Alkali-aggregate Reaction Research Articles

Evaluation of non-destructive testing and long-term durability of geopolymer aggregate concrete

Recent advancements in concrete technology focus more on increasing strength than durability. Concrete with good durability will withstand adverse conditions like frost, chloride penetration, sulfate assault, alkali-aggregate reaction, steel corrosion, etc., which will lower the strength of the concrete. Strength is vital, but so is durability. The present study examined and discussed the durability parameters of conventional concrete made with geopolymer aggregate (GPA) as a partial substitute for natural aggregate. Strength studies in this research found that the optimal level of substitution for natural coarse aggregate by GPA was 100% replacement to produce the performing concrete. Replacement of natural coarse aggregate by geopolymer aggregate exhibits 9%–15% higher compressive strength than natural aggregate concrete. The findings reveal that concrete with 100% geopolymer aggregate exhibits a compressive strength increase of 9%–15% over that of concrete made with natural aggregates. Ultrasonic pulse velocity measurements for geopolymer aggregate concrete range between 4 km/s and 4.5 km/s, indicating good quality according to IS specifications. Additionally, Rebound Hammer test results further support the enhanced quality of geopolymer aggregate concrete. However, the porosity of geopolymer aggregates results in a sorptivity that is 10%–30% higher than that of natural aggregate concrete. Despite this, the increased resistance to acid and sulfate attacks is noted, attributed to the strong bonding between geopolymer aggregates and the cement matrix.

Effect of low-heat cement Portland cement on alkali-silica reaction of aggregates with different alkali-reactivities

This study investigated the impact of cement clinker percentages on the alkali-silica reaction (ASR) mechanisms of aggregates with varying alkali-silica reactivity. Experimental findings indicated that the low-heat Portland cement (LHC) mitigated the development of the ASR process in soda-lime glass aggregate (SLGA) concrete. The ASR in ordinary Portland cement (OPC) mainly initiated within the SLGA, leading to crack propagation through the matrix. The in-situ X-ray micro-computed tomography test indicated that LHC altered the manifestation of ASR in concrete containing SLGA, leading to different destructive forms. Specifically, ASR between the LHC and SLGA primarily occurred at the periphery of the SLGA. The in-situ quantity analysis results illustrated that the LHC mitigated the ASR-induced cracks in the SLGA concrete. For the less alkali-reactive natural aggregate, the effect of LHC cement on ASR was diminished. ASR still only occurred within the natural aggregate concrete, distributing in highly alkali-reactive phases inside the aggregates. The chemical analysis results supposed that the differing ASR pathways could be attributed to the interaction between the calcium content in the LHC and the spatial distribution of alkali-reactive phases within the aggregates. These findings help interpret the mechanism of the slower ASR process in the belite-rich cement concrete.

Suppressing of alkaline aggregate reaction (AAR) through waterproofing of concrete surface, aggregates, and mortars

Water is necessary for the alkali aggregate reaction to occur and this study investigates the impact of waterproofing on alkali-aggregate reaction (AAR) in concrete by separating water from alkali reactive aggregates through surface, aggregate, and matrix treatments. Accelerated mortar bar tests (AMBT) are conducted to analyze the expansion caused by alkali aggregates. Furthermore, the suppressive mechanism of waterproofing on AAR is explored using scanning electron microscopy (SEM), while the influence of waterproof concrete aggregate and matrix on pore characteristics and hydration products is assessed using nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). The results demonstrate that surface waterproofing with silane and polyvinyl alcohol (PVA) effectively suppress AAR. Moreover, PVA-coated aggregates significantly enhance the compactness of the interfacial transition zone (ITZ) in concrete. Based on these findings, an improved model considering waterproofness is proposed to quantify the degree of alkali aggregate reaction. These findings offer valuable guidance for controlling AAR.

Electromagnetical and ultrasonic characterizations of concretes subjected to internal swelling reactions

Among pathologies of reinforced concrete structures, internal swelling reactions (ISR), including alkali-aggregate reaction and delayed ettringite formation, are at the origin of cracks and major disorders due to rebar corrosion. Visual evaluation of crack density combined to non-destructive testing techniques can be used to characterize the global swelling and then give some structural diagnosis. For the last ones, an intermediate step (assimilated to a calibration step) can be performed at laboratory to evaluate the sensitivity of electromagnetic, electrical and ultrasonic properties of concretes subject to ISR.This present study focuses on such characterizations of concrete samples presenting different levels of ISR and for several water content. Numerous samples have been extracted from mock-ups representative of two massive concrete structures, affected one by alkali-aggregate reaction and the other by delayed ettringite formation, and conditioned in homogeneous and controlled conditions. After describing the experimental campaign, results are shown and commented.

Splitting Tensile Mechanical Performance and Mesoscopic Failure Mechanisms of High-Performance Concrete under 10-Year Corrosion from Salt Lake Brine

In regions characterized by the challenging combination of brine corrosion in the salt lakes and river sand with alkali silica reaction (ASR) activity in areas of the Northwest, high-performance concrete (HPC) formulated with high-volume composite mineral admixtures as ASR suppression measures has been preferred for civil engineering structures in the region. This study investigates the splitting tensile strength, corrosion products, microscopic structure characteristics, and mesoscopic mechanical mechanisms of splitting failure of such HPC under 10-year corrosion from salt lake brine. The relationship between mechanical properties and corrosion damage, as well as the characteristics of internal crack propagation paths and failure mechanisms of HPC under splitting load, are explored. The findings reveal that as the alkali content within HPC rises, corrosion damage intensifies, resulting in a reduction in splitting tensile strength. Moreover, a linear association between mechanical properties and corrosion damage is observed. Microscopic structural analysis and numerical simulation of the splitting failure process of HPC elucidate that while the substantial presence of mineral admixtures effectively suppresses the ASR risk associated with alkali-reactive aggregates in concrete, uneven ASR gel products persist. These discontinuous micro-fine interface cracks induced by the gel products and the cracks induced by the gel products around the selective alkali-active aggregate particles distributed in the local area are the initiation sources of mortar cracks in HPC splitting failure. In terms of the overall failure state observed during the concrete splitting process, mortar cracks manifest two distinct extension paths: along the coarse aggregate interface and directly through the aggregates themselves. Notably, a greater proportion of coarse aggregates are directly penetrated by mortar cracks, as opposed to the number of interface failures bypassing coarse aggregates. More importantly, the above work establishes a theoretical reference in three dimensions: macroscopic, mesoscopic, and microscopic, for studying concrete corrosion damage in complex environments such as salt lake brine corrosion and ASR inhibition.

The Risk of Alkali–Carbonate Reaction and the Freeze–Thaw Resistance of Waste Dolomite Slag-Based Concrete

The alkali–carbonate reaction (ACR) is a type of alkali–aggregate reaction (AAR) that may lead to serious damage in concrete construction. There is sufficient research on the effect of the ACR on dolomite limestone; however, research on the effect of the ACR on pure dolomite is absent, and there are a large number of dolomite resources that cannot be effectively utilized in civil engineering. This study aims to investigate whether the ACR occurs in pure dolomite spoil and to determine the freeze–thaw resistance of pure waste dolomite slag-based concrete (PWDSC). In this study, X-ray diffraction (XRD) and the lithofacies method (LM) confirmed that the tested samples were pure dolomite. The rock cylinder method (RCM) and rapid preliminary screening testing for carbonate aggregates (AAR-5) were employed to determine the alkali activity of pure dolomite: the RCM indicated a variation of −0.09% in length during the 84-day test period, the AAR-5 exhibited a length expansion rate of 0.03% within 28 days, and the expansion rates were less than 0.1%. These findings suggest that pure waste dolomite slag (PWDS) does not possess alkali activity. The freeze–thaw cycle test showed no significant spalling on the concrete surface, the inside of the cement produced few micro-cracks according to scanning electron microscopy (SEM), and the uniaxial compressive strength (UCS) test showed a decrease of approximately 20% after 200 freeze–thaw cycles. The results verified that ACR does not occur in PWDS and that it can withstand freeze–thaw damage, to a certain extent, when used as concrete coarse aggregate.

Permittivity analysis of weathered concrete in a bridge based on open-ended probe and impedance measurements

Pathologies like corrosion of rebars or alkali aggregate reactions in a reinforced concrete (RC) bridge are usually accompanied by the existence of aqueous pore solutions with a high concentration of ions. The distribution of aqueous solutions in the concrete is inhomogeneous and depends on the RC’s location in the bridge and complex climate factors. Frequency-dependent complex permittivity is sensitive to aqueous pore solutions because the high conductivity caused by charge carriers can result in a large imaginary part of the permittivity, much higher than that caused by water. In this study, we used a non-destructive open-ended probe to measure the complex permittivity of the RC in a bridge’s pillar with different levels of pathologies. By measuring the impedance of core samples with various controlled water volumetric fractions in the laboratory, the water effect on the evolution of the loss tangent (the ratio between the imaginary part of the permittivity and the real part) can be calibrated. Comparing the loss tangent in the bridge with that of the core samples treated by water, we can map the areas with a high density of aqueous pore solution and cracks, and estimate the unhealthy area with partial damage in the pillar by an effective and non-destructive diagnosis.

From risk study to field evidence: an unprecedented and isolated case of delayed ettringite formation in Brazil

This paper describes the first ever reported case in Brazil where delayed ettringite formation (DEF) has been confirmed as the sole cause of deterioration in field concrete. Still under construction and less than 2 years old, numerous cracks were observed in the foundation structures of a building located in Recife, a city known for its history of alkali–aggregate reaction (AAR) cases. In addition to a field survey of cracks, microstructural analyses, tests for residual expansion and compressive strength, a review of the structural design, determination of sulfate content in the groundwater and simplified thermal analysis were carried out. The results confirmed that DEF was the sole cause of the damage present in cast-in-place concrete structures, with no evidence of AAR or any other deterioration process. This work corroborates previously published studies on the high risk of the occurrence of DEF in the region, demonstrating the urgent need for a preventive technical standard in the country, considering the chemical composition of cements and prior thermal analyses to adopt possible preventive measures to limit the maximum internal temperature of concrete.

Compressive creep of a concrete affected by advanced alkali-aggregate reaction

Many structures around the world are affected by Alkali-Aggregate Reaction (AAR). This pathology is characterized by the formation of a swelling gel, which leads to cracking of the concrete and degrades durability and structural behaviour. In order to better understand the coupling between AAR and creep, a comparative study investigated the behaviour of a concrete affected by AAR and a non-reactive concrete, both under maintained uniaxial compression. The conditions necessary for the development of the AAR were preserved during the creep phase. Loading corresponding to 30% of the compressive strength of the concretes was applied after the concrete had developed three quarters of its swelling potential. The radial and orthoradial strains were measured by fibre optics. The results show a resorption of 56.1% of the swellings in the loaded direction after 231 days under loading, associated with total transfer of the deformations in the free directions.

Probabilistic modelling of deterioration of reinforced concrete structures

Reinforced concrete (RC) structures deteriorate over time which affects their strength and serviceability. To develop measures for protecting new RC structures against deterioration and assess the condition of existing RC structures subjected to deterioration an understanding of the deterioration processes and the ability to predict their development, including structural consequences, are essential. This problem has attracted significant attention from researchers, including those working in the area of structural reliability (in particular within the JCSS) since there are major uncertainties associated with the deterioration processes and their structural effects. The paper presents an overview of the probabilistic modelling of various deterioration processes affecting RC structures such as corrosion of reinforcing steel, freezing-thawing, alkali-aggregate reaction, sulphate attack and fatigue, and their structural implications, including the historical perspective and current state-of-the-art. It also addresses the issues related to the inspection/monitoring of deteriorating RC structures and the analysis of collected data taking into account relevant uncertainties. Examples illustrating the application of the presented probabilistic models are provided. Finally, the current gaps in the knowledge related to the problem, which require further attention, are discussed.

The dam that fly ash built.

When the first concrete was poured in 1949 for the Hungry Horse Dam (Montana, USA), pozzolan cements had already been used in several major North American dams, including Grand Coulee on the Columbia River (diatomaceous earth explored but ultimately not used), Friant on the San Joaquin River and Altus on the North Fork Red River (pumicite) and Bonneville on the Columbia River and Davis on the Colorado River (calcined clay). But Hungry Horse Dam stands out as the first dam constructed using coal combustion fly ash. Utilising 2.4 million cubic metres of concrete, the dam is located on the South Fork Flathead River, one of the tributaries feeding one of the nation's major waterways, the Columbia River, and closely related to the adjacent Glacier National Park. In this respect, Hungry Horse is directly connected to two momentous periods in modern history - the massive adoption in the 1950s of coal as fuel for power plants, and the ongoing threats to fresh water supply and the rapid retreat of alpine glaciers due to global warming. Two concrete cores from this dam, one with fly ash and one without fly ash, are examined microscopically to explore the long-term suppression of alkali-aggregate reaction by fly ash. The core without fly ash exhibits clear evidence of alkali-aggregate reaction, manifested by sandstone coarse aggregate particles with darkened reaction rims. Sandstone coarse aggregate particles of the same lithology in the core with fly ash are without signs of alkali-aggregate reaction. A detailed examination of the darkened rims indicates that alkali-silica reaction products fill the narrow gaps between adjacent sand grains in the sandstone. This alkali-silica gel infilling allows for optical continuity between adjacent sand grains and is responsible for the classic darkened rim associated with the alkali-aggregate reaction.

Concrete Hydraulic Structures Affected by Alkali–Aggregate Reaction: Numerical and Experimental Investigations

Concrete Hydraulic Structures Affected by Alkali–Aggregate Reaction: Numerical and Experimental Investigations

Spalling of concrete caused by ASR – a review

A very well-known fact is that cracks in concrete members can allow water to enter the member, thus jeopardizing the concrete member integrity by changing the chemical composition of concrete and causing the aggregates to expand. This initiates the consequent chemical reactions that may evoke spalling of concrete thus creating a cycle of undesirable occurrences in concrete. As a final result, the concrete member can be deteriorated affecting the serviceability, but sometimes even leading the reduction of its load bearing capacity. An overlooked cause of concrete spalling of a chemical nature is the spalling caused by the Alkali-aggregate reaction. This is colloquially known as “concrete cancer”. It is a specific type of a reaction between alkali hydroxides and specific types of aggregate that occurs in concrete. Two main types of alkali-aggregate reactions are the alkali-silica reaction (ASR) and the alkali-carbonate reaction (ACR). The main goal of this research was to review the alkali-silica reaction in concrete as well as the mechanism of aggregate expansion it causes, which ultimately results in concrete spalling. Finally, the ways of prevention the alkali-silica reaction were reviewed and discussed.

Life-cycle dynamic analysis and probabilistic seismic risk assessment of cross-fault hydraulic tunnels considering AAR-induced deterioration

The alkali-aggregate reaction (AAR) triggered the deterioration of the machinistic property of concrete materials is among the major negative factor that results in the reduction of structural serviceability and performance for concrete structures, especially for those hydraulic engineering in contact with water for service life-cycle. Hydraulic tunnels, being a vital component of hydraulic engineering, are frequently employed in various lifeline projects around the world. Once the AAR effect renders the hydraulic tunnel inoperable, the government and society will suffer enormous economic losses, delaying the achievement of carbon neutrality. However, current specification for seismic design does not account for the degradation of structural performance parameters induced by AAR effects, which cannot fully reveal the earthquake performance of AAR-affected tunnels during use. Having realized this challenge, this work presents a mechanical model of the AAR effect integrating the concrete elastic-plastic damage model to conduct the inelastic dynamic response and random earthquake risk assessment of AAR-affected cross-fault hydraulic tunnels with design life-cycle. To this end, a study of the AAR-affected hydraulic tunnels, which consider the fluid-structure-surrounding rock coupling systems throughout the service period, is undertaken to associate the structural reaction with the predefined evaluation index directly. Subsequently, The nonlinear dynamic assessment of cross-fault hydraulic tunnel is conducted by using increased dynamic method to generate several data. Besides, this research constructs the three-dimensional (3D) time-dependent fragility surfaces considering the AAR effect and seismic intensity level. The results of this study underscore this point that the AAR effect possesses the capability to aggravate the response of relative displacement and extend the cumulative damage cracking area of the cross-fault hydraulic tunnels (CFHTs) with the increase in service time. Similarly, the 3D time-varying fragility surfaces show that the longer the service time of AAR-affected cross-fault hydraulic tunnels, the more likely they are to collapse. The above phenomena demonstrate that the AAR effect can be recommended for the utilization in estimating the likelihood of the erosion of the building during service life-cycle and future seismic design code.

Use of Coal Mine Overburden as Sustainable Fine Aggregate in Cement Mortar

The natural aggregate crisis is an alarming concern for the construction industry worldwide. This study provides a detailed investigation of coal mine overburden (OB) from opencast mine dumps, to evaluate its potential as a sustainable alternative to natural aggregate. The microproperties, including mineralogy, morphology, and chemistry, were evaluated, and the macroproperties, including alkali–aggregate reaction, soundness, durability, flow value, ultrasonic pulse velocity, and other mechanical properties of crushed OB, OB-based mortar, and concrete, were determined. OB was found to be mineralogically more stable (55%–77% SiO2), mechanically comparable, and durable (volume change 3%–8%) than other alternatives of natural aggregate. The toxicity characteristic due to leaching was found to have no hazardous effects on local and regional soil and water quality. The cement mortar prepared using OB had similar performance in terms of fresh and hardened density, flowability (>0.6 w/c), and durability [slake durability index (SDI) >95%] as other industrial by-products. The compressive strength of the mortar with OB was found to be comparable to that of mortar with river sand. OB-based mortar and concrete were found to have good corrosion resistance. For bulk utilization of OB, a pilot-scale study is recommended to assess its performance under real-world exposure conditions.

Study of the mechanism of inhibiting alkali-aggregate reaction and self-healing in concrete materials

Concrete is one of the most widely used materials in the world; however, several pathological manifestations can be associated with the design, execution, and selection of its constituent materials. Cracks, one of these pathological manifestations, are caused by the alkali-aggregate reaction (AAR). This is a chemical phenomenon in which silica, which is present in aggregate, reacts with alkali ions of the cement paste to produce an expansive silica-alkali gel. Herein, the clogging mechanism of the pathological cracks, which form during AAR, was investigated using a reference mortar trace, in order to select innocuous and reactive aggregates. Expansion in the mortar mix was examined using these two types of aggregates: (i) a potentially reactive aggregate, which can promote the formation of pathological cracks during AAR, and (ii) an innocuous aggregate to establish a reference trace without any expansive reaction. Subsequently, a concrete mix was characterized and reactivities of its constituents evaluated. In addition, fine and coarse granulometry analyses were performed. The concrete mix was dosed with the mortar mix, which comprised potentially reactive aggregate, and the bars were molded for the expansion tests. The crystalline mineral additive was added in these concretes to observe the clogging of the cracks. Comparative evaluation of the concrete mix, with and without reactive aggregate, suggested the occurrence of clogging because of the autogenous healing caused by chemical reactions, resulting in a reduction in the expansion of the concrete bars, with crystalline additive, at day 56.

Statistical Design of Eco-Friendly Mortar Mixtures Containing Scheelite Tailings and Quartzite Sand: Evaluation of Resistance to Alkali-Aggregate Reaction

This study focuses on addressing the challenge of society’s consumer demands through sustainable production processes, as outlined by Sustainable Development Goal 12 established by the United Nations. In this context, this study aims to assess the durability of eco-friendly mortars with mineral waste as alternative raw materials, considering the alkali-aggregate reaction (AAR). For this purpose, scheelite tailing (ST) was used to partially replace Portland cement (PC), and quartzite sand (QS) was used to fully replace conventional sand. The ST was ground and sieved (<75 μm), and part of it was used in its natural form, while the other part was calcined (1000 °C for 1 h). A mixture experimental design was created to select the compositions with the best mechanical performance. All the mortar mixtures were produced with a cementitious material to QS ratio of 1:3. Three mortar compositions (0% ST, 30% natural ST, and 30% calcined ST) were selected to study the resistance to the AAR. Linear expansion measurements, compressive strength tests, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were conducted to evaluate the phases formed and the mechanical behavior of the mortars in relation to the AAR. The expansion results demonstrated that QS does not exhibit deleterious potential. Regarding the use of ST, the results indicated that it is possible to partially replace PC with calcined ST without significantly compromising the mechanical performance and durability of the mortars. However, the use of non-calcined ST is not recommended, as it presents deleterious effects on the mechanical properties of the mortars. This study highlights a new sustainable mortar alternative for use in construction without future degradation of its properties.

Concrete Alkali–Aggregate-Reactivity-Induced Steel Reinforcement Corrosion

The alkali–aggregate reactivity (AAR) of concrete, long known for mass concrete, can also induce corrosion of steel in reinforced concrete structures. Several examples are given for which the origin of observed reinforcement corrosion and loss of concrete cover originally was attributed to chloride-induced or to carbonation-induced reinforcement corrosion. Critical reviews of these cases, using available information, suggest that, more likely, the observed crack patterns and concrete deterioration are the result of long-term AAR-induced concrete matrix expansion and loss of concrete strength and that these effects occurred prior to the eventual initiation of reinforcement corrosion. This proposition is supported by finite element and other stress analyses of various concrete–steel ensembles. They show that concrete expansion produces tensile stresses localised at and near exterior concrete surfaces or relative to the reinforcement. The locations of high-stress and -strain zones so produced correlate with field observations of long-term concrete cracking and delamination. The present interpretations highlight that AAR may be a significant contributor to initiation and subsequent long-term development of reinforcement corrosion in structurally reinforced concretes.

Evaluation of the Alkali-Aggregate Reaction Mitigation Potential of Alkali-Activated Fly Ash-Based Matrices Containing Different Reactive Aggregates

The present study evaluated the use of alkali-activated fly ash-based matrices containing different reactive aggregates (quartz, basalt and limestone) to mitigate the alkali-aggregate reaction (AAR). The fly ash activation was performed with sodium hydroxide (NaOH) solution, with a molar ratio (Na2O/SiO2) of 0.4. Reference matrices were prepared using Portland cement type V (ARI). All composites were prepared with a mass ratio of 1:2.25:0.47 (binder: aggregate: water/agglomerant ratio). The petrographic analyses allowed the identification of potentially reactive phases in the three studied aggregates. From the results, it was verified that the Portland cement-based matrices with basalt and quartz aggregates confirmed the reactivity of these aggregates. On the other hand, the reactivity of the same aggregates was not manifested in the CVAA-based matrices, classifying the basalt and quartz aggregates as innocuous in the alkali-activated matrix. Therefore, CVAA-based matrices mitigated AAR when using reactive basalt and quartz aggregates. However, the limestone aggregate did not show reactivity in the matrices studied.

Failure Mechanisms and Rehabilitation Scenarios for Concrete Hydroelectric Facilities Affected by Alkali–Aggregate Reaction

This work focuses on the failure mechanisms of concrete hydroelectric facilities affected by alkali–aggregate reaction (AAR). Identification of potential failure mechanisms is based on an original “top-down approach” using an AAR pushover analysis with multi-physics numerical simulation of a representative hydroelectric facility. Different global rehabilitation scenarios based on slot-cutting and grouting techniques are discussed and compared, using different performance metrics. A new quantitative performance metric, specifically developed for the nonlinear sophisticated analysis tool and considering the volumetric cracking caused by AAR is also suggested. Based on comparison results, a combination of grouting after a partial slot-cutting in the neighborhood of the discontinuities, appears to provide the best compromise in terms of stress relief and extent of cracking. New AAR benchmark problems, issued from the top-down approach, are also suggested for the first time in the literature.