Characteristics Of Cement Research Articles

Experimental Study on the Strength and Damage Characteristics of Cement–Fly Ash–Slag–Gangue Cemented Backfill

In order to achieve the goal of effectively utilizing solid waste resources and improving mining stability, it is necessary to incorporate various types of solid wastes in the production of cemented backfill. For investigating the compressive strength and damage characteristics of Cement–Fly Ash–Slag–Gangue (CFSG) cemented backfill under loading, real-time X-ray Computed Tomography (CT) scanning was employed to capture two-dimensional (2D) grayscale slices and three-dimensional (3D) fracture models during uniaxial compression testing. The study quantitatively assessed the evolution of cracks and microstructural damage in CFSG cemented backfill. The results indicate that the specimens underwent four stages of transformation, including compaction, linear elasticity, yielding, and residual deformation, during the uniaxial compression process. The specimens exhibited a measured compressive strength of 3.44 MPa and a failure strain of 0.95%. As the axial strain increased, there was an increase in 2D porosity observed in the CT images and a greater dispersion of crack distribution. A 3D model constructed from CT slices illustrated the feature of cracking expansion, with the fracture volume gradually increasing during the elastic deformation phase and experiencing rapid growth during the yielding and residual deformation phases. The damage variable, obtained from the volume of 3D cracks, exhibited a slow-growth pattern, characterized by a rapid increase followed by a more gradual rise with the increase in axial strain. This study serves as a significant reference for comprehending the micro-mechanisms involved in the damage process and cracking characteristics of cemented backfill mixed with solid wastes under external loading conditions.

Evaluation of nanoparticle effect on heavy and light wellbore cement slurries

Cementing around the casing in oil and gas wellbores provides multiple benefits such as proper zonal isolation, casing support, and prevention of fluid migration. Wellbore cement is an important part of the completion and abandonment process. However, wellbore cement has some drawbacks such as micro-annuli formation or loss of zonal isolation. Nanoparticles (NPs) have been shown to improve the characteristics of wellbore drilling fluids but have not been used extensively in cement. The objective of this paper is to show the effect of NPs’ concentration on wellbore cement characteristics such as thickening time, viscosity, and fluid loss properties. Nanoparticle barite and magnetite were added to heavy cement and bentonite was added to light cement in intervals of 1, 3, and 5 % by weight of cement to test the resulting cement characteristics. The results showed that the thickening time increased for all concentrations of nanoparticles, except for the 5 % magnetite. The resulting yield stress of both cement mixtures increased for all concentrations of nanoparticles. The viscosity for all concentrations of nanoparticles in the heavy cement was greater than the control case, while no change in viscosity was seen with the light cement. Fluid loss generally decreased by increasing nanoparticle concentrations for both heavy and light cement. The results of this work in combination with results from the literature show that the addition of barite, magnetite, or bentonite nanoparticles can enhance wellbore cement without diminishing the pumpability and curing time.

Microscopic analyses and performance characteristics of granite powder blended cement

This research investigates the characteristics of Granite Powder (GrP) and its potential use as a partial replacement for cement in mortar production. The GrP samples were analyzed via microscopic techniques. The effects of GrP Blended Cement (GrPBC) were examined on the workability and mechanical characteristics by partially replacing Ordinary Portland Cement (OPC) with 0–40 wt% GrP in 4 wt% increments. Life cycled assessment in terms of Embodied Energy (EE) and Global Warming Potential (GWP) of GrPBC-based mortar were assessed based on cradle-to-gate boundaries and the sustainability and economic indexes were determined at 28 days compressive strength. The study proposed new models to predict the compressive strength of GrPBC with respect to Water to Binder (W/B) ratio. The presence of active minerals depicts GrP as pozzolanic materials. The optimum replacement level of GrP in the blended mix, based on the fresh and hardened properties of GrPBC, is 20 wt% to achieve 75% of the strength activity index. GWP and EE declined as the GrP in the mixtures rose. The best sustainable and economic prospects were attained at the 25 wt% GrP replacement level. The compressive strength and the W/B ratio are highly correlated. Thus, GrP has proven to be a sustainable construction material in the construction sector.

The void characteristics of cement emulsified bitumen mixture under microwave heating by X-ray computed tomography

Excessive void content is an essential reason for the poor road performance of cement emulsified bitumen mixture (CEBM), while incorporating steel slag with high microwave responsiveness into CEBM and followed by microwave heating may be an effective method to reduce void content. To verify this hypothesis, this paper investigated the effect of microwave heating on the void characteristics of CEBM using X-ray computed tomography. The study mainly focused on the distribution characteristics of different-sized voids, the distribution uniformity of voids, and the shape characteristics of voids. The results revealed that the number of different-sized voids decreased significantly after microwave heating, especially the number of small-sized voids decreased the most. The reduction in void number improved the distribution uniformity of longitudinal and radial voids. However, it reduced the distribution uniformity of voids between the inner and outer sections of the specimen. Through the analysis of aggregate movement characteristics, it was found that the increase in the separation degree of inner and outer voids was due to the larger-sized aggregates being more efficiently distributed on the outer section of the specimen. Additionally, microwave heating reduced the complexity of void shapes. The reduction of void number and the improvement of void characteristics by microwave heating are expected to enhance the structural durability of CEBM, thereby improving its road performance.

Experimental Study on Strength and Microstructure of Loess Improved by CG-2 Curing Agent and Cement

In order to study the improvement effect of the CG-2 curing agent and cement on loess, a series of physical and mechanical property tests and microstructure tests were carried out on loess improved with different dosages of curing agent and cement to study the physical and mechanical properties, durability and microscopic pore characteristics of the CG-2 curing agent and cement-improved loess. The results show that the unconfined compressive strength of improved loess increases gradually with the increase in curing agent and cement dosage, and the higher the compaction degree and the longer the curing age, the higher the unconfined compressive strength. In the case of the same cement content, the higher the dosage of curing agent, the more the unconfined compressive strength of improved loess increases. Under the condition of reaching the same unconfined compressive strength, the addition of curing agent can significantly reduce the amount of cement. The more the content of cement and curing agent, the less the unconfined compressive strength decreases after a certain number of freeze–thaw cycles, and the higher the dry-wet cycles index after a certain number of dry-wet cycles, indicating that the addition of curing agent can significantly improve the ability of the sample to resist freeze–thaw cycles and dry–wet cycles. According to the microscopic test results, it is found that the addition of curing agent can reduce the porosity of soil particles, change the contact and arrangement mode between soil particles, and enhance the agglomeration and cementation characteristics between soil particles, and obviously improve the physical and mechanical properties of soil. The research results can provide new ideas and methods for the improvement technology of loess.

Insight into the early hydration characteristics of Portland cement with hydroxyethyl methyl cellulose highlighted by 1H low-field NMR

1H low-field nuclear magnetic resonance (1H NMR) as a non-destructive test method can effectively capture the water state changes in cement pastes. The water changes can in turn reflect the early hydration characteristics of cement pastes. Hydroxyethyl methyl cellulose (HEMC) with different viscosities affects the hydration characteristics of cement by acting on the water in different states. The following experimental results are obtained by testing hydration of cement pastes with HEMC by using 1H NMR test. Incorporating 0.1–3% HEMC with different viscosities all can effectively control the bleeding water phenomenon. HEMC can absorb a part of the water in the cement pastes. Incorporating 2–3% HEMC significantly delays the enrichment of the gel pores water and interlayer water. When the content of HEMC increases from 0% to 3%, the hydration degree of cement pastes tends to decrease. Besides, HEMC with higher viscosity of 15000–40000 mPa·s obviously delays the hydration process of cement pastes compared to HEMC with lower viscosity of 400 mPa·s.

Nonivasive methods for monitoring the characteristics of bone cement during radiotherapy in tumor patients

Nonivasive methods for monitoring the characteristics of bone cement during radiotherapy in tumor patients

Study on the effect of stress path on the deformation and non-coaxial characteristics of modified iron tailings

In order to study the deformation and non-coaxial characteristics of fiber cement modified iron tailing sand (FCIT) under different stress paths. The evolution law of the dynamic stress ratio (η) on the cumulative deformation and non-coaxial angle of FCIT under different tension-compression amplitude ratios (α) was explored through hollow torsional shear tests. The deformation behavior of FCIT is analyzed by using the stability theory. The research results show that: 1) The increase of dynamic stress level will deepen the cumulative deformation of FCIT, while the increase of α will make the deformation mode of FCIT develop into bulging failure-shear failure-tensile failure. 2) According to the development trend of cumulative strain and cumulative strain rate of FCIT, it can be divided into three stages: plastic stability, plastic creep and incremental collapse, and the cumulative strain rate development prediction model is established, and the prediction error distribution is within ±20%. 3) The stress path determines the non-coaxiality of FCIT to a certain extent, and the non-coaxial angle fluctuates and decreases with the increase of the principal stress direction angle. When α=0.125, the maximum and minimum values of the non-coaxial angle of FCIT are 1.5 rad and 0.4 rad respectively. 4) Cement hydration reaction generates calcium alumina and hydrated calcium silicate (C-S-H) to make FCIT structure more compact, fiber-matrix interfacial connections more dense, and play a role in filling the pores.

Comparison between Four-Probe and Two-Probe Electrical Resistivity Measurement to Monitor the Curing and Piezoresistivity Behavior of Smart Cement Paste Modified with Waste Steel Slag and Green Nano-magnetite

Abstract This study aims to examine the compressive strength, electrical resistivity, and piezoresistivity characteristics of ordinary Portland cement (OPC) with a constant water-to-cement ratio (w/c) of 0.38. The optimal value of steel slag (SS) was determined to be 5 % based on the compressive strength of six different mixes of cement paste modified with various SS from 0 % to 30 % weight of cement. Additionally, the investigation will include modified cement samples containing 1 % green synthesized material and commercially available nano-magnetite (NM). Because iron is the primary component of SS and NM, the electrical resistivity, which is the primary criterion for structural health monitoring of cementitious material, can be increased by adding SS and NM. Hence, a comparative analysis was conducted to assess the resistivity of cement paste throughout the early curing period up to 28 days using an alternative current (AC) and embedding wires into the specimen, employing both the two-probe (2P) and four-probe (4P) methodologies. The findings suggest that the 4P method is a more precise approach for determining electrical resistivity than the 2P method, as the wire probe is not considered in the 4P method. Hence, it is imperative to compute the correlation between the 2P and 4P methodologies in order to attain a precise resistivity measurement. The suggested model indicates that the expected 4P resistivity can be measured with high precision, a high coefficient of determination (R2) of .97, and a low root mean square error (RMSE) of 7.33 Ω·m, based on the 2P result. The piezoresistivity results demonstrated that the cement paste modified with green synthesis nano-magnetite (GSNM) had a higher electrical resistivity (ER) change, 10.85 % greater than cement paste only, 57 % higher than cement modified with SS, and 34.2 % higher than cement paste modified with commercial nano-magnetite (CNM) after 28 days of curing. In addition, the compressive strength of cement paste modified with GSNM was higher than that of cement paste, cement paste modified with SS, and cement paste modified with CNM by 15.96 %, 21 %, and 1.7 %, respectively, after 28 days of curing. A Vipulanandan p–q model was used to forecast the electrical resistivity of cement paste versus time at start hydration during 28 days of curing and the change of electrical resistivity versus compressive strength at 3, 7, and 28 days. The Vipulananda p–q model anticipated both electrical resistivity and piezoresistivity behavior well.

Study on the hydration characteristics of steel slag cement

The direct use of stainless steel slag in cement presents potential weaknesses in terms of strength and the risk of cracking, which limits its large-scale utilization. Therefore, it was crucial to explore the use of stainless steel slag in clinker cement. In this study, the hydration characteristics of stainless steel slag cement (SS) and ordinary Portland cement (OPC) were compared and analyzed using isothermal calorimetry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), and heavy metal leaching tests. The study investigated the hydration heat, compressive strength at curing ages of 1d, 3d, 5d, 7d, and 28d, hydration products, and safety aspects of SS and OPC. Results showed that the optimum calcination temperature of stainless steel slag cement (SC) and Portland cement (PC) are 1350℃ and the holding time is 2 h. The clinker composition of the two is similar. The main minerals are dicalcium silicate (C2S), tricalcium silicate (C3S), tricalcium aluminate (C3A) and aluminum ferrite tetracalcium (C4AF). Compared with OPC, SS shows a delayed heat release peak during hydration. SS exhibited a delayed exothermic peak in the heat release during hydration compared to OPC. Furthermore, during the stable hydration period, SS produced more calcium aluminate-type solid solution, tightly encapsulating the crystal surface, and exhibited lower heat release. With an increase in curing age, the contents of acicular ettringite (AFt), C-S-H gel, and hexagonal calcium hydroxide (CH) gradually increased in both SS and OPC. Due to higher contents of C4AF, C3S, and C2S in SS, it produced more AFt and C-S-H than OPC. The compressive strength of both SS and OPC increased with curing age, reaching 55.4 MPa and 42.4 MPa at 28 days, meeting the requirements of the national standard (GB/T 21372-2008) in terms of initial and final setting times and f-CaO content. Additionally, heavy metal leaching and soluble Cr6+ tests indicated that their use is safe.

Mutual Activation Mechanism of Cement–GGBS–Steel Slag Ternary System Excited by Sodium Sulfate

To promote the large-scale recycling of solid waste, the hydration characteristics of blended cement with different amounts of GGBS (ground granulated blast-furnace slag) and SS (steel slag) were investigated. The optimum blending amounts of GGBS and SS in cement were 40% and 10% by mass, and the optimum dosage of Na2SO4 in the C50-S40-SS10 (50 wt.% cement–40 wt.% slag–10 wt.% steel slag) system was 2 wt.%. The flexural and compressive strengths of the C50-S40-SS10 system after adding 2 wt.% Na2SO4 are 57.95% and 9.28% higher than that of pure cement at 28 d. XRD, FT-IR and Ca(OH)2 content analysis were chosen to investigate the hydration products of pure cement and blended cement. The results show that GGBS enhanced the hydration of both cement and SS. And GGBS contributed to the generation of calcium silicoaluminate hydrate (C–A–S–H) in the blended cement system. The addition of Na2SO4 promoted the hydration reaction and contributed to the generation of ettringite (AFt) in the ternary system. The hydration heat evolution results showed that GGBS and SS can reduce the hydration heat of cement. Na2SO4 had similar effects and delayed the time of AFt conversion to monosulfide calcium sulphoaluminate (AFm). A mutual activation mechanism of cement–GGBS–SS ternary system mixed with Na2SO4 was proposed in this study.

Field implementation to resist coastal erosion of sandy slope by eco-friendly methods

Coastal erosion is a global issue that not only compresses land space but also undermines offshore structures. In this study, two eco-friendly technologies (microbially and enzyme induced calcium carbonate precipitation) were implemented at a sandy slope field site to enhance erosion resistance. Improvement of the treated sandy slope against erosion was assessed by penetration resistance, calcium carbonate content, cone penetration testing (CPT) results, terrain data and microscopic morphology. Results indicated that the penetration resistance and calcium carbonate content of treated slopes increased first and then decreased over time because of the gradual formation of calcium carbonate and the erosion caused by the marine environment. Calcium carbonate content and penetration resistance presents an obvious linear relationship. The existence of the superficial cemented crust layer increased the water retention capacity of the sand in the atmosphere region. The calcium carbonate content and CPT results in the tidal region shows the characteristics of layered cement. The spherical calcium carbonate cementation improves the roughness and integrity of the terrain, enhances the particle size of the sand, gradually changing the topography from pre-treatment dynamic erosion to depositional patterns. The treated slope still maintained a certain penetration resistance and calcium carbonate content for 60 days until being eroded by the wind in the atmosphere region. However, the effective protection duration in the tidal zone which encounters wind, wave, tide and reflow was about 24 days, and would thus need to be reinforced periodically over time to obtain long-term protection.

Bond behaviour of smooth surface GFRP pultruded profiles with cement grout

The advantages of glass fibre reinforced polymer (GFRP) pultruded composite profiles, such as their high strength-to-weight ratio, corrosion resistance, and low maintenance costs, have attracted the attention of researchers and end users in structural applications. In spite of this, one of the challenges associated with using GFRP pultruded profiles is their smooth surfaces when bonded with concrete. To address this challenge, this study investigated four different approaches that can be used to improve the bond performance between GFRP pultruded profiles and concrete surfaces. These approaches are the incorporation of glass sand into cement grout, the variation in the size of the sand particles in the grout, the surface preparation of GFRP profiles, and the use of various cement characteristics. The experimental results show that the surface preparation of the GFRP profiles is the most effective method of improving the bond strength between the GFRP profiles and the concrete surface. Additionally, a theoretical model is developed to predict the bond behaviour, and it is observed that the linear elastic theory with the inclusion of the bond surface roughness coefficient is capable of predicting bond behaviour. The overall outcome of the study will assist design engineers and end users in the application of smooth surface GFRP profiles in concrete structures.

Carbonation of calcium sulfoaluminate belite binder: mechanism and its implication on properties

Calcium sulfoaluminate belite (CSAB) binder is an alternative low CO2 binder. CSAB cement has ye’elimite as the primary clinker phase which hydrates to form monosulfate or ettringite as the main hydration product. The hydration and mechanical characteristics of CSAB cement and PC-CSAB blended cement have been reported in several studies; however, studies on the durability characteristics such as carbonation are limited. This study focuses on evaluating the microstructural and mechanical alterations due to carbonation in a CSAB binder system and understanding the underlying mechanism of development of the carbonation front. CSAB binder was found to carbonate rapidly compared to PC binder, accompanied by a reduction in compressive strength. This was attributed to the increase in the pore volume due to the carbonation of the ettringite-rich microstructure, facilitating further ingress of CO2 into the microstructure. The rate of carbonation in CSAB binders diverged significantly from the square root of time model used for PC binders.

Proportioning of steel fiber concrete tailored composition using the method of mathematical experiment planning

Suggested proportioning of steel fiber concrete tailored composition can be made by using the method of mathematical experiment planning. A wide variety of types of fiber, the size and aggregate grain-size distribution, the number and characteristics of cement, and the need to obtain concrete mixes of different fluidity are used in the production of fiber reinforced materials. That is why it is impossible to develop a proportioning standard method. Thereby it is suggested to conduct an experiment of proportioning of steel fiber concrete tailored composition using the method of mathematical experiment planning in each specific case. The article provides an example of proportioning of steel fiber concrete on specific components. When planning the experiment, we selected water-cement ratio, cement consumption, fiber reinforcement content and the ratio of the content of coarse and fine aggregates as the independent factors. The compressive and tensile strengths of steel fiber concrete and the fluidity (stiffness) of the mixture were selected as responses. This article presents the possibility to make a choice of the ratio of the number of primary components for obtaining steel fiber concretes with the necessary characteristics by analyzing the obtained regression equations.

Piezoresistive investigation of calcium aluminate cement-based MWCNT/NCB composite at elevated temperatures

Ordinary Portland cement (OPC)-based self-sensing smart sensors can be affected by exposure to elevated temperatures, which can negatively affect their mechanical strength, electrical resistivity, piezoresistivity, stress/strain sensitivity, and reversibility. Therefore, this study aimed to investigate the mechanical properties, electrical resistivity, and piezoresistive characteristics of calcium aluminate cement (CAC)-based multiwalled carbon nanotube (MWCNT)/nano carbon black (NCB) conductive composite sensors with different concentrations at normal temperature and after exposure to 200 °C and 400 °C. The results indicate that the CAC-based MWCNT/NCB composite fillers exhibit good mechanical properties, low electrical resistivity, and fully reversible piezoresistive sensing properties at both normal and elevated temperatures. The elevated temperature treatments led to a more extensive sudden increase in piezoresistivity. Moreover, CNCB2 with higher concentrations achieved peak compressive strength and fractional changes in electrical resistivity (FCR) sensitivity at 200 °C. Therefore, this study provides a new understanding and pathway for developing CAC-based MWCNT/NCB smart sensors for structural health monitoring (SHM) and for multifunctional applications at normal and elevated temperatures.

Direct shear characteristics of cement stabilized clay subjected to previous shear

The cement stabilization techniques have been applied to various types of infrastructure and become one of the essential techniques. A lot of researches have been conducted on the physical and mechanical properties of the cement stabilized soils, many of which are the studies on the stabilized soil after the hydration. However, the number of researches is limited on the physical and mechanical behavior of cement stabilized soil during the hydration stage and subjected to shear deformation during the hydration stage. In this study, a series of direct shear tests was conducted on the shear behavior of cement stabilized soil to investigate the influence of the magnitude and timing of the shearing on the shear behavior. The researche revealed that the shear strength of the stabilized soil is recovered to the peak strength when it is subjected to the shear deformation prior to the peak strength and the shear strength increases by the cement hydration. On the other hand, when the soil is subjected to the large deformation exceeding to the peak strength, the shear strength loss is not recovered in the following shearing stage. The strength gain due to the cement hydration is also influenced by the initial shearing, where the strength of soil subjected to the large shearing remains small for the curing stage. In this manuscript, the test results are introduced to discuss the influence of the initial shearing as well as the testing procedure.

Influence of Microwave Heating on The Microscopic Characteristics of Cement Emulsified Asphalt Mixture Containing Steel Slag

Influence of Microwave Heating on The Microscopic Characteristics of Cement Emulsified Asphalt Mixture Containing Steel Slag

An Experimental Study on the Mortar Compressive Strength According to Fineness and Replacement Rate of Limestone Powder

Cement industry emits as much as about 8% of global carbon dioxide emissions, so it is necessary to develop new technologies that can effectively reduce carbon dioxide emissions to prevent global warming and to maintain industry competitiveness. The supplementary cementitious materials that can replace clinkers are limited to fly ash and blast furnace slag in Korea, but various materials such as limestone and calcined clay have been used in other nations. In this study, the characteristics of limestone powder mixed cement were reviewed in consideration of the limestone powder manufacturing process.

Hydration Characteristics of High Chloride Cement

High-chloride cement, enriched with calcium chloro aluminate (CCA), a compound of CaO-Al<sub>2</sub>O<sub>3</sub>-CaCl<sub>2</sub>, displays a higher Cl content than ordinatry portland cement. This specialized cement, incorporating limestone, clay, siliceous materials, and Cl-abundant cement kiln dust, is known for its superior early strength, making it an attractive option for resource recycling. However, the excessive Cl content can lead to reinforcement corrosion and a decrease in the durability of the hardened cement paste. Current research has primarily focused on its manufacturing characteristics, with studies on hydration reactions for practical application remaining limited. This study aims to explore the hydration reactions of high-chloride cement to determine its practicality. The experimental results reveal that high-chloride cement with abundant CCA significantly promotes the formation of ettringite, an Al-based hydrate, in the initial hydration stages. This process results in the binding of leached Cl ions with monosulfate, forming Friedel’s salt. Although the early formation of expansive hydrates might negatively affect long-term durability, mixing this cement with ordinary Portland cement in appropriate amounts can improve workability and enhance early strength and setting. Furthermore, the transformation of Cl ions into a crystallographically stable form like Friedel’s salt indicates a potential for safer usage, especially in reducing risks such as reinforcement corrosion.