Concrete Inspection, Testing, Coating Selection and Failure Analysis: Our highly experienced concrete specialists are available for onsite, laboratory testing and root cause determination for failures of concrete and concrete coatings. Our comprehensive technical reports are well structured and include photographic documentation, detailed test procedures, and results that will hold up in a court of law.
Our team of qualified materials and corrosion engineers, and concrete (petrographic) specialists have extensive experience evaluating concrete bridges, historic buildings, driveways, pole structures, foundations, floors, sea walls, and other asset type. Factors such as erosion, fatigue, cycles of freezing and thawing, and adverse chemical reactions can have a deleterious effect on the performance of this material. One of the most common problems in reinforced concrete is the corrosion of embedded metals. The corrosion of steel in concrete is primarily caused by exposure to chloride contained in seawater, roadway de-icing chemicals, and soils. Chloride contamination can also occur in new construction when using chloride-containing set accelerators, contaminated aggregate, or the use of non-potable mix water. Call us for a quote to visit your project site or to speak with one of our experts.
Onsite Concrete Inspection and Testing
Onsite concrete inspection and condition assessment of reinforced concrete typically includes the following test protocol:
If required, concrete core samples are marked and retrieved for petrographic analysis. Cores are used for visual observation, compression testing, split tensile testing, verification of NDT and petrographic analysis. Core locations are selected on the basis of visual observations, hammer soundings and impact-echo testing. Concrete core samples can be shipped to Matergenics for a petrographic analysis.
Matergenics specializes in Petrographic Analysis, a review of the concrete matrix using microscopic techniques described in ASTM C856 to determine concrete constituents, quality, and cause of inferior performance, distress, or deterioration. Concrete is composed of sand, gravel, crushed rock, or other aggregates held together by a hardened paste of cement and water. Important properties of concrete are: durability (weather resistance, resistance to chemical deterioration, resistance to erosion), workability, water tightness, strength, elasticity, creep, extensibility, and thermal properties. Entrained air content, cement and water content and type, distribution and quality of aggregates are various factors that affect properties of concrete. Estimating future performance and structural safety of concrete elements can thus be facilitated.
There are several mechanisms that can lead to corrosion of embedded steel. First, if the concrete cracks for any reason these cracks will often propagate towards the embedded steel resulting in direct access to the exterior environment of rain, snow, dirt, and wind borne contaminants. Second, as concrete ages it will chemically react with carbon dioxide in the atmosphere in a process known as carbonation. Carbonation results in a decrease in the alkalinity of the concrete such that passivation of the steel will no longer occur. Shallow depths of concrete cover over embedded steel will cause corrosion to occur at shorter time intervals. Also, high water cement ratios cause the concrete to be more porous leading to corrosion at shorter time intervals. And third, the presence of chlorides can lead to severe corrosion issues. As the steel corrodes the iron corrosion products have a greater volume than the metallic steel leading to internal pressures within the concrete which then causes cracking and spalling of the concrete above and adjacent to the corroded steel.
Based on the findings of the onsite inspection, condition assessment and laboratory petrographic analysis, an analytical review can be performed on key structural elements. This analysis can be used to determine deficiencies in an original design as well as to determine if the existing structure, even in a deteriorated condition, is still adequate to support the imposed loading.
Concrete Floors and Moisture – Hardened concrete is a permeable medium. The rate at which moisture can permeate through a concrete slab is dependent upon the overall quality of the concrete. Modern construction practices often use vapor retarders to produce a moisture resistant floor. They are not often present in older constructions. High moisture vapor transmission rates for concrete slabs can result in the debonding of tile and carpet; warping of wooden floors and even microbial growth. The moisture vapor emission rate can be determined in accordance with ASTM F1869. Most manufacturers of floor coverings will specify a maximum acceptable moisture transmission rate.
Cracking in Concrete Structures – Cracking and spalling of concrete in parking garage structures is almost always the result of corrosion of the steel reinforcement. Various factors such as depth of concrete cover over the rebar, depth of carbonation, moisture permeability of the concrete (related to the water/cement ratio), and the presence of waterproof coatings on the concrete surfaces can affect the occurrence of the corrosion process. The volume expansion that happens when iron corrosion products are formed can exert enough localized pressure to crack and eventually spall the concrete cover. The presence of melt water and the use of chloride deicing salts will exacerbate the problem. The potential for corrosion of uncoated reinforcing steel can be determined by performing half-cell potential mapping of uncoated concrete in accordance with ASTM C876.
Electrochemical Methods such as cathodic protection are an important tool to enhance the durability of concrete structures. Cathodic protection systems provide a small electrical current to the embedded steel to prevent or control active corrosion. There are many types of cathodic protection systems with various advantages and limitations. Our staff engineers are NACE certified in cathodic protection, corrosion, coatings, and materials selection and design and can assist with these aspects as well. Click here to learn more about cathodic protection.
Types of deterioration include: corrosion of reinforced steel, freeze-thaw damage; sulphate attack; alkali-aggregate reactivity; fire damage; surface scaling; popouts; effects of admixtures; and several other aspects.
Corrosion Risk Assessment Structures can be affected by many factors including erosion, fatigue, cycles of freezing and thawing, and adverse chemical reactions. One of the most common problems in reinforced concrete is the corrosion of embedded metals. The corrosion of steel in concrete is primarily caused by exposure to chloride contained in seawater, roadway de-icing chemicals, and soils. Chloride contamination can also occur in new construction when using chloride-containing set accelerators, contaminated aggregate, or the use of non-potable mix water.
Electrochemical methods such as cathodic protection are an important tool to enhance the durability of structures. Cathodic protection systems provide a small electrical current to the embedded steel to prevent or control active corrosion. There are many types of cathodic protection systems with various advantages and limitations.
Design of Suitable Corrosion Protection Measures to Mitigate Corrosion of steel Reinforcment
Cathodic protection and corrosion inhibitors will be considered to mitigate the corrosion of reinforced steel. Cathodic protection (CP) is a method wherein a sufficient amount of electric direct current (DC) is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or temporarily stop the natural corrosion processes from occurring. The DC current corrodes a sacrificial anode when it is connected to a structure to be protected. There are two methods for supplying DC to cathodically protect a structure. They are the following:
The galvanic anode cathodic protection system generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). The sacrificing metals such as magnesium (Mg), zinc (Zn) or aluminum (Al) all have a lower more negative electrical potential. The current output of this system is affected by factors such as:
The impressed current cathodic protection system comprises four main components which together constitute an electrical circuit. They are as follows:
The CP transformer rectifier can be powered by external power sources, such as alternating current (AC). The CP rectifier converts the input power source into DC. DC is discharged from impressed current anodes made of metals such as steel, high silicon cast iron, graphite, platinum and titanium mixed metal oxide. The potential current output of an impressed current CP system is limited by factors such as available AC power, rectifier size, anode material, anode size and anode backfill material. The current output of an impressed current cathodic protection system is far greater than the current output of a galvanic anode cathodic protection system. However, higher maintenance during service is required and short circuiting of anode and rebar should be taken into consideration in design and implementation of this system.
It is important to determine the condition of the steel reinforcement and current requirements for the design of a reliable cathodic protection system.
Client Involvement: No evaluation can be complete without input from the project owner or maintenance personnel. These individuals live with the project on a daily basis and typically have historical data related to building/project use, prior maintenance history, change in use of the facility, etc. In addition, a successful repair strategy can only be developed if the expectations of the client are clearly understood. For example, if the structure will be replaced in one year, it is not beneficial to the client to evaluate the structure and develop repairs for a 20-year anticipated life.
We respond to all inquiries promptly by sending a technical proposal detailing scope of work and estimated costs. Please call Dr. Zee at 412-952-9441 or Ed Larkin at 412-788-1263 for additional information, and how we may be able to assist you in the lab or at the project site. Alternatively, you can send your request to firstname.lastname@example.org. Call us today for a quote!