Characterising Penetrometer Tip Contact during Concrete Condition Assessment

Concrete condition assessing penetrometers need to be able to distinguish between making contact with a hard (concrete) surface as opposed to a semi-solid (corroded concrete) surface. If a hard surface is mistaken for a soft surface, concrete corrosion may be over-estimated, with the potential for triggering unnecessary remediation works. Unfortunately, the variably-angled surface of a concrete pipe can cause the tip of a force-sensing tactile penetrometer to slip and thus to make this mistake. We investigated whether different shaped tips of a cylindrical penetrometer were better than others at maintaining contact with concrete and not slipping. We designed a range of simple symmetric tip shapes, controlled by a single superellipse parameter. We performed a finite element analysis of these parametric models in SolidWorks before machining in stainless steel. We tested our penetrometer tips on a concrete paver cut to four angles at 20∘ increments. The results indicate that penetrometers with a squircle-shaped steel tip (a=b=1,n=4) have the least slip, in the context of concrete condition assessment.

STRUCTURAL PARAMETERS OF CONCRETE CORROSION RESISTANCE

This article describes the problem of corrosion of concrete at the enterprises of the wine and fruit and vegetable industry in Moldova, the kind of organic acids that destroy concrete are considered. Such a specific type of chemical corrosion as leaching is also considered. The reaction of the influence of malic acid on concrete is reflected, as a result of which readily soluble calcium malic acid is formed. The structural parameter of corrosion resistance to chemical corrosion has been studied. The formula for the corrosion resistance of concrete is derived and explained. The structural parameter of resistance to chemical corrosion is investigated on various types of concrete. The formula for coefficient resistance of concrete to chemical corrosion is derived. Also, two dependencies are displayed: Dependence of the coefficient of resistance of concrete to chemical corrosion on the volume of cement stone; Dependence of the coefficient of concrete resistance to leaching corrosion on the structural parameter.

INFLUENCE OF CONCRETE CORROSION FROM THE INTERACTION OF ALKALIS OF CEMENT WITH REACTIVE AGGREGATES ON DAMAGE TO REINFORCED CONCRETE SLEEPERS IN A TRACK

The article analyses the causes of cracks and other damage in reinforced concretesleepers. The effect of concrete corrosion, which is caused by the interaction of cement alkalis withreactive aggregates, on damage to sleepers has been established. The significance of each of thereasons has been established. Corrosion of concrete sleepers, which is caused by the reactionbetween alkalis and silicic acid - Alkali-Silica Reaction (ASR), in Ukraine was initially caused by ahaphazard change in suppliers of aggregates and cement. Also it influenced by the modernization ofthe production of cement plants, which led to an increase in the content of alkalis in cement by morethan 0.6%. Of all concrete structures, corrosion from ASR proceeds faster precisely in the railwaytrack structures - its signs appear on average after 2.8 years of operation, and the foundations ofoverhead catenaries - after 3 years. For other structures, these signs appear later - for bridgestructures after 3.7 years, for road surfaces - after 6.9 years. This is due to the peculiarities of thedesign and operating conditions of the sleepers, including, possibly, the effect of leakage currentsadditional to the water cut. The corrosion rate from ASR in structures in Ukraine is much higher(signs of corrosion appear on average after 2.2 years) than in the countries of North America, Central and Northern Europe (6.1 and 6.4 years, respectively). This is due to the wider use of additives inconcrete, a better regulatory framework and a culture of compliance in these countries. ASR directlycauses 15.5 % of defects, contributes to the formation and development of 32.8% of defects to thegreatest extent, does not affect 30.9 % of defects at all, and to a limited extent contributes to theemergence and development of other 20.8 % of defects. The effect of corrosion of concrete from ASRon the occurrence of damage (defects) in sleepers is explained by the fact that as a result of ASRtensile stresses arise in concrete, which lead to the formation of a spatial network of microcracks anda decrease in the tensile strength of concrete. Since the prestressing of the reinforcement has createdtensile stresses in the transverse direction, predominantly longitudinal cracks occur in the sleepers.Prestressed reinforced concrete structures are more vulnerable to damage caused by ASR concretecorrosion than conventional reinforced concrete or concrete structures.

Effects of Various Corrosive Ions on Metakaolin Concrete

In order to study and verify if the three corrosive irons of SO42−, Mg2+, and Cl− could promote or inhibit each other in concrete corrosion as time goes by, we take Metakaolin (MK) as the research object to explore the interaction mechanism among ions by testing the physical and mechanical properties, the ion content, the phase composition, and the microstructural changes of the MK concrete under the action of various ion combinations. The results show that during the initial and middle stages of the corrosion (40–80 days), SO42− and Mg2+ are in reciprocal inhibition relation, Cl− could inhibit the action of SO42−, and Mg2+ could promote the diffusion of Cl−. However, at the final stage of corrosion (120 days), SO42− and Mg2+ could mutually promote each other, and both irons could promote the diffusion of Cl−. Mg2+ could mainly produce magnesium hydroxide and M-S-H inside the concrete, SO42− mainly generates the ettringite and gypsum, while Cl− mainly produces Friedel salt and NaCl crystal.

Sustainable Corrosion Inhibitors for Concrete

Green chemistry and sustainability encourages the significance of preserving the nature and individual’s wellbeing in cost effective way that intends to avoid toxicity and reduction of wastes. Therefore, the implication of green corrosion inhibitors in the field of concrete protection has also received immense attention these days. Indeed, the usage of such inhibitors is a well-known strategy for producing high performance concrete. In view of this, the present chapter discusses the research in the area of sustainable corrosion inhibitors for concrete assurance used commercially in various industries. It also highlights the concrete corrosion mechanisms and its protective measures, recent advances in this field.