The Influence of the Physico-Chemical Properties of Water on the Compressive Strength of Concrete

Abstract

Objective: To determine the influence of the physico-chemical compositions of the different sources of water on the compressive strength of concrete.

Materials and Methods: Seventy-two 150mm x 150mm concrete specimen were cast using six different sources of water and cured using the same water sources by immersion for 7, 14, 21 and 28 days. Each water sample was used to produce 12 specimen, three each for the four different ages. Concrete cubes were weighed using digital weighing machine before testing. Test for compressive strength was done using digital compressive test machine after which the Average Compressive Strength (ACS) of the three samples was determined.

Results: The silt content of the fine aggregates used was within the recommended percentage specified by the IS part II 1963. The results obtained from the slump test classifies the concrete produced for the study as stiff or extremely dry. Though the Amissano and Aquarium water recorded some amount of slump, their slumps could still be described as no-slump and cannot be classified. The figures for the compacting factor test indicated low workability for the concrete produced for the test. It was only the concrete produced from the Kakum river water that had a medium workability. The sea water recorded the highest pH and was followed by the Kakumdo well water. The least pH was recorded by the Amissano well water. The total dissolved solid (TDS) of the Kakumdo well water and the sea water were far higher than the Ghana standards. On the other hand, the figures recorded by the Kakum water for chloride, total hardness, calcium hardness, magnesium hardness and electric conductivity were below what is prescribed by the Ghana Water Company Limited (GWCL). The calcium hardness of the Kakumdo well water was (160mg/l) more than the standard. The Amissano well water specimen recorded the least ACS both at age 7 and 28. This was the lowest among all the samples produced from the various sources of water used for the experiment. The significant strength increase of the Amissano well water samples was recorded at age 14 and 21. The Kakumdo water specimen recorded the highest earliest strength of 20.339KN/mm² and was followed by the Kakum river water. The samples from this source still recorded the highest at age 14 and 21. But at 28, it was overtaken by the Kakum river water samples with the Kakum river samples recording 26.439 KN/mm² as against the 25.484 KN/mm² registered by the Kakumdo well water samples. The Aquarium well water specimen recorded high strength at both age 7 and 28 than the Amissano well water specimen.

Conclusion:

The Aquarium water and Amissano well water were more acidic, meaning their pHs were lower than 6. This had significant influence on the ACS of the samples produced from them. This was evident in the case of the Amissano well water samples which recorded the lowest earliest strength of (12.173N/) among the six sources. The ACS difference recorded between the Aquarium and Amissano well water samples which were all acidic was 5.379KN/mm². This means that higher the acidity of the water use for the production of concrete, the lower the ACS. The Amissano well water was 10 times more acidic than the Aquarium water and 20 times higher than the Kakum river water, pipe borne water and Kakumdo well water but 40 times higher than the sea water.