Effect of Heat on some Properties of Normal and Pozzololanic Concrete

Reinforced concrete structures are sometimes subjected to astronomically high temperatures especially when gutted by fire. This research is aimed at finding the effect of heat on normal and pozzolanic concrete. This study includes the investigation of the properties of normal and pozzolanic concrete. Laboratory tests carried out are sieve analysis, slump, specific gravity, water absorption, and compressive strength. The results of sieve analysis reveal that the coefficients of uniformity (Cu) and curvature (Cc) for river sand are 2.25 and 1.00, respectively, while those for granite are 1.64 and 1.14. Slump test results indicate that the values for both normal and pozzolanic concrete vary from 57 to 60 mm, indicating medium workability. Specific gravity test results show values of 2.59 for river sand, 2.12 for rice husk ash, and 2.63 for granite. Water absorption values vary from 1.14 to 5.25% for normal concrete cubes, 1.83 to 5.89% for pozzolanic concrete cubes, and 4.11 to 8.16 % for normal and pozzolanic sandcrete blocks. The compressive strength of normal concrete cubes varies from 17.10 to 25.90 N/mm², while the values for pozzolanic concrete cubes vary from 17.00 to 26.90 N/mm². The compressive strength of Sandcrete blocks have range from 1.74 to 2.39 N/mm². The cubes and blocks produced satisfy the strength minimum requirements stated in Nigerian Industrial and International British Standards. The normal and pozzolanic concrete compressive strength reduced by 21.3 and 27.5 % respectively when subjected to temperature of 500OC at 56 days of curing. Statistical t-test, at 5 % significance level, shows that there is no significant difference between the strength of normal and pozzolanic concrete samples subjected to temperature of 500 OC. The study discovers that temperatures greater than 400 OC can significantly weaken strength of concrete. It is recommended that concrete should not be subjected to temperatures beyond 400 degrees Celsius.