高温下锂化合物抑制碱硅酸反应的研究

系统研究了高温条件下锂化合物对碱硅酸反应(ASR)的抑制作用.含沸石化珍珠岩活性集料砂浆, 在150 ℃压蒸24 h后, 置于80 ℃养护至20 个月.研究发现:分别掺加n(Li)/ n(Na)为0.6的Li2CO3, LiOH·H2O, Li2SO4·H2O, LiCH3COO·2H2O, LiNO3, LiF能长期有效地抑制ASR膨胀, 且抑制效果依次增强.在碱含量为2.0%时, 掺加相同n(Li)/n(Na)的锂化合物, 其对膨胀的长期抑制效果与溶解度有关.随着锂化合物阴离子表面电荷密度的增加, 其对膨胀的抑制效果依次增强.此外 , 本工作还探讨了锂化合物抑制ASR的作用机理.     

废弃玻璃粉对ASR膨胀抑制作用机理研究

ASR膨胀是制约废弃玻璃在混凝土中运用的关键因素,也是废弃玻璃混凝土研究热点问题.通过ASTMC1260快速砂浆棒法研究废弃玻璃粉对ASR膨胀的抑制效果,对比不同掺量和不同粒径玻璃粉掺入混凝土时试件不同龄期膨胀率,分析玻璃粉掺量与粒径对ASR膨胀抑制的影响;采用扫描电子显微镜(SEM)对砂浆棒微观结构进行对比分析,探究玻璃粉对ASR膨胀抑制的作用机理.结果 表明:掺入玻璃粉对ASR膨胀有一定的抑制效果;玻璃粉掺量越大,对ASR膨胀的抑制效果越好,且持续时间越长;对比0～13 μm、13 ～ 38 μm、38～ 75 μm三组试验发现玻璃粉粒径改变对ASR膨胀影响弱于掺量改变的影响;玻璃粉对ASR膨胀抑制作用与玻璃粉在早期水化过程中更多地参与了火山灰反应有关.     

用溶胶-凝胶膨胀法对锂化合物抑制碱-硅酸反应膨胀机理的研究

利用溶胶-凝胶膨胀法对锂化合物在碱硅酸反应中膨胀的抑制机理进行了研究,对加入锂盐后的碱-硅酸反应产物的膨胀量进行了测定,并借助扫描电镜对试样的微观形貌进行了观察,同时还测定了反应后溶液中SiO2的含量,证实了锂化合物的作用在于：抑制骨料中活性SiO2的溶出;改变凝胶产物的性质,使凝胶的吸水能力和膨胀量变小。     

粉煤灰对ASR的抑制及有效性评估

以中国快速砂浆棒法为基础，分别研究了在40，60，80℃养护条件下低钙粉煤灰对硅质砾石、沸石化珍珠岩和石英玻璃碱硅酸反应(alkali silica rection,ASR）膨胀的抑制作用。讨论了集料碱活性、养护温度对粉煤灰抑制ASR效果的影响和建立粉煤灰及其它矿物外加剂抑制ASR有效性评估方法的技术路线和问题。结果表明：粉煤灰抑制ASR的效果与集科碱活性和养护温度密切相关。一定养护温度下，集科活性越大，抑制效果越差；对特定活性集料，养护温度越高，抑制效果越差。粉煤灰对不同集料和同种集料不同养护温度下ASR膨胀抑制效果差异，主要与ASR历程有关，即与集料ASR本身特性有关。特定集料和养护条件下粉煤灰对ASR膨胀的抑制效果不能简单推广至其它种类不同的集料和养护条件。粉煤灰抑制ASR有效性应根据工程评价目的和要求分别确定。快速评估方法的结果与混凝土长期性能之间的相关性需进一步研究。     

碱含量对粉煤灰抑制ASR效果的影响

采用粉煤友部分等量替代水泥,用砂浆棒快速法和混凝土棱柱体法分别进行了不同掺量的粉煤灰抑制集料ASR的试验研究。结果表明：随着混凝土砂浆中的总碱含量的增加,粉煤灰对集抖ASR膨胀的抑制效果减弱。在同等条件下,用粉煤灰部分取代高碱水泥比取代低碱水泥抑制集料的ASR膨胀更有效。     

集料粒径与ASR膨胀关系及膨胀预测研究进展

综述了集料粒径与碱硅酸反应(ASR)膨胀关系的研究现状,指出了ASR膨胀研究存在的局限性,阐述了大粒径、多级配集料ASR膨胀规律研究的必要性.介绍了几种ASR膨胀机理及ASR膨胀预测模型,并指出基于碱硅酸反应活化能的测定预测ASR膨胀将可能成为今后研究的一个热点.     

混凝土碱硅酸反应膨胀预测模型的研究进展

本文综述了混凝土碱硅酸反应(alkali-silica reaction, ASR)膨胀预测模型的研究现状,ASR对混凝土结构造成的损伤修复难度高,修复成本大,应对这类耐久性问题主要以预防为主,补救为辅,而精确的预测模型可以评估混凝土结构的实时状态,有助于抑制混凝土中的ASR。本文首先概述了混凝土ASR的过程和机理,然后详细介绍了ASR膨胀预测模型的研究现状。ASR建模过程中需要考虑反应物含量、温度、湿度、胶凝材料组成和骨料尺寸等多种因素的影响。ASR模型主要包括理论模型、结构模型(宏观模型)和材料模型(细观模型),理论模型主要用来描述ASR的化学机理和预测骨料的最劣粒径,但该模型只适用于特定类型的骨料;材料模型在材料层面上解释了受ASR影响的混凝土的劣化机理,却忽略了混凝土收缩和徐变等因素的影响;结构模型通常被用来模拟和预测混凝土结构在ASR下的力学行为,但未充分考虑碱硅酸膨胀的化学过程以及离子扩散对ASR膨胀的影响。     

矿物掺合料和锂盐对碱-硅反应的抑制作用

碱-硅反应是混凝土碱集料反应中最易发生的环节,且潜伏期长,一般是1-10年.其一旦发生,就难以抑制,导致混凝土的膨胀和开裂,直至混凝土被破坏.本文综述了碱-硅反应的机理,并介绍了采用粉煤灰等矿物掺合料和锂盐以抑制碱-硅反应的效果.矿物掺合料主要通过减少孔溶液中碱的含量抑制碱-硅反应,锂盐主要通过生成非膨胀性的产物抑制碱...     

燧石粉对ASR膨胀性抑制作用的研究

当存在碱硅酸反应风险时,如何抑制混凝土的膨胀破坏是很重要的.本文探讨将磨细碱活性骨料作为混凝土掺合料,研究其对ASR膨胀性的抑制作用.文中对比燧石粉不同比表面积和不同掺量的胶砂试件,采用快速砂浆棒法测定其在各龄期膨胀率,并结合扫描电子显微镜( SEM)和能谱分析( EDS),研究磨细燧石粉对于ASR (Alkali-Silica Reaction, ASR)膨胀性的影响.结果表明:通过掺加一定比表面积和掺量燧石粉可以有效地抑制胶砂试件因ASR产生的膨胀;SEM和EDS分析显示掺入一定比表面积和适量的燧石粉后,燧石骨料周围碱硅酸凝胶产量减少,说明燧石粉的掺入可以有效减少活性骨料表面发生ASR;同时水化硅酸钙的钙硅比亦有所降低,提升水化硅酸钙的固碱能力,进一步有效抑制ASR.本研究结果能为使用潜在碱活性骨料时,抑制其ASR反应措施提供一定的参考.     

化学外加剂抑制碱硅酸反应原理及进展

概述了化学外加剂抑制碱硅酸反应 (ASR)膨胀的原理及其几十年来国际上的研究进展 ,并讨论了应进一步研究的问题     

Expansion of siliceous and dolomitic aggregates in lithium hydroxide solution

Autoclave expansion behaviors of siliceous and dolomite-bearing aggregates in LiOH and KOH solutions were studied. The results show that lithium hydroxide can suppress ASR expansion and induce ACR expansion. It is the duplex effect of lithium hydroxide that could be used for exploring the mechanism responsible for the expansion of dolomite-bearing aggregates in alkali environments. It has been shown that the expansion of argillaceous dolomite limestone with typical texture from Kingston, Ontario, Canada, can be attributed to ACR rather than to ASR. However, some other argillaceous dolomite limestones exhibit both ACR and ASR. Meanwhile, XRD detected that solid products of dedolomitization in LiOH solution were brucite, calcium carbonate and lithium carbonate with a consequent solid volume increase.     

Effects of lithium salts on ASR gel composition and expansion of mortars

Suppression of alkali-silica reaction (ASR) expansion in mortar and concrete by the addition of lithium salts has been confirmed by some workers. It has been revealed that lithium hydroxide tended to reduce the reaction between sodium or potassium hydroxide and reactive silica, and that the ASR gel incorporating lithium was less expansive. However, it has not been reported how the addition of a lithium salt influenced the composition of the ASR gel. The calcium in ASR gel is considered to play an important role in the expansion of the gel. Thus, it is significant to characterize ASR gel composition in mortars containing lithium salts by BSE-EDS analysis. This study aims to discuss the mechanisms of suppression of ASR expansion in mortar by lithium salts from the viewpoint of ASR gel composition. The average CaO/SiO₂ ratio in ASR gels decreased with increasing amount of added lithium salts. It should be noted that the extent of variations in the CaO/SiO₂ ratio in ASR gels significantly decreased with increasing amount of lithium salts. The addition of relatively small amounts of LiOH and Li₂CO₃ resulted in increased expansion. We also obtained an unexpected result that ASR gels became homogeneous with respect to their CaO contents at high dosage levels. However, the reduction in average CaO/SiO₂ ratios and the homogenization in the CaO content of ASR gels due to the addition of lithium salts may not be related to the expansion of mortars.     

Studies on lithium salts to mitigate ASR-induced expansion in new concrete: a critical review

This paper provides a critical review of the research work conducted so far on the suppressive effects of lithium compounds on expansion due to alkali-silica reaction (ASR) in concrete and on the mechanism or mechanisms by which lithium inhibits the expansion. After a thorough examination of the existing literature regarding lithium salts in controlling ASR expansion, a summary of research findings is provided. It shows that all the lithium salts studied, including LiF, LiCl, LiBr, LiOH, LiOH·H₂O, LiNO₃, LiNO₂, Li₂CO₃, Li₂SO₄, Li₂HPO₄, and Li₂SiO₃, are effective in suppressing ASR expansion in new concrete, provided they are used at the appropriate dosages. Among these compounds, LiNO₃ appears to be the most promising one. Although the mechanism(s) for the suppressive effects of lithium are not well understood, several mechanisms have been proposed. A detailed discussion about these existing mechanisms is provided in the paper. Finally, some recommendations for future studies are identified.     

Alteration of alkali reactive aggregates autoclaved in different alkali solutions and application to alkali-aggregate reaction in concrete (II) expansion and microstructure of concrete microbar

The effect of the type of alkalis on the expansion behavior of concrete microbars containing typical aggregate with alkali-silica reactivity and alkali-carbonate reactivity was studied. The results verified that: (1) at the same molar concentration, sodium has the strongest contribution to expansion due to both ASR and ACR, followed by potassium and lithium; (2) sufficient LiOH can completely suppress expansion due to ASR whereas it can induce expansion due to ACR. It is possible to use the duplex effect of LiOH on ASR and ACR to clarify the ACR contribution when ASR and ACR may coexist. It has been shown that a small amount of dolomite in the fine-grained siliceous Spratt limestone, which has always been used as a reference aggregate for high alkali-silica reactivity, might dedolomitize in alkaline environment and contribute to the expansion. That is to say, Spratt limestone may exhibit both alkali-silica and alkali-carbonate reactivity, although alkali-silica reactivity is predominant. Microstructural study suggested that the mechanism in which lithium controls ASR expansion is mainly due to the favorable formation of lithium-containing less-expansive product around aggregate particles and the protection of the reactive aggregate from further attack by alkalis by the lithium-containing product layer.     

Effects of externally supplied lithium on the suppression of ASR expansion in mortars

Lithium salts are being externally supplied for mitigating the progress of deterioration of ASR-affected concrete structures. However, it is not clear whether the sodium or potassium in the ASR gel in concrete is replaced by the lithium supplied from the outside. In this article, we examine changes in the composition of the ASR gel, previously formed in mortar specimens, after they are immersed in LiOH solution, using backscattered electron (BSE) imaging and energy-dispersive X-ray (EDX) analysis, associated with length change measurement of the mortar prisms. The intrusion of lithium ions into mortar specimens containing a reactive aggregate could arrest their further expansion within a relatively short time after immersion in 0.50 N LiOH solution. The alkali ions incorporated in most ASR gels, located not far away from interfaces between the cement paste and reactive aggregate particles, appear to be replaced by the lithium ions supplied from the solution. However, the ASR gel within the reacted aggregate particles did not appear to have been affected by the lithium ions.     

Examination of the effects of LiOH, LiCl, and LiNO3 on alkali-silica reaction

Lithium additives have been shown to reduce expansion associated with alkali-silica reaction (ASR), but the mechanism(s) by which they act have not been understood. The aim of this research is to assess the effectiveness of three lithium additives—LiOH, LiCl, and LiNO₃—at various dosages, with a broader goal of improving the understanding of the means by which lithium acts. The effect of lithium additives on ASR was assessed using mortar bar expansion testing and quantitative elemental analysis to measure changes in concentrations of solution phase species (Si, Na, Ca, and Li) in filtrates obtained at different times from slurries of silica gel and alkali solution. Results from mortar bar tests indicate that each of the lithium additives tested was effective in reducing expansion below an acceptable limit of 0.05% at 56 days. However, different lithium additive threshold dosages ([Li₂O]/[Na₂O_e]) were required to accomplish this reduction in expansion; these were found to be approximately 0.6 for LiOH, 0.8 for LiNO₃, and 0.9 for LiCl. Quantitative elemental analysis indicated that sodium and lithium were both bound in reaction products formed within the silica gel slurry. It is also believed that lithium may have been preferentially bound over sodium in at least one of the reaction products because a greater percent decrease in dissolved lithium than dissolved sodium was observed within the first 24 h. It appears that lithium additives either decreased silica dissolution, or promoted precipitation of silica-rich products (some of which may be nonexpansive), because the dissolved silica concentration decreased with increasing dosage of lithium nitrate or lithium chloride additive.     

Comparison of alkali-silica reaction products of fly-ash- or lithium-salt-bearing mortar under long-term accelerated curing

The alkali-silica expansion of mortar specimens bearing fly ash (FA), lithium carbonate, and lithium fluoride under long-term accelerated curing was investigated. ASTM C1260 standard test method was applied and expansions were recorded up to 56 days. The composition of alkali-silica reaction (ASR) products was also studied by environmental scanning electron microscopy (ESEM). It was observed that in Li-bearing mixtures, the expansions ceased beyond 28 days. However, in fly-ash-bearing mixtures, the reactions were continued and expansions were increased steadily throughout the test. No clear correlation was found between the composition of massive reaction products and expansion values. However, except for lithium-fluoride-bearing samples, good correlation was observed between the composition of crystallized reaction products and expansion values.     

Laboratory study of LiOH in inhibiting alkali-silica reaction at 20 °C: a contribution

At 20 °C, alkali-aggregate reaction (AAR) expansion of mortar incorporated zeolitization perlite could be long-term effectively inhibited by LiOH and the effect increased with the augment of Li/(Na+K) molar ratio. Mortar strength would decrease when LiOH was added. The more LiOH was added, the more the strength would decrease. In addition, there was more effect on 28 days' strength than 3 days', and the influence degree of LiOH to compressive strength was higher than that to flexural one. The initial and final setting times of cement were shortened when LiOH was added, and the more Li/(Na+K) molar ratio of LiOH was added, the more the setting time was cut down. Not only mortar bar expansion, the change in 20 °C, but also, the evidence of reaction and the composition of reaction products after 4-year curing was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that when both Li⁺ and K⁺ (Na⁺) were added, more Li⁺ reacted to form some matter that not as the same as normal alkali-silica reaction (ASR) gel, especially for its nonexpansive property. Such might be the main reason of the phenomenon that ASR expansion could be inhibited by adding lithium compounds.     

Lithological influence of aggregate in the alkali-carbonate reaction

The reactivity of carbonate rock with the alkali content of cement, commonly called alkali-carbonate reaction (ACR), has been investigated. Alkali-silica reaction (ASR) can also contribute in the alkali-aggregate reaction (AAR) in carbonate rock, mainly due to micro- and crypto-crystalline quartz or clay content in carbonate aggregate. Both ACR and ASR can occur in the same system, as has been also evidenced on this paper.Carbonate aggregate samples were selected using lithological reactivity criteria, taking into account the presence of dedolomitization, partial dolomitization, micro- and crypto-crystalline quartz. Selected rocks include calcitic dolostone with chert (CDX), calcitic dolostone with dedolomitization (CDD), limestone with chert (LX), marly calcitic dolostone with partial dolomitization (CD), high-porosity ferric dolostone with clays (FD). To evaluate the reactivity, aggregates were studied using expansion tests following RILEM AAR-2, AAR-5, a modification using LiOH AAR-5Li was also tested. A complementary study was done using petrographic monitoring with polarised light microscopy on aggregates immersed in NaOH and LiOH solutions after different ages. SEM-EDAX has been used to identify the presence of brucite as a product of dedolomitization. An ACR reaction showed shrinkage of the mortar bars in alkaline solutions explained by induced dedolomitization, while an ASR process typically displayed expansion. Neither shrinkage nor expansion was observed when mortar bars were immersed in solutions of lithium hydroxide.Carbonate aggregate classification with AAR pathology risk has been elaborated based on mechanical behaviours by expansion and shrinkage. It is proposed to be used as a petrographic method for AAR diagnosis to complement the RILEM AAR1 specifically for carbonate aggregate. Aggregate materials can be classified as I (non-reactive), II (potentially reactive), and III (probably reactive), considering induced dedolomitization ACR (dedolomitization degree) and ASR.