Extending the study of the behaviour of bituminous mixtures incorporating nanomaterials

Transcription

1 Extending the study of the behaviour of bituminous mixtures incorporating nanomaterials Leonor Martins Fróes Burguete Abstract: Nanotechnology is known for its particular ability to develop new and better materials. By changing the properties of a regular material at nano scale, nanotechnology turns out to be one of the most exciting and promising solutions so far. In this context, some studies have been conducted on road engineering, being the incorporation of nanomaterials in hot mixtures asphalt (HMA) one of the solutions envisaged. A number of properties can be enhanced through the incorporation of few amounts of nanomaterial in bitumen, improving its behaviour. In this study, the behaviour of HMA was evaluated, type AC 14 Surf 35/50 (EN ), incorporating three types of nanomaterials: montmorillonite, precipitated calcium carbonate (PCC) and silica. Three percentages of incorporation for the nanomaterials were analysed, 2, 4 and 6 by weight of bitumen, and also two percentages by weight of the bitumen, 5,5 and 6,5. The characterization of HMA was taken following the methodology of Marshall, allowing the analysis of determinant characteristics for its composition such as stability, deformation, and porosity. Empirical rheological tests were also done, such as determination of needle penetration and determination of softening point, in order to infer any effect modification of these properties in the resulting binder. The results indicated that the bituminous mixtures incorporating nanomaterials showed, in general, a satisfactory behaviour compared to HMA, being the nanosilica the most promising nanomaterial. This one presented the best behaviour for stability and deformation at failure, despite the fact that it was appraised as being less interesting from the economical point of view for the present production conditions. Keywords: Hot mix asphalt (HMA), Nanotechnology, Nanomaterials, Assessment of HMA incorporating nanomaterials, Marshall methodology indicators, Viscosity characteristics for bitumen incorporating nanomaterials 1. Introduction The need for a durable pavement, with good mechanical properties, has led to the study of different alternatives for hot mix asphalt (HMA). HMA must provide the necessary features for the adequate movement of vehicles during its lifetime, according to safety, convenience, and economy. For that matter, the application of nanotechnology has proved to be one of the most exciting and promising hypotheses in recent years. The interest of nanotechnology focuses on manipulating the structure and behaviour of the material at nano scale (Steyn, 2009), and its use on road engineering intends to respond to the public needs in general, through the development of better materials commonly used in this area. During the life cycle of the pavement, there are several types of failure, such as cracking, permanent deformation, disintegration, and also surface defects, which obviously decrease the quality of the pavements. Regarding these aspects, it is important to improve the behaviour of HMA used on the pavement structure, particularly in the wearing course. For that reason, nanotechnology represents a pleasant prospect, which can give to bituminous mixtures some benefits for the achievement of a good behaviour. 1

2 Hence, this work intends to contribute to the study of more alternatives to HMA. The main objective is to compare the behaviour between HMA and bituminous mixture incorporating nanomaterials, based on Marshall methodology and empirical rheological test, such as penetration and softening point (ring and ball method)). This study is also complemented with a cost analysis, in order to determine whether this type of solution is affordable or not. 2. Characterization of Bituminous Mixtures All the bituminous mixtures comprise bitumen, aggregates, and air. Bitumen is particularly important regarding the analysis of the mechanical behaviour of HMA, especially due to its rheology (Branco et al., 2005). The air present in the mixture corresponds to air voids, which are extremely important and essential to maintain controlled. On the one hand, this control prevents the exudation of bitumen, and on the other hand, prevents the risk of post-compression (Picado- Santos, 2010). According to Branco et al (2005), the aggregates form a solid skeleton, cohesive, resilient, enabling to resist the aggressive traffic, which means to shock, friction and wear. In which concerns to the nanomaterials, it is assumed that it is directly added to the binder, and it has the same role as an additive, causing the change of mixture s properties. The wearing course is lying on the top of the pavement, fully exposed to various agents, such as traffic or environmental factors, which may cause certain types of failures already mentioned before. This layer has the following functions (INIR, 2011): Provide adequate traffic circulation in comfort and safety; Ensure sufficient drainage and sealing; Distribute strains induced by traffic. Thus, the wearing course not only needs to be resistant to constant actions, but also guarantees certain qualities related to safety, durability, economy and sustainability. 2.1 Nanotechnology To better understand the concept of nanotechnology, it is vital to begin by clarifying its prefix "nano". This unit of measurement - nanometre (nm) - is one-billionth of a meter, which means 1x10-9 meters. Engineering initially was interested in properties at macro and meso scales, until the micro and nano scales stood out due to its potential in the development of science and technology (You et al., 2010). The aim is that the new materials or new applications can be useful and with unique features, as well as possibly being the solution to certain problems. However, there are inherent limitations to the application of nanotechnology, such as (Steyn, 2009): Costs; Environment and people health; Scale factors. Obviously, the fact that nanomaterials are of recent technology and the equipment used is complex, the associated cost is significantly high. This cost has been decreasing over time, especially with regards to materials, in order to challenge the evolution of traditional methods (Steyn, 2009), which continue to have a cost considerably more affordable. As for the environmental and public health, particularly in recent years, there have been some concerns about its potential effects because of what is known as "nanoparticles". It raises a possibility of damaging the DNA, resulting in the development of cancer in the future. With regards to the scale factor, this is justified by the existing big jump between nano and macro dimensional. The idea is to take advantage of the nanoscale, not jeopardizing the properties when used in macroscale, such as the performance of the nanomaterials when combined with aggregates and/or binders (Steyn, 2009). 2.2 Nanotechnology in Road Engineering The fact that there is a great development of nanotechnology in the fields of chemistry, physics, and electronics, suggests that there is a strong potential when applied in road engineering, seeking to increase the level of quality of life in society. Road engineering is mainly based on four objectives: safety, durability, economy, sustainability. In this section, a short summary of these requirements are provided. 2

3 Most pavement failures directly affect the safety of road users. Therefore, nanotechnological solutions are applied to improve the behaviour of bituminous mixtures, through the development of improved materials, by changing its properties (Steyn, 2008). A successful example in this area is the incorporation of silicon carbide (SiO 2) into tire in order to improve the wet skid resistance, and also reduce the abrasion of the tire up to 50% (Wang et al cited in Steyn, 2008). Durability has to do with the infrastructure capacity to be sustainable and have a suitable behaviour in service during the life cycle, without spending maintenance costs and unexpected repairs. For example, the abrasion resistance of cement used in concrete pavement can increase between 90 and 180% due to the introduction of SiO 2 and titanium dioxide (TiO2) (Li et al., 2006 cited in Steyn, 2008). Regarding the economy, the purpose of having the lowest possible cost solution using nanotechnology concerns a more adjusted and correct maintenance of the infrastructure. An example of an economic solution has to do with the incorporation of nanomaterials in coatings with the intent of extending the life of the infrastructure (Steyn, 2008). The sustainability of an infrastructure refers to its condition to retain, in particular to the environmental effects. For this purpose, nanotechnology has been investigating the possibility of modifying the properties of the materials commonly used in road infrastructure that are harmful to the environment, for instance the modification of asbestos (Steyn, 2008). As in other areas where nanotechnology is applied, also in this area of road engineering some disadvantages can be pointed out. Overall, the problems that nanotechnology entails when used in other areas are much the same as when applied to the pavement: public health and environment, scale and costs. Taking into account what has been said previously, the biggest concern in nanotechnology when applied in road engineering is to ensure the compatibility between the materials used in the construction and maintenance of pavements, and the natural environment (Steyn, 2009). In the nano-modified bituminous mixtures, the percentage of nanomaterials usually added varies between 2 and 5% by weight of bitumen (Jahromi and Khodaii, 2009). Among the various nanomaterials in the world of nanotechnology, this work refers only to three: montmorillonite, precipitated calcium carbonate (PCC) and silicon dioxide. Montmorillonite is one of the most well-known nanomaterials in road engineering, a type of nanoclay. It mostly consists of aluminium silicate, magnesium, and calcium hydrate. The secret of this nanomaterial is its dispersion, which when incorporated in a thermoplastic material (like changes its rheological properties and increases stiffness and also improves ageing resistances (Jahromi and Khodaii, 2009). The PCC is composed by atoms of calcium, carbon and oxygen, and can be organized in various ways. This nanomaterial has always been used exclusively as raw material in the manufacturing industry of paper and paperboard for achieving high brightness, bulk and opacity in papermaking (Omya, 2010). With regards to silicon dioxide (meaning silica), its addition to polymers increases the scratch and mar resistance, dimensional stability, stiffness and impact resistance, among others. 2.3 Characterization Studies A laboratory study was conducted to study the effects of nanoclay on rheological properties of bitumen binder (Jahromi and Khodaii, 2009). The procedure started by performing some tests that compared the unmodified bitumen mixture with bitumen modified with two types of nanoclay: cloisite- 15A and nanofil-15. The type of bitumen used was 60/70, and the amount of nanoclay used was 2%, 4% and 7% by weight of bitumen. The empirical rheological tests carried out to determine the properties of the modified and unmodified bitumen were penetration, softening point and ductility. As Jahromi and Khodaii (2009) stated, the results led to the conclusion that the incorporation of nanomaterials 3

4 changed the rheological properties of bitumen, decreasing penetration and ductility as well as increasing softening point and ageing resistance. In fact, these results confirmed that the presence of the nanoclay increased the stiffness and ageing resistances of unmodified bitumen. A laboratory study was carried out to test the application of nanomaterials on the asphalt, so as to improve its performance (You et al., 2010). The original binder that was used was PG Experimental tests intended to evaluate the viscosity and secant modulus which is estimated according to the direct tension test. Tests were made for two types of nanoclay (nanoclay A and nanoclay B) with different content: 2% and 4% by weight of binder. According to You et al. (2010), both nanoclays improved viscosity and secant modulus, which means that both improved low-temperature cracking resistance. The explanation for these results is related to the possibility of nanoclay forming very strong bonds with the binder, stiffening the mixture. 3.1 Composition of the Mixtures Analysed The mixture studied is designated by AC 14 surf 35/50, and consists of basaltic aggregates. Besides conventional HMA, three more types of mixtures incorporating montmorillonite were produced, PCC and silica. For practical reasons, the four mixtures manufactured are referred hereinafter according to the designations adopted in Table 3.1. Table Designation of the analysed mixtures Nanomaterial Type of mixture Designation incorporated - AC14 Surf 35/50 HMA Montmorillonite AC14 Surf 35/50 PCC AC14 Surf 35/50 Silica AC14 Surf 35/50 Based on the mixtures aggregate grading, the proportion of the granular materials to be adopted was determined, in order to obtain a mixture of aggregates adjusted, as well as possible, to the grading spindle defined in the standard NP EN (IPQ, 2011), as shown in Figure 3.2. The grading curve shown results in the combination of the final percentages of aggregates, presented in Table Experimental Study In Figure 3.1 it is possible to see the experimental study, based on Marshall methodology, according to EN (CEN, 2004). It should be noted that the ultimate goal is not to determine the optimum percentage of bitumen, but to make a comparative analysis of bituminous mixtures with bitumen percentages previously defined. Figure Experimental work conducted in this dissertation (adapted from Picado-Santos, 2010) Figure Placement of the grading curve in the spindle of the standard NP EN :2011 Table Percentage of aggregates used in bituminous mixtures Aggregates Percentage (%) Basalt 10/16 12 Basalt 4/10 50 Basaltic sand 0/6 31 Filler 7 Regarding the bitumen, according to standard EN (CEN, 2009), the grade designation is 35/ Laboratory Study The laboratory study started up with Marshall methodology. The first step was the manufacture of test specimens. In the HMA, the aggregates were heated at a temperature of approximately 180 C, while bitumen reached a temperature between 120 and 140 C. In the case of,, and, after bitumen 4

5 reached that temperature, the correct amount of nanomaterial was added. The mixture procedure is crucial to get the appropriate involvement of the nanomaterial by bitumen. Then, the mastic was mixed with the aggregates, and afterwards the specimens were compacted at 150 C with 75 blows in each face. The compacted specimens were demoulded ensuring that they were cool in air. Hereafter, the bulk density of each specimen was determined in accordance with EN (CEN, 2003). After bulk density, all specimens were tested using the Marshall test procedure, as provided in the standard EN (CEN, 2004), recording the stability and deformation values obtained from the test. After finishing this procedure, the maximum density test was executed and all the volumetric characteristic of the Marshall specimens were calculated (voids content and void in the mineral aggregate (VMA)) in accordance with EN (CEN, 2002). This study suggests the production of only 3 specimens for each mixture. In total, 60 samples were performed, varying the percentage of binder (5,5 and 6,5) and nanomaterial (2, 4 and 6). Also within the experimental study, two tests were conducted in order to evaluate the individual characteristics of the bitumen: penetration test, concerning the NP EN 1426 (IPQ, 2003), and determination of softening point, according to NP EN 1427 (IPQ, 2003). 4. Discussion 4.1 Marshall Test As from this point, all the obtained values correspond to the average obtained for each mixture, the respective coefficient of variation (c v) and the relative variation in comparison to the reference mixture (Δ). Taking into account the absolute results shown in Table 4.1, for mixtures containing 5,5% of bitumen, it is possible to state that bulk density obtained for the conventional HMA is quite similar to the bulk density of each bituminous mixture incorporating nanomaterials, corresponding to relative variations in maximum 1%. It can be said that the effect of any content of each nanomaterial on bulk density is negligible. The same behaviour had the mixtures containing 6,5% of bitumen, as shown in Table 4.2. There are no great variations in results, so it can be concluded the same as for mixtures containing 5,5% of bitumen. This fact can be justified probably due to some discrepancies in manufacturing conditions, regardless of a very strict control. Table Bulk density for mixtures containing 5,5% of bitumen Mixture Bulk Percentage of (5,5% density nanomaterial (%) (kg/m 3 ) HMA ,50% ,80% +0,40% ,10% +0,00% ,10% -0,20% ,70% -0,60% ,00% -1,00% ,50% -0,10% ,50% -0,30% ,70% +0,70% ,20% +0,80% Table Bulk density for mixtures containing 6,5% of bitumen Mixture Bulk Percentage of (6,5% density nanomaterial (%) (kg/m 3 ) HMA ,70% ,50% -1,20% ,50% +0,00% ,30% -1,50% ,60% +0,60% ,50% +1,40% ,60% +0,10% ,00% -0,50% ,20% +0,80% ,40% +0,10% The results obtained for stability in mixtures with 5,5% of bitumen can be seen in Table 4.3, being the same shown graphically in Figure 4.1. It is possible to verify that for most of the mixtures, the stability decreased in comparison to HMA, although this reduction was not significant. Table Stability of the mixtures containing 5,5% of bitumen Mixture Percentage of Stability (5,5% nanomaterial (kn) (%) HMA 0 8,9 13,50% - 2 8,3 9,30% -7,30% 4 8,7 11,60% -2,40% 6 8,6 10,60% -4,00% 2 8,6 6,90% -4,10% 4 9,2 11,80% +2,70% 6 8,5 8,20% -4,70% 2 8,1 10,00% -8,90% 4 8,7 8,50% -1,90% 6 8,6 7,10% -3,50% The stability results obtained for mixtures with 6,5% of bitumen are presented in Table 4.4, shown 5

6 graphically in Figure 4.2. Looking at Figure 4.2, it is possible to see that, excluding mixtures with montmorillonite, both mixtures and had a positive behaviour, achieving stability values higher than those obtained by HMA. The incorporation content of 4% is related to the best results. very interesting behaviour, particularly for 4% and 6% of nanomaterial content. Table Deformation of the mixtures containing 5,5% of bitumen Mixture Percentage of Deformation (5,5% nanomaterial (mm) (%) HMA 0 6,0 14,90% - 2 4,9 2,30% -18,20% 4 6,4 10,20% +6,20% 6 5,0 10,50% -17,20% 2 5,5 18,30% -8,60% 4 5,5 7,10% -8,50% 6 5,5 9,40% -8,60% 2 5,5 14,50% -8,20% 4 5,3 7,80% -12,00% 6 5,0 8,30% -17,10% Figure Stability of the analysed mixtures containing 5,5% of bitumen Table Stability of the mixtures containing 6,5% of bitumen Mixture Percentage of Stability (6,5% nanomaterial (kn) (%) HMA 0 8,1 9,20% - 2 7,8 7,70% -3,50% 4 8,0 7,70% -1,00% 6 7,8 6,30% -3,70% 2 8,2 9,60% +1,10% 4 10,2 5,30% +25,90% 6 7,9 18,00% -2,80% 2 8,5 6,40% +4,80% 4 9,6 6,60% +18,20% 6 8,7 4,30% +7,40% Figure Stability of the analysed mixtures containing 6,5% of bitumen Concerning the deformation, the results obtained for mixtures with 5,5% of binder are given in Table 4.5, while the comparative chart is shown in Figure 4.3. Regarding Figure 4.3, it is clear that the bituminous mixtures incorporated with nanomaterials correspond, in general, to deformation values lower than the HMA, except for 4% of montmorillonite. In general, and mixtures have proved to show a Figure Deformation of the analysed mixtures containing 5,5% of bitumen Given Figure 4.1 and Figure 4.3, it can be said that the relation between stability and deformation (S/D) increases as increases the content of nanomaterial for and, particularly because there was a great decrease/reduction in deformation. The reason for this decrease may have to do with the improvement of the mastic, due to its merger with the nanomaterial. The results obtained for the deformation for mixtures with 6,5% of binder are given in Table 4.6, shown graphically in Figure 4.4. Table Deformation of the mixtures containing 6,5% of bitumen Mixture Percentage of Deformation (5,5% nanomaterial (mm) (%) HMA 0 6,4 10,80% - 2 5,8 11,90% -9,80% 4 6,2 11,90% -3,30% 6 6,2 7,30% -3,20% 2 7,6 3,30% +19,60% 4 7 4,20% +9,30% 6 6,7 6,80% +4,70% 2 5,8 9,10% -9,80% 4 5,5 24,00% -13,80% 6 4,5 2,90% -29,30% 6

7 With regards to the information in Table 4.6, it is possible to highlight the fact that most of the mixture resulted in a decrease of the deformation relative to HMA. Taking into account only, it can be observed that the bigger amount of nanomaterial induces a reduction of the deformation, being the 6% of silica of the greatest interest. It also can be seen that presents a bad behaviour, showing higher deformation results than HMA. Figure Deformation of the analysed mixtures containing 6,5% of bitumen Focusing on Figure 4.5, relative to S/D relation, it is important to state that (in comparison to HMA): showed the best behaviour in all rates of incorporation, the mixture enhances some significance in the rate 4 but worse in others, and slightly improves in rate 2 but in reality seems to have no effect. content values lower than voids content of HMA, having mixture the worst behaviour because of the high levels of voids content. Table Results of maximum density of mixtures Percentage of Maximum density Bitumen nanomaterial (kg/m 3 ) content (%) HMA 5,5% 6,5% Table Voids content of the mixtures containing 5,5% of bitumen Mixture (5,5% Percentage of nanomaterial (%) Voids content (%) HMA 0 5,3 26,40% - 2 2,9 26,00% -45,30% 4 3,6 31,30% -31,40% 6 3,4 32,10% -35,20% 2 6,1 10,60% +15,70% 4 6,3 14,50% +18,90% 6 4,4 11,40% -17,00% 2 4,5 9,70% -15,10% 4 2,8 24,10% -47,80% 6 3,6 31,90% -31,40% c v Δ Figure S/D of the analysed mixtures containing 6,5% of bitumen In Table 4.7 it is possible to verify the maximum density, showing that the majority of mixtures had quite the same behaviour. These results were expected, since for bulk density the introduction of nano could not alter with significance the specific weight without voids. Regarding the voids content, the results obtained for mixtures with 5,5% of binder are presented in Table 4.8, shown graphically in Figure 4.6. Observing this figure, mixtures or are characterized by voids Figure Voids content of the analysed mixtures containing 5,5% of bitumen The results for voids content to mixtures containing 6,5% of binder are given in Table 4.9, shown graphically in Figure 4.7. Regarding Figure 4.7, the reduced values are remarkable to the general voids content of the mixtures produced. It is likely that the use of nanomaterials has itself a relatively small influence in this aspect, assigning the variability observed primarily due to variability in the manufacturing process. In addition, the large amount of binder probably affects the reduction of voids content, which fills the existing voids. As for VMA, the addition of any nano did not significantly affect this characteristic. In fact, the constituent more influent in 7

8 this property is the aggregate used and the way it distributes its skeleton, so the incorporation of nanomaterial (directly held in will not affect VMA. Table Voids content of the mixtures containing 6,5% of bitumen Mixture Percentage of Voids (6,5% HMA nanomaterial (%) 0 content (%) 5,3 c v 26,40% Δ - 2 2,9 15,40% -14,60% 4 1,7 15,40% -50,50% 6 2,7 9,40% -22,30% 2 2,6 23,10% -24,30% 4 3,4 15,60% -1,00% 6 2,7 56,70% -20,40% 2 4,1 23,30% +19,40% 4 1,1 19,50% -68,90% 6 2,3 15,70% -33,00% Figure Voids content of the analysed mixtures containing 6,5% of bitumen 4.2 Penetration Test Concerning the penetration test, according to NP EN 1426 (IPQ, 2003), it is extremely relevant to assess what changes may be induced by the presence of the nanomaterial in bitumen. The results obtained are shown in Table Table Results of needle penetration test Mixture Percentage of Penetration nanomaterial (x0,1mm) (%) HMA ,00% ,00% -10,26% ,70% -12,82% ,65% -10,26% ,80% -17,95% ,86% -20,51% ,94% -12,82% ,75% -15,38% ,56% -5,13% ,56% -5,13% Analysing Table 4.10, it can be observed that the results of the penetration of bitumen of the mixtures containing nanomaterials were lower than the penetration of bitumen of the reference mixture, predominantly. For low rates of nanomaterial incorporation, being in accordance with lower penetration results, it is possible to deduce that the trend of bituminous mixtures incorporating nanomaterials is to increase the bitumen s stiffness. 4.3 Softening Point The results of the determination of softening point, according to NP EN 1427 (IPQ, 2003), are shown in Table This table shows that, in general, the softening point of bitumen of the mixtures incorporated with nanomaterial decreases (although not significantly), compared to the softening temperature taken as reference. So, this test does not prove that the nanomaterial significantly alter the characteristics of the bitumen. It is, therefore, quite hard to conclude about the rheological behaviour of bitumen. Table Results obtained from softening point test Percentage of Softening Mixture nanomaterial (%) point (ºC) Δ HMA 0 56,3-2 55,4-1,60% 4 56,1-0,36% 6 56,0-0,53% 2 56,2-0,18% 4 56,1-0,36% 6 56,8 0,89% 2 55,2-1,95% 4 54,6-3,02% 6 55,8-0,89% 4.4 Validation of Results In Portugal, the bituminous mixtures need to meet certain requirements, usually expressed in the Technical Specifications from the national company Estradas de Portugal SA (EP). The limits of the asphalt properties for surface layer are indicated in Table 4.12, as defined in Technical Specifications from EP (EP, 2009). Table Limits of the asphalt properties for the surface layer, defined in the Technical Specifications from EP (EP, 2009) Limit Properties Standards values Stability S min/max EN ,5-15 kn Deformation F min/max EN mm Marshall Quotient Q min EN kn/mm VMA VFB min EN > 14 % Voids content V m EN % In Table 4.13, the values of all bituminous mixtures with 5,5% bitumen are presented, in which those that are within the allowable values distinguished, and those outside are highlighted in bold. 8

9 Through Table 4.13 it is verified that in all types of mixtures porosity reveals discrepancies. For all mixtures, the deformation exceeds the 4 mm allowed. Due to the completion of the previous point about deformation, it is natural that the quotient Marshall is affected, not reaching up to the minimum required. All values concerning the stability and VMA meet the requirements. Table Validation of the results of the analysed mixtures containing 5,5% of bitumen Mixture % of S F Q VMA V m (5,5% nano (kn) (mm) (kn/mm) (%) (%) HMA - 8,9 6,0 1,5 19,7 3,7 2 8,3 4,9 1,7 16,6 2,9 4 8,7 6,4 1,4 17,2 3,6 6 8,6 5,0 1,7 17,0 3,4 2 8,6 5,5 1,6 19,7 6,1 4 9,2 5,5 1,7 19,8 6,3 6 8,5 5,5 1,6 18,0 4,4 2 8,1 5,5 1,5 20,5 4,5 4 8,7 5,3 1,6 19,0 2,8 6 8,6 5,0 1,7 19,8 3,6 Note: nano means nanomaterial For bituminous mixtures with 6,5% of bitumen, the validation of results was done as well, and is shown in Table Table Validation of the results of the analysed mixtures containing 6,5% of bitumen Mixture % of S F Q VMA V m (6,5% nano (kn) (mm) (kn/mm) (%) (%) HMA - 8,1 6,4 1,3 19,6 3,4 2 7,8 5,8 1,3 18,9 2,9 4 8,0 6,2 1,3 17,8 1,7 6 7,8 6,2 1,3 18,5 2,7 2 8,2 7,6 1,1 18,8 2,6 4 10,2 7,0 1,5 19,7 3,4 6 7,9 6,7 1,2 18,8 2,7 2 8,5 5,8 1,5 20,1 4,1 4 9,6 5,5 1,8 17,3 1,0 6 8,7 4,5 1,9 18,4 2,3 Note: nano means nanomaterial Based on what was denoted above in Table 4.13, one can take quite the same conclusions as from Table The major difference has to do with given porosity, since most of the mixtures have a lower porosity than that one required. Based on this validation, it can be concluded that the reference mixture does not itself validate the specifications. Given that, the reference mixture should be reformulated in order to confirm the requirements presented in Table Cost Analyses In order to calculate part of the production cost of a bituminous mixture, this work refers only to the portion of the nanomaterial and bitumen. However, it is vital to emphasize the idea that cost-effectiveness during the life cycle of a pavement is (or at least should be) determinant to validate the solutions. It should be noted that Table 4.15 presents an example of costs, made for the most common situations that happen, and at the same time it is the most economically unfavourable (6% of nanomaterial content and 6,5% of. Another note on the calculation of costs has to do with the cost of each constituent, related to the average cost in Partial sums have proved what was already expected. The partial cost of production of bituminous mixtures incorporated with nanomaterials is high above the production cost of a conventional mixture. The need of road pavements requires a big quantity of bituminous mixtures containing nanomaterials over thousands of kilometres, therefore this alternative turns out to be too expensive. Given this, it is necessary to study in more detail how bituminous mixtures can profit by using nanomaterials, so that this solution can justify its additional costs. Table Analyses of partial costs of the analysed mixtures Constituents HMA Bitumen kg/ton content (HMA) Cost of /ton bitumen (HMA) 35/50 19,5 19,5 19,5 19,5 Nano %/binder Cost of /ton nano (HMA) - 230,2 1,2 176,0 Partial cost /ton of (HMA) production 16,5 407,9 21,5 331,5 Cost difference 5. Conclusions The comparative analysis of bituminous mixtures produced indicated that the adoption of certain nanomaterials promotes pleasing changes in the behaviour of HMA. The influence of the nanomaterial is more evident with the increase of its incorporation rate, in particular the properties concerning stability, deformation and voids content. %

10 Based on penetration test, it can be stated that the modified bitumen may present a more rigid behaviour caused by the presence of the nanomaterial. It is likely that the behaviour of the mastic is affected, resulting in stable and stronger chemical bonds, and hence recovering the rheology of the mastic. The best solution is the one concerning the incorporation of nanosilica. This solution is worth it because of the fact of being independent of the amount of nanomaterial chosen proved, for both percentages of binder, a very positive behaviour. Based on cost analyses, there are more disadvantages than advantages, as there are differences in cost higher than 1000%. At the outset, the costs will always be higher than the costs of HMA, as it is a technology still in development, associated to expensive materials and also complex equipment. References CEN (2002). EN Bituminous mixtures. Test methods for hot mix asphalt - Part 5: Determination of the maximum density. Comité Européen de Normalisation CEN. (2003). EN Bituminous mixtures. Test methods for hot mix asphalt. Part 6: Determination of bulk density of bituminous specimens. Comité Européen de Normalisation. CEN (2004). EN Bituminous mixtures - Test methods for hot mix asphalt Part 34: Marshall test. Comité Européen de Normalisation CEN (2009). EN Bitumen and bituminous binders. Specifications for paving grade bitumens. Comité Européen de Normalisation IPQ (2003a). NP EN 1426 Betumes e ligantes betuminosos. Determinação da penetração com agulha. Instituto Português da Qualidade IPQ (2003b). NP EN 1427 Betumes e ligantes betuminosos. Determinação da temperatura de amolecimento Método do Anel e Bola. Instituto Português da Qualidade IPQ (2011). NP EN Misturas betuminosas. Especificações dos materiais. Parte 1: Betão betuminoso. Instituto Português da Qualidade Branco, E. F., Pereira, P., Picado-Santos, L. (2005). Pavimentos Rodoviários. Livraria Almedina, Coimbra EP (2009). Caderno de Encargos Tipo Obra Pavimentação. Características dos Materiais. Estradas de Portugal, S.A. INIR (2011). Directivas para a Concepção de Pavimentos. Critérios de Dimensionamento. Instituto de Infraestruturas Rodoviárias IP, Lisboa Jahromi, S., Khodaii, A. (2009). Effects of nanoclay on rheological properties of bitumen binder. Construction and Building Materials, Vol. 23, Issue 8, pp Li, H., Zhang, M-H., Ou, J-P. (2006). Abrasion resistance of concrete containing nano-particles for pavement. Wear, Vol. 260, Issues 11-12, pp Omya (2010). Omya Syncarb S270 - ET 20%. Ficha técnica do produto, fornecida pela empresa Omya Comital Minerais e Especialidades SA, Portugal Picado-Santos, L. (2010). Vias de comunicação. Misturas Betuminosas. Formulação de misturas betuminosas. Retrieved May 30, 2013, from isturas%20betuminosas_formulacao_aula16.pdf Steyn, W. J. (2008). Research and Application of Nanotechnology in Transportation. SATC. 27th Southern African Transport Conference. Tshwane University of Technology, Pretoria, South Africa Steyn, W. J. (2009). Potential Applications of Nanotechnology in Pavement Engineering. Journal of Transportation Engineering, Vol. 135, No. 10, pp Wang, M-J., Reznek, S. R., Kutsovsky, Y., Mahmud, K. (2002). Elastomeric compounds with improved wet skid resistance and methods to improve wet skid resistance. US Patent You, Z., Mills-Beale, J., Foley, J. M., Roy, S., Odegard, G.M., Dai, Q., Goh, S. W. (2010). Nanoclay-modified asphalt materials: Preparation and characterization. Construction and Building Materials, Vol. 25, Issue 5, pp