Summary of research on the effect of LiNO3 on alkali-silica reaction in new concrete

This paper summarizes findings from a research study conducted at the University of New Brunswick in collaboration with the University of Texas at Austin, and CANMET-MTL, on the effect of LiNO₃ on ASR in new concrete. The studies included expansion testing, silica dissolution measurements and microstructural examinations of cement systems containing glass and two different reactive aggregates (NB and NS). Only a small proportion of the data are presented here for the purpose of highlighting the principal findings of this investigation.Based on these findings, it is proposed that the inhibiting effect of LiNO₃ against ASR in new concrete is attributed to the formation of two reaction products in the presence of lithium, these being a crystalline lithium silicate compound (Li₂SiO₃) crystal and a Li-bearing, low Ca silica gel. These two phases could serve as a diffusion barrier and protective layer to prevent the reactive silica from further attack by alkalis.It was found that the reason the two reactive aggregates selected responded differently to LiNO₃ was due to the difference in their textural features. The NB aggregate contained reactive volcanic glass particles, the surface of which was immediately and equally available to sodium, potassium and lithium, and thus a Li-Si barrier was able to form quickly. The reactive phase in the NS aggregate was microcrystalline and strained quartz, which was embedded in a dense matrix of a non-reactive predominantly alumino-silicate phase and was not easily accessible to lithium.     

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.     

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.     

New observations on the mechanism of lithium nitrate against alkali silica reaction (ASR)

In the current study, in order to elucidate the mechanisms for the favorable effects of lithium nitrate in controlling alkali silica reaction (ASR), vycor glass disk immersion specimens and glass disk-cement paste sandwich specimens were prepared and examined by XRD, SEM and Laser Ablation Induction Coupled Plasma Mass Spectrometry (LA-ICP-MS). Results showed that when glass disk was immersed in only NaOH solution, the glass was attacked by hydroxyl ions but no solid reaction product was found, thus the presence of calcium was essential for the formation of ASR gel. In the presence of lithium, the glass surface was covered by a thick layer of Li-Si crystal. With the addition of Ca(OH)₂, the glass surface was completely covered by Li-Si crystal and a lithium-bearing low Ca-Na-(K)-Si gel. These two phases either form a dense matrix with Li-Si crystal serving as the framework, and the gel filling in the void space, or the Li-Si crystal serving as the foundation to completely cover the entire reactive SiO₂ surface, and the gel sitting on top of these crystal particles. Hence, the suppressive effects of LiNO₃ were attributed to the formation of a layer of Li-Si crystals intimately at the reactive SiO₂ particle surface and the formation of Li-bearing low-Ca ASR gel products. The Li-bearing low-Ca ASR gels may have a dense and rigid structure, thus having low capacity to absorb moisture from the surrounding paste, and exhibiting a non-swelling property.     

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.     

Mitigation of ASR by the use of LiNO3—Characterization of the reaction products

The influence of the LiNO₃ on the ASR product was studied both in a model system and in mortars. In the model system, the addition of LiNO₃ decreases the dissolution rate and the solubility of silica. Lithium changes the 2-dimensional cross-linked (Q₃ dominated) network of the ASR product into a less structured, Q₂ dominated product, likely by adopting the role of calcium. In the mortar samples the addition of LiNO₃ decreases expansion and significantly influences the chemical composition and the morphology of the reaction product. Lithium decreases the calcium, sodium and potassium content and changes the relatively porous plate-like reaction product into a dense one without texture. The findings in the mortars indicate that the ASR-suppressing effect of lithium is caused by the lower potential of the reaction product to swell. Furthermore, it forms a protective barrier after an initial reaction slowing down ASR.     

Dual effectiveness of lithium salt in controlling both delayed ettringite formation and ASR in concretes

The influence of lithium nitrate on expansions due to delayed ettringite formation (DEF) and alkali-silica reaction (ASR) has been investigated. Effects of the lithium salt were examined in heat-cured mortars and concretes containing one or both damage mechanisms. The mortars and concretes made using reactive and/or non-reactive aggregates were subjected to heat treatment consisting of a hydration delay period of 4 h at 23 °C followed by steam-curing at 95 °C and then stored in limewater. Results showed that the lithium salt admixture was able to reduce the occurrence of deleterious expansion due to delayed ettringite formation in addition to controlling alkali-silica reaction in cementitious systems containing one or both mechanisms. In concretes made using non-reactive limestone aggregates, incorporation of lithium nitrate in a proportion of 0.74 M ratio of Li to (Na + K) was found to control delayed ettringite formation during the one-year period of this study.By analyzing the leaching properties of lithium and other alkalis from mortars during storage, it was found that a substantial amount of lithium was retained in the cementitious system in a slightly soluble form, and is expected to be responsible for reducing DEF.     

The so-called alkali-carbonate reaction (ACR) — Its mineralogical and geochemical details, with special reference to ASR

Typical examples of so-called alkali-carbonate reaction (ACR) in the Canadian field concretes in Ontario, CSA concrete prism, RILEM concrete microbars and RILEM mortar bar containing Pittsburg aggregate, were examined petrographically based on polarizing microscopy, SEM observation and quantitative SEM-EDS analysis of the reaction products. It was revealed that ASR gel was the main product responsible for the crack formation in concretes, and that this gel had a common nature to that in the typical ASR. That is, ASR gel presented distinctive compositional trend lines, passing from low-Ca ASR gel at [Ca/Si] = 1/2-1/6, [Ca]/[Na + K] = 1.0 to the “convergent point” with [Ca/Si] = 1.3-1.8, [Ca]/[Na + K] = 100 at which chemical equilibrium is attained with CSH gel. The so-called ACR is a combination of deleteriously expansive alkali-silica reaction (ASR) of cryptocrystalline quartz, and harmless dedolomitization which produces brucite and carbonate halo. In laboratory specimens, fine dolomitic aggregate undergoes dedolomitization, and brucite and ASR gel react to form non-expansive Mg-silicate gel on the dolomite crystals. This explains why the mortar bar produces smaller expansion than the concrete microbar, and why the reaction products are so minute that they escape attention by optical microscopy. As a crystalline counterpart, mountainite is a candidate for low-Ca ASR gel, while sepiolite is one for Mg-silicate gel. Concealed ASR was detected in ACR-affected field concretes undergoing ingress of deicing salt which formed Friedel's salt and Cl-doped CSH gel. Compositions of ASR products, methods of sample preparation and analysis for correct identification of ACR, and artifacts were critically reviewed.     

A thermodynamic and kinetic model for paste–aggregate interactions and the alkali–silica reaction

A new conceptual model is developed for ASR formation based on geochemical principles tied to aqueous speciation, silica solubility, kinetically controlled mineral dissolution, and diffusion. ASR development is driven largely by pH and silica gradients that establish geochemical microenvironments between paste and aggregate, with gradients the strongest within the aggregate adjacent to the paste boundary (i.e., where ASR initially forms). Super-saturation of magadiite and okenite (crystalline ASR surrogates) occurs in the zone defined by gradients in pH, dissolved silica, Na⁺, and Ca^2 +. This model provides a thermodynamic rather than kinetic explanation of why quartz generally behaves differently from amorphous silica: quartz solubility does not produce sufficiently high concentrations of H₄SiO₄ to super-saturate magadiite, whereas amorphous silica does. The model also explains why pozzolans do not generate ASR: their fine-grained character precludes formation of chemical gradients. Finally, these gradients have interesting implications beyond the development of ASR, creating unique biogeochemical environments.     

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.     

Characteristics of an aqueous rechargeable lithium battery (ARLB)

Electrochemical performance of an aqueous rechargeable lithium battery (ARLB) containing a LiV₃O₈ (negative electrode) and LiCoO₂ (positive electrode) in saturated LiNO₃ aqueous electrolyte was studied. These two electrode materials are stable in the aqueous solution and intercalation/deintercalation of lithium ions occurs within the window of electrochemical stability of water. The obtained capacity of this cell system is about 55 mAh/g based on the mass of the positive electrode, which is lower than the corresponding one in the non-aqueous lithium ion battery. However, its specific capacity can be compared with those of the lead acid and Ni-Cd batteries. In addition, initial results show that this cell system is good in cycling.     

不同结构构造硅质集料的碱硅酸反应模型

正确认识不同结构构造特征集料的碱硅酸反应（ASR）特征，对判定集料碱活性和诊断工程ASR事例以及采取正确预防措施均有重要意义、早期的以单一组分的高活性集料为基础提出的ASR模型只强调集料中活性组分对ASR的作用，仅适用于特定类型的高活性集料，本工作用扫描电镜（SEM）和光学显微镜研究了石英玻璃、沸石化珍珠岩和硅质砾石反尖特征，并综合对慢膨胀型休料ASR研究的文献，提出了结构构造特征不同的硅质活活性集料的ASR基本模型：结构构造特征不同的活性休料其ASR过程及膨胀行为不同；对以无定型SiO2为活性组分的均质高活性集料，反应特征符合传统的ASR模型；对致密、多矿物慢膨胀型集料，除活性组分类型和数量外，活性组分在集料内的分布，即集料的构造特征对ASR的速度和膨胀行为也有重要影响，结构构造特征不同的活性集料其ASR过程及膨胀行为差别的关键在于膨胀的根源和限制条件不同。     

Electrochemical properties of TiP2O7 and LiTi2(PO4)3 as anode material for lithium ion battery with aqueous solution electrolyte

Some polyanionic compounds, e.g. TiP₂O₇ and LiTi₂(PO₄)₃ with 3D framework structure were proposed to be used as anodes of lithium ion battery with aqueous electrolyte. The cyclic voltammetry properties TiP₂O₇ and LiTi₂(PO₄)₃ suggested that Li-ion de/intercalation reaction can occur without serious hydrogen evolution in 5 M LiNO₃ aqueous solution. The TiP₂O₇ and LiTi₂(PO₄)₃ give capacities of about 80 mAh/g between potentials of −0.50 V and 0 V (versus SHE) and 90 mAh/g between −0.65 V and −0.10 V (versus SHE), respectively. A test cell consisting of TiP₂O₇/5 M LiNO₃/LiMn₂O₄ delivers approximately 42 mAh/g (weight of cathode and anode) at average voltage of 1.40 V, and LiTi₂(PO₄)₃/5 M LiNO₃/LiMn₂O₄ delivers approximately 45 mAh/g at average voltage of 1.50 V. Both as-assembled cells suffered from short cycle life. The capacity fading may be related to deterioration of anode material.     

Influence of stress restraint on the expansive behaviour of concrete affected by alkali-silica reaction

The primary objective of this study was to ascertain whether the Threshold Alkali Level (TAL) of the concrete aggregates may be taken as a suitable reactivity parameter for the selection of aggregates susceptible of alkali-silica reaction (ASR), even when ASR expansion in concrete develops under restrained conditions. Concrete mixes made with different alkali contents and two natural siliceous aggregates with very different TALs were tested for their expansivity at 38 °C and 100% RH under unrestrained and restrained conditions. Four compressive stress levels over the range from 0.17 to 3.50 N/mm² were applied by using a new appositely designed experimental equipment. The lowest stress (0.17 N/mm²) was selected in order to estimate the expansive pressure developed by the ASR gel under “free” expansion conditions. It was found that, even under restrained conditions, the threshold alkali level proves to be a suitable reactivity parameter for designing concrete mixes that are not susceptible of deleterious ASR expansion. An empirical relationship between expansive pressure, concrete alkali content and aggregate TAL was developed in view of its possible use for ASR diagnosis and/or safety evaluation of concrete structures.     

Lithium/V6O13 cells using silica nanoparticle-based composite electrolyte

The electrochemical behavior of Li/V₆O₁₃ cells is investigated at room temperature (22 °C) both in liquid electrolyte consisting of oligomeric poly(ethyleneglycol)dimethylether+lithium bis(trifluoromethylsulfonylimide) and composite electrolytes formed by blending the liquid electrolyte with silica nanoparticles (fumed silica). The addition of fumed silica yields a gel-like electrolyte that demonstrates the desirable property of suppressing lithium dendrite growth due to the rigidity and immobility of the electrolyte structure. The lithium/electrolyte interfacial resistance for composite gel electrolytes is less than that for the corresponding base-liquid electrolyte, and the charge-discharge cycle performance and electrochemical efficiency for the Li/V₆O₁₃ cell is significantly improved. The effect of fumed silica surface group on the electrochemical performance is discussed; the native hydrophilic silanol surface group appears better than fumed silica that is modified with a hydrophobic octyl surface moiety.     

Nanosized α-Fe2O3 and Li-Fe composite oxide electrodes for lithium-ion batteries

Nanosized α-Fe₂O₃ (ca. 50 nm) and Li-Fe composite oxides (ca. 29 nm) powders were synthesized via gel polymer route. The gels were obtained with thermal polymerization of acrylic acid solutions of iron and lithium nitrates. The calcination of these gels at temperatures from 300 °C to 500 °C results in α-Fe₂O₃ from Fe(NO₃)₃ precursor and Li-Fe composite oxides Li₂O-Fe₃O₄-LiFeO₂ from a mixed precursors of Fe(NO₃)₃ and LiNO₃. Thermal gravimetric analysis, X-ray diffraction and transmission electron microscopy were used to investigate the precursors and products. The electrochemical performance of the Fe-based oxides was also evaluated. After 200 cycles, their capacity can be as high as 1300 mAh/g for α-Fe₂O₃ and 1400 mAh/g for Li-Fe oxide while the initial capacity loss is as low as 21.8%. The Li-Fe oxide electrodes exhibit better capacity retention than the α-Fe₂O₃ electrodes. They are interesting negative electrodes for high energy density lithium-ion batteries.     

Comparison of structure and electrochemistry of Al- and Fe-doped LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3−xM_xMn_1/3O₂ (M = Fe and Al; x = 0, 1/20, 1/9 and 1/6) have been synthesized by firing the co-precipitates of metal hydroxides. The impacts of Fe and Al doping on the structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ are compared by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge/discharge test as cathode materials for lithium ion batteries. These materials keep the same layered structure as the LiNi_1/3Co_1/3Mn_1/3O₂ host. It is found that Fe- and Al-doped LiNi_1/3Co_1/3Mn_1/3O₂ show different characteristics in lattice parameter and cycling voltage plateau with increasing dopant dose. More interestingly, low Al doping (x < 1/20) improves the structural stability while Fe doping does not have such effect even at low Fe content.     

Improvement of cycle performance of lithium ion cell LiMn2O4/LixV2O5 with aqueous solution electrolyte by polypyrrole coating on anode

The reasons of capacity fading during cycling process of LiMn₂O₄/Li_xV₂O₅ lithium ion cell with 5 M LiNO₃ aqueous solution as electrolyte were investigated. XRD and ICP results showed that the properties of the anode have more impact on the cycle life of the cell. In an attempt to improve the cycle performance of the as-assembled cell, coating with an ionic conductive polypyrrole (PPy) on the surface of the anode was proposed via in situ polymerization method. Cycling tests revealed that the stability of the lithium ion cell with surface coated anode has been greatly improved. Moreover, the capability of the cell with coated anode was also enhanced compared with the cell with bare anode.     

Coupled effects of aggregate size and alkali content on ASR expansion

This work is a part of an overall project aimed at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. First, this paper reports experimental results concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Special attention is paid to the proportions of alkali (Na₂O_eq) in the mixtures and reactive silica in the aggregate. Results show that ASR expansion is seven times larger for coarse particles (1.25-3.15 mm) than for smaller ones (80-160 μm). In mortars for which the two size fractions were used, ASR expansion increased in almost linear proportion to the amount of coarse reactive particles, for two different alkali contents. Then, an empirical model is proposed to study correlations between the measured expansions and parameters such as the size of aggregates and the alkali and reactive silica contents. Starting with the procedure for calibrating the empirical model using the experimental program combined with results from the literature, it is shown that the expansion of a mortar containing different sizes of reactive aggregate can be assessed with acceptable accuracy.     

A novel lithium intercalation compound based on the layered structure of lithium nitridonickelates Li3−2xNixN

New lithium nickel nitrides Li_3−2xNi_xN (0.20 ≤ x ≤ 0.60) have been prepared and investigated as negative electrode in the 0.85/0.02 V potential window. These materials are prepared from a Ni/Li₃N mixture at 700 °C under a nitrogen flow. Their structural characteristics as well as their electrochemical behaviour are investigated as a function of the nickel content. For the first time are reported here the electrochemical properties of a lithium intercalation compound based on a layered nitride structure. The Li_3−2xNi_xN compounds can be reversibly reduced and oxidized around 0.5 V versus Li/Li⁺ leading to specific capacities in the range 120-160 mAh/g depending on the nickel content and the C rate. Due to a large number of lithium vacancies, the structural stability provides an excellent capacity retention of the specific capacity upon cycling.