**4. Polymer concrete irradiated by gamma particles**

Studies on the effects of gamma ionizing radiation on the curing process and on final properties of polymer concrete are ongoing. Developments include the effects on the mechanical properties. Our developments regarding the influence of fiber reinforcements on polymer concrete and the different behaviors based on the components (polymer resin and mineral aggregates) [Martínez-Barrera et al., 2007; Martínez-Barrera et al., 2008a; Bobadilla-Sánchez et al., 2009; Martínez-Barrera et al., 2009; Martínez-Barrera et al., 2008b; Martínez-Barrera et al., 2010].

In principle one can obtain high compressive and flexural strength, high impact and abrasion resistance, lower weight and lower costs. In general, the compressive strength values increase with the gamma irradiation dose. Moreover, when using CaCO3, the highest compressive strength values are obtained compared to using SiO2 aggregates. Intermediate values are found when using a combination of them (CaCO3 and SiO2).

The influence of polymeric fibers has been established. The Nylon fibers have a rigid shape, which differs from the polypropylene or polyester fibers having a more elastic shape. Thus the compressive strength depends on the material type, that is to say either rigid or elastic. So, it is worth point out that the combination of two minerals and elastic fibers (polyester and polypropylene) and at least 10 kGy of gamma irradiation allows higher values of compressive strain.

The Young's modulus E, can be a defining measure of whether one will obtain a ductile or more brittle concrete. Excepting only polymer concrete with marble and calcium bentonite, the values are higher than the standard value for polyester-based polymer concrete. Moreover, the improvement above that standard is notable: a) 143 % for polymer concrete with SiO2, b) 141 % for polymer concrete with CaCO3, and c) 120 % for polymer concrete with CaCO3+SiO2. Generally the higher the gamma irradiation the higher the Young's modulus and the harder the polymer concrete becomes.

Gamma Radiation as a Novel Technology for Development of New Generation Concrete 107

Dose (kGy) 0 50 150

 **M+CB M+CB SiO2 SiO2 SiO2 SiO2 Resin 0.3%N 0.4%N 0.3%PP 0.4%PP CaC03 CaCO3 0.3%P 0.5%P**

Another important mechanical feature of the PCs is related to the compressive strain at the yield point, as seen in Figure 8. The highest compressive strain values are for PC with Marble. Except PC with SiO2 all specimens have higher values respect to the standard values reported in the literature (0.01 mm/mm) [Martínez-Barrera et al., 2009b]. On the other hand, lower values are observed for PC containing SiO2. Different phenomena are observed, for example for certain PCs specimens the values increase up to a certain dose and afterward decrease (PC with CaCO3, PC with M+CB and for 100% resin). One conclusion is that when using one mineral aggregate the compressive strain is influenced more by the

Si02 Si02+CaCO3 CaCO3 M+CB M Resin

Fig. 8. Compressive strain at yield point of polymer concrete compounded with different

Fig. 7. Compressive strength of fiber-reinforced polymer concrete compounded with

Dose (kGy) 0 50 150

40

60

80

Compressive Strength / (MPa)

different mineral aggregates.

resin than by the mineral aggregates.

0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024 0.026

Compressive Strain at Yield Point / (mm/mm)

mineral aggregates.

100

120

140

Our studies are summarized in Figures 6 to 11. In Figure 6 is shown the compressive strength of PC compounded with unsaturated polyester resin (UPR) and one or two mineral aggregates, covering gamma doses between 50 and 150 kGy; values for specimens of 100% resin are also shown.

In Figure 6 we see that the compressive strength values increase with the gamma irradiation dose. Moreover, when using CaCO3, the highest compressive strength values are obtained compared when using Marble + Calcium Bentonite (M+CB) aggregates. Intermediate values are found when using Marble aggregates. The standard value of compressive strength for polyester-based PC is 70 – 80 MPa [Martínez-Barrera et al., 2008a]. Thus, considering all PCs the maximal improvement percentage on compressive strength is 68% respect to standard values. Moreover, the values for resin are comparable with those for PC with CaCO3. Such resin could be used for certain applications.

Fig. 6. Compressive strength of polymer concrete compounded with different mineral aggregates.

With respect to fiber-reinforced PCs, Figure 7 shows that the compressive strength values increase when the gamma irradiation dose increases. Nevertheless, lower values are done when comparing with PCs without fibers (see Figure 6). Different types of fibers were used (N=Nylon, PP=Polypropylene, and P=Polyester) at varying percentages (0.3, 0.4 and 0.5 vol. %) and with similar dimensions (40-60 m of diameter and 10-20 mm long).

The lowest values of compressive strength were observed for PC with Marble + Calcium Bentonite, independently of the Nylon-fiber percentage. The Nylon fibers have a rigid shape, which differs from the polypropylene or polyester fibers having a more elastic shape. In our studies the highest values have been found in formulations combining two mineral aggregates (CaCO3 and SiO2) and one fiber. Thus the compressive strength depends on the material type, that is to say either rigid or elastic.

Our studies are summarized in Figures 6 to 11. In Figure 6 is shown the compressive strength of PC compounded with unsaturated polyester resin (UPR) and one or two mineral aggregates, covering gamma doses between 50 and 150 kGy; values for specimens of 100%

In Figure 6 we see that the compressive strength values increase with the gamma irradiation dose. Moreover, when using CaCO3, the highest compressive strength values are obtained compared when using Marble + Calcium Bentonite (M+CB) aggregates. Intermediate values are found when using Marble aggregates. The standard value of compressive strength for polyester-based PC is 70 – 80 MPa [Martínez-Barrera et al., 2008a]. Thus, considering all PCs the maximal improvement percentage on compressive strength is 68% respect to standard values. Moreover, the values for resin are comparable with those for PC with CaCO3. Such

> Dose (kGy) 0 50 150

M+CB Si02 M Si02+CaCO3 CaCO3 Resin

Fig. 6. Compressive strength of polymer concrete compounded with different mineral

%) and with similar dimensions (40-60 m of diameter and 10-20 mm long).

With respect to fiber-reinforced PCs, Figure 7 shows that the compressive strength values increase when the gamma irradiation dose increases. Nevertheless, lower values are done when comparing with PCs without fibers (see Figure 6). Different types of fibers were used (N=Nylon, PP=Polypropylene, and P=Polyester) at varying percentages (0.3, 0.4 and 0.5 vol.

The lowest values of compressive strength were observed for PC with Marble + Calcium Bentonite, independently of the Nylon-fiber percentage. The Nylon fibers have a rigid shape, which differs from the polypropylene or polyester fibers having a more elastic shape. In our studies the highest values have been found in formulations combining two mineral aggregates (CaCO3 and SiO2) and one fiber. Thus the compressive strength depends on the

resin are also shown.

resin could be used for certain applications.

40

material type, that is to say either rigid or elastic.

60

80

Compressive Strength / (MPa)

aggregates.

100

120

140

Fig. 7. Compressive strength of fiber-reinforced polymer concrete compounded with different mineral aggregates.

Another important mechanical feature of the PCs is related to the compressive strain at the yield point, as seen in Figure 8. The highest compressive strain values are for PC with Marble. Except PC with SiO2 all specimens have higher values respect to the standard values reported in the literature (0.01 mm/mm) [Martínez-Barrera et al., 2009b]. On the other hand, lower values are observed for PC containing SiO2. Different phenomena are observed, for example for certain PCs specimens the values increase up to a certain dose and afterward decrease (PC with CaCO3, PC with M+CB and for 100% resin). One conclusion is that when using one mineral aggregate the compressive strain is influenced more by the resin than by the mineral aggregates.

Fig. 8. Compressive strain at yield point of polymer concrete compounded with different mineral aggregates.

Gamma Radiation as a Novel Technology for Development of New Generation Concrete 109

In the case of fiber-reinforced PCs, the behavior of the Young's modulus is significantly varied (Figure 11). The PC with SiO2 has higher values with respect to the standard reported for polyester-based PCs (6.7 GPa) [Tavares et al., 2002]. Nevertheless, it is possible to obtain low values for PCt with CaCO3+SiO2, namely 2.8 GPa, which represents a diminution of 58 % with respect to the standard. It is therefore also possible to get a more ductile PC, which may be desirable for certain applications. For the PC with combined SiO2 and CaCO3 the irradiation has little effect, likely due to competing interactions and effects in these

> SiO2 SiO2 M+CB M+CB SiO2 SiO2 Resin CaCO3+0.3%P CaCO3+0.4%P 0.3%N 0.4%N 0.3%PP 0.4%PP

Fig. 11. Young's Modulus of fiber-reinforced polymer concrete compounded with different

Improvements of E described here have wider implications and may be indicative of improvements or modifications to other properties not directly tested. It is therefore evident that the use of gamma irradiation can be another strategic tool to modify the mechanical

To Autonomous University of the State of Mexico by grant # UAEM 3053/2011SF. Mr. Miguel Martínez López and Ms. Elisa Martínez Cruz graduated students at the Materials Science Program (Autonomous University of the State of Mexico) have participated in the

Dose (kGy) 0 50 150

materials.

properties of polymer concretes.

**5. Acknowledgements** 

experiments.

mineral aggregates

Young Modulus / (GPa)

In the case of fiber-reinforced PCs, the compressive strain values increase notably for specimens with two mineral aggregates rather than just one (Figure 9). Something notable is that when comparing these compressive strain values to the standard value reported in the literature for PC (0.01 mm/mm) [Martínez-Barrera et al., 2009b]: a) for PC with SiO2 there is 60 % improvement; b) for PC with M+CB up to 180 %, and c) for PC with CaCO3 and SiO2 up to 390 %. So, it is worth point out that the combination of two minerals, one fiber, and specific gamma radiation dose allows higher values of compressive strain.

Fig. 9. Compressive strain at yield point of fiber-reinforced polymer concrete compounded with different mineral aggregates.

A third mechanical feature studied was the Young's modulus. Excepting only PC with M+CB, the values are higher than the standard value for polyester-based PCs, namely 6.7 GPa (see Figure 10) [Tavares et al., 2002]. Moreover, the improvement above that standard is notable: a) 139 % for PC with SiO2, b) 122 % for PC with CaCO3, and c) 108 % for PC with CaCO3+SiO2. Generally the higher the gamma irradiation the higher the Young's modulus and the harder the PC becomes.

Fig. 10. Young's Modulus of polymer concrete elaborated with different mineral aggregates

In the case of fiber-reinforced PCs, the behavior of the Young's modulus is significantly varied (Figure 11). The PC with SiO2 has higher values with respect to the standard reported for polyester-based PCs (6.7 GPa) [Tavares et al., 2002]. Nevertheless, it is possible to obtain low values for PCt with CaCO3+SiO2, namely 2.8 GPa, which represents a diminution of 58 % with respect to the standard. It is therefore also possible to get a more ductile PC, which may be desirable for certain applications. For the PC with combined SiO2 and CaCO3 the irradiation has little effect, likely due to competing interactions and effects in these materials.

Fig. 11. Young's Modulus of fiber-reinforced polymer concrete compounded with different mineral aggregates

Improvements of E described here have wider implications and may be indicative of improvements or modifications to other properties not directly tested. It is therefore evident that the use of gamma irradiation can be another strategic tool to modify the mechanical properties of polymer concretes.
