The bio-clogging using bacteria can be an eco-friendly and sustainable alternative to conventional grouting methods for seepage control.However,it remains unclear to date how the dilute concentration of bacterium and ...The bio-clogging using bacteria can be an eco-friendly and sustainable alternative to conventional grouting methods for seepage control.However,it remains unclear to date how the dilute concentration of bacterium and medium during field installation can affect the setting time of bacterium and its correlation with permeability reduction.In this study,the setting time of bacterium and its effectiveness in permeability reduction were addressed through experimental and theoretical investigations.A series of sand column was cultivated using different concentrations of Leuconostoc mesenteroides and culture medium.The distribution and composition of the bacterial product(i.e.dextran)were observed by refractometer,scanning electron microscope(SEM),and energy dispersive X-ray spectroscopy(EDS).Soil permeability was recorded using a constant head test.The results revealed that bacterium was effective to produce dextran at the setting time of about 5 d after installation.This dextran can reduce the permeability of bio-mediated soil by two orders of magnitude,even without culture medium supply.In general,the dextran production decreased proportionally with increase of bacterium and medium concentration.However,at 50%bacterium and medium concentration by weight,it still has a significant influence on permeability reduction with similar setting time,compared to 100%concentration.展开更多
Plant aggregate-based building materials are a viable solution for reducing greenhouse gas emissions and providing good thermal and acoustic performances.In this study,the investigated lightweight mortars require a hy...Plant aggregate-based building materials are a viable solution for reducing greenhouse gas emissions and providing good thermal and acoustic performances.In this study,the investigated lightweight mortars require a hydraulic reaction.Laboratory and on-site empirical observations about plant aggregate-based materials indicate a delay in setting time and a decrease in the mechanical performances of concretes based on plant aggregates.The natural origin of plant-aggregates causes a lot of variability in their properties.Related studies have shown that the incompatibility between plant aggregates and cement is mainly caused by the dissolved and decomposed components of plant aggregates in alkaline environments.Currently,no research on the specific impact of each component on the setting time of lime-based binder exists.In this work,the impact of some soluble compounds(e.g.,sucrose,glucose,fructose,pectin)on the setting reaction of the lime matrix was studied using Vicat test,thermogravimetric analysis(TGA)and FT-IR spectroscopy.Experimental results showed that carbohydrates such as glucose and sucrose not only affect the setting time but also have a long-term impact on the carbonation of lime.The measure of the setting time by Vicat test appears as a possible indicator to predict the compatibility between the matrix and plant aggregates.展开更多
Occurrence of mafic dykes in Himalaya has been intriguing and debated since long because of its difficulty to ascent and emplacement through a thickened crust.Mafic dykes in Kumaun Lesser Himalaya(KLH)of central
The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice ...The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice flour has an obvious setting retarding effect on cement pastes.The optimal dosage of the glutinous rice flour is 3wt%.In this case,the initial and final setting time of the paste are delayed by 140 and185 min,respectively.The flexural and compressive strengths of the hardened paste are increased by 0.35%and 0.07%after 56 d of curing.The glutinous rice flour hinders the mineral dissolution process and decreases the concentration of calcium ion at the initial stage of hydration due to the complexation effect,thereby hindering the nucleation and growth of CH and C-S-H phases and prolonging the hydration process.However,C-S-H phases combine with the glutinous rice flour to contribute the bonding effect together,which compacts the microstructure of hardened cement pastes at the later hydration stage of cement pastes.Thus,in-depth investigation on the utilization of glutinous rice flour as the admixture for the Portland cement is expected to be meaningful for the control of hydration exothermic rate and setting time.展开更多
The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properti...The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properties such as setting times and strength were tested and the microstructures and pore characteristics of pastes with various bamboos were also studied. The experimental results indicated that bamboo charcoal affects the setting times of cement paste, but the introduction of water reducer relieves this condition. Bamboo charcoal also poses an impact on the hardened paste strength. The prominent strength decrease is found when more and larger size bamboo charcoal is mixed into the cement paste. Bamboo charcoal alters the paste microstructure and increases the porosity and pore volume, but it increases the pores with the diameter of less than 50 μm. The pastes with various bamboo charcoals are given with the good functions such as adjusting humidity and adsorption.展开更多
The exponential growth of agricultural wastes such as Balanite seed pod has resulted in waste management issues and finding alternatives through waste recycling is an interesting area of research.Balanite seed pods we...The exponential growth of agricultural wastes such as Balanite seed pod has resulted in waste management issues and finding alternatives through waste recycling is an interesting area of research.Balanite seed pods were collected in Yobe state,washed,dried,crushed.Balanite endocarp pod ash(BEPA)was calcined at 600°C for 3 hours in a muffle furnace and the biomass was characterized with X-ray fluorescence spectrometer to determine its chemical composition.The analysis showed that the ash composed of silica,alumina and ferric oxide(74.24 wt.%)indicated a strong pozzolan based on American Standard.The BEPA possessed a high loss on ignition of 8.24 wt.%owing to the presence of unburnt carbon in the ash.The ash obtained was sieved with 75µm sieve and cement was replaced with ash between 2.5 wt.%~12.5 wt.%at interval of 2.5 wt.%to assess its impact on cement properties such as setting time,consistence,mortar strength and water absorption.Results showed that as percentage replacement increases,the water absorption increased while the mortar strength diminished whereas as the curing days progressed its strength improved despite clinker diminution due to cement hydration.60 days strength for below 10 wt.%BEPA cement blend produced enhanced strength compared with control which is evidence of slow pozzolanic reactions.The optimum percentage replacement with BEPA was obtained at 7.5 wt.%replacement beyond which significantly affected the cement properties especially its strength.It could be agreed that BEPA has potentials to be considered and employed as a cement replacement material.展开更多
This work aimed to use oyster shell powder (OSP) as the partial replacement of Ag/TiO2 particle to obtain multifunctional β-hemihydrate gypsum.Thus,the β-hemihydrate gypsum was mixed with different contents of OSP a...This work aimed to use oyster shell powder (OSP) as the partial replacement of Ag/TiO2 particle to obtain multifunctional β-hemihydrate gypsum.Thus,the β-hemihydrate gypsum was mixed with different contents of OSP and Ag/TiO2 particle.Antibacterial and MB removal experiments were conducted to assess the antibacterial characteristic and photocatalytic activity of β-hemihydrate gypsum with Ag/TiO2 particle and OSP.Besides,the formaldehyde degradation test was carried out to evaluate its formaldehyde removal ratio.Moreover,their setting times,compressive and flexural strengths at 1,3,and 28 days were comparatively analyzed.The experimental results prove that the composite use of OSP and Ag/TiO2 particle provide feasible multifunction for the β-hemihydrate gypsum.They can further improve the bactericidal rates and exhibit extra MB removal ratios compared with the gypsum plasters with single Ag/TiO2 particle.Besides,they can increase the formaldehyde degradation ratios,and this promotion is related to the introduction of Ag/TiO2 particle.However,OSP delays the initial setting time but promotes the final setting time of β-hemihydrate gypsum,and Ag/TiO2 particle hardly affects the setting times.Furthermore,OSP reduces the strengths of plasters at 1,3,and 28 days.But in general,the composite addition of OSP and Ag/TiO2 particle increase the compressive and flexural strengths of gypsum plasters at 1,3,and 28 days.These results provide theoretical guidance for the recycling of OSP and the preparation of gypsum-based products with antibacterial and formaldehyde degradation capabilities.展开更多
Based on aluminum sulfate,a fluorine-free and alkali-free liquid accelerator(FF-AF-A)was prepared in this study.The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully...Based on aluminum sulfate,a fluorine-free and alkali-free liquid accelerator(FF-AF-A)was prepared in this study.The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated.The compatibility of the FF-AF-A with the superplasticizers were also investigated,and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat,X-ray diffractometry(XRD),and scanning electron microscopy(SEM).Test results indicated that adding the FF-AF-A at 8 wt%of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time.The 1-day compressive strength of the cement mortar with 8 wt%of FF-AF-A reached 13.5 MPa,which represents an increase of 35%as compared to the strength of cement mortar without the FF-AF-A,and the 28-day compressive strength ratio was 119%.In addition,the FF-AF-A also showed good compatibility with different superplasticizer dosages.The results show that,when the FF-AF-A was added to the cement paste,it promoted the formation of ettringite crystals due to the aluminum ions(Al^(3+))and sulfate ions(SO_(4)^(2-))reacted with gypsum in the cement,as well as promoted the hydration of tricalcium aluminate(C_(3)A)and tricalcium silicate(C3S)leading to the overall structure becomes more compact.As a consequence,the hydration heat rate of the cement sharply increased,the cement paste setting time is shortened,and the compressive strength of cement mortar is improved.展开更多
One of the most active fields of research embraced by many disciplines, including civil engineering, is material reuse. It is known that ceramics wastes from various construction and demolition sites and manufacturing...One of the most active fields of research embraced by many disciplines, including civil engineering, is material reuse. It is known that ceramics wastes from various construction and demolition sites and manufacturing processes are dumped away into the environment, resulting in the pollution that threatens both agriculture and public health. Therefore, the utilization of ceramic waste in construction industries would help to protect the environment from such pollutions. This paper presents the results of an experimental analysis of the effects of partial replacement of coarse aggregates, fine aggregates, and ordinary Portland cement with the ceramic waste, at percentage levels of 0%, 5%, 10%, and 20%;and the assessment of the strength property of the concrete produced with optimum combination of the constituents. Compressive strengths of this concrete were determined at 7, 28, and 56 days of curing using 150 </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">×</span><span style="font-family:Verdana;"> 150 </span><span style="font-family:Verdana;">×</span><span><span style="font-family:Verdana;"> 150 mm cube specimens. Test results showed that the compressive strength of the concrete decreased as the content of ceramic waste present in the concrete increased. Thus, concrete produced from the partial replacement of ordinary Portland cement with ground ceramics gave compressive strengths of 16.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 13.4 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> at 5% and 20% replacement levels respectively. Similarly, the compressive strengths of concrete from the partial replacement of sand with fine ceramics were 13.8 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 10.9 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> for 5% and 20% replacements respectively. For 5% and 20% replacement levels of granite with crushed ceramics in concrete gave a compressive strength of 11.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 9.7 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, respectively. For concrete derived from the partial replacement of stone dust with fine ceramics, the compressive strengths were 19.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 18.10 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> respectively for 5% and 20%. For concrete produced from the partial replacement of bush gravel with crushed ceramics, the compressive strengths obtained were 10.9 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 8.98 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> respectively for 5% and 20% replacements. Finally, the concrete derived from the optimal combination of binary cement, ternary fine, and coarse aggregate had a compressive strength of 22.20 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> which is higher than the compressive strength of the control mixture at 18.10 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">. The result of the ANOVA carried out showed that the compressive strength obtained for each partial replacement of different components is statistically significant at 5%, </span><i><span style="font-family:Verdana;">i.e.</span></i><span style="font-family:Verdana;"> the change in the compressive strength of the concrete produced is due to the presence of ceramic waste.展开更多
This research focuses on investigating the effect of quartz particle size and cement replacement on their physicomechnical properties.Portland limestone cement(PLC)was employed and replaced with quartz powder(QP)at va...This research focuses on investigating the effect of quartz particle size and cement replacement on their physicomechnical properties.Portland limestone cement(PLC)was employed and replaced with quartz powder(QP)at various particle sizes(1.19 mm,425μm,300μm,212μm,<212μm)and cement replacement between 2.5 wt.%~15 wt.%at interval of 2.5 wt.%to study their impact on the cement properties.The PLC chemical composition revealed a relatively low lime and high silica content compared to the conventional cement.QP revealed a high silica,lime and sulphur contents compared to natural sand.A high consistence,elongated setting times and lower strengths and specific gravities were observed as cement was replaced with QP at a given particle size respectively.The effect of replacing cement with QP content between 2.5 wt.%and 15 wt.%at various particle sizes resulted in average increments by 45.32%,23.13%and 36.06%for initial setting time,final setting time and water demand respectively.This increase could be related with clinker diminution coupled with enhanced QP surface area and clinker diminution.Similarly,an increase in the QP surface area at a given cement replacement led to higher water consistence,retarded setting times and lower strength.The effect of enhancing the QP’surface area between 1.19 mm and below 212μm at a given cement replacement resulted in average increments by 26.27%,8.61%and 7.49%for initial and final setting times and water demand respectively.The strength gain of the QP cement blend diminished significantly above 30%up to 15 wt.%cement replacement especially beyond 3 days.The low strength could be due to the high-water consistence linked with silica content resulting in setting time retardation.The optimal QP content was determined at 5 wt.%owing to the fact that the physicomechnical properties did not significantly deviate from the properties of control.展开更多
This paper discusses the findings of an experimental study on the effect of various curing procedures on the compressive strength of concrete produced by partially substituting portland cement with Palm Kernel S...This paper discusses the findings of an experimental study on the effect of various curing procedures on the compressive strength of concrete produced by partially substituting portland cement with Palm Kernel Shell Ash(PKSA).Palm kernel shell ash was utilized in a 1:2:4 mix ratio as a partial substitute for ordinary Portland cement(OPC)at percentage levels of 0%,10%,and 15%.River sand with particles passing a 4.75 mm BS sieve was used,as well as crushed aggregate with a maximum size of 20 mm,and palm kernel shell ash with particles passing a 212μm sieve.The compressive strength of the test cubes(150 mm × 150 mm × 150 mm)was determined after 7,28,and 56 days of curing.The results demonstrated that test cubes containing Palm kernel shell ash developed strength over a longer curing period than ordinary Portland cement concrete samples and that the strength changes depending on the amount of PKSA in the cube samples.The findings showed that at 28 days,test cubes with 5%,10%,and 15%PKSA content in all curing procedures utilized obtained a greater compressive strength.Curing by immersion produced the highest compressive strength in all replacement level while the concrete cured by sprinkling and spraying gives a lower strength in all replacement level.展开更多
Fault current magnitude in a microgrid depends upon its mode of operation,namely,grid-connected mode or islanded mode.Depending on the type of fault in a given mode,separate protection schemes are generally employed.W...Fault current magnitude in a microgrid depends upon its mode of operation,namely,grid-connected mode or islanded mode.Depending on the type of fault in a given mode,separate protection schemes are generally employed.With the change in microgrid operating mode,the protection scheme needs to be modified which is uneconomical and time inefficient.In this paper,a novel optimal protection coordination scheme is proposed,one which enables a common optimal relay setting which is valid in both operating modes of the microgrid.In this con-text,a common optimal protection scheme is introduced for dual setting directional overcurrent relays(DOCRs)using a combination of various standard relay characteristics.Along with the two variables,i.e.,time multiplier setting(TMS)and plug setting(PS)for conventional directional overcurrent relay,dual setting DOCRs are augmented with a third variable of relay characteristics identifier(RCI),which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard.The relay coordination problem is formulated as a mixed-integer nonlinear programming(MINLP)problem,and the settings of relays are optimally determined using the genetic algorithm(GA)and the grey wolf optimization(GWO)algorithm.To validate the superiority of the pro-posed protection scheme,the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.展开更多
This paper investigated the effects of different proportions of Portland cement addition(0-20%)on the setting time and early-age strength of solid-waste-based sulphoaluminate cement.The mechanism of hydration process ...This paper investigated the effects of different proportions of Portland cement addition(0-20%)on the setting time and early-age strength of solid-waste-based sulphoaluminate cement.The mechanism of hydration process was analyzed by X-ray diffraction(XRD)technology.It was found that the incorporation of Portland cement could reduce the early-age strength of the composite cement,and shorten the setting time.When the Portland cement reached 20%,the early-age strength of the composite cement was the lowest and the setting time was the shortest.The XRD analysis demonstrated that the addition of Portland cement could accelerate the hydration process of the composite cement,and the more the Portland cement was added,the faster the hydration process of the composite cement was observed.The main reason is that the addition of Portland cement could increase the alkalinity of the composite cement and promote the hydration of anhydrous calcium sulphoaluminate.This study provides an important reference for the production of solid-waste-based composite cement.展开更多
The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P....The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P.O.42.5,sulphate aluminium) are used in this test. Results show that with the addition of RSF,the setting times for these three kinds of cements are delayed. According to P.O.42.5 cement,The max temperatures of exothermic peak (Tmax) decrease,exothermic peak times (tmax) are delayed and the mechanical strengths generally drop as RSF concentration is increased. XRD test shows that the RSF hinder the formation of Ca(OH)2 phase and hydration of cement (C3S,C2S,C4AF),which resulted in the delay of setting time and hydration reaction.展开更多
Ureolytic-type bacteria has been used to improve the strength of cement mortar by the precipitation of calcium carbonate.In the present study Bacillus sphaericus has been used to improve the properties of cement morta...Ureolytic-type bacteria has been used to improve the strength of cement mortar by the precipitation of calcium carbonate.In the present study Bacillus sphaericus has been used to improve the properties of cement mortar such as setting time,compressive strength and sorptivity.The setting time is found to be unaffected by the presence of bacteria.It is found that compressive strength at both 7-days and 28-days of mortar cube increases with the increase of bacteria concentration.At the optimum bacteria dosage of 107 cells/ml,the average compressive strength increases by 58%(at 7 day)and 23%(at 28 day)over the control specimen.The sorpitivity coefficient decreases as the concentration of bac-terial cells increases.The mineralogy and morphology of the cal-cium carbonate precipitation have been tested by XRD and FESEM.展开更多
基金This work is supported by King Mongkut’s Institute of Technology Ladkrabang(Grant No.2563-02-01-014).
文摘The bio-clogging using bacteria can be an eco-friendly and sustainable alternative to conventional grouting methods for seepage control.However,it remains unclear to date how the dilute concentration of bacterium and medium during field installation can affect the setting time of bacterium and its correlation with permeability reduction.In this study,the setting time of bacterium and its effectiveness in permeability reduction were addressed through experimental and theoretical investigations.A series of sand column was cultivated using different concentrations of Leuconostoc mesenteroides and culture medium.The distribution and composition of the bacterial product(i.e.dextran)were observed by refractometer,scanning electron microscope(SEM),and energy dispersive X-ray spectroscopy(EDS).Soil permeability was recorded using a constant head test.The results revealed that bacterium was effective to produce dextran at the setting time of about 5 d after installation.This dextran can reduce the permeability of bio-mediated soil by two orders of magnitude,even without culture medium supply.In general,the dextran production decreased proportionally with increase of bacterium and medium concentration.However,at 50%bacterium and medium concentration by weight,it still has a significant influence on permeability reduction with similar setting time,compared to 100%concentration.
文摘Plant aggregate-based building materials are a viable solution for reducing greenhouse gas emissions and providing good thermal and acoustic performances.In this study,the investigated lightweight mortars require a hydraulic reaction.Laboratory and on-site empirical observations about plant aggregate-based materials indicate a delay in setting time and a decrease in the mechanical performances of concretes based on plant aggregates.The natural origin of plant-aggregates causes a lot of variability in their properties.Related studies have shown that the incompatibility between plant aggregates and cement is mainly caused by the dissolved and decomposed components of plant aggregates in alkaline environments.Currently,no research on the specific impact of each component on the setting time of lime-based binder exists.In this work,the impact of some soluble compounds(e.g.,sucrose,glucose,fructose,pectin)on the setting reaction of the lime matrix was studied using Vicat test,thermogravimetric analysis(TGA)and FT-IR spectroscopy.Experimental results showed that carbohydrates such as glucose and sucrose not only affect the setting time but also have a long-term impact on the carbonation of lime.The measure of the setting time by Vicat test appears as a possible indicator to predict the compatibility between the matrix and plant aggregates.
基金supported under a DST (ESS/16/290/2006) grant sanctioned to Santosh Kumar
文摘Occurrence of mafic dykes in Himalaya has been intriguing and debated since long because of its difficulty to ascent and emplacement through a thickened crust.Mafic dykes in Kumaun Lesser Himalaya(KLH)of central
基金Funded by the Open Fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province (JBGS008)the Research Lab Construction of Hainan University (ZY2019HN0904)the Opening Project of State Key Laboratory of Green Building Materials (2022GBM01)。
文摘The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice flour has an obvious setting retarding effect on cement pastes.The optimal dosage of the glutinous rice flour is 3wt%.In this case,the initial and final setting time of the paste are delayed by 140 and185 min,respectively.The flexural and compressive strengths of the hardened paste are increased by 0.35%and 0.07%after 56 d of curing.The glutinous rice flour hinders the mineral dissolution process and decreases the concentration of calcium ion at the initial stage of hydration due to the complexation effect,thereby hindering the nucleation and growth of CH and C-S-H phases and prolonging the hydration process.However,C-S-H phases combine with the glutinous rice flour to contribute the bonding effect together,which compacts the microstructure of hardened cement pastes at the later hydration stage of cement pastes.Thus,in-depth investigation on the utilization of glutinous rice flour as the admixture for the Portland cement is expected to be meaningful for the control of hydration exothermic rate and setting time.
基金Funded by the National Natural Science Foundation of China(Nos.51678442,51578412,51478348,and 51508404)the National High-speed Train Union Fund(U1534207)+1 种基金the Key Project of the Shanghai Committee of Science and Technology(No.15DZ1205003)the Fundamental Research Funds for the Central Universities
文摘The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properties such as setting times and strength were tested and the microstructures and pore characteristics of pastes with various bamboos were also studied. The experimental results indicated that bamboo charcoal affects the setting times of cement paste, but the introduction of water reducer relieves this condition. Bamboo charcoal also poses an impact on the hardened paste strength. The prominent strength decrease is found when more and larger size bamboo charcoal is mixed into the cement paste. Bamboo charcoal alters the paste microstructure and increases the porosity and pore volume, but it increases the pores with the diameter of less than 50 μm. The pastes with various bamboo charcoals are given with the good functions such as adjusting humidity and adsorption.
文摘The exponential growth of agricultural wastes such as Balanite seed pod has resulted in waste management issues and finding alternatives through waste recycling is an interesting area of research.Balanite seed pods were collected in Yobe state,washed,dried,crushed.Balanite endocarp pod ash(BEPA)was calcined at 600°C for 3 hours in a muffle furnace and the biomass was characterized with X-ray fluorescence spectrometer to determine its chemical composition.The analysis showed that the ash composed of silica,alumina and ferric oxide(74.24 wt.%)indicated a strong pozzolan based on American Standard.The BEPA possessed a high loss on ignition of 8.24 wt.%owing to the presence of unburnt carbon in the ash.The ash obtained was sieved with 75µm sieve and cement was replaced with ash between 2.5 wt.%~12.5 wt.%at interval of 2.5 wt.%to assess its impact on cement properties such as setting time,consistence,mortar strength and water absorption.Results showed that as percentage replacement increases,the water absorption increased while the mortar strength diminished whereas as the curing days progressed its strength improved despite clinker diminution due to cement hydration.60 days strength for below 10 wt.%BEPA cement blend produced enhanced strength compared with control which is evidence of slow pozzolanic reactions.The optimum percentage replacement with BEPA was obtained at 7.5 wt.%replacement beyond which significantly affected the cement properties especially its strength.It could be agreed that BEPA has potentials to be considered and employed as a cement replacement material.
基金Funded by the National Natural Science Foundation of China(51878479)。
文摘This work aimed to use oyster shell powder (OSP) as the partial replacement of Ag/TiO2 particle to obtain multifunctional β-hemihydrate gypsum.Thus,the β-hemihydrate gypsum was mixed with different contents of OSP and Ag/TiO2 particle.Antibacterial and MB removal experiments were conducted to assess the antibacterial characteristic and photocatalytic activity of β-hemihydrate gypsum with Ag/TiO2 particle and OSP.Besides,the formaldehyde degradation test was carried out to evaluate its formaldehyde removal ratio.Moreover,their setting times,compressive and flexural strengths at 1,3,and 28 days were comparatively analyzed.The experimental results prove that the composite use of OSP and Ag/TiO2 particle provide feasible multifunction for the β-hemihydrate gypsum.They can further improve the bactericidal rates and exhibit extra MB removal ratios compared with the gypsum plasters with single Ag/TiO2 particle.Besides,they can increase the formaldehyde degradation ratios,and this promotion is related to the introduction of Ag/TiO2 particle.However,OSP delays the initial setting time but promotes the final setting time of β-hemihydrate gypsum,and Ag/TiO2 particle hardly affects the setting times.Furthermore,OSP reduces the strengths of plasters at 1,3,and 28 days.But in general,the composite addition of OSP and Ag/TiO2 particle increase the compressive and flexural strengths of gypsum plasters at 1,3,and 28 days.These results provide theoretical guidance for the recycling of OSP and the preparation of gypsum-based products with antibacterial and formaldehyde degradation capabilities.
基金grateful funding provided by National Key Research and Development Program of China(Project 2019YFC1906202)Guangxi Key Research and Development Plan(Guike AB19259008)Major Science and Technology Special Project of Guangxi Province(Guike AA18242007-3).
文摘Based on aluminum sulfate,a fluorine-free and alkali-free liquid accelerator(FF-AF-A)was prepared in this study.The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated.The compatibility of the FF-AF-A with the superplasticizers were also investigated,and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat,X-ray diffractometry(XRD),and scanning electron microscopy(SEM).Test results indicated that adding the FF-AF-A at 8 wt%of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time.The 1-day compressive strength of the cement mortar with 8 wt%of FF-AF-A reached 13.5 MPa,which represents an increase of 35%as compared to the strength of cement mortar without the FF-AF-A,and the 28-day compressive strength ratio was 119%.In addition,the FF-AF-A also showed good compatibility with different superplasticizer dosages.The results show that,when the FF-AF-A was added to the cement paste,it promoted the formation of ettringite crystals due to the aluminum ions(Al^(3+))and sulfate ions(SO_(4)^(2-))reacted with gypsum in the cement,as well as promoted the hydration of tricalcium aluminate(C_(3)A)and tricalcium silicate(C3S)leading to the overall structure becomes more compact.As a consequence,the hydration heat rate of the cement sharply increased,the cement paste setting time is shortened,and the compressive strength of cement mortar is improved.
文摘One of the most active fields of research embraced by many disciplines, including civil engineering, is material reuse. It is known that ceramics wastes from various construction and demolition sites and manufacturing processes are dumped away into the environment, resulting in the pollution that threatens both agriculture and public health. Therefore, the utilization of ceramic waste in construction industries would help to protect the environment from such pollutions. This paper presents the results of an experimental analysis of the effects of partial replacement of coarse aggregates, fine aggregates, and ordinary Portland cement with the ceramic waste, at percentage levels of 0%, 5%, 10%, and 20%;and the assessment of the strength property of the concrete produced with optimum combination of the constituents. Compressive strengths of this concrete were determined at 7, 28, and 56 days of curing using 150 </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">×</span><span style="font-family:Verdana;"> 150 </span><span style="font-family:Verdana;">×</span><span><span style="font-family:Verdana;"> 150 mm cube specimens. Test results showed that the compressive strength of the concrete decreased as the content of ceramic waste present in the concrete increased. Thus, concrete produced from the partial replacement of ordinary Portland cement with ground ceramics gave compressive strengths of 16.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 13.4 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> at 5% and 20% replacement levels respectively. Similarly, the compressive strengths of concrete from the partial replacement of sand with fine ceramics were 13.8 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 10.9 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> for 5% and 20% replacements respectively. For 5% and 20% replacement levels of granite with crushed ceramics in concrete gave a compressive strength of 11.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 9.7 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, respectively. For concrete derived from the partial replacement of stone dust with fine ceramics, the compressive strengths were 19.6 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 18.10 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> respectively for 5% and 20%. For concrete produced from the partial replacement of bush gravel with crushed ceramics, the compressive strengths obtained were 10.9 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> and 8.98 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> respectively for 5% and 20% replacements. Finally, the concrete derived from the optimal combination of binary cement, ternary fine, and coarse aggregate had a compressive strength of 22.20 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;"> which is higher than the compressive strength of the control mixture at 18.10 N/mm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">. The result of the ANOVA carried out showed that the compressive strength obtained for each partial replacement of different components is statistically significant at 5%, </span><i><span style="font-family:Verdana;">i.e.</span></i><span style="font-family:Verdana;"> the change in the compressive strength of the concrete produced is due to the presence of ceramic waste.
文摘This research focuses on investigating the effect of quartz particle size and cement replacement on their physicomechnical properties.Portland limestone cement(PLC)was employed and replaced with quartz powder(QP)at various particle sizes(1.19 mm,425μm,300μm,212μm,<212μm)and cement replacement between 2.5 wt.%~15 wt.%at interval of 2.5 wt.%to study their impact on the cement properties.The PLC chemical composition revealed a relatively low lime and high silica content compared to the conventional cement.QP revealed a high silica,lime and sulphur contents compared to natural sand.A high consistence,elongated setting times and lower strengths and specific gravities were observed as cement was replaced with QP at a given particle size respectively.The effect of replacing cement with QP content between 2.5 wt.%and 15 wt.%at various particle sizes resulted in average increments by 45.32%,23.13%and 36.06%for initial setting time,final setting time and water demand respectively.This increase could be related with clinker diminution coupled with enhanced QP surface area and clinker diminution.Similarly,an increase in the QP surface area at a given cement replacement led to higher water consistence,retarded setting times and lower strength.The effect of enhancing the QP’surface area between 1.19 mm and below 212μm at a given cement replacement resulted in average increments by 26.27%,8.61%and 7.49%for initial and final setting times and water demand respectively.The strength gain of the QP cement blend diminished significantly above 30%up to 15 wt.%cement replacement especially beyond 3 days.The low strength could be due to the high-water consistence linked with silica content resulting in setting time retardation.The optimal QP content was determined at 5 wt.%owing to the fact that the physicomechnical properties did not significantly deviate from the properties of control.
文摘This paper discusses the findings of an experimental study on the effect of various curing procedures on the compressive strength of concrete produced by partially substituting portland cement with Palm Kernel Shell Ash(PKSA).Palm kernel shell ash was utilized in a 1:2:4 mix ratio as a partial substitute for ordinary Portland cement(OPC)at percentage levels of 0%,10%,and 15%.River sand with particles passing a 4.75 mm BS sieve was used,as well as crushed aggregate with a maximum size of 20 mm,and palm kernel shell ash with particles passing a 212μm sieve.The compressive strength of the test cubes(150 mm × 150 mm × 150 mm)was determined after 7,28,and 56 days of curing.The results demonstrated that test cubes containing Palm kernel shell ash developed strength over a longer curing period than ordinary Portland cement concrete samples and that the strength changes depending on the amount of PKSA in the cube samples.The findings showed that at 28 days,test cubes with 5%,10%,and 15%PKSA content in all curing procedures utilized obtained a greater compressive strength.Curing by immersion produced the highest compressive strength in all replacement level while the concrete cured by sprinkling and spraying gives a lower strength in all replacement level.
文摘Fault current magnitude in a microgrid depends upon its mode of operation,namely,grid-connected mode or islanded mode.Depending on the type of fault in a given mode,separate protection schemes are generally employed.With the change in microgrid operating mode,the protection scheme needs to be modified which is uneconomical and time inefficient.In this paper,a novel optimal protection coordination scheme is proposed,one which enables a common optimal relay setting which is valid in both operating modes of the microgrid.In this con-text,a common optimal protection scheme is introduced for dual setting directional overcurrent relays(DOCRs)using a combination of various standard relay characteristics.Along with the two variables,i.e.,time multiplier setting(TMS)and plug setting(PS)for conventional directional overcurrent relay,dual setting DOCRs are augmented with a third variable of relay characteristics identifier(RCI),which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard.The relay coordination problem is formulated as a mixed-integer nonlinear programming(MINLP)problem,and the settings of relays are optimally determined using the genetic algorithm(GA)and the grey wolf optimization(GWO)algorithm.To validate the superiority of the pro-posed protection scheme,the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.
基金support of the National Key Research and Development Program of China(No.2017YFC0703100)Shandong Provincial Major Scientific and Technological Innovation Project(No.2019JZZY020306).
文摘This paper investigated the effects of different proportions of Portland cement addition(0-20%)on the setting time and early-age strength of solid-waste-based sulphoaluminate cement.The mechanism of hydration process was analyzed by X-ray diffraction(XRD)technology.It was found that the incorporation of Portland cement could reduce the early-age strength of the composite cement,and shorten the setting time.When the Portland cement reached 20%,the early-age strength of the composite cement was the lowest and the setting time was the shortest.The XRD analysis demonstrated that the addition of Portland cement could accelerate the hydration process of the composite cement,and the more the Portland cement was added,the faster the hydration process of the composite cement was observed.The main reason is that the addition of Portland cement could increase the alkalinity of the composite cement and promote the hydration of anhydrous calcium sulphoaluminate.This study provides an important reference for the production of solid-waste-based composite cement.
基金supported by"the Fundamental Research Funds for the Central Universities"(No.2010-Ⅳ-057)
文摘The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P.O.42.5,sulphate aluminium) are used in this test. Results show that with the addition of RSF,the setting times for these three kinds of cements are delayed. According to P.O.42.5 cement,The max temperatures of exothermic peak (Tmax) decrease,exothermic peak times (tmax) are delayed and the mechanical strengths generally drop as RSF concentration is increased. XRD test shows that the RSF hinder the formation of Ca(OH)2 phase and hydration of cement (C3S,C2S,C4AF),which resulted in the delay of setting time and hydration reaction.
文摘Ureolytic-type bacteria has been used to improve the strength of cement mortar by the precipitation of calcium carbonate.In the present study Bacillus sphaericus has been used to improve the properties of cement mortar such as setting time,compressive strength and sorptivity.The setting time is found to be unaffected by the presence of bacteria.It is found that compressive strength at both 7-days and 28-days of mortar cube increases with the increase of bacteria concentration.At the optimum bacteria dosage of 107 cells/ml,the average compressive strength increases by 58%(at 7 day)and 23%(at 28 day)over the control specimen.The sorpitivity coefficient decreases as the concentration of bac-terial cells increases.The mineralogy and morphology of the cal-cium carbonate precipitation have been tested by XRD and FESEM.
