The Effect Of Sulphate, Chloride, Fluoride And Phosphate On Sewer Fabrics With Emphasis On The Concrete Systems
Karuu, Simon PK
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A research programme to investigate the detrimental effects of'sulphate, chloride, fluoride and phosphate of effluent origin on concrete was conducted. The irrq::ortanceof these effects is increasing because most of the sewer fabrics through which both domestic and in- dustrial effluents flow, are made of concrete. Since the effects of these ions lead to corrosion of concrete, one of the objectives was to provide information as to which of the four cement types used, was best for each of the aggressive environments. The research programme included four cement types, namely, Ordinary Portland Cement, Sulphate-Resistant Portland Cement, Moderate Type II Cement and Pozzolanic Cement, whose Compositi®ns are 9iven in table 4-1. Two sizes of cubes, 13.0 mm and 70.7 mm were made out of each cement type. The 70.7 mm cubes were prepared using r\T/c ratio of 1:3 and 13.0 mm cubes were of Hlc of 1:5 bv usin( stabilised cement paste (Sec. 3.5.1. and, 3.5.2. The 13.0 mm cubes were immersed in sulphate. chloride, fluoride and phosphate solutions, of different concentrations, after curing in water for a period of twenty eight days. Compressive strengths were measured for cubes after every 28 days, ie. after hydration in water, 28 days after immersing in ionic solutions, 56 and 84 days respectively. The 70. 7 mm cubes we re submerged in ionic sol u-- tions of the same conc ent.r at.Lons as f or the small - ii - cubes, for a period of six months. Since the solu- tions were acidic, their pH was adjusted weekly to make sure that the pH was constant throughout the peri- od of investigation. At the same time the mass and length changes were taken on a weekly basis. Before each pH adjustment, some solution was sam- pled from the bulk of the solution for ionic analysis. This enabled us to estimate the amount of each of the ions used up for chemical reaction with the cement and hence the effect of the ion as measured by the mass and volume changes. During the period of the investigation both the pH and volume of the solution was kept as constant as possible. The 70.7 mm cubes were crushed after six months for compressive strength measurements. The compressive "." . strengths measurement was another yardstick to measure the effect of the various ions on the cement cubes. Portions of the 70.7 mm crushed cubes were sampled for ionic penetration measurements. It was found that most of the ions were found on the surface and very few at the centre of the cubes. A comparison of mass and volume changes, compresive strengths, ionic analyses and ion penetration measurements, showed that the four rypes of ccrrrrent.s responded differently to the -four types of ions investigated. It was found that under sulphate environment the sul- phate-resistant Portland ce~ent could be used while in - iii - chloride and fluoride environments, type II would be recommended as the best. Pozzolanic cement can be used for environment with low sulphate, interchangeably with type II cement. The phosphate does not have deleterious effect on the four cement types used, and infact it has the advantage of increasing' compressive strength and resistance to corrosion. However, under moving water conditions we could not predict the fate of the crys- tals formed from the phosphate cement reaction.