4. Flotation practice

In industries froth flotation is a continuous process involving a regular flow of feed pulp and separation of minerals into the regular respective product streams. The major elements of flotation operations are:

#### 4.1 Importance of reagent conditioning

As the choice of specific reagent for a given ore is difficult and challenging, so is the selection of quantity, mode and time of addition of the reagents. The selection of reagent quantity does not pose much problem as a more or less precise reagent type and quantity for a specific ore system are available through reagent manufacturers and practising personnel. Whether the total quantity is to be added at different stages is a matter of difficult choice and is to be based upon carefully laboratory investigation regarding the case of floatability of minerals.

Adsorption of surfactant is in direct correlation with the solid-water-air interfaces as the main role of surfactants is to modify the properties of interfaces for increased adsorption of reagents and enhanced flotation process. Modified starches and blended polymers can be better alternatives to normal starches due to their higher solubility and better flocculation action.

#### 4.2 Applications of flotation other than mineral industries

Application of flotation has been envisaged in other areas besides mineral engineering. Some of the examples are:

3.3.3 Dispersants

Table 2.

Modifying agents

Frothers All iron

Surfactants and Detergents

oxides, silica, alumina, phosphorus

Direct and reverse iron ore flotation

3.3.4 pH regulators

and acids.

22

These are used to minimize the deleterious effect of undesired slime coating

Reagents Application Classification Composition Functioning process

1:2 Mass ratio of 4:1 ether monoamine to nonylphenol

The reagents are used as undiluted and also prepared as solution in H2O

Slurry Dry

5–10% solution 10% solution Solution Solution of 0.30–0.80 kg/ton Solution of 0.5–1.2 kg/ton

hydrophobicity Decreased surface tension at liquid-gas interface and reduce froth depth

Provides most viscous, stable froth, have collecting action Less viscous but stable froth, have collecting

Fine, fragile froth; inert

pH regulator; disperses gangue slimes Activates silica with fatty acid collectors Disperses siliceous gangue slimes; Fragile froth Depress iron-bearing

action

to rubber Slightly stable froth Slightly stable froths Fine-textured froth; frequently used with ores containing slimes

minerals

ether amine

etheramine

fatty alcohol

collectors

250, DF 450 5. Fuel oil

7. MIBC

Ca(OH)2 2. Soda ash, NaOH Caustic soda, NaOH Sulphuric acid, H2SO4 3. Ca2+ (CaCl2), Mg2+ (MgCl2)

4. Na2SiO3 5. Starch, dextrin

gum, PAM

Reagent types used in mineral oxide industries (specifically for iron ores).

6. Aliphatic alcohols,

1. Lime (CaO) or slaked lime

Quebracho, tannic acid, gaur

with fatty acids 2. Fatty acids (anionic collectors) and amphoteric

4. Non-phenol ethoxylated with ethylene oxide and

5. Mixture of amine and hydrochloric acid

6. N-dodecyl ethylene diamine (mixture of 1-bromododecane, ethanol and ethylenediamine 7. Mixture of primary ether monoamine, oxyethylated nonylphenol and oxyethylated

1. Non-polar oils emulsified

1. Pine oil (alpha-terpineol) 2. Cresylic 'acid' (cresols) 3. Polypropylene glycols 4. DF (Dow Froth) 200, DF

The pH regulators help in maintaining adequate pH of the pulp, which determines the selective separation of minerals. These are achieved by variety of bases

(Tables 2 and 3), e.g. sodium silicate and sodium metasilicate.


may appear. Finally, if the crisis implies a recession in the economy and a very slow recovery, we would be describing the L-shape [56].

There is widespread uncertainty about the economic effects of the crisis [57]. Some authors argue that the recovery will be similar to that which occurred in China between 2005 and 2013, following the tendency of L-shaped growth [58]. This economic effect may be very different in the other countries. In this case, what counts is the adaptation of the population to this "new normality" [59].

This means that people have to adapt quickly, and be flexible in how they proceed. People have to understand that spirits are exacerbated, and act accordingly, both for employees and employers [60]. The second thing is to know that we are in a situation that demands priorities, and here it is the health issue. It would be interesting to measure this problem and understand that very complex weeks are coming, and take measures to try to stop or mitigate the impacts on the environment through the application of waste management policies [44].

In the first part of this chapter we described three dimensions of analysis, now we will briefly delve into the economic dimension. The economic growth and labor issues corresponds to π = 100%, z = 0 and w = 0 in **Figure 1**. It is useful to recognize waste management workers by definition, formal and informal, in daily contact with waste, who are more vulnerable than other categories of the population to potential health problems.

In this way, one of the key issues that is arising all over the world is the need to protect waste workers, formal or informal, as a special asset that provides an essential service. Not only the International Labour Organization, but also many unions and NGOs are advocating putting the protection of waste workers in the center of our attention in this period. For countries outside of the EU and North America, outside of the high-income countries, most recycling is done by independent or informal recyclists who collect materials simply to feed their families [41].

Some countries which have informal recyclers are countries such as South Africa, but also some countries in Europe such as Serbia. There are many people who cannot eat because they are in lockdown. They would normally be picking up recyclables and now they are not allowed to go out. Also people who are in formalized recycling situations. For those in Colombia or Brazil, the government often tells people to stop recycling. At the same time, we even see in the Netherlands a tremendous amount of littering, and so the environment is changing quickly and nobody is really thinking about what these informal workers actually need [61].

Some authors claim that recycling is determined by the country's income level. Low and middle income countries where most recycling happens by independent or informal recyclers, whether formalized as in Brazil and Colombia, or tolerated or semi formalized as in India should have these systems reestablished [62]. What is really important is to figure out a way for them to continue to provide the service that they provide for the city by managing its recyclables and giving the people and their families a way of making a living by thinking actively about how they can safely go about their work [40].

#### **4. Conclusions**

We really hope that the post-crisis crisis will be the momentum for radical change in society worldwide. We also propose that people should be referring to expert guidance, not only from their national and regional governments, but also coming out of the World Health Organization and also for low-and middle-income countries.

**111**

**Author details**

Paris, France

Jean Pierre Doussoulin1,2

<EMAIL_ADDRESS>
provided the original work is properly cited.

1 Universidad Austral de Chile, Economic Institute, Valdivia, Chile

\*Address all correspondence to<EMAIL_ADDRESS>
2 Université Gustave Eiffel, Research Team on the Use of Panel Data in Economics,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*COVID-19: Turning a Threat into an Opportunity for the Circular Economy*

resources, not mention which trials and which patients?

recovery efforts between these dimensions? How to allocate time and humans

In this chapter we have not wanted to give specialized answers from an economic, or medical or environmental point of view, but rather to relate these

There is an abundance of guidance to discuss about the economy, and to adapt it for the environment, and economically, an austere fiscal policy, which prioritizes employment and reactivation, through the optimization of resources and efforts. We need to reprioritize our priorities. What is important and what is not important is central, and this is why we also need to face changes in human behavior. We want to argue that one of the things that seem to be a very important thing is the idea of solidarity. It is just a matter of finding it with respect to health care waste because there is a great deal that has been written and it is just necessary that persons access that which it is suitable for the situation. We can build all this knowledge

The government response needs to act on three issues. First, to ensure that essential services are carried out without any interruption. Secondly, to ensure worker's safety above any other measure, because we need these teams, we need these people, and we need these heroes on the streets and, thirdly, we need to ensure frequent and easy communication to the citizens to stop fake news and to

Finally, a good way to face the crisis is to win small battles, in health, through the territorial management of contagions, in the environment avoiding very long-term

objectives, and instead targeting more short- and medium-term goals.

*DOI: http://dx.doi.org/10.5772/intechopen.94619*

answers to other topics of interest to society.

during this new situation, every one of us.

avoid dissemination of misunderstanding.

The COVID-19 crisis assumes that the effects are divided among economic growth, medical and sustainability. So how do we distribute the effect and the

#### *COVID-19: Turning a Threat into an Opportunity for the Circular Economy DOI: http://dx.doi.org/10.5772/intechopen.94619*

recovery efforts between these dimensions? How to allocate time and humans resources, not mention which trials and which patients?

In this chapter we have not wanted to give specialized answers from an economic, or medical or environmental point of view, but rather to relate these answers to other topics of interest to society.

There is an abundance of guidance to discuss about the economy, and to adapt it for the environment, and economically, an austere fiscal policy, which prioritizes employment and reactivation, through the optimization of resources and efforts.

We need to reprioritize our priorities. What is important and what is not important is central, and this is why we also need to face changes in human behavior. We want to argue that one of the things that seem to be a very important thing is the idea of solidarity. It is just a matter of finding it with respect to health care waste because there is a great deal that has been written and it is just necessary that persons access that which it is suitable for the situation. We can build all this knowledge during this new situation, every one of us.

The government response needs to act on three issues. First, to ensure that essential services are carried out without any interruption. Secondly, to ensure worker's safety above any other measure, because we need these teams, we need these people, and we need these heroes on the streets and, thirdly, we need to ensure frequent and easy communication to the citizens to stop fake news and to avoid dissemination of misunderstanding.

Finally, a good way to face the crisis is to win small battles, in health, through the territorial management of contagions, in the environment avoiding very long-term objectives, and instead targeting more short- and medium-term goals.

### **Author details**

*Circular Economy - Recent Advances, New Perspectives and Applications*

recovery, we would be describing the L-shape [56].

potential health problems.

safely go about their work [40].

**4. Conclusions**

may appear. Finally, if the crisis implies a recession in the economy and a very slow

There is widespread uncertainty about the economic effects of the crisis [57]. Some authors argue that the recovery will be similar to that which occurred in China between 2005 and 2013, following the tendency of L-shaped growth [58]. This economic effect may be very different in the other countries. In this case, what

This means that people have to adapt quickly, and be flexible in how they proceed. People have to understand that spirits are exacerbated, and act accordingly, both for employees and employers [60]. The second thing is to know that we are in a situation that demands priorities, and here it is the health issue. It would be interesting to measure this problem and understand that very complex weeks are coming, and take measures to try to stop or mitigate the impacts on the environ-

In the first part of this chapter we described three dimensions of analysis, now we will briefly delve into the economic dimension. The economic growth and labor issues corresponds to π = 100%, z = 0 and w = 0 in **Figure 1**. It is useful to recognize waste management workers by definition, formal and informal, in daily contact with waste, who are more vulnerable than other categories of the population to

In this way, one of the key issues that is arising all over the world is the need to protect waste workers, formal or informal, as a special asset that provides an essential service. Not only the International Labour Organization, but also many unions and NGOs are advocating putting the protection of waste workers in the center of our attention in this period. For countries outside of the EU and North America, outside of the high-income countries, most recycling is done by independent or informal recyclists who collect materials simply to feed their families [41]. Some countries which have informal recyclers are countries such as South Africa, but also some countries in Europe such as Serbia. There are many people who cannot eat because they are in lockdown. They would normally be picking up recyclables and now they are not allowed to go out. Also people who are in formalized recycling situations. For those in Colombia or Brazil, the government often tells people to stop recycling. At the same time, we even see in the Netherlands a tremendous amount of littering, and so the environment is changing quickly and nobody is really thinking about what these informal workers actually need [61]. Some authors claim that recycling is determined by the country's income level. Low and middle income countries where most recycling happens by independent or informal recyclers, whether formalized as in Brazil and Colombia, or tolerated or semi formalized as in India should have these systems reestablished [62]. What is really important is to figure out a way for them to continue to provide the service that they provide for the city by managing its recyclables and giving the people and their families a way of making a living by thinking actively about how they can

We really hope that the post-crisis crisis will be the momentum for radical change in society worldwide. We also propose that people should be referring to expert guidance, not only from their national and regional governments, but also coming out of the World Health Organization and also for low-and middle-income countries. The COVID-19 crisis assumes that the effects are divided among economic growth, medical and sustainability. So how do we distribute the effect and the

counts is the adaptation of the population to this "new normality" [59].

ment through the application of waste management policies [44].

**110**

Jean Pierre Doussoulin1,2

1 Universidad Austral de Chile, Economic Institute, Valdivia, Chile

2 Université Gustave Eiffel, Research Team on the Use of Panel Data in Economics, Paris, France

\*Address all correspondence to<EMAIL_ADDRESS><EMAIL_ADDRESS>
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[30] Liu K, Wang H, Liu H, Nie S, Du H, Si C. COVID-19: Challenges and perspectives for the pulp and paper industry worldwide. BioResources. 2020;15(3):4638-41.

[31] Sharma HB, Vanapalli KR, Cheela VS, Ranjan VP, Jaglan AK, Dubey B, et al. Challenges, opportunities, and innovations for effective solid waste management during and post COVID-19 pandemic. Resour Conserv Recycl. 2020;162:105052.

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[13] Morlat C. Sustainable Production System: Eco-development versus

Sustainable Development. John Wiley &

[14] Korhonen J, Honkasalo A, Seppälä J. Circular Economy: The Concept and its Limitations. Ecol Econ. 2018;143:37-46.

[15] McDonough W, Braungart M. Cradle to cradle: Remaking the way we make things. North point press; 2010.

[16] Esposito M, Tse T, Soufani K. Introducing a Circular Economy: New Thinking with New Managerial and Policy Implications. Calif Manage Rev.

[17] Kirchherr J, Reike D, Hekkert M. Conceptualizing the circular economy: An analysis of 114 definitions. Resour Conserv Recycl. 2017;127:221-32.

[18] de Jesus A, Mendonça S. Lost in Transition? Drivers and Barriers in the Eco-innovation Road to the Circular Economy. Ecol Econ. 2018;145(C):75-89.

[19] Kirchherr J, Piscicelli L, Bour R, Kostense-Smit E, Muller J, Huibrechtse-

Truijens A, et al. Barriers to the Circular Economy: Evidence From the European Union (EU). Ecol Econ.

2018;150:264-72.

Where do we stand? Ecol Econ.

2008;67(2):281-310.

Sons; 2020.

2018;60(3):5-19.

[1] Klenert D, Funke F, Mattauch L, O'Callaghan B. Five Lessons from COVID-19 for Advancing Climate Change Mitigation. Available SSRN

[2] Wolf LJ, Haddock G, Manstead AS, Maio GR. The importance of (shared) human values for containing the COVID-19 pandemic. Br J Soc Psychol.

[3] Maslow A, Lewis KJ. Maslow's hierarchy of needs. Salenger Inc.

Rev Econ Policy. 2020;36.

Francisco; 1973.

Serv. 2018;29:240-50.

1991;3(2):95-122.

1;5(5):359-68.

Organization; 2020.

[5] O'Connell M. To be a machine: adventures among cyborgs, utopians, hackers, and the futurists solving the modest problem of death. Anchor; 2018.

[6] Daly HE. Toward a steady-state economy. Vol. 2. WH Freeman San

[7] Pastén R, Olszynski M, Hantke-Domas M. Does slow and steady win the race? Ecosystem services in Canadian and Chilean environmental law. Ecosyst

[8] O'Connor M. Entropy, structure, and organisational change. Ecol Econ.

[9] Doussoulin JP. A paradigm of the circular economy: the end of cheap nature? Energy Ecol Environ. 2020 Oct

[10] World Health Organization. Water, sanitation, hygiene and waste management for COVID-19: technical brief, 03 March 2020. World Health

[4] Hepburn C, O'Callaghan B, Stern N, Stiglitz J, Zenghelis D. Will COVID-19 fiscal recovery packages accelerate or retard progress on climate change? Oxf

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### *Edited by Tao Zhang*

Nowadays, the restriction of resources and the environment is very severe. A circular economy is the only way to sustainable development, but how this works still needs more exploration. The series of studies carried out by the author are described in detail in this book.

Published in London, UK © 2021 IntechOpen © Ratchat / iStock

Circular Economy - Recent Advances, New Perspectives and Applications

Circular Economy

Recent Advances, New Perspectives

and Applications

*Edited by Tao Zhang*


**Victoria Eugenia García-Vera 1, Antonio José Tenza-Abril 2,\*, José Miguel Saval 2 and Marcos Lanzón 1**

Received: 7 December 2018; Accepted: 22 December 2018; Published: 27 December 2018

**Abstract:** Using durable materials is a sustainable solution for extending the lifetime of constructions. The use of crystalline admixtures makes cementitious materials more durable. They plug pores, capillary tracts and microcracks, blocking the entrance of water due to the formation of crystals that prevent the penetration of liquids. The literature has covered the performance of these admixtures on concrete, but studies on mortars are still scarce. The aim of this study is to investigate the effect of an aggressive environment (sulphuric acid solution—3 wt%) on mortars produced with different percentages of a crystalline admixture (1%, 1.5% and 2% by weight of cement content). Physical and mechanical properties were studied after immersing the mortars in a H2SO4 solution for 90 days. It was found that, after a 90-day sulphuric acid exposure, mortars with the crystalline admixture showed greater compressive strength than the control mortar, besides exhibiting lower mass loss. However, the crystalline admixture did not produce any significant effect on the capillary water absorption coefficient. In a nonaggressive environment, and in the short term, the crystalline admixture did not have a significant effect on the compressive strength, the capillary water absorption coefficient or the ultrasonic pulse velocity.

**Keywords:** crystalline admixture; chemical exposure; sulphuric acid attack; durability; Xypex

#### **1. Introduction**

Nowadays, cement-based materials are exposed to acids because of environmental pollution, contact with some soils, ground waters, industrial waste-waters or sewers. These conditions can be found in some foundations, sanitation networks, treatment plants, agricultural and farm facilities, etc. [1–3]. Materials that are designed to work in aggressive chemical conditions must be durable materials, that is, materials with the capacity to withstand, for its service life, the physical and chemical conditions to which they are exposed [4]. Architects and engineers are vested with the responsibility of designing and building constructions by optimising the existing but limited resources in nature. Working with durable materials contributes to sustainability since they help to maintain the existing resources and avoid causing harm to the environment.

Concrete is susceptible to acid attack because of its alkaline nature. Sulphuric acid is particularly corrosive due to the sulphate ion in addition to the dissolution caused by the hydrogen ion causing the deterioration of cement-based materials. The reaction of the sulphuric acid (H2SO4) with the chemical compounds of cement hydration (calcium silicate hydrate, portlandite and calcium sulphoaluminate hydrate) generates gypsum, amorphous hydrous silica and aluminum sulphate. [3]. These chemical reactions, located in the regions close to the surface, provoke a profound degradation of the hydrated

cement paste in terms of physical and mechanical aspects, such as compressive strength loss, mass variation, cracking, softening and decohesion. This process leads to spalling and exposure of the interior of the concrete structure [5,6].

To improve acid attack resistance in cement-based materials, the matrix must be dense, with low permeability, and it is advisable to use in the production a sulphate-resistant cement, high alumina cement, etc. [7–9]. Some authors state that effective strategies for manufacturing cementitious materials that are durable when exposed to acid attacks involve the following: (i) controlling the materials used during the manufacturing process; (ii) producing them with a low water/cement ratio; and (iii) guaranteeing suitable curing conditions [10,11].

A very popular strategy used to produce durable cement-based material is adding admixtures and additives [12–15]. Some studies utilise nanomaterials to reduce the porosity and water absorption of cement-based materials [16,17], which leads to enhanced durability and improved performance when these materials are exposed to acid attacks. Examples of such nanotechnologies are nano silica, nano alumina, titanium oxide, carbon nanotubes and polycarboxylates [18–22]. Water-repellent materials are also used to increase durability in acid attacks, since they reduce the affinity of capillary pore surfaces to moisture [23,24]. Examples of hydrophobic compounds used as admixtures are powdered stearates, oleates and products based on silanes and silicones [25–27]. When adequate recycling materials are available, another strategy to enhance the concrete durability is the use of aggregates derived from sanitary ceramics. Such concretes are characterised by low water absorption, higher mechanical strength and higher water-resistance compared to conventional concrete. Moreover, they have more resistance to chemically aggressive environments compared to conventional concretes [28–31].

Crystalline admixtures can also help increase the durability of cement-based materials, especially when cementitious materials are in acid environments. According to various manufacturers of products for crystalline waterproofings for concrete—Xypex, Kryton, Penetron, etc.—there are three ways of applying the waterproofing systems: (i) a coating applied as a cementitious slurry to the surface of existing concrete structures; (ii) an admixture added to the concrete at the time of batching; and (iii) a dry-shake to the fresh concrete surface. In all cases, the protection system is a blend of Portland cement, fine treated silica sand and undisclosed chemicals that are the intellectual property of the manufacturer. The catalytic reaction of the chemicals in the admixture occurs as long as there is moisture in the cement-based materials. These chemicals react with calcium hydroxide and other products resulting from cement hydration. The reaction generates nonsoluble crystalline formations that fill the pores and capillary tracks of cement-based materials. The crystalline structure becomes a permanent and integral part of the concrete matrix. Thus, the concrete becomes permanently sealed against the penetration of water or liquids from any direction [32].

The crystallisation process of these admixtures is not immediate, and the complete waterproofing effect is not achieved until approximately 12 days after the concrete creation [33], as long as there is enough moisture for chemical reactions to occur. Moreover, it is especially important to have a moist curing environment to obtain better performance [34]. There are several studies that focused on testing the waterproofing effect of these admixtures [33,35], as well as the impact of an aggressive medium on concretes made with crystalline-based waterproofing products [36,37].

However, it is still a challenge to find high durability mortars manufactured with these types of admixtures in aggressive environments. In this study, a crystalline protection product (applied as an admixture) was used to make mortars with different percentages of admixture (1 wt%, 1.5 wt% and 2 wt%). Their behaviour when they were exposed to an aggressive environment (sulphuric acid solution—3 wt%) was evaluated. Physical (mass loss, ultrasonic pulse velocity and capillary water absorption coefficient) and mechanical (compressive strength) properties were studied after the mortars were immersed in an H2SO4 solution for 28 and 90 days. Moreover, the textural alterations due to the acid attack were evaluated using microscopy.

#### **2. Materials and Methods**

#### *2.1. Materials*

The cement used for the manufacture of the mortars was a high early strength type belonging to the European cement class CEM I 52.5 R [38]. Limestone sand was used as a fine aggregate (Di/di = 0/4). The particle-size distribution was calculated according to the procedure of UNE-EN 933-1 standard [39]. The distribution was obtained for three samples of sand and the mean values were calculated (Figure 1a). Xypex Admix C-1000 NF (Xypex Chemical Corporation, Richmond, BC, Canada) was added in three different concentrations (1 wt%, 1.5 wt% and 2 wt% of the cement weight) depending on the kind of mortar. The specific surface areas of the cement and crystalline admixture (Xypex Admix) used were 1.48 and 0.642 g/m2, respectively (determined by the Brunauer–Emmett–Teller—BET—method), and their particle-size distributions are plotted in Figure 1b. In total, four types of mortars were made: (i) control mortar (A mortar); (ii) mortar with 1 wt% of Xypex (B Mortar); (iii) mortar with 1.5 wt% of Xypex (C Mortar); and (iv) mortar with 2% of Xypex (D Mortar). The dosage used for all mortars was 1 part cement, 0.65 parts water and 3 parts limestone sand.

**Figure 1.** (**a**) Particle-size distribution of the limestone sand. (**b**) Particle-size distribution (done by laser granulometry) of the cement (CEM I 52.5 R) and the admixture (Xypex Admix).

#### Chemical–Physical Characterisation

The crystallographic phases present in the composition of the cement and the admixture (Xypex Admix C-1000 NF) were analysed with X-ray diffraction (XRD) using a Bruker D8-Advance diffractometer (Bruker Española S.A., Madrid, Spain) with mirror Goebel, and a generator of X-ray KRISTALLOFLEX K 760-80F (power: 3000W, voltage: 20–60 KV and current: 5–80 mA) equipped with a X-ray tube with copper anode. The spectra were registered with angles from 4◦ to 60◦ at 0.05◦ stepping intervals in Ө-Ө mode, and the X-ray tube was utilised at 40 kV and 40 mA. The diffraction patterns were evaluated with HighScore software (Malvern Panalytical, Madrid, Spain) and powder diffraction database PDF4+. Moreover, the chemical compositions of the binder and the admixture were analysed with X-ray fluorescence (XRF) using an X-ray sequential spectrometer PHILIPS MAGIX PRO (Philips Ibérica, Madrid, Spain) equipped with a rhodium X-ray tube and beryllium window. The spectrometer was controlled with the software package SuperQ (Malvern Panalytical, Madrid, Spain) that also stored the measurements and results.

The XRF results (Table 1) show that both materials were mainly composed of CaO (cement: 55.4%; Xypex: 59.8%) and SiO2 (cement: 14.9%; Xypex: 8.1%), containing moderate proportions of Al2O3, SO3 and Fe2O3 (percentages between 1.9% and 4.6%). Only the cement contained moderate proportions of MgO (3.3%). The XRD spectra (Figure 2) revealed that both materials had common crystalline compounds, such as alite (C3S), belite (C2S), tetracalcium aluminoferrite (C4AF) and calcite (CaCO3). Gypsum was only detected in the cement, and portlandite and quartz were only detected in the Xypex

admixture. The peak of portlandite in Xypex Admix may indicate that this admixture was partially constituted by hydrated cement.

**Figure 2.** X-ray diffraction (XRD) spectra of cement type CEM I 52.5 R and Xypex Admix. **Table 1.** X-ray fluorescence (XRF) characterisation of CEM I 52.5 R and Xypex Admix.


**Abstract**

Intracranial atherosclerotic stroke differs from extracranial atherosclerotic stroke in many aspects, including risk factors and stroke patterns. It occurs in association with in situ thrombotic occlusion, artery-to-artery embolism, branch occlusion, and hemodynamic insufficiency. Intracranial atherosclerotic stenosis (ICAS) could have only been diagnosed by transcranial Doppler (TCD) and transcranial color-coded sonography (TCCS), which are burdened by a risk of bias, or catheter angiography (DSA), which, on the contrary, is very precise, but rarely it is done in clinical practice due to its invasiveness. Computed tomography angiography (CT-A) and magnetic resonance imaging angiography (MR-A) have increased the identification of ICAS in a wider stroke population.

**Keywords:** intracranial atherosclerotic stenosis (ICAS), transcranial Doppler (TCD), transcranial color-coded sonography (TCCS), catheter digital subtraction angiography (DSA), computed tomography angiography (CT-A), magnetic resonance imaging angiography (MR-A)