Influence of pore structure on the strength behavior of particle- and fiber-reinforced metakaolin-based geopolymer composites

Akono, Ange-Thérèse; Korić, Seid; Kriven, Waltraud M.

doi:10.1016/j.cemconcomp.2019.103361

Cited by 40 publications

(20 citation statements)

References 44 publications

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“…Because both the Si/Al ratio and the Na/Al ratio were optimally selected according to the literature data [17] and our previous work [19], all the MKG mortars showed high compressive strengths. Our data did not follow the observation that materials with higher capillary pore volumes have lower strengths [45]. The reason is that the enhanced polymerization extents of geopolymer at the higher Na/Al ratio (or Na/Si ratio) could increase the compactness of the nanostructure, thus decreasing the nanopores and promoting the capillary pores [20].…”

Section: Roles Of the Materials' Compositioncontrasting

confidence: 90%

Compositional Dependence of Pore Structure, Strengthand Freezing-Thawing Resistance of Metakaolin-Based Geopolymers

et al. 2020

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The understanding of the composition dependent properties and freezing-thawing (F-T) resistance of geopolymer materials is vital to their applications in cold regions. In this study, metakaolin-based geopolymer (MKG) mortars were fabricated by controlling the Si/Al ratio and the Na/Al ratio. The pore structure and strength were measured by mercury intrusion porosimetry and compression tests, respectively, which both showed obvious correlations with the material composition. Mass loss, strength loss, visual rate, and microscopic observation were adopted to assess the changes of the material properties and microstructure caused by F-T loads. The results showed that the strength-porosity relationship roughly followed a linear plot. Increases of the Si/Al ratio increased the capillary pore volume, but decreased the gel pore volume and the F-T resistance. Increases of the Na/Al ratio decreased the gel pore, but roughly enhanced the F-T resistance. The MKG mortar at the Na/Al ratio of 1.26 showed the lowest total pore volume and the best F-T resistance. The mechanisms of our experimental observations were that the abundantly distributed air voids connected by the capillary pores facilitated the relaxation of hydraulic pressures induced by the freezing of the pore liquid. The findings of this work help better clarify the compositional dependence of the pore structure, strength, and freezing-thawing resistance of MKG materials and provide fundamental bases for their engineering applications in cold regions.

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Section: Roles Of the Materials' Compositioncontrasting

confidence: 90%

Compositional Dependence of Pore Structure, Strengthand Freezing-Thawing Resistance of Metakaolin-Based Geopolymers

et al. 2020

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“…For instance, for a statistically disordered morphology with spherical spheres and for

, we have

[ 25 ]. Meanwhile, the indentation hardness nonlinear upscaling function,

, can be derived via yield design analysis [ 24 , 26 ].…”

Section: Materials and Methodsmentioning

confidence: 99%

Nanostructure and Fracture Behavior of Carbon Nanofiber-Reinforced Cement Using Nanoscale Depth-Sensing Methods

Akono

2020

Materials

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In recent years, carbon nanofibers have been investigated as a suitable reinforcement for cementitious composites to yield novel multifunctional materials with improved mechanical, electrical, magnetic, and self-sensing behavior. Despite several studies, the interactions between carbon nanofibers and Portland cement hydration products are not fully understood, with significant implications for the mechanical response and the durability at the macroscopic lengthscale. Thus, the research objective is to investigate the influence of carbon nanofibers on the nanostructure and on the distribution of hydration products within Portland cement paste. Portland cement w/c = 0.44 specimens reinforced with 0.0 wt%, 0.1 wt%, and 0.5 wt% CNF by mass fraction of cement are cast using a novel synthesis procedure. A uniform dispersion of carbon nanofibers (CNF) via a multi-step approach: after pre-dispersing carbon nanofibers using ultrasonic energy, the carbon nanofibers are further dispersed using un-hydrated cement particles in high shear mixing and mechanical stirring steps. High-resolution scanning electron microscopy analysis shows that carbon nanofibers fill nanopores and connect calcium–silicate hydrates (C–S–H) grains. Grid nano-indentation testing shows that Carbon nanofibers influence the probability distribution function of the local packing density by inducing a shift towards higher values, η = 0.76–0.93. Statistical deconvolution analysis shows that carbon nanofibers result in an increase in the fraction of high-density C–S–H by 6.7% from plain cement to cement + 0.1 wt% CNF and by 10.7% from plain cement to cement + 0.5 wt% CNF. Moreover, CNF lead to an increase in the C–S–H gel porosity and a decrease in both the capillary porosity and the total porosity. Based on scratch testing, adding 0.1 wt% CNF yields a 4.5% increase in fracture toughness and adding 0.5 wt% CNF yields a 7.6% increase in fracture toughness. Finally, micromechanical modelling predicts an increase of respectively 5.97% and 21.78% in the average Young’s modulus following CNF modification at 0.1 wt% CNF and 0.5 wt% CNF levels.

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“…Geopolymers are usually produced by combining a precursor material (e.g., metakaolin or fly ash) with a highly alkaline chemical reagent (activator) [7][8][9]. They are innovative materials that are being studied for a number of applications, including fiber-reinforced composites [10][11][12], refractory composites (aerated geopolymers) [13], precursors for the formation of ceramics [14][15][16], and waste adsorption [17]. Environmentally, these materials reduce CO 2 emission rates, compared to those of Portland cement, as they do not use the clinker process, thereby reducing energy consumption [9,18].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the properties of a foamed geopolymer developed with different types of metakaolin

et al. 2021

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The physical and mechanical properties of foamed geopolymers were determined. The geopolymers were made with two different metakaolins (from Metacaulim do Brasil -MB, and Pantano Grande/RS -MPG) as precursors, with NaOH and Na 2 SiO 3 as activators, and with the addition of foam, which was produced with the foaming agent diethanolamide of coconut fatty acid with a minimum of 80% concentration. Also, two times (2.5 and 4 h) were used for the calcination of MPG at 750 °C. The results showed that all factors (precursors type, alkali content, silica modulus, and foam content) had a significant influence on the response variables, which presented the following variations: compressive strength of 0.36 to 3.23 MPa; thermal conductivity from 0.22 to 0.42 W/(m.K); saturated bulk density from 1176 to 1364 kg/m 3 ; dry bulk density of 619 to 864 kg/m 3 ; air void from 46.4% to 62.5%; and water absorption from 55.7% to 95.4%. It was also concluded that the precursor type was the factor that had the most influence on the properties of foamed geopolymers, with MPG calcined for 4 h being the best, as greater compressive strength and low thermal conductivity were obtained.

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Influence of pore structure on the strength behavior of particle- and fiber-reinforced metakaolin-based geopolymer composites

Cited by 40 publications

References 44 publications

Compositional Dependence of Pore Structure, Strengthand Freezing-Thawing Resistance of Metakaolin-Based Geopolymers

Compositional Dependence of Pore Structure, Strengthand Freezing-Thawing Resistance of Metakaolin-Based Geopolymers

Nanostructure and Fracture Behavior of Carbon Nanofiber-Reinforced Cement Using Nanoscale Depth-Sensing Methods

Evaluation of the properties of a foamed geopolymer developed with different types of metakaolin

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