The engineering properties of high performance concrete with HCWA–DSF supplementary binder

High calcium wood ash (HCWA) and densified silica fume (DSF) exhibit good cementitious properties and has a great potential as supplementary binder material for the concrete production industry. The experimental investigation was conducted to study the properties of HCWADSF cement and the mechanical behaviour of HCWA–DSF high performance mortar. A total of twelve different blended cement pastes and mortar mixes were fabricated with the use of HCWA at various cement replacement levels of 0% to 20% in combination with 7.5% densified silica fume (DSF) by total binder weight and subjected to rheological and mechanical strength tests. The rheological properties of blended cement paste studied are standard consistency, initial setting time and final setting time. The mechanical strength parameters of mortar covered in the study are compressive strength, flexural strength, static modulus of elasticity and dynamic modulus of elasticity. Experimental results indicated that the inclusion of HCWA at the content of 2–20% by binder weight does not have significant influence on the standard consistency of HCWA–DSF blended cement but significantly prolonged the setting times of the blended cement paste. The combined use of HCWA (2–6% by binder weight) and DSF (7.5% by binder weight) as supplementary binder material produced mortar mixes which exhibited compressive and flexure strengths which are 2.4–31.2% higher than equivalent ordinary Portland cement (OPC) mortar. Besides, the use of HCWA at cement replacement levels between 2% and 12% with 7.5% DSF by weight of binder was found to enhance the static and dynamic modulus of Portland cement mortar by 1.9–24.7%. The observed improvement in the mechanical properties is due to a significant densification in the microstructure of cement paste matrix in the presence of HCWA and DSF hybrid supplementary binder as observed from micrographs obtained in the study.