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.
Onsite Concrete Inspection and Testing
Onsite concrete non-destructive and core inspection and condition assessment of reinforced concrete typically includes the following test protocol:
- Review of background information.
- Photographic documentation, site evaluation, environmental considerations.
- Visual examination – to identify surface defects.
- Hammer/chain – to detect delaminations.
- Phenolphthalein – to determine depth of carbonation.
- Chloride content – to identify chloride corrosion.
- Half-cell potential mapping – to determine corrosion risk (map corrosion hot areas).
- Linear polarization – to determine corrosion rate.
- Continuity – to determine continuity / connectedness of rebar.
- Stray current identification – to determine stray current corrosion risk.
- Resistivity – to determine concrete resistivity and corrosion risk.
Identifying corrosion is only the beginning
determining its severity and immediately responding can prevent disasters and save hundreds, or even thousands of lives
mechanisms Leading to corrosion of embedded 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 to determine root cause of corrosion
CONCRETE FOUNDATION EXHIBITING ACCELERATED CORROSION
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. 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.
CRACKING IN CONCETE
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, and the presence of waterproof coatings on the concrete surfaces can affect the occurrence of the corrosion process.
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.
Routine corrosion risk assessments
identify corrosion risk, but they can also quantify the severity of corrosion and offer remaining life estimates
Tiered Approach Corrosion Risk Assessment Protocol
We recommend performing a tiered inspection and testing to reduce costs for corrosion risk assessment. If Tier I inspections exhibit poor results with a high uncertainty from a corrosion engineering view, Tier II evaluation should be performed.
The approach is formulated and reached by Dr. Zee and his concrete team. He is a certified corrosion engineer with over thirty-five years of experience in condition assessment and corrosion mitigation.
TIER I INSPECTIONS
Include non-destructive tests for concrete of a minimum three (3) areas of each balcony. The following tasks will be performed:
- Pre-assessment and visual examination to determine the locations for Tier 1 tests. These are locations that water (and corrosive ions) can be trapped or accumulated, loose tiles, discolored areas and repaired areas due to corrosion
- Determination of two (2) suspect areas and one (1) “good” area for comparisons
- Rebar location determination by electromagnetic techniques
- Removal of tile, mortar, water proofing and coating barriers by Matergenics technicians and preparation of surface of concrete for non-destructive testing (NDT) and corrosion risk assessment of reinforced rebars
- Concrete electrical resistivity measurement
- Electrical continuity study by drilling to the rebar and gathering concrete sample(s) if feasible. This requires small repair by other contractor(s) after drilling
- Electrochemical potential measurement, per ASTM C876
- Compressive strength determination of concrete using a Schmidt hammer, per ASTM C805
- Report generation for each inspected condo and specific recommendations as if Tier 2 inspections should be performed at a specific condo site. Matergenics will examine the balconies for drainage and slope Tier 1 will also determine if rebar in concrete is actively corroding, and tiles are popping up due to spalling of concrete. If so, Tier 2 testing should be performed.
Note: Building board member(s) should be present during all onsite investigations.
TIER II INSPECTIONS
Will be conducted once Tier 1 inspections confirm high corrosion risk and requirements for further testing. To determine the integrity of concrete and profile concentration of chlorides, it is best to remove a 3-inch diameter concrete core marked in Tier I. The following task will be performed:
- Corrosion rate measurement by LPR technique per ASTM G102 and ASTM G59 will be performed at the site of core.
- In-lab analysis of core sample will be performed for chloride profile analysis.
- Concrete resistivity measurement on the bottom side of the balcony slab to determine the extent of chloride permeation (this required access to the balcony below).
- Current requirement testing for cathodic protection and engineering solution will be performed at this stage if feasible.
Note: Other contractor(s) to be selected by the client will be responsible for repair and restoration of test areas once Tier 1 and Tier 2 inspections are completed.
Note: For each balcony, access to the balcony below is necessary when Tier II inspections are required.
Tier II testing and evaluation is highly recommended when we find evidence of accelerated corrosion of rebar in Tier I inspections.
Corrosion Risk Assessment for Aging Reinforced Concrete in C4 and C5 Salt Environment
Tiered Approach to identify risk
Corrosion risk assessment should be performed on aging concrete structures in C3, C4, C5 environments to prevent incidents or accidents.
Recommendations For Building Inspection And Condition Assessment
Corrosion mapping should be performed for condominium tower certifications in order to look at the thickness of the concrete around the rebars and load bearing members. Is especially true for buildings on the sea front which are at increased risk of such corrosion due to their proximity to the salt in the ocean.
This was not a one-night event or a sudden failure. Rather, it was a long time in the making because of the accelerated corrosion and loss of thickness. Once the thickness loss gets critical, the failure is catastrophic.
It seems rather apparent that current building regulations in Miami-Dade, as well as throughout Florida, do not adequately address the serious structural concerns that this tragedy has brought to the forefront. Matergenics’ and Dr. Zee’s specific inspection and condition assessment recommendations for nearby buildings of similar age are given here.
The on-site inspection and condition assessment includes a detailed investigation of all areas of the reinforced concrete structure and may require several hours to several days, depending upon the size of the structure.
Concrete core samples should be retrieved from corroded areas (identified in corrosion mapping) for petrographic analysis to determine if the concrete is structurally sound or requires repair or replacement.
Based upon on-site surveying and laboratory analysis result, and employing sound materials and structural engineering principles, determination of extent of damage and remaining service life are undertaken. Critical questions to be answered here are the following.
- Is the reinforced concrete structurally sound?
- Does the reinforced concrete require repair or replacement?
Consideration should be given to materials selection for repair and/or replacement of the components of the reinforced concrete structure. In addition to concrete repair materials, this will include alternative materials to non-concrete auxiliary materials and maintenance coatings which may be applied to mitigate corrosion.
Specifically, it is imperative that future regulations require that both corrosion engineering experts, in addition to structural engineers, take part in building inspections to provide detailed reporting and an exact quantification of corrosion risk in their condition assessments. Condominium associations are also now on notice that they need to take immediate action with respect to corrosion assessment.