Fresh properties, mechanical strength and microstructure of fly ash geopolymer paste reinforced with sawdust

This work aims to verify the feasibility of utilizing sawdust in geopolymer to make reinforced composites and broaden application of sawdust in geopolymer. Fresh properties including workability and setting time, density, nailing ability, drying shrinkage, mechanical strength and microstructure of fly ash geopolymer activated by sodium silicate and sodium hydroxide solutions blended with 0-20% of sawdust by mass with an interval of 5% were investigated. The experimental results uncover that sawdust addition influences the workability of geopolymer. The sawdust content is inversely proportional to the setting time and a good linear relation is found between density and sawdust content. Sawdust is beneficial for the resistance to cracking and drying shrinkage especially the later ages. Sawdust exhibits little effect on compressive strength before 14 days of curing and it possesses positive effect after 28 days. 5% of sawdust addition exhibits little effect on flexural strength regardless of days of curing. The flexural strength increases with increasing content of sawdust. With the increasing addition levels of sawdust, the porosity decreases and compact matrix can be observed. Sawdust addition leads to the formation of an optimal microstructure. The results from mechanical properties and microstructure observation are compatible. (C) 2016 Elsevier Ltd. All rights reserved.