Durability performance of ternary blend alkali activated mortars for concrete surface damage repair

Abstract

The progressive deterioration of concrete surface structures being the major concern in construction engineering requires special protection and precise repairing. The adverse physical, chemical, thermal and biological processes that cause such rapid decay need to be overcome. The durability of concrete structure is found to be strongly influenced by inappropriate use of materials as well as their physical and chemical condition of the surroundings. The immediate consequence is the anticipated need of maintenance and execution of repairs. Lately, many alkalis activated mortars are synthesized by selectively combining some waste materials containing alumina and silica compounds which are further activated via strong alkaline solution. Despite the emergence of various alkalis activated as prospective material toward emergency repairs and coating, a functional alkali activated with efficient repairing attributes and endurance is far from being achieved. Generally, the alkaline solution prepared by mixing concentrated sodium silicate and sodium hydroxide restrict the broad array of repairing applications of alkalis activated mortar. Furthermore, they are not only expensive and hazardous to the workers but negatively impact the environment. The research attempted to produce environmental friendly alkali activated by blending different ratios of sodium hydroxide and sodium silicate at low concentration. Durability and mechanical strength of the synthesized ternary blend alkalis activated mortars were evaluated to inspect their repairing effectiveness towards concrete surface damage. Tests were performed for determining the porosity, shrinkage, compressive strength and slant bond shear strength. Microstructures and thermal properties were evaluated using XRD, SEM, TGA, DTG and FTIR measurements. The prepared ternary blend contained the ground blast furnace slag, fly ash and palm oil fuel ash or ceramic waste powder. The prepared fresh, hardened and durable mortars were activated with affable alkaline solution (at low concentration) of sodium hydroxide and sodium silicate. The ground blast furnace slag that acted as the main resource of Ca++ was used to replace the low amount of Na+ in the geopolymerization process. The amount of slag in the blend varied in the range of 20 - 70%. The addition of slag to the blend had improved the strength and durability properties as well the microstructure characteristics. This improvement is majorly attributed to the participation of calcium silicate hydrate and calcium aluminosilicate hydrate beside sodium aluminosilicate hydrate bonds in reaction products. The results revealed that all the prepared mixes developed appreciable strength under mild alkaline solution. Furthermore, the alkali activated specimens prepared with high slag content displayed good durability including abrasion, thawing-freezing and shrinkage. The research has established that the ternary blend alkalis activated mortars with friendly alkaline solution contributes towards the development of high strength and durable repairing materials for concrete structures.