WATER QUALITY EFFECT ON CONCRETE COMPRESSIVE STRENGTH:
OGUNPA STREAM WATER CASE STUDY
Gbenga Matthew AYININUOLA
RESULTS AND DISCUSSIONS
The chemical constituents of the three water samples were determined immediately the cubes were cast. The results of the chemical properties of the water samples are displayed in Table 1. At the end of 7th, 14th, 21st, 28th, 56th and 84th days, eights cubes from each mix type and water sample were taking for compressive strength determination. Altogether, 48 cubes were crushed at every test day. At the end of 84th day, 288 cubes had been crushed. The results of the compressive strength of concrete cubes were displayed in Table 2.
Table 1: Water test results
Except pH and level of acidity, the unit is mg/l
Table 2 The cubes compressive strength
MO = Middle Ogunpa; LO = Lower Ogunpa
The results got from the chemical analyses showed that the three water samples have different concentrations of chemical composition. The concentrations of chemicals in water sample at Lower Ogunpa stream were higher than that of the middle one as a result of discharging of more wastewater into the stream at this section. Moreover, the chemical properties of potable water from the University of Ibadan Water Treatment Plant were lower than that of water from Ogunpa stream. The concentration of Na and K of Ogunpa stream almost doubled that of potable water. The level of acidity, pH, CO3- and HCO3- of water at Lower Ogunpa were higher than that of Middle one due to presence of more impurities as water moves downstream.
The compressive strength of cubes produced with potable water increased with ages as shown in Figures 1 and 2. Pre-28 days, the increment in strength was very rapid but beyond, its rate of strength development reduces as expected for a normal concrete. On the other hand, the strength development of cubes cast with Ogunpa stream water was not as that rapid on comparing with those of potable water as shown in Figures 1 and 2. The cubes started to loose compressive strength after 14th day of concreting. The highest compressive strength for concrete cubes of mix ratio 1:1:2 cast with water got from Middle Ogunpa was 27.2N/mm2 whilst that of Lower Ogunpa was 26.1N/mm2.
Referring to Table 2 for concrete mix ratio of 1:1:2, the expected compressive strength should be 40N/mm2 or thereabout. Only cubes cast with potable water have mean compressive strength of 43.2N/mm2. On the other hand, the 28th day mean compressive strengths of concrete cubes of mix ratio 1:1.5:3 cast with water from Middle and Lower Ogunpa were 20.6 and 19.2N/mm2 respectively. For a normal concrete cube of mix ratio 1:1.5:3, the expected 28th day compressive strength should be 30N/mm2 or thereabout. This shows clearly that the water from Ogunpa stream contains chemicals that retard development of concrete compressive strength. On comparing with chemical constituents of portable water, these can be attributed to the presence of very high concentrations of Na, K, SO42-, Cl-, CO3-, HCO3- and PO4- . In addition, the level of acidity of Ogunpa stream water was higher than that of potable water. Moreover, the Ogunpa stream water has high pH value prohibiting its usefulness in concrete production. The compressive strength values of cubes cast with water from Lower Ogunpa stream were lower than that of Middle Ogunpa. This can traced to presence of higher concentrations of K, Na, SO42-, CO3- and Cl- in water at Lower Ogunpa stream section.
Figure 1: Compressive strength of concrete cubes with mix 1:1:2
Figure 2: Compressive strength of concrete cubes with mix 1:1.5:3
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Last updated on Thursday November 29, 2012