New world record of altitude transportation of concrete (532 m) was reached on the 2nd of June 1994 in Riva del Garda Hydroelectric Power Plant. The requirement involved the construction of a new piezometric well and intake conduit and the replacing of the existing surface penstock with a new one built underground to reduce environmental impact. Two parallel tunnels were excavated: one for Ledro - Garda lakes location, the other for transporting penstock's metal elements. The self supporting metal pipe has been blocked for all its length (790 m) by filling of the ring space between the excavation wall and the piping with 5,000 m2 of concrete. In order to reduce environmental impact it was decided to pump concrete from the lower end from and excavated chamber near the Powerhouse. The record level: 532 m (vertical) and 790 m (total length) widely exceeded the former one (432 m) obtained in 1985 in Spanish "ESTANGENTO SALLENTE" Power Plant.
1994年6月2日，Riva del Garda水电站的混凝土高度运输创下了新的世界纪录(532米)。该项目要求建造一个新的测压井和进水管道，并将现有的地面压力管道替换为一个新的地下压力管道，以减少对环境的影响。两条平行的隧道被挖掘:一条用于莱德罗-加尔达湖的位置，另一条用于运输管道的金属元素。通过用5000平方米的混凝土填充开挖墙和管道之间的环形空间，将自支撑金属管的所有长度(790米)都堵住了。为了减少对环境的影响，决定从厂房附近的下端和挖掘室泵送混凝土。记录高度:532米(垂直)和790米(总长度)远远超过1985年西班牙“ESTANGENTO SALLENTE”发电厂获得的前记录(432米)。
{"title":"Concrete Pumping: A New World Record","authors":"Giovanni Ticozelli, D. Galbiati, A. Pasqualini","doi":"10.14359/6220","DOIUrl":"https://doi.org/10.14359/6220","url":null,"abstract":"New world record of altitude transportation of concrete (532 m) was reached on the 2nd of June 1994 in Riva del Garda Hydroelectric Power Plant. The requirement involved the construction of a new piezometric well and intake conduit and the replacing of the existing surface penstock with a new one built underground to reduce environmental impact. Two parallel tunnels were excavated: one for Ledro - Garda lakes location, the other for transporting penstock's metal elements. The self supporting metal pipe has been blocked for all its length (790 m) by filling of the ring space between the excavation wall and the piping with 5,000 m2 of concrete. In order to reduce environmental impact it was decided to pump concrete from the lower end from and excavated chamber near the Powerhouse. The record level: 532 m (vertical) and 790 m (total length) widely exceeded the former one (432 m) obtained in 1985 in Spanish \"ESTANGENTO SALLENTE\" Power Plant.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72725923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
When the historical buildings of the Republic of Venice were erected all the construction materials and the corresponding techniques were always carefully selected. Even at that time architects were aware of the importance of the durability of buildings in a very hostile environment such as that existing in Venice characterized by permanent humid air and capillary rise of salty water from the foundations. In particular cementitious materials were adopted in agreement with the empirical rules of the Romans' experience and adapted for the particular Venetian environment. The present paper examines two specific cementitious materials which became very popular throughout the world: the stucco plaster and the terrazzo concrete. At the time of the Republic of Venice, chemical admixtures were not available. Therefore, masonry artisans and architects developed a special know-how to manufacture durable materials. This was based on the use of mineral admixtures and natural substances, the invention of innovative binders and the development of special application techniques. After the advent of portland cement and especially of chemical admixtures, modern stucco plaster and terrazzo concrete can be produced with different (not necessarily beter) properties and at higher rates of productivity. The present paper examines the microstructural aspect, the composition, the performance, and the manufacturing process of the original and modern materials.
{"title":"A Historical Review of the Development of Chemical and Mineral Admixtures for Use in Stucco Plaster and Terrazzo Floor","authors":"M. Collepardi","doi":"10.14359/6208","DOIUrl":"https://doi.org/10.14359/6208","url":null,"abstract":"When the historical buildings of the Republic of Venice were erected all the construction materials and the corresponding techniques were always carefully selected. Even at that time architects were aware of the importance of the durability of buildings in a very hostile environment such as that existing in Venice characterized by permanent humid air and capillary rise of salty water from the foundations. In particular cementitious materials were adopted in agreement with the empirical rules of the Romans' experience and adapted for the particular Venetian environment. The present paper examines two specific cementitious materials which became very popular throughout the world: the stucco plaster and the terrazzo concrete. At the time of the Republic of Venice, chemical admixtures were not available. Therefore, masonry artisans and architects developed a special know-how to manufacture durable materials. This was based on the use of mineral admixtures and natural substances, the invention of innovative binders and the development of special application techniques. After the advent of portland cement and especially of chemical admixtures, modern stucco plaster and terrazzo concrete can be produced with different (not necessarily beter) properties and at higher rates of productivity. The present paper examines the microstructural aspect, the composition, the performance, and the manufacturing process of the original and modern materials.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82735446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The significant increase in large high-rise concrete structures has dictated diverse requirements for concrete. Concrete technology has improved, widening the range of applications of this material. In this regard, the technology of polycarboxylate-based superplasticizers has made remarkable progress; a number of new superplasticizers have been developed and applied to big construction projects. To elucidate the fluidizing mechanism of superplasticizers in cement, we focused on the fact that the chemical structure of these superplasticizers changes in an alkali environment. We determined the absolute molecular weight of the superplasticizers using the light scattering method, measured the amount absorbed, zeta potential, and nuclear magnetic resonance. Based on our finding pertaining to polycarboxylate-based superplasticizers, we discuss the fluidizing mechanism of cement compositions with relevance to dispersibility retention, and flowability. We refer to DLVO theory, stearic repulsion effect theory, depletion effect theory, tribology effect, as well as the results of mortar and concrete tests. We also reported on the applications at big projects, such as the anchorage of the Akashi Channel Bridge and the deep ground continuous wall of the Tokyo Trans-Bay Highway.
{"title":"Fluidizing Mechanism and Application of Polycarboxlate-Based Superplasticizers","authors":"Y.Tanaka","doi":"10.14359/6193","DOIUrl":"https://doi.org/10.14359/6193","url":null,"abstract":"The significant increase in large high-rise concrete structures has dictated diverse requirements for concrete. Concrete technology has improved, widening the range of applications of this material. In this regard, the technology of polycarboxylate-based superplasticizers has made remarkable progress; a number of new superplasticizers have been developed and applied to big construction projects. To elucidate the fluidizing mechanism of superplasticizers in cement, we focused on the fact that the chemical structure of these superplasticizers changes in an alkali environment. We determined the absolute molecular weight of the superplasticizers using the light scattering method, measured the amount absorbed, zeta potential, and nuclear magnetic resonance. Based on our finding pertaining to polycarboxylate-based superplasticizers, we discuss the fluidizing mechanism of cement compositions with relevance to dispersibility retention, and flowability. We refer to DLVO theory, stearic repulsion effect theory, depletion effect theory, tribology effect, as well as the results of mortar and concrete tests. We also reported on the applications at big projects, such as the anchorage of the Akashi Channel Bridge and the deep ground continuous wall of the Tokyo Trans-Bay Highway.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90942073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work a paste viscometer with concentric cylinders is used to evaluate the mineral- and chemical admixtures' impact on fresh fine mortar rheology. Rheology results have been evaluated according to the Bingham model, which describes the rheology with parameters; yield stress and plastic viscosity. Seven dolomite fillers have been investigated in combination with one superplasticizer and two cement types. The fillers originate from the same deposit, i.e. having the same mineralogy but different particle size distribution. Relationships have been established between rheology results and particle size analysis of cements and fillers. Increasing fineness leads to higher yield stress and plastic viscosity. Addition of superplasticizers results in a parallel displacement of these relationships towards lower rheology values. The results also show a significantly large difference in rheology depending on type of cement. Rheologically, the finer cement exhibits lower yield stress and public viscosity than the coarser cement, when adding the same amount of filler. The results for the reference mixes, when no filler is added, are the opposite. Rheology tests using a paste viscometer with concentric cylinders on the fine mortar part of the concrete is an effective method to describe additives' influence on fresh concrete rheology.
{"title":"The Effect of Mineral and Chemical Admixtures on Fine Mortar Rheology","authors":"P. Billberg","doi":"10.14359/6190","DOIUrl":"https://doi.org/10.14359/6190","url":null,"abstract":"In this work a paste viscometer with concentric cylinders is used to evaluate the mineral- and chemical admixtures' impact on fresh fine mortar rheology. Rheology results have been evaluated according to the Bingham model, which describes the rheology with parameters; yield stress and plastic viscosity. Seven dolomite fillers have been investigated in combination with one superplasticizer and two cement types. The fillers originate from the same deposit, i.e. having the same mineralogy but different particle size distribution. Relationships have been established between rheology results and particle size analysis of cements and fillers. Increasing fineness leads to higher yield stress and plastic viscosity. Addition of superplasticizers results in a parallel displacement of these relationships towards lower rheology values. The results also show a significantly large difference in rheology depending on type of cement. Rheologically, the finer cement exhibits lower yield stress and public viscosity than the coarser cement, when adding the same amount of filler. The results for the reference mixes, when no filler is added, are the opposite. Rheology tests using a paste viscometer with concentric cylinders on the fine mortar part of the concrete is an effective method to describe additives' influence on fresh concrete rheology.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83863943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The diversity of concreting methods in recent years has led to a demand for long retardation of concrete setting. Conventional research has achieved retardation for up to about 3 days by the addition of a set retarder, but few studies have dealt with concrete that is placable after a much longer period. This paper reports the effects of the set-time limits for superplasticizing and compressive strength of concrete. The use of concrete with long-retarded setting is discussed as well.
{"title":"Effect of High Dosage of a Set Retarder on the Properties of Fresh and Hardened Concrete","authors":"S. Nagataki, T. Takeuchi","doi":"10.14359/6210","DOIUrl":"https://doi.org/10.14359/6210","url":null,"abstract":"The diversity of concreting methods in recent years has led to a demand for long retardation of concrete setting. Conventional research has achieved retardation for up to about 3 days by the addition of a set retarder, but few studies have dealt with concrete that is placable after a much longer period. This paper reports the effects of the set-time limits for superplasticizing and compressive strength of concrete. The use of concrete with long-retarded setting is discussed as well.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77879596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New construction or repair of existing structures dealing with the placement of concrete underwater poses certain challenges that require special placement techniques, and more specifically, specialized mixture proportions. Anti-washout admixtures (AWA), based on water-soluble polymers of various types, have been developed for use in concrete placed underwater in order to minimize cement washout and provide in-place concrete of satisfactory quality. These admixtures create a cohesive paste phase either by binding free mix water or by enhancing interparticle attraction. Hence, they are finding additional uses such as segregation or bleed control agents, and viscosity modifiers. Recently, the need for a viscosity modifying agent arose in a dam rehabilitation project in Alabama where a grout curtain was being placed to control seepage under the dam. To verify the feasibility of using an AWA in the grout mixtures for this project, a preliminary study was performed in the laboratory to investigate the performance of fluid grouts treated with a unique cellulose-based liquid AWA developed for underwater concreting. The effect of this unique AWA on the plastic properties of fluid and flowable grouts are presented in this paper. The results indicate that it is possible to use this admixture to modify grout viscosity, minimize bleeding characteristics, and improve washout resistance of fluid and flowable grout mixtures. Applications that might benefit from these improvements include: grouting riprap in tidal zones; and placement of grout curtains to minimize water seepage under dams.
{"title":"Laboratory Evaluation of a Unique Anti-Washout Admixture in Grouts","authors":"J. Bury, H. Farzam","doi":"10.14359/6197","DOIUrl":"https://doi.org/10.14359/6197","url":null,"abstract":"New construction or repair of existing structures dealing with the placement of concrete underwater poses certain challenges that require special placement techniques, and more specifically, specialized mixture proportions. Anti-washout admixtures (AWA), based on water-soluble polymers of various types, have been developed for use in concrete placed underwater in order to minimize cement washout and provide in-place concrete of satisfactory quality. These admixtures create a cohesive paste phase either by binding free mix water or by enhancing interparticle attraction. Hence, they are finding additional uses such as segregation or bleed control agents, and viscosity modifiers. Recently, the need for a viscosity modifying agent arose in a dam rehabilitation project in Alabama where a grout curtain was being placed to control seepage under the dam. To verify the feasibility of using an AWA in the grout mixtures for this project, a preliminary study was performed in the laboratory to investigate the performance of fluid grouts treated with a unique cellulose-based liquid AWA developed for underwater concreting. The effect of this unique AWA on the plastic properties of fluid and flowable grouts are presented in this paper. The results indicate that it is possible to use this admixture to modify grout viscosity, minimize bleeding characteristics, and improve washout resistance of fluid and flowable grout mixtures. Applications that might benefit from these improvements include: grouting riprap in tidal zones; and placement of grout curtains to minimize water seepage under dams.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76584012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper examines the rheological and mechanical behavior of superplasticized microcement grouts to be used for the consolidation of porous systems (e.g. sand deposits, masonry walls of historical buildings). Five micro cements were used: they differed in chemical composition of the clinker, type of mineral addition (natural pozzolan or silica fume), and particle size distribution. Three different superplasticizing chemical admixtures - acrylic, napthalene, and melamine bases - were used, all with an active polymer content of 0.4% by mass of cement. The following properties of the grouts were investigated: fluidity (Marsh cone), compressive strength, stability (bleeding test). The acrylic polymer proved to be more effective than the naphtalene and melamine based products in reducing the mixing water to produce a given initial fluidity. Furthermore, the grouts produced with this superplasticizer displayed a lower fluidity loss with time. The performance of a specific mixture was also strongly dependent on the fineness of the binder and on the type of mineral addition. The compressive strength of the hardened grouts was primarily affected - especially at latter ages - by the water-binder ratio, independently of the type of superplasticizer. None of the mixtures considered showed any significant bleeding. A limited number of injection tests in columns of dense sand were also performed. For a given water binder ratio, the groutability of a mixture was greatly improved using the acrylic based superplasticizer in place of the melamine- and naphtalene-based products.
{"title":"Superplasticized Microcement Grouts","authors":"M. Santagata, G. Bonora, M. Collepardi","doi":"10.14359/6219","DOIUrl":"https://doi.org/10.14359/6219","url":null,"abstract":"This paper examines the rheological and mechanical behavior of superplasticized microcement grouts to be used for the consolidation of porous systems (e.g. sand deposits, masonry walls of historical buildings). Five micro cements were used: they differed in chemical composition of the clinker, type of mineral addition (natural pozzolan or silica fume), and particle size distribution. Three different superplasticizing chemical admixtures - acrylic, napthalene, and melamine bases - were used, all with an active polymer content of 0.4% by mass of cement. The following properties of the grouts were investigated: fluidity (Marsh cone), compressive strength, stability (bleeding test). The acrylic polymer proved to be more effective than the naphtalene and melamine based products in reducing the mixing water to produce a given initial fluidity. Furthermore, the grouts produced with this superplasticizer displayed a lower fluidity loss with time. The performance of a specific mixture was also strongly dependent on the fineness of the binder and on the type of mineral addition. The compressive strength of the hardened grouts was primarily affected - especially at latter ages - by the water-binder ratio, independently of the type of superplasticizer. None of the mixtures considered showed any significant bleeding. A limited number of injection tests in columns of dense sand were also performed. For a given water binder ratio, the groutability of a mixture was greatly improved using the acrylic based superplasticizer in place of the melamine- and naphtalene-based products.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80863087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recently in Japan, foamed cement paste and foamed mortar have frequently been used as embankment material on soft ground because of their low unit weight, flowability, and ease of strength control. Conventional uses of these foamed materials include grouting for tunnel voids and for securing pipelines in tunnels. Since each material for foamed cement milk and foamed mortar have a different specific gravity, segregation can occur during mixing, pumping and placing. The mixture proportions of these foamed mixtures is very important, and are usually determined by trial and error. Experiments were carried out on the rheological properties of cement paste, mortar, foamed cement milk and foamed mortar. Compressive strength of these materials were also examined. Obtained results are as follows: (1) Plastic viscosity of foamed cement pastes or mortars are as same as that of cement pastes or mortars. (2) Yield value of foamed mixture decreases with addition of foam less than 30% by volume, and decrease with addition of foam more than 40%. (3) Relation between plastic viscosity and yield value is almost the same as mixtures without foam. (4) Compressive strength of foamed mixtures decreases with increase of foam content, and the tendancy is apparent in lower w/c.
{"title":"Experimental Study on the Rheological Properties of Fresh Foamed Cement Paste and Mortar","authors":"T. Goto, A. Yoshino, ShinzouNishibayashi","doi":"10.14359/6191","DOIUrl":"https://doi.org/10.14359/6191","url":null,"abstract":"Recently in Japan, foamed cement paste and foamed mortar have frequently been used as embankment material on soft ground because of their low unit weight, flowability, and ease of strength control. Conventional uses of these foamed materials include grouting for tunnel voids and for securing pipelines in tunnels. Since each material for foamed cement milk and foamed mortar have a different specific gravity, segregation can occur during mixing, pumping and placing. The mixture proportions of these foamed mixtures is very important, and are usually determined by trial and error. Experiments were carried out on the rheological properties of cement paste, mortar, foamed cement milk and foamed mortar. Compressive strength of these materials were also examined. Obtained results are as follows: (1) Plastic viscosity of foamed cement pastes or mortars are as same as that of cement pastes or mortars. (2) Yield value of foamed mixture decreases with addition of foam less than 30% by volume, and decrease with addition of foam more than 40%. (3) Relation between plastic viscosity and yield value is almost the same as mixtures without foam. (4) Compressive strength of foamed mixtures decreases with increase of foam content, and the tendancy is apparent in lower w/c.","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82837231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. ICoppola, C. Pistolesi, P. Zaffaroni, M. Collepardi
{"title":"Properties of Polymer-Cement Coatings for Concrete Protection","authors":"L. ICoppola, C. Pistolesi, P. Zaffaroni, M. Collepardi","doi":"10.14359/6188","DOIUrl":"https://doi.org/10.14359/6188","url":null,"abstract":"","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75076643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Calcium nitrate (CN) has been increasingly used as a chloride free set accelerator in later years. Mature cement pastes and concrete have been subjected to microstructure investigations in order to identify possible and long term changes when a high dosage of CN was added to the fresh mixes. The following changes ere found for 2 year old cement pastes (w/c = 0.50) based on ordinary Portland cement (OPC) and sulphate resistant Portland cement (SRPC) when 5.26% CN was added: (1) The degree of hydration was only marginally lower. (2) The amount of calcium hydroxide (CH) was significantly lowered (= 10%) in the case of OPC and unaltered for SRPC. (3) The amount of chemically bound water in both pastes was increased. (4) The average length of the polysilicate anions in the amorphous CSH-gel was prolonged (17% for OPC and 5% for SRPC). (5) The porosity of the OPC paste was increased (+7%) and inhomogeneously distributed, while it was decreased (-2%) for the SRPC paste. (6) The morphology of calcium hydroxide (CH) in the pastes was changed from being evenly distributed to be gathered in larger (=50um diameter) clusters. This phenomenon may be explained by restricted diffusion due to the high Ca2+ concentration supplied by CN. This latter effect was also observed for a plain concrete (w/c = 0.57) based on high strength Portland cement (HSPC) and 3.86% CN>
{"title":"Changes in the Microstructure of Cement Paste and Concrete due to Calcium Nitrate Addition","authors":"H. Justnes, E. Nygaard","doi":"10.14359/6207","DOIUrl":"https://doi.org/10.14359/6207","url":null,"abstract":"Calcium nitrate (CN) has been increasingly used as a chloride free set accelerator in later years. Mature cement pastes and concrete have been subjected to microstructure investigations in order to identify possible and long term changes when a high dosage of CN was added to the fresh mixes. The following changes ere found for 2 year old cement pastes (w/c = 0.50) based on ordinary Portland cement (OPC) and sulphate resistant Portland cement (SRPC) when 5.26% CN was added: (1) The degree of hydration was only marginally lower. (2) The amount of calcium hydroxide (CH) was significantly lowered (= 10%) in the case of OPC and unaltered for SRPC. (3) The amount of chemically bound water in both pastes was increased. (4) The average length of the polysilicate anions in the amorphous CSH-gel was prolonged (17% for OPC and 5% for SRPC). (5) The porosity of the OPC paste was increased (+7%) and inhomogeneously distributed, while it was decreased (-2%) for the SRPC paste. (6) The morphology of calcium hydroxide (CH) in the pastes was changed from being evenly distributed to be gathered in larger (=50um diameter) clusters. This phenomenon may be explained by restricted diffusion due to the high Ca2+ concentration supplied by CN. This latter effect was also observed for a plain concrete (w/c = 0.57) based on high strength Portland cement (HSPC) and 3.86% CN>","PeriodicalId":21898,"journal":{"name":"SP-173: Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79373165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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