Development of geopolymer with pyroclastic flow deposit called Shirasu

Abstract

. The study presents a preliminary investigation on the applicability of Shirasu (a pyroclastic flow deposit characterized by high percentage of volcanic glass) in geopolymer. Comparative study on compressive strength and internal pore structure has been done between geopolymers with alkali activated Shirasu and fly ash as aluminosilicates. Mortar mix proportions are selected based on variations in ratio of alkaline activators to aluminosilicate and also on silica to alkali hydroxide ratio. From the experimental study, Shirasu geopolymer exhibited fairly good compressive strength. Mix proportion based on silica to alkali hydroxide ratio is observed to have profound effect on strength development. Development of geopolymer with pyroclastic flow deposit Shirasu and blast furnace slags as aluminosilicates. The present study is an attempt to utilize unused natural resource called Shirasu as aluminosilicate source in geopolymer. “Shirasu”, a kind of volcanic ash abundantly deposited due to a big pyroclastic flow in the southern part of Kyushu Island, Japan, in 20 to 100 thousand years ago, is one of the unused natural resources. Shirasu is sandy but porous material with large amount of very fine particles. It has about 80% density of that of sea sand and three times higher water absorption capacity when compared to sea sand. It also has high quantity of volcanic glasses in its mineral composition and has been confirmed by Takewaka (2004) to show pozzolanic reaction. Shirasu concrete (Shirasu as fine aggregate) is successfully applied to the concrete foundation for piers constructed in hot spring environment and investigations have proved that Shirasu concrete behaves well in hot conditions and is resistant to sulfate attacks (Takewaka and Kawamata (1991)). Laboratory tests on Shirasu concrete by Katpady (2012) proved that Shirasu concrete is highly resistant to chemical attacks and possess higher capabilities in corrosion protection of reinforcement. As Shirasu is rich in silica and alumina, it can be potentially used as aluminosilicate source in geopolymer. The present investigation is an attempt to study the performance of geopolymer with Shirasu as aluminosilicate source. The behavior of Shirasu geopolymer is compared with that of geopolymer mortars prepared with fly ash. Past researches have proved that fly ash geopolymer are generally stronger and durable (Duxson et al . 2007). With this knowledge, Shirasu geopolymer with different mix proportions is tried. As Shirasu and fly ash have different characteristics, an attempt to study the strength development of mortars and to obtain optimum strength is done assuming silica to alkali hydroxide ratio