The first edition of ASTM standard F 2304, Practice for Rehabilitation of Sewers Using Chemical Grouting, has been on the street for just over one year. Recently, someone asked what has been the technical and economic impact of this new standard on the industry. A simple, honest answer is that it is too early to tell and thus there is no apparent business impact to date, but that is not a fair evaluation of the standard nor the impact the standard is expected to have over the next 10 years.

The process of chemical grouting of sewer main and manhole joints and cracks to stop ground-water infiltration and stabilize the bedding soil around these structures is over 40 years old. While it is a small market niche within the larger sewer rehabilitation industry, it is a sound rehabilitation process that, when properly done and used in the right applications, can significantly reduce the ground-water loading on sewage treatment plants; it should not be pushed into the background of sewer rehab technology. Thus the issuing of three ASTM standard practices covering the chemical grouting of sewer mainlines, manholes and laterals should go a long way toward keeping this process in the forefront of sewer rehabilitation.

The Process
Chemical grouting is a soil-sealing process that stops the flow of ground water through the soil exterior to a leaking sewer joint, thus preventing ground-water infiltration into the sewer pipe. When injected, the chemical has the viscosity of water and flows around the internal surface of the sewer joint and out through the pipe joint leak or non-structural crack into the soil surrounding the pipe leak. The chemical fills the void spaces between the soil and bedding particles, then rapidly gels, forming a sealed soil particle mass. The soil’s interstitial areas are blocked and the flow of infiltrating water to the leaking joint or crack is stopped. Grouting does not work in all soil conditions nor can it compensate for shifting ground conditions that may misalign sewers and open pipe joints. It is not a structural repair, but it is a very good and cost-effective process to consider in structurally sound sewer pipes where the original joint materials have failed.

Chemical grouting of sewer lines has a strong contingent of supporters and satisfied customers, yet it has not always had the full support of engineers and utility operators within the greater sewer rehabilitation industry. There were common methods, yet no national standards, for applying or testing the installed product. Further, it is neither economical nor practical to monitor or inspect the work-in-process product, because representative samples of sealed soil around the sewer lines are not obtainable. As in many industries, a small percentage of applicator-contractors used the absence of standards and methods as an opportunity to do less than what was specified and required.

Thus, all too often, grouting was referred to as a “temporary fix” using a “witch’s brew” of chemicals applied using a “black art.” Without flow monitoring equipment on grouted line segments recording the before- and after-effect of grouting and correlating the flow data with changing ground water conditions, it is difficult to monitor and document the short- and long-term performance of chemically grouted sewer joints and thus it is seldom done.

Background to the Standard
Passage of the first Clean Water Act by the U.S. Congress and various state water resource legislation in the 1970s mandated “clean water” outfalls from sewage treatment plants and focused attention on the proper design and operation of sewage treatment plants. Rapidly it became apparent that treatment plants could not economically be built large enough to handle the storm and seasonal ground-water infiltration loads that were entering the nation’s sewage collection systems. Chemical grouting became the first line of defense for reducing ground-water infiltration into the sewer collection systems.

During the 1970s and ’80s, the majority of funding went for treatment plant upgrade and construction. It was not until the ’90s that a significant portion of state and federal funding began shifting to sewer collection system upgrades through new construction and rehabilitation of existing mains and manholes. The entry of new sewer relining processes, strong marketing of pipe relining and rehabilitation, and the cost reduction of relining brought on by competition further cast doubt as to the suitability of chemical grouting even as a means of sewer rehabilitation of structurally sound pipe in light of the decreasing pipe relining prices.

The response from the sewer chemical grouting industry was the formation of a trade marketing association with a small, aggressive marketing and promotional campaign directed at the municipal and consulting engineers responsible for sewer line rehabilitation. This marketing group, the North American Grout Marketing Association, was effective in promoting interest in the sewer grouting process, but soon found it was missing a few key technical elements in its presentation. The lack of a nationally recognized specification or standard made it difficult to promote the grout process to new customers and engineers.

At this time the National Association of Sewer Service Companies, a trade association consisting of sewer contractors, and equipment and process/chemical suppliers, were publishing the only available independent grouting specification. The NASSCO document was a blend of contract and performance language contained in their specification guidelines booklet. This type of specification and the lack of technical performance data did not meet the needs of the professional engineering community, which was advising and managing the municipal utilities’ sewer rehabilitation programs. The grouting process’ main competitors, major sewer pipe relining companies, had developed ASTM pipe standards as their technical foundation. It was apparent to a group of concerned NASSCO members who had a strong interest and commitment to the grouting process, that the sewer grouting industry had to develop certain standards and technical information if sewer line grouting was to grow and survive as a viable technique.

Chemical grouting of selected sewer line joints continues to be a very successful way of reducing ground-water infiltration in many sewer collection systems. Engineers and utilities that use the process have for the most part been very satisfied, but there were examples (as in all technologies and workmanship) where the end result did not meet expectations. Where the process was successful in reducing infiltration and sewage plant loading, the users learned to accept it with minimal technical foundation and standards.

Chemical grout application is very dependent upon the skill, knowledge and integrity of the firm and operator doing the grout work. It is a process that takes place underground, out of sight, and can only be witnessed in a secondary fashion through the use of sewer television inspection equipment used to confirm visual evidence of infiltration and test pressure transmitter readings that provide pre- and post-injection pressure test data of the leaking joint. Many engineering firms have questioned the tradeoff between the lower first cost of grouting and the perceived performance and longevity difference between the sewer grouting process with no national standard and the relining processes that were all supported by ASTM material standards. In application, these are really two complementary sewer rehabilitation processes. Grouting stops a substantial portion of ground- water infiltration into sewer lines that are structurally sound and relined pipe lateral cutouts. Relining builds a structural replacement pipe within the original failed pipe. When the relined pipe has holes cut into the new liner for house lateral connections, then the new liner does a questionable job of reducing infiltration. In areas with high infiltration, chemical grout is often used to seal the infiltration coming from the annulus space between the old and new pipes draining into the sewer line through the often numerous lateral connection cutouts.

A New Standard
By the late 1990s, NAGMA re-formed as the International Chemical Grout Association within NASSCO and a task force of those NASSCO/ICGA members concerned with grouting met and agreed upon goals that would provide specifications for grout application, technical evidence of grout’s longevity and promotion of safe practices for sewer line chemical grouting. NASSCO/ ICGA approached ASTM International, asking how the grouting process could be structured as a national standard.

By 1999, ASTM had introduced the NASSCO grout task force to ASTM Committee F36 on Technology and Underground Utilities and helped the task force understand the ASTM standards development process. In that same year, Subcommittee F36.20 on Rehabilitation of Sewers Using Chemical Grouting Techniques was formed. This subcommittee completed one standard
in 2003, the aforementioned F 2304, with one Practice for Sealing Sewer Manholes Using Chemical Grouting and another Practice for Sealing Lateral Connections and Lines from the Mainline Sewer System by the Lateral Packer Method Using Chemical Grouting due out soon. All three of these applications are used in conjunction with the relining processes in area of high ground-water infiltration.

Conclusion
The success of chemical grouting is dependent upon the operator in many ways. The operator has to mix and test two chemical solutions. He has to follow the manufacturer’s safety and mixing instructions, that then perform an above-ground test confirming the mixed chemicals are gelling correctly within a fixed time. The chemical gel time can change, extending with ground water dilution and shortening with increased temperature; chemical adjustments are needed to correct the gel time. During chemical injection the operator monitors the void pressure transducer readings, correlating void pressure increases with the volume of chemical injected to sense the point at which grouting should be complete. Based on experience, interpreting the void pressure readings and watching pumped chemical volumes, the operator determines what type of joint opening and soil conditions are being encountered and when chemical injection and sealing is complete.

One can easily understand why engineers do not readily accept a process such as this. The inability to monitor injection conditions, obtain samples of grouted soil, confirm correct installation, test compliance with a material standard and then monitor sealed joint conditions over time make the whole process very difficult to accept. But it works and thus acceptable guidelines are needed. Many in the grouting industry now believe that the advent of the new ASTM standards in this area will provide guidelines for both those who perform grouting work and a new level of acceptability among those for whom we do this work. •