Chemical deformation of metakaolin based geopolymer

TLDR: In this paper, the chemical deformation of metakaolin-based geopolymer (MKG) was investigated and correlations between the chemical deformations and the reaction processes during geopolymers were found.

About: This article is published in Cement and Concrete Research.The article was published on 2019-06-01 and is currently open access. It has received 113 citations till now. The article focuses on the topics: Shrinkage & Deformation (meteorology).

Figures

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Fig. 5. 29Si NMR spectra of MK and MKG pastes.

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Fig. 2. Chemical deformation of (a) MKG paste, and (b) OPC paste. A representative curve is shown in solid line while the other two curves are shown in grey dashed lines. The curves indicate a good repeatability of the measurement.

Fig. 6. Deconvolution results for 29Si NMR spectra of MK (a) and MKG pastes cured for 4 hours (b), 8 hours (c) 16 hours (d), 48 hours (e) and 240 hours (f).

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Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Delft university of technology chemical deformation of metakaolin based geopolymer" ?

This work, for the first time, reports an in-depth investigation on the chemical deformation of metakaolin based geopolymer ( MKG ). The insights into the chemical deformation provided by this study will play a fundamental role in further understanding, controlling and even utilizing the deformation behaviours of geopolymers. 

Q2. What are the future works mentioned in the paper "Delft university of technology chemical deformation of metakaolin based geopolymer" ?

Further research on quantitative analysis and prediction of chemical deformation is absolutely helpful, which may be done by the combination of thermodynamic modeling and experimental work. In addition, the conceptual model of the chemical deformation proposed in this study can be adapted for different geopolymer mixtures under various curing conditions in future researches. This study provides important insights into the chemical deformation associated with geopolymerization, which will play a fundamental role for further understanding, controlling and even utilizing deformation behaviour ( especially the autogenous deformation ) of geopolymers in engineering applications. 

Q3. What is the way to explain the chemical deformation of MKG?

Building up relationships between the volumetric changes with the corresponding reaction products could be a feasible approach to reveal mechanisms of the chemical deformation of MKG related to different stages of geopolymerization. 

Q4. What is the reason for the formation of Si-rich gel in this stage?

The formation of Si-rich gel in this stage might result from the polymerization between Al-rich nuclei and Si-rich oligomers available in the interstitial solution [60]. 

Q5. What is the effect of the presence of occluded volume on the formation of LTA?

In addition, due to the existence of occluded volume, part of the interstitial water that cannot stay within the framework will be expelled out [71]. 

Q6. What is the reason for the chemical shrinkage of MKG paste?

In the very early age, MKG paste showed chemical shrinkage due to the continuous dissolution of the precursor to form monomers or small oligomers. 

Q7. What is the reason why the crystalline structures of zeolites occupy a larger?

The occluded volume within the crystalline structures is the main reason why the (nano-) zeolites and water produced from polymerization occupy a larger volume than the reactants (monomers or oligomers). 

Q8. What is the reason for the formation of Si-rich gels?

When the samples were cured for more than 48 hours, the Al-rich entities were reorganized and further polymerized with the silicate oligomers available in the interstitial solution to produce a Si-rich geopolymer network. 

Q9. What is the chemical formula of the main gels formed in the third stage?

Since the Si-rich gels formed in the third stage are mainly Q4(3Al)/Q3(1Al) and Q4(2Al) with an overall Si/Al ratio around 1.5, here the authors assume the chemical formula of one ofthe main gels formed in this stage is Na·AlO2·1.5SiO2·H2O. 

Q10. How can the authors calculate the chemical deformation of the formation of LTA?

Using LTA (Na12(AlO2)12(SiO2)12·27H2O) as an example, the chemical deformation of the formation of LTA can be roughly calculated as shown in equation 2, assuming the reactants are purely monomers. 

Q11. What is the chemical deformation of the LTA type zeolite?

According to the available data of zeolites in [71], it can be calculated that the formation of different kinds of zeolites (e.g. zeolite LTA, faujasite, phillipsite, etc) from monomers can generate different amounts of chemical expansions, but never chemical shrinkage, due to the large intrazeolitic porosities and the large occluded volumes in these zeolites. 

Q12. What is the dissolved fraction of the amorphous phase?

The dissolved fraction corresponding to the mass loss after chemical dissolution treatment is determined as the amorphous phase content. 

Q13. What is the reason for the volume of pores in zeolites?

When these species are polymerized to form crystalline structures like zeolites, pores within these frameworks are created and occupy a certain amount of volume.