Fly ash-based geopolymers: The relationship between composition, pore structure and efflorescence

Zhang, Zuhua; Provis, John L.; Reid, Andrew; Wang, Hao

doi:10.1016/j.cemconres.2014.06.004

Cited by 355 publications

(179 citation statements)

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“…However, this has not proven to be the case either in field or laboratory investigations [56][57][58][59][60]. Studies of efflorescence in alkali-activated binder systems [61][62][63] have generally concluded that the white 'bloom' which can appear on the surfaces of some alkali-activated mortars or concretes is usually related to the carbonation of mobile alkalis from the pore solution, and is best addressed through the implementation of curing conditions or addition of pore-refining additives (i.e. mineral admixtures rich in calcium and/or aluminium) to reduce the rate of moisture movement through the hardened cements.…”

Section: Durability Of the Technologymentioning

confidence: 99%

Alkali-activated materials

Provis

2018

Cement and Concrete Research

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This paper, which forms part of the UNEP White Papers series on Eco-Efficient Cements, provides a brief discussion of the class of cementing materials known as 'alkali-activated binders', which are identified to have potential for utilization as a key component of a sustainable future global construction materials industry. These cements are not expected to offer a like-for-like replacement of Portland cement across its full range of applications, for reasons related to supply chain limitations, practical challenges in some modes of application, and the need for careful control of formulation and curing. However, when produced using locallyavailable raw materials, with well-formulated mix designs (including in particular consideration of the environmental footprint of the alkaline activator) and production under adequate levels of quality control, alkali-activated binders are potentially an important and cost-effective component of the future toolkit of sustainable construction materials.

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Section: Durability Of the Technologymentioning

confidence: 99%

Alkali-activated materials

Provis

2018

Cement and Concrete Research

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“…Blending fly ash and slag together as raw materials is a common practice of geopolymer manufacturing in industry, as the incorporation of slag can accelerate the setting at ambient temperatures and the compressive strength development (Yang et al, 2012;Lee and Lee, 2013;Gao et al, 2015). In this study, it is also desirable to use slag to partially replace fly ash to increase the early age strength, instead of using excessive alkalis, particularly given the potential of efflorescence (Zhang et al, 2014a).…”

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confidence: 99%

The Pore Characteristics of Geopolymer Foam Concrete and Their Impact on the Compressive Strength and Modulus

Zhang

Wang

2016

Front. Mater.

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The pore characteristics of geopolymer foam concretes (GFCs) manufactured in the laboratory with 0-16% foam additions were examined using image analysis (IA) and vacuum water saturation techniques. The pore size distribution, pore shape, and porosity were obtained. The IA method provides a suitable approach to obtain the information of large pores, which are more important in affecting the compressive strength of GFC. By examining the applicability of the existing models of predicting compressive strength of foam concrete, a modified Ryshkevitch's model is proposed for GFC, in which only the porosity that is contributed by the pores over a critical diameter (>100 μm) is considered. This "critical void model" is shown to have very satisfying prediction capability in the studied range of porosity. A compression-modulus model for Portland cement concrete is recommended for predicting the compression-modulus elasticity of GFC. This study confirms that GFC have similar pore structures and mechanical behavior as those Portland cement foam concrete and can be used alternatively in the industry for the construction and insulation purposes.

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“…Najafi Kani et al (2012) ground AAC pastes (could be very fine) and used the stable leaching method at a water to solid ratio of 20:1 and reported that after 24 h the leached alkali is 1-7%, depending on the Si/Na and Na/Al ratios. Zhang et al (2014) crushed alkali activated fly ash pastes into 1.25-1.5 mm particles, used the stable leaching method at water/solid ratio of 25:1 and found that after 24 h the leached sodium is 12-16%, depending on the activator type, curing temperature and slag replacement. These results are in agreement with the above hypothesis.…”

Section: Roles and States Of Alkalis In Aacsmentioning

confidence: 99%

“…et al, 2012). Efflorescence is one such problem which has been raised as a concern in some AAC formulations and this has been discussed briefly by Bernal et al (2014), and more recently, systematically investigated by Zhang et al (2014).…”

Section: Introductionmentioning

confidence: 99%

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Critical thinking on efflorescence in alkali activated cement (AAC)

Zhang¹,

Provis²,

Wang³

2015

Proceedings of the Second International Conference on Performance-Based and Life-Cycle Structural Engineering (PLSE 2015)

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Alkali-activated cement (AAC), also known as "geopolymer", has been extensively investigated over the past 40 years and has been developed from laboratory mock ups to real structural usage in construction in the last decade. While numerous life cycle analyses and carbon accounting studies show the "green potential" of this material compared to Portland cement, some authors state that the high alkali concentration in AAC is a potentially unstable factor which may lead to, for example, efflorescence. This paper presents a critical thinking on the literature and some new experimental work regarding the possibility of efflorescence in AAC products. Subjects of the discussion include: (1) the role of alkalis in AACs, (2) the effect of alkali concentration on efflorescence, (3) the effect of solid precursor selection on efflorescence, (4) the effect of curing scheme and chemical additives on efflorescence, and (5) the impacts of efflorescence on the microstructural properties of AACs. Particular attention is given to the relationship between pore structure and efflorescence behaviour, and consequently the mechanical properties of AACs suffering from either efflorescence or alkali loss (by leaching). The changes in sodium aluminosilicate hydrate (N-A-S-H) gels due to efflorescence or alkali loss are critical to the durability of AACs. This paper emphasizes that the nature of the solid precursor and the pore structure of the resulting AAC are the two most important factors that control efflorescence rate. However, considering its alkaline nature, it seems difficult or impossible to avoid this issue in AAC products, although kinetically controlled diffusion of alkalis using phase transformation techniques may help to mitigate efflorescence. Efflorescence in AAC is a "skin issue" that needs to be carefully treated. It is recognized to be different from the visually similar, but chemically distinct, efflorescence that occurs in Portland cement based materials.

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Fly ash-based geopolymers: The relationship between composition, pore structure and efflorescence

Cited by 355 publications

References 28 publications

Alkali-activated materials

Alkali-activated materials

The Pore Characteristics of Geopolymer Foam Concrete and Their Impact on the Compressive Strength and Modulus

Critical thinking on efflorescence in alkali activated cement (AAC)

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