PURCHASE AND ACCEPTANCE OF PRECAST STEEL REINFORCED CONCRETE PIPE UTILISING THE AUSTRALIAN STANDARD, AS

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1 IPWEA NSW Division Annual Conference 2006 PURCHASE AND ACCEPTANCE OF PRECAST STEEL REINFORCED CONCRETE PIPE UTILISING THE AUSTRALIAN STANDARD, AS Stephen Manwarring Bankstown City Council, New South Wales, Australia Paper Summary Precast concrete pipe has been made in Australia for one hundred years. The current product Standard, AS , provides useful information to purchasers and asset owners on buying and inspecting manufactured concrete pipe that can be used in accepting or rejecting a pipe up to the point of pipe installation. When installed and backfilled, other methods may be invoked to determine the acceptance, or otherwise, of the pipeline. This paper presents a brief history of precast concrete pipe in Australia. Testing requirements of AS 4058 are discussed and information on what should be given to the manufacturer outlined. Discussion is offered on what is acceptable in a pipe delivered to site. Reference to the Draft for Public Comment, DR 04237CP, released by Standards Australia in 2004 as part of the revision process for both AS 4058 and NZS 3107 will also be presented. It is emphasized that at this time the Draft is not an Australian Standard but a document for public comment. Introduction Public Works professionals are routinely called upon to participate in the construction and renewal of drainage infrastructure. In doing so, concrete pipes for stormwater conveyance are incorporated into design drawings for construction by day-labour staff, into specifications for the calling of tenders or for development projects being constructed by others. The professional requires a comprehensive understanding of concrete pipe to get on with the job in either direct purchase or inspecting concrete pipe to a specification during installation. In this paper, guidelines for purchasing will be discussed together with inspection criteria available in the product Standard for precast concrete pipe, AS This paper will be restricted to rubber-ring jointed, steel reinforced concrete pipe intended for stormwater drainage applications. It is not intended to elaborate upon fibre reinforced concrete pipe and flexible pipe and which may also be utilised in these applications. How It Began It is likely that the first pipe-making machine came to Australia via Europe. In 1896 a Civil Engineer, W. Baltzer, brought a Monier machine to Sydney and by 1898 Monier pipes for sewerage and stormwater drainage were manufactured in large quantities in Sydney (Dawson, 1989). A significant development occurred around this time in the world with the introduction of steel reinforcement into concrete pipe. It is known steel reinforcement was used in France in 1896 and the concept taken to North America in 1905 and it is probable its introduction to Australia also occurred around this time. By 1909, Walter Hume had derived a centrifugal spinning technique for manufacturing concrete pipes, which he patented the following year, and in 1911 began production of concrete pipe (Humes, 2004). Humespun concrete pipe is still made throughout Australia by this high-speed spinning process and for larger pipe sizes by vertical casting using high frequency vibration. Walter Robertson and Heaton Clark (today s Rocla Pipeline Products) had developed the first roller-suspension pipemaking machine by the Second World War. This machine, nicknamed the "Wild machine" in honour of the company s long-time employee Wally Wild, produced concrete pipes by suspending a steel mould containing Page 1

2 a reinforcement cage on a horizontal roller. The mould is rotated and concrete is fed and compacted between the mould and roller during spinning. Other companies now also manufacture steel reinforced concrete pipe in Australia. Reinforced Concrete Pipes (RCP) was established in 1994 beginning commercial production in 1998 and now operates plants in Perth, Melbourne and Brisbane. The pipe is manufactured by vertical casting. A reinforcing cage is placed in a steel mould and the pipe is cast from the socket throughout the pipe barrel to the spigot. A bidirectional roller assembly rotates inside and compacts the concrete against the steel mould as the concrete pipe is formed. Hunter Concrete Pipe (HCP) located near Maitland north of Sydney also operates this bidirectional ( Bi-Di ) pipe making technology. James Hardie produces concrete pipe but uses reinforcing fibres in lieu of steel reinforcement in the manufacturing process. The first experimental production of an autoclaved cellulose fibre concrete pipe was undertaken in 1980 and commercial production began in July 1984 (Seach, 1988). Cellulose fibre-reinforced concrete pipe is widely distributed in Australia and in the south-western United States. This product is not manufactured to AS 4058 but to AS The Australian Standard, AS 4058 The first Standards Association publication for concrete pre-cast drainage pipes was released in 1937 as Technical Standard A35. The Standard covered non-reinforced and reinforced concrete pipes intended to be used for the conveyance of sewage, industrial waste and stormwater not under internal pressure. A second edition was published in 1957 and introduced two more load classes of pipe ( Y, in AS4058 Class 3 and Z, Class 4 ) and the method for determining water absorption was changed. In the late sixties, Australian Standards underwent metrification in line with the government requirements of the day. AS 1342, Precast Concrete Drainage Pipes replaced A35 and also introduced test-crack measuring gauge widths for differing cover to reinforcement requirements. AS 4058 released in 1992 was prepared to amalgamate AS 1342 covering pipes conveying flows not under pressure with pressure pipes manufactured to AS Definition of terms was clarified, the methods of measuring geometric properties of the pipes and the criteria for acceptance and rejection of defects was further refined. Load classification was rationalized and extended beyond Load Class 4. Requirements for sampling, testing and compliance were presented in detail and expanded. This sampling and testing regime was designed to apply to all existing manufacturing processes at that time. AS4058 is now applied to the more recent manufacturing processes in commercial production in Australia post Purchasing And Specifying Concrete Pipe AS 4058 in Appendix B contains advice on information to be supplied by the purchaser to the manufacturer. It is important to note that the place of acceptance contained in this non-mandatory appendix is the place of manufacture, unless otherwise stated by the purchaser. At the time of placing an order and in the specification the place of acceptance of concrete pipe (for example, at delivery on site) should be clearly identified to avoid any later dispute between parties. The intended application should be made clear by the purchaser together with the pipe size class (nominal diameter), joint type (rather ambiguously nomenclatured in DR 04237CP) and required load class. Nonstandard pipe length requirements (that is, other than an effective length of 2.44 m) should be provided to the manufacturer. (DR 04237CP conversely requires inclusion of a specified length(s).) Unless the purchaser specifies the required minimum clear cover to reinforcement, the delivered pipe will have concrete cover to reinforcement appropriate for a normal environment (which is also the default condition in the Public Comment Draft). If the concrete pipe is intended for a more aggressive environment, such as Page 2

3 installation in some acid-sulfate soils or under tidal influence, a greater cover may need to be identified by the purchaser/specifier or other protective measures nominated to compliment the intended in-service life performance. It is important that the purchaser/specifier clearly identifies what cover is required or seeks the manufacturer s advice of what cover to steel reinforcement would be appropriate for other than a normal condition. The water absorption test in the Australian Standard is a durability performance parameter to ensure the pipe s hardened concrete matrix is dense and protective of the reinforcing steel. If a special cement type is required, the purchaser should specify the type of cement to the manufacturer. AS 4058 does not mandate a minimum concrete strength grade or minimum cement content. (However, DR 04237CP does provide informative advice on minimum binder content in Draft Clause ) For drainage pipes, the maximum water absorption allowed by AS 4058 is 8.0% where no other requirement is identified by the purchaser or included in the specification; and, 6.5% where specified by the purchaser in a marine or other aggressive environment. DR 04237CP limits water absorption to 6.0% irrespective of the intended installation environment. This limit is consistent with percentages published by industry. For example, roller suspended concrete pipe has been promoted in a range of 2.8% to 5.5% (Rocla, 1994) and vertically roller compacted pipe up to 6% (RCP, 2006). It is important to confirm with the manufacturer the maximum water absorption (and preferably no greater than 6%) guaranteed in the delivered product to ensure long-term durability will be enhanced. Although concrete pipe is routinely load tested to a crack load as part of the normal production regime, AS 4058 does not mandate any other routine testing during manufacture for stormwater applications. proven design) to be tested for loading, water absorption, cover, dimensional accuracy and joint assembly. Subsequent to the design complying with the specified quality parameters, routine testing of pipe only requires crack load testing (typically, being a loading of two-thirds of the required ultimate load). Table 1 summarises this testing regime which is unchanged in DR 04237CP. AS Test TYPE Testing ROUTINE Testing Crack Load, T c Required Required Ultimate Load Required Only (Typically, 1.5 x T c ) Hydrostatic Pressure (90 kpa) Only Only Water Absorption Required Only Cover To Steel Required Only Reinforcement Dimensional Accuracy Required Only Joint Assembly Required Only Table 1 Summary Of Test Requirements Public Works professionals should not overlook the importance of testing. The evidencing of testing as a requirement in a specification and reinforced at the time of purchase for water absorption and cover (for durability) and dimensional accuracy and joint assembly (for installation) is recommended. Concrete pipe product presented, as being generally in accordance with AS , should be closely examined to identify what is not in accordance with this Standard before purchase. Testing Concrete Pipe AS 4058 requires new pipe designs (and where there is a significant departure from a Inspecting Concrete Pipe On Site Clause of AS 4058 classifies defect types in steel reinforced concrete pipe by Page 3

4 category, called Types. Visible inclusion of foreign matter (particularly organic in origin) in the pipe wall with a surface area of 0.1% or greater in the pipe, either inside or outside, is not acceptable and the concrete pipe should be rejected on site and returned. Where the defect is located in the jointing surface or where in the wall is less than this percentage and, no individual inclusion exceeds 400mm 2 in area, the pipe may be repaired and thence installed. For dents, bulges, chips and spalls, a drainage pipe is acceptable where the defect s depth or height is no more than onequarter of the concrete cover to steel reinforcement and does not extend in any direction more than 50mm. Surface blow holes ("air pockets") of 10mm diameter and less than half this diameter in depth are also acceptable. Where such defects extend beyond these limits, the defect requires repair. Surface craze cracks and clearly visible cracks in the pipe wall that do not extend through the wall and whose width at a depth of 3 mm does not exceed 0.1 mm at any six adjacent points over a length of 300mm (for a pipe where the cover to reinforcement is no greater than 10mm or a pipe subject to a marine environment) is also acceptable. (As the cover increases, the acceptable crack width can increase up to a maximum of 0.20 mm for a normal environment application.) Where wider cracks have been repaired, the pipe may be approved for installation. However, for cracks that have extended through the pipe wall or are greater than the crack width limits for load testing, not only must the crack be repaired but it must also be established that the pipes have passed load testing. A brief overview only of the requirements presented in Clause for the pipe barrel and for up to 10mm cover is provided in Table 2. (Joint surface requirements and concrete pipes with greater cover are also contained in Clause but are not presented in the following Table.) These acceptability criteria are similar to DR 04237CP. Defect Type Description 1 Crack not extending through wall and no greater than 0.1mm in width. 2 Crack not extending through wall and no greater than 0.15mm. 3 Crack extending through wall or of a width greater than 0.15mm. 4 Dent, bulge, chip or spall of depth or height no more than 1/4 of concrete cover and extends in any direction up to 50mm. Surface blow holes of 10mm diameter and up to 4mm in depth. 5 & 6 Dent, bulge, chip, spall or boney patch extending in any direction up to 50mm. Surface blow holes > 10mm diameter. 7 Inclusion Of foreign matter of 0.1% and greater and any area >400 mm 2. Table 2 Defect ability (Pipe Wall) Action If Repaired If Repaired & Load Tests Passed If Repaired Not abl e The superceded Standard A35 (Clause 10) did not permit coating with a cement wash without the prior agreement of the purchaser. This requirement was also included in AS 1342 (Clause 2.5.1). However, AS 4058 now qualifies finishing by coating with cement wash is that such a practice may not occur in the pipe barrel until after the pipe has been tested. (Clause AS4058, Clause ). It is therefore important that the purchaser/specifier clarifies with the manufacturer what manner of finishing and what repair materials are to be used. This advice is given in the purchasing guidelines of AS 4058 and reinforced in Note 1 to Clause Where no requirement is stipulated, normal practice adopted by the pipe manufacturer will apply. Page 4

5 Cracking In Installed And Backfilled Concrete Pipe In 1998, Brisbane City Council reported on a number of audits conducted on pipe assets in the nineties. The objective of the audits was to measure the standard of construction, establish the likely impact on maintenance costs and the community of substandard assets and determine the accuracy of asconstructed drawings. (Lee Et Al, 1998) A total of twenty-five subdivisions were audited of which seven were internally inspected. In 1997 five subdivisions were audited and each included the internal inspection of stormwater pipes. Table 3 presents a summary by pipe size of both these audits. Lee concluded that there was a proven link between the premature cracking of small diameter concrete pipes and loading during construction and that the design and selection of pipe class must consider construction loading. These authors surmised that the only way to confidently certify the condition of small diameter pipe after construction is by video inspection. AS 4058 does not provide guidance on acceptable crack widths for concrete pipe in a buried installation where the pipe is under load. However, providing the flexural crack is not excessively wide (no more than 0.5mm) and does not extend longitudinally along the pipe length for any sizable distance, it is unlikely such cracking will significantly impair service life, particularly in a normal installation environment. Cctv inspections are important and do evidence the orientation and incidence of cracking. This imaging is less effective in assessing crack width and depth. Wide longitudinal cracks along the inside top and bottom of a pipe can indicate an overloading condition. This condition may result from construction activity where the design pipe strength as reflected in its load class has been exceeded. Such extension can result from compaction equipment selection or from inadequate cover over the pipe for the construction traffic being used on the site. Although structural failure is likely to be the exception rather than the norm, the pipeline may no longer be watertight and groundwater can enter carrying fines and become a source of intrusion. Fines loss over a pipeline can also cause localized surface subsidence. (Young & Trott, 1989). Pipe Diameter Audit Length Surveyed Sections Of Observed Cracking (m) (mm) (m) Table 3 Internal Inspection Of Stormwater Pipes (Brisbane City 1994/1995 & 1997 Audits) The Concrete Pipe Association of Australasia has prepared load charts of common compaction loading (such as rammers and vibrating drum rollers to compaction wheels) and advice on the appropriate pipe load class to control cracking (CPAA, 1999). These charts can be of assistance to both designers and construction personnel during installation of concrete pipes. Circumferential cracking can result from uneven bedding or variable settlement along the trench. A concentrated surcharge load over a pipe where cover is low can also generate such cracking. At worst, these defects can be an obstacle to flow and a point of intrusion of tree roots. Page 5

6 Pipes built into a pit can generate circumferential cracking providing a makeshift hinge to accommodate differential settlement between the installed pit and the pipeline. Built-in pipes should therefore be no longer than twice the nominal diameter before jointing with a standard length pipe. (Young & Trott, 1989.) Conclusion AS 4058 can be a useful tool for Public Works professionals in getting on with the job. This Standard provides guidance on information to be supplied between the purchaser and the manufacturer and also on what are acceptable defects in concrete pipe. Beyond this point, closed circuit television can be used to inspect the finished product. However, the interpretation of these images can form an area of dispute. It is therefore more appropriate to avoid such disputes by ensuring the design load class is appropriate for construction and that the pipes are installed under supervision in accordance with best practice. References American Concrete Pipe Association. (1998). Concrete Pipe Handbook, 5th Printing, ACPA, Concrete Pipe Association Of Australasia. (1999). The Installation Of Steel Reinforced Concrete Pipes Minimum Pipe Cover Required For Various Compactors, CPAA Drawing 2. Concrete Pipe Association Of Australasia. (2005). Cracking In Steel Reinforced Concrete Pipe, Fact Sheet, FS4/05. Dawson, B. (1989). Strength In Concrete, 1st ed., Dawson, ACT. Humes TM Construction News. (2004). Humes Heritage Logo History, July ed., Issue 14. Lee, D., Hansen, B. and Demartini, C. (1998). The Cracking Of Stormwater Pipes And The Significance Of Construction Loads, Institute Of Municipal Engineers Australia (Queensland), Conference Papers. Reinforced Concrete Pipes Pty Ltd. Durability Testing, 17 February Rocla. (1994). Roller Suspension Concrete Pipe, Extraordinary Concrete Pipe, Brochure Amatek Ltd. Seach, B. G. (1988) "The Development Of FRC Pipes", Proceedings Of Fourteenth ARRB Conference - Part 7, Standards Australia. (2004). Precast Concrete Pipes (Pressure And Non- Pressure), Draft For Public Comment DR 04237CP. Young, O.C. and Trott, J.J. (1989). Buried Rigid Pipes - Structural Design Of Pipelines, 1 st ed., Elsevier Applied Science Publishers, London & New York, 121, Page 6

7 Author Biography Stephen Manwarring leads a team at Bankstown City Council responsible for preparing and administrating capital works civil contracts. He is a graduate in Civil Engineering from the University of New South Wales and a Member of Standards Australia Committees WS/08 for fibre reinforced concrete pipes and WS/28 for flexible pipelines. He is a past Member of Standards Committee WS/06 responsible for the revision of AS/NZS He has been employed in both the public and private industry since graduation in 1977 and is a Councillor for the National Australian Certification Authority For Reinforcing Steel (ACRS). Postal Address: Bankstown City Council, P.O. Box 8, Bankstown NSW Stephen.manwarring@bankstown.nsw.gov.au Website: Page 7