Alkali-aggregate Reaction Research Articles

Mitigating alkali-silica reaction induced concrete degradation through cement substitution by metakaolin and bentonite

This paper reports the results of an investigation on the efficiency of cement modification with clay minerals in preventing deteriorations of concrete due to alkali-aggregate reactions. Coupled substitution of metakaolin and bentonite in Portland cement was studied for a synergistic effect to mitigate alkali-silica reactivity (ASR). The expansion and cracking behavior of mortar bars were investigated. Hydration products of cement blends in two environments, immersion in saturated lime water and “mortar bar test” environment (i.e., in 1 N sodium hydroxide solution at 80 °C), were characterized. The role of the clay-based minerals in mitigating ASR was also evaluated by monitoring the strength development and characterizing the microstructural defects of the cement blends. The results indicate that cement modification with a combination of metakaolin and bentonite can effectively mitigate ASR-induced concrete deteriorations. By replacing 10% and 30% cement, expansion of mortar was decreased from deleterious to innocuous level. With 50% cement substitution, no ASR expansion was observed, and accordingly, no crack could be detected. The incorporated aluminum originating from the minerals slowed down the SiO2 dissolution, and formation of gel and its swelling potential. In addition, the decreased alkalinity and consumption of calcium in the modified cement matrix also contributed to the suppressed ASR. This paper demonstrates a low-cost approach to mitigating ASR; and metakaolin, bentonite, or both can effectively replace other supplementary cementitious materials used for the same purpose (e.g., fly ash) which may not be available or cost effective.

Mapeamento do potencial álcali reativo das areias no Rio Grande do Sul

Existem vários processos de deterioração que interferem no desempenho e durabilidade de um concreto, dentre estes processos encontra-se a reação álcali-agregado (RAA). A RAA é um termo geral utilizado para descrever a reação química que ocorre internamente em estruturas de concreto, entre os hidróxidos alcalinos presentes no cimento e fases minerais reativas presentes nos agregados. Como resultado da reação, forma-se um gel sílico-alcalino que, na presença de umidade, absorve água, sendo capaz de expandir no interior da massa de concreto, podendo causar expansão e, consequentemente, fissuração interna e externa nas estruturas de concreto. As medidas preventivas à ocorrência da RAA são conhecidas há muito tempo e aplicadas rotineiramente apenas em estruturas de usinas hidrelétricas. Sabendo-se que qualquer estrutura sujeita a intensa umidade pode desenvolver a RAA, a prevenção é necessária também nas edificações residenciais, por exemplo, em locais onde o concreto esteja exposto à umidade, a fim de garantir estruturas mais duráveis e, portanto, mais sustentáveis, uma vez que a geração de resíduos pela necessidade de manutenção constante, ou demolição, vai na contramão dos pilares da sustentabilidade na construção. Nesse contexto, a primeira etapa do processo de prevenção da ocorrência da RAA é conhecer o potencial reativo dos agregados, pois conhecendo esse parâmetro é possível empregar materiais cimentícios adequados à inibição do desencadeamento da reação. Esta pesquisa, tem como objetivo avaliar o potencial álcali-reativo de oito amostras de areia, provenientes das jazidas fornecedoras do insumo para produção de concreto no Rio Grande do Sul. O estudo foi realizado baseando-se no método acelerado de barras de argamassa, de acordo com a ABNT NBR 15577-4 (2018) e na avaliação das características mineralógicas dos agregados, através da análise petrográfica. Os resultados apontaram um alto potencial deletério das amostras avaliadas. Verificou-se que 7 de um total de 8 amostras analisadas foram classificadas como potencialmente reativas. A variação percentual entre a amostra de maior para a de menor expansão foi de 93,44% (0,61%-0,04% respectivamente), sendo potencialmente inócua apenas a amostra de areia da cidade de Osório/RS.

Evaluation of a direct shear test setup to quantify AAR-induced expansion and damage in concrete

Alkali-Aggregate Reaction (AAR) is one of the most harmful distress mechanisms affecting the durability and serviceability of concrete infrastructure worldwide. Over the years, a number of comprehensive testing protocols have been developed to appraise the amount of damage, expansion attained to date and mechanical properties reductions of concrete affected by AAR. Promising results were found through the use of advanced mechanical and microscopic techniques such as the Stiffness Damage Test (SDT) and Damage Rating Index (DRI). However, there is still a need to develop new “simple” yet “reliable” test procedures able to quantify AAR expansion and damage. This paper presents the use of a modified shear strength setup to appraise AAR development. Concrete samples incorporating a wide range of reactive aggregates were fabricated, monitored and tested under the proposed shear setup at distinct damage degrees. Results show that AAR influences significantly the shear strength of affected concrete and thus the proposed test setup seems promising in assessing AAR expansion and damage. Yet, further data is still needed to confirm the reliability of the results gathered in this research.

Material, structural and modelling aspects of alkali aggregate reaction in concrete

Concrete nuclear structures have been identified as suffering from alkali aggregate reaction (AAR) in both Canada and the United States. Although much research effort has been directed toward understanding its effect on reinforced concrete structures, unresolved issues still remain. Among them are the effect of multiaxial stress states, commonly developed in nuclear structures, on the response of AAR-affected concrete; also of concern is the possible invalidity of conventional methods of analysis for structural assessment due to the induced anisotropy in the mechanical properties of concrete. The Canadian Nuclear Safety Commission initiated and funded an extensive study aimed to reveal the implications of concrete deterioration due to AAR on structural integrity, which included material and structural testing and modeling. This paper presents an overview of the entire research program and discusses the key results.

Synergistic effect of RHA and FCW in alkali-aggregate reaction mitigation

Abstract Pozzolans rich in silica, such as Rice Husk Ash (RHA), contribute to compressive strength gain but at the same time might increase alkali-aggregate reaction (AAR) in mortar mixtures. Pozzolans that have aluminates, such as Fired Clay Brick Waste (FCW), can be efficient to mitigate AAR but tend to lead to a slower compressive strength development. The association of different types of pozzolans, however, may result in a synergistic effect, compensating individual deficiencies. This paper presents a study of mixtures containing RHA, FCW and these two materials combined, aiming to obtain benefits in the mechanical behavior and in the durability regarding AAR. A substitution rate of 20% Portland cement by pozzolanic material was used. Through accelerated AAR tests and compressive strength measurements, it was found that while RHA is considered harmful to AAR - even when using an innocuous aggregate - FCW presents benefits, also avoiding this deleterious effect when combined with RHA. The same occurs in the compressive strength development, where RHA compensates a small loss of compressive strength associated with the use of FWC alone.

Resistance of selected aggregates from igneous rocks to alkali-silica reaction: verification

The paper presents investigations into the reactivity of aggregates from igneous rock, carried out in accordance with the procedures contained in the GDDKiA General Technical Specification "Concrete pavements". The aim of the investigations was evaluation of the suitability of the aggregates for road structures and pavements built using cement based concrete technology. Aggregates produced from extrusive rocks (basalt, melaphyre and porphyry) and from intrusive rocks (granite and gabbro) were analysed. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. Expansion tests on mortar bar and concrete prism specimens with analysed aggregates and a microscopic analysis of the alkali-aggregate reaction products were carried out. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz and volcanic glass were found in the grains of the porphyry and melaphyre aggregates. On the basis of the conducted investigations the two aggregates made of igneous rocks (melaphyre and porphyry) were classified into category R1 (moderately reactive). The basalt aggregate, the granite aggregate and the gabbro aggregate were assigned to category R0 (non-reactive).

Susceptibility of selected aggregates from sedimentary rocks to alkali-aggregate reaction

The paper presents the results of investigations into the reactivity of domestic aggregates produced from selected sedimentary rocks, carried out using the new testing methods, consistent with the RILEM and ASTM methods, implemented by GDDKiA (Polish General Directorate for National Roads and Motorways) documents. The range of the investigations covered coarse crushed aggregates produced from limestone, dolomite, sandstone and greywacke rocks, potentially suitable for making strong and durable concrete. No reactive forms of quartz were found in the mineralogical composition of the limestone aggregates and the dolomite aggregates. Micro- and cryptocrystalline quartz occurred in the particles of the greywacke aggregates and the sandstone aggregates. On the basis of the expansion of mortar and concrete specimens the aggregates produced from the sedimentary rocks were classified into the reactivity categories: R0, R1 and R2. A sodium-potassium-calcium silicate gel, whose composition (consistent with that reported in the literature) was characteristic of the alkali-silica reaction products, was found. The investigations resulted in a consistent assessment of the reactivity of the aggregates.

Effect of fly ash and limestone powder on inhibiting alkali aggregate reaction of concrete

Abstract The alkali aggregate reaction (AAR) about the aggregate marked with W1# was studied by using of four kinds of methods, including accelerated mortar bar test (AMBT), mortar bar length test (MBLT), concrete prism method (CPM) and rock column method (RCM). AMBT showed that the expansion ratio of the specimens at 14 days was 0.200%, and the expansion ratio at 28 days was 0.404%; MBLT showed that the expansion ratio at 3 months was higher than 0.050%, and the expansion ratio at 6 months was higher than 0.100%; CPM showed that the expansion ratio at 39 weeks was higher than 0.040%. These studies above indicated that W1# aggregate was the aggregate with potential alkali-silica activity. RCM tests showed that the aggregate doesn’t have potential alkali-carbonate activity. The inhibiting experiments showed that the expansion ratio at 14 days and 28 days were less than 0.10% by adding more than 45% (Wt/%) limestone powder or adding 15% (Wt/%) fly ash, meanwhile, the expansion ratio at 14 days and 28 days were all less than 0.10% after adding 15% (Wt/%) limestone powder and 30% (Wt/%) fly ash or adding 25% (Wt/%) limestone powder and 25% (Wt/%) fly ash, respectively. Mesh structures were formed by the hydration products in the micro structure, and no micro cracks and the white flocculent products could be observed inside and outside of the samples. All the results above confirm that AAR of the aggregate was inhibited effectively, and it will play the useful role in AAR research.

Potential alkali silica reactivity of aggregates from different sources of Kashmir and mitigation measures thereof

The present study envisages the potential alkali–silica reactivity; the most common form of alkali aggregate reaction of various aggregate sources of Kashmir and mitigation measures thereof using petrographic analysis and various designated ASTM codes. The chemical analysis was carried out for different aggregate samples possessing different lithology hence varied reactive nature. Comparatively some samples showed more reactive nature than others due to presence of higher reactive silica. The results show the innocuous nature of all aggregate samples according to ASTMC-289 standard curve. The study reveals that addition of Fly ash reduced the elongation of bars resulted due to alkali silica reactivity of the aggregates and hence should be widely used as a mitigation measure to overcome the alkali reactive nature of the aggregates in the region.

Reaktywność alkaliczno-krzemionkowa wybranych krajowych kruszyw drobnych

The paper presents selected information on the quality of the aggregates, especially natural sands, extracted and manufactured in Poland. The sands usually meet the basic quality requirements (e.g. concerning grading and purity) for fine aggregates to be used in road construction. Tests of the alkali reactivity of natural sands and manufactured (by crushing compact rock) sands are described in detail. The results of the reactivity tests carried out in accordance with domestic standards PN-B-06714 show the tests to be poorly reliable. Exemplary abridged petrographic descriptions of selected sands and the results of reactivity tests carried out on mortar beams in accordance with standard ASTM C1260 are presented. The beam linear expansion values were geographically assigned by marking them on a contour map of Poland. The tested fine aggregates were found to greatly vary qualitatively as regards their mineral composition and the likelihood of occurrence of the alkali-aggregate reaction. Over half of the tested sands were characterized by an expansion over 0.1%, which according to the AASHTO R-80 classification means that they are moderately reactive aggregates.

Acoustic Emission and Ultrasonic Characteristics in the Failure Process of Cemented Waste Concrete-Coal Gangue Backfilling (CWCGB) under Uniaxial Loading

The acoustic emission (AE) characteristics, change law of the ultrasonic velocity, and internal failure mode of cemented waste concrete-coal gangue backfilling (CWCGB) with 600 days of curing time were studied under uniaxial loading conditions. Waste concrete particles of 5 mm acting as fine aggregates substituted for 30% and 50% fine coal gangue in the cemented coal gangue backfilling (CGB). AE was used to test the ring count and changing rule of the accumulated energy, locate the event for positioning, and calculate the number of events. The average ultrasonic wave velocity was measured via an ultrasonic detector. The characteristics of the microfractures were observed via a scanning electron microscope. The results showed that the specimens with 30% and 50% waste concrete replacement rates underwent ultrasonic wave velocity stabilization and a rapid decline stage under uniaxial compression; for the former case, the decline started earlier. The AE ring count attained peaks at the pore compression stage, yield stress point, stress peak value, and residual stress stage with no added waste concrete and 30% and 50% waste concrete substitution rates. The value and consequent frequency of the ringing count peak and cumulative energy slope increased with increasing waste concrete substitution rate. A microcrack was observed at the interfacial transition zone between the cement paste and gangue owing to the alkali-aggregate reaction effect. However, a better bonding performance was exhibited by the waste concrete particles and paste.

Lessons learned about the diagnosis of pathologies in concrete dams: 30 years of research and practice

Studies on the diagnosis of pathologies of concrete dams are a valuable reference for professionals managing such assets. However, detailed information is rarely reported in the literature. This paper compiles the most important lessons learned during 30 years of practical experience in this area. The diagnostic procedure is illustrated through 4 of the most interesting dams analysed and monitored by the authors. All were subjected to a first stage that included inspection and analysis of historical documentation, leading to the proposal of a diagnose hypothesis. This was followed by a second stage that included an experimental programme with laboratory tests and, in some cases, numerical simulations to confirm or reject the hypothesis. The analysis of the information shows different pathologies and provide a wide spectrum of boundary conditions, symptoms and diagnoses (from internal sulphate attack and alkali-aggregate reaction to soil-structure interaction).

Structural implications of internal swelling reactions in concrete: review and research needs

The chemical and physical processes associated with alkali–aggregate reaction and delayed ettringite formation, otherwise known as internal swelling reactions (ISRs), have been the subject of considerable research spanning several decades, yet the implications for affected structures are still open to debate. A major knowledge gap currently exists between the diagnosis and prognosis of ISR mechanisms, and the quantification and management of risk associated with ISR expansion in structures. This lack of understanding of the effects of ISRs on structural behaviour may be attributed to the fact that parameters such as confinement, boundary conditions, anisotropy and loading conditions are complex and vary greatly in existing structures. Furthermore, the correlation between the results of microscopic/macroscopic analyses on concrete core samples and the in situ performance of large-scale structures is still not well understood, even at a fundamental level. The aim of this paper is to summarise current knowledge of the structural implications of ISR mechanisms in concrete structures and stimulate a discussion of the importance of pursuing multi-scale experimental testing programs for the assessment of ageing infrastructure. A parametric analysis is included using the software VecTor2.

Investigation on the performance control technologies of hydraulic concrete in harsh conditions

In view of the series of major technical problems faced by hydraulic concrete in harsh construction and service conditions such as high temperature environment, high clay content aggregate, long distance transportation, high alkali activated aggregate application, high corrosive environment with multiple ions, high water head and large discharge, the technologies for construction performance control, the evaluation and inhibition of alkali aggregate reaction, the evaluation of corrosive resistance, and the effect evaluation and performance optimization of abrasion and cavitation are systematically explored and summarized herein. Furthermore, the long time slump-retaining mechanism of polycarboxylate superplasticizer with slump-retaining and clay-tolerance properties in concrete, the rapid risk assessment method of alkali aggregate reaction, the mechanism of self-immunity to alkali-aggregate reaction, the theoretical models of chloride ion diffusion and sulfate attack, as well as the equipment, method and optimization of abrasion and cavitation are expatiated. These study achievements enrich the theory and technology of hydraulic concrete performance control, and can provide important guarantee for scientific decision-making of major engineering.

Some Progresses in the Challenges for Geopolymer

Geopolymer is manufactured by chemical activation of industrial by-products, which include blast furnace slag, fly ash, steel slag, phosphorus slag etc, with alkali activators, such as the sodium silicate, sodium carbonate and sodium hydroxide and their mixtures. It has attracted worldwide attention due to its advantages of simple production process, low energy consumption, effective utilisation of industrial by-products and reduction of greenhouse gas emissions. However, as materials vary substantially in physicochemistry properties, hardening, workability and durability of deriving geopolymer products vary accordingly. Slag-based geopolymer usually set within a very short period of time (less than 30 min), while low calcium fly ash-based geopolymer takes long time (a couple of days) to set. Geopolymer binders cured at room temperature exhibited significantly higher shrinkage than Portland cement does, while thermal cured products are very volumetrically stable. Moreover, alkali-aggregate reaction can happen when alkali-reactive aggregates are used with geopolymer binders. These issues need to be considered in large scale applications. This paper reviews the current advance in the research of geopolymer.

A review of recent developments in geopolymer concrete

Geopolymer concrete is proved to have high strength, lesser shrinkage, resistance against reinforcement corrosion, acid and sulphate resistance, freeze-thaw resistance, fire resistance and resistance to alkali-aggregate reaction. There are many parameters which influence the strength characteristics of Geopolymer Concrete. They are types and fineness of Source alumino silicate material used, concentration and type of alkaline activators used, curing temperature and curing time, utilization of M-sand etc. High performance characteristics could be achieved through the correct choice of these parameters. This review paper focuses on the influence of different variables on the properties of geopolymer concrete and the progress in the field of geopolymer concrete. Consequently many research papers pertaining to the geopolymer have been reviewed in this state of art paper.

Expansion prediction of alkali aggregate reactivity-affected concrete structures using a hybrid soft computing method

The phenomenon of alkali aggregate reactivity (AAR) in concrete structures corresponds to the reaction between aggregates with some ingredients and alkali hydroxide in concretes. This AAR could potentially lead to concrete deformation, micro-cracks and eventually wide visible cracks. In this study, to predict the expansion of the concrete caused by AAR, a novel hybrid model is proposed based on support vector machine (SVM). In the proposed model, the inputs are the aggregate components and concrete age, while the output is the induced expansion in the concrete. To improve the generalisation capacity of the proposed model, the enhanced particle swarm optimisation algorithm is employed to select optimal SVM parameters. The proposed method is evaluated and compared with other conventional soft computing methods based on the experimental data. Finally, the evaluated results endorse the effectiveness of the proposed hybrid model.

Sensitivity and uncertainty analysis of AAR affected reinforced concrete shear walls

Whereas many publications report on alkali aggregate reaction (AAR) expansion or test analyses, very few address the more pressing issue of its impact on structures. Furthermore, given the uncertainties associated with characterization of the material, probabilistic based approach are not known to have been reported in the literature. This paper addresses these limitations through an analysis of a reinforced shear wall. A two-prone approach is followed: first a sensitivity analysis is performed to narrow the number of random variables (RVs) to the most relevant ones. Then, an uncertainty quantification is performed through Latin Hypercube Sampling with and without AAR expansion. Then the capacity curves (including the summarized ones to 16, 50 and 84% fractiles) are developed. Probability of non-exceedance of a specific capacity (i.e., limit state) is shown though the so-called fragility curves. It is found that in some cases AAR increases the shear capacity, while in others it decreased it. It highly depends on the initial combination of the RVs.

Alkali-activated Portland blast furnace slag cement mortars: Performance to alkali-aggregate reaction

This report evaluates the performance to alkali-aggregate reaction of two types of binder systems: a Portland blended cement and an Alkali-activated Portland blended cement. The first system consists of 80% granulated blast furnace slag and 20% Portland cement (OPC) and was hydrated in the presence of water (CE), whereas the second incorporated an alkaline activator, making it a hybrid cement (HB). Expansion measurements of mortar bars were carried out, and their behaviour was compared to a reference system based on 100% OPC. Additionally, a microstructural characterization was performed using scanning electron microscopy. The results show that CE and HB cements had smaller expansions than OPC, although Rosette and pseudo-Rosette structures were observed.

The use of lithium compounds for inhibiting alkali-aggregate reaction effects in pavement structures

Internal corrosion of concrete caused by the reaction of reactive aggregate with sodium and potassium hydroxides from cement is a threat to the durability of concrete pavements. Traditional methods for reducing the negative effects of the reaction include the use of unreactive aggregates, low alkali cements, mineral additives or chemical admixtures, incorporated during mixing. Lowering the relative humidity of the concrete below 80% is another measure for limiting the destructive reaction.The incorporation of lithium compounds, in particular lithium nitrate and lithium hydroxide, to the concrete mix is a method of limiting alkali-silica reaction effects. The challenge is to reduce the negative effects of aggregate reactivity in members in which the reaction has occurred because the aggregate happened to be reactive. The paper presents ways of limiting the deterioration of ASR-affected concrete in road pavements and other forms of transportation infrastructure, mainly through the use of lithium compounds, i.e. lithium nitrate. Impregnation methods that allow the penetration of lithium ions into the concrete structure were characterized, as was the effectiveness of the solutions applied.