Grantee Research Project Results
Final Report: Development of New Wastewater Infrastructure Systems With Enhanced Durability and Structural Efficiency
EPA Contract Number: 68D03065Title: Development of New Wastewater Infrastructure Systems With Enhanced Durability and Structural Efficiency
Investigators: Chowdhury, Habibur
Small Business: Technova Corporation
EPA Contact: Richards, April
Phase: II
Project Period: October 1, 2003 through December 31, 2004
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2003) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Watersheds , SBIR - Water and Wastewater
Description:
The goal of this research project was to develop strategies to enhance the resistance of concrete-based sanitary sewer infrastructures to microbial-induced corrosion. A host of physical, chemical, microbial, and structural factors govern the resistance of concrete-based sanitary sewer infrastructures to microbial-induced corrosion. Control of these factors provides complementary means of mitigating microbial-induced corrosion of reinforced concrete pipes and other elements of the concrete-based infrastructures in sanitary sewer systems. Technova Corporation screened various strategies to assess their effectiveness in controlling microbial-induced corrosion of concrete through physical, chemical, microbial, and structural effects. The results were used to select two categories of mix formulations for further laboratory and field studies. Accelerated microbial attack tests in the laboratory as well as water sorption, acid resistance, mechanical performance, and abrasion resistance, together with field evaluation of resistance to microbial-induced corrosion, provided the basis for devising modified concrete formulations with substantially enhanced resistance to microbial-induced corrosion. Modified structural designs with synthetic fibers complementing conventional steel reinforcement were developed that increase the protective concrete cover thickness and thus the service life of concrete pipes in sanitary sewer environments.
Summary/Accomplishments (Outputs/Outcomes):
Introduction of polymer emulsion, hydrophobic admixture, fine pozzolan, and antimicrobial additives emerged, based on experimental screening of various strategies, as a viable means of enhancing concrete resistance to moisture penetration, acid attack, and microbial growth. The following strategies were selected based on preliminary test results for further investigation: (1) hydrophobic additives reducing the moisture affinity of capillary pore surfaces in concrete, thereby mitigating moisture penetration and acid attack and potentially lowering microbial activity within concrete; (2) polymer emulsions to line capillary pore surfaces and partially block the capillary pore system, thereby lowering moisture penetration, acid attack, and microbial activity within concrete; and (3) fine pozzolans for refinement of concrete chemistry and capillary pore size distribution and connectivity to enhance the resistance of concrete to moisture sorption and acid attack. To explore the potential for enhancement of service life through refinement of the structural design, a competitive performance and cost analysis was conducted using different fiber types (polyvinyl alcohol [PVA], alkali resistant glass, aramid, and carbon), based on which PVA fibers of high elastic modulus and desirable bonding to concrete were chosen for use in the structural design of concrete pipes. Industrial-scale production and testing of concrete pipes suggested that alternative pipe designs with increased protective cover thickness of concrete over steel (achieved through reduction of steel reinforcement with the introduction of 0.8 percent of PVA fibers) yielded desirable cracking resistance in three-edge bearing tests, but fell somewhat short in terms of ultimate load-bearing capacity. Direct joint shear tests also demonstrated the potential of fiber reinforcement to eliminate the need for enlarged joint area (commonly used with smaller pipes), thus enabling streamlined shipment and installation of concrete pipes.
Accelerated laboratory tests indicated that concrete formulations modified with hydrophobic and fine pozzolanic additives provided particularly high resistance to moisture sorption. Concrete formulations modified with combinations of hydrophobic/fine pozzolanic additives and polymer emulsion/fine pozzolanic additives provided significant gains in terms of acid resistance.
Accelerated microbial attack tests were developed for comparative evaluation of different strategies toward enhancement of concrete resistance to microbial-induced corrosion under controlled laboratory conditions. Concrete specimens exposed to accelerated microbial tests exhibited a substantial drop in surface pH after about 1 year of exposure. The rate of microbial attack, however, was relatively low to distinguish between different concrete formulations based on their resistance to deterioration under microbial attack. Hence, concrete specimens were exposed to actual sanitary sewer environments in mid-Michigan and southern California. The damage caused by microbial-induced corrosion to concrete specimens with unmodified formulations was noticeable after about 10 months of exposure, and the extent of damage varied substantially between different concrete formulations. Exposure to selected sewer environments thus provides a viable basis to distinguish between different concrete formulations, over time periods of about 1 year, in terms of their resistance to microbial-induced corrosion. Performance of different concrete formulations in actual sanitary sewer environments, based on visual observations and measurements of weight loss and flexural strength, proved to be inconsistent with laboratory assessments of such formulations based on their resistance to acid attack and moisture sorption.
Hydrophobic admixtures (together with fine pozzolan), which offered excellent performance in laboratory acid resistance and water sorption tests, lowered the resistance of concrete to microbial-induced corrosion in the sanitary sewer environment. Highly desirable results were obtained for concrete formulations modified with polymer emulsion and fine pozzolan. This particular formulation offers the promise of substantially enhancing the resistance of concrete to microbial-induced corrosion in the sanitary sewer environments. This strategy, after optimization, is anticipated to increase the initial production cost of concrete pipes, depending on the specific dosages of admixtures for optimum performance, by 20-30 percent, which is commercially viable. The substantial benefits in terms of life-cycle economy would more than compensate for this initial cost increase.
A comprehensive industrial-scale production and test program was implemented to verify the constructability and structural performance of different concrete pipe designs incorporating mineral, chemical, polymeric, and fibrous admixtures for enhanced resistance to microbial-induced corrosion. The production effort in Northern Concrete Pipe, Inc. (Charlotte, MI), confirmed that concrete formulations incorporating PVA fibers as well as mineral and chemical admixtures are compatible with conventional pipe production practices, and can be conveniently implemented in today’s pipe production facilities. Tests on structural performance of concrete pipes demonstrated the potential of synthetic fibers to enhance the service life of reinforced concrete pipes by increasing the protective concrete cover thickness over steel; microbial-induced corrosion then would take longer to reach the level of steel (soon after which, corrosion of steel would mark the end of service life).
The structural test results confirmed that mineral, chemical, and polymeric admixtures introduced for the enhancement of concrete resistance to microbial-induced corrosion do not compromise the structural performance of concrete pipes. Test results on concrete pipes indicated that coarser PVA fibers, which exhibit a pronounced tendency toward fiber pull-out (in lieu of fiber rupture) at cracks, yield pronounced benefits in terms of the cracking resistance and ductility of steel-reinforced concrete pipes as well as the damage tolerance of plain concrete pipes. Cost analyses also were conducted to assess the impact of synthetic fibers on the initial production cost of concrete pipes. Fibers should be used at relatively low volume fractions (about 0.5%) to offer the promise of performance gain at a viable cost. The combination of fiber tensile and bond strengths and geometric attributes should make fiber pull-out (in lieu of rupture) predominant at cracks for fibers to effectively enhance the damage tolerance and structural performance of reinforced and plain concrete pipes.
Analytical models were developed for prediction of the flexural strength and load-carrying capacity of concrete pipes reinforced with synthetic fibers, with or without steel reinforcement. These models account for the contribution of fibers to tensile load-carrying capacity of concrete through pull-out or rupture modes of failure at cracks. The models were refined based on the outcomes of experiments on pipes with different combinations of steel and synthetic fiber reinforcement, and provided a reasonable basis to predict the experimental values of the ultimate load and cracking resistance of concrete pipes.
Conclusions:
Modified concrete formulations incorporating selected polymer emulsions and fine pozzolans greatly enhance the durability of concrete-based infrastructure systems in sanitary sewer environments. The modified formulations suit industrial-scale production of concrete pipes and do not compromise the structural performance of reinforced concrete sanitary sewer infrastructure systems. Modified structural designs of concrete pipes, with complementary use of synthetic fibers and conventional steel reinforcement, can increase the protective concrete cover thickness over steel, thereby further increasing the service life of reinforced concrete systems in sanitary sewer environments. The initial cost implications of the new strategies for enhancement of the longevity of concrete-based infrastructures in sanitary sewer systems are modest and yield tremendous life-cycle cost savings. These research outcomes were presented at the 97th Annual Meeting of the American Concrete Pipe Association in March 2005.
Supplemental Keywords:
wastewater infrastructure, concrete, sanitary sewer, microbial growth, microbial-induced corrosion, additives, service life, fine pozzolan, polyvinyl alcohol, PVA, durability, pipes, EPA, small business, SBIR,, Scientific Discipline, Water, TREATMENT/CONTROL, Wastewater, Civil/Environmental Engineering, Engineering, Chemistry, & Physics, Environmental Engineering, Water Pollution Control, wastewater treatment, microbial degradation, municipal sewers, wastewater pipeline, microbial-induced corrosion, concrete , concrete materials, municipal wastewater, wastewater systems, synthetic fiber, sewer infrastructureSBIR Phase I:
Development of New Concrete-Based Wastewater Infrastructure Systems With Enhanced Durability, Structural Efficiency, and Hydrological Performance | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.