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Screw loosening in spine surgery is a clinical complication in patients with poor bone quality. Pedicle screws are subjected to bending moments and axial loads that may cause toggling during daily movements of spine. The purpose of this study was to assess the previous studies related to toggling effect on pullout performance of pedicle screws by surveying the whole literature and to provide some discussion for new studies about pullout performance of pedicle screws after toggling. The search was performed by combining terms of pedicle screw, toggling, screw loosening, fatigue, cyclic loading, and pullout. The retrieved articles dealing with determined terms and also their references were reviewed. Some of these articles were eliminated after review process. Toggling was determined to be crucial for the stabilization performance of pedicle screw because the loosening mechanism of screws was affected directly by cyclic loading. The toggling or cyclic loading affected the holding capacity of pedicle screws negatively, and the possibility of loosening or failure problem for pedicle screws increased with cyclic loading magnitude. Loading conditions, screw properties, test medium, level of spinal region, and cement usage were determined by many researchers as the most important parameters affecting the toggling performance as well as the pullout strength of pedicle screws. The pullout strength of pedicle screws generally decreased with cyclic loading. The parameters of cyclic loading were fairly important for pullout performance of pedicle screws. Screw properties and cement augmentation had critical effects on the stability of screws under cyclic loading, as well. [ABSTRACT FROM AUTHOR]

Sustained casing pressure (SCP) in shale gas wells has been of growing interest in the industry, owing to its effects on the safety and efficiency of shale gas production. In terms of the current literature, this issue should be attributed to the elastic failure of the cement sheath under high inner pressure during the hydraulic fracturing process. However, the current calculation of cement sheath stress neglects the influence of the drilling and cementing processes and the dramatic temperature change of a well system during the hydraulic fracturing process. In this work, a novel elastic–plastic model incorporating the effects of drilling, cementing, and dramatic temperature change of the well system during the hydraulic fracturing is established to describe the stress of cement sheath. The failure mechanism of cement sheath is fully revealed. The proposed model for cement sheath integrity is successfully verified through its excellent agreement with field observations from the Fuling shale gas field, China. In addition, based on the proposed model, the impacts of the geometrical and material parameters of casing and cement are studied and analyzed. The results illustrate that the tensile failure more likely occurs at the inner face of the cement sheath, which turns out to be more severe as the true vertical depth decreases. The density of cement slurry is in favor of decreasing the tensile stress in the cement sheath. On the contrary, the thicker cement sheath would increase the risk of tensile failure in the cement sheath, which would lead to serious SCP. The extremely low elastic modulus and thermal conductivity of the cement sheath are beneficial for maintaining its integrity, which, unfortunately, is difficult to achieve in actual operations. • A new elastic-plastic model for cement sheath integrity in shale gas wells is raised. • The effects of drilling, cementing and temperature change are considered. • The reliability of new model is successfully verified through field observations. • The cement slurry density is in favor of decreasing tensile stress in cement sheath. • The cement sheath thickness has negative effect on integrity of cement sheath. [ABSTRACT FROM AUTHOR]

Highlights • We studied hysteresis in superabsorbent polymer swelling behavior. • This was studied to realize rapid crack self-sealing. • Swelling behavior varied with swelling/deswelling under wet/dry cyclic conditions. • Reduction in flow rates measured every cycle was compared with predicted values. • The polymer repeatedly revealed rapid crack self-sealing performance. Abstract In this study, the hysteresis in the swelling behavior of spherical superabsorbent polymers (SAPs) on rapid self-sealing of cracks in cementitious materials under wet/dry cycles was evaluated experimentally. The results from an experiment using the tea-bag method showed that the absorption capacity of SAPs was lower in a cement pore solution compared to that in distilled water. As the SAP particles repeatedly swelled/deswelled, their absorption capacity increased until 3–cycle and then gradually decreased. The water-flow test results showed that the mean reduction ratios in water runoff through cracks for the cracked specimens containing spherical SAP particles were 0.278 and 0.367 for SAP dosages of 0.5% and 1.0% in 1–cycle, respectively. As the wet/dry cycles were repeated, however, the ratios gradually increased and converged to about 1.75 times and 1.99 times those of 1–cycle, respectively. A non-linear regression analysis was performed on the measured reduction ratios in flow rates per cycle. The modification factors for the volume fraction of a crack sealed by the swollen spherical SAP particles gradually increased and then converged with the repeated wet/dry cycles, and they were approximately 1.0259–1.0599 and 1.0657–1.0943 for the S–0.5 and S–1.0 specimens after 4–cycle, respectively. In conclusion, the experimental results indicated that SAPs can repeatedly exhibit rapid crack self-sealing performance in cementitious materials. [ABSTRACT FROM AUTHOR]

Abstract This work proposes a method for numerically investigating the fracture mechanism of cement paste at the microscale based on X-ray computed tomography and nanoindentation. For this purpose, greyscale level based digital microstructure was generated by X-ray microcomputed tomography with a resolution of 2 μm/voxel length. In addition, statistics based micromechanical properties (i. e. Young's modulus and hardness) were derived from the grid nanoindentation test which was set to have an interaction volume the same as the resolution of the digital microstructure. A linear relationship between the two probability density functions of greyscale level and local Young's modulus was assumed and verified by the two-sample Kolmogorov-Smirnov (K S) statistic. Based on this assumption, the fracture and deformation of a digital cubic volume with a dimension of 100 μm under uniaxial tension was simulated using a lattice fracture model. In addition, the influence of heterogeneity on fracture response was studied. Furthermore, the proposed method was compared with the results obtained from a traditional approach used previously by the authors in which discrete phases (capillary pore, anhydrous cement clinker, outer and inner hydration products) were considered. The two methods show similar crack patterns and stress-strain responses. The proposed method is regarded more promising as it captures also the gradient of material properties (within the discrete phases) in the cement paste. [ABSTRACT FROM AUTHOR]

Abstract This paper concerns understanding the influence of drying induced microcracking on water absorption by capillary suction. Paste, mortar and concrete samples with different binder type, w/b ratio, thickness, aggregate size, and curing age were tested. Samples were subjected to gentle stepwise drying at 21 °C/93% → 55% RH, or drying at 21 °C/55% RH, 21 °C/0% RH, 50 °C or 105 °C to induce microcracks <100 μm wide. Results show that the presence of microcracks causes cumulative water absorption to scale non-linearly with t. The observed relationship is approximately sigmoidal/ S -shaped, with the position of inflection point related to microcracking and the degree of non-linearity increasing with drying severity. A simple fluorescence imaging method was developed to enable continuous monitoring of the advancing wetting front and to study the effect of microcracks. Quantitative image analysis of water penetration produced results consistent with gravimetric measurements. [ABSTRACT FROM AUTHOR]

Abstract In this study, a continuum poromechanics approach is presented to model the plastic shrinkage cracking of fresh cementitious materials. The boundary conditions are according to the modified ASTM C1579–13 standard for mortars. The restrained deformations are linked to the restraint stresses according to the Cauchy-Navier equations of elasticity, assuming an incremental stress-strain relationship. The Bresler-Pister and Rankine failure criteria are utilized to model failure. The material parameters are adapted according to the Drucker-Prager and Griffith criteria. The crack initiation and propagation is verified experimentally by X-ray radiography. Eventually, the cracking mechanism is discussed and a safe capillary pressure limit is proposed. It is found that capillary pressure stiffening occurring before air entry, when deformations take place in the saturated state, is the predominant cause of plastic shrinkage cracking in the drying state. [ABSTRACT FROM AUTHOR]

Abstract Cracking occurrence due to shrinkage related effects is a widely recognised issue which is frequently evaluated with the shrinkage restraining ring test. This paper provides a state-of-the-art review of the ring test method, which has been used for the last four decades. The last review on such matter was conducted only in early 2000s; however, a significant amount of studies has been conducted since then and considerable advancements or modifications in this testing method have taken place over the last decade. Studies on the traditional ring test, i.e. a circular concrete ring cast around a steel ring, are identified and the history, tendencies, practices and quantitative methods are analysed thoroughly. Furthermore, any modifications/advancements in the testing method with respect to their purpose, applications and capabilities based on current knowledge, are addressed. Finally, an insight on the challenges that the developers of testing methods for restrained shrinkage are faced with is given together with perspectives for their future potential improvement. [ABSTRACT FROM AUTHOR]

Highlights • The surface structure of the cement paste thermal cracks was evaluated. • The influence of the sample shape and size to the cracks geometry was investigated. • As the sample size increases, the area of clusters also increases. • Cement paste subjected to 250 °C is very chemically and thermally stable. Abstract The article evaluates the structure of thermal cracks created on the surface of cement paste. The samples were loaded with an elevated temperature of 250 °C. Due to the volumetric deformations and increasing water vapor pressure, thermal cracks appeared on the material's surface. The analysis was performed using the computer image analysis; three stereological parameters were proposed for the description of the cracks' structure: the cluster average area (A -), the cluster average perimeter (L -), and the crack average width (I -). The aim of the research was to determine how the geometry of the thermal cracks changes in a situation in which the shape and size of the sample changes. The tests were carried out in two variants: in the first the sample's width was variable, and in the second – its height. Using the least squares method (LSM), the dependencies that occur between the sample's size and the geometry of the cracks were developed. Considering cement paste as a highly concentrated dispersion system, an attempt was made to identify factors shaping the cracks' structure due to the change in the size of the sample. The considerations were supplemented with microstructural investigations using a scanning electron microscope (SEM) and a X-ray microanalyzer (EDS). The cluster structures were analyzed at a lower level of observation; there were no significant differences in the composition of cement paste, which confirmed its high chemical and thermal stability in the studied temperature range. [ABSTRACT FROM AUTHOR]

Abstract Well-cementing (cementation) is an influential stage of a wellbore completion, as the cement sheath is responsible for providing a complete zonal isolation. Therefore, it is of utmost importance to understand the cement mechanical failure mechanisms since well cement failure and interfacial debonding between the cement and casing and cement and rock formations can lead to a barrier failure. During the wellbore lifetime, a cement sheath is subjected to pressure loading variations. This paper demonstrates the results of an experimental-numerical study to investigate the cement sheath integrity after being subjected an enhanced pressure. A constitutive model specifically formulated for the modelling of quasi-brittle materials is applied to the investigation of cement sheath integrity, incorporating both compression and tensile damage mechanisms. Laboratory experiments are carried out to obtain strength properties of cement class G followed by calibration of the model parameters based on the obtained experimental results. A three-dimensional finite element framework employing the constitutive model for cement sheath and a surface-based cohesive behaviour for the interfaces is developed for integrity investigations. The effects of different orientations of in-situ stresses, different stiffness's of surrounding rock, and the eccentricity of the casing within the wellbore on the integrity of the cement and interfaces are investigated. The significance of cement sheath centralisation and elevated risk of cement mechanical failure caused by wellbore operations in anisotropic fields with soft rocks formation were highlighted. Furthermore, the relatively high magnitude of tensile damage (cracking index) within the cement sheath confirms the importance of tensile properties to be incorporated into the constitutive modelling. Highlights • A constitutive model considering the difference in tensile and compression response of cementitious material (quasi-brittle) was employed. • Experimental studies were carried out to obtain cement class G properties along with calibration of the constitutive model parameters. • The cement sheath centralisation is emphasised to prevent cement sheath mechanical failure. • The destructive effect of in-situ stress anisotropy in fields with soft rocks is shown by the crushing and cracking indices. • The significance of tensile damage is shown to be incorporated into the constitutive modelling to prevent cracking and increasing the cement sheath permeability. [ABSTRACT FROM AUTHOR]

Highlights • Current pavement designs based on regular BBR grades fail to provide control of cold temperature cracking. • It is imperative to test extracted and recovered asphalt cement for specification grading. • Extended BBR grades for 3–5 year old pavements showed deficits ranging from 3 °C to 17.3 °C. • Extended BBR grades correlate well with limiting phase angle temperatures. Abstract Binder extracted and recovered from pavement core samples at two different locations from 18 contracts showed small differences within contracts, well within the minor borderline acceptance criteria. Serious discrepancies were found between original tank sampled asphalt binder and material recovered from pavement cores. Regular BBR grades for recovered materials were on average 2.7 °C in deficit, which is considered high for 3–5 years of service. EBBR grades were on average 7.6 °C in deficit (range 3 °C to 17.3 °C). Equilibrium grades, after 72 h of conditioning, correlated well with temperatures where the phase angle reached 30° after minimal conditioning, suggesting that a limit on phase angle may provide a practical quality assurance measure. [ABSTRACT FROM AUTHOR]

Highlights • A two-dimensional approach to evaluate distress in cementitious systems due to sulphate attack is described. • The effect of embedded aggregate on the outcomes from sulphate attack is illustrated. • Effect of curing conditions and duration of exposure to sulphate attack are shown. • Crack growth over time is predicted using the measured sulphate ingress and constitutional properties. Abstract This paper describes experimental approaches to evaluate two-dimensional sulphate attack behaviour inside cement-based systems. First, the sulphate content at various depths was measured using titration. This was followed by mechanical evaluation on cylindrical samples to establish the associated stress-strain response. Three types of binder namely, Portland cement conforming to CSA Types GU and HS and, a 30:70 blend of fly ash and Portland cement Type GU, were employed. The specimens were immersed in a sulphate rich solution for up to 12 weeks. The results show that all specimens suffered more from two-dimensional sulphate attack as compared to that seen with exposure in one dimension. Also, the positive role played by an embedded aggregate emerged in that it was seen to impede the transport of sulphate ions inside the cement-based system. As well, self-healing under prolonged exposure was observed, which was more significant with both binders that contained Portland cement Type GU. [ABSTRACT FROM AUTHOR]

Highlights • Formation of four main zones within the cement matrix. • The residence time and the aperture size determine cracks’ behaviour. • A cement matrix is damaged more than its surrounding rock. • Self-sealing behaviour is likely, when a well is properly cemented. Abstract The purpose of this study is to examine previous works undertaken that characterise the cement alteration due to its exposure to CO 2 -bearing fluids attacking on the interfaces of cement-rock and cement-casing, or through cement cracks, and the cement matrix itself. Numerous studies have reported carbonation of well cements. The majority of studies reported self-healing behaviour of cements cracks observed under general CO 2 storage conditions. In addition, defective cement matrix and bonding between cement and casing were also found to be potential causes for leakage pathways. Albeit, severe conditions, such as high acidity degree of brine and high flow velocity, may negatively affect the self-healing behaviour of the cement. [ABSTRACT FROM AUTHOR]

This study investigates the self-healing performance of cement-based materials using the water absorption test. The experimental method was performed in compliance with ASTM C 1585 on paste specimens mixed with research cement (RC), ground granulated blast-furnace slag (GGBS), anhydrite, and calcium sulfo-aluminate (CSA) expansion agents as inorganic binders. The water flow test was also performed for comparison and the self-healing products were analyzed. The results showed that the proposed method using the water absorption test could effectively evaluate the self-healing performance and that the mixture with GGBS and CSA expansion agents displayed the best performance. The temporal variation in water absorption rates was used to analyze the effects of primary self-healing (due to the further hydration of unreacted materials) and secondary self-healing (due to ion diffusion). The analysis provided results similar to those of the water absorption test. A comparison with an experiment on self-healing products confirmed that the amount of generated calcite had a larger effect on self-healing than the total amount of self-healing products. [ABSTRACT FROM AUTHOR]

As concrete freezes and thaws cracks may develop. These cracks can provide a path for water and ionic species to penetrate the concrete. This may reduce the service-life of the concrete element. In this study, X-ray computed tomography (CT) was used as a non-destructive technique to characterize the microstructure of mortar samples that were exposed to different levels of freeze-thaw damage by varying degree of saturation in the samples (75, 90, 95, and 100% degrees of saturation). Acoustic emission (AE) experiments were performed during freezing and thawing to investigate sample cracking behavior. The volume of cracks present within the mortar samples after freezing and thawing were determined using X-ray CT and compared to passive acoustic emission data. The location/source of cracks was also determined using X-ray CT. The crack sources (i.e., void, aggregate, interfacial transition zone, or paste) were determined using X-ray CT and were related to AE activities during cracking. Crack volumes were found to increase with increased levels of saturation, and visual observations of cracking were found to correlate with AE signatures of various crack sources. [ABSTRACT FROM AUTHOR]

Loosening of the acetabular liner component caused by the failure of the cement mantle is a complex phenomenon in a total hip arthroplasty. This failure is often associated with the occurrence of cracking in the cement mantle. Investigation of this cracking can be performed by fat igue test or simulat ion. Cracking can be caused by initial cracks (porosity), defects of cement mantle, or stress due to repeated loading. An initial crack may be caused by material defects. The stress depends on the load and on the strength of the material itself. To reduce crack failure, one can minimize the init ial crack or optimize the thickness of the cement mantle and reduce stress that occurs in the cement mantle. This study offers a solution for reducing the intensity of stress on the cement mantle by providing an additional metal layer between the liner and the acetabular component cement mantle. The study is performed by simulating static contact using finite element analysis. Results show that the additional layer between the acetabular liner and the cement mantle can significantly reduce the stress on the contact surface of the cement mantle. [ABSTRACT FROM AUTHOR]

The aim of the study involves quantitatively evaluating rapid self-sealing of cracks in cementitious materials incorporating superabsorbent polymers (SAPs). To this end, the study proposes a model to predict changes in the amount of water runoff through cracks over time when spherical SAPs in cementitious materials exhibit rapid swelling by absorbing the first water ingress after the occurrence of cracks. X-ray computed tomography analysis demonstrates that the swelling of SAPs in the cracks of the specimens by distilled water was less than that in a free state. The water flow test results indicate that the ratio of water runoff over time decreases sharply in SAP-added specimens immediately after the commencement of the water flow test. Additionally, the reduction ratio of the flow rate for the specimens with a crack width range of 0.24–0.36 mm corresponds to 0.343–0.519, 0.524–0.716, and 0.631–0.826 in specimens S-0.5, S-1.0, and S-1.5, respectively. A nonlinear regression analysis was performed on the results of the water flow test, and this reveals that the modification factor for the volume fraction of cracks sealed by the swelling of spherical SAPs corresponds to 0.7056, 0.6642, and 0.6574 for SAP 0.5%, SAP 1.0%, and SAP 1.5%, respectively. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) monitoring during compressive loading was employed to investigate micro-crack formation and coalescence in cement paste specimens. To establish a correlation between damage and AE activity, the data was categorized on the basis of amplitude and cumulative signal strength (CSS). Three distinct stages of crack behavior, illuminated by changes in the slope of the cumulative signal strength versus time relationship, were identified. Micro-crack initiation, crack extension, and unstable crack growth (crack coalescence) were assigned to these stages. An unsupervised pattern recognition approach was employed to separate the data into signal subsets which were then classified and assigned to differing mechanisms. To gain further insight into the crack growth network and behavior, specimens were loaded to varying levels of ultimate capacity and micro-CT scanning was employed to investigate the dimensional extent of micro-cracking and to correlate the images with AE data. [ABSTRACT FROM AUTHOR]

Owing to its exceptional strain capacity, which can reach hundreds of times that of normal concrete, and its reduced crack width, engineered cementitious composites (ECC) are a very promising solution for mitigating many of the problems that generate colossal backlogs of deteriorated concrete structures worldwide. However, research is needed to develop more sustainable ECC with flexible formulation that uses local materials. This paper investigates the coupled effects of using limestone powder in ECC as partial or total replacement for silica sand aggregate, coupled with using high-volume fly ash as a binder. The compressive and flexural strengths and fracture toughness for the formulated ECCs were examined at 3, 28 and 90 days. The results of this study demonstrate that sustainable ECC for resilient structural applications can be produced. It is aimed that more flexible formulations of ECC using local materials with lower environmental footprint could emerge and contribute to more durable and sustainable civil infrastructure. [ABSTRACT FROM AUTHOR]

The entrained air-void system in concrete is closely related to freeze-thaw durability in concrete pavements or other structures. For either research or forensic purposes, reliable and economical methods for the quantification of entrained air are desirable. This study explores the potential of using micro X-ray computed tomography (μCT) to measure entrained air-void parameters in concrete. A series of small cores (6 mm dia.) were retrieved from larger (100-mm-dia.) cores from two different concrete pavements, representing both adequate and marginal air contents, and scanned at a resolution of 7.5 μm/pixel. A systematic procedure based on image processing is proposed to address practical difficulties such as void/solid thresholding, air-type discernment (entrained air-voids vs. voids in aggregate) and the separation of bubbles within close proximity to each other (e.g. clustered air-voids). Air content and specific surface were measured directly from the three-dimensional (3D) reconstructed X-ray images, while values for paste content were derived from manual point counts performed on two-dimensional (2D) slices obtained from the 3D images. The derived values for air content, specific surface and paste content were used to calculate Powers’ spacing factor. To assess the issue of local fluctuations of material constituents and the limited dimensions of the small cores, uncertainty associated with the sample volume of concrete under measurement was also estimated. Based on the results in this study with regard to the work involved in sample preparation, data analysis and uncertainty bounds, μCT has been found to be a viable option for measurement of spacing factor and specific surface, but due to limitations imposed by the dimensions of the sample size (6-mm-dia. cores), the method is not appropriate for bulk air content determination. [ABSTRACT FROM AUTHOR]

This paper presents the corrosion-induced cracking process of a corroded reinforced concrete beam exposed to a chloride environment for 26 years. The cracking maps of the beam were drawn during different corrosion periods. The first corrosion-induced cracks in the compression zone occurred at about the 5th year and then developed significantly. The corrosion-induced cracks in the tension zone appeared at about the 7th year, followed by the stirrup zones in the transversal sections. At about the 14th year, the width of the cracks in the tension zone exceeded that in the compression zone. The cracks in the tension zone became connected almost throughout the span. The top-bar effect, bleeding and the “top surface ponding effect” led to the appearance of corrosion-induced cracks first in the compression zones, while the corrosion-induced cracks in the tension zone increased more significantly in both length and width as a result of the sustained load. [ABSTRACT FROM AUTHOR]

Textile reinforced cement (TRC) is a composite material being increasingly used for load bearing applications. Damage in TRC as in all cementitious materials is an important issue in civil engineering. Acoustic emission (AE) exhibits promising outcomes in laboratory and in in-situ monitoring applications. Evaluation of the fracture mode is crucial as generally, shearing phenomena occur later than tensile (bending) cracking and indicate more severe damage. The acoustic signatures of the damage modes influence most of AE parameters including the average frequency AF and RA-value. However, there are no universal classification boundaries between tensile and shear signals mainly due to geometric effects, material properties, as well as sensor location and response function. In order to highlight this problem and discuss the possibility of a solution, the study occupies not only with the evaluation of the damage mode based on AE parameters but in addition uses multiple sensors to investigate the effect of the wave propagation distance. This is crucial in thin cementitious laminates since damping, scattering, reflections and plate wave dispersion seriously distort the signal having a strong effect on the classification result. It is seen that the classification boundaries between tensile and shear fracture should incorporate the information of propagation distance. [ABSTRACT FROM AUTHOR]

Internal curing technology has been developed as a method for the reduction of autogenous shrinkage and cracking potential in high-performance concretes. The combination of autogenous and drying shrinkage, i.e. total shrinkage, of internally cured concrete is reported in the literature, almost unchanged after exposure to drying in a long term. On the other hand, the studied range of water to cement ratios is quite narrow. Accordingly, great interest aroused in the research of the effect of water to cement ratio on total shrinkage, as well as cracking potential of internally cured concrete. In this research, the restrained drying shrinkage of concrete with water to cement ratio of 0.33, 0.25 and 0.21, internally cured by means of water-saturated lightweight aggregate was studied. Strength, free drying shrinkage and mass loss of these concretes were also tested. The experimental results demonstrate that water to cement ratio has a considerable impact on cracking potential of internally cured concrete. [ABSTRACT FROM AUTHOR]

In order to reveal the differences and conversion relations between the tensile, compressive and flexural moduli of cement stabilized macadam, in this paper, we develop a new test method for measuring three moduli simultaneously. By using the materials testing system, we test three moduli of the cement stabilized macadam under different loading rates, propose a flexural modulus calculation formula which considers the shearing effect, reveal the change rules of the tensile, compression and flexural moduli with the loading rate and establish the conversion relationships between the three moduli. The results indicate that: three moduli become larger with the increase of the loading rate, showing a power function pattern; with the shear effect considered, the flexural modulus is increased by 47% approximately over that in the current test method; the tensile and compression moduli of cement stabilized macadam are significantly different. Therefore, if only the compression modulus is used as the structural design parameter of asphalt pavement, there will be a great deviation in the analysis of the load response. In order to achieve scientific design and calculation, the appropriate design parameters should be chosen based on the actual stress state at each point inside the pavement structure. [ABSTRACT FROM AUTHOR]

This paper provides a theoretical derivation for the unconfined compression strength of artificially cemented granular soils. The proposed developments are based on the concept of superposition of failure strength contributions of the soil and cement phases. The granular matrix obeys the critical state soil mechanics concept, whereas the strength of the cemented phase can be described using the Drucker-Prager failure criterion. In the process, the analytical relation is suitably adjusted to parallel a recently proposed empirical relationship that links unconfined compression strength of artificially cemented granular soils to an adjusted porosity/cement ratio parameter. Although the proposed analytical relation fits the experimental data for different granular soils and cement curing time well, further parametric analysis offers the possibility of exploring the effect of some material parameters on the unconfined compression strength of artificially cemented granular soils. [ABSTRACT FROM AUTHOR]

The dynamic compressive modulus, damping ratios, dynamic intensity and other kinetic parameters of argillaceous slate cement-improved soil were studied using dynamic tri-axial test in this paper. The effects of confining pressure and loading frequency on these dynamic parameters were analyzed. By comparing the dynamic parameters of unimproved soil and improved soil, the improvement effect was analyzed and evaluated. Research shows that: i) the dynamic compressive modulus of cementimproved soil decreases with the increase of dynamic strain amplitude, the relationship between them is approximately a hyperbolic function; ii) the damping ratios increases with the increase of dynamic strain amplitude, the relationship between them is also approximately a hyperbolic function; iii) the initial dynamic compression modulus increases with the increase of confining pressure, while the maximum damping ratio decreases with the increase of confining pressure; iv) the initial dynamic compressive modulus increases with the loading frequency, but the loading frequency has little effect on the maximum damping ratio; v) the dynamic stress intensity is linear with the logarithm of failure cycle times, and the dynamic stress intensity decreases with the increase of the failure cycle times. The dynamic strength and the initial compressive modulus of argillite-slate soil have been significantly improved after the cement improvement while the maximum damping ratio changes little. [ABSTRACT FROM AUTHOR]

This work aims to provide a method for numerically and experimentally investigating the fracture mechanism of cement paste at the microscale. For this purpose, a new procedure was proposed to prepare micro cement paste cubes (100 ⨰ 100 ⨰ 100 μm3) and beams with a square cross section of 400 ⨰ 400 μm2. By loading the cubes to failure with a Berkovich indenter, the global mechanical properties of cement paste were obtained with the aid of a nano-indenter. Simultaneously the 3D images of cement paste with a resolution of 2 μm3/voxel were generated by applying X-ray microcomputed tomography to a micro beam. After image segmentation, a cubic volume with the same size as the experimental tested specimen was extracted from the segmented images and used as input in the lattice model to simulate the fracture process of this heterogeneous microstructure under indenter loading. The input parameters for lattice elements are local mechanical properties of different phases. These properties were calibrated from experimental measured load displacement diagrams and failure modes in which the same boundary condition as in simulation were applied. Finally, the modified lattice model was applied to predict the global performance of this microcube under uniaxial tension. The simulated Young's modulus agrees well with the experimental data. With the method presented in this paper the framework for fitting and validation of the modelling at microscale was created, which forms a basis for multi-scale analysis of concrete. [ABSTRACT FROM AUTHOR]

This paper presents laboratory experiments exploring the interaction between hydraulic fractures and preexisting natural fractures that are strongly cemented relative to the host material strength but over only a portion of the natural fracture. Two sets of experiments were conducted, including the central region cemented case and the top-bottom region cemented case. Three main patterns are observed for the interaction between hydraulic fractures and partially cemented natural fractures: (1) complete crossing, (2) crossing with mismatched crack path and (3) no crossing. The results show that a hydraulic fracture penetrates directly through a fully and strongly cemented preexisting natural fracture. When the proportion of the strongly cemented region decreases or the height of the weak natural fracture increases, the hydraulic fracture is observed to persist through the entire height of the specimen both before and after the interface. However, the fracture path proceeds directly through strongly cemented portions while causing mismatched crack path at uncemented portions. No crossing results are obtained when the strongly cemented region is sufficiently small, around 30 % of the natural fracture's height. Results of this seldom considered but almost certainly realistic configuration of partial cementing suggest that the hydraulic fracture path is strongly influenced by the size of the cemented region of the natural fracture. [ABSTRACT FROM AUTHOR]

Experimental work has demonstrated that cracks can be healed in ordinary cementitious materials in the presence of water. The primary healing mechanisms are hydration of the unreacted nuclei of cement particles and the long-term formation of calcite. A mathematical model for simulating early-age autogenous healing of ordinary cement-based materials is proposed, which employs a coupled thermo-hygro-chemical (THC) framework and which uses a reactive water transport component to predict the movement of healing materials. A single concentration variable is employed for the healing component of the model that is derived directly from the quantity of unreacted cement and computed using a generalised cement hydration model component. The hydration component is directly linked to an expression for capillary porosity and for the porosity of the material within a healed crack. The results from a series of model simulations are in good general agreement with experimental data from tests on autogenous healing. [ABSTRACT FROM AUTHOR]

Engineered cementitious composite (ECC) is a unique group of fiber-reinforced strain-hardening cementitious composites exhibiting crack self-healing. Due to the absence of coarse aggregates in the ECC mix design, high amount of supplementary cementitious materials (SCM) are generally used to reduce the cement content. The inclusion of slag not only changes the chemical compositionss of the matrix but also alters the crack width of ECC. Both may influence the autogenous healing potential of the slag-based ECC. This paper systematically investigates the influence of the individual factor, i.e. slag content, crack width, and environmental alkalinity, on the autogenous healing efficiency of ECC. Specifically, single-cracked ECC specimens with different slag content and crack width were conditioned under water/dry or NaOH/dry cycles. The autogenous healing performance was evaluated based on crack width reduction, resonant frequency recovery and microstructure analysis. The results show that autogenous healing is determined by a couple effect of physical properties (crack width), chemical compositionss (slag content), and environmental conditions (conditioning alkalinity). At a given slag content and certain alkalinity, there exists a maximum allowable crack width for complete healing, beyond which only partial or no healing would happen. The dominant healing product for the water/dry conditioning is CaCO 3 while the NaOH/dry cycles promote slag hydration and results in the formation of C S H and CaCO 3 as main healing products. It is concluded that CaCO 3 precipitation is more effective to engage autogenous healing than the formation of C S H. The concept to associate allowable crack width and slag content is proposed, which would guides ingredients selection and component tailoring to engage robust autogenous healing in ECC in the future. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation of the shear behavior of beams consisting of steel Reinforced Engineered Cementitious Composites (R/ECC). This study investigates and quantifies the effect of ECC's strain hardening and multiple cracking behavior on the shear capacity of beams loaded in shear. The experimental program consists of R/ECC beams with short (8 mm) randomly distributed Polyvinyl Alcohol (PVA) fiber and conventional Reinforced Concrete (R/C) counterparts for comparison with varying shear reinforcement arrangements. Beams were loaded until failure while a Digital Image Correlation (DIC) measurement technique was used to measure surface displacements and crack formation. The shear crack mechanisms of R/ECC are described in detail based on findings of DIC measurements and can be characterized by an opening and sliding of the cracks. Multiple micro-cracks developed in a diagonal arrangement between the load and support points due to the strain-hardening response of ECC in tension. The strain-hardening response strongly influenced the shear response of the beam specimen. [ABSTRACT FROM AUTHOR]

The potential leakage of hydrocarbon fluids or carbon dioxide (CO2) out of subsurface formations through wells with fractured cement or debonded microannuli is a primary concern in oil-and gas production and CO2 storage. The presence of fractures in a cement annulus with apertures on the order of 10–300 µm can pose a significant leakage danger with effective permeability in the range of 0.1–1.0 md. Leakage pathways with small apertures are often difficult for conventional oilfield cement to repair; thus, a low-viscosity sealant that can be placed into these fractures easily while providing a long-term robust seal is desired. The development of a novel application with pH-triggered polymeric sealants could potentially be the solution to plugging these fractures. The application is based on the transport and reaction of a low-pH poly(acrylic acid) polymer through fractures in strongly alkaline cement. The pH-sensitive microgels viscosify after neutralization with cement to become highly swollen gels with substantial yield stress that can block fluid flow. Experiments in a cement fracture determined the effects of the viscosification and gel deposition with real-time visual observation and measurements of pressure gradient and effluent pH. Although the pH-triggered gelling mechanism and rheology measurements of the polymer gel show promising results, the polymer solution undergoes a reaction caused by the release of calcium cation from cement that collapses the polymer network (syneresis). It produces an undesirable calcium-precipitation byproduct that is detrimental to the strength and stability of the gel in place. As a result, gel-sealed leakage pathways that were subjected to various degrees of syneresis often failed to hold backpressures. Multiple chemicals were tested for pretreatment of cement cores to remove calcium from the cement surface zone to inhibit syneresis during polymer placement. A chelating agent, sodium triphosphate (Na5P3O10), was found to successfully eliminate syneresis without compromising the injectivity of polymer solution during placement. Polymer-gel strength is determined by recording the maximum-holdback pressure gradients during liquid breakthrough tests after various periods of pretreatment and polymer shut-in time. Cores pretreated with Na5P3O10 successfully held up to an average of 70 psi/ft, which is significantly greater than the range of pressure gradients expected in CO2-storage applications. The use of such inexpensive, pH-triggered polyacrylic acid polymer allows the sealing of leakage pathways effectively under high-pH conditions. [ABSTRACT FROM AUTHOR]

X-ray microtomography (XMT) imaging combined with three-dimensional (3D) computational fluid dynamics (CFD) modeling technique was used to study the effect of geochemical and geomechanical processes on fracture permeability in composite Portland cement-basalt caprock core samples. The effect of fluid density and viscosity and two different pressure gradient conditions on fracture permeability was numerically studied by using fluids with varying density and viscosity and simulating two different pressure gradient conditions. After the application of geomechanical stress but before CO2-reaction, CFD revealed fluid flow increase, which resulted in increased fracture permeability. After CO2-reaction, XMT images displayed preferential precipitation of calcium carbonate within the fractures in the cement matrix and less precipitation in fractures located at the cement-basalt interface. CFD estimated changes in flow profile and differences in absolute values of flow velocity due to different pressure gradients. CFD was able to highlight the profound effect of fluid viscosity on velocity profile and fracture permeability. This study demonstrates the applicability of XMT imaging and CFD as powerful tools for characterizing the hydraulic properties of fractures in a number of applications like geologic carbon sequestration and storage, hydraulic fracturing for shale gas production, and enhanced geothermal systems. [ABSTRACT FROM AUTHOR]

We model and assess the possibility of shear failure along the vertical well by using the Mohr–Coulomb failure model and employing a rigorous coupled flow-geomechanic analysis. To this end, we take various values of cohesion between the well casing and the surrounding cement to represent different quality levels of cementing operation (low cohesion corresponds to low-quality cement and/or incomplete cementing). The simulation results show that there is very little fracturing when the cement is of high quality. Conversely, incomplete cementing and/or weak cement can cause significant shear failure and evolution of long fractures/cracks along the vertical well. Specifically, low cohesion between the well and cemented areas can cause significant shear failure along the well, while high cohesion does not cause shear failure. The Biot and thermal dilation coefficients strongly affect shear failure along the well casing, and low Young's modulus causes fast failure propagation. Still, for the high quality of the cementing job, failure propagates very little. When the hydraulic fracturing pressure is high or when permeability increases significantly, low cohesion of the cement can cause fast propagation of shear failure and of the resulting fracture/crack, but a high-quality cement with no weak zones exhibits limited shear failure that is only concentrated near the bottom of the vertical part of the well. Thus, high-quality cement and complete cementing along the vertical well appears to be the strongest protection against shear failure of the wellbore cement and, consequently, against contamination hazards to drinking water aquifers during hydraulic fracturing operations. [ABSTRACT FROM AUTHOR]

This paper develops a three-dimensional (3D) microscopic model to investigate the mechanical response of cement mortar with random defects at high strain rates. Ellipsoids with randomness in size, shape, and spatial distribution are used to simulate the defects in mortar matrix. First, we propose the steps to generate the ellipsoid. Second, a "take and place" algorithm is employed to generate a model of cement mortar composed of defects. The mapping algorithm is used to generate a finite-element grid. In finite-element modeling, the material model is used in an advanced general-purpose multiphysics simulation software package to simulate the nonlinear behavior of mortar matrix with strain rate effects. Numerical simulations of the specimen under static loadings agree well with test observations, which reveal that the proposed 3D microscopic model and finite-element analytical approach can give reliable predictions. Finally, numerical studies are conducted, focusing on the effect of the defects on the dynamic responses of cement mortar. It is demonstrated that the defects have effects both on the dynamic behavior and failure pattern under high strain rate loading. [ABSTRACT FROM AUTHOR]

Sealed cracks are frequently observed on the road pavement due to pavement crack sealing. A sealed crack is a type of road surface distress, whose assessment is essential in pavement management system. In this paper, the state-of-the-art in automated pavement surface crack detection is presented. An algorithm is also developed to automatically detect sealed cracks in pavement surface images. The algorithm steps are elaborated with case study samples. Moreover, in image segmentation step, a method is developed based on a local minimum approach. The proposed algorithm is tested through various pavement surface images collected in an exhaustive case study. The evaluation is conducted with respect to the performance and robustness perspectives. The experimental results indicate that the developed algorithm has high accuracy and can consistently detect sealed cracks in different environments. [ABSTRACT FROM AUTHOR]

In a hydrocarbon well, cement fills the annular gap between two steel casings or between a steel casing and rock formation, forming a sheath that isolates fluids in different zones of the welt. For a well as long as several kilometers, the cement sheath covers a large area and inevitably contains small cracks. The cement sheath fails when a small crack grows and tunnels through the length of the well. We calculate the energy release rate at a steady-state tunneling front as a function of the width of the tunnel. So long as the maximum energy release rate is below the fracture energy of the cement, tunnels of any width will not form. This failsafe condition requires no measurement of small cracks, but depends on material properties and loading conditions. We further show that the critical load for tunneling reduces significantly if the cement/casing and cement/formation interfaces slide. [ABSTRACT FROM AUTHOR]

Time dependence of fluid flux up a leaky well has significant implications for the feasibility of geologic CO 2 storage. We present laboratory experiments that study various boundary conditions, fluid fluxes, and residence times to understand the range of behavior in fractured cement cores. Carbonic acid progressively reacts with cement by dissolving phases which neutralize the acid and liberate calcium ions. This dissolution does not increase the aperture of the fracture, due to the formation of an amorphous silicate residue. Where aqueous calcium concentration and pH are sufficiently high calcium carbonates become insoluble and precipitate in the open fracture. When the driving force for fluid flux is a constant pressure differential precipitation leads to a progressive reduction in fluid flux and the development of self-limiting behavior. With sufficient residence time precipitation leads to sealing of the leaky well. [ABSTRACT FROM AUTHOR]

Fracture characterization under mode I loading of a cement-based material using the single-edge-notched beam loaded in tree-point-bending was performed. A new method based on beam theory and crack equivalent concept is proposed to evaluate the Resistance-curve, which is essential to determine fracture toughness with accuracy. The method considers the existence of a stress relief region in the vicinity of the crack, dispensing crack length monitoring during experiments. A numerical validation was performed by finite element analysis considering a bilinear cohesive damage model. Experimental tests were performed in order to validate the numerical procedure. Digital image correlation technique was used to measure the specimen displacement with accuracy and without interference. Excellent agreement between numerical and experimental load-displacement curves was obtained, which validates the procedure. [ABSTRACT FROM AUTHOR]

Shrinkage cracking is a major issue that affects the durability of concrete structures. Plastic shrinkage of cementitious materials can lead to cracking within 24 h of casting and sets the stage for premature deterioration. Although test techniques exist that can be used to evaluate the plastic shrinkage cracking potential of cement-based materials, mathematical models that predict the influence of various parameters such as water-cement ratio (w/c), aggregate to cement ratio, and the effect of fibers on cracking are not available. This paper presents a model that can be used to predict plastic shrinkage cracking in cement-based materials. The model is developed by using factorial design and utilizes representative data generated with a technique developed by the authors. The effectiveness and limitations of the model in predicting crack areas and width are discussed. The effect of variables such as w/c, sand/cement ratio, fiber dosage, and the interaction between these variables is also presented in this paper. [ABSTRACT FROM AUTHOR]

The main objective of the study presented in this paper was to investigate the influence of cracking and self-healing on the gas permeability of Engineered Cementitious Composites (ECC). To deliberately introduce microcracks, specimens were pre-loaded to different deformation levels under splitting tensile loading and exposed to different environmental conditionings for the assessment of self-healing. Gas permeability (GP) and resonant frequency (RF) tests, crack characteristics observation and microstructural analysis were conducted to analyze the effect of cracking and healing on the properties of cementitious composites. Test results indicate that the self-healing effect determined through GP and RF tests was strongly influenced by changes in the chemical compositions of the mixtures. Application of pre-loading led to significant increases in GP results, so that even microcracks of less than 50 μm caused a GP coefficient fifty times higher than that of sound specimens. However, the recovery in GP results could be escalated up to 96% after only a month through proper material design and conditioning. It therefore appears that microcracking and subsequent healing is influential on the GP recovery rates of specimens, but not on RF recovery rates. [ABSTRACT FROM AUTHOR]

Fractures and defects in wellbore cement can lead to increased possibilities of CO2 leakage from abandoned wells during geological carbon sequestration. To investigate the physicochemical response of defective wellbore cement to CO2-rich brine, we carried out a reactive flow-through experiment using an artificially fractured cement sample at a length of 224.8 mm. A brine solution with dissolved CO2 at a pH of approximately 3.9 was injected through the sample at a constant rate of 0.0083 cm3/s. Surface optical profilometry analysis and 3-D X-ray microtomography imaging confirmed fracture closure and self-healing behavior consistent with the measured permeability decrease. Visual inspection of the reacted fracture surface showed the development of reactive patterns mapping the flow velocity field inside the fracture, as well as restricted flow toward the sample outlet. The postexperiment permeability of the core sample was measured at half of its initial permeability. A reactive transport model was developed with parameters derived from the experiment to further examine property evolution of fractured cement under dynamic flow of CO2-rich brine. Sensitivity analysis showed that residence time and the size of initial fracture aperture are the key factors controlling the tendency to self-healing or fracture opening behavior and therefore determine the long-term integrity of the wellbore cement. Longer residence time and small apertures promote mineral precipitation, fracture closure, and therefore flow restriction. This work also suggests a narrow threshold separating the fracture opening and self-sealing behavior. [ABSTRACT FROM AUTHOR]

Introduction and objective: In elderly patients with reduced bone quality, insufficiency fractures of the sacrum are relatively common and are typically accompanied by severe, disabling pain. The objective of this study was to evaluate the feasibility of cement augmentation by RFS, as well as to determine postinterventional leakages and present the patients' outcomes. Material and method: In 20 patients (18 women, 2 men) with an average age of 80.4 (65-92) years, a fracture of the sacrum was detected by CT and MRI. Clinically manifest osteoporosis with QCT values of below 50 mg/ml was found in all patients. An initially performed conservative treatment over a period of 3 weeks did not achieve a satisfactory reduction in the severe, disabling pain. The cement augmentation was performed under CT guidance by means of RFS under intubation anaesthesia. A Jamshidi needle was advanced into the respective fracture zone in the sacrum from dorsal to ventral (short axis) or from lateral to medial transiliac (transiliac axis). After removing the inner needle, a flexible osteotome was inserted through the positioned hollow needle and used to extend the spongious space in the fracture zone and thus prepare a cavity for the cement filling. The highly viscous polymethyl methacrylate (PMMA) cement, activated by radiofrequency, was then inserted into the prepared fracture zone through a substituted screw cannula. Cement filling was performed discontinuously under instrumental guidance at 1.3 ml/min under CT guidance. Cement leakages were determined in CT images and conventional X-rays on the day after the intervention. Pain was documented on a visual analogue scale (VAS) on the day before the intervention, on the second day, and after 6 and 12 months after the intervention. Additionally occurring complications were recorded, and the patients were asked to state how satisfied they were after 12 months. Results: RFS was technically feasible in all patients. In the control CT scans and X-rays, sufficient cement distribution and interlocking with vital bone was found along the course of the fracture in the sacrum. 7.2 (4-9) ml of cement were inserted per fracture. Leakage could be ruled out. The mean pain score on the VAS was 8.8 ± 1.2 before the intervention, and a significant reduction in pain ( p < 0.001) was seen on the second postoperative day, with an average value of 2.3 ± 0.7, which was stable at 2.2 ± 1.3 after 6 months and 2.1 ± 1.1 after 12 months. All of the patients could be fully re-mobilised and discharged back home. A high level of patient satisfaction was found after 12 months, with 18 of the 20 patients stating that they would undergo the intervention again. One patient died of a stroke, another of cancer over the course. Conclusion: As a minimally invasive procedure, RFS is an effective and safe method of treatment for rapid, significant and sustained pain reduction. [ABSTRACT FROM AUTHOR]

The use of hydraulic calcium phosphate cements (CPCs) as bone substitute is impaired by their relatively poor handling due to the need to mix a powder and a liquid during surgery. The aim of the present study was to assess the possibility to design CPCs as inorganic dual-paste cements, where both pastes would be stable for years, but would react as soon as they are mixed together. Results showed that aqueous pastes of α-tricalcium phosphate (α-TCP) powder could be stabilized for up to a year at room temperature by the use of 0.1 M Mg chloride solution. Adding a calcium chloride solution in a 1:4 volume ratio activated α-TCP pastes provided the Ca/Mg ratio was larger than one. Mechanistic investigations suggest that Ca ions can displace Mg cations adsorbed at the surface of α-TCP particles to initiate α-TCP transformation to calcium-deficient hydroxyapatite and concomitant paste hardening. The compressive strength (29 MPa) was similar to that of commercial formulations (5-80 MPa). Other divalent cations (Ba, Ni, Sr) had a similar effect although with a different degree of efficacy. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This paper presents the results of the condition assessment of twenty concrete mixtures incorporating ten different reactive aggregates through the Damage Rating Index (DRI), a microscopic and semi-quantitative petrographic tool, with the aim of verifying the development of distress due to alkali-aggregate reaction (AAR) as a function of the specimen's expansion (i.e. from 0.05 to 0.30%). The DRI was found to provide a reliable assessment of the degree of damage in the concretes incorporating reactive fine or coarse aggregates. An envelope of DRI damage assessments against the expansion level of the affected materials is proposed. For all alkali–silica reactive aggregates investigated, the progress in counts and proportions of opened cracks in the aggregate particles and in the cement paste, with and without gel, as well as the crack density parameter, were found to be diagnostic petrographic features for quantifying ASR progress. Moreover, a qualitative ASR distress model in concrete was defined. [ABSTRACT FROM AUTHOR]

Low temperature cracking is one of the main distresses observed in pavements made of hot mix asphalt mixtures. As a material property, the fracture toughness of asphalt pavements is a fundamental parameter for estimating the load bearing capacity and resistance of cracked pavements against crack growth. In this paper, the fracture toughness (KIc) of different and various compositions of asphalt mixtures is obtained experimentally, and the effects of asphalt characteristic specifications and its composition are investigated on the value of KIc. Several asphalt mixtures were prepared with three aggregate sizes, two aggregate types (limestone and siliceous), different air void percentages ranging from 3.5 to 8%, and two binders (60/70 and 85/100). Other similar work has only studied the influence of limited characteristic parameters on the low temperature fracture resistance of asphalt mixtures. Several Semi-Circular Bend (SCB) specimens subjected to three point bend loading were manufactured with different compositions and were then tested at -15°C. The experimental results showed the noticeable influence of characteristic specifications of asphalt mixtures on the value of KIc. Generally, the value of KIc decreases for those mixtures containing a smaller size of aggregates made of siliceous, with higher percentages of air voids and softer binder types. [ABSTRACT FROM AUTHOR]

This paper presents an ultrasonic method, based on the nonlinear acoustic mixing of coda waves with lower-frequency swept pump waves, for providing an efficient global detection of small cracks in cementitious materials. By simultaneously comparing, for both uncracked and cracked mortars, the ultrasonic velocity variations and decorrelation coefficients between the unperturbed and perturbed signals with pump amplitude, this method makes it possible to accurately detect cracks with widths of around 20 µm in correlation with velocity variations of approximately 0.01%. The potential influence of certain material parameters such as microscopic damage is also discussed. [ABSTRACT FROM AUTHOR]

This study reports on the use of polyvinyl alcohol–based needle punched nonwoven fabrics in cement-based composites as a low-cost reinforcement. In this study, a nonwoven reinforcement using crimped polyvinyl alcohol fibers for cement-based composites was developed. The incorporation of nonwoven fabric in composites improved tensile and flexural properties compared to a discrete polyvinyl alcohol fiber-reinforced composite. Formation of multiple fine cracks, crimped fibers and mechanical interlocking of fibers in the nonwoven fabric structure resulted in superior mechanical performance. The failure mode was due to a single macro-crack for the discrete fiber reinforced composite as opposed to a number of fine cracks for the nonwoven reinforced composite. [ABSTRACT FROM PUBLISHER]

This study investigated the antifungal effects of cement paste containing Paenibacillus polymyxa E681 against Aspergillus niger, a deleterious fungus commonly found in cement buildings and structures. To test the antifungal effects, cement paste containing P. polymyxa E681 was neutralized by CO gas, and the fungal growth inhibition was examined according to the clear zone around the cement specimen. In addition to the antifungal effects of the cement paste added with bacteria, calcium crystal precipitation of P. polymyxa E681 was examined by qualitative and quantitative analyses. The cement paste containing P. polymyxa E681 showed strong antifungal effects but fusA mutant (deficient in fusaricidin synthesis) showed no antifungal activity. Crack sealing of the cement paste treated with P. polymyxa E681 was captured by light microscope showed fungal growth inhibition and crack repairing in cement paste. [ABSTRACT FROM AUTHOR]