Role In Cracking Research Articles

The Role of Cracks in Chloride-Induced Corrosion of Carbon Steel in Concrete—Review

The majority of works in the field of chloride-indued corrosion of steel in concrete are focused on the cracks formed by the corrosion products. However, the number of studies on the influence of cracks (pre-cracked concrete) on corrosion is limited. Cracks create preferential/free paths for the penetration of chlorides, water, and oxygen into concrete; thus, the presence of cracks in concrete can intensify chloride-induced corrosion of steel reinforcement. This paper presents a review of the effects of cracking on the corrosion of steel in concrete. It was widely reported in the reviewed papers that cracks have a negative impact on concrete durability. They influence the chloride penetration and the chloride-induced corrosion of reinforcement in terms of the initiation and propagation stages. This influence is a complex function of many factors, including mix design, exposure conditions, crack frequency, crack orientation, crack width, and cover depth. Although there is a general agreement on the effects of cracks on the initiation of corrosion, the role of cracks and their widths on the propagation of corrosion in the long term is still under debate.

Models of co-evolution of structural elements of building composites

It is shown that construction material changes its properties as a result of operational loads action. There are situations when construction leaves its working state with satisfactory material characteristics. This is due to the process of formation and development of cracks as structural elements. The article proposes to analyze history of the development process, which makes it possible to study mechanisms of its flow and to determine factors of process control. The analysis of the studies carried out on the effect of prescriptional and technological factors on the properties of materials and products, the phenomena of self-organization and the role of cracks in materials and products showed that the emergence of critical events cannot be foreseen when assessing properties accepted by averaged characteristics. The construction is considered to be a complex self-organizing system. This determined the work aim: to justify the choice of dynamic models, allowing to determine the structure elements, interaction of which ensures functional state of the structure. The qualitative method of verbal description of the structure of systems with the use of cognitive approaches was laid in basis of adopted methodology. Conservative, metastable and active elements are distinguished in the construction-system. It is emphasized that the active history of the system is determined by active elements, to which cracks refer to. Cracks are considered as some necessary structural elements, present at all scale levels. It is shown that the formation of cracks-systems, treated as parasitic systems, terminates the end of construction-system development and the beginning of parasite system development. Completion of crack-system life cycle removes the construction-system from its working state. To get constructions with a given set of structural elements, a creative community of materials and designers is needed, which will create a common terminology dictionary for both specializations.

Fracture analysis of plates and shells using FEM and XFEM

Fracture mechanics is the field of mechanics concerned with the study of propagation of cracks in materials and recognizes the role of cracks in the performance of structures leading to damage tolerant design approach. Cracks or crack like defects is observed in many structures which may lead to their catastrophic failure under a tensile stress field. In this paper, the structural integrity of plates with surface and embedded cracks is investigated using ABAQUS FEA code and the fracture parameter—stress intensity factor (SIF)—is evaluated. Convergence study is conducted to arrive at the optimum mesh parameters using both the conventional finite element method and the extended finite element method (XFEM). The FE model is validated by comparing FE results with published numerical solutions. The effect of varying crack depth and location on SIF is studied. The FE results matched well with the closed-form solutions and experimental results. It is observed that the crack depth and its location have significant influence on SIF. The conventional finite element method requires a mesh that conforms to the crack geometry, typically with a very detailed, focused mesh at the crack tip. The crack front must be defined explicitly and must specify the virtual crack extension direction in addition to matching the mesh to the cracked geometry. XFEM gives better result for cylindrical shells without mesh refinement around crack tip.

Low-temperature alkaline pyrolysis of sewage sludge for enhanced H2 production with in-situ carbon capture

Pyrolysis has been recognized as one of the promising thermal technologies on the account of satisfying the principles of waste reduction, resource recovery, and detoxification. This study proposed the alkaline thermal treatment of sewage sludge of enhanced H2 production and in-situ carbon capture. The maximum H2 yield of ∼10 mmol g−1 biomass was achieved at 1:3 sludge: NaOH ratio, 10 °C min−1 heating rate, and 500 °C temperature, with the H2 purity of 79.1% in the gaseous products. The presence of NaOH significantly promoted H2 production and substantially suppressed CO and CO2. Temperature also played an important role in cracking of CC and CH bonds and gave H2-rich gas (H2 formation rate 0.34 mmol min−1 g−1) with a high yield of 10.3 mmol g−1 at 500 °C. The solid residue analysis via XRD verified the existence of Na2CO3 in the solid, implying the inherent carbon management potential of the NaOH during the sludge pyrolysis process.

Synthesis and characterization of gaseous fuel from Jatropha oil through catalytic reactor and its performance in DI diesel engine

Increase in fossil fuel depletion and increase in fuel price forced the researchers to find an alternate source to petro fuel. The scope of this research article is to give an insight into the synthesis and utilization of catalytically cracked bio-oil in a DI diesel engine. The catalyst selection and its characterization are playing a vital role in cracking of bio-oil. The aluminum oxide catalyst is used in this study, because of its availability and cost. The properties of the catalyst were analyzed before and after cracking using SEM, EDAX and XRD. The catalyst pellets are placed in a fixed bed catalytic reactor where the jatropha oil is introduced to get the cracked gaseous fuel. The cracked fuel was tested with FTIR, TGA and DSC for finding its properties. From the results, properties of the cracked fuel are nearly matched with diesel fuel. The catalytically cracked jatropha biofuel (CCJB) is fumigated into the inlet manifold in the proportion of 10, 20 and 30% in specific fuel consumption of the diesel engine. The maximum brake thermal efficiency was observed for 30% of fumigated CCJB compared with diesel fuel. The exhaust emissions such as CO and smoke were considerably reduced when compared with diesel fuel. A significant increase in NOx emission than diesel can be seen for all operating conditions.

Hydrogeodynamic processes in carbonate rocks. Part II. Karst and its influence on geological environment

Formulation of the problem. Chemical activity of groundwater in the natural geological environment is caused by chemical reactions in a complex physical-chemical system "rock-water-gas". Leaching and dissolution play the leading role in carbonate rocks. These processes can best be described by the laws of chemical thermodynamics, which can justify the existence of the relationship between the reactions themselves, and determine the amount of energy consumed by them. This enables to establish not only direction of physical and chemical transformations but also their results in certain geological, hydrogeological and geochemical conditions. The consequences of chemical activity of groundwater can be the following: 1) physical and chemical destruction and formation of minerals and rocks; 2) migration and concentration of chemical elements and their compounds in solutions; 3) formation of groundwater chemical composition.Presentation of main material. Sorption and ion exchange processes play an important role in carbonate water systems. Sorption is the process of selective absorption of liquid and gaseous substances by solid phase and contributes to penetration of various chemical composition in water solutions into rocks.Depending on the depth of karst cavities, karst is divided into young and ancient according to the time of formation. According to the development of covering sediments on the rocks, karst is distinguished by open (without soil-vegetation cover) and closed (blocked by younger formations). Formation and development of closed karst is almost exclusively due to the action of groundwater located in the aquifer, in the rocks where there is karst formation. Instead, open karst is formed with the participation of both underground and surface infiltration waters.Anthropogenic (man-made) factors play an important role in geochemical processes in the "rock-water" system in urban and industrial conditions. They can manifest both through physical and chemical destruction of rocks, on which buildings and structures were constructed, and due to artificial groundwater contamination up to the change of their geochemical type.Conclusions. Karst is a geodynamic consequence of geological activity of groundwater, manifested in dissolution and removal of rocks with the formation of a liquid runoff. For the karst to develop, the following basic conditions are required: a) physical - significant thickness of carbonate rocks and low groundwater level; b) chemical - alkalinity of underground waters of bicarbonate-sodium composition and presence of soluble and free carbon dioxide in them.Hydrogeological peculiarities of karst development on the territory of research are based on the role of cracks and cavities in the filtration of groundwater of different formations and ascending unloading of aggressive to carbonates water from deep horizons and carbon dioxide, as well as unfavorable physical-chemical conditions of marl and chalk rocks dissolution.

Study on compressive strength of self compacting mortar cubes under normal & electric oven curing methods

In the majority of civil engineering applications, the basic building blocks were the masonry units. Those masonry units were developed as a monolithic structure by plastering process with the help of binding agents namely mud, lime, cement and their combinations. In recent advancements, the mortar study plays an important role in crack repairs, structural rehabilitation, retrofitting, pointing and plastering operations. The rheology of mortar includes flowable, passing and filling properties which were analogous with the behaviour of self compacting concrete. In self compacting (SC) mortar cubes, the cement was replaced by mineral admixtures namely silica fume (SF) from 5% to 20% (with an increment of 5%), metakaolin (MK) from 10% to 30% (with an increment of 10%) and ground granulated blast furnace slag (GGBS) from 25% to 75% (with an increment of 25%). The ratio between cement and fine aggregate was kept constant as 1: 2 for all normal and self compacting mortar mixes. The accelerated curing namely electric oven curing with the differential temperature of 128°C for the period of 4 hours was adopted. It was found that the compressive strength obtained from the normal and electric oven method of curing was higher for self compacting mortar cubes than normal mortar cube. The cement replacement by 15% SF, 20% MK and 25%GGBS obtained higher strength under both curing conditions.

Biocomposite Fiber-Matrix Treatments that Enhance In-Service Performance Can Also Accelerate End-of-Life Fragmentation and Anaerobic Biodegradation to Methane

Biodegradable resins can enhance the environmental sustainability of wood-plastic composites (WPCs) by enabling methane (CH $$_4$$ ) recovery via anaerobic digestion (AD). An under appreciated step in biocomposite AD is the role of cracking and fragmentation due to moisture uptake by the wood fiber (WF) fraction. Here, we use batch microcosms to simulate AD at end-of-life and to assess the effects of fiber-matrix treatments used to retard in-service moisture uptake. The composites evaluated were injection molded poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) with WF (0, 20%) using two fiber-matrix compatibilization treatments: (1) hydrophobic silane treatment of the wood fiber and (2) grafting of hydrophilic maleic anhydride groups to the PHBV matrix. Both treatments accelerated rates of mass loss and CH $$_4$$ production by a factor of 1.2–2.3 compared to neat PHBV. The fragmentation rate, as measured by mass loss, increased significantly for treated samples compared to untreated samples. A ranking of test samples from lowest to highest rates of mass loss gave the following sequence: neat PHBV $$\approx$$ maleated PHBV < PHBV plus untreated WF < maleated PHBV plus untreated WF < PHBV plus silane-treated WF. Compared to the untreated samples, maleic anhydride treatment increased the mass loss rate by 30%, and silane treatment increased the mass loss rate by 92%. Onset of cracking in silane-treated composites was observed at 2 weeks (using X-ray micro-computed tomography). At the same time, solid mass loss and CH $$_4$$ production peaked, implicating cracking and physical disintegration as the rate-limiting step for accelerated anaerobic degradation. When modified to account for bioplastic matrix degradation, a previously derived moisture-induced damage model could predict the onset of composite fragmentation at end-of-life. These results are significant for design of bio-WPCs and demonstrate that treatments designed to improve in-service performance can also improve end-of-life options.

Experimental model of the role of cracks in the mechanism of explosive eruption of St. Helens-80

A unique mini model of explosive volcano eruption through a formed system of cracks is developed. The process of crack formation and development is simulated by electric explosion of a conductor in a plate of optically transparent organic glass submerged into water. The explosion of a wire aligned with a through hole in the plate generates shock-wave loading along the plate and forms cracks. The fundamental role of high velocity flow in crack wedging by a high power hydrodynamic flow of a pulsating explosion cavity has been demonstrated.

The role of cracks in the crystal nucleation process of amorphous griseofulvin

In this paper we have investigated the recrystallization properties of amorphous griseofulvin obtained by melt quenching. We have shown that the maximum nucleation rates of crystalline forms 2 and 3 are located around the glass transition temperature. However, it appears that these nucleation rates are strongly increased by the sudden formation of cracks into the amorphous solid during deep quenches below Tg. Suitable thermal treatments have revealed that these cracks strongly promote the development of crystalline nuclei, but do not produce the nuclei themselves. The investigations have been performed by differential scanning calorimetry and by thermal microscopy.

Residual stress distribution along interfaces in thermal barrier coating system under thermal cycles

The residual interfacial stress plays an important role in crack initiating and propagating along the interface, which could result in delamination failure of the thermal barrier coatings (TBCs). In this study, the finite element model of air plasma spraying(APS) TBCs was established to assess the level and distribution of residual stress along top coat(TC)/thermally grown oxide (TGO) and bond coat (BC)/TGO interfaces under thermal cycles. Instead of using vertical stress S22 in global coordinate system, the normal and tangential components in the local system along the interfaces, transformed from stress components S11, S22, and S12 in the global one, were used to evaluate the way the cracks initiate and propagate along the interfaces. Firstly, the effect of the number of thermal cycles on residual stress was investigated. It was found that, for the TBCs model without TGO growth and crack, the impact of the number of thermal cycles on the stress is very insignificant and could be ignored. So the present study only chose to focus on the first thermal cycle. Then the influence of the TGO thickness and the interface amplitude on the normal and tangential residual stresses for both homogeneous and inhomogeneous temperature fields was explored. The results show that the TGO thickness, interface amplitude and temperature field affect the residual stress level and distribution, leading to different fracture mechanisms along TC/TGO and TGO/BC interfaces. Finally, the difference between the vertical stress in the global coordinate system and the normal stress in the local coordinate system was studied. Compared with vertical stress S22, the stress components normal and tangential to the TC/TGO and TGO/BC interfaces are more appropriate to describing the stress distribution along the interfaces and predicting the propensity of crack initiating and propagating along the interfaces.

Stress intensity factors of double edge cracks in large groove plates under mode I tension

The solutions of stress intensity factors (SIFs) of double edge cracks in large groove plates are investigated. The plate is assumed to fulfil the plain strain condition and it is axially stressed. According to the literature, the SIFs of the cracks in circular notches are available. However, the roles of cracks in large groove are difficult to obtain. Therefore, different grooves and crack geometries are modelled numerically using the ANSYS finite element software. The present model is first validated using an existing model of double edge cracks without notches and it is found that both models are in close agreement. The large grooves are then introduced and the cracks are positioned in the mid-point. It is found numerically that the SIFs are strongly affected by the relative crack depth and the groove geometries. It is also found that the large groove is capable of reducing the SIFs in comparison with the circular notched due to lower stress concentration factors.

Analysis of Cracking in a Reinforced Concrete Beam

Numerical models describing crack formation and growth in reinforced concrete give reasonably good estimates of the bearing capacity and durability of an element of the structure without expensive full-scale tests. In this paper, a finite-element model is proposed to study the failure of a rectangular reinforced concrete beam subjected to four-point bending. The results of quasi-static simulation and the data obtained by taking into account inertial forces are compared. The feasibility of taking into account inertial forces is justified by assessing the contribution from kinetic energy (above 30%) at the instant of crack formation to the total mechanical energy of the system. Comparison of the experimentally obtained and calculated crack patterns is performed. It is shown that the mechanism of debonding between the reinforcement and concrete plays a key role in cracking.

Effects of solvent addition and ultrasound waves on viscosity reduction of residue fuel oil

In this work, the influence of temperature, solvent concentration and ultrasonic irradiation time on viscosity reduction of residue fuel oil (RFO) are studied. The main feature of this research is using ultrasonic irradiation at low frequency of 24kHz and power of 280W, for viscosity reduction and quality enhancement of RFO. Kinematic viscosity of RFO was found to decrease from 4940 cSt to 2679 cSt due to application of ultrasonic irradiation for 5min at initial temperature of 20°C. Results showed that combination of ultrasonic irradiation with solvent led to intensified decrease of viscosity and API gravity promotion. The maximum reduction of viscosity (at 133cSt) occurred in ultrasonic irradiation time of 5min, temperature of 50°C and acetonitrile loading of 5% by volume. API gravity, distillation and FT-IR analyses revealed that ultrasonic waves have an effective role in cracking and lightening of the examined heavy fuel oil. The measured results including 336 data points of eighty-four samples were analyzed by the feed-forward back propagation of artificial neural network (ANN). The relative importance percent of input variables was calculated and it was found that ultrasonic irradiation time and acetonitrile concentration has maximum and minimum relative importance in viscosity reduction, respectively.

Patterns of soil water repellency change with wetting and drying: the influence of cracks, roots and drainage conditions

AbstractLaboratory experiments were used to investigate the influence of simulated cracks and roots on soil water repellency (SWR) dynamics with and without basal drainage impedance in wetting–drying cycles. Observations and measurements were taken following water application equivalent to 9.2‐mm rainfall and then periodically during 80 h of drying. In total, 180 experiments were carried out using 60 samples of three homogeneous, reconstituted soils with different organic matter contents and textures, but of similar initial severity of SWR [18% molarity of an ethanol droplet (MED)]. Water flowing down the cracks and roots left the soil matrix largely dry and water repellent except for vertical zones adjacent to them and a shallow surface layer. A hydrophilic shallow basal layer was produced in experiments where basal drainage was impeded. During drying, changes in SWR were largely confined to the zones that had been wetted. Soil that had remained dry retained the initial severity of SWR, while wetted soil re‐established either the same or slightly lower severity of SWR. In organic‐rich soil, the scale of recovery to pre‐wetting MED levels was much higher, perhaps associated with temporarily raised levels (up to 36% MED) of SWR recorded during drying of these soils. With all three soils, the re‐establishment of the original SWR level was less widespread for surface than subsurface soil and with impeded than unimpeded basal drainage.Key findings are that as follows: (1) with unimpeded basal drainage, the soils remained at pre‐wetting repellency levels except for a wettable thin surface layer and zones close to roots and cracks, (2) basal drainage impedance produced hydrophilic basal and surface layers, (3) thorough wetting delayed a return to water‐repellent conditions on drying, and (4) temporarily enhanced SWR occurred in organic‐rich soils at intermediate moisture levels during drying. Hydrological implications are discussed, and the roles of cracks and roots are placed into context with other influences on preferential flow and SWR under field conditions. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Experimental and Theoretical Investigation on Three α,ω-Diarylalkane Pyrolysis

Pyrolysis of three α,ω-diarylalkane compounds (biphenyl, diphenylmethane, and bibenzyl) was performed below 30 Pa between 573 and 1473 K. Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry was used to detect the reactants, radicals, and products. The relative concentration profiles of the pyrolysis species were estimated by a semi-quantitative analysis method. Experimental results indicated that the length of the C–C bridge bond plays an influential role in cracking of corresponding bonds in the α,ω-diarylalkane pyrolysis process. The C–H bond scission is dominant in pyrolysis of diphenylmethane at low temperatures, while the C–C bond scission competes with it when the temperature increases. The symmetrical homolysis of bibenzyl is a dominant reaction at low temperatures and will compete with the unsymmertrical cleavage reaction with increase of the temperature. In addition, the formation mechanism of fluorene, which plays a significant role in polycyclic aromatic hydrocarbon generation, during diphenylmethane pyrolysis was discussed by combining the experimental observation with the theoretical calculation. The theoretical calculation supported these experimental results at the mPW2PLYP level.

Corrosion fatigue of a magnesium alloy in modified simulated body fluid

For magnesium (Mg) alloys to be used as temporary biodegradable implants it is essential to establish their resistance to body fluid-assisted cracking. In this paper the fatigue behaviour of a common magnesium alloy, AZ91D, is studied in air and in modified simulated body fluid (m-SBF), and the effect of different electrochemical conditions on corrosion fatigue life is investigated. The alloy was found to be susceptible to corrosion fatigue. Results suggest inclusions and corrosion pits to be the crack initiation sites, and hydrogen embrittlement to play a dominant role in cracking of AZ91D Mg alloy in m-SBF.

Microtubule dynamic instability: the role of cracks between protofilaments

Microtubules (MTs) are cytoplasmic protein polymers that are essential for fundamental cellular processes including the maintenance of cell shape, organelle transport and formation of the mitotic spindle. Microtubule dynamic instability is critical for these processes, but it remains poorly understood, in part because the relationship between the structure of the MT tip and the growth/depolymerization transitions is enigmatic. In previous work, we used computational models of dynamic instability to provide evidence that cracks (laterally unbonded regions) between protofilaments play a key role in the regulation of dynamic instability. Here we use computational models to investigate the connection between cracks and dynamic instability in more detail. Our work indicates that while cracks contribute to dynamic instability in a fundamental way, it is not the depth of the cracks per se that governs MT dynamic instability. Instead, what matters more is whether the cracks terminate in GTP-rich or GDP-rich regions of the MT. Based on these observations, we suggest that a functional "GTP cap" (i.e., one capable of promoting MT growth) is one where the cracks terminate in pairs of GTP-bound subunits, and that the likelihood of catastrophe rises significantly with the fraction of crack-terminating subunits that contain GDP. In addition to helping clarify the mechanism of dynamic instability, this idea could also explain how MT stabilizers work: proteins that introduce lateral cross-links between protofilaments would produce islands of GDP-bound tubulin that mimic GTP-rich regions in having strong lateral bonds, thus reducing crack propagation, suppressing catastrophe and promoting rescue.

Stress and Strain Distributions During Compressive Deformation of Titanium Alloy Affected by Microstructure

In the research of the microstructural influence on dynamic compression, an assumption that the α and the β phases in titanium alloys were linearly strengthened was proposed, and a two-dimensional model using ANSYS (ANSYS, Inc., Canonsburg, PA) focusing on the role of microgeometrical structure was developed. By comparing the stress and strain distributions of different microstructures, the roles of cracks and phase boundaries in titanium compression were studied.

Water repellent surface impregnation for extension of service life of reinforced concrete structures in marine environments: The role of cracks

Abstract The enhancement of long-term durability of marine structures is a matter of interest to many researchers. The study presented in this paper examines the effectiveness of a water reducer and chloride barrier surface impregnation of the concrete cover of reinforced concrete (RC) structures, exposed to a marine environment. Specific focuses is on how surface cracks created (1) before impregnation and (2) after impregnation, affect the effectiveness of the surface treatment. The experiments are conducted in an environment which is as close as possible to the real humid subtropical marine environment. A series of reinforced concrete (RC) prisms and concrete cylinders, each treated with various commercial surface impregnation agents, were exposed to cyclic sea water shower under an outdoor environment to accelerate the dry/wet cycles for 1 year. Six types of surface impregnation agents, including four types of silane-based water repellent agents and two types of sodium silicate-based pore blockers (water–glass) were applied. Three types of RC prisms were prepared to simulate the different cracking possibilities, which may occur in surface impregnated concrete structures, during their service life. No cracks were introduced in the first prism group, while cracks were introduced before and after surface impregnation, in the second and third groups, respectively. The time-dependent water absorption of all specimens was monitored during exposure to the dry/wet cycles. Finally the specimens were split open to measure the penetration depths of the surface impregnation agents and the chloride penetration profiles. The areas with corrosion evident in the steel reinforcement in the RC prisms were also measured. Sodium silicate-based pore blockers were found to be inefficient in preventing chloride penetration of concrete under simulated marine exposures. The long-term efficiency of water repellent agents used for surface impregnation was found to be highly dependent on the type of agent and whether impregnation was carried out before or after crack formation.