EXPERIMENTAL STUDY ON REACTIVITY OF PYROCLASTIC FLOW DEPOSIT CALLED SHIRASU AS BINDER IN MORTAR AND GEOPOLYMER

Abstract eng:
The study aims at using Shirasu, which is a pyroclastic flow deposit like volcanic ash, as one of the binders in mortar or concrete. It is one of the unused natural resources, available in Kyushu Island of Japan, and pose potential threat to environment and health. From the view points of effective use of the unused natural resource and CO2 free material, Shirasu is used as a cement replacement material. In the experiment, size under 150μm of “Shirasu” is used. Comparison between strengths of mortars using Shirasu with the ones made of ordinary Portland cement mortars or mortars with fly ash partially replacing cement is done up to 1 year curing. From test results of the mortars in which the Shirasu replacement levels of 10%, 20%, 30% in binder and water binder ratio of 40%, 50% and 60%, the mortar having 10% of Shirasu replacement level with water binder ratio of 40% shows optimum mechanical property up to 1 year. Geopolymer has lately attracted considerable attention as one of the CO2 free construction materials, because of concrete free from any cementitious material. Therefore, an attempt is made to study Shirasu as aluminosilicate source in geopolymer. Geopolymer mortar is made with Shirasu of size under 75μm, chemical admixtures of NaOH and Na2SiO3 as alkaline activators, and river sand. Three types of water binder ratio, 40%, 50%, 60% are set and heat cured at 80ºC and 90ºC. The mixture polymerizes under high temperature to form hard mass which is subjected to compressive strength test. From the results obtained, the compressive strength is highest for water to binder ratio of 40% under 90ºC of curing condition. The strengths are also compared with geopolymer mortars using fly ash as binder and the ones with fly ash as binder and Shirasu as fine aggregate. KEYWORDS: shirasu, pyroclastic flow deposit, CO2 free material, geopolymer, alkaline activators

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