Ceki Halmen

Corrosion of metallic materials in controlled low-strength materials - Part 3

Among the impediments to the use of controlled low-strength materials (CLSM) is the lack of knowledge about the long-term corrosion performance of metallic materials embedded in this material. Parts 1 and 2 of the present study revealed that pipes completely embedded in CLSM showed lower corrosion activity than pipes embedded in sand. Methods and models currently used to assess the corrosivity of soils on pipes, however, are still being used to assess the corrosivity of CLSM on pipes. Such methods and models limit the use of CLSM. New models are needed to reliably assess the corrosion performance of pipes embedded in CLSM. As such, this study describes the results of the first part of the Phase II research where the corrosion performance of ductile iron and galvanized pipes were completely embedded in 13 CLSM mixtures. A comprehensive model was developed to predict the mass loss of pipes embedded in CLSM.

Controlled Low-strength Materials Composed Solely of By-products

A series of low-cost controlled low-strength materials (CLSMs) mixtures were produced without cement, using only by-products, including Class C fly ash, large quantities of limestone quarry fines, and synthetic gypsum. Flow, setting time, compressive strength, elastic modulus, and freezing-and-thawing resistance of mixtures were evaluated. Results indicated that CLSM mixtures solely comprised of by-products can be designed to provide a wide range of flow, setting time, and strength values. Obtained flow values varied between 200 and 600 mm (8 and 24 in.), setting time varied between a couple of hours and a day, and strength values varied between 237.4 and 9932 kPa (34.4 and 1440.5 psi). The maximum measured mass loss after 12 freezing-and-thawing cycles was 8%. Results showed that the addition of synthetic gypsum significantly improved strength and freezing-and-thawing resistance of mixtures.

Corrosion of Metallic Pipe in Controlled Low-Strength Materials-Parts 1 and 2

Controlled low-strength material (CLSM) is a cementitious material that is commonly used as a backfill for trenches, often when these trenches are located in roadways and undergo repeated loadings from vehicular traffic. However, when CLSM are proposed for use, engineers are often forced to use predictive corrosion performance tools applicable for pipes embedded in soils. These tools may not accurately represent the corrosion performance of pipe embedded in CLSM. This article reports on a two part study that investigated the corrosion performance of ductile iron pipe in sand (Part 1), in 30 different CLSM mixtures (Part 1), and in a combination of sand and CLSM (Part 2). Results show that for nearly all cases, the corrosion (measured by mass loss) of ductile iron coupons completely embedded in CLSM was less than the corrosion of pipe coupons embedded in sand backfill material. The results from Part 2 of the study indicate that embedding ductile iron pipe in different environments (in this case CLSM and sand) results in an increase in the corrosion activity. The authors conclude that because CLSM exhibits the potential to minimize corrosion of metallic pipes embedded in this material, proper precautions in preventing galvanic corrosion (corrosion caused as a result of being placed in different environments) may be worthwhile.

Economical Tests for Assessing Corrosion Performance of Steel in Concrete

The repair and rehabilitation of corroding infrastructure systems consumes significant resources. It is well documented that significant value is gained by using durable materials that exhibit long-term, repair-free performance. In the US, most state highway agencies (SHAs) are approached by material producers and requests are made to evaluate the material for possible use in the infrastructure system. SHAs have limited resources and are in need of new evaluation methods that are reliable, fast, and cost-effective. This research evaluated four different accelerated test methods for evaluating the corrosion performance of steel in cementitious materials. Results were compared with results from the commonly used standard ASTM G 109 test method. The corrosion performance of conventional bars, stainless steel bars, galvanized bars, and epoxy-coated bars were evaluated using concrete and mortar mixtures with different water-cement ratios and containing different amounts of a corrosion inhibitor. The effectiveness, time requirements, complexity, and costs of the new test methods were compared with the ASTM G 109 method. This research found that the Rapid Macro-cell Test (RMT) is relatively simple to perform and provides reasonable results for most products in a reasonable time frame with minimal relative cost.

Accelerating Standard Test Method for Assessing Corrosion of Steel in Concrete

This article describes how the time required to quantitatively assess the corrosion performance of steel embedded in concrete can limit the introduction of new materials and systems into the market to extend the life of reinforced concrete structures that have been exposed to corrosive environments. Many state and federal highway agencies, public utilities and infrastructure developers are aggressively pursuing corrosion protection methods for reinforced concrete structures. New test methods that can quickly provide quantitative results for assessing corrosion resistance are needed. Results from a research program that assessed the influence of exposure environment on the time to corrosion of steel embedded in concrete following the ASTM G109 test procedures are presented in the article. The results indicate that the modified test can provide quantitative results for reinforced concrete specimens containing different materials and that increasing the temperature and humidity reduces the time to initiation of corrosion. However, the reduction in time is not significant for specimens containing materials that resist corrosion, and increasing the temperature and humidity is not sufficient to generate results over reasonable durations.

Influence of Environmental Exposure Conditions on Mechanical Properties of High-Strength Concrete

High-strength concrete (HSC) is regularly used for prestressed concrete bridge girders. Producers of prestressed concrete often have to modify their mixture proportions due to environmental conditions and time of day when casting to achieve the required release strengths. In addition, the properties of the concrete at later ages have to be sufficient such that the design requirements for the service and ultimate limit states are met. This research investigated the influence of temperature and humidity on the compressive strength and flexural tensile strength of HSC mixtures at different ages. Results were compared with standard prediction equations, including the expression used by the American Association of State Highway and Transportation Officials (AASHTO) for estimating the flexural tensile strength. It was determined that early-age environmental exposure conditions can influence the mechanical properties of HSC and new equations, based on environmental exposure factors, may be applicable.