Determination of shear strength by Iosipescu (V-notch) method of metakaolin-based geopolymeric resins activated by different silicate and hydroxide combinations

Abstract

Geopolymers (inorganic polymers) were developed and patented by Joseph Davidovits in the 1970’s and have gained significant attention in the civil construction industry. Since then, the properties of geopolymers have been studied by many researchers, such as their use as a repair material on reinforced concrete structures. Thus, this study aimed to evaluate the mechanical properties of metakaolin-based repair geopolymeric resins. The geopolymeric resins were prepared with alkaline activators composed by sodium and potassium silicates combined to sodium and potassium hydroxides to determine the properties of fresh mixtures (workability, setting times), the adhesion coefficient at the interface substrate/resin and the gain in compressive and indirect tensile strengths up to 28 days of age. The Iosipescu or V-Notch shear tests were used to determine the shear strength and shear modulus, according to ASTM D 5379 (1998) specifications, as these are the most important mechanical properties when studying structural repairs. The results indicated that all geopolymeric resins achieved high mechanical strength in the early ages, which is fundamental for structural repair applications. The gain in compressive strength ranged from 60% on the first day to 85 to 93% after 3 days when compared to the results obtained at 28 days of age. All resins reached compressive strengths greater than 80 MPa and indirect tensile strengths between 5 and 6 MPa at 28 days of age. The shear strength (τ) values were around varied from 4.31 to 7.55 MPa. The resins with combination of sodium silicate with potassium hydroxide and potassium silicate with sodium hydroxide showed higher shear moduli, being respectively 6,13 and 8,20 GPa. The results obtained show that the resins developed in this work have enormous potential for use in repairing reinforced concrete structures.