Internal curing agents (ICA) based on super absorbent polymer have poor alkali tolerance and reduce the early strength of concrete.An alkali tolerate internal curing agent (CAA-ICA) was designed and prepared by using ...Internal curing agents (ICA) based on super absorbent polymer have poor alkali tolerance and reduce the early strength of concrete.An alkali tolerate internal curing agent (CAA-ICA) was designed and prepared by using sodium carboxymethyl starch (CMS) with high hydrophilicity,acrylic acid (AA) containing anionic carboxylic group and acrylamide (AM) containing non-ionic amide group as the main raw materials.The results show that the ratio of CAA-ICA alkali absorption solution is higher than that existing ICA,which solves the low water absorption ratio of the ICA in alkali environment.The water absorption ratio of CAA-ICA in saturated Ca(OH)_(2) solution is 95.8 g·g^(-1),and the alkali tolerance coefficient is 3.4.The application of CAA-ICA in cement-based materials can increase the internal relative humidity and miniaturize the pore structure.The compressive strength of mortar increases up to 12.95%at 28 d,which provids a solution to overcome the reduction of the early strength.展开更多
In order to explore the internal curing mechanism of sepiolite in cement-based materials,the effects of sepiolite on the water consumption of standard consistency,setting time,viscosity,strength,pore structure charact...In order to explore the internal curing mechanism of sepiolite in cement-based materials,the effects of sepiolite on the water consumption of standard consistency,setting time,viscosity,strength,pore structure characteristics,micro-hardness characteristics and two-dimensional surface characteristics of cement paste were studied,respectively.The experimental results show that the water consumption of standard consistency increases linearly with the increase of sepiolite content.The setting time and viscosity are also lengthened and increased with the addition of sepiolite,respectively.When the content of sepiolite exceeds 5%,the strength of the specimen increases significantly.The BET results show that the pore structure of the interfacial transition zone(ITZ)in hardened cement paste(HCP)with sepiolite is optimized after curing for28 d and its pore volume content with below 10 nm is decreased,especially for the specimen with a lower watercement ratio.The characteristics of microhardness and strength of specimens have the same law.Backscattered electron image(BSE-IA)shows that the ITZ of the specimen with sepiolite is denser and the unhydrated cement particles are less than the reference specimen.展开更多
Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this probl...Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this problem, water-releasing material with water storage and releasing characteristics was incorporated into high strength micro-expansive concrete to provide internal curing, and expansive effect of expansive agent was improved. Migration of water from initially saturated water-releasing material to the surrounding hydrating cement paste was investigated. Based on a given efficient diffusion distance of water stored in water-releasing material, the mass and real water-cement ratio of cured cement paste were estimated. At the same time, the effect of internal curing of water-releasing material on the volume deformation of high strength micro-expansive concrete was investigated.展开更多
A solution polymerization method has been used to synthesize a polyacrylic-type superabsorbent polymer(SAP).The influence of various influential factors,such as the temperature,neutralization degree,cross-linking agen...A solution polymerization method has been used to synthesize a polyacrylic-type superabsorbent polymer(SAP).The influence of various influential factors,such as the temperature,neutralization degree,cross-linking agent,and initiator,on the water absorption capacity of SAP has been investigated.The results show that the absorption can display a non-monotonic behavior depending on the synthesis conditions.The absorption can also change according to the pH,ion types and ion concentration.As the pH value increases,the water absorption capacity decreases significantly.It also decreases if the N^(a+)concentration becomes higher and becomes particularly low in solutions containing Mg^(2+).With the addition of SAP,the compressive strength of cement mortar decreases;the internal relative humidity can be maintained at 96%within 200 hours;and autogenous shrinkage can be reduced by nearly 69%.展开更多
To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs)...To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.展开更多
Shrinkage-induced cracking is a common issue in concrete structures,where the formation of cracks not only affects the aesthetic appearance of concrete but also potentially reduces its durability and strength.In this ...Shrinkage-induced cracking is a common issue in concrete structures,where the formation of cracks not only affects the aesthetic appearance of concrete but also potentially reduces its durability and strength.In this study,the effect of ceramsite sand addition on the properties of a ternary system of cement-ground granulated blast furnace slag(GGBFS)-phosphogypsum(PG)is investigated.In particular,the fluidity,rheology,hydration heat,compressive strength,autogenous shrinkage,and drying shrinkage of the considered mortar specimens are analyzed.The results indicate that an increase in PG content leads to a decrease in fluidity,higher viscosity,lower exothermic peak,and lower compressive strength.However,the shrinkage of the mortar specimens is effectively compensated.The incorporation of internal curing water from ceramsite sand improves fluidity,decreases both yield stress and viscosity,enhances the degree of hydration,and induces mortar expansion.However,the inferior mechanical properties of the ceramsite sand generally produce a decrease in the compressive strength.展开更多
The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investi-gated. The results show that, in ea...The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investi-gated. The results show that, in early age the dry LWA has significant effect on the formation of dense paste around it and improving the concrete impermeability. However the prewetted LWA has strong water-releasing effect in later age, which increases the hydration degree of the paste around it, and makes the adjacent paste develop a structure with low porosity and finer aperture, furthermore the concrete impermeability can be improved. It is suggested that, as for concrete with low durability requirement, the LWA without pre-wetting treatment can be used as long as meet the workability re-quirement of fresh concrete, the good impermeability of concrete can be gained as well. As for con-crete with high durability requirement, the prewetted LWA should be used, and the pre-wetting time should be extended as long as possible, in order to optimize the concrete structure in long term, and improve the concrete durability.展开更多
The pre-soaked shale employed as an internal curing agent and CaO employed as expansion agent were incorporated into concrete to investigate their effects on the mechanical properties and autogenous deformation of ear...The pre-soaked shale employed as an internal curing agent and CaO employed as expansion agent were incorporated into concrete to investigate their effects on the mechanical properties and autogenous deformation of early-age concrete.We have conducted the relevant tests for setting time,mechanical properties,internal relative humidity and autogenous deformation of early-age concrete with shale or/and CaO incorporation.The results indicate that the set behavior is delayed by shale addition but is accelerated with CaO.The shale addition firstly enhances and subsequently decreases the strength,but CEA addition has a weakening effect.Additionally,shale or/and CaO incorporation deteriorates the elastic modulus.The shale and CaO incorporation significantly improve the internal relative humidity of concrete.The internal curing efficacy of shale could synergistically mitigate the autogenous shrinkage,that is,could enhance the expansion of CaO and then greatly reduce the contraction,which is significantly beneficial to impede the shrinkage-introduced cracks of early-age concrete.展开更多
The heavyweight ultra-high performance concrete(HUHPC)was prepared with barite sand partially replaced by titanium-rich heavy slag sand(THS)at replacement proportion of 0%,30%,50%,70%and 100%in this work.The results s...The heavyweight ultra-high performance concrete(HUHPC)was prepared with barite sand partially replaced by titanium-rich heavy slag sand(THS)at replacement proportion of 0%,30%,50%,70%and 100%in this work.The results show that THS incorporation can effectively improve the mechanical properties and reduce the volume shrinkage of HUHPC.The HUHPC with 50%THS replacement reaches an apparent density of 2890 kg/m^(3)(for fresh HUHPC),28 d compressive strength of 129 MPa,28 d flexural strength of 23 MPa,28 d flexural toughness of 28.4,56 d volume shrinkage of 359×10^(-4) and,as expected,excellent durability.Microstructural investigation demonstrates that the internal curing of pre-wetted THS promotes the hydration of the surrounding cement paste thereby strengthening the interfacial transition zone,resulting in the“hard shell”formation around aggregate to“protect”the aggregate.Additionally,the“pin structure”significantly improves the cement paste-aggregate interfacial connection.The combination of“hard shell protection”and“pin structure”remarkably improve the mechanical properties of HUHPC produced with porous THS aggregate.展开更多
Superabsorbent polymers(SAPs)are cross-linked polymers that can absorb and retain large amounts of water.In recent years,a growing interest was seen in applying SAPs in concrete to improve its performance due to its e...Superabsorbent polymers(SAPs)are cross-linked polymers that can absorb and retain large amounts of water.In recent years,a growing interest was seen in applying SAPs in concrete to improve its performance due to its efficiency in mitigating shrinkage.This paper presents findings in a study on effect of SAPs on performance of cement-treated base(CTB),using the experience of internal curing of concrete.CTB specimens with and without SAPs were prepared and tested in the laboratory.Tests conducted include mechanical property testing,dry shrinkage testing,differential thermal analysis,mercury intrusion porosimetry and scanning electron microscope testing.It was found that 7-day and 28-day unconfined compressive strength of CTB specimens with SAPs was higher than regular CTB specimens.28d compressive strength of CTB specimens with SAPs made by Static pressure method was 5.87 MPa,which is 27%higher than that of regular CTB specimens.Drying shrinkage of CTB specimens with SAPs was decreased by 52.5%comparing with regular CTB specimens.Through the microstructure analysis it was found that CTB specimens with SAPs could produce more hydration products,which is also the reason for the strength improvement.展开更多
基金Funded by the National Key Research and Development Program of China (No.2019YFC1906202)the Guangxi Key Research and Development Plan (Nos.Guike AA18242007-3, Guike AB19259008, and Guike AB20297014)。
文摘Internal curing agents (ICA) based on super absorbent polymer have poor alkali tolerance and reduce the early strength of concrete.An alkali tolerate internal curing agent (CAA-ICA) was designed and prepared by using sodium carboxymethyl starch (CMS) with high hydrophilicity,acrylic acid (AA) containing anionic carboxylic group and acrylamide (AM) containing non-ionic amide group as the main raw materials.The results show that the ratio of CAA-ICA alkali absorption solution is higher than that existing ICA,which solves the low water absorption ratio of the ICA in alkali environment.The water absorption ratio of CAA-ICA in saturated Ca(OH)_(2) solution is 95.8 g·g^(-1),and the alkali tolerance coefficient is 3.4.The application of CAA-ICA in cement-based materials can increase the internal relative humidity and miniaturize the pore structure.The compressive strength of mortar increases up to 12.95%at 28 d,which provids a solution to overcome the reduction of the early strength.
基金Funded by the Natural Science Foundation of China(No.51408380)the Science and Technology Plan of He Bei Province(No.E2021210033)the Scientific and Technological Development Funds of the Central Government Shall Guide Local(No.216Z3801G)。
文摘In order to explore the internal curing mechanism of sepiolite in cement-based materials,the effects of sepiolite on the water consumption of standard consistency,setting time,viscosity,strength,pore structure characteristics,micro-hardness characteristics and two-dimensional surface characteristics of cement paste were studied,respectively.The experimental results show that the water consumption of standard consistency increases linearly with the increase of sepiolite content.The setting time and viscosity are also lengthened and increased with the addition of sepiolite,respectively.When the content of sepiolite exceeds 5%,the strength of the specimen increases significantly.The BET results show that the pore structure of the interfacial transition zone(ITZ)in hardened cement paste(HCP)with sepiolite is optimized after curing for28 d and its pore volume content with below 10 nm is decreased,especially for the specimen with a lower watercement ratio.The characteristics of microhardness and strength of specimens have the same law.Backscattered electron image(BSE-IA)shows that the ITZ of the specimen with sepiolite is denser and the unhydrated cement particles are less than the reference specimen.
基金Funded by the Project of National Natural Science Foundation (No. 50508034)Guangxi Key Laboratory for the Advance Materials and New Preparation Technology(No. 063006-5C-13)
文摘Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this problem, water-releasing material with water storage and releasing characteristics was incorporated into high strength micro-expansive concrete to provide internal curing, and expansive effect of expansive agent was improved. Migration of water from initially saturated water-releasing material to the surrounding hydrating cement paste was investigated. Based on a given efficient diffusion distance of water stored in water-releasing material, the mass and real water-cement ratio of cured cement paste were estimated. At the same time, the effect of internal curing of water-releasing material on the volume deformation of high strength micro-expansive concrete was investigated.
基金The authors would like to acknowledge the National Natural Science Foundation of China(51902095).
文摘A solution polymerization method has been used to synthesize a polyacrylic-type superabsorbent polymer(SAP).The influence of various influential factors,such as the temperature,neutralization degree,cross-linking agent,and initiator,on the water absorption capacity of SAP has been investigated.The results show that the absorption can display a non-monotonic behavior depending on the synthesis conditions.The absorption can also change according to the pH,ion types and ion concentration.As the pH value increases,the water absorption capacity decreases significantly.It also decreases if the N^(a+)concentration becomes higher and becomes particularly low in solutions containing Mg^(2+).With the addition of SAP,the compressive strength of cement mortar decreases;the internal relative humidity can be maintained at 96%within 200 hours;and autogenous shrinkage can be reduced by nearly 69%.
基金Funded by the National Natural Science Foundation of China(No.52378213)the Technology Development Project(No.20201902977180010) of CABR Technology Co.,Ltd。
文摘To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.
基金funded by the China Railway Major Bridge Engineering Group Co.,Ltd.,Project(2023-48-Key Project).
文摘Shrinkage-induced cracking is a common issue in concrete structures,where the formation of cracks not only affects the aesthetic appearance of concrete but also potentially reduces its durability and strength.In this study,the effect of ceramsite sand addition on the properties of a ternary system of cement-ground granulated blast furnace slag(GGBFS)-phosphogypsum(PG)is investigated.In particular,the fluidity,rheology,hydration heat,compressive strength,autogenous shrinkage,and drying shrinkage of the considered mortar specimens are analyzed.The results indicate that an increase in PG content leads to a decrease in fluidity,higher viscosity,lower exothermic peak,and lower compressive strength.However,the shrinkage of the mortar specimens is effectively compensated.The incorporation of internal curing water from ceramsite sand improves fluidity,decreases both yield stress and viscosity,enhances the degree of hydration,and induces mortar expansion.However,the inferior mechanical properties of the ceramsite sand generally produce a decrease in the compressive strength.
基金Funded by the Western Transportation Construction of Communication Ministry (No. 200331882008)
文摘The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investi-gated. The results show that, in early age the dry LWA has significant effect on the formation of dense paste around it and improving the concrete impermeability. However the prewetted LWA has strong water-releasing effect in later age, which increases the hydration degree of the paste around it, and makes the adjacent paste develop a structure with low porosity and finer aperture, furthermore the concrete impermeability can be improved. It is suggested that, as for concrete with low durability requirement, the LWA without pre-wetting treatment can be used as long as meet the workability re-quirement of fresh concrete, the good impermeability of concrete can be gained as well. As for con-crete with high durability requirement, the prewetted LWA should be used, and the pre-wetting time should be extended as long as possible, in order to optimize the concrete structure in long term, and improve the concrete durability.
基金Funded by National Natural Science Foundation of China(Nos.U1965105,51878245,52008189)Fundamental Research Funds for the Central Universities(No.B200203197)+2 种基金National Key Research and Development Program of China(No.2017YFB0310100)Ningbo 2025 Science and Technology Major Project(No.2020Z035)the State Key Laboratory of High Performance Civil Engineering Materials(No.2019CEM001)。
文摘The pre-soaked shale employed as an internal curing agent and CaO employed as expansion agent were incorporated into concrete to investigate their effects on the mechanical properties and autogenous deformation of early-age concrete.We have conducted the relevant tests for setting time,mechanical properties,internal relative humidity and autogenous deformation of early-age concrete with shale or/and CaO incorporation.The results indicate that the set behavior is delayed by shale addition but is accelerated with CaO.The shale addition firstly enhances and subsequently decreases the strength,but CEA addition has a weakening effect.Additionally,shale or/and CaO incorporation deteriorates the elastic modulus.The shale and CaO incorporation significantly improve the internal relative humidity of concrete.The internal curing efficacy of shale could synergistically mitigate the autogenous shrinkage,that is,could enhance the expansion of CaO and then greatly reduce the contraction,which is significantly beneficial to impede the shrinkage-introduced cracks of early-age concrete.
基金Funded by National Natural Science Foundation of China(Nos.52008002,U2006224 and 51878003)Doctoral Scientific Research Startup Foundation of Anhui Jianzhu University(No.2019QDZ66)。
文摘The heavyweight ultra-high performance concrete(HUHPC)was prepared with barite sand partially replaced by titanium-rich heavy slag sand(THS)at replacement proportion of 0%,30%,50%,70%and 100%in this work.The results show that THS incorporation can effectively improve the mechanical properties and reduce the volume shrinkage of HUHPC.The HUHPC with 50%THS replacement reaches an apparent density of 2890 kg/m^(3)(for fresh HUHPC),28 d compressive strength of 129 MPa,28 d flexural strength of 23 MPa,28 d flexural toughness of 28.4,56 d volume shrinkage of 359×10^(-4) and,as expected,excellent durability.Microstructural investigation demonstrates that the internal curing of pre-wetted THS promotes the hydration of the surrounding cement paste thereby strengthening the interfacial transition zone,resulting in the“hard shell”formation around aggregate to“protect”the aggregate.Additionally,the“pin structure”significantly improves the cement paste-aggregate interfacial connection.The combination of“hard shell protection”and“pin structure”remarkably improve the mechanical properties of HUHPC produced with porous THS aggregate.
基金funded by the International Cooperation Project of Jiangsu Science and Technology Department[Grant No.BZ2017011].
文摘Superabsorbent polymers(SAPs)are cross-linked polymers that can absorb and retain large amounts of water.In recent years,a growing interest was seen in applying SAPs in concrete to improve its performance due to its efficiency in mitigating shrinkage.This paper presents findings in a study on effect of SAPs on performance of cement-treated base(CTB),using the experience of internal curing of concrete.CTB specimens with and without SAPs were prepared and tested in the laboratory.Tests conducted include mechanical property testing,dry shrinkage testing,differential thermal analysis,mercury intrusion porosimetry and scanning electron microscope testing.It was found that 7-day and 28-day unconfined compressive strength of CTB specimens with SAPs was higher than regular CTB specimens.28d compressive strength of CTB specimens with SAPs made by Static pressure method was 5.87 MPa,which is 27%higher than that of regular CTB specimens.Drying shrinkage of CTB specimens with SAPs was decreased by 52.5%comparing with regular CTB specimens.Through the microstructure analysis it was found that CTB specimens with SAPs could produce more hydration products,which is also the reason for the strength improvement.