Preparation and Characterization of Plasters with ... - MDPI

buildings Article

Preparation and Characterization of Plasters with Photodegradative Action Pierantonio De Luca 1, * ID , Pasquale De Luca 2 , Sebastiano Candamano 1 , Anastasia Macario 2 , Fortunato Crea 1 and Jànos B. Nagy 1 1

2

*

Dipartimento di Ingegneria Meccanica, Energetica e Gestionale, University of Calabria, I-87030 Arcavacata di Rende (CS), Italy; [email protected] (S.C.); [email protected] (F.C.); [email protected] (J.B.N.) Diparitmento di Ingegneria per l’Ambiente e il Territorio e Ingegneria Chimica, University of Calabria, I-87030 Arcavacata di Rende (CS), Italy; [email protected] (P.D.L.); [email protected] (A.M.) Correspondence: [email protected]; Tel.: +39-0984-496757

Received: 26 July 2018; Accepted: 30 August 2018; Published: 3 September 2018

Abstract: The aim of this project is to investigate the behaviour of several special types plasters specifically designed to degrade the most common pollutants which are present in the atmosphere. In particular, specific additives have been added to these plasters, in order to obtain a broad spectrum of active and synergic response, each of which have peculiar functions: - microporous materials, such as clinoptilolite, a natural zeolite, that promotes the adsorption of air pollutants thanks to its porous nature; - nano-fillers, such as carbon nanotubes, that behave both as reinforcing agents as well as adsorbent materials; - photochemical agents, such as titanium oxide, that degrade air pollutants, previously adsorbed on carbon nanotubes and zeolites, thanks to the action of light that activates photodegradation reactions. All the samples were also characterized in terms of mechanical properties, adhesion to supports and water absorption. Furthermore, photodegradation tests were carried out by exposing plaster surfaces, wetted with a Rodamine solution, to Ultraviolet rays (UV) for different times. Plasters photodegradative capacity was evaluated and the results highlighted the fact that the designed admixtures showed an important photodegradative action, strictly dependent on the types and specific ratios of the selected additives. Keywords: photodegradative action; plaster; carbon nanotubes; clinoptilolite; titanium oxide; zeolite

1. Introduction Even though construction in the past represented a sector with a high consumption of materials with a great impact on the environment, it is now becoming an increasingly sustainable and environmental friendly sector [1–4]. Environmental protection involves the adoption of policies that take into consideration many aspects such as the reduction of and impact of materials [5–9]. There are many different types of materials that are used in construction such as plasters, binders, insulating panels, paints etc. The preparation of which requires the use of components that often do not reconcile with respect and protection towards the environment, such as the use of adhesives and paints that in time may release harmful substances and thus creating a potentially dangerous environment health wise giving rise to the so-called Sick Building Syndrome [10–15]. This is why over the last years, many studies have turned towards the research of innovative materials that are, above all, prepared with possible natural and safe components [16–23].

Buildings 2018, 8, 122; doi:10.3390/buildings8090122

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Further studies were aimed towards the production of building materials using a variety of waste from civil to industrial with the dual advantage of offering a new location and value to waste and in order to be able to prepare innovative materials [24–27]. Therefore, one of the most significant aspects, of our present time, is to guarantee and preserve the link between innovation and the environment which reaches its maximum expression as in the case of multifunctional materials, i.e., those that add new functions to traditional ones thanks to the combination of other materials. These materials, therefore can be intended as composite materials consisting of a matrix of traditional composition and of additives of different nature and with particular peculiarities. The additives with photodegradative action make it possible to obtain materials that will guarantee a performance of self-cleaning and de-pollution in the presence of light [28–33] by activating a strong oxidation process that leads to the decomposition of certain pollutants, when these come into contact with the surface of a cement product. The pollutants present in the atmosphere may become even more dangerous in the presence of atmospheric particulate as they can impregnate onto it by depositing onto the surfaces more easily thus increasing their duration in the environment [34–38]. However, if this phenomenon occurs on surfaces that are photocatalyzed all this may improve degradation of pollutants. Amongst photodegradative agents we find titanium oxide [39–41] most commonly used together with other oxides [42–48]. In recent years, new photocatalytic species such as titano silicates given rise to much many interests. In particular, the Engelhard titanium silicate phases [49–56] have shown to have a photocatalytic activity which adds to their characteristics of being microporous materials, therefore also capable of acting as adsorbent materials [57–61]. The aim of our research was to find the optimal conditions in order to obtain special mortars to be used as finishing plasters which, in addition to their traditional functions, may also have the ability to adsorb and degrade any pollutants in the atmosphere. The presence of titanium oxide, as already extensively studied and reported in literature [39], allows the photodegradation of pollutants such as VOC’s, improved in our case, from adsorption of the latter by the zeolite and carbon nanotubes that favor in this way the contact between titanium oxide and pollutants. 2. Materials and Methods Three special additives were added to a mixture of traditional mortar, intended for use as plaster, each of which had different functions. These selected additives were: a photocatalytic agent, a microporous agent and a nano-fibro strengthening agent with adsorbent capacity. The base mortar, i.e., without additives, was prepared with lime putty mixed together with sand previously washed in the proportion of 2/5 of lime and 3/5 of sand, and to which a quantity of white portland cement of 5% of the total weight obtained from the sum of lime plus sand was added. This mixture called base mortar was indicated with “S”. Particular importance has been given to the identification of the S/A ratio (S = base mortar, A = water) more suitable according to the quantity and nature of the additives added, since this depends on the characteristics of the hardened material and its workability for an efficient installation. In particular, titanium oxide, TiO2 , was used as a photodegradative agent. in the form of anatase (Alfa-Aesar). The adsorbent agents used were a natural zeolite, clinoptilolite [62–66], and carbon nanotubes [67,68]. The latter were used both as adsorbents and as reinforcing nano-fibers [69–72]. The clinoptilolite used is a commercial zeolite. The carbon nanotubes used are multi-walled nanotubes (MWCNTs) synthesized and characterized as already reported in our previous article [68]. Both systems were studied, those with only one additive, as well as those with mixed systems, in order to evaluate any synergistic action resulting from the simultaneous presence of more additives in the mortar. The range of variability of the percentages used of the additives has been provided by preliminary investigations with respect to the characteristic of the mortar obtained in the fresh state. Larger percentages of additives compared to those used were discarded because the mortars had poor

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“spread” onto a wall surface, it should therefore be easly malleable, but at the same time it must not characteristics their use. Initfact, since it is a finishing which “spread” onto a wall “spread” afor wall surface, should therefore be easlymortar, malleable, butmust at thebesame time it must not drip onceonto applied. surface, it should therefore be easly malleable, but at the same time it must not drip once applied. drip once applied. The characterization of the systems was carried out through tests in order to determine: The characterization characterization of the the systems systems was carried carried out through through tests in in order order to determine: determine: The of was out tests to mechanical compressive strength, photodegradative activity, water absorption coefficient and tear mechanical compressive strength, photodegradative activity, water absorption coefficient and mechanical resistance. compressive strength, photodegradative activity, water absorption coefficient and tear tear resistance. resistance. The compressive strength of the prepared mortars was carried out on pellets-shaped The compressive strength the prepared mortars was on moulds pellets-shaped specimens. The compressive strength of pellets the prepared mortars was out carried out on(Figure pellets-shaped specimens. The preparation ofofthe was carried outcarried using metal 1a). Five The preparation of the pellets was carried out using metal moulds (Figure 1a). Five specimens specimens. The prepared preparation thesystem. pelletsAfter was acarried using 1a). were Five specimens were for of each 10 daysout period of metal curing,moulds at room(Figure temperature and prepared for each system.level, After a 10 days period at room temperature environmental specimens were prepared for each system. Afterwere a of 10curing, days period of curing, at room temperature and environmental humidity the specimens deformed thus obtaining a and series of pellets of humidity level, the specimens were deformed thus obtaining a series of pellets of cylindrical form environmental humidity level, the specimens were deformed thus obtaining a series of pellets of cylindrical form with a radius equal to 1.2 cm and a height of approx. 1.0 cm (Figure 1b). with a radius equal to 1.2 and equal a height of 1.0 (Figure Subsequently compressive cylindrical form with a cm radius 1.2approx. cm on and height of1b). approx. 1.0 cm Vk (Figure 1b). Subsequently compressive strength wasto measured theacm pellets with a Vanderkamp 200 tester strength was measured on the pelletswas with a Vanderkamp 200 tester 1c). Subsequently compressive strength measured on the Vk pellets with a(Figure Vanderkamp Vk 200 tester (Figure 1c). (Figure 1c). a) a)

b) b)

c) c)

Figure 1. (a) Moulds; (b) Mortar pellets; (c) Hardness tester. Figure 1. (a) Moulds; (b) Mortar pellets; (c) Hardness tester. Figure 1. (a) Moulds; (b) Mortar pellets; (c) Hardness tester.

In order to determine the photodegradative activity, then specimens were prepared with the In order order to determine determine the photodegradative photodegradative activity, then specimens were prepared prepared withofthe the In to the then specimens were with previously selected composition mortars, 1 × 6 × 9activity, cm in size then left to mature for a period 10 previously selected composition mortars, 1 × 6 × 9 cm in size then left to mature for a period of previously selected composition mortars, 1 × 6 × 9 cm in size then left to mature for a period of 10 days. Subsequently a solution of Rodamine with a concentration of 0.2g/L was brushed onto the 10 days. Subsequently a solution Rodamine with concentration of 0.2g/L 0.2 g/Lwas was brushed onto the days. Subsequently a solution ofofRodamine with aaconcentration of brushed surface of the specimens. Finally, the latter were subjected to UV irradiation by the use of onto a 100the W surface of the specimens. Finally, the latter were subjected to UV irradiation by the use of a 100 W UV surface of the specimens. Finally, latter to UV2a). irradiation by the use of a 100 W λ = 365 nm for a the period of were three subjected hours (Figure Prior to irradiation, part of the lamp and λ =shielded 365λnm for anm period three hours (Figure Prior to irradiation, part surface = 365 forradiation aofperiod of order three hours (Figure 2a). Prior to irradiation, part of was the surface was from the in to be2a). able to observe, at the end of of the these tests, the shielded from the radiation in order to be able to observe, at the end of these tests, the color variations surface was shielded from the radiationand in order to be able to observe, at2b). the end of these tests, the color variations between the irradiated the screened surfaces (Figure between the irradiated and screenedand surfaces (Figure surfaces 2b). color variations between thethe irradiated the screened (Figure 2b). a) b) a) b)

Figure 2. (a) Lamp Box UV 100 W − λ = 365 nm; (b) Specimen brushed with a solution of Rodamine Figure 2. shielded. (a) Lamp Box UV 100 W − λ = 365 nm; (b) Specimen brushed with a solution of Rodamine partially Figure 2. (a) Lamp Box UV 100 W − λ = 365 nm; (b) Specimen brushed with a solution of Rodamine partially shielded. partially shielded.

In order to be able to determine the coefficient water absorption, a series of prismatic specimens order to beAfter able to water absorption, series of prismatic wereInprepared. a determine period of the 28 coefficient days of maturation, in an aenvironment with aspecimens constant Inprepared. orderand to be able ato period determine the coefficient water aoven series prismatic were After of 28 days of dried maturation, in an environment with aspecimens constant temperature humidity level, these were then in absorption, a ventilated at of a temperature of 60 °C were prepared. After a period of 28 days of maturation, in an environment with a constant temperature temperature and wereconsider then dried inconstant a ventilated oven a temperature of 60two °C until reaching thehumidity constantlevel, mass.these We may that mass hasatbeen reached when ◦ C until reaching and humidity level, these were then dried inconsider a ventilated oven at a temperature of by 60 until reaching the constant mass. We may constant mass hasdiffer been reached when0.2%. two consecutive weighing procedures, at distance of 24 that h apart each, do not more than the constant mass.mass Weprocedures, may consider that constant mass has been when twoisconsecutive consecutive weighing at the distance of 24 h apart each, do not differ by more than 0.2%. Once the constant is reached on specimens, the coefficient ofreached water absorption calculated, weighing procedures, at distance of 24 h apart each, do not differ by more than 0.2%. Once the Once the constant massreported is reached on the specimens, following procedures in the standard [73]. the coefficient of water absorption is calculated, following procedures reported in the standard [73].

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constant massstandards is reached[74] on the the“tearing-off” coefficient oftest. water absorption is calculated, following European wasspecimens, used for the This test determined the adhesion procedures reported in athe standard [73]. in this case was a brick. Traction force was applied by a between the mortar and support, which European standards was used the “tearing-off” test. Thiswas testsubsequently determined the adhesion steel cylinder glued onto the[74] surface of thefor specimen (Figure 3a) which connected the mortar andtester a support, which this case was a brick. force was applied by atest steel tobetween the tear-off-adhesive (Figure 3b). in Figures 3c,d show steelTraction cylinders and sample after cylinder glued onto the surface of the specimen (Figure 3a) which was subsequently connected to the respectively tear-off-adhesive tester (Figure 3b). Figure 3c,d show steel cylinders and sample after test respectively

Figure with steel steelcylinders cylinders connected to the instrument formeasurement the measurement of Figure3.3.(a) (a)Sample Sample with connected to the instrument for the of adhesion adhesion strength; (b) tear-off-adhesive tester; steel cylinders after test; (d)sample after test. strength; (b) tear-off-adhesive tester; (c) steel (c) cylinders after test; (d)sample after test.

3. 3. Results and Discussion Results and Discussion This project was carried out through consecutive phasesphases as illustrated below:below: This project was carried out through consecutive as illustrated 

Identification of the S/A ratio optimal (S = base mortar, A = water) according to the different Identification of the S/A ratio optimal (S = base mortar, A = water) according to the different quantities of additives, through compression resistance tests. quantities of additives, through compression resistance tests.  Characterization of systems with only one additive. • Characterization of systems with only one additive.  Characterization of systems with multiple additives. • Characterization of systems with multiple additives.

•

3.1. Identification of the S/A Ratio and the Quantity of Optimal Additives 3.1. Identification of the S/A Ratio and the Quantity of Optimal Additives Initially, different systems had been previously prepared in order to identify the S/A ratio and Initially, different systems had been previously prepared in order to identify the S/A ratio and the quantity of optimal additive. Figures 4a–c show the compressive strength values of the mortars the quantity of optimal additive. Figure 4a–c show the compressive strength values of the mortars produced as a function of the S/A ratio and the quantity of the different additives added as, produced as a function of the S/A ratio and the quantity of the different additives added as, respectively respectively for clinoptilolite, titanium oxide and carbon nanotubes. for clinoptilolite, titanium oxide and carbon nanotubes. As the values shown in Figure 4 demonstrate; we may note, as expected, that as the S/A ratio As the values shown in Figure 4 demonstrate; we may note, as expected, that as the S/A ratio increases, so does the mechanical resistance. By using an equal S/A ratio, it is clear that the addition increases, so does the mechanical resistance. By using an equal S/A ratio, it is clear that the addition of of clinoptilolite improves mechanical strength, up to a percentage of 10% (Figure 4a). Pozzolanic clinoptilolite improves mechanical strength, up to a percentage of 10% (Figure 4a). Pozzolanic effect of effect of zeolite, due to the reaction of soluble SiO2 and Al2O3 with Ca(OH)2 to produce C–S–H zeolite, due to the reaction of soluble SiO and Al O3 with Ca(OH)2 to produce C–S–H densified the densified the plaster matrix, thus reducing 2porosity2and improving mechanical properties. plaster matrix, thus reducing porosity and improving mechanical properties. We may observe that anything above this percentage causes a lowering of the resistance due to We may observe that anything above this percentage causes a lowering of the resistance due to a a more difficult cohesion of the mortar in the presence of an excessive quantity of zeolite. This trend more difficult cohesion of the mortar in the presence of an excessive quantity of zeolite. This trend is is registered for all three values of S/A used. Analysis of the data shown in Figure 4b shows that for registered for all three values of S/A used. Analysis of the data shown in Figure 4b shows that for an an S/A ratio of 2 and 3, the resistance value at compression increases up to a percentage of TiO2 equal S/A ratio of 2 and 3, the resistance value at compression increases up to a percentage of TiO2 equal to to 0.5% and then decreases. For a ratio S/A = 4, there is a gradual decrease in compressive strength as 0.5% and then decreases. For a ratio S/A = 4, there is a gradual decrease in compressive strength as the percentage of TiO2 increases. Most probably, the ratio S/A = 4 is too high and a further addition the percentage of TiO2 increases. Most probably, the ratio S/A = 4 is too high and a further addition of of TiO2 makes the homogenization and hydration of the components even more difficult. The TiO2 makes the homogenization and hydration of the components even more difficult. The analysis analysis of the data in Figure 4c shows that the compressive strength increases, only for a ratio S/A = of the data in Figure 4c shows that the compressive strength increases, only for a ratio S/A = 3 and 3 and a percentage of Carbon Nanotubes equal to 0.025%. As regards, all the other systems, a percentage of Carbon Nanotubes equal to 0.025%. As regards, all the other systems, however, the however, the mechanical resistance was found to be lower than that of the basic mortar. mechanical resistance was found to be lower than that of the basic mortar.

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(a)

(b)

(c)

Figure 4. Compressive strength of the mortars obtained by varying the S/A ratio and the amount of

Figure 4. Compressive strength of the mortars obtained by varying the S/A ratio and the amount of additive for (a) clinoptilolite, (b) titanium oxide, (c) carbon nanotubes, respectively. additive for (a) clinoptilolite, (b) titanium oxide, (c) carbon nanotubes, respectively. 3.2 Characterization of Systems with a Single Additive

3.2. Characterization of Systems with a Single Additive Systems with a single additive have been formulated and characterized on the basis of data obtained, above mentioned. A constant ratio S/A = 3 was chosen for these systems,which resulted Systems as with a single additive have been formulated and characterized on the basis of data in being the most optimal even from an applicative point of view. The following Table 1 shows obtained, as above mentioned. A constant ratio S/A = 3 was chosen for these systems, which the resulted composition of the chosen systems, with only one additive, for the course of the characterization. in being the most optimal even from an applicative point of view. The following Table 1 shows the composition of1.the chosen systems, withsystems, only one forcharacterization, the course of with the characterization. Table Composition of the selected for additive, course of the one additive only.

Table 1. Composition of the selected systems, for course of the characterization, with one additive only. Systems S/A Clinoptilolite (%) TiO2 (%) Carbon Nanotubes (%) 1 3 0 0.0 0.000 Nanotubes (%) Systems S/A Clinoptilolite (%) TiO2 (%) Carbon 2 3 5 0.0 0.000 1 3 0 0.0 0.000 3 3 0 0.5 0.000 2 3 5 0.0 0.000 4 3 0 0.0 0.025 3 3 0 0.5 0.000 4 3 0 0.0 0.025

3.2.1. 3.2.1.Colorimetric ColorimetricTests TestsofofPhotoactivity Photoactivity The following Table 2 2shows to UV The8, following showsthe theimages imagesofofthe thespecimens specimensbefore beforeand andafter afterexposure exposure to UV Buildings x xFOR REVIEW 6 6of 1414 Buildings2018, 2018, 8, FORPEER PEERTable REVIEW of

irradiation, irradiation,regarding regardingdifferent differentsystems systemscontaining containingonly onlyone oneadditive. additive. 3.2.1. Colorimetric Tests ofofREVIEW Photoactivity 3.2.1. Colorimetric Tests Photoactivity Buildings 2018, 8, x FOR PEER

of 14 Buildings 2018, 8, 1228, x FOR PEER 66 6of 14 Buildings 2018, REVIEW of 14 Table 2.2.Images Table Imagesofofspecimens specimensbefore beforeand andafter afterUV UVirradiation irradiationfor for3 3h.h. Buildings 2018, 8, x FOR PEER REVIEW 6 of 14 14 Buildings 2018, 8, x FOR PEER REVIEW 6 of The following Table 2 shows the images of the specimens before and after exposure to UV The following Table 2 shows the images of the specimens before and after exposure to UV

3.2.1. Colorimetric Tests of Photoactivity Before Systems After irradiation, regarding different systems only Systems Before After irradiation, regarding different systemscontaining containing onlyone oneadditive. additive. 3.2.1. Colorimetric Tests ofofPhotoactivity 3.2.1. Colorimetric Tests Photoactivity 3.2.1. Colorimetric Tests of Photoactivity The following Table 2 shows the images of the specimens before and after exposure to UV The Table 2Images the ofofthe specimens before and after exposure totoUV Table 2.2.Images of before and after UV irradiation for 3 3h. Table ofspecimens specimens before and after UV irradiation for h. Thefollowing following Table 2shows shows theimages images the specimens before and afterexposure exposureto UV irradiation, regarding systems containing only one additive. The following Table 2different shows the images of theonly specimens before and after UV irradiation, regarding different systems containing one additive. 11 irradiation, regarding different systems containing only one additive. Systems Before After irradiation, regarding Systemsdifferent systems containing Before only one additive. After Table 2. Images of specimens before and after UV irradiation for 3 h. (without (withoutadditive) additive) Table 2. Images of specimens before and after UV irradiation for 3 h. Table 2. Images of specimens before and after UV irradiation for 3 h.

Table 2. Images of specimens Before before and after UV irradiation for 3 h. Systems After Systems Before After Systems Before After 11 Systems Before After (without additive) (without additive) 1 1 2 (without12additive) (without additive) (with (withclinoptilolite) clinoptilolite) (without additive)

1 (without additive)

22 (with clinoptilolite) (with clinoptilolite) 2 2 23 (with clinoptilolite) 3 (with clinoptilolite) (with TiO 2)2) (with clinoptilolite) (with TiO 2 (with clinoptilolite)

33 (with (withTiO TiO2)2) 34 33 4 (with TiO 2) (with Carbon (withTiO Carbon (with 2) 2) (with TiO 2 Nanotubes) Nanotubes)

3 4 4 (with TiO2 )

(with (withCarbon Carbon Nanotubes) 4 Nanotubes) 44 (with Carbon (with Carbon (with Carbon Nanotubes) Nanotubes) Nanotubes)

4 (with Carbon Nanotubes)

The images show that the specimen relative to system 1, that is constituted solely by the base mortar without additives, does not present photodegradative activities, in fact following irradiation there are no chromatic variations nor formation of an imprint relative to the covered part. System 2, which contains zeolite, presents an immediate discoloration, however without the formation of an imprint, which reveals an adsorbing action of the zeolite on the colorant rather than a photodegradation phenomenon. System 3, containing TiO2 , presents a marked imprint on the surface, showing, as we had expected, its photodegradative capacity. System 4, which contains carbon nanotubes, reveals a surprisingly photodegradative action; in fact the presence of an imprint on the specimen is evident, although less important than the titanium oxide system 3. 3.2.2. Water Absorption Coefficient Table 3 shows the values of the water absorption coefficients applied to the specimens of mortar with variable composition.


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Table 3. Water absorption coefficient. Systems

(kg/m2 min0.5 )

1 (without additive) 2 (with clinoptilolite) 3 (with TiO2 ) 4 (with Carbon Nanotubes)

0.4 0.3 0.4 0.5

The reported data show that the addition of titanium oxide (system 3) does not change the capacity of water absorption compared to the base mortar containing no additive (system 1). As far as system 2 is concerned; which contains zeolite, there is a lowering of the coefficient probably due to the zeolite which has already reached its complete hydration during the specimens preparation. System 4, containing carbon nanotubes, shows an increase in the coefficient due to the excellent adsorbent capacities of the latter. 3.2.3. Determination of the Tear Adhesion Strength Table 4 as follows, shows the data obtained after tear adherence tests carried out with the methods as previously reported in paragraph 2. The results show that system 2, containing zeolite, has a greater adhesion strength than the base mortar (system 1), whereas the presence of titanium oxide (system 3) lowers adhesion. In the case of system 4, in the presence of carbon nanotubes, adhesion is low therefore unable to be measured Table 4. Adhesion strength of mortars with variable composition containing one additive only. Systems

Adhesion Strength (N/mm2 )

1 (without additive) 2 (with clinoptilolite) 3 (with TiO2 ) 4 (with Carbon nanotubes)

0.498 0.585 0.241 -: unable to be measured.

3.3. Characterization of Systems With Multiple Additives The mortars were then subsequently prepared by adding more additives in order to evaluate their possible synergistic action. Table 5, as follows, shows the compositions of mixed systems prepared with more additives. Table 5. Composition of mixed systems with multiple additives. Systems

S/A

Clinoptilolite (%)

TiO2 (%)

Carbon Nanotubes (%)

5 6 7 8

3 3 3 3

5 5 5 -

0.5 0.5 0.5

0.025 0.025 0.025

-: unable to be measured.

3.3.1. Compressive Strength Table 6 shows the compressive strength values for specimens with two or three additives.

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Buildings 2018, 8, x FOR PEER REVIEW Table 6. Resistance to compression of systems additives. Table 6. Resistance to compression of systems withwith moremore additives. Buildings2018, 2018,8, FORPEER PEER REVIEW Buildings REVIEW Buildings 8,8,xxxFOR FOR PEER REVIEW Buildings 2018,2018, 8,Table x FOR PEER REVIEW 6. Resistance to compression of systems with more additives.

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Table 6. Resistance to compression of systems Carbon withCarbon more additives. Clinoptilolite TiO Compressive Table6. Resistance tocompression compression of2systems systemswith withmore moreadditives. additives. Table Resistance to of Clinoptilolite TiO Compressive Table 6.6. Resistance to compression of systems with additives. 6. Resistance to compression of2systems with moremore additives. Systems Table S/A Nanotubes Systems S/A Nanotubes Carbon Compressive Clinoptilolite (%) (%) Strength Carbon (%) (%) Strength (N) (N) TiO2 (%) Systems S/A (%)(%) Carbon Clinoptilolite TiO2 Compressive Carbon (%) Carbon Nanotubes Strength (N) (%) Carbon Clinoptilolite TiO 2 Compressive Systems S/A Nanotubes Clinoptilolite TiO 2 Compressive Clinoptilolite Compressive Clinoptilolite TiO 20.0 2 Compressive Systems S/A Nanotubes 1 3 0 0.000 83.10 (%) (%)TiO Strength (N) Nanotubes 1Systems 3 S/A 0 (%) 0.0 0.000 83.10 Systems S/A Nanotubes Systems S/A Nanotubes (%) Strength (N) (%) (%) Strength 1 3 0 0.0 (%)(%) 0.000 83.10 (%) (%) Strength (N) (%) Strength (N)(N) (%) 0.025 66.68 (%) 5 35 3 3 5 5 5 0.5 0.5 0.025 66.68 (%) (%) 5 0.5 0.025 66.68 1 3 0 0.0 0.000 83.10 0.5 0.000 72.39 0.0 0.000 83.10 0.0 83.10 61 36111 33 333 5 50 5000 0.000 72.39 0.000 83.10 6 0.5 0.5 0.000 72.39 0.0 0.000 83.10 5 3 5 0.5 0.0 0.025 66.68 7 3 5 0.0 0.025 87.31 5 3 5 0.5 0.025 66.68 5 0.5 66.68 7 3 5 0.0 0.025 87.31 0.025 66.68 7 0.0 0.5 0.025 87.31 56 35 33 3 5 55 5 0.025 66.68 0.5 0.5 0.000 72.39 8 3 0 0.5 0.025 78.02 6 3 5 0.5 0.000 72.39 6 5 0.000 72.39 8 3 0 0.5 0.025 78.02 8 0.5 0.5 0.5 0.025 78.02 0.000 72.39 67 36 33 3 0 55 5 0.000 72.39 0.0 0.025 87.31 7 3 5 0.0 0.025 87.31 7 3 5 0.0 0.025 87.31 0.025 87.31 78 7 33 3 50 5 0.0 0.025 87.31 0.5 0.0 0.025 78.02 data show a slight lowering of compressive strength compared to the base mortar 8 3 0 0.5 0.025 78.02 8 3 0 0.5 0.025 78.02 TheThe data show a slight lowering of compressive strength compared to the base mortar for for 8 0.025 78.02 8 slight 3 3 0 0 0.5 0.5 compared 0.025 78.02 Thesystems data show lowering of significant compressive strength base mortar for systems systems 6 and 8. The lowering regards system 5the where all three additives 5, 6 5,aand 8. The mostmost significant lowering regards system 5 to where all three additives are are The datasignificant show a slight lowering of compressive strength to the are basepresent, mortar for 5, 6 andpresent, 8. The most regards system 5 where allcompared three additives due present, toshow difficult homogenization and hydration of the components of mortar; the value Thedue data showhomogenization slight lowering of compressive strength compared tothe the base mortar for The data aaalowering slight lowering of compressive strength compared to the for to difficult hydration of the components of the mortar; themortar value The show slight lowering of compressive strength to the base mortar Thedue data show a slight lowering ofand compressive strength compared basebase mortar for systems 5, 6 data and 8. The most significant lowering regards system 5compared wheretoallthe three additives are for still remains acceptable. An increase in resistance is recorded for system 7 where clinoptilolite and systems 5, 6 and 8. The most significant lowering regards system 5 where all three additives are to difficult homogenization and hydration of the components of the mortar; the value still remains systems 5, 6 and 8. The most significant lowering regards system 5 where all three additives are still remains acceptable. increase in resistance is regards recorded forsystem system where clinoptilolite and systems and 8. An The most significant lowering regards 5 7where all three additives systems 5, 65, and 8. The most significant lowering system 5 where three additives are are present, due to6difficult homogenization and hydration of the components ofallthe mortar; the value carbon nanotubes are present. present, dueto to difficult homogenization and hydration ofthe the components ofthe themortar; mortar; thevalue value present, due difficult homogenization and hydration of components of the carbon nanotubes are present. acceptable. An increase in resistance is recordedand for system 7 where clinoptilolite and carbon nanotubes present, due to difficult homogenization and hydration of the components of the mortar; the value present, due to difficult homogenization hydration of the components of the mortar; the value still remains acceptable. An increase in resistance is recorded for system 7 where clinoptilolite and still remains acceptable. An increase in resistance is recorded for system 7 where clinoptilolite and still remains acceptable. An increase in resistance is recorded for system 7 where clinoptilolite are present. still remains acceptable. increase in resistance is recorded for system 7 where clinoptilolite and still remains acceptable. An An increase in resistance is recorded for system 7 where clinoptilolite andand carbon nanotubes are Tests present. 3.3.2. Colorimetric of Photoactivity 3.3.2. Colorimetric Tests of Photoactivity carbon nanotubes are present. carbon nanotubes are present. carbon nanotubes are present. carbon nanotubes are present. 3.3.2. Colorimetric Tests of Photoactivity The photodegradation performed on “mixed” specimens revealed diverse results The photodegradation teststests performed on “mixed” specimens revealed diverse results as as 3.3.2. Colorimetric Tests of Photoactivity 3.3.2.Colorimetric ColorimetricTests Testsof ofPhotoactivity Photoactivity 3.3.2. 3.3.2. Colorimetric Tests of Photoactivity 3.3.2. Colorimetric Tests of Photoactivity shown below in Table 7. below in Tabletests 7. performed on “mixed” specimens revealed diverse results as shown Theshown photodegradation The photodegradation tests performed on “mixed” specimens revealed diverse results as The photodegradation photodegradation tests tests performed performed on on “mixed” “mixed” specimens specimens revealed revealed diverse diverse results results as as The The photodegradation performed “mixed” specimens revealed diverse results The7. photodegradation teststests performed on on “mixed” specimens revealed diverse results as as below inshown Table below in Table 7. Table 7. Images of specimens before and after UV irradiation for a 3 h period. Table 7. Images of specimens before and after UV irradiation for a 3 h period. shown below in Table 7. shown below in shown below in Table Table 7. shown below in Table 7. 7. Before After Table 7.Systems Images of specimens before and and afterafter UVUV irradiation forfora a3After Table 7. Images of specimens before irradiation 3hhperiod. period. Systems Before Table7. Imagesof ofspecimens specimensbefore beforeand andafter afterUV UVirradiation irradiationfor foraaa333hhhperiod. period. Table Table 7.7.Images Images of specimens before UV irradiation period. Table 7. Images of specimens before and and afterafter UV irradiation for afor 3 h period.

Systems Systems Systems Systems Systems Systems 5 5 (Clinoptilolite + 2TiO (Clinoptilolite + TiO + 2+ 5 Carbon Nanotubes) 5 5 Carbon Nanotubes) 5 5+ TiO2 + (Clinoptilolite 5(Clinoptilolite TiO2 2++ (Clinoptilolite +++TiO (Clinoptilolite TiO (Clinoptilolite + TiO 2 + 2 + Carbon Nanotubes) (Clinoptilolite + Carbon TiO 2 + Carbon Carbon Nanotubes) Nanotubes) Carbon Nanotubes) Carbon Nanotubes) Nanotubes)

Before Before Before Before Before Before

After After After After After After

6 6 (Clinoptilolite + 2TiO (Clinoptilolite + TiO ) 2) 6 6 6 6 6+ TiO2) (Clinoptilolite (Clinoptilolite+++TiO TiO22)2)) (Clinoptilolite (Clinoptilolite (Clinoptilolite + TiOTiO 2) 6 (Clinoptilolite + TiO2 ) 7 7 (Clinoptilolite (Clinoptilolite + + 7 Carbon Nanotubes) 7 Carbon Nanotubes) 7 77 + (Clinoptilolite (Clinoptilolite+++ (Clinoptilolite (Clinoptilolite (Clinoptilolite + Carbon Nanotubes) CarbonNanotubes) Nanotubes) 7Carbon Carbon Nanotubes) Carbon Nanotubes) (Clinoptilolite + Carbon Nanotubes)8 8 2 + Carbon (TiO(TiO 2 + Carbon 8 Nanotubes) 888 Nanotubes) (TiO2 +8Carbon (TiO 2++Carbon Carbon (TiO 2 (TiO 2 + Carbon (TiO 2 + Carbon Nanotubes) Nanotubes) Nanotubes) Nanotubes) Nanotubes) 8 (TiO2 + Carbon Nanotubes)

We may observe from the images how the simultaneous presence of several additives, zeolite, carbon nanotubes and titanium oxide, enables us to set up a synergy between the components and


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to improve the photodegradative action of the prepared mortar. The best results are obtained with system 5 where all three additives used are present. Furthermore, systems 6 and 7 show an important photocatalytic activity although slightly lower than system 5. Compared to other systems, system 8 presents the lowest photocatalytic activity. As emerges from the results that the union of clinoptilolite and titanium oxide is the winning one whereas the first one, thanks to its nature, favors the adsorption of the rodamine thus facilitating contact with the titanium oxide which in turn exerts its photodegradative action. System 8, titanium oxide and carbon nanotubes, also highlights a photodegradative action although the impression on the surface of the shielded part is only slightly visible probably due to the adsorbing action of the nanotubes on the rodamine as well. Compared to systems with titanium oxide alone, there is a substantial improvement in photocatalytic activity when the latter is combined with clinoptilolite or with clinoptilolite and carbon nanotubes. 3.3.3. Water Absorption Coefficient The results obtained concerning the water absorption of systems containing more additives are shown in the following Table 8. Table 8. Water absorption coefficient. Systems

Clinoptilolite (%)

TiO2 (%)

Carbon Nanotubes (%)

Water Absorption Coefficient (kg/m2 min0.5 )

1 5 6 7 8

0 5 5 5 0

0.0 0.5 0.5 0.0 0.5

0.000 0.025 0.000 0.025 0.025

0.4 0.7 0.2 0.3 0.5

The presence of zeolite tends to lower the coefficient water absorption (systems 6 and 7) most probably due to the mortar being in a saturated state of hydration. There is a significant increase in absorption coefficients where carbon nanotubes enhance their adsorbing capacity (system 8). System 5 shows the highest capacity which is characterized by the simultaneous presence of all three additives. 3.3.4. Determination of Tear Adhesion Force Tear-off tests performed on systems with more additives, were carried out through procedures as previously shown in paragraph 2. As follows, Table 9 shows the values of adhesion strength obtained. Regarding systems 5 and 6, breakage of the specimens was of the adhesive type to the substrate, i.e., there were no detachments inside the mortar however a detachment from the surface of the brick occurred. As for systems 7 and 8 the adhesion strength was not measurable. By analyzing all the results, we may observe how the simultaneous presence of the three additives, clinoptilolite, titanium oxide and carbon nanotubes (system 5), creates a synergy thus increasing the adhesive force as compared to the mortar only (system 1). A negative role is played by carbon nanotubes when these are in the presence of zeolite only (system 7) or titanium oxide alone (system 8).

(%) (%)


1 5 6 7 8

11 55 66 77 88

0 5 5 5 0

00 55 55 55 00

(%) (%) 0.0 0.0 0.5 0.5 0.5 0.5 0.0 0.0 0.5 0.5

0.0 0.5 0.5 0.0 0.5

(N/mm ) (N/mm )

(%) (%) (%) 0.000 0.000 0.000 0.025 0.025 0.025 0.000 0.000 0.000 0.025 0.025 0.025 0.025 0.025 0.025

0.498 0.498 0.498 0.532 0.532 0.532 0.413 0.413 0.413 -- -- -

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unable measured. -:-:unable totobebeto measured. -: unable be measured.

Table 9. Adhesion strength of mortars with a variable composition containing more additives. Conclusions 4.4.Conclusions 4. Conclusions Wemay may draw thefollowing following conclusions from results obtained whole, summary Table We draw the conclusions from results obtained asasaawhole, asasininas summary Table We may draw the following from results obtained as aAdhesion whole, in summary Table Clinoptilolite TiO Carbon Nanotubes Strength 2 conclusions Systems 2 10 below. It is necessary to underline that, from the evaluation of the 4 parameters considered, 10 below. is necessary to (%) underline the evaluation of 4the 4 (N/mm parameters considered, 10 below. It is It necessary to underline that, that, fromfrom the (%) evaluation of the parameters considered, (%) ) (compressive strength, absorption coefficient, adhesion strength andphotoactivity), photoactivity), thebest bestsystems systems (compressive absorption coefficient, adhesion strength and photoactivity), the best systems strength, absorption coefficient, adhesion strength and the 1(compressive 0strength, 0.0 0.000 0.498 have been identified, among those thatrepresented represented fair compromise between the0.532 lowering some been identified, those that aafair between the lowering ofofsome have been identified, among those that represented acompromise fair compromise between the lowering of some 5have 5 among 0.5 0.025 characteristics, although always within acceptable limits, andthe theimprovement improvement others. Particular characteristics, always acceptable limits, and the improvement of others. Particular although always within acceptable limits, and ofof0.413 others. Particular 6characteristics, 5 although 0.5 within 0.000 importance wasgiven given the improvement the photocatalytic activity. was totothe ofofthe activity. importance was toimprovement the improvement ofphotocatalytic the photocatalytic activity. 7importance 5 given 0.0 0.025 8 0 0.5 0.025 Table 10.Summary. Summary. 10. 10. Summary. -: unableTable to beTable measured.

Systems Systems Systems

4. Conclusions

Carbon Compressive Absorption Adhesion Carbon Compressive Compressive Absorption Absorption Adhesion Adhesion Carbon Clinoptil TiO 2 Clinoptil 2 TiO Clinoptil TiO 2 Nanotubes Strength Coefficient Strength Photoactivity Nanotubes Coefficient Nanotubes Strength Strength Coefficient Strength StrengthPhotoactivity Photoactivity (%) (%) (%) (%) (%) (%) 0.5) 0.5 2 2min 2)2) 2 0.5 2) (%) (%) (N) (N) (kg/m min (N/mm (%) (N) (kg/m ) (kg/m min ) (N/mm (N/mm

We may draw the following conclusions from results obtained as a whole, as in summary 83.183.1 0.4 0.4 0.498 11 1 -- -- 83.1 0.498 0.498 Table 10 below. It is necessary to- -underline that, from the evaluation of0.4 the 4 parameters considered, (compressive strength, absorption coefficient, adhesion strength and photoactivity), the best systems 5 5 127.01 0.3 0.3 0.585 5among - - that -- 127.01 0.3 0.585 2 127.01 0.585 of some have been2 2identified, those represented a fair compromise between the lowering characteristics, although always within acceptable limits, and the improvement of others. Particular 0.5 0.5 91.20 0.4 0.4 0.241 3 3 was - -to the 0.5 - -of the 91.20 0.4 0.241 3 given - photocatalytic 91.20 activity. 0.241 importance improvement 44 55 Systems 1 2 3 4 5 6 7 8

4

--

-

5 5 TiO 5 5 2 Clinoptil (%) (%)

66

6

77

7

88

8

5 5 5 5 -

55 55 --

50.5 50.5 -0.5 0.5

--

-

0.025 92.37 0.025 92.37 0.025 92.37 Table 10. Summary.

0.5 0.5 0.5

Compressive Absorption 0.7 0.5Carbon 0.025 66.68 0.7 0.5 0.025 66.68 0.5 0.025 66.68 Nanotubes Strength Coefficient 2 0.5 (%) (N) (kg/m min ) 0.5 0.5 72.39 0.2 0.5 - - - 83.1 72.39 0.2 72.39 0.4 127.01 0.3 91.20 0.4 0.025 87.31 0.3 - - 0.025 0.025 0.3 0.025 87.31 0.5 92.37 87.31 0.025 66.68 72.39 0.5 0.5 0.025 0.5 0.025 0.025 0.025 87.31 0.025 78.02

Values withrespect respect system Values with respect toto system 1:1: 1: Values with respect to system Values with to system 1:

greater greater greater

0.7 78.0278.0278.02- 0.2 0.3 0.5

lower lower lower

--

-

Adhesion 0.532 0.532 0.7 0.532 Strength Photoactivity 2 (N/mm ) 0.413 0.2 0.498 0.413 0.413 0.585 0.241 -- 0.3 0.532

0.5 0.5 0.413 0.5 -

--

-

equal equal equal

Clinoptilolite tends to increase compressive and adhesion strength, decreases water absorption Clinoptilolite tends increase compressive andadhesion adhesion strength, decreases water absorption Clinoptilolite tends to increase compressive and adhesion strength, decreases water absorption Clinoptilolite tends totoincrease compressive and strength, decreases water absorption and does not give photodegradative properties to the mortar, however neither is it compromised in anddoes doesdoes notgive givegive photodegradative properties the mortar, however neither and not photodegradative properties tomortar, the mortar, however neither iscompromised it compromised and not photodegradative properties totothe however neither isisititcompromised inin in systems where other additives are present (systems 5, 6 and 7). systems where other additives arepresent present (systems and 7). 7). systems where other additives are present (systems 5, 6 7). and systems where other additives are (systems 5,5,66and As expected, titanium oxide gave good response as a photodegrading additive; in fact, for systems in which it is present (systems 3, 5, 6 and 8) response to the photodegradative tests has always been positive. Carbon nanotubes, whether inserted individually into the mortar, or mixed with other additives, gave a good photodegradative response. However they increased water absorption coefficient and limited the adhesion force of the mortar on the substrate. Furthermore, in the mixture containing all three additives (system 5) contemporaneously, adhesion force to the substrate was not compromised, on the contrary increased as compared to that of the base mortar. The different additives used have played particular roles; it is possible to create systems in which these operate synergistically from their union and for their particular composition. Amongst these systems that we studied No. 5 (which has all three additives) and No. 6 (which has both zeolite and titanium oxide additives, turn out to be the best compromise between the lowering, which still remains acceptable, and the recovery of some of the characteristics as regards to the basic mortar.


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These identified systems, in particular allow the preparation of mortars which propose a greater photodegradation activity as against systems in which titanium oxide is individually used. Author Contributions: Conceptualization, P.D.L. (Pierantonio De Luca); Data curation, P.D.L. (Pierantonio De Luca), P.D.L. (Pasquale De Luca) and S.C.; Formal analysis, S.C. and A.M.; Methodology, P.D.L. (Pierantonio De Luca); Supervision, P.D.L. (Pierantonio De Luca), F.C. and J.B.N.; V.S.C. and A.M.; Writing—original draft, P.D.L. (Pierantonio De Luca). Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest

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