Effect of Saw Dust Ash and Eggshell Powder on the Properties of Cement Blends

Abstract

The presence of calcium hydroxide (CH) can pose deteriorating effect on the durability of the cement from the inclusion of Eggshell powder (ESP) into the cement matrix. The incorporation of supplementary cementitious materials (SCM) such as Saw dust ash (SDA) could improve the properties of ESP-cement blends by eliminating some undesirable effects at the later age. This paper tries to explore the effect of possibility of replacing eggshell powder (ESP) cement blend with SDA and cement replacement on the properties such as consistence, setting times, volume expansion and strength gain. Saw dust was calcined at 600°C for 1 hour and sieved with 90µm sieve to obtain SDA. Portland limestone cement CEM II A-L was blended with ESP was replaced with SDA between 0 – 20 wt.% at 5 wt.% intervals and 0 -12.5 wt.% at 2.5 wt.% interval for physical properties and mortar compressive strength using 50 mm cubes with mixing ratio 1:3:5 (water, binder and sand) respectively. The chemical analysis of SDA revealed a high silica content (56.81 wt.%) with SiO₂+Al₂O₃+Fe₂O₃ > 70% (72.2 wt.%), thus classified as Class F pozzolan according to ASTM C618 while ESP indicated a high lime content (48.5 wt.%) and considered a filler. Results indicated an increase in the consistence and setting time of the ternary blends as ESP was replaced with SDA owing to the unburnt carbon present in the SDA as well as clinker diminution. Likewise, an increase in the cement replacement led to an increase in water consistence and setting times. The retarded setting times of SDA-ESP cement blends could be attributed to increased water required due to SDA’s unburnt carbon whereas, ESP-cement blend produced accelerated setting times. A decrease in the volume expansion of the cement blends was observed as ESP was replaced with SDA which could be attributed to the decrease in the available lime while an increase in the volume expansion was also experienced as the cement replacement was increased from 0 – 20 wt.% at various SDA/SDA-ESP ratios from 0 – 0.8 except ratio of 1.0. The mortar compressive strength of cement blended with ESP and SDA experienced an increase as curing age was lengthened despite clinker diminution. This enhanced strength could be linked with SDA’s pozzolanic reactivity, provision of nucleation sites and formation of muscovite resulting in denser CSH with the optimal cement replacement observed at 5 wt.% with SDA/SDA-ESP ratio of 0.2 and 0.4 respectively.