**Acknowledgements**

substantially, having a maximum value at 400 kGy when compressive evaluation is done; while for flexural test, maximal deformation is obtained at 500 kGy. Such improvements are due to

In the case of polymer concrete for improvement of the interfacial surface, gamma irradiation is a novel proposal. As it is known that in a composite material only physical interactions are present between matrix and aggregates, nevertheless, by using gamma irradiation, chemical bonds can be obtained [26]. In **Figure 5**, the irradiation process in the polyester resin causes chain scission and it also produces some cross-linking, chain relaxation, and cage breaking. As a consequence, the formation of bonds into polymer chains increases the degree of polymerization of the resin matrix. Homogenous surface is affected by gamma radiation because a higher number of chemical bonds are established and a rougher surface is observed (**Figure 5**), and for higher radiation dose, voids and small particles created from the cross-linking of the resin are observed. One can achieve good control of the dimensions and the elimination of internal stress, which cause reduction in mechanical strength [27, 28].

Other studies show different behaviors, for example: (a) molecular defects on mineral aggregates such as calcium bentonite have been observed [29]; (b) compressive strength values increased while total porosity and water absorption values decreased with increasing irradiation dose, in polymer-modified cement mortar specimens, with styrene-acrylic ester as adding polymer [30]; and (c) improvement on mechanical properties such as compressive strength and Young's modulus was observed for concrete reinforced with polypropylene fibers

The main aim of this chapter is to show how both waste and recycled materials as well as gamma irradiation are adequate tools for improvement of mechanical properties of construction composites. Such materials are reused to replace partially those component concrete

the cross-linking and degradation processes in both cellulose and polyester resin.

**Figure 5.** SEM images of irradiated polyester resin.

172 Composites from Renewable and Sustainable Materials

[31].

**5. Conclusions**

Financial support of the Autonomous University of the State of Mexico (UAEM), located at Toluca City, is acknowledged.
