Determination of Tolerance Limit of Silt and Clay Impurities in the Strength of Concrete made with Abuja Sand

This research work is aimed at establishing the percentage at which silt and clay content in river bed
fine sands sourced in Abuja and environ are not suitable for concrete work. Fine aggregate samples were
collected from five major locations within Abuja and environ namely: Bwari, Mararaba, Kuje, Jere and
Gwagwalada. The percentage silt and clay content present in each sample was examined to be 9.76%, 9.68%,
5.7%, 2.99% and 15.38%, and named as samples 1, 2, 3, 4 and 5. Afterwards, sixty (60) concrete cube samples
of 150 x 150 x 150 mm dimension were cast using a 1: 2: 4 mix ratio and water - cement ratio of 0.5 and cured
for 7, 14, 21 and 28 days prior to crushing. In addition, the average compressive strength results of the samples
were established. Thereafter, to determine the percentage of silt and clay content not fit for concrete works,
sample five (5) was thoroughly washed and dried to zero moisture content and thereafter, eighty-four (84)
standard concrete cubes of 150 x 150 x 150 mm dimension were cast using a 1: 2: 4 mix ratio and water -
cement ratio of 0.5. The washed sand was partially replaced with processed silt and clay at 0%, 2%, 4%, 6%,
8%, 10% and 12% and crushed at 7, 14, 21 and 28 days. From the study, the percentage at which silt and clay
content in river bed fine sands is not fit for engineering uses particularly concrete was established to be 7%.
Keywords - Tolerance limit, silt and clay, fine aggregate, concrete strength, compressive strength.