Shrinkage Of Cement Research Articles

Early-age shrinkage behavior of cement mixtures regulated with metakaolin-based internal conditioning

Shrinkage occurs in concrete during its hardening and strength gain process leading to undesired deformation, cracking, and decreases in strength and durability. While metakaolin-based internal conditioning (MIC) has been validated as a promising technique for modifying cement and mitigating alkali-silica reactions in concrete, its impact on the early-age shrinkage behavior of cement remains unexplored. This study delves into the effects of MIC and its coupling with lithium on the chemical shrinkage, autogenous shrinkage, and drying shrinkage of portalnd cement incorporating 30 % metakaolin with varying degrees of saturation (50 %, 75 %, and 100 %). The results indicate that the hydration of cement can be substantially enhanced by MIC with 29.0 % more heat released and a 32.3 % decrease in calcium hydroxide content. As a result of the enhanced hydration, cement with MIC yielded increased chemical shrinkage. Compared with dry MK, the autogenous shrinkage and drying shrinkage of cement were decreased by 38.0 % and 11.0 %, respectively, in the presence of MIC. A synergistic effect between MIC and lithium was suggested by the higher efficacy in suppressing autogenous shrinkage.

Multiscale model for concrete cured under geothermal environment: Theoretical analysis and experimental validation

Concrete poured as linings of geothermal tunnel would deviate normal curing condition. A multiscale model based on continuum micromechanics, accounting for temperature-dependent factors, is established from the cement paste level to the concrete level. This model predicts the physical properties and compressive strength of concrete and is validated against measured strength, which incorporates the impact of high-temperature curing on the hydration degree, density of C-S-H, and chemical shrinkage of cement. Evolutions of the average hydration degree and compressive strength of concrete were experimentally investigated to this end, and then simulated with multiscale approach. The specimens were subjected to curing temperature 20°C, 40°C, 60°C, and 80°C for first 7 days while maintaining constant relative humidity of 100 %, and then water curing at 20°C for the rest days till tests. The high-temperature curing accelerates the hydration process, but the variance in hydration degree between standard temperature (20°C) and high-temperature conditions diminishes with prolonged water curing. An enhancement in compressive strength is also observed in the early stages of high-temperature curing, succeeded by a decline compared with standard curing after the 50th curing day. Quantitative analysis reveals that volume fractions of hydrates and porosity subjected to high-temperature curing show a substantial increase in the first 7 curing days, and the denser layer of hydration products formed on cement slows down the hydration in later curing ages. The complex evolution of strength in concrete undergoing high-temperature curing is influenced by temporal consideration (the hydration degree) and spatial considerations (the density of C-S-H and the chemical shrinkage of cement). The surge in hydration significantly contributes to strength promotion in early stages. However, the pivotal factor leading to strength deterioration is the increase of porosity when the difference in the hydration degree is less than 0.065.

Study of Structural Defects Evolution in Fine-Grained Concrete Using Computed Tomography Methods

Introduction. When studying composite materials for construction purposes, it is needed to consider the mechanisms of formation of the structure and properties of modern concretes in the process of strength development. In studies of modern composite materials based on cement binder, there is no information about the development of structural defects and destruction of the material at the initial stages of strength development. This information can be obtained using X-ray computed tomography, a promising method of nondestructive testing of the state of the material. Therefore, the objective of this work was to study the formation and propagation of cracks in samples of fine-grained concrete with different fractional composition of sand due to natural processes of cement shrinkage, as well as the mechanics of destruction of samples of modified fine-grained concrete when applying a compressive load at the early stages of strength development. Materials and Methods. The study used fine-grained concrete mixtures of three compositions with different sand gradation. The tomography samples were made by placing fresh mixtures in polymer cylindrical containers. Tomography of the samples immediately after manufacture, as well as after 8 and 51 days, was performed in a YXLON Cheetah microfocus X-ray machine. The composition with two-fraction sand was modified by mechanical activation of the components, 20×20×20 mm cube samples were made. Further, compression tests were performed at the Instron installation after 3 and 7.5 hours, and then — tomography of the destroyed samples.Results. It was established that the destruction of contact zones depended on the ratio of the size of the fractions. In the presence of a bulk of coarse sand grains in concrete, the destruction of contact zones was more pronounced and had a main mode. When using fine or polyfraction sand, contact zones were destroyed locally and had a visually smaller area. The images of the destroyed modified sample, tested 3 hours after manufacturing, showed clear cracks and indents on the edges, which indicated the elastic-plastic nature of the destruction. In 7.5 hours, the edges of the sample upon destruction were covered with a network of small cracks; inside the sample there were also numerous cracks and microcracks, which indicated brittle fracture. Based on the obtained images of the deformed structure of modified concrete, the mechanism of transition from elastic-plastic destruction of the material to brittle one was clearly visible.Discussion and Conclusion. The studied dependences of the influence of the size of fine aggregate on the mechanisms of formation and propagation of structural defects contribute to the theory of the processes of destruction of fine-grained concretes. The results obtained prove the prospects of using X-ray computed tomography as a method of nondestructive testing of the internal structure of fine-grained concrete, including at the early stages of strength development.

Investigation of shrinkage mechanism of alkali-activated slag

Slag is a highly active waste product that can be added to alkali-activated cement to improve their mechanical properties, but also creates significant shrinkage, which limits its usefulness. This study examines the reasons behind the shrinkage of alkali-activated slag (AAS). The research uses a comprehensive approach that includes linear shrinkage testing, comparative chemical analysis, microscopic structural characterization, internal relative humidity evaluations, pore size distribution assessments, and nanoindentation testing. The results show that AAS has more chemical shrinkage, self-drying shrinkage, and drying shrinkage than ordinary Portland cement. AAS’s shrinkage deformation increases with variations in the activator modulus. Chemical reactions that produce aluminosilicate gel with smaller particle sizes and lower bound water are the primary factors contributing to chemical shrinkage in AAS. The high self-drying and drying shrinkage of AAS can be attributed to several factors: AAS experiences a more rapid decrease in internal humidity during the early curing stages, AAS materials typically exhibit smaller most probable pore sizes, and hardened AAS products tend to have a lower creep modulus. The addition of oil shale semi-coke (OSS) to AAS can modify the composition and microstructure of the reaction products, resulting in an increase in porous reaction products and ultimately reducing shrinkage. This study's findings are significant for understanding the causes and potential solutions for alkali-activated cement shrinkage issues.

Mitigating autogenous shrinkage of cement with carbon nanotube sponge

Autogenous shrinkage can be mitigated by the addition of superabsorbent polymer (SAP), however, typically at the cost of a significant strength loss. To overcome such dilemma, hydrophilic carbon nanotube sponge (H-CNTSP) was proposed in this study as a novel internal curing agent. Due to the high porosity and enriched hydrophilic functional groups, H-CNTSP can absorb pore solution at 72 g/g driven by the capillary force, which is 176%–620 % higher than the commercial SAPs. The autogenous shrinkage of cement can be reduced or mitigated with the addition of 0.05–0.2 wt% H-CNTSP due to the continuous water release after final setting. Interestingly, the compressive strength loss resulting from the addition of H-CNTSP can be greatly diminished and even be overcompensated by the formation of CNT/hydrate nanocomposite shell with a higher modulus. This study illustrates the great potential to optimize concrete performance through proper design of assembly structures with chemically functionalized nanomaterials.

Effects of NaHCO3 as the activator and the in-situ carbonate seeding on the properties of high-dosage Ca(OH)2 + slag (HCHS) cement

This study investigated the effects of the addition of NaHCO3 (5, 10, and 15% molar amount of Ca(OH)2) on the setting time, compressive strength, drying shrinkage, and hydration process of high-dosage Ca(OH)2 + Slag (HCHS) cement. The results indicated that the NaHCO3 addition could significantly increase the 1-day compressive strength of HCHS cement from almost 0 to 10 MPa and decrease the drying shrinkage of HCHS cement up to 46.1% compared to it without NaHCO3. But the addition of NaHCO3 above 5% would result in accelerated setting, increased porosity, and decreased strength in the later stages. NaHCO3 played an in-situ carbonate seeding effect, forming CaCO3 crystals through the initial reaction of Ca(OH)2, and the activator that increased solution alkalinity promoted the formation of hydration products. These could contribute to the HCHS cement with high early compressive strength, good volume stability and certain porosity, suitable for further carbon capture.

Dry Shrinkage and Frost Resistance Performance of Cement Stabilized Aggregate Materials

In this paper, the mechanical, dry shrinkage and frost resistance performance of cement stabilized aggregate materials were investigated. Furthermore, the nonlinear analysis between dry shrinkage strain and frost resistance performance was conducted. The results showed that the mechanical performance of cement stabilized aggregate with different cement content showed a linear improving relationship. A higher cement content owns a correspondingly better mechanical performance. With the different moisture content, the dry shrinkage and frost resistance performance of cement stabilized aggregate material showed a similar improving and deteriorating trend. With the increasing moisture content, the dry shrinkage strain and dry shrinkage coefficient were improved and reached to the optimum values, and then started to deteriorate. The optimum dry shrinkage and frost resistance performance were obtained with 6.0% moisture content. The nonlinear relationship between dry shrinkage strain and frost resistance coefficient was gained and the correspondingly optimum dry shrinkage strain and frost resistance was discerned, i.e. 94.3×10-6 and 47.6, respectively. The moisture content significantly influence the pore parameters of prepared samples, whose trend followed those of dry shrinkage and frost resistance performance. The pore size distribution of these composites shifted toward smaller pore size scope with a proper moisture content. In addition, scanning electron micrographs (SEM) showed that the denser microstructure of prepared cement stabilized aggregate materials.

Investigation on the equivalent strength of Portland cement and PC-CSA blends: Experimental findings and thermodynamic modelling

Mixing calcium sulfoaluminate (CSA) cement and Portland cement (PC) can provide several benefits for certain applications, especially reducing the carbon footprint of PC. This study investigated the heat of hydration, hydration products, mechanical properties, autogenous shrinkage and microstructure of blended cement, and phase composition calculations were also made with thermodynamic modelling. The results show that the autogenous shrinkage of the cement paste is effectively mitigated due to the swelling produced by the rapid hydration of ye'elimite before 1 d. However, when the CSA admixture is 15 wt%, many large holes and obvious cracks can be found by three-dimensional rendition of X-ray computed tomography (X-CT), this may be attributed to the adverse effects of phase transformation, specifically the conversion of ettringite into monosulfate. Combined with the thermodynamic modelling results, the hydration of PC and CSA in the blended cement is a competitive relationship, and the presence of AH3 is not found in the PC-rich blended systems. In addition, the compressive strength of the blended mortars with addition of 5 wt% CSA at 28 d reached 61.5 MPa which is equivalent to that of plain PC. However, the strength of 15 wt% CSA addition is about 30 MPa lower than that of 5 wt% CSA. This is significantly correlated with AFt/AFm, and once AFt/AFm exceeds a certain limit, the strength of PC-CSA blends is significantly lower than that of plain PC.

Evaluating the Sealing Performance of Plug and Abandonment Cement Systems Under Downhole Conditions

Summary Microannuli are an important cause of post-abandonment seepage along abandonment plugs set in wells. Autogenous cement shrinkage, occurring when the cement sets, is a contributing factor to the formation of such flaws. Cement shrinkage and its potentially deleterious effects can be mitigated by using a properly designed and placed expanding cement system. Reliable evaluation of cement plugs’ sealing performance requires testing under elevated temperature and pressure conditions representative for downhole conditions. In this contribution, two laboratory setups designed for this purpose are described, namely (i) small-scale tests on 2-in. plugs and (ii) large-scale tests on 8-in. plugs. In both setups, plugs are cured and tested under downhole conditions inside sections of steel pipes. These pipes are equipped with lateral pressure-temperature sensors, which allow the recording of stresses that develop on the cement-steel interface when the hydrating cement plug expands. Using this bespoke cement testing equipment, a strong positive correlation was found between the amount of interface stress buildup and the sealing performance of the set cement plug against gas flow. This demonstrates that cement systems that expand effectively under downhole conditions can reduce post-plug and abandonmen (P&A) seepage risks. While providing valuable insight, the 2-in. and 8-in. plug setups are labor intensive to operate and hence impractical to use in field laboratories for cement slurry verification. Unfortunately, standard industry methodologies to verify the effectiveness of the cement expansion additives (CEAs) do not take into account in-situ well conditions. To allow the industry to still evaluate cement plug sealing performance with low complexity while maintaining reliability, a conventional ultrasonic cement analyzer (UCA) was modified to enable simultaneous measurement of interface stress development. Similar to the 2-in. and 8-in. plug sealing evaluation setups, this modified UCA vessel was equipped with a lateral pressure-temperature sensor, to monitor interface stress between the cement and vessel wall with time. For this contribution, multiple cement slurries were cured and evaluated in the 2-in. and 8-in. plug evaluation setups, as well as in this newly developed modified UCA vessel. Strong correlations were found among the stress buildups in all three setups. This enables the modified UCA test results to be used as a proxy for sealing performance of P&A cement plugs under downhole conditions.

Early age hydration and autogenous shrinkage of blended cement containing brick powder

Early age hydration and autogenous shrinkage of blended cement containing brick powder (BP) was investigated using hydration heat, internal relative humidity (IRH) and 1H NMR methods. The results show that BP can promoting the early nucleation and growth process of cement. The unique porous structure of BP gives it water absorption property, which plays a role in internal curing. The internal curing effect of BP reduced the rate of decrease of IRH in cement paste and effectively reduced the autogenous shrinkage of cement paste. These findings suggest that moderate adjustment of the dosage of BP can effectively promote the hydration and control the autogenous shrinkage of cement-based materials.

Experimental study of pure Class G cement hydration up to 150 °C and 50 MPa

A comprehensive experimental investigation of Portland cement hydration kinetics in a wide temperature range from 35 °C to 150 °C with pressure up to 50 MPa was performed by heat of hydration, chemical shrinkage and ultrasonic measurements. Increasing curing temperature was found to have a stronger acceleration effect during the main hydration period while increasing curing pressure had a stronger acceleration effect during the pre-induction period of cement hydration. By comparing chemical shrinkage test results with other methods of estimating cement degree of hydration, such as quantitative X-ray diffraction, non-evaporable water content measured by thermogravimetric analysis, as well as heat of hydration, it was observed that total chemical shrinkage of cement at complete hydration decreased with curing temperature from 35 °C to 75 °C and then stayed stable between 75 °C and 150 °C. Similarly, the P-wave velocity of cement (which is an indicator of physical and mechanical properties) as a function of hydration degree decreased with increasing curing temperature in the range between 35 °C to 75 °C, then remained relatively stable between 75 °C and 130 °C. The reduction of gel water content in C–S–H from 35 °C to 75 °C is believed to be the primary cause of these observed phenomena.

Cellulose nanocrystals (CNCs) as a potential additive for improving API class G cement performance: An experimental study

Integral cement sheaths are crucial for safe and economical hydrocarbon production throughout the well lifecycle. Cement additives tailor short- and long-term cement properties for various well conditions to ensure well integrity. Although various additives exist, the current trend in reducing the carbon footprint motivates the developing "greener” additives that are environmentally friendly and made from renewable and sustainable sources such as cellulose nanocrystals (CNC). CNCs exhibit superior properties and have shown significant impact on cement slurry, including increased degree of hydration, strength, and altered properties. However, most studies on CNCs are intended for construction industry rather than hydrocarbon and geothermal well cementing. Investigating the use of CNCs as high-performance cement additives is therefore of interest due to their potential benefits. This study aims to determine the effect of CNC on vital well cement properties. The effects of CNC were determined using standard American Petroleum Institute (API) test procedures and equipment in an experimental approach. The experimental findings indicate that the addition of cellulose nanocrystals (CNC) at a concentration of 2 vol% resulted in a notable increase of 7% in viscosity, a significant decrease of 50% in free water, a remarkable reduction of 78% in cement shrinkage, and no discernible effect on slurry thickening time. Furthermore, the inclusion of a 0.2 vol% of CNC yielded a significant surge of 56% in compressive strength after 21 days and accelerated 500 psi strength development by 9%. However, the investigation revealed that a concentration of 1.5 vol% of CNC represents a threshold concentration or the turning point, beyond which the addition of CNC can negatively impact the studied cement properties.

Understanding the role of a novel internal conditioning technique with functionalized montmorillonite in cement hydration kinetics

A novel internal conditioning (InCon) technique based on saturated sodium montmorillonite (sMT) functionalized with two non-ionic surfactants, polyoxyethylene (9) nonylphenylether and t-octyl phenoxy poly ethoxyethanol, is investigated in this study. With the integration of water for internal curing and pozzolanic reactivity in a single system, the role of InCon in modifying cement hydration kinetics is comprehensively elucidated. The results indicate that, in the presence of InCon, both silicate reaction and secondary aluminate reaction rates are enhanced, and the apparent activation energy (Ea) of cement hydration was decreased from 34.3 KJ/mol to 28.7 KJ/mol indicating a lower temperature sensitivity and threshold of the cement hydration reactions. In addition, decreased CH contents, improved degree of hydration, increased chemical shrinkage, and the formation of additional CSH and aluminum-containing phases were obtained from the cement with InCon. The autogenous shrinkage of cement and the negative impact of dry sMT on the early age strength of cement can be offset by InCon paving a new path to improve the overall properties of concrete.

Effect of Particle Size and Morphology of Siliceous Supplementary Cementitious Material on the Hydration and Autogenous Shrinkage of Blended Cement

Supplementary cementitious material (SCM) plays an important role in blended cement, and the effect of the particle size and morphology of siliceous supplementary cementitious material on hydration should not be ignored. In this study, 0.5 h and 1 h of wet grinding was applied to pretreat iron ore tailing powder (TP), and the divergence in pozzolanic behavior and morphology were investigated. Then, the treated TPs were used to replace the 30% cement contents in preparing blended cementitious paste, and the impact mechanism of morphology on performance was studied emphatically. M, the autogenous shrinkages of pastes were tested. Finally, hydration reaction kinetics was carried out to explore the hydration behavior, while X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the hydration product properties, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize the pore structures of hardened specimens. Results indicated that wet grinding has a dramatic effect on particle size and morphology, but hardly affects the phase assemblages and pozzolanic reactivity of TP, while the particle shape of TP changes from sub-circular to clavate and, finally, back to sub-circular. The results of hydration reaction kinetics, representing the morphology of particles, had a significant effect on hydration rate and total heat, and compared with the sub-circle one, the clavated particle could inhibit the hydration procedure. With the increasing grinding time, the compressive strength of cementitious paste was increased from 17.37% to 55.73%, and the micro-pore structure became denser; however, the autogenous shrinkage increased.

Exploring the Mechanical Properties, Shrinkage and Compensation Mechanism of Cement Stabilized Macadam-Steel Slag from Multiple Perspectives

Steel slag is characterized by high strength, good wear resistance and micro-expansion. This study aims at exploring the potential of steel slag in cement stabilized aggregates, mainly including mechanical properties, shrinkage and compensation mechanisms. For this purpose, the compressive strength and compressive resilient modulus of cement stabilized aggregates with different steel slag contents (CSMS) were initially investigated. Subsequently, the effects of steel slag and cement on dry shrinkage, temperature shrinkage, and total shrinkage were analyzed through a series of shrinkage test designs. Additionally, in combination with X-ray diffraction (XRD) and Scanning electron microscope (SEM), the characteristic peaks and microscopic images of cement, steel slag and cement-steel slag at different hydration ages were analyzed to identify the chemical substances causing the expansion volume of steel slag and reveal the compensation mechanism of CSMS. The results show that the introduction of 20% steel slag improved the mechanical properties of CSMS by 16.7%, reduced dry shrinkage by 21%, increased temperature shrinkage by 5.8% and reduced its total shrinkage by 19.2%. Compared with the hydration reaction of cement alone, the composite hydration reaction of steel slag with cement does not produce new hydrates. Furthermore, it is noteworthy that the volume expansion of the f-CaO hydration reaction in steel slag can compensate for the volume shrinkage of cement-stabilized macadam. This research can provide a solid theoretical basis for the application and promotion of steel slag in cement-stabilized macadam and reduce the possibility of shrinkage cracking.

Development of Underwater Mortar Using Belitic Calcium Sulfoaluminate Cement

Abstract Rapid-setting belitic calcium sulfoaluminate (BCSA) cement has established advantages compared to portland cement in terms of environmental benefits, lower shrinkage, and faster strength gain. There is a dearth of experimental studies on practical applications of this cement. The aforementioned fast setting and low shrinkage of BCSA cement make it an ideal cement for underwater applications such as repairs or rapid construction. This study details preliminary mixture design guidance for proportioning an underwater repair mortar with BCSA cement that can self-consolidate underwater and achieve a compressive strength exceeding 28 MPa in 3 hours or less. By varying the sand-to-cement ratio (s/c) and water-to-cement (w/c) ratio, an acceptable mixture was achieved at a w/c of 0.42 and an s/c of 1.25. Observations on the effect of mix parameters on flow, compressive strength gain, and physical appearance of the specimens are also reported. Future work should investigate the interaction of this cement with different water-reducing and viscosity-modifying admixtures, as this was out of the scope of this study.

Application of Polyacrylic Hydrogel in Durability and Reduction of Environmental Impacts of Concrete through ANN.

While adding superabsorbent polymer hydrogel particles to fresh concrete admixtures, they act as internal curing agents that absorb and then release large amounts of water and reduce self-desiccation and volumetric shrinkage of cement that finally result in hardened concrete with increased durability and strength. The entrainment of microscopic air bubbles in the concrete paste can substantially improve the resistance of concrete. When the volume and distribution of entrained air are adequately managed, the microstructure is protected from the pressure produced by freezing water. This study addresses the design and application of hydrogel nanoparticles as internal curing agents in concrete, as well as new findings on crucial hydrogel–ion interactions. When mixed into concrete, hydrogel particles produce their stored water to power the curing reaction, resulting in less volumetric shrinkage and cracking and thereby prolonging the service life of concrete. The mechanical and swelling performance qualities of the hydrogel are very sensitive to multivalent cations found naturally in concrete mixes, such as aluminum and calcium. The interactions between hydrogel nanoparticles and alkaline cementitious mixes are described in this study, while emphasizing how the chemical structure and shape of the hydrogel particles regulate swelling behavior and internal curing efficiency to eliminate voids in the admixture. Moreover, in this study, an artificial neural network (ANN) was utilized to precisely and quickly analyze the test results of the compressive strength and durability of concrete. The addition of multivalent cations reduced swelling capacity and changed swelling kinetics, resulting in fast deswelling behavior and the creation of a mechanically stiff shell in certain hydrogel compositions. Notably, when hydrogel particles were added to a mixture, they reduced shrinkage while encouraged the creation of particular inorganic phases within the void area formerly held by the swelled particle.

Influence of Polymer Latexes on the Properties of High Performance Cement–Based Materials

The application of polymer latex provides an additional approach when optimizing the properties of high–performance cement–based materials. Given that cement–based materials are extraordinarily sensitive to the characteristics and relative content of polymer latexes, identifying their influence is essential for application. This paper investigates the impact of polymer latex types and its relative content on the mechanical properties, hydration product, pore structure, and drying shrinkage of cement–based materials with a low water to binder ratio. The results showed that the mechanical properties, pore structure, and drying shrinkage of the styrene butadiene latex modified samples were better than those of ethylene vinyl acetate latex and silicone acrylic latex modified ones. Incremental increases to the polymer to cement ratio induces a slight reduction on compressive strength, and styrene–butadiene latex promotes tensile strength. Polymer latex hinders the transformation from ettringite to monosulfate, reducing the bound water and portlandite generated. Increasing the polymer content induces more significant stretching in the vibration peak of SO4 from ettringite. Further incorporation of polymer latex contributes to ettringite precipitation and the decline of harmful pores. Polymer addition also results in lower drying shrinkage compared with the reference group.

Rapid regeneration cement-stabilized macadam: Preparation, mechanical properties, and dry shrinkage performance

Based on the mechanical strength and dry shrinkage of cement mortar, the early strength anti-cracking materials ZFP (mixture of single early strength agents Z1 and Z3 and expansion agent P) and ZSP (mixture of single early strength agents Z1, Z2, and Z3 and expansion agent P) are optimized. Using waste cement-stabilized macadam in road base maintenance as an aggregate, rapid regeneration cement-stabilized macadam containing early strength anti-cracking materials with different contents was prepared, and the mechanical properties and dry shrinkage performances were tested. The early strength anti-cracking mechanism of rapidly regenerated cement-stabilized macadam with different ZSP contents was explored via microscopic experiments. The results show that ZFP and ZSP have an optimal mixing ratio, which makes the setting time, mechanical properties, and dry shrinkage of cement mortar the best. The 2 d compressive strength of rapidly regenerated cement-stabilized macadam containing 8% ZSP was 6.23 MPa, while the 3 d compressive strength of the rapid regeneration cement-stabilized macadam containing 7% ZFP was 6.14 MPa, and the corresponding dry shrinkage coefficients were 91.6% and 11.2% lower than those of the control group, respectively. The chlorine salt, sulfate, and organic amine in ZSP react with calcium hydroxide, which accelerates the hydration process of cement and improves the early strength of rapidly regenerated cement-stabilized macadam. Hydration products, such as expansive sulfuraluminate and chloroaluminate produced by cement hydration in rapidly regenerated cement-stabilized macadam and calcium oxide in ZSP, inhibit early dry shrinkage cracking.

Testing and Evaluation Method Investigates Cement Expansion in Cased-Hole Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208679, “Cement Expansion in Cased-Hole Environments: A Novel Laboratory Testing and Evaluation Method With Successful Field Implementation,” by Vasilii Sukhachev, Amir Salehpour, SPE, and Ilshat Akhmetzianov, SPE, Schlumberger, et al. The paper has not been peer reviewed. Preventing bulk shrinkage of cement in cased-hole wells is important when dealing with the risk of sustained casing pressure (SCP). Current studies based on membrane tests suggest that, even with a high-percentage content of expanding agents, cement systems show little or no expansion in dry media. An alternative laboratory method for measuring cement expansion, followed by a successful field application, was used to evaluate the total bulk volume change of the cement based on curing in a dry environment and in water. Optimal cement-slurry properties were obtained. The developed cement system, which was successfully implemented in the field, provided long-term zonal isolation with no indication of SCP to date. Introduction For a major operator in the Caspian region, drilling development wells required passing through shallow overpressured permeable zones containing water and biogenic gas. The optimal casing design used to minimize the likelihood and severity of SCP consisted of isolating the shallow-soil zone by use of a cemented 24-in. liner followed by a 20-in. surface casing cemented using a two-stage method (Fig. 1). During the first stage, the cement was pumped inside of the 24-in. liner. Then, an external casing packer placed in the 20-in. casing was inflated against the 24-in. liner before performing the second-stage cement job. The second-stage cementing operation brought the cement above the top of 24-in. liner and provided sufficient length to isolate against the shallowest distinct permeable zone. Cement is considered a primary wellbore barrier element. However, the cement placed between the 24-in. liner and the 20-in. casing and in the annulus of the 30-in. conductor and 20-in. casing is subject to shrinkage. This shrinkage leaves a potential leak path all the way to the wellhead on an offshore platform. The cement systems chosen consisted of the 1.92-SG (16-lbm/gal) slurry for the second stage cementing of the 20-in. casing because this stage was the system most susceptible to shrinkage. This slurry was placed in the annular space of the 20-in. casing and both the 24-in. liner and the 30-in. conductor. The curing temperatures and pressures in the field are 32°C and 6.74 MPa at the bottom of the well and 28°C and 2.48 MPa at the top of the cement. The top of the cement will be in direct contact with the spacer, a fluid with 89% water content; however, the remainder of the cement column will not have access to excess water during curing. If acceptable results could be achieved with the 1.92-SG cement system, then the same blend could be used for the 24-in. liner tail and the first-stage tail slurry of the 20-in. casing. This method is a possible solution to obtain a more-robust system that prevents the risk of SCP.