Simulated Concrete Research Articles

Biomineralization and corrosion inhibition of steel in simulated bio-inspired self-healing concrete

The concrete possessing quasi brittle nature is always prone to the transport of aggressive ions leading to corrosion of embedded steel. The use of bacteria-based self-healing concrete has been tremendously practiced since the last decade to repair such blemishes of concrete. In this research, interaction of 2 gram positive Chryseomicrobiam species with the simulated concrete and reinforcing steel has been studied in the chloride's environment. The effect of chlorides and varying pH conditions on the microbially induced CaCO3 precipitation (MICP) capability was explored along with the forensic investigations of the precipitates. The biofilm formation potential and electrochemical measurements were done to assess the corrosion inhibition tendency of steel bars by bacteria. The MICP potential of Chryseomicrobiam amylolyticum (CA) was high at each pH compared to the Chryseomicrobiam imtechense (CI). However, both of the strains produced vaterite and maximum amount was observed at a pH of 10. The CI strain formed denser and 42.27 % thicker biofilm compared to the CA. The corrosion inhibition efficiency of the rebars by CA and CI was 6.62 % and 90.42 % more than the control sample, respectively.

Effects of Temperature on Corrosion Behavior of Reinforcements in Simulated Sea-Sand Concrete Pore Solution

The effects of temperature on the chloride-induced corrosion behavior of reinforcing steel in simulated sea-sand concrete pore solution are studied by means of linear polarization resistance. The results show that the Ecorr (corrosion potential) and icorr (corrosion current density) of the reinforcing steels are temperature and/or chloride concentration (CCl)-related parameters. A linear correlation between Ecorr and temperature and a natural logarithmic correlation between icorr and CCl are observed. It is proved that the relationship between the corrosion rate and temperature follows the Arrhenius equation, whereas the activation energy of corrosion reaction increases with the increase of CCl.

Corrosion of steel bar in carbonated concrete treated with realkalisation and inhibitor

The combination of realkalisation and migrating corrosion inhibitor (MCI) was proposed as a protective technique for structures subjected to carbonation-induced corrosion; the effects on passivated steel bars in partly carbonated concrete were investigated. The corrosion behaviours of treated steel bars under three exposure conditions (natural indoor environment, accelerated carbonation and simulated carbonated concrete pore solution) were examined and the effects of amino-alcohol-based and amino-carboxylate-based MCIs were compared. The surface morphology of steel bars was observed by scanning electron microscopy, which indicated that MCIs could be adsorbed on the bar surfaces. Moreover, potentiodynamic polarisation curves were obtained and electrochemical impedance spectroscopy was performed. Results corresponding to a natural indoor environment and accelerated carbonation showed that current would destabilise the passivated steel bars but that the corrosion resistance of treated steel bars was significantly enhanced. According to the results in simulated carbonated concrete pore solution, the corrosion behaviour of steel bar was related to the type of MCI and the treatment parameters. Compared with amino-carboxylate-based MCI, the adsorption of amino-alcohol-based MCI was more stable although it was weakened with a decrease in pH. In general, treatment by realkalisation and MCI is more effective than simple application of realkalisation or MCI.

Predicting the capacity of an off-road self-loading drum mixer with different concrete consistencies through three-dimensional fluid dynamics analysis

The design features of machinery for concrete production are closely connected with the maximum volume capacity of processed material. Regarding the design of off-road concrete mixer trucks, there are many key parameters that define the final capacity, for example the geometric dimensions, the rotational speed and the concrete consistency. This paper presents a numerical investigation of an Eulerian–Eulerian multiphase CFD model applied to an off-road self-loading concrete truck mixer, which simulates the maximum concrete capacity by varying the concrete consistency. The calibration is performed by matching the maximum capacity of a commercially available drum, under different concrete consistency classes, with the yield stress value of the non-Newtonian Bingham model applied to the rheological properties of the simulated fresh concrete. This model can be used for the design of new concrete mixers, in order to predict the maximum capacity of the drum under different conditions and geometric design aspects. This work intends to highlight the calibration method and the numerical Bingham values applied to fresh concrete, in order to quantify concrete drum capacity while changing the fresh concrete consistency.

Seismic Performance of CAP1400 Nuclear Power Station considering Foundation Uplift

Under earthquake action, the reinforced concrete structure at the edge of the CAP1400 nuclear power plant foundation slab will be uplifted. In order to determine the seismic performance of this structure, a 1 : 12 scale shaking table test model was fabricated using gypsum as simulated concrete in order to meet scaled design requirements. By testing this model, the seismic response of the structure with consideration of the foundation uplift was obtained. Numerical analyses of the test model and the prototype structure were conducted to gain a better understanding of the structural seismic performance. When subjected to earthquakes, the foundation slab of the nuclear power plant experiences a slight degree of uplift but remains in the elastic stage due to the weight of the structure above, which provides an antioverturning moment. The numerical simulation is in general agreement with the test results, suggesting numerical simulations could be accurately employed in place of physical tests. The superstructure displacement response was found not to affect the safety of adjacent structures, and the seismic performance of the structure was shown to meet the relevant design requirements, demonstrating that this approach to modelling can serve as a design basis for the CAP1400 nuclear power demonstration project.

Inhibiting Steel Corrosion in Simulated Concrete with Low Phosphate to Chloride Ratios

Phosphate ions are studied as corrosion inhibitors in pore simulating solutions highly contaminated with chloride ions. The investigation aims at understanding the role of phosphates in the corrosion inhibition mechanism, employing potentiodynamic polarization tests, micro-Raman spectroscopy, impedance spectroscopy, X-ray photo electronic spectroscopy (XPS) and weight loss tests. Two inhibitor/chloride ratios were assessed, [PO43−]/[Cl−] = 0.2 and 0.6. When [PO43−]/[Cl−] = 0.6, pitting is inhibited, even after 90 days exposure. [PO43−]/[Cl−] = 0.2 only delayed the onset of localized attack. XPS showed that phosphates incorporate to the surface film. Phosphate ions behaved as mixed-type corrosion inhibitors. The results are interpreted by the participation of phosphates in the duplex passive film being formed on carbon steel.

The effect of a proprietary inorganic coating on compressive strength and carbonation depth of simulated fire-damaged concrete

This paper describes the effect of an inorganic coating of concrete (ICC) on the residual compressive strength and carbonation depth of fire-damaged concrete. The concrete specimens were cooled by water-spraying, which is usually used for fire extinguishing in a real fire. The ICC was applied to enhance the residual compressive strength and to reduce the carbonation depth of fire-damaged concrete at different recuring periods. The results showed that the performance of concrete with ICC was better than that of uncoated concrete. After being exposed to 150, 300, 450, 600 and 750°C, compared to uncoated concrete, the compressive strength of concrete with ICC was enhanced by 3·8%, 3·7%, 11·0%, 17·3% and 6·1%, respectively. For concrete exposed to temperatures below 750°C, the carbonation depth of concrete with ICC was reduced significantly compared to the uncoated concrete. In the case of 750°C, the concrete was neutralised completely for both uncoated and coated concrete. The most obvious enhancement of the compressive strength and the most significant reduction of carbonation depth of concrete with ICC can be found after the concrete was exposed to 600°C. Similar results were confirmed with the other two types of concrete with different compressive strength.

Corrosion resistance of stainless steel reinforced bars in contact with simulated concrete

The corrosion behaviour of stainless steel reinforced bars used in civil engineering was studied. Different electrochemical tests were performed using several stainless steel bars (austenitic and duplex), hot and cold rolled, in the presence of a solution, which simulates the contact with salt contaminated concrete. The corrosion rates were determined and also their behaviour against localized corrosion (pitting).

Perimeter Load Transfer in Model Drilled Shafts Formed under Slurry

Experimental laboratory‐scale studies were conducted on the effect of the use of various mineral and polymer drilling slurries on the perimeter load transfer in drilled shafts in saturated sand. Parallel measurements were also made of the rheological properties of the slurries studied in order to develop ranges of slurry control properties consistent with predictable load transfer. Polymer slurries, mixed in medium to high doses, were found to be as effective as the more familiar mineral slurries in the development of load transfer. No slurry, however, produced the magnitude of perimeter load transfer that was developed on model drilled shafts constructed by inserting casing ahead of the drill in medium‐dense, saturated sand and withdrawing the casing as the simulated concrete was placed.

Hydration behaviour of simulated high-performance concrete pastes using synchrotron energy-dispersive diffraction

Synchrotron radiation energy-dispersive diffraction has been used for the first time to evaluate the hydration behaviour of simulated high-performance concrete (hpc) pastes. The hydration of the alite and ferrite and formation of Ca(OH)2 were monitored as a function of the initial H2O content. A significant and stable ettringite (AFt) content was found in all pastes, perhaps close to 6·5% in certain mixes. The morphology of AFt depended on the initial mix design. Monosulphate (AFm) was detected, the amount present increasing with increasing initial H2O content. The technique has the advantage of monitoring the overall hydration behaviour of the paste while it is still ‘wet’. By such an approach the less stable phases such as AFt and AFm can be detected and characterized. These are of potential importance in relation to the long-term durability of hpc.

Projectile impact damage analysis

Small, flat-fronted cylindrical steel projectiles haw been fired at normal obliquity against simulated concrete and steel plate targets. Deformation measurements from these firings are compared with nonlinear finite element analysis results. For firings against simulated concrete, good agreement between analysis and experiment is obtained when an initial transient is added to a quasi-steady-state penetration theory. For firings against steel plates, large element distortions result in computational difficulties.