used to replace ordinary Portland cement in 15 % with a water-to-binder ratio of 0.54. Moreover, this work is to perform both experimental and numerical studies to have a better insight for controlling the different FA, reflecting its durability. FA from five different sources were assessed to investigate the impacts on its chemical composition and physical properties. The blended FA-cement systems were also prepared and evaluated on its flow, compressive strength of mortar, hardened porosity, ability to resist chloride penetration, apparent chloride diffusivity coefficients (Da), and carbonation resistance after 7, 28, and 91 days, and degree of reaction. Because the chemical composition of each country’s fly ash is slightly different, their chemical reaction with cement is marginally different. Thus, the durability performances of the mortar are better for finer fly ash types at an early age. The service life model using Life365 was performed to predict the service life of blended FA-cement system. The experimental results were statistically analyzed using analysis of variance (ANOVA) and sensitivity analysis with linear regression. The analyses indicate that chemo-physical mechanisms of multi-scale structures are the main factors, and both degree of reaction of blended FA-cement systems and its hardened porosity are among the most positive factors influencing its durability.

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Natural and accelerated carbonation behaviour of high-volume fly ash (HVFA) mortar: Effects on internal moisture, microstructure and carbonated phase proportioning

Cited by 11 publications

References 13 publications

Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Relationship between Moisture Transportation, Efflorescence and Structure Degradation in Fly Ash/Slag Geopolymer

Effect of fly ash in Southeast Asia on the properties of concrete

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