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Zuhua Zhang - One of the best experts on this subject based on the ideXlab platform.
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phase changes under Efflorescence in alkali activated materials with mixed activators
Construction and Building Materials, 2021Co-Authors: Lakshmikanth Srinivasamurthy, Zuhua Zhang, Venkata S Chevali, Hao WangAbstract:Abstract Efflorescence in alkali-activated materials is a strong function of precursor and activator composition, which dictates their engineering properties and durability. In this study, the Efflorescence of naturally cured NaOH/Na2SiO3 alkali-activated fly ash and alkali-activated fly ash-slag blended binder mixes was assessed with alkali concentration of 9 wt% Na2O, and 10 to 30 wt% of slag, and compared with binder mixes with 9 wt% Na2O, and 10 to 30 wt% of slag along with 2 wt% Na2CO3. The effects of Efflorescence were assessed using visual and leaching inspections, and the compressive and split tensile strengths were determined post activation. Atomic absorption spectrometry was used to quantify free alkalis in the leachate, and X-ray diffraction, and Fourier transform infrared spectroscopy, magic-angle-spinning nuclear magnetic resonance and thermo-gravimetric analysis were performed to analyse the phase changes in binder pastes after Efflorescence. The increased slag content facilitated the formation of C-A-S-H gel and enhanced both chemical and mechanical properties of binder pastes. Furthermore, the inclusion of slag content also led to the reduction of the open porosity and Efflorescence formation. Subsequent exposure of binder specimens to Efflorescence conditions aided the formation of carbonate products, degradation of N-A-S-H and N-(C)-A-S-H gel, and a decrease in split tensile strength in the binder paste specimens.
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Efflorescence of Alkali-Activated Cements (Geopolymers) and the Impacts on Material Structures: A Critical Analysis
Frontiers Media S.A., 2019Co-Authors: Márlon A. Longhi, Zuhua Zhang, Erich D. Rodríguez, Ana Paula Kirchheim, Hao WangAbstract:Even with the rapid development of the alkali-activated cement (AAC) technology in the past few years, some phenomena still needs to be better understood, that may alter the durability of the material. In many industrial uses and laboratory researches the formation of the salts on the surface alkali-activated type cements was observed, which was identified as Efflorescence. This occurs due to the presence of an alkali transported in contact with the humidity and CO2 environment. It may present externally from the formation of salts on the surface and internally with the carbonation of the alkalis in capillary pores. The effects of Efflorescence on the material in use, as well as all factors that can influence its formation are not yet fully understood or reported. The search for papers was conducted using the search words Efflorescence and geopolymer/alkali-activated, combined in the electronic data base. Due to the limited quantity of papers published related to Efflorescence in geopolymers, the review was complemented using papers that discuss this behavior in Portland cement (PC) and based on the main properties that can influence the formation of Efflorescence. In this paper, to understand the nature of Efflorescence, upon which proper methods of minimizing of this issue can be based, the following aspects are discussed and re-examined: (1) the development of Efflorescence's in PC concrete, (2) the role of alkalis in AACs, (3) Efflorescence in AACs, and (4) effect from a physical and microstructural point of view of Efflorescence's on the ACCs. This paper highlights that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control Efflorescence rate and changes in mechanical behavior. However, the stability of the alkalis and their relationship with the formed gel, which are determining factors in the formation of Efflorescence, remain not completely understood. In the same way, the effect of Efflorescence in tensile strength and shrinkage needs to be evaluated
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Efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash based geopolymers
Cement & Concrete Composites, 2018Co-Authors: Zuhua Zhang, John L Provis, Andrew Reid, Hao WangAbstract:This paper reports the effects of Efflorescence on the microstructural and mechanical properties of fly ash-based geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying Efflorescence behaviour. The geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow Efflorescence rate and low Efflorescence potential. The Efflorescence occurring on the surface of the geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended Efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.
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compressive strength development and shrinkage of alkali activated fly ash slag blends associated with Efflorescence
Materials and Structures, 2016Co-Authors: Xiao Yao, Tao Yang, Zuhua ZhangAbstract:This study reports the changes in the compressive strength and shrinkage property of alkali-activated fly ash and slag (AAFS) blends associated with Efflorescence. The AAFS specimens cured in air for different periods were further aged under the following three conditions: bottom-contact with water, fully immersed in water and in air. The second condition, i.e., bottom in contact with water, was used to accelerate Efflorescence of AAFS. The Efflorescence of the AAFS binders was dependent on the reaction extent of the solid precursors. A higher reaction extent present in the binder by extending initial-curing age can reduce Efflorescence rate. The incorporation of low percentage of slag (lower than 50 wt%) in the AAFS binders has little influence on the Efflorescence potential, while with the increased contents of slag higher than 50 %, the binders exhibit more rapid Efflorescence than the 100 % fly ash binders. The Efflorescence led to the strength loss because of the formation of carbonate crystals in the binder and the damage of the microstructure. The linear shrinkage of the binders was also related to Efflorescence and alkali leaching. The slag addition can reduce the negative effects of Efflorescence and alkali leaching on the absolute compressive strength and shrinkage of the binders.
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critical thinking on Efflorescence in alkali activated cement aac
International Conference on Performance-based and Life-cycle Structural Engineering, 2015Co-Authors: Zuhua Zhang, John L Provis, Hao WangAbstract:Alkali-activated cement (AAC), also known as “geopolymer”, has been extensively investigated over the past 40 years and has been developed from laboratory mock ups to real structural usage in construction in the last decade. While numerous life cycle analyses and carbon accounting studies show the “green potential” of this material compared to Portland cement, some authors state that the high alkali concentration in AAC is a potentially unstable factor which may lead to, for example, Efflorescence. This paper presents a critical thinking on the literature and some new experimental work regarding the possibility of Efflorescence in AAC products. Subjects of the discussion include: (1) the role of alkalis in AACs, (2) the effect of alkali concentration on Efflorescence, (3) the effect of solid precursor selection on Efflorescence, (4) the effect of curing scheme and chemical additives on Efflorescence, and (5) the impacts of Efflorescence on the microstructural properties of AACs. Particular attention is given to the relationship between pore structure and Efflorescence behaviour, and consequently the mechanical properties of AACs suffering from either Efflorescence or alkali loss (by leaching). The changes in sodium aluminosilicate hydrate (N-A-S-H) gels due to Efflorescence or alkali loss are critical to the durability of AACs. This paper emphasizes that the nature of the solid precursor and the pore structure of the resulting AAC are the two most important factors that control Efflorescence rate. However, considering its alkaline nature, it seems difficult or impossible to avoid this issue in AAC products, although kinetically controlled diffusion of alkalis using phase transformation techniques may help to mitigate Efflorescence. Efflorescence in AAC is a “skin issue” that needs to be carefully treated. It is recognized to be different from the visually similar, but chemically distinct, Efflorescence that occurs in Portland cement based materials.
Hao Wang - One of the best experts on this subject based on the ideXlab platform.
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phase changes under Efflorescence in alkali activated materials with mixed activators
Construction and Building Materials, 2021Co-Authors: Lakshmikanth Srinivasamurthy, Zuhua Zhang, Venkata S Chevali, Hao WangAbstract:Abstract Efflorescence in alkali-activated materials is a strong function of precursor and activator composition, which dictates their engineering properties and durability. In this study, the Efflorescence of naturally cured NaOH/Na2SiO3 alkali-activated fly ash and alkali-activated fly ash-slag blended binder mixes was assessed with alkali concentration of 9 wt% Na2O, and 10 to 30 wt% of slag, and compared with binder mixes with 9 wt% Na2O, and 10 to 30 wt% of slag along with 2 wt% Na2CO3. The effects of Efflorescence were assessed using visual and leaching inspections, and the compressive and split tensile strengths were determined post activation. Atomic absorption spectrometry was used to quantify free alkalis in the leachate, and X-ray diffraction, and Fourier transform infrared spectroscopy, magic-angle-spinning nuclear magnetic resonance and thermo-gravimetric analysis were performed to analyse the phase changes in binder pastes after Efflorescence. The increased slag content facilitated the formation of C-A-S-H gel and enhanced both chemical and mechanical properties of binder pastes. Furthermore, the inclusion of slag content also led to the reduction of the open porosity and Efflorescence formation. Subsequent exposure of binder specimens to Efflorescence conditions aided the formation of carbonate products, degradation of N-A-S-H and N-(C)-A-S-H gel, and a decrease in split tensile strength in the binder paste specimens.
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Efflorescence of Alkali-Activated Cements (Geopolymers) and the Impacts on Material Structures: A Critical Analysis
Frontiers Media S.A., 2019Co-Authors: Márlon A. Longhi, Zuhua Zhang, Erich D. Rodríguez, Ana Paula Kirchheim, Hao WangAbstract:Even with the rapid development of the alkali-activated cement (AAC) technology in the past few years, some phenomena still needs to be better understood, that may alter the durability of the material. In many industrial uses and laboratory researches the formation of the salts on the surface alkali-activated type cements was observed, which was identified as Efflorescence. This occurs due to the presence of an alkali transported in contact with the humidity and CO2 environment. It may present externally from the formation of salts on the surface and internally with the carbonation of the alkalis in capillary pores. The effects of Efflorescence on the material in use, as well as all factors that can influence its formation are not yet fully understood or reported. The search for papers was conducted using the search words Efflorescence and geopolymer/alkali-activated, combined in the electronic data base. Due to the limited quantity of papers published related to Efflorescence in geopolymers, the review was complemented using papers that discuss this behavior in Portland cement (PC) and based on the main properties that can influence the formation of Efflorescence. In this paper, to understand the nature of Efflorescence, upon which proper methods of minimizing of this issue can be based, the following aspects are discussed and re-examined: (1) the development of Efflorescence's in PC concrete, (2) the role of alkalis in AACs, (3) Efflorescence in AACs, and (4) effect from a physical and microstructural point of view of Efflorescence's on the ACCs. This paper highlights that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control Efflorescence rate and changes in mechanical behavior. However, the stability of the alkalis and their relationship with the formed gel, which are determining factors in the formation of Efflorescence, remain not completely understood. In the same way, the effect of Efflorescence in tensile strength and shrinkage needs to be evaluated
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Efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash based geopolymers
Cement & Concrete Composites, 2018Co-Authors: Zuhua Zhang, John L Provis, Andrew Reid, Hao WangAbstract:This paper reports the effects of Efflorescence on the microstructural and mechanical properties of fly ash-based geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying Efflorescence behaviour. The geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow Efflorescence rate and low Efflorescence potential. The Efflorescence occurring on the surface of the geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended Efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.
-
critical thinking on Efflorescence in alkali activated cement aac
International Conference on Performance-based and Life-cycle Structural Engineering, 2015Co-Authors: Zuhua Zhang, John L Provis, Hao WangAbstract:Alkali-activated cement (AAC), also known as “geopolymer”, has been extensively investigated over the past 40 years and has been developed from laboratory mock ups to real structural usage in construction in the last decade. While numerous life cycle analyses and carbon accounting studies show the “green potential” of this material compared to Portland cement, some authors state that the high alkali concentration in AAC is a potentially unstable factor which may lead to, for example, Efflorescence. This paper presents a critical thinking on the literature and some new experimental work regarding the possibility of Efflorescence in AAC products. Subjects of the discussion include: (1) the role of alkalis in AACs, (2) the effect of alkali concentration on Efflorescence, (3) the effect of solid precursor selection on Efflorescence, (4) the effect of curing scheme and chemical additives on Efflorescence, and (5) the impacts of Efflorescence on the microstructural properties of AACs. Particular attention is given to the relationship between pore structure and Efflorescence behaviour, and consequently the mechanical properties of AACs suffering from either Efflorescence or alkali loss (by leaching). The changes in sodium aluminosilicate hydrate (N-A-S-H) gels due to Efflorescence or alkali loss are critical to the durability of AACs. This paper emphasizes that the nature of the solid precursor and the pore structure of the resulting AAC are the two most important factors that control Efflorescence rate. However, considering its alkaline nature, it seems difficult or impossible to avoid this issue in AAC products, although kinetically controlled diffusion of alkalis using phase transformation techniques may help to mitigate Efflorescence. Efflorescence in AAC is a “skin issue” that needs to be carefully treated. It is recognized to be different from the visually similar, but chemically distinct, Efflorescence that occurs in Portland cement based materials.
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fly ash based geopolymers the relationship between composition pore structure and Efflorescence
Cement and Concrete Research, 2014Co-Authors: Zuhua Zhang, John L Provis, Andrew Reid, Hao WangAbstract:Abstract This study reports the observation of Efflorescence in fly ash-based geopolymers. The Efflorescence rate strongly depends on the activation conditions; at the same alkali content under ambient temperature curing, NaOH-activated geopolymers show less and slower Efflorescence than sodium silicate-activated specimens. Geopolymers synthesised at high temperature exhibit much lower Efflorescence than those synthesised at low temperature, except for the sodium silicate-activated samples. The substitution of 20% fly ash by slag reduces the Efflorescence rate. A relationship between alkali leaching from monosized fractured particles and ‘Efflorescence potential’ is proposed. Soluble silicate and slag addition are beneficial in reducing Efflorescence rate, but have very limited influence on the overall Efflorescence potential, as they appear to have a delaying rather than mitigating effect. The partial crystallisation of geopolymers, by curing at high temperature, appears to be the most effective method of reducing the Efflorescence potential.
Yu Liu - One of the best experts on this subject based on the ideXlab platform.
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effect of nano silica on the Efflorescence of waste based alkali activated inorganic binder
Construction and Building Materials, 2018Co-Authors: Jinbang Wang, Tongtong Zhou, Zonghui Zhou, Ning Xie, Xin Cheng, Yu LiuAbstract:Abstract The Efflorescence caused by carbonate weathering is one of the dominant causes of deterioration of alkali-activated inorganic materials. In order to inhibit the Efflorescence of waste based alkali-activated inorganic binder, the effects of nano -silica on the compressive strength, carbonate ions concentration, hydration rate and pore size distribution of the obtained alkali-activated inorganic binder have been investigated, and the Efflorescence inhibition mechanism has been also analyzed. The results revealed that compressive strength and microstructural properties could be further developed with inclusion of nano-silica in alkali-activated inorganic binder. In addition, the Efflorescence decreased with increasing nano-silica content and decreasing of the nano-silica particle size. Besides, the hydration rate results indicated that the hydration of waste based alkali-activated inorganic binder was accelerated before hydration for 3d with the incorporation of nano-silica. The suggested inhibition mechanisms discussed were mainly; micro-aggregate filling effect, induced nucleation, and accelerated hydration effects of nano-silica.
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effect of zeolite on waste based alkali activated inorganic binder Efflorescence
Construction and Building Materials, 2018Co-Authors: Jinbang Wang, Zonghui Zhou, Ning Xie, Xin Cheng, Yu LiuAbstract:Abstract Alkali-activated inorganic binder has been a research hot spot in the field of building materials owing to its wide range of raw materials, low energy consumption, less pollution and superior performances. The bicarbonate salt weathering is one of prime cause of deterioration of porous materials. To inhibit the Efflorescence of waste based alkali-activated inorganic binder, 5A zeolite powder was blended and the Efflorescence inhibition mechanism was analyzed. Effect of 5A zeolite content on the mechanical properties, bicarbonate ions concentration, pH value and pore size distribution of the obtained alkali-activated inorganic binder were investigated. The results showed that the compressive strength and bending strength of the waste based alkali-activated inorganic binder are improved with adding moderate content of 5A zeolite powder, and the pH value of specimens decreases with increasing amount of 5A zeolite powder content, the average pore size of samples decreases with adding moderate content of 5A zeolite powder due to its micro-aggregate filling effects. The Efflorescence of waste based alkali-activated inorganic binder is effectively reduced with the adding of 5A zeolite powder, and the inhibition mechanisms mainly are that the special ion-exchange properties and micro-aggregate filling effects.
Jinbang Wang - One of the best experts on this subject based on the ideXlab platform.
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effect of nano silica on the Efflorescence of waste based alkali activated inorganic binder
Construction and Building Materials, 2018Co-Authors: Jinbang Wang, Tongtong Zhou, Zonghui Zhou, Ning Xie, Xin Cheng, Yu LiuAbstract:Abstract The Efflorescence caused by carbonate weathering is one of the dominant causes of deterioration of alkali-activated inorganic materials. In order to inhibit the Efflorescence of waste based alkali-activated inorganic binder, the effects of nano -silica on the compressive strength, carbonate ions concentration, hydration rate and pore size distribution of the obtained alkali-activated inorganic binder have been investigated, and the Efflorescence inhibition mechanism has been also analyzed. The results revealed that compressive strength and microstructural properties could be further developed with inclusion of nano-silica in alkali-activated inorganic binder. In addition, the Efflorescence decreased with increasing nano-silica content and decreasing of the nano-silica particle size. Besides, the hydration rate results indicated that the hydration of waste based alkali-activated inorganic binder was accelerated before hydration for 3d with the incorporation of nano-silica. The suggested inhibition mechanisms discussed were mainly; micro-aggregate filling effect, induced nucleation, and accelerated hydration effects of nano-silica.
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effect of zeolite on waste based alkali activated inorganic binder Efflorescence
Construction and Building Materials, 2018Co-Authors: Jinbang Wang, Zonghui Zhou, Ning Xie, Xin Cheng, Yu LiuAbstract:Abstract Alkali-activated inorganic binder has been a research hot spot in the field of building materials owing to its wide range of raw materials, low energy consumption, less pollution and superior performances. The bicarbonate salt weathering is one of prime cause of deterioration of porous materials. To inhibit the Efflorescence of waste based alkali-activated inorganic binder, 5A zeolite powder was blended and the Efflorescence inhibition mechanism was analyzed. Effect of 5A zeolite content on the mechanical properties, bicarbonate ions concentration, pH value and pore size distribution of the obtained alkali-activated inorganic binder were investigated. The results showed that the compressive strength and bending strength of the waste based alkali-activated inorganic binder are improved with adding moderate content of 5A zeolite powder, and the pH value of specimens decreases with increasing amount of 5A zeolite powder content, the average pore size of samples decreases with adding moderate content of 5A zeolite powder due to its micro-aggregate filling effects. The Efflorescence of waste based alkali-activated inorganic binder is effectively reduced with the adding of 5A zeolite powder, and the inhibition mechanisms mainly are that the special ion-exchange properties and micro-aggregate filling effects.
John L Provis - One of the best experts on this subject based on the ideXlab platform.
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Efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash based geopolymers
Cement & Concrete Composites, 2018Co-Authors: Zuhua Zhang, John L Provis, Andrew Reid, Hao WangAbstract:This paper reports the effects of Efflorescence on the microstructural and mechanical properties of fly ash-based geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying Efflorescence behaviour. The geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow Efflorescence rate and low Efflorescence potential. The Efflorescence occurring on the surface of the geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended Efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.
-
critical thinking on Efflorescence in alkali activated cement aac
International Conference on Performance-based and Life-cycle Structural Engineering, 2015Co-Authors: Zuhua Zhang, John L Provis, Hao WangAbstract:Alkali-activated cement (AAC), also known as “geopolymer”, has been extensively investigated over the past 40 years and has been developed from laboratory mock ups to real structural usage in construction in the last decade. While numerous life cycle analyses and carbon accounting studies show the “green potential” of this material compared to Portland cement, some authors state that the high alkali concentration in AAC is a potentially unstable factor which may lead to, for example, Efflorescence. This paper presents a critical thinking on the literature and some new experimental work regarding the possibility of Efflorescence in AAC products. Subjects of the discussion include: (1) the role of alkalis in AACs, (2) the effect of alkali concentration on Efflorescence, (3) the effect of solid precursor selection on Efflorescence, (4) the effect of curing scheme and chemical additives on Efflorescence, and (5) the impacts of Efflorescence on the microstructural properties of AACs. Particular attention is given to the relationship between pore structure and Efflorescence behaviour, and consequently the mechanical properties of AACs suffering from either Efflorescence or alkali loss (by leaching). The changes in sodium aluminosilicate hydrate (N-A-S-H) gels due to Efflorescence or alkali loss are critical to the durability of AACs. This paper emphasizes that the nature of the solid precursor and the pore structure of the resulting AAC are the two most important factors that control Efflorescence rate. However, considering its alkaline nature, it seems difficult or impossible to avoid this issue in AAC products, although kinetically controlled diffusion of alkalis using phase transformation techniques may help to mitigate Efflorescence. Efflorescence in AAC is a “skin issue” that needs to be carefully treated. It is recognized to be different from the visually similar, but chemically distinct, Efflorescence that occurs in Portland cement based materials.
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fly ash based geopolymers the relationship between composition pore structure and Efflorescence
Cement and Concrete Research, 2014Co-Authors: Zuhua Zhang, John L Provis, Andrew Reid, Hao WangAbstract:Abstract This study reports the observation of Efflorescence in fly ash-based geopolymers. The Efflorescence rate strongly depends on the activation conditions; at the same alkali content under ambient temperature curing, NaOH-activated geopolymers show less and slower Efflorescence than sodium silicate-activated specimens. Geopolymers synthesised at high temperature exhibit much lower Efflorescence than those synthesised at low temperature, except for the sodium silicate-activated samples. The substitution of 20% fly ash by slag reduces the Efflorescence rate. A relationship between alkali leaching from monosized fractured particles and ‘Efflorescence potential’ is proposed. Soluble silicate and slag addition are beneficial in reducing Efflorescence rate, but have very limited influence on the overall Efflorescence potential, as they appear to have a delaying rather than mitigating effect. The partial crystallisation of geopolymers, by curing at high temperature, appears to be the most effective method of reducing the Efflorescence potential.
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Efflorescence a critical challenge for geopolymer applications
2013Co-Authors: Zuhua Zhang, Hao Wang, John L Provis, Andrew ReidAbstract:Efflorescence is the formation of white salt deposits on or near the surface of concrete. For ordinary Portland cement (OPC) concrete, Efflorescence is generally harmless except for the discolouration, and is best described as being 'a skin trouble and not a deep-seated disease'. However, for geopolymers, as they contain much higher soluble alkali content than conventional cement, Efflorescence can be a significant issue when the products are exposed to humid air or in contact with water. In this study, the Efflorescence phenomenon of geopolymers that synthesised using different activators, solid materials and curing conditions is observed. The Efflorescence product is mainly sodium carbonate heptahydrate (Na2CO3·7H2O). The Efflorescence potential has been compared via measurements of cation concentrations by atomic absorption spectroscopy (AAS), and determination of pH and electrical conductivity of geopolymer leaching solutions. At the same alkali content (in terms of Na2O), geopolymers synthesised at high temperature (80°C×28 d) exhibit less Efflorescence rate than those synthesised at low temperature (20°C×28 d). NaOH activated geopolymers possess slower Efflorescence than the sodium silicate solution activated specimens. Adding 20% slag can effectively reduce the initial Efflorescence of a fly ash geopolymer. From a long term view, however, the Efflorescence potential of such samples could be equivalent to the activated 100% fly ash when considering the alkali leaching results. Further investigations to prevent Efflorescence, or at least to reduce its rate, are urgently required for wider applications of fly ash-based geopolymers.
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Efflorescence control in geopolymer binders based on natural pozzolan
Cement & Concrete Composites, 2012Co-Authors: Ebrahim Najafi Kani, Ali Allahverdi, John L ProvisAbstract:Abstract This paper addresses methods to reduce Efflorescence in a geopolymer binder based on a pumice-type natural pozzolanic material from Taftan, Iran. Geopolymer pastes samples are analyzed for compressive strength and Efflorescence formation after curing at 95% humidity for 28 days. To reduce the extent of Efflorescence, Al-rich mineral admixtures such as metakaolin, ground granulated blast-furnace slag, and three types of calcium aluminate cements are incorporated into the dry binder at a range of concentrations. Hydrothermal curing at elevated temperatures also shows a positive effect in Efflorescence reduction. Calcium aluminate cements show the greatest effect in Efflorescence reduction, which is attributed to their dissolution in alkaline media releasing high amounts of alumina into the aluminosilicate geopolymer gel. These results confirm that it is possible to develop a more reliable geopolymer binder with improved properties either by adding a suitable amount of active alumina to precursors such as natural pozzolan, or by manipulating the curing conditions to enhance alumina release from less-reactive precursor phases.
