WO2018109729A1

WO2018109729A1 - Colored cement mortars with optimized thermal and optoenergetic properties

Info

Publication number: WO2018109729A1
Application number: PCT/IB2017/057979
Authority: WO
Inventors: Federica ROSSO; Marco FERRERO; Anna Laura PISELLO; Franco COTANA
Original assignee: Univerista' Degli Studi Di Roma "La Sapienza"; Universita' Degli Studi Di Perugia
Priority date: 2016-12-15
Filing date: 2017-12-15
Publication date: 2018-06-21
Also published as: IT201600127043A1

Abstract

A method for preparing a colored cement mortar, comprising the step of mixing white Portland cement, glass aggregates and at least one pigment composition. The pigment composition comprises a mixture of an infrared-reflecting white pigment, having an intrinsic reflectance of more than 40% in the entire range 800-2500nm, with at least one colored pigment selected from the group consisting of black pigment having an intrinsic reflectance of less than 10% in the entire range 800-2500nm, red pigment having an intrinsic reflectance of less than 55% in the entire range 800-2500nm, and blue pigment having an intrinsic reflectance of less than 70% in the entire range 800-2500nm.

Description

Colored cement mortars with optimized thermal and optoenergetic properties

The present invention relates to energy saving techniques in the construction sector.

It is known to use infrared reflecting pigments in colored paint or finishing coats to be applied in particular on the facades of buildings to obtain cool, colored facades, on roof elements, or on urban pavements.

In US 9 073 786 B2 a cement paste with high reflectance is also described, which uses colored pigments, reflective in the infrared.

The use of pigments able to reflect the solar radiation in the infrared field allows i) a cooler surface temperature to be maintained, ii) less heat to enter the building, thus optimizing the energy performance of the envelope, minimizing the energy demand for cooling, iii) less thermal stress due to high temperatures and the successive heating-cooling of the envelope and adjacent elements.

Mortars with the same color but not optimized in effect reflect solar radiation to a lesser extent, thus absorbing more heat and then transmitting it into the interior space, raising the temperature and resulting in a higher energy demand for cooling spaces. Moreover, heating more when irradiated by the sun, these mortars entail higher thermal stress, leading more quickly to degradation phenomena.

An object of the present invention is to provide an alternative solution for making available colored cement mortars with high infrared reflectance.

In view of this aim, the object of the invention is a method for preparing a colored cement mortar, comprising the step of mixing white Portland cement, glass aggregates, and at least one pigment composition,

wherein the pigment composition comprises a mixture of an infrared reflective white pigment having an intrinsic reflectance greater than 40% in the entire range 800- 2500nm when measured according to ASTM E903-96 on a film of water-based binder of acrylic resin having a thickness of 1 ΙΟμηι and containing 28% by weight of pigment, and at least one colored pigment selected from the group consisting of

black pigment having an intrinsic reflectance less than 10% in the entire range 200- 2500nm when measured according to ASTM E903-96 on a film of water-based binder of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment,

red pigment having an intrinsic reflectance less than 55% in the entire range 800- 2500nm when measured according to ASTM E903-96 on a film of water-based binder of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment, and

blue pigment having an intrinsic reflectance less than 70% in the entire range 800- 2500nm when measured according to ASTM E903-96 on a film of water-based binder of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment.

Preferably, the black pigment is a carbon black, and has an intrinsic reflectance of less than 7% in the entire range 300-2500nm.

Preferably, the red pigment is an iron oxide red, and has an intrinsic reflectance of less than 12% in the range 300-600nm, less than 30% in the range 600-900nm, and less than 55% in the range 900-2500nm.

Preferably, the blue pigment is a cobalt blue, and has a reflectance of less than 35% in the range 300-600nm, less than 70% in the range 600-1200nm, less than 10% in the range 1200-1500nm, and less than 40% in the range 1500-2500nm.

The infrared reflective white pigment may be, for example, an Altiris® pigment marketed by Huntsman Corporation.

Unlike the method described in US 9 073 786 B2, which uses pigments of different colors reflecting in the infrared, the method according to the invention provides for the use of infrared reflecting pigments exclusively in white, to be mixed with standard colored pigments as desired to obtain the cement mortar of the desired color. The authors of the present invention have verified that with this method it is possible to obtain cement mortars with performances close to those obtained with the method known from US 9 073 786 B2.

This is an advantage in particular on site, since the availability of a wide range of different infrared-reflecting pigments is not required, but rather only the white pigment, which is added to conventional colored pigment.

The mortars made using the method according to the invention may be used as restoration mortars, assuming different colors depending on the characteristics of the building wherein they are to be applied: they are able to maintain a lower surface temperature with respect to traditional mortars with the same color.

Although the application on historical buildings - upon verification of the compatibility of the cement materials with existing ones - is the most promising, any application involving the use of cement pastes may benefit from the use of the invention where this use occurs outside: in effect, it is the answer to solar radiation that provides the best performance with respect to traditional, non-optimized cement pastes.

The use as a finish for external pavements (courtyards, squares, public and private spaces in general) allows colored floors to be obtained according to the aesthetic and architectural needs of the area, which are suitable also in this case in areas with historical character, obtaining at the same time the aforementioned benefits for the built environment and the comfort of the citizens.

For the same reasons, also applications on the facades of buildings as surface finish or envelope elements lead to advantages such as heat island mitigation (especially in highly vertically developed cities) and improvement of outdoor comfort for users of outdoor spaces adjacent to the building; another important advantage is the absorption of smaller quantities of heat that are then transmitted into the building, decreasing the cooling demand during the summer months and improving the internal thermal comfort. Also in this case, the invention allows colored surfaces to be obtained as needed, with better performances than identically colored traditional surfaces.

The mortars made according to the invention may bring benefits and advantages to the built environment and to the building itself also when used as a roof finish by providing a cool roof, which is a preferred strategy to reduce the heat island and improve . the conditions of internal comfort without increasing the energy demand for cooling. Also in this case, the radiation is reflected in a higher percentage in the infrared part and then penetrates to a lesser extent into the building, allowing the advantages described above to be achieved.

Further characteristics and advantages of the method according to the invention will become more apparent in the following detailed description, made with reference to the appended drawings, provided purely by way of non-limiting example, wherein:

- figure 1 is a graph showing the solar reflectance, along the entire spectrum, of samples of red cement mortars, comparing the conventional ones with those optimized in the infrared according to the invention;

- figure 2 is a graph showing the solar reflectance, along the entire spectrum, of samples of black cement mortars, comparing the conventional ones with those optimized in the infrared according to the invention; and

- figure 3 is a graph showing the solar reflectance, along the entire spectrum, of samples of blue cement mortars, comparing the conventional ones with those optimized in the infrared according to the invention;

In order to test the invention, several mortar samples were made with different mixtures, similar in components, but with different colors and amounts of pigment (Table 1 , the percentages are expressed with respect to the total weight of the mixture).

Table 1

Color Name % colored % IR pigment % white sample pigment pigment

BK-IR-0 0.50 0.50 0.00

Black

BK-IR-2 2.25 2.25 0.00 BK-IR-5 5.00 5.00 0.00

BK-0 0.50 0.00 0.50

BK-2 2.25 0.00 2.25

BK-5 5.00 0.00 5.00

BL-IR-0 0.50 0.50 0.00

BL-IR-2 2.25 2.25 0.00

BL-IR-5 5.00 5.00 0.00

Blue

BL-0 0.50 0.00 0.50

BL-2 2.25 0.00 2.25

BL-5 5.00 0.00 5.00

R-IR-0 0.50 0.50 0.00

R-IR-2 2.25 2.25 0.00

R-IR-5 5.00 5.00 0.00

Red

R-0 0.50 0.00 0.50

R-2 2.25 0.00 2.25

R-5 5.00 0.00 5.00

Samples of the same color were prepared and compared, with and without infrared reflecting pigments (hereinafter referred to as "IR pigments" for the sake of brevity). Since the IR pigments are white, the samples without IR pigment were mixed with conventional white pigment to obtain the same color. For the purposes of the present description, a conventional white pigment means a white pigment, for example commercially available titanium dioxide white, the reflectance of which in the infrared range (800-2500 nm) falls below 40% (measured according to ASTM E903-96 on a film of water-based binder in acrylic resin having a thickness of 120μηι, and containing 28% by weight of pigment [1]). For example, the sample R-IR-5 has the same color as R-5; the former, however, contains a IR white pigment, while the latter contains a conventional white pigment.

Each sample contains white Portland cement, recycled glass aggregates, and pigments as indicated in table 1.

The IR pigments used are Altris® pigments supplied by Huntsman Corporation (http://www.huntsman.conValtiris/a/Home) and are commercially available. Such pigments have an intrinsic reflectance greater than 40% over the entire range 800-2500nm when measured according to ASTM E903-96 on a film of water-based binder of acetate resin having a thickness of Ι ΙΟμηι and containing 28% by weight of pigment [1]. "Intrinsic reflectance", in the present description, means reflectance of only the pigment powder, not mixed with materials other than the water-based resin binder used to make the film on which the measurements are taken. Therefore, such intrinsic reflectance is in general different from the reflectance of the cement mortar made with the pigments mixed with the Portland cement according to the present invention.

Conventional, commercially available black pigment is a carbon black and has an intrinsic reflectance less than 10% over the entire range 800-2500nm measured according to ASTM E903-96 on a film of water-based binder made of polyvinyl acetate resin having a thickness of 0.5mm and containing 40%) by volume of pigment. In particular, the black pigment has an intrinsic reflectance less than 7% over the entire range 300-2500nm.

Conventional, commercially available red pigment is an iron oxide red and has an intrinsic reflectance less than 55% in the entire range 800-2500nm measured according to ASTM E903-96 on a film of water-based binder made of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment. In particular, the red pigment has an intrinsic reflectance less than:

12% in the range 300-600nm,

30% in the range 600-900nm,

55% in the range 900-2500nm.

Conventional, commercially available blue pigment is a cobalt blue and has an intrinsic reflectance less than 70% over the entire range 800-2500nm measured according to ASTM E903-96 on a film of water-based binder made of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment. In particular, the blue pigment has an intrinsic reflectance less than:

35% in the range 300-600nm,

70% in the range 600-1200nm, 10% in the range 1200-1500nm,

40% in the range 1500-2500nm.

After preparation and hardening, the mortar samples were analyzed in the laboratory in terms of optical and thermal properties.

Regarding the optical properties, the reflectance was determined by spectrophotometer measurements, according to ASTM E903 (ASTM E903 - 12 Standard Testing Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres, American Society of Testing Materials: West Conshohocken, PA, USA, 1996). For thermal properties, the emissivity was measured according to the instructions given in ASTM C1371-15 (ASTM C1371-04a(2010)el Standard Test Method for Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers; American Society for Testing Materials: West Conshohocken, PA, USA, 2010). In addition, measurements of thermal conductivity were made using Hot Disk 2500 according to ISO Standard 22007-2 (International Organization for Standardization, ISO 22007-2:2008 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part. 2: Transient plane heat source (hot disc) method, Geneva, Switzerland).

The results are shown in the following table 2: SRI is the solar reflectance index; UV is the ultraviolet reflectance, measured between 300 and 380 nm of the solar spectrum; VIS is the reflectance in the visible spectrum, measured between 380 and 780 nm; NIR is the infrared reflectance, measured between 780 and 2500 nm.

Table 2

Optical characteristics Thermal characteristics

Name

Color SRI UV VIS NIR Thermal Thermal

Sample

emissivity conductivity

BK-IR-0 29.2 15.7 31.7 32.9 0.90

BK-IR-2 18.3 17.1 20.6 18.4 0.90

Black 0.99-1.1

BK-IR-5 16.9 15.0 19.8 16.9 0.88

BK-0 34.7 35.1 40.4 27.5 0.90 BK-2 18.6 27.1 20.1 11.4 0.90

BK-5 15.6 12.5 18.3 12.4 0.90

BL-IR-0 52.3 40.6 54.0 46.7 0.89

BL-IR-2 49.7 39.6 53.6 54.8 0.90

BL-IR-5 49.9 23.5 46.7 55.2 0.90

Blue

BL-0 54.1 30.9 58.1 51.2 0.91

BL-2 53.2 34.0 56.3 51.1 0.91

BL-5 48.3 34.6 40.1 42.8 0.91

R-IR-0 39.5 22.2 34.7 47.2 0.90

R-IR-2 38.0 23.7 31.2 47.9 0.89

R-IR-5 34.5 1 1.27 24.0 51.1 0.90

Red

R-0 46.3 26.2 45.0 49.7 0.88

R-2 41.7 25.4 35.8 50.6 0.89

R-5 35.0 10.1 22.6 46.7 0.89

Figure 1 also shows the comparison between the solar reflectance, along the entire spectrum, of a conventional red cement mortar (R-5), and that of a red cement mortar optimized in the infrared (R-IR-5).

Figure 2 also shows the comparison between the solar reflectance, over the entire spectrum, of a conventional black cement mortar (BK-5), and that of a black cement mortar optimized in the infrared (BK-IR-5).

Figure 3 also shows the comparison between the solar reflectance, over the entire spectrum, of a conventional blue cement mortar (BL-5), and that of a blue cement mortar optimized in the infrared (BL-IR-5).

The samples were also tested to verify their behavior when subjected to solar radiation. The samples were placed on the roof of the building at the University of Perugia. They were positioned at a sufficient distance from each other, in such a way that they did not become shaded, but at the same time close enough to be exposed to the same paving material and the same solar radiation. After exposure on the roof, the surface temperatures were checked during the central sun hours of the day, i.e. the hottest hours. Three measurements were conducted by infrared camera, the first at 1 1 :00, the second at 13:00 and the last at 15:00. The analysis was carried out on August 31, while monitoring the meteorological conditions through a meteorological station (humidity, wind speed, air temperature and global and direct solar radiation) located on the same roof, a few meters away from the samples.

Comparisons were then made between i) IR and non-IR samples and ii) samples that differed in the percentages of pigment added to the mixture. Given the preliminary evaluation made possible by the measurements in the laboratory, the purpose of such analysis was to identify a statistically significant general trend, the same for all the colored and natural samples, as the addition of IR or non-IR pigments and their percentage in the blend varied.

The Wilcoxon test was used, which is a non-parametric test used to compare two related samples; in this case it was used to verify the significance of the differences observed between the reflectance values of the samples.

From the data obtained it is possible to carry out two analyses: one takes into account the modifications of the optical characteristics when the percentage of pigment changes (e.g. R-IR-5 compared to R-IR-2), the other, considering samples of the same color, compares IR and non-IR pigments.

By comparing samples with different percentages of pigment, the results vary depending on the color (figures 1-3).

For the black cement, by adding, for example, 5% of IR pigment, the same amount of conventional black colored pigment was added, resulting in a significant darkening of the sample: as a result, although the percentage of IR pigment is increased, the Vis and NIR reflectance decrease in this comparison.

For the blue cement, going from the percentage of 0.5% to 2.25% and 5% of the IR and conventional blue colored pigments, the sample likewise became darker. In this case, however, while the Vis reflectance falls by -7.3% from BL-IR-0 to BL-IR-5, the NIR reflectance increases by +8.5% due to the presence of IR pigments.

Similar results were obtained for the red cement: while the Vis reflectance falls by 10.7% from R-IR-0 to R-IR-5, at the same time the NIR reflectance increases by about 4%.

Therefore, with the exception of the black cement, for the blue and red cements, adding IR and conventional colored pigments, while decreasing Vis reflectance due to the darker color obtained, increases the NIR reflectance, thus optimizing the thermal performance of such dark materials even on darker colors (Table 3). For the black cement, both the Vis and NIR reflectances are diminished by simultaneous adding more IR pigment and more black pigment, in the same quantity.

Table 3

For the second comparison, samples with IR pigments were compared with samples of the same color, obtained with conventional white pigments (Table 4).

For the black sample, greater reflectance was observed in samples with IR pigments compared to samples of the same color with conventional white pigments (BK-IR-5 and BK-5): the SRI increase is 1.3%, similar to the increase in the Vis, which is +1.5%; in the NIR part of the spectrum the BK-IR-5 sample is able to reflect +4.5% more than the conventional BK-5.

As for the blue samples, i.e. the comparison between BL-IR and BL, in the optimized samples, there is a higher reflectance compared to that of conventional samples with the same percentage of pigment, and thus with the same color. Such difference is +1.3% for the sample with IR pigment relative to the SRI; the NIR part shows an increase of +12.4%, while in the Vis the increase is +6.6%. The major differences in the optical characteristics were found in the comparison BL-IR-5 and BL-5, while in the samples with 0.5% pigments, the differences were not homogeneous.

For the red samples, the most significant increase was observed again in the NIR part of the spectrum (+4.4%); in the Vis, such difference is +1.4%.

Statistically, the Wilcoxon test to compare correlated pairs of IR and conventional samples with the same color has confirmed, when considering all the colors together and therefore looking for a general trend, that the, difference in the reflectance values is significant. In particular, it was verified that, in conventional sets, the Vis reflectance increases compared to that of optimized samples for the same color, while conversely, the reflectance decreases in the NIR spectrum, which is thus greater in the IR samples.

Table 5

IR-conventional comparison ASR [%] AUV[%] AVIS p/oJ ANIR [%]

BK-IR-O-BK-0 -5.5 -19.4 -8.7 5.4

Black BK-IR-2-BK-2 -0.3 -10 0.5 7

BK-IR-5-BK-5 1.3 2.5 1.5 4.5

BL-IR-O-BL-0 -1.8 9.7 -4.1 -4.5

Blue BL-IR-2-BL-2 -3.5 5.6 -2.7 3.7

BL-IR-5-BL-5 1.6 -1 1.1 6.6 12.4

R-IR-O-R-0 -6.8 -A -10.3 -2.5

Red R-IR-2-R-2 -3.7 -1.7 -4.6 -2.7

R-IR-5-R-5 -0.5 1.17 1.4 4.4 The experimental exposure of the samples on the roof made it possible to evaluate the temperatures reached by them during the hours of measurement (Table 5).

Within the three hours of measurement, the highest surface temperatures were measured at 12:00; from the meteorological monitoring, at twelve o'clock a peak in the global radiation occurs, while at three o'clock the wind speed is greater.

In accordance with the conclusions obtained from the optical characterization, different colors show different behaviors when exposed to solar radiation in the experimental situation of use as a covering material.

Table 5

Sample T [°C]

1 1 :00 12:00 15:00

BK-I -0 43.2 43.7 43.8

BK-IR-2 47.7 48.5 46.1

BK-IR-5 44.2 45.6 45.1

BK-0 44.4 45.6 44.9

BK-2 48.7 48.1 46.3

BK-5 45.2 44.8 46.8

BL-IR-0 39.9 41.8 41.7

BL-IR-2 39.8 41.5 41.5

BL-IR-5 39.8 41.7 41.8

BL-0 39 40.6 41.3

BL-2 40 41.9 41.3

BL-5 40.9 42.9 43

R-IR-0 41.1 43.2 42.2

R-IR-2 43.7 44.2 43.4

R-IR-5 42.2 42.9 43.7

R-0 41.8 42.3 42.3

R-2 40.9 43.9 43.7

R-5 43.6 44.9 44 Considering the black cement sample, lower temperatures characterize the BK-IR samples compared to the conventional BK samples of the same color (-1.9°C for BK-IR-0 with respect to BK-0), demonstrating the effectiveness of IR pigments in lowering the temperatures of the darker samples.

The blue colored samples showed no difference in surface temperatures when the percentage of pigment changed (BL0=BL2=BL5), while a decrease is obtained by adding IR pigments instead of simple white pigments (the BL-IR temperature is lower than 1 ,2°C with respect to BL), especially in samples with 5% pigments.

Similar results were observed by analyzing the red samples: the R-IR samples reach lower temperatures than the conventional R samples, especially in the comparison R-IR-5/R-5, where the temperature of R-IR-5 is 42.9°C and that of R-5 44.9°C, with a difference equal to 2.0°C.

In conclusion, the invention makes it possible to obtain cement-based colored mortars with optimized optical characteristics, starting from conventional colored pigments which may be mixed with infrared reflecting pigments in the desired amount and combination.

Bibliographical references

1. Jianrong S. et al. The effect of particle size distribution on the optical properties of titanium dioxide rutile pigments and their applications in cool non-white coatings. Solar Energy Materials & Solar Cells, 130 (2014), 42-50

Claims

1. A method for preparing a colored cement mortar, comprising the step of mixing white Portland cement, glass aggregates and at least one pigment composition,

characterized in that the pigment composition comprises a mixture of an infrared reflective white pigment having an intrinsic reflectance greater than 40% in the entire range 800-2500nm when measured according to ASTM E903-96 on a film of water-based binder of acrylic resin having a thickness of Ι ΙΟμιη and containing 28% by weight of pigment, and at least one colored pigment selected from the group consisting of

black pigment having an intrinsic reflectance less than 10% in the entire range 800- 2500nm when measured according to ASTM E903-96 on a film of water-based binder of polyvinyl acetate resin having a thickness of 0.5mm and containing 40% by volume of pigment,

2. A method according to claim 1, wherein the black pigment has an intrinsic reflectance less than 7% in the entire range 300-2500nm.

3. A method according to claim 2, wherein the black pigment is a carbon black.

4. A method according to any of the preceding claims, wherein the red pigment has an intrinsic reflectance less than:

12% in the entire range 300-600nm,

30% in the entire range 600-900nm,

55% in the entire range 900-2500nm.

5. A method according to claim 4, wherein the red pigment is an iron oxide red.

6. A method according to any of the preceding claims, wherein the blue pigment has an intrinsic reflectance less than:

35% in the entire range 300-600nm,

70% in the entire range 600- 1200nm,

10% in the entire range 1200- 1500nm,

40% in the entire range 1500-2500nm.

7. A method according to claim 6, wherein the blue pigment is a cobalt blue.

8. A method according to any of the preceding claims, wherein the infrared reflective white pigment is an Altiris® pigment.