The influence of anti-freezing admixture on the alkali aggregate reaction in mortar was analyzed with accelerated methods. It is confirmed that the addition of sodium salt ingredients of anti-freezing admixture accele...The influence of anti-freezing admixture on the alkali aggregate reaction in mortar was analyzed with accelerated methods. It is confirmed that the addition of sodium salt ingredients of anti-freezing admixture accelerates the alkali silica reaction to some extent, whereas calcium salt ingredient of anti-freezing admixture reduces the expansion of alkali silica reaction caused by high alkali cement. It is found that the addition of the fly ash considerably suppresses the expansion of alkali silica reaction induced by the anti-freezing admixtures.展开更多
A comparative study of amorphous and crystalline forms of commercial aluminum hydroxides as inhibitors of alkalisilica reactions in Portland cement mortars has been performed. It was found that at dosages of 1% to 3%,...A comparative study of amorphous and crystalline forms of commercial aluminum hydroxides as inhibitors of alkalisilica reactions in Portland cement mortars has been performed. It was found that at dosages of 1% to 3%, amorphous aluminum hydroxide can efficiently inhibit alkali-silica expansion of Portland cement compositions. High inhibiting activity of amorphous Al(OH)3 additives may be explained by their ability to actively bind Ca(OH)2 formed by the hydration of silicate phases of cement, to form ettringite (with participation of gypsum). Crystalline Al(OH)3 additives that do not possess the ability to interact with Ca(OH)2 even after additional grinding, however, demonstrate week properties to inhibit alkali-silica expansion. This may indicate that the inhibitory effect of Al(OH)3 at least—partly, may be given by its influence on the concentration of Al3+ ions in the pore solution. Some expansion of the samples with admixtures of Al(OH)3 observed during the alkaline expansion accelerated test procedure is not associated with the formation of ettringite and is only due to alkali-silicate reactions.展开更多
Study of sulfate resistance of mortars with aluminum- and iron-bearing admixtures (Al(OH)3, Al2(SO4)3, FeSO4, Fe2(SO4)3) in conditions close to those established in ASTM C 1012, and the study of the mitigation effect ...Study of sulfate resistance of mortars with aluminum- and iron-bearing admixtures (Al(OH)3, Al2(SO4)3, FeSO4, Fe2(SO4)3) in conditions close to those established in ASTM C 1012, and the study of the mitigation effect of these admixtures on alkali-silica reaction in accordance with accelerated “mortar bar” test ( GOST 8269.0, ASTM C 1260) were performed. Iron (II) and (III) sulfates show ability for mitigation alkali-silica reaction, while also, in contrast with Al-bearing substances, do not induce the drastic reducing of the initial setting time and do not promote the progress of sulfate corrosion. Compared with FeSO4, iron (III) sulfate has moderate deleterious impact on the early strength of cement paste and can be of interest alone as an inhibitor of ASR. Iron (II) sulfate may be used together with aluminum sulfate to offset the accelerating effect of the latter on the setting of cement paste and to reduce a risk of sulfate corrosion. During prolonged water storage, the mortar elongation and secondary ettringite formation do not occur, even when Al2(SO4)3 is available. Therefore, the investigated admixtures cannot act as agents of internal sulfate attack, however, Al2(SO4)3 can enhance the outer sulfate attack.展开更多
The effect of the composite of natural zeolite and fly ash on alkali-silica reaction (ASR) was studied with natural alkali-reactive aggregate and quartz glass aggregate respectively.The expansive experiment of mortar ...The effect of the composite of natural zeolite and fly ash on alkali-silica reaction (ASR) was studied with natural alkali-reactive aggregate and quartz glass aggregate respectively.The expansive experiment of mortar bar and concrete prism was completed.The results show that ASR can be suppressed effectively by the composite of natural zeolite and fly ash.展开更多
The influence of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃ is studied. The results show that silica, slag and fly ash may inhibit alkali-silica reaction only under suitable c...The influence of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃ is studied. The results show that silica, slag and fly ash may inhibit alkali-silica reaction only under suitable content. When the content is less than 10%, silica fume does not markedly influence the expansion of alkali- silica reaction. When the content is 15%-20%, silica fume only may delay the expansion of alkali-silica reaction. When the content is 30%-70%, slag may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is 10%, fly ash does not markedly influence the expansion of alkali-silica reaction. When the content is 20%-30%, fly ash may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is over 50%, it is possible that fly ash can inhibit effectively alkali-silica reaction.展开更多
The effect of fly ash on controlling alkail-silica rection （ASR） in simudated alkali solution was studied. The expausion of mortar bars and the content of Ca（ OH）2 in cement paste cured at 80 °G for 91 d were...The effect of fly ash on controlling alkail-silica rection （ASR） in simudated alkali solution was studied. The expausion of mortar bars and the content of Ca（ OH）2 in cement paste cured at 80 °G for 91 d were measured. Traasmission electron microscopy （TEM） and high-resolution transmission electron microscot9 （HRTEM） were employed to study the microstructure of C-S-H. TEM/ energy dispersive spectroscopy （EDS） leas then used to determine the composition of C-S-H. The pore structure of the paste was analyzed by mercury intntsion porosimetry （MIP）. The results show that the contents of fly ash of 30% and 45% can well inhibit ASR. And the content of Ca（OH） 2 decreases with the increase of fly ash. That fly ash reacted with Ca（OH）2 to produce C-S-H with a low Ca/Si molar ratio could bind more Na^＋ and K^＋ ious, and produce a reduction in the amount of soluble alkali available for ASR. At the same time, the C- S- H produced by pozzolanic reaction converted large pores to snudler ones （ gel pores smaller than 10 nm ） to deusify the pore structure. Perhaps that could inhibit alkali trausport to aggregate for ASR.展开更多
On the base of the influence rule of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃, the mechanism of the effect of mineral admixtures on alkali-silica reaction is studied further...On the base of the influence rule of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃, the mechanism of the effect of mineral admixtures on alkali-silica reaction is studied further in the paper. The results show that the effects of mineral admixtures on alkali-silica reaction are mainly chemistry effect and surface physichemistry effect. Under suitable condition, the chemistry effect may make alkali-silica reaction to be inhibited effectively, but the physichemistry effect only make alkali-silica reaction to be delayed. The chemistry effect and the physichemistry effect of minerals admixture are relative to the content of Ca（OH）2 in system. Under the condition that there is a large quantity of Ca（OH）2, mineral admixture cannot inhibit alkali-silica reaction effectively. Only when Ca（OH）2 in the system is very less, it is possible that mineral admixture inhibits alkali-silica reaction effectively.展开更多
Calcined clay pozzolan has been used to replace varying portions of high alkali Portland limestone cement in order to study its effect on the alkali-silica reaction (ASR). Portland limestone cement used for the study ...Calcined clay pozzolan has been used to replace varying portions of high alkali Portland limestone cement in order to study its effect on the alkali-silica reaction (ASR). Portland limestone cement used for the study had a total Na2Oeq of 4.32. Mortar-bar expansion decreased as pozzolan content in the cement increased. The highest expansion was recorded for reference bars with no pozzolan, reaching a maximum of 0.35% at 42 days whilst the expansion was reduced by between 42.5% and 107.8% at 14 days and between 9.4% and 16.4% at 84 days with increasing calcined clay pozzolan content. Mortar bars with 25% pozzolan were the least expansive recording expansion less than 0.1% at all test ages. X-ray diffractometry of the hydrated blended cement paste powders showed the formation of stable calcium silicates in increasing quantities whilst the presence of expansive alkali-silica gel, responsible for ASR expansion, decreased as pozzolan content increased. The study confirms that calcined clay pozzolan has an influence on ASR in mortar bars and causes a significant reduction in expansion at a replacement level of 25%.展开更多
A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance ...A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance to the GOST 8269.0 specification. Solid-state 29Si-MAS NMR spectroscopy and thermogravimetric analysis were used to describe Portland cement hydration, supplementary cementitious material pozzolanic reaction and to establish a structure of products of those processes. It was found that long-term test conditions, in contrast to the accelerated test, do not affect the composition of products formed too much, compared to normal conditions. This allows results obtained with long-term test to be expected as more relevant in terms of predicting of supplementary cementitious materials inhibiting properties.展开更多
An ability of aluminum-bearing substances-amorphous aluminum hydroxide, aluminum sulphate and basic aluminum sulphate to mitigate alkali-silica reactions in Portland cement mortars has been studied. At equivalent dosa...An ability of aluminum-bearing substances-amorphous aluminum hydroxide, aluminum sulphate and basic aluminum sulphate to mitigate alkali-silica reactions in Portland cement mortars has been studied. At equivalent dosages in terms of Al2O3, these substances are ranged in the following order in respect of inhibiting effect: Al(OH)1.78(SO4)0.61 ≥ Al2(SO4)3 > Al(OH)3. It is found that the plasticizing agents of the main types used in cement compositions have no influence on the inhibiting effect of aluminum-bearing admixtures. To control the setting time of cement paste, iron(II) sulphate may be used for partial substitution of Al2SO4·18H2O, and this operation is not influence on the results of ASR expansion test.展开更多
文摘The influence of anti-freezing admixture on the alkali aggregate reaction in mortar was analyzed with accelerated methods. It is confirmed that the addition of sodium salt ingredients of anti-freezing admixture accelerates the alkali silica reaction to some extent, whereas calcium salt ingredient of anti-freezing admixture reduces the expansion of alkali silica reaction caused by high alkali cement. It is found that the addition of the fly ash considerably suppresses the expansion of alkali silica reaction induced by the anti-freezing admixtures.
文摘A comparative study of amorphous and crystalline forms of commercial aluminum hydroxides as inhibitors of alkalisilica reactions in Portland cement mortars has been performed. It was found that at dosages of 1% to 3%, amorphous aluminum hydroxide can efficiently inhibit alkali-silica expansion of Portland cement compositions. High inhibiting activity of amorphous Al(OH)3 additives may be explained by their ability to actively bind Ca(OH)2 formed by the hydration of silicate phases of cement, to form ettringite (with participation of gypsum). Crystalline Al(OH)3 additives that do not possess the ability to interact with Ca(OH)2 even after additional grinding, however, demonstrate week properties to inhibit alkali-silica expansion. This may indicate that the inhibitory effect of Al(OH)3 at least—partly, may be given by its influence on the concentration of Al3+ ions in the pore solution. Some expansion of the samples with admixtures of Al(OH)3 observed during the alkaline expansion accelerated test procedure is not associated with the formation of ettringite and is only due to alkali-silicate reactions.
文摘Study of sulfate resistance of mortars with aluminum- and iron-bearing admixtures (Al(OH)3, Al2(SO4)3, FeSO4, Fe2(SO4)3) in conditions close to those established in ASTM C 1012, and the study of the mitigation effect of these admixtures on alkali-silica reaction in accordance with accelerated “mortar bar” test ( GOST 8269.0, ASTM C 1260) were performed. Iron (II) and (III) sulfates show ability for mitigation alkali-silica reaction, while also, in contrast with Al-bearing substances, do not induce the drastic reducing of the initial setting time and do not promote the progress of sulfate corrosion. Compared with FeSO4, iron (III) sulfate has moderate deleterious impact on the early strength of cement paste and can be of interest alone as an inhibitor of ASR. Iron (II) sulfate may be used together with aluminum sulfate to offset the accelerating effect of the latter on the setting of cement paste and to reduce a risk of sulfate corrosion. During prolonged water storage, the mortar elongation and secondary ettringite formation do not occur, even when Al2(SO4)3 is available. Therefore, the investigated admixtures cannot act as agents of internal sulfate attack, however, Al2(SO4)3 can enhance the outer sulfate attack.
文摘The effect of the composite of natural zeolite and fly ash on alkali-silica reaction (ASR) was studied with natural alkali-reactive aggregate and quartz glass aggregate respectively.The expansive experiment of mortar bar and concrete prism was completed.The results show that ASR can be suppressed effectively by the composite of natural zeolite and fly ash.
文摘The influence of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃ is studied. The results show that silica, slag and fly ash may inhibit alkali-silica reaction only under suitable content. When the content is less than 10%, silica fume does not markedly influence the expansion of alkali- silica reaction. When the content is 15%-20%, silica fume only may delay the expansion of alkali-silica reaction. When the content is 30%-70%, slag may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is 10%, fly ash does not markedly influence the expansion of alkali-silica reaction. When the content is 20%-30%, fly ash may only delay the expansion of alkali-silica reaction, but cannot inhibit the expansion of alkali-silica reaction. When the content is over 50%, it is possible that fly ash can inhibit effectively alkali-silica reaction.
基金Founded bythe National Basic Research Programof China"973"(No.2001CB610706)
文摘The effect of fly ash on controlling alkail-silica rection （ASR） in simudated alkali solution was studied. The expausion of mortar bars and the content of Ca（ OH）2 in cement paste cured at 80 °G for 91 d were measured. Traasmission electron microscopy （TEM） and high-resolution transmission electron microscot9 （HRTEM） were employed to study the microstructure of C-S-H. TEM/ energy dispersive spectroscopy （EDS） leas then used to determine the composition of C-S-H. The pore structure of the paste was analyzed by mercury intntsion porosimetry （MIP）. The results show that the contents of fly ash of 30% and 45% can well inhibit ASR. And the content of Ca（OH） 2 decreases with the increase of fly ash. That fly ash reacted with Ca（OH）2 to produce C-S-H with a low Ca/Si molar ratio could bind more Na^＋ and K^＋ ious, and produce a reduction in the amount of soluble alkali available for ASR. At the same time, the C- S- H produced by pozzolanic reaction converted large pores to snudler ones （ gel pores smaller than 10 nm ） to deusify the pore structure. Perhaps that could inhibit alkali trausport to aggregate for ASR.
文摘On the base of the influence rule of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 ℃, the mechanism of the effect of mineral admixtures on alkali-silica reaction is studied further in the paper. The results show that the effects of mineral admixtures on alkali-silica reaction are mainly chemistry effect and surface physichemistry effect. Under suitable condition, the chemistry effect may make alkali-silica reaction to be inhibited effectively, but the physichemistry effect only make alkali-silica reaction to be delayed. The chemistry effect and the physichemistry effect of minerals admixture are relative to the content of Ca（OH）2 in system. Under the condition that there is a large quantity of Ca（OH）2, mineral admixture cannot inhibit alkali-silica reaction effectively. Only when Ca（OH）2 in the system is very less, it is possible that mineral admixture inhibits alkali-silica reaction effectively.
文摘Calcined clay pozzolan has been used to replace varying portions of high alkali Portland limestone cement in order to study its effect on the alkali-silica reaction (ASR). Portland limestone cement used for the study had a total Na2Oeq of 4.32. Mortar-bar expansion decreased as pozzolan content in the cement increased. The highest expansion was recorded for reference bars with no pozzolan, reaching a maximum of 0.35% at 42 days whilst the expansion was reduced by between 42.5% and 107.8% at 14 days and between 9.4% and 16.4% at 84 days with increasing calcined clay pozzolan content. Mortar bars with 25% pozzolan were the least expansive recording expansion less than 0.1% at all test ages. X-ray diffractometry of the hydrated blended cement paste powders showed the formation of stable calcium silicates in increasing quantities whilst the presence of expansive alkali-silica gel, responsible for ASR expansion, decreased as pozzolan content increased. The study confirms that calcined clay pozzolan has an influence on ASR in mortar bars and causes a significant reduction in expansion at a replacement level of 25%.
文摘A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance to the GOST 8269.0 specification. Solid-state 29Si-MAS NMR spectroscopy and thermogravimetric analysis were used to describe Portland cement hydration, supplementary cementitious material pozzolanic reaction and to establish a structure of products of those processes. It was found that long-term test conditions, in contrast to the accelerated test, do not affect the composition of products formed too much, compared to normal conditions. This allows results obtained with long-term test to be expected as more relevant in terms of predicting of supplementary cementitious materials inhibiting properties.
文摘An ability of aluminum-bearing substances-amorphous aluminum hydroxide, aluminum sulphate and basic aluminum sulphate to mitigate alkali-silica reactions in Portland cement mortars has been studied. At equivalent dosages in terms of Al2O3, these substances are ranged in the following order in respect of inhibiting effect: Al(OH)1.78(SO4)0.61 ≥ Al2(SO4)3 > Al(OH)3. It is found that the plasticizing agents of the main types used in cement compositions have no influence on the inhibiting effect of aluminum-bearing admixtures. To control the setting time of cement paste, iron(II) sulphate may be used for partial substitution of Al2SO4·18H2O, and this operation is not influence on the results of ASR expansion test.
