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Effects of Gamma Irradiation on Polymer-Modified Concrete (PMC): A Review

Since the 1950s, when synthetic polymers began to be incorporated into Portland cement mortars and concrete, there has been widespread interest in the use of synthetic polymer latex instead of rubber latexes in construction industries. Polymer latexes are suspended and water-insoluble polymer particles [1]. It is made of a core made of water-insoluble polymer and a stabilization system used to prevent agglomeration in the colloidal system [2]. Currently, latexes of a single or polymer options, such as polyvinyl acetate, vinyl acetate-ethylene, styrene-butadiene copolymers, styrene-acrylic, and acrylic and styrene-butadiene rubber emulsions are generally used in the manufacture of cement composites [3-8]. So far, many effective polymer modification systems have been developed for cement mortar and concrete and have been used in various applications in the construction industry since the concept of polymer modification for cement mortar and concrete was introduced more than 80 years ago. Recently, the application of concrete-polymer composites, in particular polymer modified mortar and concrete, is rapidly expanding due to its good properties compared to conventional cement mortar and concrete [9-11]. The term acrylic in acrylic polymers, which has long been used to develop Portland cement composites, represents a broad family of materials with a similar chemical structure but with a wide range of properties [12]. It is well known that by exposure of polymers to radiation, the structures prior to exposure are separated and degraded by the release of atoms, molecules and molecular particles. This event generates a series of transformed species, ions, free radicals and induces scission and crosslinking, or both. Gamma radiation causes both crosslinking and degradation during application, but one of these effects may be predominant in some materials. Crosslinking is the most important effect of polymer irradiation, since it usually leads to the formation of a network structure with an increase in the number of polymeric chains under the irradiation dose. Thus, as a result of improved inter-phase bonding, the mechanical strength, thermal and chemical environmental properties, workability, abrasion, bond strength, adhesion with substrates or waterproofing properties of mortars and concrete can be improved.


Introduction
Since the 1950s, when synthetic polymers began to be incorporated into Portland cement mortars and concrete, there has been widespread interest in the use of synthetic polymer latex instead of rubber latexes in construction industries. Polymer latexes are suspended and water-insoluble polymer particles [1]. It is made of a core made of water-insoluble polymer and a stabilization system used to prevent agglomeration in the colloidal system [2]. Currently, latexes of a single or polymer options, such as polyvinyl acetate, vinyl acetate-ethylene, styrene-butadiene copolymers, styrene-acrylic, and acrylic and styrene-butadiene rubber emulsions are generally used in the manufacture of cement composites [3][4][5][6][7][8]. So far, many effective polymer modification systems have been developed for cement mortar and concrete and have been used in various applications in the construction industry since the concept of polymer modification for cement mortar and concrete was introduced more than 80 years ago. Recently, the application of concrete-polymer composites, in particular polymer modified mortar and concrete, is rapidly expanding due to its good properties compared to conventional cement mortar and concrete [9][10][11]. The term acrylic in acrylic polymers, which has long been used to develop Portland cement composites, represents a broad family of materials with a similar chemical structure but with a wide range of properties [12].
It is well known that by exposure of polymers to radiation, the structures prior to exposure are separated and degraded by the release of atoms, molecules and molecular particles. This event generates a series of transformed species, ions, free radicals and induces scission and crosslinking, or both. Gamma radiation causes both crosslinking and degradation during application, but one of these effects may be predominant in some materials. Crosslinking which is further reduced by hydration or drying, polymer particles located in the gel particles and cavities combine to form continuous films. Thus, a co-matrix is formed which binds the hydrates with aggregates and is interconnected to the cement paste [13].

Application
Polymer modified concrete is suitable for use in different structural and non-structural precast products such as tile adhesives, facade coatings, slabs, decorative coatings and as repair material in road buildings [14]. Resurfacing, flooring, and patching are among the current applications as the others like overlays on roadways and bridges, both as new construction and as repairs of existing deteriorated structures.
Polymer modified concrete has also recently been used with fiber reinforcement to reduce crack formation where high tensile strength, bond strength and impermeability is required [15][16][17]. In the future, it is considered to be used in roller-compacted concrete (RCC) for roadways and parking lots as well as marine and offshore structures.

Examples from Literature
MR Ismail et al [18] presented a study to investigate the effects of different doses of gamma rays on physico-chemical properties of prepared blended cement mortars. In this context, nano-calcined clay (NCC) replaced with Portland cement by different ratios and polyvinyl alcohol (PVA) were added to the resulting cement blend with percentages between 2 and 8. NCC used for the study obtained by heating at 750 °C for 2 hours with particle size of 60.6 nm. Results of this study showed that irradiation of blended cement mortars with the addition of PVA increased the compressive strength and bulk density up to 30 kGy of γ-irradiation absorbed dose value.
However, between 30 & 50 kGy, a significant decrease has been observed for both properties. Total porosity and water absorption percentages improved due to increased PVA and irradiation dose.
The reason for this was the deposition of solid materials in the pore system of composite. As a final conclusion, XRD, SEM and TGA applications have confirmed that chemical reactions between composite components occurred as a result of gamma irradiation [18]. MM Khattab [19] stated the effects of replacing the standard sand (SS) used for cement mortar production with white sand for white sand (WS) cement mortar production. In addition, alterations in physico-mechanical properties were also discussed by adding In addition, it has been reported that the SAE polymer affects the microstructure of the hydration products of the cement blend to form a denser matrix [20]. M Martinez-Lopez et al [21] reported the evaluation of mechanical, morphological and thermal properties of polyester resin and silica sand-based composites which are formed by partial replacement of Tetra Pak particles with silica sand and applied to gamma rays. Tetra Pak has a total of six layers, four of which are polyethylene, one cellulose and one aluminum. Samples prepared for experiments were a composite material prepared by milling a Tetra Pak package to 2 -4 mm sized rectangular particles and replacing those by silica sand in per-centages of 1, 2, 4 and 6 and adding them to the cement mix. Samples have been exposed to gamma rays at doses between 100 and 500 kGy to provide a better interfacial surface coupling between the matrix and Tetra Pak particles. It is concluded that highest compressive and flexural strength values were achieved when 1 wt.% of Tetra Pak particle is added. At high doses of irradiation, the composites showed a considerable increase deformation due to pressure and bending; maximum deformation was observed at 400 kGy (26% higher than control mortar) and 500 kGy at bending (36% higher than control mortar). It was suggested that gamma rays created cross-linking and degrading effects on polyethylene, cellulose and polyester matrix [21]. AAM Yassene et al [22] observed the effect of styrene-butadienerubber (SDR) polymer/cement ratio under the conditions of gamma irradiation dose on physico-mechanic properties of cement mortar. Samples were prepared in different SBR/cement mass ratios (2.5, 5, 10, 15 and 20), then wet and dry curing method was applied. Gamma irradiation were applied to the resulting samples at 10, 30 and 50 kGy doses. Ordinary Portland cement (OPC) was used as cement type and standard sand was used as aggregate. and SEM studies were consistent with the physico-chemical and mechanical results obtained from experiments [22].