Alkali-aggregate Reaction Research Articles

Study on Durability of Concrete under Alkali-Aggregate Reaction

The alkali-aggregate reaction has always had a great impact on the safety and durability of concrete projects. Therefore, the study of concrete failure mechanism under alkali-aggregate reaction has become a hot topic in the engineering field. This paper takes the Longtanqing debris flow ditch concrete treatment project as the background. Based on the alkali-aggregate reaction inhibition test under different conditions, regression analysis and trend surface analysis were used to study the correlation between fly ash content, expansion rate of concrete specimens, and curing age. And the engineering measures are put forward to effectively inhibit the alkali-aggregate reaction: (1) the optimum amount of fly ash appears at 30%-40%, fly ash has the strongest ability to inhibit alkali-aggregate reaction; when the content of fly ash is less than 20%, the fly ash ability to inhibit alkali aggregate reaction is weak. (2) To lower the height of the alkali content of concrete, there is 35% of the grade I class F coal ash as concrete admixture.

STUDY ON SOME DURABILITY PROPERTIES OF HIGH-STRENGTH FINE-GRAINED CONCRETE USING SALINE SAND AND CRUSHED AGGREGATE

This paper presents the results of research on some durability properties of high-strength fine-grained concrete made from saline sand and crushed aggregates with different mixing ratios. The specific mechanical properties and durability of concrete when working in a saline environment were tested, including compressive strength, water absorption, sulfate durability, and the alkali-aggregate reaction of concrete. The results show that: when replacing regular aggregate in C50 concrete with a mixture of salted sand and crushed aggregate with an appropriate mixing ratio, the concrete has a compressive strength of over 50 MPa, and water absorption reduces significantly. The sulfate and alkali-aggregate reaction are guaranteed to meet the requirements set forth by the standards for sulfate and alkali-resistant durability concrete. This result has great significance in the study and application of high-strength fine-grained concrete made from saline sand to build the constructions in marine and island environments.

Impact of fly ash production and sourcing changes on chemical and physical aspects of concrete durability

Changes in coal-fired power technology have recently been introduced, influencing emissions and efficiency, which may affect fly ash. Similarly, shortages of low lime fly ash, with power stations being taken out of service, mean recovery/processing of material from wet holding areas (e.g. stockpiles) is receiving attention. Previous research has considered the effect of these fly ashes on chloride ingress and carbonation of concrete. In the current study, chemical (sulfate attack and alkali-aggregate reaction (AAR)) and physical (freeze–thaw (salt) scaling and abrasion) processes causing concrete deterioration are investigated. These used laboratory tests and practical concrete mixes, with comparisons made against three reference fly ashes of different fineness, and data from earlier studies (late 1990 s/early 2000 s). The results indicate minor differences between fly ash concretes for sulfate attack and AAR, where small expansions were obtained. Although specific fly ash influences were not identifiable, air-entrained concretes gave acceptable freeze–thaw scaling performance (0.45 water/cement ratio), while abrasion generally followed concrete strength. Similar effects were found to the earlier studies. The changing technologies and wet storage may influence fly ash characteristics, however, they generally follow typical behaviour for the concrete properties examined and suggest continued suitability for use.

Mesoscale Modeling Study on Mechanical Deterioration of Alkali-Aggregate Reaction-Affected Concrete.

The alkali–aggregate reaction (AAR) is a harmful chemical reaction that reduces the mechanical properties and weakens the durability of concrete. Different types of activated aggregates may result in various AAR modes, which affect the mechanical deterioration of concrete. In this paper, the aggregate expansion model and the gel pocket model are considered to represent the two well-recognized AAR modes. The mesoscale particle model of concrete was presented to model the AAR expansion process and the splitting tensile behavior of AAR-affected concrete. The numerical results show that different AAR modes have a great influence on the development of AAR in terms of expansion and microcracks and the deterioration of concrete specimens. The AAR mode of the gel pocket model causes slight expansion, but generates microcracks in the concrete at the early stage of AAR. This means there is difficulty in achieving early warning and timely maintenance of AAR-affected concrete structures based on the monitoring expansion. Compared with the aggregate expansion model, more severe cracking can be observed, and a greater loss of tensile strength is achieved at the same AAR expansion in the gel pocket model. AAR modes determine the subsequent reaction process and deterioration, and thus, it is necessary to develop effective detection methods and standards for large concrete projects according to different reactive aggregates.

Durability of Repairs under Freezing and Thawing and Alkali-Aggregate Reaction

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Mechanical, Physico-Chemical and Morphological Characterization of Energy Optimised Furnace (EOF) Steel Slag as Coarse Aggregate in Concrete.

This research tests energy optimised furnace (EOF) steel slag as substitution for natural coarse aggregate in concrete. Steel slag’s usefulness as a substitute for natural coarse aggregate in concrete is the primary goal of this research. According to IS:2386-1963, the characterization of EOF steel slag, as coarse, is done by examining the shape and size of a particle, mechanical properties, physical properties, soundness, and alkali-aggregate reactivity. Tests for detection of staining material in steel slag and hardness of inter-facial transition zone in hardened cement paste were also carried out. The chemical analysis of the steel slag reveals the stability of oxides present in the steel slag. Microstructural characterization by SEM (scanning electron microscope) analysis of steel slag aggregate was also employed to support the characterization and XRD analysis, and it was found that the EOF steel slag is crystalline. The digital image processing technique (DIP) is adopted to study the shape indices, circularity, sphericity, shape factor, and roundness of natural and EOF steel slag aggregate. According to the characterization and strength investigation, steel slag aggregate outperforms natural coarse aggregate.

Monitoring the structural effects of internal swelling reactions in Aguieira bridges

São João das Areias Bridge and Criz II Bridge, located in the reservoir of Aguieira dam, in the centre of Portugal, were affected by internal swelling reactions of concrete, which particularly affected their piers and foundations. Laboratory tests diagnosed both alkali–aggregate reaction and delayed ettringite formation as the causes of the expansions. This situation motivated important rehabilitation works on the piers and foundations of both bridges. These rehabilitation works were based on the construction of six piles around the footing of every pier founded on the riverbed. The corresponding pile cap was connected to the immersed part of the pier. In the course of these works, a structural health monitoring system was installed on both bridges in order to characterise the structural effects of the swelling reactions, both in the loss of rigidity and the temporal evolution of this degradation. The instrumentation applied on the bridges is described in this paper and the preliminary results achieved are presented.

Finite-element modelling of alkali–aggregate reaction in a concrete hydraulic structure

Alkali–aggregate reaction (AAR) in concrete has been found to cause serious concerns for the operation and integrity of many mass and reinforced concrete structures, hydraulic structures (dams, powerhouses, etc.) and any other concrete structure that is exposed to moisture. It is known that the kinetics of AAR is strongly driven by temperature and moisture, among other parameters, and the induced strain is assumed to be oriented according to the stress state. Due to complexity of the AAR and its multi-physical nature, the use of chemomechanical modelling is very helpful for making predictions in terms of displacements and concrete damage. Moreover, macro-modelling approaches are frequently preferred for engineering work in real structures. In this context, this paper presents the implementation of a chemomechanical model of AAR for concrete using Abaqus/Explicit modelling software. With this approach, the effects of AAR are introduced by way of the Vuexpan user subroutine jointly with the concrete damage plasticity model of Abaqus. Verification of the proposed model was carried out at the material level. Moreover, a case study of a real hydraulic structure affected by AAR located in North America is presented.

Seismic performance evaluation of AAR-affected concrete gravity dams under main aftershock sequence

Once the alkali-aggregate reaction (AAR) of the concrete dam occurs, the mechanical properties of the dam concrete will be degraded with the increase in the operating years. Besides, a large number of strong earthquake cases show that aftershocks usually occur after the main shock, and the evaluation of the seismic performance of concrete dams under the main aftershock has become the focus of research. This study establishes the overall damage mechanics model of the dam body and foundation. Degradation of concrete properties due to AAR and the influence of main shock and aftershock are considered to calculate the response of the dam-water and foundation coupled system at different ages. The overall seismic damage evaluation model of the dam is established to evaluate the seismic performance of the AAR-affected concrete dam with different operating years. The research results show that the damage of the dam is greatly affected when the AAR-affected of the dam concrete is considered under the action of earthquake. The overall damage index of the dam increases significantly with the increase in the dam's operating years. Within the period of 20 < T < 60, the growth rate of the damage index is the largest and aftershocks have different effects on the secondary damage caused by dams under different operating years. When the dam damage is light after the main shock, the secondary damage caused by the aftershocks on the dam is relatively minor. With the increase of dam operating years, the concrete strength decreases gradually while the secondary damage caused by aftershocks increases.

Lotus-Leaf-Inspired Biomimetic Coatings: Different Types, Key Properties, and Applications in Infrastructures

A universal infrastructural issue is wetting of surfaces; millions of dollars are invested annually for rehabilitation and maintenance of infrastructures including roadways and buildings to fix the damages caused by moisture and frost. The biomimicry of the lotus leaf can provide superhydrophobic surfaces that can repel water droplets, thus reducing the penetration of moisture, which is linked with many deterioration mechanisms in infrastructures, such as steel corrosion, sulfate attack, alkali-aggregate reactions, and freezing and thawing. In cold-region countries, the extent of frost damage due to freezing of moisture in many components of infrastructures will be decreased significantly if water penetration can be minimized. Consequently, it will greatly reduce the maintenance and rehabilitation costs of infrastructures. The present study was conducted to explore any attempted biomimicry of the lotus leaf to produce biomimetic coatings. It focuses on anti-wetting characteristics (e.g., superhydrophobicity, sliding angle, contact angle), self-cleaning capability, durability, and some special properties (e.g., light absorbance and transmission, anti-icing capacity, anti-fouling ability) of lotus-leaf-inspired biomimetic coatings. This study also highlights the potential applications of such coatings, particularly in infrastructures. The most abundant research across coating materials showed superhydrophobicity as being well-tested while self-cleaning capacity and durability remain among the properties that require further research with existing promise. In addition, the special properties of many coating materials should be validated before practical applications.

Influence of coarse aggregate size on deterioration of concrete affected by alkali-aggregate reaction

The alkali-aggregate reaction (AAR) is one of the main factors to reduce the durability of concrete structures. Dam concrete contains very large aggregates, and the influence of coarse aggregate size on AAR-induced deterioration requires a deep understanding. In this paper, a mesoscale particle model of concrete was presented to simulate the AAR process and mechanical testing of AAR-affected concrete. Four types of concrete with different sizes of coarse aggregates were considered. The experimental AAR expansion of dam concrete containing aggregates up to 150 mm was used to validate the mesoscale model. The numerical simulation results show that the coarse aggregate size significantly affects the AAR expansion and the degradation of mechanical properties. Dam concrete with 150 mm aggregates exhibits smaller expansion but earlier cracks than general concrete with small coarse aggregates. The mechanical properties in terms of elastic modulus, compressive strength and splitting tensile strength are reduced more in concrete with larger aggregates at the same AAR expansion. These phenomena illustrate that it is not appropriate to assess the AAR-induced deterioration of the mechanical properties of dam concrete using an index based on concrete with 5 ∼ 20 mm aggregates.

A case study for exploring the alkali-aggregate reactivity of Cyprus aggregates

Concrete is the most commonly used construction material in Cyprus Island as it is all around the world. Even though thousands of tons of concrete are manufactured in both North and South Cyprus, the alkali-aggregate reactivity (AAR) of the crushed (quarried) aggregates has not been previously investigated in a systematic way. The lack of information on the AAR likelihood of Cyprus aggregates in the related literature has caused a lack of awareness about this durability problem in the island and hence, sufficient controls for taking necessary levels of precautions could not be made over the past decades. Two aggregate samples from North Cyprus and another type of aggregates from South Cyprus were obtained from active quarries and tested within this case study for the first time with RILEM tests in order to verify the likelihood of both alkali-silica and alkali-carbonate reactivities of Cyprus Aggregates. The results obtained from RILEM tests and the supplementary SEM analysis showed that both the North (limestone) and South (diabase) Cyprus aggregates exhibit significant levels of alkali-silica reactivity when they are used with composite cement, which is commonly preferred for its advantages. Results also indicated that the mortar batch including the second type of North Cyprus aggregates (dolomitic limestone) with the mentioned cement is potentially reactive for alkali-carbonate reaction as well. The experimental information provided for the first time with this case study is critical both for further Cyprus durability research studies to be carried out and also for improving the quality of local construction activities.

Alkali-silica reactions in granite-based aggregates: The role of biotite and pyrite

Concrete structures built in granite-based aggregate develop and proliferate contour-like cracks as they aged. Such cracks are often associated to alkali-aggregate reactions (AAR). Though, in most cases, the alkali-silica reaction (ASR) involving these aggregates has shown to be non-destructive to concretes, their contents of iron-contained minerals, including biotite and pyrite predict novel chemical route for AAR. This study aims to investigate the alkali reactivity of granite-based aggregates, and the rule of biotite and pyrite as potential contributors to AAR. Aggregate samples were collected from three different deposits in tropical Africa, denoted: Deposit I, Deposit II and Deposit III. Mineralogical and microstructural characteristics of the aggregates, by XRD, optical microscopy and ESEM-EDX, indicated micaceous, felspathic, garnet and sulphide mineral groups. XRF shows quite significant levels of FeO + Fe2O3, ranging from 6.38 wt% to 9.86 wt%. Optical microscopy and ESEM analysis of NaOH-leached residues showed quite elevated fractions of Fe Sulphur was quantified in the leached residues of most corroded aggregate samples from deposit III, pointing to the dissociation of pyrite. The absence of S and the presence of ample amounts of Fe in the less degraded aggregates leached residues of deposits I and II points to the release of Fe by other iron containing minerals, including biotite. Findings of this study is a reference point for the development of control and mitigation of AAR involving pyrite and biotite – rich aggregates.

Exploration of Waterproofness of Concrete and Alkali-Aggregate Using Hydrophobic Impregnation and Coating

Part of the tunnel spoil can not be used for concrete due to alkali-aggregate reaction (AAR). Water is an indispensable condition for AAR, so separating the alkali-aggregate from water is of great benefit to controlling the AAR. This paper investigates the modification of concrete and aggregate by hydrophobic impregnation and organic coating and then evaluates their waterproof and mechanical properties by dynamic contact angle (DCA), ultrasonic wave velocity, scanning electron microscope (SEM), nuclear magnetic resonance (NMR), and so on. For waterproofness, hydrophobic impregnation and organic coating can both improve the waterproofness of concrete and aggregate. The organic coating is suitable for aggregate because it wrap aggregate well. And aggregate coated by PVA can improve the interfacial transition zone (ITZ). For mechanical properties, both materials will weaken the strength of the interface. Furthermore, concrete made by aggregate with organic coating shows plastic deformation and has a good correlation with the film thickness, a plastic estimation model based on film thickness is proposed. This paper evaluates the waterproof of concrete and aggregate and finds plastic concrete with good aggregate waterproofness which provides a new idea for the application of alkali-aggregate in seepage control facilities of water conservancy projects.

Effect of Recycled Concrete Aggregate with Different Degrees of Initial Alkali–Aggregate Reaction Damage on the Mechanical Behavior and Porosity of Self-Compacting Recycled Aggregate Concrete

Effect of Recycled Concrete Aggregate with Different Degrees of Initial Alkali–Aggregate Reaction Damage on the Mechanical Behavior and Porosity of Self-Compacting Recycled Aggregate Concrete

Durable Steel-Reinforced Concrete Structures for Marine Environments

Even in harsh marine environments, concrete structures reinforced with steel can show excellent long-term durability, with little or no reinforcement corrosion. Very few actual reinforced concrete (RC) structures have been closely scrutinized over many years and subject to interpretation using recent state-of-the-art understanding gained from detailed laboratory observations. Such a case is described for an 80-year-old RC structure observed annually over about 30 years in what is essentially an extraordinary long experiment. Despite very high chloride concentrations, field excavation evidence showed that reinforcement corrosion overall remains minimal, except where insufficient concrete compaction permitted air-voids to initiate quite severe, very localized corrosion even with still high concrete pH. It is possible that the use of blast furnace slag as aggregate may have assisted the observed durability. The case study supports other studies that show that it is possible to achieve long-term durable and therefore sustainable RC structures without additives and using only conventional reinforcement steels and conventional cements and aggregates. However, the potential dangers of deep narrow cracking extending to the reinforcement and the potentially deleterious effects of alkali–aggregate reactivity of some aggregates needs to be considered.

Pressure Relief Joint for Preventing Concrete Pavement Blowup

Blowup refers to concrete pavement distress resulting from compressive failure at joints or cracks when excessive concrete expansion occurs, compressive forces are generated, and the horizontal movement of the pavement is constrained. Blowup occurs because of many reasons including heatwaves caused by abnormal climatic conditions, improper installation spacing between expansion joints, pavement expansion due to an alkali-aggregate reaction, concrete pavement aging, and contraction joint failure. In the summer of 2018, the Korean peninsula experienced the worst heatwave ever recorded, and hence, the possibility of blowup increased. Consequently, the Korea Expressway Corporation established a draft policy for installing pressure relief joints (PRJs) to prevent blowup. In this draft, three installation classes were specified for installing PRJs on in-service roads, and the installation priority for each class was set such that the limited budget could be used efficiently. In addition, the draft presented specific guidelines for installing each class of PRJs and suggested PRJ cross sections that could ensure structural stability. However, the draft lacks systematic research on the causes of blowup and the development of countermeasures and does not provide an engineering basis for the suggested technological solutions to prevent blowup. Therefore, this study aimed to reexamine and complement the suitability of the existing PRJ installation standards through field studies, laboratory experiments, and analytical techniques.

Resistance to the alkali-aggregate reaction of sustainable mortars produced with scheelite tailings in replacing natural sand aggregates

This work produced coating mortars with scheelite tailings (ST) in total replacement of natural sand aggregate. The chemical and mineralogical composition of the scheelite tailings was determined by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Mortar samples with a mass proportion of 1:2:9 (cement: lime: sand/scheelite tailings) were prepared with and without the scheelite tailings. The mortars were evaluated by mercury intrusion porosimetry and compressive and flexural strength tests. The resistance to the alkali-aggregate reaction was assessed from the bar expansion test and by scanning electron microscopy (SEM) in the crack and pore regions. The results indicate that until the 22nd day, the scheelite tailings were not reactive; however, in 28 days, the expansion was deleterious. SEM images did not detect the presence of amorphous alkaline gel characteristic of the alkali-aggregate reaction. Therefore, although the mortar with scheelite tailings aggregate has shown the deleterious potential to 28 days, mechanical tests indicate that it has the potential to be used as a coating mortar.

Tapas de sílice - a smörgåsbord of reactive mineralogies and textures.

A source of sand is proposed as an educational tool to aid in the identification of silica mineralogies and textures susceptible to alkali-silica reaction. This particular silica sand originates in the southern portion of the state of Veracruz, Mexico, and exhibits a wide variety of lithologies, A thin section produced from a cross-section through a mortar bar subjected to ATSM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) exhibits plentiful examples of reactive silica.

Recommendation of RILEM TC 258-AAA: RILEM AAR-11: determination of binder combinations for non-reactive mix design or the resistance to alkali-silica reaction of concrete mixes using concrete prisms − 60 °C test method

The RILEM AAR-11 concrete prism test (CPT) is a performance test method for testing aggregate combinations together with various binder combinations (i.e. composite cements or pure Portland cements + Supplementary Cementitious Materials; SCMs). The method covers the measurement of expansion produced by alkali-aggregate reaction of concrete prisms stored at 60 °C in a humid environment which accelerates the alkali-silica reaction (ASR). The principle of the method is founded upon the RILEM AAR-4.1 aggregate test method. The method has three different applications, i.e., (1) AAR-11.1: Assessment of how SCM content may reduce ASR susceptibility of an aggregate combination: Enabling the use of a specific reactive aggregate product together with critical binder combination(s) (minimum binder requirements) for producing non-reactive concrete. (2) AAR-11.2: Assessment of how available binder alkali content can be reduced by SCMs: Enabling the determination of the required general binder composition together with a regional worst-case aggregate combination for producing non-reactive concrete (within that region). (3) AAR-11.3: Assessment of the ASR-resistance of specific concrete compositions to verify its suitability in a performance test.