Mechanical strength, durability and drying shrinkage of structural mortar containing HCWA as partial replacement of cement

Potential use of high calcium wood ash (HCWA) as partial cement replacement material in production of mortar was investigated. Chemical composition and phases of HCWA were evaluated using X-ray Fluorescence (XRF) and X-ray Diffraction (XRD) analytical methods respectively. Physical properties of HCWA namely particle size distribution, average particle size d50 and specific surface area were assessed by laser particle size analyser. In addition, mechanical strength, durability and shrinkage properties of structural grade mortar mixtures produced by partial replacement of cement using HCWA were investigated. A total of six mortar mixtures including control mortar (containing only neat cement as binder) and HCWA mixtures with varying level of cement replacement using HCWA were produced. For the HCWA mortar, HCWA was used at partial cement replacement level of 5%, 10%, 15%, 20% and 25% by total binder weight. Water to binder ratio was held constant at 0.35 for all mortar mixtures. Results indicated that the use of HCWA as partial cement replacement did not have significant adverse effect on workability of fresh mortar. Mortar mix with 15% HCWA exhibited highest compressive strength at the age of 90 days. Enhanced flexure strength was observed for mortar mixture with HCWA content of 5% and 10% at the same age. Incorporation of HCWA at level of cement replacement ranging between 5% and 15% was observed to have beneficial effect on durability properties of mortar namely air permeability and carbonation resistance. Reduction in shrinkage of mortar was observed for mortar mixtures containing up to 10% HCWA.

► Major oxide compound present in HCWA is silica (28%) and calcium oxide (39%).
► Use of HCWA as replacement level up to 25% marginally increased water demand of mortar mix.
► Mortar containing HCWA at replacement level of 15% exhibited optimum mechanical strength.
► Reduction in air permeability was recorded for mortar containing up to 15% HCWA content.
► Inclusion of HCWA at replacement level of 5% enhances resistance of mortar against carbonation.