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A violet color indicates still alkaline areas and thus non-carbonated concrete. Carbonated zones favorable for steel corrosion and concrete degradation are colorless. [3] [4] The presence of water in carbonated concrete is necessary to lower the pH of concrete pore water around rebar and to depassivate the carbon steel surface at low pH.
A fairly well-defined reaction front can often be observed in thin sections; ahead of the front the concrete is normal, or near normal. Behind the reaction front, the composition and the microstructure of concrete are modified. These changes may vary in type or severity but commonly include: Extensive cracking; Expansion
To assess some of the durability design parameters, the use of accelerated laboratory test is suggested, such as the so called Rapid Chloride Migration Test to evaluate chloride penetration resistance of concrete [11] '. Through the application of corrective parameters, the long-term behaviour of the structure in real exposure conditions may be ...
Carbonatation is a slow process that occurs in concrete where lime (CaO, or Ca(OH) 2 ) in the cement reacts with carbon dioxide (CO 2) from the air and forms calcium carbonate. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5.
ASTM C1293: "Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction". It is a long-term confirmation test (1 or 2 years) at 38 °C in a water-saturated moist atmosphere (inside a thermostated oven) with concrete prisms containing the aggregates to be characterised mixed with a high-alkali ...
MICP has been shown to prolong concrete service life due to calcium carbonate precipitation. The calcium carbonate heals the concrete by solidifying on the cracked concrete surface, mimicking the process by which bone fractures in human body are healed by osteoblast cells that mineralize to reform the bone. [ 36 ]
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