Mechanical properties and reaction mechanism of one-part geopolymer mortars

Abstract

The use of traditional two-part geopolymers is limited to small scale engineering applications, due to difficulties with the transportation, storage and prefabrication of alkaline activator solutions. In this study, “just adding water” or one-part geopolymers were developed using solid activators. Flow tests, flexural and compressive strength tests were carried out on a number of one-part and two-part geopolymer mortar specimens to evaluate the effect of concentration, modulus and type of activators on the workability and mechanical properties of geopolymer mortar. The reaction heat during the first 7 curing days and the degree of reaction of one-part and its two-part geopolymer counterparts were measured to compare their reaction mechanism. The test results showed that the flexural and compressive strengths of one-part geopolymer mortar specimens were 88%-94% and 65%-95% respectively, of the corresponding strengths of the two-part counterparts. The results also revealed that anhydrous sodium silicate (Na2SiO3) is a more effective solid activator than the combination of hydrous Na2SiO3 and sodium hydroxide (NaOH) for metakaolin and fly ash blending precursor. Due to a higher degree of geopolymerization reaction, the highest compressive strength of one-part geopolymer mortar using anhydrous Na2SiO3 with modulus of 1.4, reached 49.2 MPa after 7-day ambient temperature curing. When using a combination of solid hydrous Na2SiO3 and NaOH as an activator, the strength difference between one-part and its corresponding two-part geopolymer mortar specimens decreased with an increase in the modulus of the activator.