Te Testing and Inspection Te Techniques fo for Transportation and Offshore an and Mar arin ine Structures Mo Mohammad S. Khan, Ph.D., P.E. Ex Exec ecut utive e Vice e Pres esiden dent High Hi h Per erforma manc nce e Tec echno hnologies es, Inc Inc. (HP HPTec ech) T h T h e c c o n t e n t s o o f t t h i s p p r e s e n t a t i o n a a r e c c o p y r i g h t e d .
§ Background § Types of Transportation and Offshore and Marine Structures § Construction QA/QC § Concrete Deterioration Mechanisms Outline § Above-Water Testing and Inspection Techniques § Underwater Testing and Inspection Techniques § Concluding Remarks
§ There are many transportation structures that are marine structures but not necessarily all marine structures are transportation structures § There are lots of commonalities in the testing and inspection techniques of the two types of Background structures, but some offshore and marine structures present special testing and inspection challenges due to their difficult accessibility and lack of visibility below water § Some of the testing and inspection personnel need to be divers, and some of the testing and inspection techniques become impractical in submerged conditions even with a diver
§ Testing and inspection techniques assure quality of new construction § Testing and inspection techniques help assess the condition of existing structures § Different environmental and exposure Background conditions (wetting/dry cycles, high chloride/sulfate, marine growth, wind loads, ice loads, vessel impacts) § Current ACI documents: 201.2R-16, ACI 201.1R-08, ACI 222R-01, ACI 228.2R-13 § ACI 357-84, ACI 357.2R-10, ACI 357.3R-14 § DNV-OS-C502 of Det Norske Veritas
§ 90,500 dams § 239 locks § 11,900 levees (30,000 miles) § Average age of water infrastructure 60 years Background § Both qualitative and quantitative testing and inspection techniques needed (…continued) § Ownership of water infrastructure diverse § Lack of uniform guidelines for testing and inspection § “Technical experts and specialists may be required to evaluate individual features and conditions.” (NJ Dam Safety Inspection Prog.)
Background (…continued)
§ Offshore structures are gigantic structures in the middle of sea, away from shores and in a marine environment. § The world’s tallest structure is an offshore structure in the North Sea – Troll A Oil Offshore and Platform. Marine Structures § Height of 1,549 ft. including 994 ft. (303 m) below water. § Most offshore structures are fixed. § Constructed onshore and the floated to the site of installation.
Other Marine Structures § Floating bridges § Barges § Concrete ships § Docks Offshore and Marine Structures § Nearshore terminals § Wharfs § Dams, locks and levees § Immersed concrete tunnels § Breakwaters.
Offshore and Marine Structures
Offshore and Marine Structures
Offshore and Marine Structures Photo: WashingttonState DOT
§ Construction QA/QC of offshore and marine structures is generally no different than any other structure § Offshore and marine structures are generally fabricated onshore and then transported to their location § Better QA/QC procedures can be employed in Construction onshore fabrication yards than in cast-in-place QA/QC construction on actual project sites § Construction defects and problems are relatively easy to be rectified in a a fabrication yard than in cast-in-place construction § There is still a need for limited QA/QC on-site for offshore and marine structures, which can be performed on barges
Construction QA/QC Photo: U.S. Army Corps of Engineers
Construction QA/QC Photo: U.S. Army Corps of Engineers
§ Qualification testing of constituent materials (cement, pozzolan, water, aggregates, admixtures, etc.) Construction QA/QC Photo: NB Power Corp. ASR Damage at Mactaquac Generating Station in New Brunswick, Canada (Source: NB Power Corp.)
§ Proportioning of concrete mixtures § ACI Committee 211, Proportioning Concrete Mixtures, has a number of documents that provide guidance on proportioning concrete mixtures that meet project specifications. Construction § Trial batches in real field conditions help assure QA/QC that concrete mixtures with required properties will be delivered on the project site as designed. § Testing and inspection during pre-placement, placement, and post-placement phases of the construction
§ Pre-placement: base preparation formwork, joints, embedded items, reinforcing steel, cleanliness of placement equipment, weather conditions, and consolidation § After placement: finishing, curing, repair of placement defects, and form removal Construction § During placement: slump (ASTM C143/143M), QA/QC entrained air content (ASTM C231/231M and ASTM C173/C173M), concrete temperature, unit weight and yield (ASTM C138/138M), and compressive strength (ASTM C39/39M) § Other testing may be added to the QA/QC program specific to the nature and sensitivity of the project
§ Freezing and thawing § Alkali-aggregate reactions Concrete § Sulfate attack Deterioration § Corrosion of reinforcing steel Mechanisms § Interactive effect of different deterioration mechanisms
Freezing and Thawing § Freezing of internal moisture of concrete, and water entering from external sources § Freezing within the concrete is accompanied with an about 9% increase in volume Concrete § Low w/cm and good curing help control freezable Deterioration internal moisture Mechanisms § Non-freezable aggregates and a cement paste with adequate air void system help protect freezing from external water § Surface scaling most visible damage, but can cause internal damage to concrete
Alkali-Aggregate Reactions § Reaction between aggregates of certain mineralogical compositions and alkalis in the cement, in the presence of moisture, creating expansive stresses in the concrete Concrete § Depending upon the type and mineralogical Deterioration composition of the aggregate, this reaction can be classified as an alkali-carbonate reaction (ACR) or Mechanisms alkali-silica reaction (ASR) § ASR is much more common and widespread than ACR § In ACR, certain dolomitic limestones react with the sodium or potassium hydroxide of concrete
Alkali-Aggregate Reactions § In ACR, some argillaceous dolomitic limestones, characterized by a matrix of fine calcite and clay minerals, react with the sodium or potassium hydroxide of concrete § ASR is an expansive chemical reaction involving Concrete alkalis contained in the cement paste and certain Deterioration reactive forms of silica within the aggregates Mechanisms § A reaction between silica and alkalis produces an alkali-silica gel, which absorbs moisture and expands § Cements with Na 2 O equivalent of more than 0.6% are susceptible to ASR when used with reactive aggregates
Sulfate Attack § Sulfate reactions in concrete could occur due to both internal and external sources of sulfates § Deleterious sulfate reactions generally occur from sulfates entering the concrete from external Concrete sources Deterioration § Sulfates considered to be deleterious to concrete Mechanisms are generally the sulfates of sodium, potassium, calcium, and magnesium § Calcium sulfate in the cement reacts with 3CaO•Al 2 O 3 (commonly known as C3A) to form 3CaO•Al 2 O 3 •3CaSO 4 •32H 2 O (ettringite)
Sulfate Attack § Remaining available C3A reacts with the previously formed ettringite to create the compound 3CaO•Al 2 O 3 •CaSO 4 •12H 2 O ( calcium monosulfoaluminate) § Even this calcium monosulfoaluminate is not Concrete considered destructive if it forms at the time of Deterioration placement of concrete Mechanisms § When calcium monosulfoaluminate reacts with external sulfates, it regenerates ettringite § The formation of ettringite in hardened concrete is detrimental because ettringite crystals at this stage do not have an available space to reside, resulting in expansive forces
Corrosion of Reinforcing Steel § Normally, concrete is a highly alkaline material, with a pH of more than 12.5 § The high alkalinity provides protection against corrosion of embedded steel by forming a Concrete passive iron oxide film on the steel surface § There are two mechanism that destroy the passive Deterioration film – carbonation, chloride ion attack Mechanisms § Chloride ions attack and destroy the passive film even in the presence of high alkalinity § Carbonation, a reaction between atmospheric CO 2 and Ca(OH) 2 of the paste leading to the formation of Ca(CO) 3 . lowers the pH from more than 12.5 to less than 9 and destroys the passive film
Corrosion of Reinforcing Steel § Once the passivity of the reinforcing steel is destroyed, an electrochemical corrosion cell sets up with the formation of anodic and cathodic sites and corrosion initiates and propagates in the presence of moisture and oxygen Concrete § The locations where the passivity of the Deterioration reinforcing steel is destroyed act as anodic sites and the locations where the passivity is still intact Mechanisms act as cathodic sites. § The concrete pore solution acts as an electrolyte Fe → Fe ++ + 2e – 2H 2 O + O 2 + 4e – → 4(OH) –
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