Final Setting Time Research Articles

Study on properties of sewage sludge cemented paste backfill and leaching mechanism of heavy metals.

In order to achieve sustainable development and control environmental pollution, this paper proposes sewage sludge (SS) as an auxiliary cementitious material, which is mixed with ordinary Portland cement (OPC), fly ash (FA), and gangue to produce sewage sludge cemented paste backfill (SS-CPB) material. The fluidity and mechanical properties of backfill materials with different SS contents and the heavy metal leaching mechanism of SS-CPB are investigated. The results reveal that (1) with the increase of SS content from 10 to 30%, the slump of fresh SS-CPB mortar decreased from 21.7 to 18.2cm, the initial setting time decreased from 2.83 to 0.58h, and the final setting time decreased from 4.92 to 0.83h. (2) Compared with the control group, the 3-day unconfined compressive strength (UCS) of the SS-CPB mixed with 10% SS increased by 49.5%, and the UCS decreased slightly in the later stage, but it also met the actual needs of coal mines. (3) Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were used to study the SS-CPB samples. It was found that the free Al3+ in SS promoted the formation of ettringite (AFt), provided part of the early UCS, and accelerated the setting time. (4) The leaching rule of heavy metal ions was analyzed in combination with leaching kinetics, and the change of heavy metal ion mass concentration in the rising stage was in line with the contraction core model controlled by diffusion.

Performance analysis of coagulation hardening effect of geopolymer prepared from high calcium-based ladle furnace slag

With the increasing demand for specialty and high-quality steel, ladle furnace refining technology has been widely used, which produces a large amount of ladle furnace slag (LFS). LFS has problems such as poor stability and early setting, which largely limit the utilization of LFS in the cement industry. In this study, the carbonization technique was used to improve the above-mentioned problems of LFS and to establish the relationship between macro performance and microstructural characteristics. In addition, the setting time, high-temperature resistance, and chemical resistance of the original LFS-based geopolymer (OLFGP) and carbonated LFS-based geopolymer (CLFGP) were compared. The results showed that the structure of LFS was denser after carbonation, and the carbonation products were mainly calcite. The compressive strength of CLFGP was significantly higher than that of OLFGP, reaching 22.6 MPa at 28 days. The initial and final setting times of CLFGP were prolonged by 15 min and 20 min, respectively, compared with OLFGP. In addition, CLFGP exhibited superior chemical resistance. The high-temperature resistance test showed that below 400 ℃ contributed to the development of mechanical properties of LFS-based geopolymer. The problems of poor stability and early setting of LFS were alleviated after carbonation, and the properties of the products were improved, which can be considered as a substitute for cement in the future.

Promoting the resource utilization of oil-based drilling cuttings pyrolysis residues in cement products

This study assessed the feasibility of manufacturing clinker and cement from oil-based drilling cuttings pyrolysis residues (ODPR). The effects of calcination temperature, ODPR content, and ODPR/GGBS (ground granulated blast furnace slag) ratio on the performance of cement were studied. In addition, the environmental performance of clinker and cement products were evaluated. The results showed that the addition of ODPR lowered the calcination temperature and improved the burnability of raw cement meal. The physical-mechanical and chemical compositions of cement products (compressive strength (28-d) of 36.43 MPa, initial setting time of 302 min, final setting time of 386 min, SO3 content of 3.06%, and Cl− content of 0.05%) could meet the Chinese standard of “Common Portland Cement (GB 175-2007)” under the optimum raw material mixing (ODPR contents of 2.17% for produced clinker and 7.5% for ternary blended cement). Approximately 98.44 kg of ODPR could be utilized when manufacturing 1 tonne of cement products, which is higher than the latest study.Moreover, the environmental performance test of clinker and ternary blended cement could meet the requirements of corresponding Chinese standards. This study provides an effective solution for recycling ODPR in the oil and gas industry.

Microstructural and optimization studies on novel one-part geopolymer pastes by Box-Behnken response surface design method

This paper reports the work on developing an optimized mix proportion of novel one-part geopolymer (OPG) binder produced by dry blending the solid aluminosilicate precursor and solid alkali source and then adding free water to the blended mix similar to the preparation of Ordinary Portland Cement (OPC). A three-level Box-Behnken Response Surface Method (RSM) design was used to study the properties of OPG mixes at fresh and hardened state and to test and develop the regression models. The Ground Granulated Blast Furnace Slag (GGBS) substitution, water to geopolymer solids (w/s) ratio, and the activator dosage were considered as the independent variables. The response target values were the flow value, initial and final setting time, and compressive strength. The multiple regression analysis with the quadratic polynomial model was used to fit the data, which offered an accurate and reliable match to the actual data. Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were used to study changes in microstructure, mineral phase, and molecular bonding of OPG mixes, respectively. Based on the material characterization observation, the change in GGBS addition, w/s ratio, and activator dosage were discovered to have a considerable impact on both the fresh and hardened properties. The optimum mix proportion obtained was 51.39% GGBS substitution, 0.32 w/s, and 12.35% activator content, with 191 mm flow, 68.56 MPa of compressive strength, 59 and 191 mins of initial and final setting time, respectively. The target values obtained using the one-part geopolymer mix with 50% GGBS substitution, 0.3 w/s, and 12% activator content were in close agreement with the target values predicted by the optimized mix, confirming the efficiency of RSM in obtaining the optimum one-part geopolymer mix proportion.

Sılıcon Based Gel to Shut-Off of Water in the Well-Bore

The quality of gel - based silicon, which forms an insulating content to prevent water and sand in oil and gas wells, have been improved. Based on the reaction between the liquid glass and hydrochloric acid, the optimal concentration of the initial reagents for the formation of the gel process was determined. The rheology, initial and final setting time of the silicon based gel, and the temperature dependencies of the gel forming process were also studied by adding 0.1-1.0% (mass ratio) of urea as cross-linking to the Na2SiO3/HCl solution. At the same time, the impact of the obtained gel of the permeability of the rock pores was determined and the filtration characteristics were studied. It has been determined that with 0.1-0.8% mass concentration of the urea added to the Na2SiO3/HCl solution, the setting time of the gel could be regulated according to the well-layer regime. The resulting silicone-based gel can be used as an injection solution that can set in 3-22 hours in oil and gas wells between the temperature of 20-80 °C.

Evaluation of cement grouted bituminous macadam technology: a laboratory study

ABSTRACT Cement Grouted Bituminous Macadam (CGBM) is a composite pavement that can offer sustainability in the pavement construction sector. The main objective of this study emphasises designing and evaluating the CGBM mixes prepared with different cementitious grouts and aggregate gradations. Compressive strength (7 and 28 days), Flexural strength (28 days), Marsh cone flow, and Initial and final setting time were considered for optimising the cementitious grouts. The details of several investigations on CGBM that include Marshall stability, Compressive strength, Indirect Tensile Strength (ITS), Resilient Modulus (Mr), Fracture energy, and Cantabro abrasion test were reported. The experimental results showed that sand and micro silica influence the mobility of grout to a greater extent. Percolation of grouts into Open Graded Friction Course (OGFC) mixes was a critical concern for grouts with flow time longer than 35 s. A reduction in the pore volume and reduced interconnected links in finer gradation resulted in improper full-depth penetration (FDP) characteristics. Mixture level tests for CGBM revealed that Mr of CGBM improved by about 6 times compared to the bituminous mix. In addition, CGBM showed high tensile strength with rapid crack propagation behaviour. Further, pavement design demonstrated a 35% of thickness reduction and cost reduction due to CGBM implementation.

Evaluation of sisal fiber and aluminum waste concrete blend for sustainable construction using adaptive neuro-fuzzy inference system

This research study presents evaluation of aluminum waste-sisal fiber concrete’s mechanical properties using adaptive neuro-fuzzy inference system (ANFIS) to achieve sustainable and eco-efficient engineering works. The deployment of artificial intelligence (AI) tools enables the optimization of building materials combined with admixtures to create durable engineering designs and eliminate the drawbacks encountered in trial-and-error or empirical method. The features of the cement-AW blend's setting time were evaluated in the laboratory and the results revealed that 0–50% of aluminum-waste (AW) inclusion increased both the initial and final setting time from 51–165 min and 585–795 min respectively. The blended concrete mix's flexural strength tests also show that 10% sisal-fiber (SF) substitution results in a maximum flexural strength of 11.6N/mm2, while 50% replacement results in a minimum flexural strength of 4.11N/mm2. Moreover, compressive strength test results show that SF and AW replacements of 0.08% and 0.1%, respectively, resulted in peak outcome of 24.97N/mm2, while replacements of 0.5% and 0.45% resulted in a minimum response of 17.02N/mm2. The ANFIS-model was developed using 91 datasets obtained from the experimental findings on varying replacements of cement and fine-aggregates with AW and SF respectively ranging from 0 to 50%. The ANFIS computation toolbox in MATLAB software was adopted for the model simulation, testing, training and validation of the response function using hybrid method of optimization and grid partition method of FIS at 100 Epochs. The compressive strength behavior is the target response, and the mixture variations of cement-AW and fine aggregates-SF combinations were used as the independent variables. The ANFIS-model performance assessment results obtained using loss function criteria demonstrates MAE of 0.1318, RMSE of 0.412, and coefficient of determination value of 99.57% which indicates a good relationship between the predicted and actual results while multiple linear regression (MLR) model presents a coefficient of determination of 82.46%.

Final Setting Judgment and Safety Evaluation of Mass Concrete Based on Strain Monitoring

A judgment method of the final setting time of mass concrete based on strain monitoring and the selection criterion of the starting point of effective deformation are proposed, and the safety of the concrete structure is evaluated based on this. Firstly, the strain monitoring theory of mass concrete is analyzed to clarify the temperature effect component and monitoring mechanism of an early strain of concrete. Then, taking the mass concrete plate of an engineering project as the research object combined with the mechanical analysis, the early strain monitoring data are segmented, and the relationship between the strain response and the temperature in different stages is fitted based on robust regression, so as to explore the correlation between strain and temperature in each stage and better explain the setting process of the concrete structure. Finally, taking the final setting time as the starting point of the effective strain, the safety of the concrete structure is further evaluated. The results show that there is a clear linear relationship between the strain response and temperature, and a high negative correlation between strain and temperature after the final setting. The time point when the frequency modulus corresponding to the strain enters a steady change and decreases with the increase of temperature is taken as the final setting time, which conforms to the concrete condensation mechanism and the temperature effect of early strain monitoring.

Comparative study of the effects of a natural pozzolan and an artificial pozzolan on the hydraulic properties of Portland cement mortar

The comparative study of some effects of natural and artificial pozzolans on the hydraulic properties of Portland cement mortar is performed in this work. The natural pozzolan used coming from the Djoungo deposit, Moungo department in the Littoral region (Cameroon) was finely ground and then sieved at 100 μm. The artificial pozzolan used is the alluvial clay of Etoa collected from Yaoundé III District in Mfoundi Division of the Centre Region of Cameroon. It was thermally activated at 700°C after grinding and sieving. The chemical and mineralogical analysis of the raw materials were studied by X-ray fluorescence, infrared spectrometry (FTIR) and X-ray diffraction (XRD) then the specific surfaces and the absolute densities were determined. The formulation of the pastes and mortar was obtained by substituting Portland cement with different pozzolans at different percentages, while the initial and final setting time of the fresh pastes were determined. Linear shrinkage, water absorption, apparent density, flexural strength and compressive strength tests at 7 and 28 days were determined on the hardened mortars. The results obtained show an increasing in the initial and final setting time with the addition of the amount of pozzolan (natural or artificial), the pozzolans played the role of setting retarder in the mixtures, finer particles of the artificial pozzolan speed up the setting time of pastes as compared to that with natural pozzolan. The shrinkage of the hardened mortars increased with the addition of the pozzolans, but it was less than 0.2% in all the samples, the specimens with artificial pozzolans were more affected by the drying shrinkage. The mortars had good mechanical resistance but from 30 to 40% pozzolan, whether artificial or natural, the resistance dropped, the dilution phenomenon caused by the partial replacement of the cement was responsible for the drop in resistance with the addition of pozzolans. The water absorption rate and the apparent density of the specimens decrease when the percentage of pozzolan increases in the mortars. Artificial pozzolan offers a better water absorption rate compared to natural pozzolan due to its higher specific surface. Natural pozzolan makes it possible to obtain a denser mortar.

A fast-setting and eco-friendly superhydrophobic high belite sulphoaluminate cement mortar

High belite sulphoaluminate cement (HBSC) has shown great potential as new lower CO2 footprint cementitious material. It makes sense to improve the hydrophobic property of HBSC to obtain high durability performance. In this paper, nontoxic short carbon chain lauric acid (LA) is used to match the early strength characteristic of HBSC to prepare fast-setting and eco-friendly LA-modified HBSC mortar (M-HBSCM). Sands modified with LA provide low surface energy for an integral hydrophobic effect. M-HBSCM exhibits superhydrophobicity even after hammering to expose the fractured internal structure, with a contact angle of 153.2°. And it shows outstanding self-cleaning property against contaminants such as sand and wet mud and a reduction in water absorption to around 23% of the ordinary HBSCM (O-HBSCM). The fabricated M-HBSCM has fast-setting property with an initial setting time of 29 min and a final setting time of 36 min. The abrasion test displays that the scratched area remains well superhydrophobic with high mechanical robustness when the droplets roll off on the inclined surface. Field-emission scanning electron microscope (FESEM) indicates that M-HBSCM contains more pores and coarser hydration products. The system of calcium alumina and pores exhibits a distinct hierarchical structure, providing the multilevel roughness required for the superhydrophobic surface. Fourier transform infrared (FTIR) spectrometer indicates that low surface energy functional groups have been successfully grafted onto M-HBSCM. The superhydrophobic concrete has good mechanical robustness, corrosion resistance, and fast-setting property, which can meet the demands of grouting reinforcement projects, the repair of various concrete structures, corrosion protection of marine structures and other projects.

Sulfate resistance of class C/class F fly ash geopolymers

Sulfate attack is one of the significant durability problems for the geopolymer applied for various severe conditions. In this study, the effects of the water-to-fly ash ratio (W/FA), class C fly ash (CF) content, and alkaline content on the setting times and compressive strength of geopolymer pastes were investigated. According to the results, geopolymer samples of three different strength grades (low, medium, and high) were exposed to a 10% magnesium sulfate (MgSO₄) solution at 80 °C. The weight changes, ultrasonic flight-times, and compressive strengths of the specimens were measured to evaluate their sulfate resistances. Control samples were exposed to water at the same temperature. Finally, microstructural analyses using Fourier-transform infrared spectroscopy, X-ray diffraction, and mercury intrusion porosimetry were performed to investigate the corrosion mechanism. The results indicated that higher CF contents led to shorter initial and final setting times and a higher compressive strength regardless of the W/FA and alkaline content. In addition, there was a small weight change for all the geopolymer with different strength grades after they were exposed to an MgSO4 solution. The low strength geopolymer exhibited a better sulfate resistance because of the sustainable increase in the compressive strength and reduction in the ultrasonic flight-time. Moreover, there was a close relationship between the corrosion resistance and the inner structure of the geopolymer mortars. This research provides a theoretical foundation for the application of geopolymers—particularly in coastal and saline areas, which are often subject to sulfate attack.

Potential utilization of regional cashew nutshell ash wastes as a cementitious replacement on the performance and environmental impact of eco-friendly mortar

Globally, agro-waste ashes are increasing significantly due to the rapid implementation of biomass-based power plants. In the present trend, agro-wastes are disposed of in an unsustainable manner. The recycling of agro-waste has significantly contributed to sustainable goals. In the construction sector, it is possible to dispose of waste more efficiently. However, the efficiency of locally available agro-residual waste in cementitious composites is not well understood. In the present investigation, the practicability of using agro-residual ash obtained from the burning of cashew nutshells on the properties of eco-friendly blended cement paste and mortars is explored. Blended cement mixtures containing cashew nutshell ash (CNSA) were prepared at five replacement levels, 5, 10, 15, 20, and 25%, relative to the weight of the cement. To understand the characteristics of CNSA, microstructure investigations such as X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy, and energy-dispersive spectroscopy analyses were performed. Paste properties of CNSA-based cement are observed through consistency, setting time, mini-slump flow, and expansion tests. For the CNSA-based mortars flow table, compressive strength, ultrasonic pulse velocity (UPV), electrical resistivity (ER), water absorption, bulk density, and porosity tests were performed to understand its efficiency. The strength indices of mortars were used to quantify the pozzolanic effect of CNSA. With the incorporation of CNSA, water demand increased by 57%, initial and final setting time decreased by 90% and 83%, respectively. Results showed that CNSA-based mortars absorbed more water and had higher porosity, which reduced compressive strength, UPV, and ER values. CNSA blended mortar is more suitable for applications that do not require high compressive strength. Results indicated that the compressive strength, UPV, and ER are within the limit specified. Strength indices indicated that CNSA has a positive and negative pozzolanic effect during early and later ages, respectively. Further, the sustainable assessment showed that the introduction of CNSA in mortar could substantially reduce embodied carbon, embodied energy, and strength efficiency over the control mortar. The inadequate amount of SiO2, Fe2O3, and Al2O3 in CNSA makes it an unsuitable pozzolanic material. However, it can be utilized in smaller amounts as a fractional replacement of cement and is found to be promising for specific desired properties of cement as a cost-effective accelerator.

The Effect of Magnetized Water on the Fresh and Hardened Properties of Slag/Fly Ash-Based Cementitious Composites

The physicochemical structure of the mixing water used in concrete has a significant effect on the physical and mechanical properties of cementitious composites. The studies on the effect of magnetized water (MW) on the properties of FA/BFS-based cementitious composites are still in their infancy. This study explores the effect of MW on the fresh and hardened properties of fly ash (FA)/blast furnace slag (BFS)-based cementitious composites. A total of 22 different mixture groups having FA/BFS (0, 5, 10, 15, 20, and 25%) by weight of cement were produced using tap water (TW) and MW. The fresh-state properties (the initial and final setting times and the consistency) and hardened-state properties (the compressive strength, water absorption properties, and rapid chloride ion permeability test) of produced cementitious composites were investigated. The development of hydration products was analyzed using scanning electron microscopy (SEM) and the mercury intrusion porosimetry (MIP) test. The results reveal that the fresh- and hardened-state properties of cementitious composite samples produced with MW are significantly improved. The properties of the samples utilizing MW showed that FA and BFS could be used at a higher rate for the same target properties in cementitious composites by using MW as mixing water. Using up to 25% FA/BFS in cementitious composites prepared with MW is recommended.

Performance studies on quaternary blended Geopolymer concrete

This experimental work studied the mix design, mechanical properties and durability properties for G40 and G60 Quaternary Blended Geopolymer Concrete. Quaternary means fourth in sequence; hence Geopolymer Concrete is composed of four binder materials: fly ash, ground granulated blast furnace slag (GGBS), rice husk ash, and Metakaolin. For the Binary mixed geopolymer mix, the ratio of flyash to ground granulated blast furnace slag was 70:30 for G40 grades and 60:40 for G60 rates. For the Ternary geopolymer mixture, Flyash: Ground granulated blast furnace slag: Metakaolinratio was taken as 50:30:20 and 40:40:20 for G40 and G60 grades, respectively. For quaternary blended geopolymer mix, Fly ash: Ground granulated blast furnace slag: Metakaolin: Ricehuskash ratio was taken as 30:30:20:20 and 20:40:20:20 for G40 and G60 grades, respectively. As an alkaline solution, sodium with silicate and hydroxide actuated the binder components. The ratio of alkaline activator (NaOH/Na2SiO3) was set at 2.5, and the concentration of NaOH was kept at eight molalities. The total ratio was calculated to be 5.18 for G40 and 4.18 for G60 grades. In this experimental investigation, flexural strength, split tensile strength tests, compressive strength (CS), Rapid Chloride Penetration Test (RCPT), sorptivity, and chloride permeability, were conducted. On geopolymer mortar, tests for Normal Consistency (mm), Initial and Final Setting Time (min), and CS(MPa) were undertaken. Results had shown that ternary blended geopolymer mortar had optimum values in CS. Quaternary composite geopolymer mortar had shown low CS. In quaternary blended geopolymer mortar, Initial and Final Setting Times were delayed. It had not performed well in the flexural strength test, compression strength test and split tensile strength test. It also showed low resistance for sorptivity, Rapid chloride permeability, and acid attack when compared with ternary and binary blended Geopolymer Concrete. Ternary mixed Geopolymer Concrete had optimal results in CS, flexural strength, and split tensile strength tests, as well as superior sorptivity, fast chloride permeability and acid attack resistance.

Enhancing the performance of alkali-activated material based coral concrete through microbubble aeration clean technology

The porous nature of coral aggregate challenges the manufacturing of high performance coral concrete, which obstacles its development and application. By using microbubble aeration clean technology, this study reports an ecofriendly and economical method to modify coral aggregates. This improvement can overcome the technical bottleneck of manufacturing high performance coral concrete. Innovatively, phosphoric acid (which is also a retarder) was used to clean the original coral aggregate particles, and alkali-activated materials (AAMs) were used to coat coral aggregates. Subsequently, AAMs were used as binder to manufacture the high performance coral concrete. The microbubble aeration cleaning removed loose attachments and soft layer on the surface of coral aggregates. It improved the filling effect of AAM coating into pores and enhanced the interfacial bonding between the aggregate and the AAM coating. The microbubble aeration clean technology modified the interfacial transition zone of coral concrete, successfully solved the problem of poor interface between coral aggregates and mortar. The residual phosphoric acid and phosphate on the aggregates could prolong the setting time of AAM based coral concrete. Comparing to the concrete prepared with original coral aggregates, the concrete prepared using the proposed new method extended initial and final setting times by 34 min and 54 min, improved flexural strength by 32.9% and compressive strength by 35.1%, meeting the performance requirements of the most ocean reef construction requirements.

Preparation, characterization and hydration-retarding mechanism of a new type of highly alkali-resistant superabsorbent polymer for sustainable concrete structures

The low absorbency and instability of superabsorbent polymer (SAP) in alkaline solution, as well as its high cost, limit its development and application in concrete. In this work, an eco-friendly SAP with high alkali-absorption for cement-based materials was synthesized through graft copolymerization of organic monomers onto xanthan gum and metakaolin. Meanwhile, the hydration-retarding mechanism of SAP in cement-based materials was revealed by the isothermal microcalorimetric testing technique. The results show that the current study successfully synthesized a new SAP (SAPN). SAPN not only presents better absorption capacity in alkaline solutions, but also extends the time required to reach swelling equilibrium. The main effect for SAP after being swelled by cement filtrate is the decrease of their water absorption capacity due to the internal blockage of the structure of SAP. The addition of SAPN significantly prolongs the initial and final setting times of the cement-based material system. SAPN improved the 28-day compressive strength of mortar by 7.51%. SAP has a certain “negative effect” on the crystallization nucleation and crystal growth period of cement-based materials.

Concrete made from waste paper sludge (WPS): a sustainable material

PurposeThe growing quantity of waste is a worrying reality that has resulted in environmental sustainability challenges. Waste paper sludge (WPS) in large quantities from paper mill industry are produced every year. Their disposal in landfills, in general, pollutes the environment. Cement manufacture also contributes to global warming by emitting carbon dioxide. As a result, a novel use of industrial wastes as a supplemental cementitious ingredient in concrete formulation can help to mitigate the environmental problem. This paper aims to study the possibility of usage of WPS as partial replacements of cement for sustainable development of concrete.Design/methodology/approachThis study aims at testing the mechanical properties of concrete that has been mixed with WPS. Between 5% and 20% of the weight of cement, WPS was used to substitute it. The water binder ratios of 0.55, 0.50, 0.45 and 0.42 were all considered for an experiment to better understand the impact of WPS on concrete. In terms of workability, density, water absorption (WA), compressive strength (CS) and flexural strength (FS), concrete mixtures were created, tested and compared to traditional concrete mixes.FindingsAccording to the findings, the initial and final setting times of the concrete mixtures were both significantly delayed, and the workability and density of the concrete mixtures were both significantly lowered at all water binder ratios and replacement levels. Both compressive and FS of concrete made with WSP declined significantly at all water binder ratio. Substitution of cement by WPS enhanced the WA of all the concrete mixes. The mechanical performance of concrete mixtures that were made with a replacement level of 5% exhibited noticeable improvements. Whereas the more is the replacement levels the more the loss in the mechanical properties were noted. The ideal replacement levels for the WPS are up to 5% only.Originality/valueThis paper contributes to the literature by exploring the ecological and sustainable effects of using WPS in construction materials.

Evaluation of physico-mechanical properties of dental plaster modified with pulverized acrylic waste

Background: Dental plaster is most widely used to make temporary casts and as an investment medium during the fabrication of removable complete and partial denture prostheses. Dental plasters exhibit poor mechanical properties. Aim: This study aimed to evaluate the physico-mechanical properties of dental plaster modified with various concentrations of pulverized acrylic waste. Materials and Methods: A total of 120 specimens were fabricated using dental plaster and were divided into four groups of 30specimens each to evaluate setting time, one-hour compressive strength, 24-hour compressive strength, and surface reproducibility. Each group was subdivided into five groups of six specimens (n=6), each with the incorporation of various concentrations of pulverized acrylic powder. The specimens incorporated with various concentrations of pulverized acrylic powder (0.5 wt%, 1.0 wt%, 5.0 wt% and 10.0 wt%) were considered as modified groups and the dental plaster with no additives was considered as a control group. The initial and final setting times were measured using a Gillmore needle apparatus, the compressive strength was measured using a universal testing machine, and the surface reproducibility was analyzed using a stereo microscope. The obtained data were subjected to statistical analysis using one-way ANOVA and post hoc analysis. Results: The incorporation of 0.5 wt% resulted in more final and initial setting times. The one-hour and 24-hour compressive strengths of the dental plaster increased with increasing concentration of acrylic waste. Poor surface details were observed with an increase in the concentration of acrylic waste. Conclusions:The addition of acrylic waste resulted in an increase in the one-hour and 24-hour compressive strengths, decreased initial and final setting times, and poor surface reproducibility.

Monitoramento do período de pega de misturas de concreto com ultrassom

Abstract The setting behavior of concrete mixtures can be indirectly monitored by the penetration resistance test given by ASTM C 403. Arbitrary values of penetration resistance are associated to the initial and final set times. This test is carried out on the previously sieved mortar portion of the concrete mixture, which makes its practical use rare. Alternatively, ultrasound testing can be used to characterize this transition period, since the propagation of ultrasonic waves is greatly affected by the formation of cement hydration products and the extent of microstructure development. In this research, the propagation of ultrasonic waves in fresh concrete during the setting period was studied. In addition to the ultrasonic pulse velocity (UPV), other ultrasonic parameters such as group velocity, parameters related to ultrasonic energy and frequency were monitored during the setting period of various concrete mixes. It was observed that as setting progressed, there was a greater ease of ultrasonic transmission with a continuous increase of wave amplitudes. The results indicated that a combined analysis of the time domain parameters of UPV, group velocity and the time that 10% of energy has propagated (t10) could be used to improve the characterization of the microstructure development regarding the setting behavior of concrete mixtures.

The comparative study of using wood ash in lieu of fly ash in South African blended cement paste and mortar

A comparative analysis of the properties of fly ash (FA) and wood ash (WA) blended cement, produced in the controlled environment of a cement factory was examined. Since FA has been adopted in South Africa as a material for blended cement, the possibility of using wood ash in lieu of FA to produce blended cement was investigated. The blended cements were prepared and tested at AfriSam (South Africa) Ltd. Roodepoort, with 10 % and 25 % FA and WA as partial substitution for Ordinary Portland Cement (OPC) clinker (CEM1). The chemical composition of FA and WA, the setting times of the blended cement pastes and the compressive strengths of the blended cement mortars were analyzed and discussed. The results indicated that FA and WA have combined SiO2, Al2O3 and Fe2O3 constituents of 89.29% and 72. 58%, respectively. Also, lower initial and final setting times were observed with 25% WA samples as compared to the control sample and FA samples. WA blended cement showed faster rate of hydration than FA blended cement at early curing age resulting in mortar compressive strength of 26.2 MPa and 25.4 MPa as well as 22.6 MPa and 19.2 MPa for 10% and 25% WA and FA substitution respectively. However, FA blended cement mortar exhibited higher late strength than WA blended cement mortar with 10% FA blended cement mortar resulted in higher compressive strength than control sample at 90 days. The combined synergy of WA and FA in blended cement is envisaged to produce mortar of desirable early and late strengths.