Cement Cracks Research Articles

Pemanfaatan Fly Ash Limbah Pembakaran Batubara sebagai Zat Mineral Tambahan (Additive) terhadap Perbaikan Kualitas dan Kuat Tekan Semen

A series of tests were carried out to determine the effect of the addition of coal combustion fly ash as an additional mineral (additive) on improving the quality and compressive strength of cement according to the Indonesian National Standard (SNI 15-2049-2004). Research methods include sample preparation, manufacture of cement with 0%, 5%, 8%, 12%, and 15% fly ash variations, chemical and physical properties of cement. The parameters measured were the level of chemical composition (%) using X-Ray Fluorescence Spectroscopy (XRF) ARL 9800 OASIS, free lime content (%) by volumetry, insoluble residue level (%) by gravimetry, compressive strength (kg/cm2), and smoothness cement (cm2/g). The results showed that the addition of fly ash increased the SiO2 content of cement, thereby increasing C3S and C2S compounds which are compressive strength components of a cement. Besides, the addition of fly ash is directly proportional to IR levels, compressive strength, smoothness, and inversely proportional to free lime levels. So the addition of fly ash can improve the quality of cement by increasing chemical components, increasing compressive strength, and reducing cracking or expansion of cement.

Magnetic tunnel junction based gradiometer for detection of cracks in cement

Magnetic flux leakage (MFL) testing is a widely used technology for detecting structural defects in industry, where new magnetic sensors can provide an enhanced detectability. We have fabricated and developed vortex magnetic tunnel junctions (MTJs) into a new MFL probe, by designing a well-balanced magnetic gradiometer with a base length of 4 cm. Such gradiometer has exhibited a field detectability of 1.6 nT/Hz at 1 kHz, and a superior common-mode rejection ratio (CMRR) of 82 dB. We have studied multiple configurations of crack detection in weakly magnetic cement by simulations, and provided corresponding experimental confirmations by this MFL probe. It has achieved a large standoff distance of 22 mm, which finds its applications in energy industry and other infrastructural systems.

Numerical simulation of CO2 migration into cement sheath of oil/gas wells

It is generally recognized that the CO2 dissolved in formation water poses a serious threat to the cement sheath in oil and gas wells. A numerical model was developed in this study to investigate CO2 migration into oil/gas well cement sheath through pore space and cracks. The convective velocities were formulated on the basis of balance of capillary and frictional forces. Case studies and sensitivity analyses with the model indicate that CO2 invasion into cement sheaths through the pore space increases with pore size, diffusion coefficient, interfacial tension, and decreases with cement-CO2 contact angle. It should take over 400 years for CO2 to fully penetrate a 3.5 cm-thick cement sheath through the pore space of cement, suggesting that CO2 attack on cement sheath through pore space is not a concern during the life (<50 years) of oil/gas wells. For CO2 migration into cement sheaths through cracks, it will be accelerated by the increase in crack width, diffusion coefficient, interfacial tension, and reduced by the decrease in cement-CO2 contact angle. It will take 9 months at most for CO2 breakthrough the cement sheath, indicating that special attention should be paid to CO2 migration through cracks. Cement crack width is a dominating factor affecting CO2 migration velocity compared to other factors. Therefore, oil/gas wells should be completed/operated in safe ranges of pressure to prevent formation of cement cracks.

Effect of Addition of Alccofine on the Compressive Strength of Cement Mortar Cubes

In the modern era, many research works are going on throughout the world for finding suitable cementitious material for the replacement of cement since it causes environmental pollution. In this order Fly ash, Silica fume, GGBS, Metakaolin, Micro materials, Quartz powder, etc. are tried out for replacing partially or fully the cement in concrete. A new ultrafine material called Alccofine (AF) which is manufactured from glass wastes is tried out for replacing partially in this research. Compressive strength is one of the important properties of cement. Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Cement mortar of 1:3 mix proportion is used to cast the cubes having an area of 50 cm2 are used for the determination of compressive strength of cement as per IS: 4031-1988 (Part-6). The graded Indian Standard sand (Ennore Sand -ES) confirming to IS: 650-1991 is used for preparing the cubes. In the same mix proportion, the same size cubes are cast with the River Sand (RS) to study the difference of the compressive strength between the Indian standard sand and river sand. Ordinary Portland cement (OPC) and Portland Pozzolana Cements (PPC) are used. The present study is the influence of Alccofine on cement mortar cubes by replacing the cement by Alccofine with various proportions like 5%, 10%, 15%, 20% were cast and tested in the laboratory as per Indian Standard 4301-1988 (Part-6) and the results were analysed and presented in the form of charts and graphs. It is observed that the early age strength is obtained for all the combinations but 10 percent of Alccofine yields more strength than other dosages. Doi: 10.28991/esj-2021-01265 Full Text: PDF

Mechanical response and acoustic emission characteristics of cement paste backfill and rock combination

Backfill mining method plays an important role in the treatment of tailings, and the failure law of a cement paste backfill (CPB) and rock combination under pressure has essential guiding significance for the safe production of mines using the backfill mining method. In this work, uniaxial compression acoustic emission (AE) experiments were conducted on single CPB and CPB–rock combinations with different cement tailings ratios, based on referring to fractal theory to investigate the crack evolution of the specimens at different stages. The results show that the content of the tailings has a significant influence on the crack evolution and AE characteristics at the different stages of the CPB. When the cement tailings ratio of the CPB is reduced from 1:4 to 1:10, the crack evolution in the compaction stage gradually changes from initial crack closure to tailing–cement cracking. The crack evolution in the instability stage changes from the production of a large number of microcracks to that of several macrocracks. After entering the instability stage, the elastic energy release of the upper rock in the combinational specimens aggravates the post–peak damage of the CPB, and the change in the fractal dimension changes from “rising with severe fluctuations” to “declining with small fluctuations”. There are significant similarities in the ring–down count fluctuation laws of the rock and CPB in the combinational specimens. Before approaching the stress peak, the ring–down counts and fractal dimensions of the specimens show a significant downward trend. Among them, the fractal dimensions of the CPB–rock combinations with ratios of 1:4, 1:8, and 1:10 decrease by 21.1%, 16.7%, and 16.8%, respectively. The research results of this work can provide guidance for predicting the instability and failure of a CPB–rock combination in a mine using the backfill mining method.

Hybrid effect of basalt fiber and carbon fiber on the mechanical properties and microstructure of oil well cement

In order to study the hybrid effect of basalt fiber and carbon fiber on the mechanical properties of oil well cement, the response surface design method was adopted to optimize the mixed content of basalt fiber and carbon fiber in oil well cement. With the help of X-ray diffraction (XRD) and scanning electron microscope (SEM) characterization, the crushed samples of oil well cement mixed basalt fiber and carbon fiber was micro-analyzed, and the enhancement mechanism of basalt fiber and carbon fiber on the compressive strength and splitting tensile strength of oil well cement was explored. The research results showed that basalt fiber and carbon fiber mixed can significantly increase the compressive strength and splitting tensile strength of oil well cement. Compared with oil well cement without fiber, the maximum compressive strength of oil well cement with mixed fiber for the curing time of 3 days, 7 days and 28 days was increased by 48.94%, 24.05% and 25.68%, respectively. The maximum splitting tensile strength of oil well cement with mixed fiber for curing time of 3 days, 7 days and 28 days was increased by 151.14%, 68.01% and 46.28%, respectively. Moreover, addition of 0.55 wt% basalt fibers and 0.09 wt% carbon fibers in oil well cement leads to more ductile behavior with higher peak compressive strength after 3 days curing time. Addition of 0.29 wt% basalt fibers and 0.32 wt% carbon fibers in oil well cement leads to more ductile behavior with higher peak splitting tensile strength after 3 days curing time. The addition of carbon fiber and basalt fiber does not change the hydrates of oil well cement after oil well cement hydration. The improvement of the mechanical properties of fiber-reinforced oil well cement mainly depends on the fiber bridging, crack deflection and fiber pulling out or breaking. Based on the theory of linear elastic fracture mechanics, a fiber oil well cement crack resistance model was constructed. The results of this study provide a certain reference for the application of fiber-reinforced oil well cement with requirements for tensile and crack resistance in oil and gas well cementing projects.

Cement sensors with acoustic bandgaps using carbon nanotubes

Cement is widely used in wellbores to stabilize the steel casing used in wellbore operations for oil and gas production, enhanced geothermal systems and carbon sequestration, and to limit fluid movement between sub-surface strata. Flaws such as microcracks in wellbore cement can lead to leakage along the wellbore compromising wellbore integrity. There is an increasing need for methods to monitor cement crack propagation in wellbore environments. In this study, we develop and report the first cementitious sensors capable of exhibiting high frequency acoustic bandgaps (ABGs) using carbon nanotubes (CNTs). Computational simulations of a sensor unit cell are used to design cement-multi walled carbon nanotubes (MWCNTs) sensors that show a wide bandgap. When the cement-MWCNTs sensors is embedded in cement specimens, bandgaps were measured experimentally under 300 kHz and under 600 kHz, consistent with the computationally predicted bandgaps in the range of 290–360 kHz, 410–460 kHz and 515–585 kHz. These bandgap features were absent in homogeneous cement specimens. X-ray tomographic reconstructions showed microscopic debonding at cement-MWCNTs sensor interface. Frequency response analysis of a three-dimensional computational model indicated a shift of frequency of minimum transmission due to the interface debonding, but no perturbation of bandgap response was observed. The cement-MWCNTs sensors developed in this study show the potential of a packed CNT inclusion material in cementitious matrix to create ABGs in a cement matrix.

The Effect of Superabsorbent Polymers on the Microstructure and Self-Healing Properties of Cementitious-Based Composite Materials

Cementitious structures have prevailed worldwide and are expected to exhibit further growth in the future. Nevertheless, cement cracking is an issue that needs to be addressed in order to enhance structure durability and sustainability especially when exposed to aggressive environments. The purpose of this work was to examine the impact of the Superabsorbent Polymers (SAPs) incorporation into cementitious composite materials (mortars) with respect to their structure (hybrid structure consisting of organic core—inorganic shell) and evaluate the microstructure and self-healing properties of the obtained mortars. The applied SAPs were tailored to maintain their functionality in the cementitious environment. Control and mortar/SAPs specimens with two different SAPs concentrations (1 and 2% bwoc) were molded and their mechanical properties were determined according to EN 196-1, while their microstructure and self-healing behavior were evaluated via microCT. Compressive strength, a key property for mortars, which often degrades with SAPs incorporation, in this work, practically remained intact for all specimens. This is coherent with the porosity reduction and the narrower range of pore size distribution for the mortar/SAPs specimens as determined via microCT. Moreover, the self-healing behavior of mortar-SAPs specimens was enhanced up to 60% compared to control specimens. Conclusively, the overall SAPs functionality in cementitious-based materials was optimized.

Compaction Banding in High‐Porosity Carbonate Rocks: 1. Experimental Observations

AbstractIdentifying the mechanisms that control the formation of compaction bands is of high interest in reservoir mechanics since these structures may drastically affect the performance of geosystems operations. Considering the difficulty to identify compaction bands in carbonate samples tested in the laboratory, the Digital Volume Correlation technique is applied here and proves to be a relevant method. X‐Ray Computed Tomography (XRCT) images of Saint‐Maximin limestone centimetric samples are recorded before and after several triaxial loading stages and deformation maps are built. A new postprocessing method based on the analysis of the kinematics throughout the observed localization bands is proposed to identify their type. Compaction bands are identified at relatively high‐confining pressures, while shear bands are observed at lower confinements. The brittle‐ductile transitional regime reveals the formation of compactive shear bands, while a diffuse compaction is observed under hydrostatic loading. The effect of porosity heterogeneities on strain localization is explored by computing 3D porosity maps from calibrated XRCT images. Compaction bands are found to dominantly lay inside high‐porosity zones, while shear bands can cross both high‐ and low‐porosity zones. The band orientation is found to be controlled primarily by the confining pressure. Moreover, the porosity heterogeneity strongly affects the volumetric behavior inside the deformation bands, with a dilatant behavior identified in low‐porosity zones in contrast to a compactive behavior observed in high‐porosity zones. Finally, Scanning Electron Microscopy observations reveal that calcite grain crushing is dominant in high‐porosity zones, while intergranular cement cracking occurs in denser zones.

Identification of damage mechanisms during splitting test on SFP at different temperatures based on acoustic emission

While as a jointless cementitious asphalt material, semi-flexible pavement material (SFP) behaves well in rutting resistance, cracking has been a major barrier in its application promotion. Although many material modifications have been proved effective to improve SFP’s performance to some degree, it is still unclear what the crack mechanism is and whether it is similar in asphalt concrete until now. Thus, splitting test was conducted on SFP at three different temperatures (−10 °C, 10 °C and 25 °C) to investigate SFP’s damage process. Acoustic Emission (AE) technique was employed at the same time to collect signals from various of damage sources. An unsupervised method, k-means, was used to classify AE data. The X-ray scanning images of the samples after fracture were observed to assist in cluster identification, together with the images of the fracture cross sections. Three damage mechanism clusters were identified as skeletal aggregate moving friction, together with cement cracking, asphalt cohesive damage and debonding. The result reveals that SFP cracks more easily at 25 °C. There is a temperature effect in the damage process of SFP: the damage mode shifts from main macro-crack to distributed meso-cracks, as well as from interface debonding, aggregate cracking to asphalt/cement damage. Besides, the absolute energy development of each cluster indicates that damage in cement caused by uncoordinated deformation contributes much to capability loss in SFP at 25 °C.

A Study on the Modified Cement-Based Crack Injection Materials

Human constructed harbours are large infrastructure projects that use cement to reinforce embankments and build protective walls. However, like all concrete building projects maintenance is required. Cracks form and if left unattended will grow, eventually leading to a dangerous situation where a structure's integrity is compromised. As a result, the concrete repair industry, particularly in relation to marine infrastructure, is a large one and various mixtures of cement and other materials are designed to fill these cracks. Researchers at the National Taiwan Ocean University in Taiwan are now investigating the best ways to design injectable materials to repair cement cracking in a marine setting in order to develop new cement recipes that will work in marine environments and protect vital harbours from deterioration.

Understanding the Toughening Mechanism of Silane Coupling Agents in the Interfacial Bonding in Steel Fiber-Reinforced Cementitious Composites.

Interfacial bonding between a fiber and a matrix plays an essential role in composites, especially in fiber-reinforced cementitious composites that are superior forms for bearing flexural and tension load in construction applications. Yet, despite the importance, effective and economic approaches to improve the interfacial bonding between a steel fiber and a cementitious matrix remain unfeasible. Herein, we report a pathway adopting a silane coupling agent (SCA) to modify an interfacial transition zone (ITZ) and enhance interfacial bonding. This approach involves coating a SCA layer onto a steel fiber, where tight physical and chemical bondings (via cross-linking of silicate chains) with a cementitious matrix are formed, leading to an 83.5% increase in pullout energy. Combining nanoindentation and an atomistic force microscope with molecular simulation, we find that SCA increases the surface roughness of the steel fiber, accelerates the hydration reaction of cement clinker, and promotes the volume fraction of the C-S-H phase, inducing a denser and more uniform ITZ with an adequate stress-transfer capability that shifts the mode of failure from interfacial debonding to cement cracking. This work presents an effective and economical approach to improve interfacial bonding, and it enables us to design more durable fiber-reinforced cementitious composites, which can be massively used to build innovative infrastructures.

The Effects of Cyclic Loading and Motion on the Implant-Cement Interface and Cement Mantle of PEEK and Cobalt-Chromium Femoral Total Knee Arthroplasty Implants: A Preliminary Study.

This study investigated the fixation of a cemented PEEK femoral TKA component. PEEK and CoCr implants were subjected to a walking gait cycle for 10 million cycles (MC), 100,000 cycles or 0 cycles (unloaded control). A method was developed to assess the fixation at the cement–implant interface, which exposed the implants to a fluorescent penetrant dye solution. The lateral condyles of the implants were then sectioned and viewed under fluorescence to investigate bonding at the cement–implant interface and cracking of the cement mantle. When tested for 100,000 cycles, debonding of the cement–implant interface occurred in both PEEK (61%) and CoCr (13%) implants. When the duration of testing was extended (10 MC), the percentage debonding was further increased for both materials to 88% and 61% for PEEK and CoCr, respectively. The unloaded PEEK specimens were 79% debonded, which suggests that, when PEEK femoral components are cemented, complete bonding may never occur. Analysis of cracks in the cement mantle showed an absence of full-thickness cracks in the unloaded control group. For the 100,000-cycle samples, on average, 1.3 and 0.7 cracks were observed for PEEK and CoCr specimens, respectively. After 10 MC, these increased to 24 for PEEK and 19 for CoCr. This was a preliminary study with a limited number of samples investigated, but shows that, after 10 MC under a walking gait, substantial debonding was visible for both PEEK and CoCr implants at the cement–implant interface and no significant difference in the number of cement cracks was found between the two materials.

Interfacial load monitoring and failure detection in total joint replacements via piezoresistive bone cement and electrical impedance tomography

Aseptic loosening, or loss of implant fixation, is a common complication following total joint replacement. Revision surgeries cost the healthcare system over $8 billion annually in the United States. Despite the prevalence of aseptic loosening, timely and accurate detection remains a challenge because traditional imaging modalities, such as plain radiographs, struggle to reliably detect the early stages of implant loosening. Motivated by this challenge, we present a novel approach for in vivo monitoring and failure detection of cemented joint replacements. Poly(methyl methacrylate) (PMMA) bone cement is modified with low volume fractions of chopped carbon fiber (CF) to impart piezoresistive-based self-sensing. Electrical impedance tomography (EIT) is then used to detect and monitor load-induced deformation and fracture of CF/PMMA in a phantom tank. We therefore show that EIT indeed is able to detect loading force on a prosthetic surrogate, distinguish between increasing load magnitudes, detect failure of implant fixation, and even distinguish between cement cracking and cement de-bonding without direct contact to the surrogate. Because EIT is a low-cost, physiologically benign, and potentially real-time imaging modality, the feasibility study herein presented could positively impact orthopedic researchers by providing, via in vivo monitoring, insight into the factors that initiate aseptic loosening.

Investigation for the Effects of Newly Designed Hip Prosthesis on Crack Propagation Using Probabilistic Methodology

In orthopedic prosthesis design, finite element method is one of the commonly used mathematical methods for performing structural analyzes and reducing test costs before it is applied to the patient. Surgeons and engineers should work together to design reliable durable and hip replacement. Desirable functional requirements for prosthesis design include high fatigue life, small relative displacement between the prosthesis-cement interface, and reduced stress on the bone and prosthesis. For this purpose, the progression of the fracture was calculated by applying the scenario of the presence of crack in the bone cement of the designed prosthesis using optimization methodology. The same conditions were analyzed in commercially available Charnley type prosthesis and the results were compared. When the obtained results are examined, it is seen that the newly designed prosthesis is more effective than the Charnley type prosthesis.

Insight into the role of polyacrylamide polymer powder on the cracking in plastic period of cement mortar

It is still uncertain whether polyacrylamide polymer powder can restrain the cracking of cement mortar in the plastic period and the mechanisms, which are responsible for this role, still need to be systematically clarified. Thus the different contents of the polyacrylamide polymer powder were mixed and various pastes with polyacrylamide were prepared. The cracking behaviors and water evaporation losses of mortars were evaluated. The bleeding percentages, chemical shrinkages, ions concentrations, ultraviolet visible spectra and the characteristics of hydration heat liberations of cement pastes with polyacrylamide polymer powder were investigated to carry out the insight into the role of polyacrylamide polymer powder on the cracking of cement paste in the plastic period. The experimental results indicate that the polyacrylamide polymer powder improves the mortar resistance to the cracking in the plastic period. It decreases the water evaporation loss and bleeding percentage. But it enhances the chemical shrinkage and the increased chemical shrinkage is mainly attributed to the role of polyacrylamide polymer powder on the promotion of cement hydration in the tested ages, especially in the initial fast reaction and the first deceleration periods. The existence of the intermolecular hydrogen bonds is the main reason for lowering the water evaporation loss and bleeding percentages. Acting forces from the intermolecular hydrogen bonds may be additional contributor to the improved resistance to the cracking of cement mortar in the plastic period. The results from this work will provide a reference for the alleviation of the plastic cracking of cement based paste.

Effect of Pore Structure and Ion Concentration of Solution on the Formation of Ettringite in Composite Cement Paste

Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO42- and Al(OH)4- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.

Assessment on the cement integrity of CO2 injection wells through a wellbore flow model and stress analysis

This work aims at assessing the cement integrity during CO2 injection by illustrating the relevance of injection operations to the failure modes of cement. A single-phase flow model for pure CO2 is developed to provide the temperature and pressure profiles in the well and solved by a finite difference method. With the downhole temperature predicted by the flow model as a boundary condition, we present a mechanical model to estimate the stress state in the well section under plane-strain conditions as well as the stress intensity factor at a radial crack tip. This study introduces four failure factors corresponding to shear compressive failure, radial cracking, interfacial debonding, and fracture propagation. Further parametric studies are implemented to reveal the effects of injection operations, including injection temperature, rate, and time, on the above failure factors. They indicate that the injection rate is the most influential factor for cement integrity. High injection rates could cause radial cracking and its propagation as well as interfacial debonding but reduce the risk of shear compressive failure. Low injection temperatures or a long injection time would undermine the tensile and interfacial strength and extend the radial crack in cement while they benefit on shear compressive strength. The results provide guidelines to optimize injection operations for long-term well integrity during CO2 injection.

Evolution of silicate structure during corrosion of tricalcium silicate (C3S) and dicalcium silicate (C2S) with hydrogen sulphide (H2S)

H2S corrosion affects the molecular structure collapse of the cement matrix leading to cement cracking scanned by SEM. This research investigates whether C3S and C2S in cement react and undergo phase changes with high concentrations of corrosive H2S examined by XRD, TGA and RS. The products were evaluated to examine their bonds and moieties for H2S corrosion and to compare the molecular structure changes of silicates for further assessment based on 29Si SSNMR results. A lower mass of corrosion products and fewer molecular structure changes were observed in C2S specimens when compared with C3S specimens under H2S corrosion conditions.

The potential of using micro-sized crosslinked polymer gel to remediate water leakage in cement sheaths

Cementing is a major step in the construction and sealing of hydrocarbon wells. During the life cycle of the well, cement is prone to cracking due to a change in downhole conditions. This research investigates the use of micro-sized crosslinked polymer gel as a sealant material to mitigate cracked cement sheaths. Two experimental setups were designed to investigate water leakage through cement. The impact of polymer gel strength on the gel’s ability to seal cement cracks was investigated using four gel strengths, including 500 pa, 1200 pa, 1450 pa, and 2440 pa. The impact of the width of the cement crack was also investigated using 0.5, 2, 3.2, and 6.75 mm. Results showed that the polymer gel propagated across fractures like a piston with no gravity effect and with angle with gravity effect. Blocking efficiency to water flow is controllable, and it can be increased if a high strength polymer gel is selected. To the authors’ knowledge, very little experimental work has been conducted to investigate the use of crosslinked micro-gel in cement zonal isolation. This study can provide the oil and gas industry with a better understanding of the materials to use in improving cement zonal isolation and thus reduce the impact of cement failure.