An Investigation of the combined use of Palm Kernel Shell Ash and Cow Dung Ash as Partial replacement of Cement in Mortar
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The potential use of both Palm Kernel Shell Ash (PKSA) and Cow Dung Ash (CDA) as alternatives to cement has widely been researched about. However, both materials have shown uncertainty in terms of water required during mixing. Water increases with increase in CDA whereas water decreases with increase in PKSA. This implies that in both cases, the strength of the final mix is compromised as a result of either little or more water. This study therefore used both materials with an aim of bringing a balance in water. The main tests that were conducted included chemical test, standard consistency, water absorption, compressive strength and strength activity index. The chemical results showed that CDA has more silica content than both OPC and PKSA. This implies that a lot of water was required while using CDA only in replacing cement. PKSA showed a high percentage of loss on ignition (L.O.I) which implies carbonation. This clearly shows why standard consistency of PKSA decreases as its percentage increases. However, the lime content of PKSA was 47% less than that of OPC but 79% more than that of CDA, whose percentage was 89% less than that of OPC. This implies that PKSA has more lime than CDA. Results for standard consistency showed that there was a decrease in water required in the mix when the two materials were combined in replacing cement as compared to when CDA only was used in replacing cement. More so, there was an increase in water while using PKSA-CDA as compared to Amartey, (2013) results when PKSA alone was used, whereby increasing the PKSA content led to a subsequent decrease in water. The standard consistency results for all the different ash replacement levels (0%, 10%, 20% and 30%) remained within the required range of 25% to 35% for normal hydraulic cement. The strength of mortar decreased with increase in the percentage of ash. However, the strength increased with age of curing irrespective of the amount of ash used to replace cement. For instance, the average compressive strength at 10% PKSA-CDA cured for 7 days was 6.9N/mm2. This value increased by 40% and 64% at the end of 14 days and 28 days respectively. There was also an observed increase in strength activity index of 76.2%, 82.2% and 85% after 7 days, 14 days and 28 days of curing respectively which was above the minimum required of 75% as per ASTM C 618-05. This clearly signifies that the added pozzolan will react with the cement at later ages of curing to produce the required strength. There was also a decrease in water absorption with increase in age of curing. For instance, the WAC at 10% PKSA-CDA content cured for 7 days was 9.53%. This value decreased by 5% and 6% at the end of 14 days and 28 days respectively. More so, a corresponding increase in water absorption with increased PKSA-CDA content in mortar was also observed. For example, at 7 days of curing, the WAC increased by 6.3%, 17.9% and 28.3% at 10%, 20% and 30% PKSA-CDA content respectively. From the laboratory tests, the standard consistency of cement increased as explained above with increase in PKSA-CDA content but remained within the limits of standard consistency of normal hydraulic cement. This implies that utilizing the two materials together brought a balance in the amount of water required in the mix.