Molybdenum tailings are the solid waste left from ore processing,which damages soil and water resources.To address that,molybdenum tailings(MTs)powder obtained from molybdenum tailings sands was processed as an admixt...Molybdenum tailings are the solid waste left from ore processing,which damages soil and water resources.To address that,molybdenum tailings(MTs)powder obtained from molybdenum tailings sands was processed as an admixture.Compared with moisture-cured conditions,the influence of MTs on the steam-cured mortar’s mechanical properties,surface and internal pore characteristics,and microscopic morphology was investigated.The results show that steam-cured mortar containing appropriate MTs can still have high early strength.When the content of MTs doesn’t exceed 15%,the mechanical strength of mortar steam-cured for 3 d can reach 85%of that of corresponding mortar moisture-cured for 28 d,and that of mortar steam-cured for 28 d isn’t lower than 90%of that of pure cement mortar.The proportion of harmful pores(HFP)and more harmful pores(MHFP)and most probable pore diameters(MPD)on the mortar surface containing MTs steam-cured for 28 d are significantly decreased.When MTs’content is 15%,the proportion of HFP and MHFP on the surface of paste is decreased by 71.4%and 72.2%,respectively,with MPS decreasing from 12.7 nm to 10.8 nm.SEM analysis shows that the surfaces of steam-cured paste containing 15%MTs have more hydration products and dense microstructures.The effect of pozzolanic and dense filling of MTs effectively refines the pore structure,reducing the large pore-size pores.展开更多
The effects of steam curing on mechanical properties,drying shrinkage,cracking sensitivity,anti-permeability,and carbonation resistance of C50 shield segment concrete were investigated,which were compared with the sta...The effects of steam curing on mechanical properties,drying shrinkage,cracking sensitivity,anti-permeability,and carbonation resistance of C50 shield segment concrete were investigated,which were compared with the standard curing conditions. The results indicated that steam curing could increase early strength of concrete and reduce its drying shrinkage. However,steam curing reduced later strength of concrete,increased its crack sensitivity and deteriorated its anti-permeability and carbonation resistance. Moreover,the incorporation of fly ash could improve the durability of steam-cured concrete.展开更多
The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration,XRD,LF-NMR and rapid chloride migration test.The results show that the curing regime...The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration,XRD,LF-NMR and rapid chloride migration test.The results show that the curing regime has influences on the types and structure of the hydration products,which in turn affects their ability to bind chloride ions.The binding capacity of cementitious materials to chloride ions,porosity and chloride ion migration coefficient increased with the increase of water-cement ratio,while steam curing increased the porosity and chloride ion migration coefficient at the same time as it increased the chloride ion binding capacity of the materials.At lower water-cement ratios,the effect of steam curing on the resistance of cementitious materials to chloride ingress is negligible.展开更多
The manufacturing of Ordinary Portland Cement(OPC)significantly contributes to global carbon dioxide(CO_(2))emissions,necessitating the exploration of alternative binders like alkali-activated materials(AAM).Despite i...The manufacturing of Ordinary Portland Cement(OPC)significantly contributes to global carbon dioxide(CO_(2))emissions,necessitating the exploration of alternative binders like alkali-activated materials(AAM).Despite its environmental benefits,AAM generally faces challenges such as drying shrinkage and efflorescence,limiting its industrial application.This study focuses on investigating the impact of steam curing on addressing these challenges in high strength slag-based AAM.The results indicates that high strength AAM can be developed by carefully optimizing the activator-to-binder and water-to-binder ratios,and incorporating steam curing.Specifically,a compressive strength of 112.4 MPa was achieved after one day of steam curing,compared to 100.8 MPa after 28 days of standard curing.This demonstrates the ability of steam curing to accelerate strength development of AAM.Furthermore,steam curing proved to be highly effective in reducing drying shrinkage,which was decreased from 17351 microstrains to 1440 microstrains.This reduction aligns the shrinkage levels of AAM with those of OPC,addressing a major limitation of AAM.This study also found that efflorescence was notably mitigated,with a significant reduction observed after a 24-hour steam curing period.These findings highlight steam curing as a cost-effective and practical-effective method in improving the performance of AAM.By addressing the key challenges,steam curing facilitates the broader adoption of AAM in sustainable construction practices.展开更多
The present study focuses on the improvement of pozzolanic reaction of fly ash particles with the cement hydration products.Low and high volume fly ash concrete mixtures were studied systematically with the addition o...The present study focuses on the improvement of pozzolanic reaction of fly ash particles with the cement hydration products.Low and high volume fly ash concrete mixtures were studied systematically with the addition of accelerating admixtures and accelerated curing of the concrete specimens in a steam chamber for 18 h at 75℃.Also,the reinforcing effects of glued steel fibers addition on the compressive and flexural performance of fly ash concrete were investigated.The test results indicated that the addition of accelerator improved the rate of hardening and the inclusion of steel fibers provided higher flexural performance.Also,it can be noted that the high volume fly ash(50%)addition in concrete showed a reduction in strength;however,the addition of accelerator has compensated the deceleration in strength gain.The proper selection of concrete ingredients,addition of accelerator and initial steam curing for 18 h showed better improvement on the engineering properties in fly ash concrete.A maximum increase(41.7%)in compressive strength of fly ash concrete around 52.90 MPa was noticed for 25%fly ash substitution and 1.5%steel fibers addition.Dynamic elastic modulus was also calculated in loaded concrete specimen using ultrasonic pulse velocity test and showed a good agreement with the experimental value.展开更多
基金Project(LM(2022)-F-053)supported by the China Railway Resources Science and Technology。
文摘Molybdenum tailings are the solid waste left from ore processing,which damages soil and water resources.To address that,molybdenum tailings(MTs)powder obtained from molybdenum tailings sands was processed as an admixture.Compared with moisture-cured conditions,the influence of MTs on the steam-cured mortar’s mechanical properties,surface and internal pore characteristics,and microscopic morphology was investigated.The results show that steam-cured mortar containing appropriate MTs can still have high early strength.When the content of MTs doesn’t exceed 15%,the mechanical strength of mortar steam-cured for 3 d can reach 85%of that of corresponding mortar moisture-cured for 28 d,and that of mortar steam-cured for 28 d isn’t lower than 90%of that of pure cement mortar.The proportion of harmful pores(HFP)and more harmful pores(MHFP)and most probable pore diameters(MPD)on the mortar surface containing MTs steam-cured for 28 d are significantly decreased.When MTs’content is 15%,the proportion of HFP and MHFP on the surface of paste is decreased by 71.4%and 72.2%,respectively,with MPS decreasing from 12.7 nm to 10.8 nm.SEM analysis shows that the surfaces of steam-cured paste containing 15%MTs have more hydration products and dense microstructures.The effect of pozzolanic and dense filling of MTs effectively refines the pore structure,reducing the large pore-size pores.
文摘The effects of steam curing on mechanical properties,drying shrinkage,cracking sensitivity,anti-permeability,and carbonation resistance of C50 shield segment concrete were investigated,which were compared with the standard curing conditions. The results indicated that steam curing could increase early strength of concrete and reduce its drying shrinkage. However,steam curing reduced later strength of concrete,increased its crack sensitivity and deteriorated its anti-permeability and carbonation resistance. Moreover,the incorporation of fly ash could improve the durability of steam-cured concrete.
基金Funded by the National Natural Science Foundation of China (Nos. 51972249, 52172026, 51772226)。
文摘The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration,XRD,LF-NMR and rapid chloride migration test.The results show that the curing regime has influences on the types and structure of the hydration products,which in turn affects their ability to bind chloride ions.The binding capacity of cementitious materials to chloride ions,porosity and chloride ion migration coefficient increased with the increase of water-cement ratio,while steam curing increased the porosity and chloride ion migration coefficient at the same time as it increased the chloride ion binding capacity of the materials.At lower water-cement ratios,the effect of steam curing on the resistance of cementitious materials to chloride ingress is negligible.
基金funded by‘Micro-structural,thermal and mechanical properties of concrete incorporating recycled materials(PGRS2012023)’and The Hong Kong Polytechnic University.
文摘The manufacturing of Ordinary Portland Cement(OPC)significantly contributes to global carbon dioxide(CO_(2))emissions,necessitating the exploration of alternative binders like alkali-activated materials(AAM).Despite its environmental benefits,AAM generally faces challenges such as drying shrinkage and efflorescence,limiting its industrial application.This study focuses on investigating the impact of steam curing on addressing these challenges in high strength slag-based AAM.The results indicates that high strength AAM can be developed by carefully optimizing the activator-to-binder and water-to-binder ratios,and incorporating steam curing.Specifically,a compressive strength of 112.4 MPa was achieved after one day of steam curing,compared to 100.8 MPa after 28 days of standard curing.This demonstrates the ability of steam curing to accelerate strength development of AAM.Furthermore,steam curing proved to be highly effective in reducing drying shrinkage,which was decreased from 17351 microstrains to 1440 microstrains.This reduction aligns the shrinkage levels of AAM with those of OPC,addressing a major limitation of AAM.This study also found that efflorescence was notably mitigated,with a significant reduction observed after a 24-hour steam curing period.These findings highlight steam curing as a cost-effective and practical-effective method in improving the performance of AAM.By addressing the key challenges,steam curing facilitates the broader adoption of AAM in sustainable construction practices.
文摘The present study focuses on the improvement of pozzolanic reaction of fly ash particles with the cement hydration products.Low and high volume fly ash concrete mixtures were studied systematically with the addition of accelerating admixtures and accelerated curing of the concrete specimens in a steam chamber for 18 h at 75℃.Also,the reinforcing effects of glued steel fibers addition on the compressive and flexural performance of fly ash concrete were investigated.The test results indicated that the addition of accelerator improved the rate of hardening and the inclusion of steel fibers provided higher flexural performance.Also,it can be noted that the high volume fly ash(50%)addition in concrete showed a reduction in strength;however,the addition of accelerator has compensated the deceleration in strength gain.The proper selection of concrete ingredients,addition of accelerator and initial steam curing for 18 h showed better improvement on the engineering properties in fly ash concrete.A maximum increase(41.7%)in compressive strength of fly ash concrete around 52.90 MPa was noticed for 25%fly ash substitution and 1.5%steel fibers addition.Dynamic elastic modulus was also calculated in loaded concrete specimen using ultrasonic pulse velocity test and showed a good agreement with the experimental value.
