Acid resistance of sewer pipe concrete
Master Thesis
2007
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University of Cape Town
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A hydrochloric acid solution laboratory test was developed to assess the resistance of concrete used in the manufacture of pipes to sulphuric acid environments encountered in sewers. A hydrochloric acid solution (pH of 1,00) simulates the attack on concrete sewer pipes at the average daily sewage level region and in severely corrosive sulphuric acid environments (pH of less than 1,00) commonly encountered in South African sewers. Calcium sulphate, which precipitates in a sulphuric acid solution and masks further attack, is eliminated simulating the constant dissolution of the precipitate at the average daily sewage level region and loosely attached precipitate in the severely corrosive sewer environments. A straightforward procedure is used to determine the acid resistance of dolomite aggregate concrete used in the manufacture of sewer pipes for exposure to sulphuric acid sewer environments. Acid resistance and neutralisation capacity of the concrete are measured as functions of mass loss and hydrogen ion consumption with time (over a period of approximately 96 hours or less). A procedure to determine the acid resistance of siliceous aggregate concrete requires a longer test period (approximately 200 hours or more). A concrete containing calcium aluminate cement and a synthetic alag™ aggregate made from the calcium aluminate cement clinker gave the best resistance to the hydrochloric acid solution (pH of 1,00) and a severely corrosive biologically-induced sulphuric acid environment (pH of less than 1,00). A similar concrete containing dolomite aggregate gave poorer resistance to the respective solutions. A dolomite aggregate concrete containing calcium aluminate cement gave better resistance in the biologically-induced sulphuric acid environment than a similar concrete containing ordinary portland cement but both concretes were of similar resistance in the hydrochloric acid solution. A poor quality dolomite stone (low strength and high porosity), which fractures during pipe manufacture gave poorer resistance in the hydrochloric solution than a concrete containing a sound dolomite stone but better resistance in the biologically-induced sulphuric acid environment. Concrete containing siliceous aggregate gave the poorest resistance to both the acidic environments. Assessing acid resistance using the hydrochloric acid solution test method illustrates the manner in which the physical and chemical properties influences the attack and dissolution of concrete in an acidic environment, which is crucial in the development of a sewer pipe concrete to resist and neutralise a biologically-induced sulphuric acid sewer environment.
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Fourie, C. 2007. Acid resistance of sewer pipe concrete. University of Cape Town.