Geopolymers termed as “Green Materials” because of the

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Last updated: September 25, 2019

Geopolymersare emerging as a new class of high performance materials because of theirexcellent properties, since the later half of the 20th century withgrowing interest by researchers, engineers and technologists in generating newmaterials with array properties exihibted by exhibited by these materials overother conventional materials including the low cost of raw materials and itsenviromental friendly manufacturing process. Geopolymers are fire and hightemperature resistant up to 1300 oC 1,2 they are stable andcan perform without any loss of properties at high temperatures, highcompressive strength, long term durability and heavy metal ion fixiation 3,4.These materials have good acid and sulfates resistance; develop rapid strengthup to 70% within four hours of casting 5, 6.

Geopolymersare castable, sprayable, extrudable, stick to many materials including metals,concretes and give glassy finishes. These materials are termed as “GreenMaterials” because of the low energy consumption and low toxic gasemission for their production. Geopolymers can be synthesized using wastematerials like industrial slag, fly ash, volcanic ash and along-with alkaliactivators 7.

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These materials have excellent compressive strength, rangingfrom 48 MPa to 120 MPa, depending on the starting materials, method of preparationand the added aggregates. Such properties make these materials a veryattractive choice for a range of potential applications. In spite these advantages, geopolymers havenot been used in their full potential as of today there are some technical aswell as commercial obstacles that hinder the growth of the geopolymer industry;one of the outstanding problems with geopolymers is their processibility 8,9,also Geopolymers present a typical brittle mechanical behavior with the consequentlow ductility and low fracture toughness 10. These characteristics canlimit their applications as a structural material. Inorder to improve these drawbacks of geopolymer materials, organic polymers areoften incorporated in their structure 11, 12, 13, 14, 15, 16. asone important factor in choosing the added organic polymer is to be stable orbecome reactive under extreme basic condition of the geopolymer which can besatisfied by ethylene glycol. Addition of organic polymers also impartedflexibility to the cured samples opposing to the brittle nature of the puregeopolymer systems.

Thestudy by Kecheng Gong 16 mentions the requirement of organic componentfor the mineralization process of inorganic materials. It also mentions the functionof organic component to bind the micro-crystals of inorganic materials andarrange their orientation to form natural composite materials with superiormechanical properties as compared to ceramics.

Polyethyleneglycol (PEG) is a polyether compound with many applications in industrialmanufacturing.PEG is one of the most well-known water-soluble polymers, while it can also bedissolved in many organic solvents including aromatic hydrocarbons. PEG is usedas a plasticizer to increase lubricity and acts as a water retention agent inceramic mass, adhesives and binders and soldering fluxes with good spreadingproperty 11.

In a study of Catauroa et al. 17, the influence on mechanical strengthof the different percentages of PEG added to geopolymer was investigated. Inabsence of PEG, the tests showed overall strength regularity with aging timedue to the chemical composition of sample. PEG-free samples can reach finalmechanical strength faster than hybrid systems.

The stretching effect of PEG,that in general provides the characteristic of elasticity to the base material togetherwith the longer time required to reach the final structural strength, justifiesthe increase of flexural and compressive strengths with aging time.Colangeloet al. 18concluded that polymer-modified mortars have improved compressive strength in comparisonto unmodified ones and polymer helps restrain micro-crack propagation. Theyalso found out that total porosity decreases with the addition of organicpolymer and this may contribute in improved durability.

Hereby the aim of thiswork is to explore the amount of PEG that can be added to geopolymer systems,in order to improve their properties. The rather limited literature in thisfield of study necessitates the expansion of knowledge on this topic.Zhanget al. 16 added to theuncalcined-kaolinite geopolymeric matrix some organic polymers (1 wt %)characterized by carboxyl or amino groups or even hydroxide radicals; inparticular, they used polyacrylic acid, sodium polyacrylate, polyethyleneglycol, polyvinyl alcohol and polyacrylamide, increasing the compressivestrength of the mere inorganic polymer up to 29%; still larger increases wereobtained for bending, up to about 65%, but in any case that resistance ischaracterized by very low values.

In that way crack propagation resistance isincreased by a bridging action which prevents the matrix from cracking. Feroneet al.14 obtained significantly enhancedcompressive strengths and toughness compared to the mere geopolymer by addingepoxy based organic resins to the geopolymeric matrix.

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