Physical and Long-Term Mechanical Properties of Walnut Shell Ash Blended Cement

Abstract

Walnut shell ash (WSA) is a new supplementary cementitious material (SCM) for cement. Tests for water of consistency, setting time, pozzolanicity, free lime content, flexural and compressive strength were conducted. Results demonstrated that the cement pastes incorporating up to 25 wt. % WSA possesses suitable and satisfactory setting times, physical, pozzolanic activity and mechanical properties. The addition of WSA increased the w/c ratio and setting times. The total porosity gradually decreased with the increase of WSA content while the bulk density increased. The strength improvements were due to of formation of fibrous CSH gel, high hydration level, low porosity, high density and pozzolanic reactions of WSA with the resulting free lime from the hydration process.  The free lime contents of the OPC (W0) increased with the curing times, while with WSA the free lime content decreased due to the pozzolanic activity of WSA. Any further increase of WSA content more than 25 wt. %, all properties adversely effected. So, the optimum content of WSA is 25 wt. %.