Cemented Components Research Articles

Effect of acidic amino acids on wet pre-carbonation of β-C2S in steel slag

Wet pre-carbonation of steel slag is an important solution to the steel slag soundness problem. This method, however, can consume a significant amount of silicate phase in steel slag. To address this issue, it is proposed that the consumption of calcium silicate can be reduced while the hydration performance of steel slag can be improved by adding acidic amino acids into the wet carbonation of steel slag. β-C2S is the main cementitious component in steel slag. Synthetized β-C2S was used to simulate the reaction mechanism of steel slag during carbonation and to study the role of acidic amino acids in carbonation. The carbonation products were characterized by XRD, FT-IR, TG-DTG, and SEM. The results demonstrated that without the addition of acidic amino acids, the carbonation degree of β-C2S reaching the maximum at 1 h under the experimental conditions. Calcite and amorphous silica was formed as a result of the carbonation of β-C2S. The final carbonation degree was lower after adding higher concentrations (0.1 mol/L) of acidic amino acids than before. Higher concentrations of acidic amino acids increased the content of metastable CaCO3, primarily vaterite. Acidic amino acids were added in the pre-carbonation of steel slag, then the steel slag was mixed with cement to prepare cementitious materials. The cementitious materials’ 28-day compressive strength was higher than without amino acids, and the maximum of strength increased by 9.45 % compared to that without amino acids. Whether amino acids were added or not, the boiling expansion value decreased to 0 after 1 h of carbonation, indicating that the carbonation reaction improved the soundness of cementitious materials.

Using micro-XRF to characterize chloride ingress through cold joints in 3D printed concrete

Digital fabrication methods with concrete have been rapidly developing, with many problems related to component production and material control being solved in recent years. These processes produce inherently layered cementitious components that are anisotropic, and in many cases, produces a weak interface between layers, which are generally referred to as cold joints. While material strength at these interfaces has been well studied in recent years, durability has received less attention, even though cold joints can function as channels for aggressive agents, such as chlorides. This work presents a method using micro-X-ray fluorescence (μXRF) to image chloride ingress into layer interfaces of 3D printed fine-grained concrete specimens produced with varying layer deposition time intervals, and also compares it to neutron imaging of moisture uptake. The results show that cold joints formed after a 1 day time interval are highly susceptible to chloride ingress, and that curing conditions play a major role in how quickly interfacial transport can take place. The μXRF method is also shown to be useful for study of transport of chlorides in cold joints, due to its spatial resolution and direct analysis of an aggressive species of interest.

Superimposed hydration exothermic model of cement slurry considering different reaction rates of various active substances

Cement components usually contain two or more hydration active substances with different hydration reaction rates, and the existing hydration exothermic model of cement-based materials do not consider the difference of reaction rates of active substances. This paper proposes a new exothermic hydration model of cement-based materials, which takes into consideration the different reaction rates of multi-component active substances. Firstly, the hydration heat and the representative temperatures of cement slurry with the water-cement ratio of 0.3, are tested through adiabatic and dissolution heat methods. Secondly, the total hydration reaction process is assumed as the composition of the reaction processes of multi-component active substances. Then, a hydration exothermic model witch is superimposed by several exponential functions is fit according to the exothermic hydration experimental data and the Arrhenius chemical expression. The comparison results show that the proposed model is more accurate than the monomial exponential function model, especiallyat the early age before the initial setting time. In conclusion, the proposed model can better explain the influence of the reaction rate difference of different active substances of cement on the exothermic process, and the accuracy of hydration analysis is more accurate by using it than others.

Calcined marl as a potential main component of cement

The cement industry is facing the challenge of a lack of supplementary cementitious materials substituting clinker. This applies primarily to granulated blast furnace slag, the most commonly used as the main component of cements, due to changes in the metallurgical industry, and to siliceous fly ash due to the abandonment of fossil fuels in the world. A potential new main component of common cements may be calcined marls, which are available in large quantities for every producer of Portland clinker. In this article, research was carried out on calcined marls from the Folwark deposit, near Opole, Poland. The conducted experiments showed that marls after calcination show pozzolanic-hydraulic properties and can replace both granulated blast furnace slag and silica fly ash in the composition of cement. The best pozzolanic-hydraulic properties are obtained by calcination of Folwark marls at 900°C

Metal-Backed Patella Implants in Knee Arthroplasty: Can the Past Predict the Future?

BackgroundThere is a renewed interest in uncemented total knee arthroplasty to potentially provide longer durability, including the use of newer design metal-backed patellae (MBPs). The purpose of this study was to review survivorship with failure mode and time to failure of an earlier version MBP at up to 10-30 years of follow-up that may influence the desirability of using these components today. MethodsA retrospective review was performed of patients that had uncemented total knee arthroplasty with an uncemented MBP. All-cause revision rates were obtained from chart reviews and telephone discussions with patients and family members of deceased patients. Kaplan–Meier plots were used to determine the implant survivorship. Outcome scores were compared between revised and nonrevised patients. ResultsThe 97 knees that had an end point of an aseptic revision or last known contact with implant survivorship averaged 15 years (range, 0-32 years). There were 40 knees that underwent revision that included 37 patella component failures (38.1%). All patellar failures had polyethylene wear or fracture. None were revised due to loosening. Survivorship was 97.9% at 5 years, 88.7% at 10 years, and 53.0% at 20 years. Median time to failure was 11 years. ConclusionLoosening is not a failure mode with this MBP. There were 75% of the failures occurring after 10 years. Use of contemporary MBP with improved but still thin polyethylene warrants guarded optimism when used in younger patients where longer survivorship than with a cemented all-polyethylene patellar component is the goal.

USE OF CEMENTED FEMORAL COMPONENT FOR REVISION IN PERIPROSTHETIC FEMORAL FRACTURES (PFF) IN THE ELDERLY

PFFs are an increasing burden presenting to the acute trauma services. The purpose of this study is to show that cemented revision for Vancouver B2/B3 PFFs is a safe option in the geriatric population, allows early pain-free weight bearing and comparable to a control-group of uncemented stems with regard to return to theatre and revision surgery.A retrospective review was conducted of all PFFs treated in a Level 1 trauma centre from 2015-2020. Follow up x-rays and clinical course through electronic chart was reviewed for 78 cemented revisions and 49 uncemented revisions for PFF. Primary endpoints were all cause revision and return to theatre for any reason. Secondary endpoints recorded mobility status and all-cause mortality.In the cemented group there were 73 Vancouver B2, 5 Vancouver B3 PFF; the mean age was 79.7 years and mean radiological follow-up of 11.9 months. In the cementless group there were 32 Vancouver B2 and 17 Vancouver B3 PFFs; with all 49 patients undergoing distally bearing uncemented revision, the mean age was 72.7 years and mean radiological follow-up of 21.3 months.Patients treated with a cemented prosthesis had significantly higher ASA score (2.94 -v- 2.43, p<0.001). The primary endpoints showed that there was no significant difference in all cause revision 3/78 and 5/49 p=0.077, or return to theatre 13/78 -v- 12/49 p=0.142.Secondary endpoints revealed no significant difference in in-hospital mortality. The cementless group were more likely to be mobilising without any aid at latest follow-up 35/49 -v- 24/78 p<0.001.The use of cemented revision femoral component in the setting of PFFs is one option in the algorithm for management of unstable PFFs according to the Vancouver classification. Evidence from this case-control study, shows that the all-cause revision and return to theatre for any cause was comparable in both groups.

Calcite‐cemented concretions in non‐marine sandstones: An integrated study of outcrop sedimentology, petrography and clumped isotopes

AbstractCalcite‐cemented concretions can reduce reservoir quality and form important low‐permeability baffles for fluid flow in sandstone hydrocarbon carrier beds/reservoirs. Understanding the origin and distribution patterns of concretions has important implications for characterizing reservoir heterogeneity and developing fields. The origin of calcite concretions in non‐marine sandstones lacking detrital carbonate to source the cement is poorly studied. The practical difficulty of obtaining the precipitation temperature of the concretions prevents the precise determination of the source of cement components, solute flux, pore water type and the geochemical microenvironments in which cement precipitated. Carbonate clumped isotope thermometry can give unique constraints to the temperature of concretionary cement precipitation. This study focused on outcrops of the Lower Cretaceous non‐marine Qingshuihe Formation in the Urho area, on the north‐western margin of the Junggar Basin (West China). Four depositional facies associations were recognized, corresponding to channel, mid‐channel bar, abandoned channel and overbank floodplain environments. Calcite concretions occur only in sandstones and include spherical, ellipsoidal and tabular forms. They are isolated and/or mutually aligned in layers that tend to be either at the top, base, or within channel and mid‐channel sand bodies. The clumped isotope temperatures for the concretionary calcite range from 31 to 45°C with a standard error of <3°C. The calcite has highly variable, low δ13C values ranging from −16.91 ± 0.01 to −2.93 ± 0.02‰ (Vienna Pee Dee Belemnite). The 13C‐depleted bicarbonate source was linked to biodegradation of migrated oils at shallow burial owing to tectonic uplift and erosion. Calcite δ18O values are very consistent and fall between −12.30 ± 0.04 to −9.79 ± 0.31‰ (Vienna Pee Dee Belemnite). Introduction of meteoric water was a dominant mechanism for the pronounced 18O‐depletion in the oxygen isotopes of pore water, along with water–rock interaction during alteration of volcaniclastic materials in sandstones. Meteoric groundwater flushed the Qingshuihe sandstones as confined aquifers down the regional palaeo‐slope, biodegrading the migrated oils and enabling a sufficient solute flux for precipitation of concretions.

Suitability Study of Using UAVs to Estimate Landfilled Fly Ash Stockpile.

The decrease in fly ash production due to the shift in coal industries toward a green environment has impacted many concrete industries as fly ash is a significant component in cement and concrete. It is critical for concrete industries to identify the availability of fly ash in landfills to meet their demand if the supply decreases. This paper aims to analyze the suitability of UAVs in determining the fly ash stockpile volumes. A laboratory test is performed to validate the proposed UAV method. Then, a real quarry site is selected to demonstrate the suitability in a large scale. The results indicate that the UAVs estimate the most accurate volume of the stockpile when the flight height is about five times the stockpile height. A considerable range of 3.5-5 times the stockpile height is most suitable for quantity takeoff. The findings of this study provide a recommendation for choosing the most appropriate technology for the quantitative estimation of fly ash in existing landfills on a large scale.

Mid‐ to Long‐term Follow‐up of Severe Acetabular Bone Defect after Revision Total Hip Arthroplasty Using Impaction Bone Grafting and Metal Mesh

In revision total hip arthroplasty (THA), reconstruction of severe acetabular bone defect continues to be problematic for orthopedic surgeons. This study reports the mid- to long-term survivorship, radiological outcomes, and complications of impaction bone grafting (IBG) and metal mesh with a cemented acetabular component in the reconstruction of severe acetabular bone defects in revision THA. This retrospective consecutive study included 26 patients (29 hips: type II B, four; type II C, three; type III A, 10; and type III B, 12) who underwent revision THA, which was performed using IBG and metal mesh, between 2007 and 2014 in our institution. All patients were followed up regularly for clinical and radiographical assessments. Migration and loosening of prosthesis graft integration and complications were observed and analyzed. Survival analysis was performed using a Kaplan-Meier survival analysis. At the time of revision, 75.9% of the hips (22 hips) were classified as type III bone defects. The average follow-up period was 9.4 ± 2.8 (range, 2.4-14.0) years. Of the 29 hips, four hips (13.8%) were assessed as clinical failures; at the last follow-up, two had undergone re-revision THA, and two had not been scheduled for re-revision THA despite radiological failure of the acetabular component. Among them, three clinical failures (10.3%) were due to aseptic loosening, and one (3.4%) was due to infection. Radiographic evaluation showed bone graft integration in all hips during the follow-up. The Kaplan-Meier survivorship analysis revealed an acetabular reconstruction survival rate of 86.5% (95% confidence interval, 61.4%-95.7%) at 10 years. IBG and metal mesh with a cemented acetabular component for revision THA is an effective technique for treating severe acetabular bone defects, with effective mid- to long-term outcomes due to the solid reconstruction of the acetabular bone defect and restoration of the hip rotation center.

Uncemented total hip replacement with impaction bone grafting in protrusio acetabuli

Protrusio acetabuli is a central acetabular defect resulting from migration of femoral head medial to Kohler’s line. Idiopathic central displacement of femoral head within the acetabulum is quite rare. However, it may be seen in arthritic hips secondary to rheumatoid arthritis, ankylosing spondylitis, previous trauma, osteomalacia, etc. Primary Total Hip Replacement (THR) in such cases is difficult because of the deficient medial bone, decreased peripheral bony support to the acetabular component and proximal and medial migration of the joint centre. Several techniques described previously in the surgical management of protrusio acetabuli include cemented acetabular components with cement alone or in association with morselized bone graft to reconstruct the acetabulum. However, cement has high rates of migration and loosening of cemented acetabular components in young patients leads to more revision surgeries within the first decade of implantation. The purpose of the study is to describe the technique and results of using impacted morselized bone graft with a porous coated cementless acetabular component in patients with protrusio acetabuli.A total of 20 primary THR’s (10 unilateral and 5 bilateral) in 15 patients (8 females and 7 males) with protrusio acetabuli were performed between 2018 and 2021, out of which 4 had mild,7 had moderate and 9 had a severe grade of protrusion. A total of 10 hips were affected by rheumatoid arthritis,3 by ankylosing spondylitis and 7 had unknown etiology. After the surgery, all bone grafts had united by the sixth month with no perceptible change in acetabular component position in any case. The mean preoperative Harris Hip Score was 48 which improved to 82 at the latest follow-up. 45% had excellent,33% had good, and 22% had fair results. There was no dislocation. The use of impacted morselized autograft with a cementless porous acetabular component is a good technique of restoration of hip biomechanics and sound fixation in cases of protrusio acetabuli.

Functional outcomes of a Lima modular shoulder replacement

BackgroundThe use of metal backed glenoid (MBG) components over polyethylene (PE) for total shoulder arthroplasty (TSA) remains controversial. While their advantages and disadvantages are documented, few studies exist demonstrating their efficacy in TSA and conversion rates to a reverse total shoulder arthroplasty (RSA). This study aims to evaluate acute postoperative complications, shoulder pain, functional outcomes, and conversion rates to RSA in patients who underwent TSA using a modular MBG component. MethodsA retrospective review of individuals undergoing TSA between October 2014 and March 2019 was performed. Inclusion and exclusion criteria were defined. Baseline surgical characteristics were collected and outcomes were assessed preoperatively and postoperatively using the visual analog scale and American Shoulder and Elbow Surgeons score at preoperative, 1 year, 2 year, and final follow-up. Revision rates were documented. Summary statistics were performed using a two-tailed Student’s t-test. ResultsThe study’s final cohort consisted of 91 patients, with a mean age of 66.5 ± 8.1 years, an average body mass index of 32.8 ± 6.9 kg/m2, and 53.8% being male. Majority of patients underwent a TSA on the right side (64.9%), with an average operative duration of 105 minutes and EBL of 148.8 mL. The mean follow-up time was 38.8 months. Thirteen patients (14.3%) went onto conversion to an RSA. Among these individuals, 30.8% (n = 4) was due to a traumatic rotator cuff tear (RCT), 23.1% (n = 3) due to excessive PE wear, and 46.2% (n = 6) due to nontraumatic RCT. The average time to revision for all patients was 27.7 ± 24.8 months. Mean time to revision was 17.5 ± 9.8 months for trauma patients, 51.0 ± 3.5 for patients with signs of excessive PE wear, and 22.9 ± 31.3 months for nontrauma patients. Mean preoperative visual analog scale scores were 6.8 ± 2.3 and American Shoulder and Elbow Surgeons scores were 28.5 ± 15.6. Both significantly improved at 1-year, 2-year, 3-year postoperative timepoints as well as the final postoperative timepoint (P < .001). ConclusionPatients undergoing TSA using a MBG component reported no acute postoperative complications and improved shoulder function. A small proportion of patients were converted to RSA for signs of a RCT and excessive component wear. This study may suggest that the MBG design demonstrates a failure rate equivalent to cemented PE component systems; thereby, does not expose patients to subsequent higher rates of revision procedures.

Chloride binding behaviors and early age hydration of tricalcium aluminate in chloride-containing solutions

Understanding the hydration kinetics and interactions of hydration products of cement components with chlorides is crucial for designing durable cement-based materials. The most reactive component of ordinary Portland cement (OPC), tricalcium aluminate (C3A), was investigated on its hydration kinetics, chloride binding behaviors and hydrated phase assemblages through multiple ex-situ and in-situ methods. The hydrated phases of C3A demonstrated different chloride binding isotherms in NaCl and CaCl2 solutions at different ages. Chloride ions can suppress the formation of calcium aluminate hydrates (OH-AFm and C3AH6) while calcium ions were favorable to increase the content of hydrocalumite (Cl-AFm) and regulate its crystal structure. The carbonation process deteriorated the chloride binding capacity of C3A pastes through producing more calcium mono/hemi-carboaluminate phases (Mc/Hc) or forming a solid solution between Mc and Cl-AFm. These findings can be used as a guide for corrosion protection design of cement-based materials.

A Review on The Compressive Strength and Workability of Concrete with Agricultural Waste Ash as Cement Replacement Material

Concrete is commonly used as a construction material because of the important properties is broadly utilized as development materials within the development segment. Unfortunately, the component of cement within the concrete results in many side-effects such as affecting the environment. Therefore, this paper presented the review of essential to seek out an alternative materials which may be utilized as cement replacement materials by reutilizing agricultural waste ash. Selected agricultural waste ash which are Palm Oil Fuel Ash (POFA), Rice Husk Ash (RHA), Groundnut Shell Ash (GSA), Sugarcane Bagasse Ash (SBA) and Oyster Shell Powder (OSP) were review in terms of their compressive strength and slump height of the mixture. The treated palm oil ash which is going to be used as partial cement replacement material for the proper design mix and optimal ash replacement. The replacement percentage of palm ash in the concrete were set at 10%, 20%, and 30% by weight with the optimal replacement ratio of the supplementary cementitious content. Palm Oil Fuel Ash (POFA) is a material that having sufficient requirements to be a good pozzolana and cementitious material according to ASTMC618 in terms of chemical composition. POFA is a material that consists high silica contents. By having more silica contents, it will help to improve the properties, in particular its compressive strength, bond strength, and abrasion resistance. After conducting several research, it was concluded that the optimal replacement for POFA is 20% and it is better to have finer POFA. POFA also proved some of the important properties is the CO2 emissions would be reduce.

Effects of White Chicken Eggshell Powder on Compressive Strength, Water Solubility, and Setting Time of Calcium-Enriched Mixture.

The present study aimed to evaluate the effects of adding chicken eggshell powder (CESP) to calcium-enriched mixture (CEM) cement on its compressive strength (CS), solubility, and setting time. In this study, CESP was added at weight percentages of 3% and 5% to the powder component of the CEM cement. To measure the CS, a total of 36 samples (height, 6 mm; diameter, 4 mm) were tested in a universal testing machine. The setting time was assessed for 18 disk-shaped samples (diameter, 10 mm; height, 1 mm). Additionally, solubility test was performed on 18 samples (diameter, 8 mm; height, 1 mm) after 24 hours, 72 hours, seven days, and 14 days under dehydration conditions by calculating the weight changes; the results were then subjected to a normality test. Next, for the comparison of different test groups, parametric ANOVA test and post-hoc Tukey's multiple comparison test were performed at a significance level of 0.05. The addition of 5% CESP to the CEM cement significantly reduced its setting time and water solubility (P=0.02 and P=0.01, respectively). Moreover, it significantly increased the CS over a 21-day period (P<0.001). Additionally, the addition of 3% CESP also resulted in a significant increase in CS (P<0.001). While 3% CESP reduced setting time and water solubility, the difference was not statistically significant. The findings suggest that the addition of 5% CESP to CEM cement has the potential to improve its sealing ability, durability, and ability to withstand chewing forces in endodontic treatments. These results highlight the relevance of CESP as an additive for cement modifications and indicate its potential clinical implications.

Simultaneous lice eggshell removal from wool and anti-felting with a single protease treatment

The residue of wool lice eggshells and felting are both important factors that affect the quality of wool. Since the main components of the eggshell cement and the wool scales are proteins, it is possible to remove the eggshells and decrease felting at the same time by protease treatment. In this work, AtP, a fungal protease from Aspergillus tubingensis, was discovered to be suitable for simultaneous eggshell removal and anti-felting. By optimizing the process, AtP can remove 88% of the eggshells and reduce the feltability by 29.4%, with only 6.3% reduction in the tensile strength of the wool. Mechanistic studies show that AtP is sensitive to the flatness of substrate surface and the density of disulfide bonds, which endows its relative selectivity between eggshell cement and wool. To our knowledge, this work reports the first ecofriendly technique to complete eggshell removal and anti-felting in one step, which will be not only beneficial for the wool industry, but can also be extended to similar use for pet or human hair.

Powder-bed-based 3D printing with cement for sustainable casting

3D printing allows for the cost-effective fabrication of moulds and can cast complex shapes. In this study, alumina cement and fine aggregates for refractories were used as the main raw materials, and saturation was adjusted to an appropriate level to control the cement binder mixture for sand casting. For cast iron, the mould must withstand temperatures of up to 1400 °C and must exhibit sufficient strength, gas permeability, and thermochemical durability at high temperatures. To accomplish these requirements, 3D printing powder was prepared by adjusting the ratio of fine aggregate (D50: 30 μm) and an even finer cement component (D50: 4 μm). To improve the moulding quality, a green body was used to optimise the cement admixtures to increase the strength, and the saturation level of the 3D printer was adjusted for dimensional accuracy. The high-temperature durability of the mould was evaluated by measuring its strength after heat treatment, using Simultaneous Thermal Analysis (TG-DSC), and through dimensional stability assessment. In addition, the pores of the specimens were analysed through microscale X-ray tomography. The surface resolution and tolerance of the final casting were determined by a 3D image roughness test using a surface roughness scanner. The cement exhibited the shortest curing time and the highest strength when the mass ratio of CA (CaO·Al2O3) to C12A7 (12CaO·7Al2O3) was 8:2. The final mixing mass ratio of cement to the fine aggregate was 8:2, which was determined based on the relationship between flowability and powder bed surface quality. The results proved the high-temperature thermal stability of the 3D-printed mould, which showed a total mass reduction of less than 3% and a low coefficient of linear expansion up to 1300 °C. Consequently, the suitability of the 3D-printed moulded body, composed of casting sand with cement as a binder, for casting at temperatures >1400 °C was demonstrated. Additionally, the final printed porous mould de-powdered easily, and its recyclability was verified by strength testing various mass ratios of fresh and recycled powder. Therefore, through optimisation of the material combinations and adjustment of the 3D printing process parameters, optimal gas permeability and moulding resolution could be achieved without any casting defect, while maintaining handling strength. The findings of this study demonstrate the potential of expanding the scope of powder-bed-based 3D printing of cement material to the casting market.

Keratose sponges in ancient carbonates – A problem of interpretation

AbstractReports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine to peritidal carbonates include cases interpreted to be keratose sponges. However, living keratose sponges have elaborate, highly elastic skeletons of spongin (a mesoscopic end‐member of a hierarchical assemblage of collagenous structures) lacking spicules, thus have poor preservation potential in contrast to the more easily fossilized spicule‐bearing sponges. Such interpreted fossil keratose sponges comprise diverse layered, network, amalgamated, granular and variegated microfabrics of narrow curved, branching, vesicular–cellular to irregular areas of calcite cement, thought to represent former spongin, embedded in microcrystalline to peloidal carbonate. Interpreted keratose sponges are presented in publications almost entirely in two‐dimensional (thin section) studies, usually displayed normal to bedding, lacking mesoscopic three‐dimensional views in support of a sponge body fossil. For these structures to be keratose sponges critically requires conversion of the spongin skeleton into the calcite cement component, under shallow‐burial conditions and this must have occurred prior to compaction. However, there is no robust petrographic–geochemical evidence that the fine‐grained carbonate component originated from sponge mummification (automicritic body fossils via calcification of structural tissue components) because in the majority of cases the fine‐grained component is homogenous and thus likely to be deposited sediment. Thus, despite numerous studies, verification of fossil keratose sponges is lacking. Although some may be sponges, all can be otherwise explained. Alternatives include: (i) meiofaunal activity; (ii) layered microbial (spongiostromate) accretion; (iii) sedimentary peloidal to clotted micrites; (iv) fluid escape and capture resulting in bird's eye to vuggy porosities; and (v) moulds of siliceous sponge spicules. Uncertainty of keratose sponge identification is fundamental and far‐reaching for understanding: (i) microfacies and diagenesis where they occur; (ii) fossil assemblages; and (iii) wider aspects of origins of animal clades, sponge ecology, evolution and the systemic recovery from mass extinctions. Thus, alternative explanations must be considered.

Effect and mechanism of composite early-strength agents on sulfoaluminate cement-based UHPC

Some major construction projects require materials that can quickly and easily obtain high mechanical properties. Nowadays sulfoaluminate cement (SAC) has attracted attention for such projects due to its fast hardening rate, high early strength, and low alkalinity. Added early strength agents are commonly used to improve the early strength of Ultra-high performance concrete (UHPC). Most early-strength agent research has focused on Portland cement systems. Due to the different components of SAC and Portland cement, the compatibility between different early strength agents and SAC needs to be further explored.This paper selected three inorganic early-strength agents, calcium formate (Ca(HCOO)2), aluminum sulfate (Al2(SO4)3), and lithium carbonate (Li2CO3), and an organic early-strength agent, triethanolamine (TEA), which are commonly used. Experimental studies were carried out for single and compound early-strength agent systems in a SAC-based Ultra-high performance concrete (UHPC) system with a low water-cement ratio of 0.23. The results showed three inorganic early-strength agents reduced the setting time and improved the strength of the UHPC. The 4 h compressive strength of UHPC with 0.4 % Ca(HCOO)2 increased from 22.1 MPa to 41.2 MPa due to the improved microstructure and denser matrix.The composite mixture of Ca(HCOO)2 and Li2CO3 had a good synergistic effect in the early and middle stages, the compressive strength can reach 88.7 when curing 3 days. Different from Portland cement system, TEA had an adverse effect in the both single and compound systems.

Effect of curing regime on the immobilization of municipal solid waste incineration fly ash in sustainable cement mortar

Stabilizing/solidificating municipal solid waste incineration fly ash (MIFA) with cement is a common strategy, and it is critical to study the high-value utilization of MIFA in ordinary Portland cement (OPC) components. With this aim, binary-binding-system mortar was produced by partially replacing OPC (∼50%) with MIFA, and the effects of different curing regimes (steam curing and carbonation curing) on the properties of the cement mortar were studied. The results showed that the setting time of the cement paste was shorten with the increase of MIFA content, and steam curing accelerated the hardening of the mixture. Although the incorporation of MIFA reduced the strength of the mortar, compared to conventional curing method, steam curing and carbonation curing increased the 3-d strength of the mortar. For high-volume MIFA mortars, the CO2-cured samples had the highest long-term strength and lowest permeability. The incorporation of MIFA increased the initial porosity of the mortar, thereby significantly increasing the carbonation degree and crystallinity of the reaction product - CaCO3. Steam curing also further narrowed the difference in the hydration degree between MIFA-modified sample and plain paste, which may be due to the enhanced hydraulic reactivity of MIFA at high temperatures. Although the incorporation of MIFA increased the porosity of the mortar, this waste-derived SCM refined the bulk pore structure and decreased the interconnected porosity. Additionally, the heavy metal leaching contents of MIFA-modified mortars were all below 1%, which meet the requirements of Chinese standards. Compared with standard curing, steam curing and carbonation curing made the early-age and long-term performance of MIFA-modified mortar better, which can promote the efficient application of MIFA in OPC products.

Plasticity role in strength behavior of cement-phosphogypsum stabilized soils

Dredged soil and phosphogypsum are frequently regarded as wasted materials, which require further treatment to control their environmental impact. Hence, phosphogypsum is proposed as a binder to stabilize dredged soil, aiming at efficiently reducing and reusing these waste materials. In this study, the engineering properties of cement-phosphogypsum stabilized dredged soils were investigated through a series of unconfined compression tests, and the effects of plasticity index of original soils on the strength improvement were identified. Then, the microstructure test and mineralogical test were performed to understand the mechanism of physical role of original soils in strength improvement. The results revealed that the unconfined compressive strength significantly decreased with the increase in plasticity index at the same binder content. The essential factor for strength improvement was found to be the formation of cementitious materials identified as calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), and ettringite (Aft). The normalized integrated intensity of cementitious materials (CSH + CAH + Aft) by pore volume decreased with the increase in plasticity index. Consequently, the density of cementitious materials filling the soil pores controlled the effectiveness of strength improvement. More cementitious materials per pore volume were observed for the original soils with lower values of plasticity index. That is, the higher strength of stabilized soils with lower values of plasticity index was attributed to a packed structure forming by integrated fabric through denser cementitious components. It can be anticipated from the above findings that the effectiveness of stabilization treatment will significantly reduce with the increase in plasticity of origin soil. • Phosphogypsum is sufficient to stabilize dredged soil as geological material. • Establishing strength gain – normalized water content reduction relation. • Correlating strength gain with normalized cementitious materials intensity. • Proposing micro-mechanism of plasticity role in strength improvement of stabilized soils.