(87e) On Evaluation, Prevention and Repair of Microbial Acid-Produced Attack of Concrete

The damage due to corrosion of concrete in the United States is estimated to be $276 billion.  Microbial Influenced Corrosion, MIC has been found to be responsible for 50% of the total cost of corrosion.   The microorganisms responsible for the corrosion may be fungi, algae, sulfur oxidizing and nitrifying bacteria.  Different mechanisms are involved in the formation of corroded layer in the concrete pillars in the water bodies in the interstate highways in Texas. The microorganisms may grow in the water phase and generate acid that may diffuse into the solid phase through an interface and react with cementicious portion in the concrete. By another mechanism, the microorganisms may directly grow in the solid phase using cementicious portion of the concrete as nutrients. Carbonation reactions between carbon dioxide and calcium hydroxide forming calcium carbonate may lower the alkalinity of the cement accelerating other microbial reactions that are favored in an acidic environment. 16 single stranded ribosomal riboxynucleic acid, 16S rRNA sequence distribution of the microorganisms responsible for the corroded concrete can be obtained using microarray sequence measurements (Sharma, 2008). The corrosion and organisms both are proposed to be characterized using sequence alignment algorithms and bioinformatics databases and SEM, scanning electron microscopy. Mathematical models that take into account the Michael Menten kinetics, Fick’s diffusion and generalized Fick’s diffusion and the liquid phase and solid phase reactions have been developed. Damped wave diffusion effects are also studied. Field corrosion rates are compared between experiment and theory. Simulation studies of biodeterioration on fresh concrete  are presented. Remedial actions are provided to delay or avoid corrosion of concrete piers that serve as substructure in bridges. 

             The deterioration of concrete is by diverse mechanisms (1).  A better understanding of the mechanisms that cause the damage to concrete structures is needed.  After the damage, the effect of different mechanisms on the damage needs to be delineated from each other.  The microorganisms that colonize the concrete needs to be identified and characterized using ribosomal riboxynucleic acid, rRNA sequencing studies. The reactions that participate in the corrosion needs to be mapped out.  The mechanism can be one or combination of several such as: i) microorganism such as algae, fungi, nitrifying bacteria and sulfur oxidizing bacteria which may generate acids in the water phase and the acid will diffuse and attack the cementicious portion of the concrete by leaching; ii) chlorine ions in the salt present in water may diffuse and attack the steel portion of the concrete by a process called salt induced corrosion; iii) the carbon dioxide, CO₂, participates in the carbonication of the cementicious portion of the concrete decreasing the alkalinity of the concrete from 13 to a level where bacteria that thrive in a acid environment can act upon, thus microbial succession is not clear by a process called carbonation. By carbonation

              CO₂ +  Ca(OH)₂ ----------à  CaCO₃

 ;  iv) the microorganism may grown in the cementicious portion of the concrete and excrete the acid which in turns further attacks the cementicious portion of the concrete. The role of each of these mechanisms in the said locations of the concrete structures in the state of Texas needs to be better evaluated. 

 

 

Who is impacted by the problem ?

             The concrete industry is impacted by the problem.  The size of the concrete industry is US $35 billion.  In 2006,  over 7 km³ of concrete are used every year. Concrete industry employs more than 2 million workers in US. Over 55,000 miles of highways in the nation are paved with concrete.  Concrete word originates from the Latin concretus that means hardened.  By a process of hydration concrete solidifies and hardens upon mixing with water.  A stone like material is created after reactions of cement with water and bond formation between various components of the concrete.  Among other things, concrete is used to make motorways/roads and bridges.  Concrete is the most used man-made material.

Significance/Scope of the problem

             Approximately US $20 billion are needed for bridge repairs in the US Interstate highways because of ‘salt induced corrosion’. Per a recent survey,  damage due to corrosion in the United States is estimated at $276 billion.  Surveys in United Kingdom,  Japan, Australia and Germany place the cost of corrosion to be 1-5% of the gross domestic product, GDP. MIC has been found to be responsible for 50% of the total cost of corrosion.   Corrosion of reinforced concrete and pre-stressed and other concrete structures is a multi-billion dollar problem in US and other countries.  A parking garage collapsed in Minnesota and the damage was attributed to de-icing salts. Another spectacular failure was the collapse of the Berlin congress hall (32).

             Per a 1997 report, amongst 581,862 bridges in and off the US federal-aid-system about 101,518 bridges were rated structurally deficient.  The repair costs can range from US $78 - $112 billion.  By 2011 the annual maintenance cost of bridges would be US $ 5.2 billion.  The US department of commerce census bureau states that the dollar impact of corrosion on highway bridges is considerable.  The annual direct cost of corrosion on highway bridges is considerable.  The annual direct cost of corrosion on highway bridges is estimated to be US $6.43 - $10.15 billion.  The break-up of the total cost is as follows: i) about US $ 3.79 billion is needed to replace structurally deficient bridges over the next decade;  ii) US $ 1.07-2.93 billion is needed for maintenance and cost of capital for concrete deck bridges;  iii) US $0.5 billion is needed in painting cost of corrosion.

             Per the Federal Highway Administration about 30% of the nation’s bridges are structurally deficient or functionally obsolete.  Chloride induced corrosion of the reinforcing steel has been attributed as a cause of premature rehabilitation of the bridge structures.  Better service life models are needed.  This allows planners to determine the remaining time to first repair and subsequently rehabilitate a given bridge or set of brides and evaluate the effectiveness of the various protection methods.