Revista Iberoamericana de ftolmerosMartnez et al.Volumen 13(4), Septiembre 2012Concreto polimrico reforzado

CONCRETO POLIMRICO REFORZADO CON FIBRAS: EFECTO DE LA RADIACIN GAMMA

Gonzalo Martnez Barrera*, Elisa Martnez Cruz, Miguel Martnez Lpez

Laboratorio de Investigacin y Desarrollo de Materiales Avanzados (LIDMA), Facultad de Qumica, Universidad Autnoma del Estado de Mxico, Km.12 de la carretera TolucaAtlacomulco, San Cayetano 50200, Mexico; email: gonzomartinez02@yahoo.com.mx

Recibido:Enero 2012; Aceptado:Junio 2012

OVERVIEWThe polymer concrete (PC) is a very versatile composite material due to its use in: construction and repair of structures, roads and bridges, pipes wastewater and structural, as well as decorative building panels. These reinforced materials presented higher values in properties such as mechanical strength, rigidity, high temperature performance, resistance to corrosion, hardness or conductivity. The advantage of using polymers in the PCs is the high sensitivity to changes in chemical bonds; that it cause different values in crystallinity, density, coefficient of thermal expansion, module of elasticity, permeability, as well as resistance to corrosion, abrasion and solvents. This modification should be using gamma radiation. This work studied the effects of gamma radiation on the properties of mechanical deformation of PCs based on resin marble, unsaturated polyester and polypropylene (PP) fibers. We used different particle sizes of marble (0.71, 1.40 and 2.36 mm) and doses of 200, 250 and 300 kGy.Key words : concrete polymer, fibres of polypropylene, marble, strength and radiation gammaABSTRACTPolymer Concrete (PC) is a composite material which having a variety of applications: Building and repair structures, in highway or bridges pavements; as underground wastewater pipes, or as precast components for bridge panels. Some advantages compared to PCC such as: increase bond strength; increase freeze/thaw resistance, abrasion resistance, flexural, compressive and tensile strengths. Such advantages are due to the chemical modifications which provoking changes on cristalinity, density, thermal expansion, elastic modulus, permeability as well as corrosion and wear resistance. Such modifications can be carried out by gamma radiation. In the present work, we have studied the gamma irradiation effects on the Young modulus of polyesterbased PCs with marble and polypropylene fibers (PP). Several size marble particles were used (0.71, 1.40 and 2.36 mm), and 200, 250 and 300 kGy of gamma doses.Keywords: Polymer concrete, polypropylene fibers, marble, strength, gamma radiation.

1. IntroductionToday has been revealed the need to produce materials with enhanced properties that exceed existing limitations, tala is the case of reinforced materials ("composite"). Which are the combination of two or more materials, and constituted by a matrix (continuous phase) and any reinforcement (discrete phase); the matrix (metal, polymer or ceramic) is the major material and contains the reinforcement, which can be in the form of particles, plates or fibers. Composite materials with improved properties such as mechanical strength, rigidity, high temperature performance, resistance to corrosion, hardness or conductivity with higher values than the materials original.

Polymer concrete (PC: for its acronym in English) is a composite material formed by thecombination of mineral aggregates (sand, gravel, among others) and a polymer resin. Due to its fast drying (two hours), high values in mechanical properties and its ability to withstand corrosive environments, the use of PCs has increased in many applications, as an alternative to hydraulic concrete. For example, in construction and repair of structures, paving of roads, bridges, pipelines of wastewater and structural, decorative building panels between other.

Due to its low cost, the most used PC polymer matrices are based on unsaturated polyester. Resin polyester has good mechanical strength, accession relatively good with other materials, and good chemical resistance to freezing and thawing [1].

The choice of the mineral aggregates is very important in the development of PCs, it is convenient to have the lowest volume of empty spaces [2, 3], used calcium bentonite, sand silica, calcium carbonate, marble, among others. In some works organic or synthetic fibres were added to PCs; within these last are polypropylene (PP) fibres that offer lower cost compared with the fibres of nylon, polyester or polyacrylate [4-6]. Little effect on the mechanical behaviour of the PCs of these reinforcements before suffering a fracture, however they substantially improve the response post-cracking: improvement of hardness and ductility, as well as resistance to traction, bending and impact resistance [7 - 11].

When polymer is subjected to the action of ionizing radiation, chemical and physical effects that depend on the dose applied and the nature of the polymer in question occur. It is well known that gamma radiation causes three types of modification of polymers: degradation (scission), Criss Cross (cross-linking) and grafting (grafting), which can be controlled by means of a proper dose of radiation [12, 13]. It the advantage of working with polymers is the high sensitivity to changes in the chemical bonds, resulting in materials with different properties in: crystallinity, density, coefficient of thermal expansion, module of elasticity, permeability, as well as resistance to corrosion, abrasion and solvents.

Changes in the properties of a polymer after irradiation, are primarily due to geometric reordering of its link structure. Some mechanical properties can be explained on the basis of the rigidity of the chains that tends to prevent these from slipping over others as a result of the orientation of the side chains, inducing a certain degree of crystallinity.

The radiation gamma be has used in PCs for improve the support between the matrixpolymer and aggregates by means of structural and surface modifications of components [3]. The present study investigated the effect of ionizing energy (gamma radiation) on the properties of compression and mechanical deformation of reinforced materials made with resin unsaturated polyester, marble and fibers of polypropylene..

2. Part EXPERIMENTAL2.1. Material . For the development of PCs was employed: such as matrix, unsaturated polyester resin marketed with the name Polylite 32493-00. Their properties and characteristics are shown in table 1. As load was employed marble of different particle sizes: mesh 25 (0.71 mm); mesh 14 (1.40 mm); and mesh 8 (2.36 mm), whose properties are shown in table 2. Polypropylene fibers, were added to the properties shown in table 3. Initiator, was used as peroxide, methyl ethyl ketone (MEKP) diluted in phthalate de methyl.Table 1 properties of resin unsaturated polyester.

NamePOLYLITE

Key3249300

ApplicatinConcrete Polymr

ChesmistryOrto

ReactivityMedia

Gel (minutes)68

Exothermal (C)145163

Curing (minutes)120

Viscosity (cps)100200

No. cid in slid1226 in solutin

2.2. Team. Gamma radiation. Polymer concretes and polypropylene fibers were irradiated with gamma rays in a Irradiator Gammabeam 651 PT company Nordion, which works with pencils of cobalt-60 ( )60Co) with half-life of 5.261 years. The average dose rate was 8.5 kGy/h

Table 2. mechanical properties of the marble.

Property

Value

Density (g/cm3)

2,38 3,10

Compressive (MPa)

58 98

Flexural strength (MPa)

9,8 19,6

Impact resistance (cm)

30 45

Absorption coefficient (%)

0.2

Hardness

3 4

Apparent porosity (%)

0,2 1,2

Table 3. the fiber properties of polypropylene.

Property

Value

Force to the traction

0,67 MPa

Module of elasticity

4 MPa

Point of melt

165C

Point of ignition

600C

Gravity specifies

0,91

Compression testing . The evaluation of the mechanical resistance to compression test specimens concrete polymer was carried out in a universal testing machine brand ControlsMR with a capacity of 30 tons. Table 4 shows the test conditions of compression.Table 4. universal machine working conditions of tests.

Conditions

Value

Type of test

Control

Speed (in force)

25 kgf/s

Speed (in position)

0,30 mm/min

Upper limit of force

25 t

Upper limit of position

20 mm

Revista Iberoamericana de ftolmerosMartnez et al.Volumen 13(4), Septiembre 2012Concreto polimrico reforzado

. X-ray diffraction . Polypropylene fibers were studied by diffraction of X rays on a diffractometer brand Bruker D8 Advance. The test conditions were: power window of 5-80 , passage of time of 0.3 and 0.03 size tube of 30 kV, s/step2.3. Methodology2.3.1. Design of formulations . Polymer concrete was prepared using a 30% resin and 70% of marble in volume. The formulation base (for three specimens of CP) is shown in the table 5.Table 5. quantity in weight and volume of the components of the specific polymer.

Component

Weight g

Density in gcm-3Volume cm 3

Resin

124,021,1112,5

Marble

682,52,6262,5

Catalyst

2,481,182,92

The concentration of the marble had different compositions, depending on the size of the particles (0.7, 1.4 and 2.36 mm). I.e., were developed specific size, with two sizes, or with three sizes of particle.For the design of the formulations of concrete with polypropylene fibers (to 0.1, 0.2 and 0.3% by volume), only partially replaced the original marble volume, as shown in the table 6.Table 6. quantity in weight and volume of the components of the polymer concrete with 0.1% by volume of polypropylene fibers.

Componentweight gDensityg/cm3Volume cm3

Resin124.021.1112.5

Mrble682.52.6262.5

Fiber

0.3420.9130.375

Catalyst

2.481.182.92

2.3.2. Sample preparation . For the determination of resistance to compression, distortion and static modulus of elasticity of the PCs, 5 x 5 x 5 cm cubes were developed (volume of each specimen, 125 cm )3). The preparatory process was carried out according to the following steps: 1. weigh the required quantities of marble, resin, fiberglass PP and catalyst for each formulation; 2. mix the marble and the resin up get a mix homogeneous; 3. forconcrete with fiber, add PP gradually to avoid crowds; 4 Add the catalyst and mix (must be done in one period not longer than 4 minutes), 5. Empty the mixture in the molds of gradual, that is, add one sufficient amount to cover one-third of the height of the cube, tamp this amount, add another third, tamp and add the rest of the material to fill the mould and return to tamp, and 6) material, though it heals in a couple of hours, is unmolding 24 hours (figure 1).

Figure 1. Preparation of test specimens concrete polymer.RESULTSStatic modulus of elasticity. Whereas all polymer concretes, obtained the maximum values of Young's modulus when added 0.1% of PP fiber and radiating with 250 kGy (for any combination of sizes of particle).For concrete with a single particle size the highest values are achieved with marble mesh 14 and radiating with 250 kGy. These values are 27% higher in relation to concrete without fiber (figure 2).Revista Iberoamericana de ftolmerosMartnez et al.Volumen 13(4), Septiembre 2012Concreto polimrico reforzado

Figure 2. Static modulus of elasticity of concrete with a single particle size of marble and 0.1% of fiber from polypropylene.If two sizes of particles are combined, the maximum values of the elastic modulus is achieved by mixing marble mesh 25 and 14 mesh (for concrete with 0.1% fiber) and applying a dose of 250 kGy (figure 3),

Figure 3. Static modulus of elasticity of concrete with two different sizes of particle of marble and 0.1% of fiber from polypropylene.

For concretes with three sizes of particle, according to figure 4, is observed a slight increase in the highest values of modulus Young (no more than 8%) for concrete with 0.1 and 0.2% of fibres, with respect to the concrete without fiber; but a decrease for concrete with 0.3% fiberglass PP. Respecto the effect of ionizing energy , shows a characteristic behavior: to radiate with 250 kGy elastic modulus presented the highest values, being the highest of the concrete made with 0.1% fiber from PP.

Figure 4. Static modulus of elasticity of concrete with three different particle sizes of marble.The static modulus of elasticity presents increments by adding 0.1% polypropylene fiber since fibers break off and stabilize the microcracks caused by the applied force. To be stabilized cracks by the fibres, increases the resistance to compression which is reflected in the increase in the values of the static modulus of elasticity.By adding 0.2 and 0.3% of fiber to concretes made with one or two sizes of particle, decrease the higher values of the elastic modulus (values less than 1.3 GPa) with regard to those containing 0.1% fiber (2 GPa). This is due to the poor distribution of the fiber during the mixing process caused by the quantity of polypropylene. There are an estimated optimum content of fibres (based on maximum strength) for each content of resin.

The elastic modulus of the concrete is increased by subjecting them to gamma radiation since ionizing energy produced effects in the polymer which constitute them, such as the formation of links between chains and chains cross-linked. The higher values are obtained to radiate with 250 kGy, but decrease to reach 300 kGy. This behavior is consistent for any combination of particle sizes. The increases are due to polymer concretes are becoming more resistant to compression, so it decreases the deformation, i.e. they obtained concrete with greater rigidity. The former It is attributed to reordering the geometric structure of the polymer matrix and fibres of polypropylene link, as well as the increase in the degree of polymerization of the resin, which improves the mechanical behaviour of the concrete.When the concrete subjected to 300 kGy decrease the values of compressive strength, elastic modulus is lower. This is due to the effect of gamma radiation on the polymer chains of the concrete (is broken of chains).X-ray diffraction . Figure 5 shows the XRD patterns of the fibres of polypropylene non-irradiated and irradiated at 200, 250 and 300 kGy.

Figure 5. Diffractogram of polypropylene fibers, non-irradiated and irradiated at 200, 250 and 300 kGy.Polypropylene fibers undergo gamma radiation increases its crystallinity which improves its mechanical properties. To relate the values in the change of intensity of the

fibers irradiated with the results of the mechanical tests, is observed that these changes are consistent with the maximum values of compressive strength of polymer concrete. I.e. 250 kGy of gamma radiation, results in greater resistance to compression by modules which increase of elasticity.4 conclusionsBased on the mechanical tests established that: to) the particle size and concentration of the mineral aggregates and influencing the mechanical properties of the specific polymer because of the degree of compaction, as well as its adherence to the polymer matrix; (b) in general terms, Young modules increase by increasing the dose of gamma radiation up to 250 kGy due to a higher degree of polymerization of the resin and the Crosslinking of the polymer chains; What concrete generates more rigid; (c) by adding polypropylene compared with resin fibers, polymer concretes are notable increases in compressive strength and consequently elastic modules are higher since the fibers provide support to concrete by its homogeneous distribution; (d) the use of gamma radiation as a treatment for curing of concrete polymer is a suitable alternative for improving their behavior mechanical.Thanks . To CONACYT for the financing of the project 49899.

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