# Water Quality Changes in Cement-Lined Water Pipe Networks
## 1 Introduction  
Ductile iron is an alloy of iron and carbon in which, during solidification of the casting--owing to the addition of small amounts of magnesium or cerium--graphite nodules are produced. This form of graphite improves the mechanical properties of the material when compared to grey cast iron. Ductile iron pipes display higher plasticity, which makes them survive local strain without cracking and produces only local pipe deformations. These pipes are also highly resistant to lateral stress and high internal pressure. For the above reasons, for the past few decades they have been used for building water supply networks, especially in areas with shock risk, that is underneath motorways and streets with heavy traffic, in urbanised areas, in large urban and industrial agglomerations and in areas with complex geology. Ductile iron, just like most metal goods in contact with water, undergoes chemical and biological corrosion [1; 2]. To prevent corrosion, different types of protective coatings are applied to the internal and external surfaces of the pipes. The most commonly used internal linings are made of cement mortar. In the case of the water intended for consumption, linings made of Portland cement or alumina cement are usually employed for contact with water characterized by greater corrosivity(lower pH value, low alkalinity and high CO\({}_{2}\) content). External pipe surfaces are covered with zinc or zinc and aluminium coatings or with black varnish or epoxy plastic [3; 4; 5]. The primary ingredient of the cement is Portland clinker, its content--depending on cement type--ranging from 95% (additive-free Portland cement) to 15% (blast-furnace cement). Portland clinker is the product of heating (sintering) the mixture of limestone and aluminosilicate materials at the temperature of about 1450 \({}^{\circ}\)C. Primary elements contained in the cement include silicon, calcium, aluminium, iron and sulphur, possibly complemented with potassium, titanium, magnesium, manganese and phosphorus. During fuel combustion in rotary furnaces, some amount of heavy metals contained in the fuels are accumulated in the clinker. In recent years, different types of waste materials have been combusted in these furnaces, such as used motor oils or car types, which may have significantly higher heavy metal content than natural raw materials. Elements contained in the primary components of the cement coating released into water in most cases do not affect its health claims. They do, however, have some impact on its organoleptic properties such as taste, odour or turbidity. Leaching of mechanical impurities, such as sand, may lead to corrosion of the fittings and any other components of water supply networks and systems [6; 7; 8]. Examination of damage to new cement coatings caused by water with varied corrosive properties conducted by [PERSON] and [PERSON] [9] showed that low-alkalinity aggressive water may significantly raise pH (from 7 to 12 after one week of testing), alkalinity and calcium content in water contacting cement mortar coatings. Application of a bitumen coating covering the cement layer considerably reduces the solubility of cement components [9]. [PERSON] and [PERSON] [10] listed the following water quality parameters that are recommended to be met in order to prevent dissolution of cement-based materials, including asbestos cement, cement pipes and cement coatings: pH? 7, alkalinity? 15 mg/L in the form of CaCO\({}_{3}\), calcium?10 mg/L, sulphates! 200 mg/L, aggressive CO\({}_{2}\)! 5 mg/L. Trace elements such as chromium, lead, zinc, nickel, arsenic, cadmium, vanadium or copper [11] are released from the cement lining into the water flowing through the pipeline. A study examining the leaching of trace elements from the cement, conducted by [PERSON] et al. [12] also showed that the use of waste materials for clinker firing increases element cement content to a minor extent. Reported relationships were not clear-cut however, as they were influenced by many factors, including method used and solubility testing.