Seawalls are typically composed of concrete materials and are used to act as a barrier between land mass and the encroaching waters from the sea or other bodies of water that will cause damage to property owners. Many of the seawalls located in inter-coastal and residential canals and waterways are constructed of reinforced concrete precast panels that may be subject to the harmful effects of constant wind and sea currents that may result in shifting and or cracking. Additional forms of failure include:
The degree of seawall failure for each of the above concerns can often be linked to two very important criteria: (1) the possibility of including reactive aggregates that are used to manufacture concrete, and (2) the use of carbon steel rebar that is used to support the concrete mix during construction.
The type of gravel/sand mix that is used to construct seawalls is one of the most important considerations that should be indicated prior to the design/build phase of seawalls. If seawalls are already in place that are relatively new and appear to be degrading at an accelerated rate, a test on a core drilling of a concrete sample can be used to determine if the type of concrete mix is adequate to ensure safekeeping of landowner structures and prevent property damage. Concrete cores are evaluated by a variety of laboratory test procedures designed specifically for concrete that is referred to as “petrographic analysis.” A petrographic analysis can be used to determine a variety of important conditions within concrete that may result in failure. If observed within a time frame indicated by the seawall constructor, property owners can often times benefit from a petrographic analysis to identify air void content, compressive strength, reinforcing steel corrosion, and a variety of other conditions that may affect the ability of a seawall to withstand the constant forces applied due to wind loading and seawater currents. A photograph showing a concrete core with network porosity is shown in the picture on the left, and a concrete core sample with a crack in it due to carbonation is shown on the right.
Typical petrographic analyses require that a core drilling be obtained for the concrete structure in question. This typically does not cause damage to the integrity of the concrete structure from which it is obtained. The use of petrographic analysis is very effective to identify structures that are at risk for corrosion degradation due steel reinforcement deterioration which is often exacerbated by seawater, which has a very high level of salt containing chlorides that can erode the concrete materials used in seawall construction over time. An example of corroded steel reinforcement encased in cracked concrete is shown on the left, below. An example of the steel reinforcement crossing members exhibiting corrosion and cracking is shown on the right, below.
Standard practices for seawall assessment are typically those that include criteria that is used to describe the condition of the concrete rather than the seawall itself. These standard practices include some of the better known aspects of concrete evaluation such as air void content, compressive strength, depth of carbonation and chloride content. The following is a partial list of the standard practices used by Matco engineers and our in-house Petrographic Specialist, Ed Larkin.
- ASTM C856 - 04 Standard Practice for Petrographic Examination of Hardened Concrete
- ASTM C457 / C457M - 10a Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete
- ASTM C1084 - 10 Standard Test Method for Portland-Cement Content of Hardened Hydraulic-Cement Concrete
- ASTM C1218 / C1218M - 99(2008) Standard Test Method for Water-Soluble Chloride in Mortar and Concrete
- ASTM C1152 / C1152M - 04e1 Standard Test Method for Acid-Soluble Chloride in Mortar and Concrete
- ASTM C39 / C39M - 10 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
There are also a variety of on-site inspection methods including visual assessment and ultrasonic testing that are used to identify seawall degradation. These procedures are effective to some degree; however they do not provide an indication of the condition of the concrete encased steel reinforcement (rebar) in terms of corrosion or metal loss, both of which are the most often observed forms of failure for seawalls. Examples of some of the issues commonly observed in seawalls that are in need of inspection and repair are provided in the following photographs.
Left: Seawall exhibiting a long horizontal crack. A common occurrence to concrete that exhibits cracking is corrosion of the steel reinforcement members. Middle: Exposed steel reinforcement under the seawall cap exhibiting corrosion is shown. Right: Chunks of concrete have fallen off and areas where steel reinforcements were exposed have been repaired.
As part of Matco Services' test protocol to identify corrosion and metal loss on steel reinforcement encased in concrete, testing in accordance with ASTM C 876, standard test method for half-cell potentials of uncoated reinforcing steel in concrete is used. This test method is considered one of the most advanced forms of evaluation that can be used to identify corrosion or metal loss prior to any outwardly signs of corrosion, such as the appearance of red rust, which is often the only parameter considered when inspections are performed by other testing firms. As this test method does not require destructive testing of any kind in order to perform the assessment, it is also considered by many to be the single most important test method that should be performed prior to any other procedure performed other than visual inspection.
Left: Seawall exhibiting exposed steel reinforcement member with EIS electrodes attached. Middle: EIS test set-up. Right: EIS testing to determine if, and how advanced, internal corrosion of the steel reinforcement members is present.
In the following listing a guideline is provided that can be used to assist those where there is concern regarding an existing seawall:
Identify property lines and right-aways in order to determine who the responsible party will be in the event a seawall requires inspection, maintenance or repair.
Determine the liability of property owners with seawalls that have begun to deteriorate and the methods required to ensure structure integrity from a corrosion and concrete point of view.
Seek the advice of experts that are knowledgeable in seawall construction materials including steel reinforcement (rebar) corrosion and concrete.
Determine the level of risk to property owners in the event a seawall collapses and was not properly inspected or maintained.
Identify seawall problem areas that appear to have the highest potential for failure. These areas should be (1) photographed or recorded with a video camera, and (2) summarized in field notes that include the date and location where observations were made. This will enable the seawall to be evaluated over time using comparative photos and written observations.
Utilize qualified inspection firms that endorse test methods designed to identify internal corrosion of steel reinforcement members and metal loss in order to ensure problem areas are detected prior to any outward signs of failure be required, such as red rust.
Utilize qualified materials testing firms that specialize in concrete (petrographic) analysis to identify seawalls that may not have had the proper mixture of sand/gravel during construction.
Engineering Solutions and Mitigation Techniques: As experienced materials and corrosion engineering experts, Matco Services' staff members are geared towards providing innovative and cost effective engineering solutions designed to meet the specific needs of our clients. These solutions often incorporate the use of cathodic protection, application of protective coatings or tape wrappings, or the use of some other form of corrosion mitigation or early detection method. Although Matco Services' has had the capability to carry out an assortment of these procedures for many years, we are delighted to now offer an additional scope of repair work that includes application of protective paints and coatings, structural repair and weld repair. These repair procedures are performed by NACE certified technicians that have undergone extensive training in performing these repair procedures and corrosion mitigation techniques.
Matco Services' Team Members - Our team includes experts in a variety of desciplines including corrosion engineering, materials engineering, mechanical engineering, paint and coatings specialists, electrochemists, chemists, Ph.D. level scientists in materials selection and design, polymer and elastomer specialists, and concrete (petrographic) specialists that often work as a team to identify a the root cause of a materials failure. We also have a vast array of laboratory and field testing equipment that is enlisted at times when a repair or refurbishment of a structure is required. All of Matco Services' testing equipment is calibrated on a routine basis in accordance with both national and international standards, and is ready to be put to use at a moment's notice. Matco Services' staff includes a variety of experts in corrosion and materials engineering, as well as the methods used to repair and retrofit a variety of structures.
We Value Our Customers... Throughout the years we have noticed that much of our business comes from repeat customers. Our expertise and well-equipped lab can account for much of this, but we believe there is something more to it. We attribute it to the fact that we promote an open and friendly environment that is never too busy to meet your needs. At Matco Services we value your business whether you are a large corporation or a small enterprise. We will provide you with the attention you need and deserve. We invite you to visit us and get to know our staff, and share in the learning experience.
Why Choose Matco Services? As one of the premier testing, inspection, and repair firms, Matco Services is able to provide a unique and diverse blend of services. Thousands of investigations have been performed at Matco Services, ranging from jet engines and boiler tubes, to computer components and implants that have promoted the advanced understanding of why these components fail to meet expectations. Combined with our new repair and retrofit capabilities for a variety of structure types we are now able to offer our clients a comprehensive array of services from project start, to project finish. As always, projects are conducted discretely so that client confidentiality is ensured.