WATER QUALITY EFFECT ON CONCRETE COMPRESSIVE STRENGTH:
OGUNPA STREAM WATER CASE STUDY
Gbenga Matthew AYININUOLA
Well graded granite coarse aggregate of maximum size 19mm was obtained from a granite quarry located in Ibadan and stockpiled. The fine aggregate, marine deposit was obtained from a stream located in the University of Ibadan, air dried and stockpiled. About four bags of ordinary Portland cement were purchased for the research work. Enough formworks (moulds) made of wood of size 150mm x 150mm x 150mm were prepared with the inside coated with oil.
The concentration of chemicals in the stream water was expected to be higher during dry weather flow than in wet weather. Also, the dry weather flow in Ibadan would reach its peak in January. Consequently, water for the research was collected in the month of January at two designated points in Ogunpa stream. The collection points were (i) Felele (lower Ogunpa) labelled A and (ii) Ogunpa market Oke Bola area (Middle Ogunpa) labelled B. Potable water was also collected at the University of Ibadan Water treatment Plant labelled C for production of controlled concrete cubes. The water samples were stored in three different black kegs. Representative samples from the three black kegs were set aside for chemical analyses.
Two major concrete mix ratios were investigated namely 1:1:2 and 1::3. The batching of materials for concreting was done by weighing. The mixing of concrete constituents (water, cement and aggregate) was manually done on a hard surface to produce homogeneous fresh concrete. Water / cement ratio of 0.6 was adopted throughout the concrete cubes production.
Concrete cubes production was carried out in accordance with BS 1881: Part 108: 1983. Each layer of concrete received 35 strokes of a 25mm square steel prunner. The cubes 288 in number still in moulds were left overnight at room temperature. At the end of this period, the moulds were stripped and the cubes were further cured in bath filled with potable water by completely immersion throughout the cubes compressive strength determination period.
Compressive Strength Test
The cured cube was placed with the cast faces in contact with the platens of the universal testing machine electrically operated. In accordance with BS 1881: Part 116:1983, the load on the cube was applied at constant rate of stress equal to 0.26MPa/sec. The force or load that resulted to failure of each cube was taken and used in calculating the compressive strength. The test was carried out at end of 7th, 14th, 21st, 28th, 56th and 84th day of concreting.
Water Samples Analyses
These representative water samples were taken to laboratory for analyses. The parameters monitored were sodium Na, potassium K, calcium Ca, sulphate SO42-, nitrate NO3-, carbonate CO3-, bicarbonate HCO3-, chloride Cl-, fluoride Fl-, phosphate PO4-, iron Fe, acidity, pH, manganese levels amongst others.
The level of acidity of water sample was obtained by titrating a known quantity of tested sample with barium hydroxide. The presence of nitrate was determined by the addition of phenol-di-sulphonic acid with potassium hydroxide to a known quantity of tested sample. The colour formed was compared with standard colours. The chloride content of each water sample was measured by adding to a known sample volume of 1.5ml of K2CrO4 and titrating the resulting solution with silver nitrate solution. The amount of iron, manganese and other metals in each water sample were determined by adding a colouring agent to the sample and comparing with solution of known amount of metal. Other monitored parameters were determined in line with laid down standard.
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Last updated on Thursday November 29, 2012