CEMENT LINING Cement-mortar lining for ductile iron pipe and fittings for water service is in accordance with ISO 4179 and AWWA C104. Cement-lined pipe is also furnished for sewage service and a number of other applications. ACIPCO applies a sulphate-resisting cement-mortar lining to ductile iron pipe. The sulphate-resisting cement-mortar lining is a Portland-type cement per ASTM C150 and meets the chemical requirements of BS 4027. The lining is applied by using a high-speed centrifugal process. By using this method, excellent quality control of the cement-mortar lining is maintained. The cement linings ACIPCO produces are dense, smooth, uniform, well bonded to the pipe wall, and offer very little frictional resistance to the flow of water. The pipe is spun at a very high rate accompanied by vibration to produce a dense lining. This high-speed lining brings water and latence to the lining surface. The latence is immediately washed out of the pipe with water. By using this unique process developed by ACIPCO, there is no need to grind linings or use additives to the cement mortar. The immediate result is a smooth, dense, and well-compacted cement-mortar lining. After the application process, the linings are then cured in a controlled environment to prevent too rapid a loss of moisture from the mortar.

Cement-lined ductile iron pipe lies ready for shipment. INT Standard Cement Lining Thickness Standard Cement Lining Thickness Pipe Size (mm) Nominal Thickness (mm) 100-350 3 350-600 5 700-1200 6 1400-1600 9 This table shows recommended thicknesses from ISO 4179 for cement-lined ductile iron pipe. For some service conditions, greater lining thickness may be preferred. Consult ACIPCO for specific details.

HISTORICAL DEVELOPMENT OF CEMENT-MORTAR LININGS The first cast iron (gray iron) water mains were not coated or lined, but were installed in the same condition in which they came from the molds following cleaning. After many years, it became evident that the interior of the pipe might be affected by certain types of water. The use of bituminous coatings was proposed, and most of the gray iron pipe sold for waterworks service after about 1860 was provided with a hot-dip bituminous lining and coating, usually of molten tar pitch. In those systems where the water was relatively hard and slightly alkaline, bituminous linings were generally satisfactory. Where soft or acid waters were encountered, however, problems occurred -- such as the water being red or rusty and/or a gradual reduction of the flow rate through the pipe. Aggressive water penetrated the pinholes in the tar coating and tuberculation ensued. The need for a better pipe lining to combat tuberculation led to experiments and research with cement mortar as a lining material. In 1922, ACIPCO developed the first cement-lined gray iron pipe, which was installed in the water distribution system of Charleston, South Carolina. This pipe was lined by means of a projectile drawn through the pipe. Friction flow tests conducted in 1981 show that this original cement-lined gray iron pipe has retained a Hazen-Williams coefficient ("C" value) of 130. Since 1922, many improvements have been made in the production of cement-lined iron pipe. Cement-mortar-lined pipes are centrifugally lined at the factory to ensure that the best possible quality control is maintained and that a uniform thickness of mortar is distributed throughout the entire length of pipe. Cement linings prevent tuberculation by creating a high pH at the pipe wall, and ultimately by providing a physical barrier to the water. Cement linings are also smooth, which results in a high flow coefficient. Ductile iron pipe installed in water systems today is normally furnished with a cement-mortar lining, unless otherwise specified by the purchaser. For existing unlined gray iron pipe, on-site cleaning and lining may be economically feasible to restore hydraulic capacity. PROPERTIES OF CEMENT LININGS The protective properties of cement linings are due to two properties of cement. The first is the chemically alkaline reaction of the cement, and the second is the gradual reduction in the amount of water in contact with the iron. When a cement-lined pipe is filled with water, water permeates the pores of the lining, thus freeing a considerable amount of calcium hydrate. The calcium hydrate reacts with the calcium bicarbonate in the water to precipitate calcium carbonate, which tends to clog the pores of the mortar and prevent further passage of water. The first water in contact with iron through the lining dissolves some of the iron, but free lime tends to precipitate the iron as iron hydroxide, which also closes the pores of the cement. Sulfates are also precipitated as calcium sulfate. Through these reactions, the lining provides a physical as well as a chemical barrier to the corrosive water. FLEXURAL BEHAVIOR Ring-bending tests have been performed on full-length cement-mortar-lined pipe to check its behavior under backfill loads. These tests revealed that the cement-mortar lining failure and subsequent spalling occurred on the sides of the pipe (at the 3 o'clock and 9 o'clock locations) due to compression with deflections in the range of 6% - 12% of the initial diameter. The thickness design of ductile iron pipe has limited the maximum allowable deflection of the pipe ring section to 4%. This results in a safety factor of at least 1.5, and sometimes as high as 3. RESISTANCE TO SOFT AND ACIDIC WATERS Waters carry varying amounts of different ions resulting from the disassociation of soluble salts found in soils. Waters that have a very low ion content are aggressive to calcium hydroxide contained in hydrated cements due to the waters' low content of carbonates and bicarbonates. Soft waters may also have acidic characteristics due to the presence of free CO2. When cement-mortar linings are subjected to very soft water, calcium hydroxide, CA(OH)2, is leached. The concentration of leachates increases with the aggressiveness of the water and its residual time in the pipe and is inversely proportional to the diameter of the pipe. These waters will also attack calcium silicate hydrates, which form the larger portion of cement hydrates. Although calcium silicate hydrates are almost insoluble, soft waters can progressively hydrolyze them into silica gels, resulting in a soft surface with reduced mechanical strength. Seal-coat will retard this leaching and attack to a great extent; however, as mentioned before, there are very few countries that have sufficiently aggressive waters to necessitate the use of a seal-coat. Also, such aggressive waters may cause toxic metals to leach from piping in customers' homes, making it difficult to pass water quality standards requiring tests at first draw from customers' taps. Therefore, water quality standards requiring better balanced water chemistry may cause these few communities to treat their water, and further diminish the need for seal-coat. Utilities or municipalities who are concerned that their water may be aggressive to cement-mortar linings without a seal-coat are encouraged to follow the procedure detailed in Section II.A., "Use of Seal-Coat," in the foreword to the ANSI/AWWA C104/A21.4 Standard to determine if a cement-mortar lining without seal-coat will impart objectionable hardness or alkalinity to the water. Also, in instances where utilities or municipalities are concerned that water may be aggressive, they may want to consider specifying thicker cement linings. Please contact ACIPCO for details on cement linings thicker than AWWA C104 or ISO 4179. Standard non-seal-coated, cement-mortar-lined ductile iron pipe is generally considered to be suitable for continuous use at pH between 6 and 12. For service with pH outside this range, contact ACIPCO.

FLOW TEST RESULTS ON CEMENT-MORTAR-LINED DUCTILE AND GRAY IRON PIPE Friction head loss or drop in pressure in a pipeline is an everyday concern for the waterworks engineer. Head-loss calculations are based on equations developed by hydraulic engineers after conducting numerous flow tests on actual working mains. Several formulas were developed by Darcy, Chezy, Cutter, Manning, Hazen-Williams, and others. Of these, the formula and tables prepared by Hazen-Williams have proven to be the most popular. A pipe lining, to be satisfactory, must provide a high Hazen-Williams flow coefficient, "C," initially and must have sufficient durability to maintain a high flow coefficient over many years of service. Unless the lining meets the above requirement, its other properties, chemical or physical, are of little significance. Numerous flow tests have been made on operating lines throughout the United States to determine how well cement-mortar linings meet these basic requirements. Tests on both new and old water mains have established the average value of "C" that can be expected of new cement-lined iron pipe, and have also provided a measure of the continued effectiveness of such linings over extended periods of service.

Cement-mortar-lined ductile iron pipe has a Hazen-Williams "C" value of 140, a realistic value that is maintained over time.

FLOW COEFFICIENT OF CEMENT-MORTAR-LINED DUCTILE IRON PIPE For laminar, fully developed flow in a pipe, friction depends only on the Reynolds number (a function of velocity, inside pipe diameter, and the kinematic-viscosity of the fluid being transported). It is interesting to note that the roughness of the pipe wall is not considered. The reason is that, for the parabolic laminar flow velocity profile, very little of the flow comes in contact with the roughness elements of the wall surface; the velocities in the vicinity of the wall surface are quite low. When laminar flow exists, the fluid seems to flow as several layers, one on another. Because of the viscosity of the fluid, a shear stress is created between the layers of the fluid. Energy is lost from the fluid by the action of overcoming the frictional force produced by the shear stress. For turbulent flow of fluids in circular pipes, there is a layer of laminar flow adjacent to the pipe wall called the laminar sublayer. Even in turbulent boundary layers, this sublayer exists where laminar effects predominate. In the case of a pipe, the greater the Reynolds number, the thinner the laminar sublayer is. It has already been noted that the roughness has no effect on the head loss for laminar flow. If the laminar sublayer is thicker than the roughness of the pipe wall, then the flow is hydraulically smooth and the pipe has attained the ultimate in hydraulic efficiency. If this flow were plotted on the Moody diagram, it would coincide with the "smooth pipe" curve. DIPRA and its predecessor, CIPRA, have long advocated a Hazen-Williams "C" value of 140 for use with cement-lined gray and ductile iron pipe. This recommendation of a "C" value of 140 for design purposes is sound. It recognizes that the real world of pipelines is a far cry from the gun-barrel geometry of the laboratory pipeline. Furthermore, DIPRA's continued field testing of operational pipelines has shown a "C" value of 140 to be realistic, and one that is maintained over time -- even when transporting highly aggressive waters. THE EFFECT OF A LARGER INSIDE DIAMETER In all normally specified pipe sizes, cement-mortar-lined ductile iron pipe has an internal diameter that is larger than the nominal diameter, which is larger than the nominal pipe size. For most substitute pipe materials, the inside diameter is equal to -- or in some cases, even less than -- the nominal pipe size. The head loss encountered in a piping system is much more sensitive to available pipe inside diameters than normal flow coefficients. FIELD REPAIR OF DAMAGED CEMENT LININGS Cement lining will withstand normal handling; nevertheless, pipe or fittings may be found at times to have damaged linings which need to be repaired before placing in service. AWWA C104, EN545, and ISO 4179 provide that damaged linings may be repaired, and the following repair procedure is recommended by ACIPCO: Cut out the damaged lining to the metal. Square the edges. Thoroughly wet the cut-out area and adjoining lining. With the damaged area cleaned and the adjoining lining wet, spread the mortar (see recommended mix below) evenly over the area to be patched. After the lining has become firm and adheres well to the surface, finish it with a wet paint brush or similar soft-bristle brush. The repaired lining should be kept moist by placing a wet burlap over the required area of the pipe or fitting for at least 24 hours. RECOMMENDED CEMENT MIX Cement mix by volume: Three parts Portland Cement; Two parts clean sand; necessary water for slump of 125mm to 200mm. The sand should be free of clay and screened. PRECAUTIONS Mortar for lining should not be used after it has been mixed for more than one hour. Too rapid a loss of moisture from fresh linings due to hot weather or high wind will prevent proper cure, resulting in the lining being soft and powdery. To prevent this loss of moisture, (a) do not line hot castings and (b) close the ends of the castings with wet burlap. Fresh linings which become frozen will not be serviceable. Avoid lining in freezing weather.