Strength and water absorption characteristics of bamboo leaf ash blended cement concrete
The study examined the compressive strength, tensile strength and water absorption of bamboo leaf ash (BLA) blended cement concrete with a view to ascertaining its suitability for structural purposes in building construction. It investigated the chemical composition of BLA calcined at different temperatures of 500oC, 600oC, 700oC, 800oC, 900oC and 1000oC with a view to determining the optimum temperature that will yield the most amorphous BLA; it further determined the physical properties of the most amorphous ash. The study also determined the effects of replacing cement with various percentages of the most amorphous BLA on the strength and water absorption characteristics of BLA blended cement concrete. Bamboo leaves collected in Obafemi Awolowo University, Ile-Ife were first dried and burned in an open air and later calcined in a furnace to temperatures of 500oC, 600oC, 700oC, 800oC, 900oC and 1000oC. Two factorial experimental arrangements namely 9 × 6 × 2 × 3 and 9 × 3 were used. Two (2) strength tests namely compressive and tensile strength tests were conducted. For these tests, the cement replacement by BLA was at nine (9) levels (0%, 2%, 4%, 6%, 8%, 10%, 15%, 20% and 25%) and curing age at six(6) levels (7, 14, 28, 60, 90 and 120 days). For water absorption test carried out at the end of 28 days curing age, the cement replacement by BLA was also at nine (9) levels, using three (3) replicates in all the tests, a total of 351 cubes were cast and tested. American method of mix design for 28-day target strength of 25 N/mm2 was adopted and this was taken as control. All specimens were tested using ELE compression testing machine of capacity 2000 kN. Data obtained were analyzed using percentages, mean and analysis of variance (ANOVA). The result revealed that the chemical property of BLA varies with calcination temperatures, BLA ash obtained at calcined temperatures of 500 oC, 600 oC, 700 oC, 800 oC, 900 oC and 1000 oC had a combined percentage acidic content (SiO2 + A12O3 + Fe2O3) of more than 70% (ASTM C618 – 2008).The ash calcined at 10000C had the highest combined acidic content of 90.90% and hence is the most amorphous ash. The compressive strength of tested concrete specimen decreased significantly (p ≤ 0.05, R2 = 0.996) with increase in the BLA content, and BLA content ≤ 8% met the design strength of 25 N/mm2 at 28 days hydration period; while the tensile splitting strength of BLA blended cement concrete specimen decreased significantly (p ≤ 0.05, R2 = 0.998) as BLA replacement of cement increased above 10%. The water absorption generally decrease with increase in the BLA content, and increased with high replacement BLA content greater than or equal to 15%. Optimal BLA substitution with respect to water absorption was 10%. Based on the test results the study concluded that between 8% and 10% BLA content would be adequate as cement substitution for structural concrete works.