Alkali-silica Reactive Aggregates Research Articles

A visual condition assessment of a reinforced concrete railway bridge subject to alkali silica reaction (ASR) deterioration in Johannesburg

In the 1940’s, a reinforced concrete (RC) railway bridge located in central Johannesburg was constructed using Witwatersrand Quartzite, at the time, unknown to be an alkali-silica reactive aggregate. The bridge currently displays signs of distress in the form of severe map-cracking. This study presents preliminary results of a series of tests that have been conducted to characterise the severity of alkali silica reaction (ASR) deterioration in the bridge. Twelve concrete cores were extracted for testing from various locations of the railway bridge, which displayed varying degrees of distress. A visual assessment was conducted globally on the entire structure as well as locally (using modified damage rating index (DRI) approach) on the extracted cores. The findings showed that there was extensive map-cracking present on all thirteen railway bridge elements examined, revealing signs of distress in the bridge. Even elements that were sheltered from exposure to direct rain, such as the underside of three arch surfaces, also exhibited extensive map-cracking. Furthermore, the modified DRI method was a useful technique to assess and compare the relative extent of damage of concrete taken from various locations of a RC structure, using local images of the cylindrical surface of the concrete cores.Graphical

Assessment of potential alkali-silica reactivity of aggregates for concrete

The detection of concrete structures affected by Alkali-Silica Reaction (ASR) has increased dramatically over the past couple of decades in Portugal. Due to the complexity and multiplicity of factors involved in ASR together with the variability of the materials used, no International or European standards exist for assessing the aggregates potential alkali-reactivity, and each country must rely on national regulations or specifications. Because of that, in Portugal, LNEC Specification E 415 was prepared in 1993 and LNEC Specification E 461 was introduced in 2004 and revised in 2007. However, due to the scientific developments occurred since then, new revised versions were prepared and will soon be published. Although, LNEC Specifications provide guidance on the identification of potentially alkali-silica reactive aggregates, there are still some knowledge gaps on how to reliably assess the potential reactivity of some minerals present in granites and similar rocks, which are the type of aggregate most used in large concrete structures in Portugal. Therefore, to contribute to the current ongoing discussion on the role of the main components of these rocks on ASR development, this paper presents the methodology that was applied in the evaluation of concrete granitic aggregates used in recently built hydroelectric projects as well as in a dam constructed abroad several decades ago, and in which the deleterious development of ASR was detected 15 years after construction.

Preliminary evaluation of Pier cap from an ASR affected bridge in Central Canada

The Bridge, a highway bridge structure, was built using a suspected alkali-silica reactive aggregate in the 1960’s in a city in central Canada. Its concrete elements experienced rapid deterioration resulting in the need for costly increased repairs and rehabilitations. Alkali-silica reaction (ASR) is one of several damage mechanisms which might be contributing to damage of concrete elements. Infrastructure in central Canada experiences frequent freeze-thaw cycles, and heavy use of de-icing salts in winter as well as high heat and humidity in summer which might intensify distress. In recent years several concrete elements were selected for further assessment. Among them, five segments of a decommissioned Pier cap were selected for preliminary evaluation through visual inspection (conventional, semi-quantitative and quantitative using the cracking index) and non-destructive techniques (Schmidt hammer, ultrasonic pulse velocity and surface resistivity). Preliminary assessment results will be used to determine the appropriate locations (i.e., demonstrating the lowest/ highest deterioration) to extract cores for further assessment. Future work will be conducted on extracted cores using a multi-level assessment technique consisting of mechanical (compressive testing and stiffness-damage test) and microscopic procedures (the damage rating index and SEM) to assess the condition of the Pier cap.

Condition assessment of an ASR-affected overpass after nearly 50 years in service

RBC overpass was a highway bridge structure that was built using an alkali-silica reactive aggregate. Over nearly 5 decades, many signs of distress were developed on the various RBC structural members mainly due to alkali-silica reaction (ASR). In 2010/2011, RBC overpass was demolished and thus a number of cores from the various structural members were extracted, which enabled the condition assessment of the structure through a comprehensive multi-level protocol. This paper presents the outcomes obtained from the overall evaluation of RBC members. Results show that the damage degree of the distinct members vary according to the member’s type and condition. Very high, high and moderate damage levels were found for the foundation blocks, bridge deck and columns of the structure, which indicates that RBC overpass was not in accordance with Canadian safety protocols by the time of its demolition and raises concerns regarding the structural implications of ASR-affected infrastructure.

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.

GEOLOGICAL STUDY AND MINING PLAN IMPORTANCE FOR MITIGATING ALKALI SILICA REACTION IN AGGREGATE QUARRY OPERATION

More than 80 million tonnes of construction aggregate are produced in Peninsular Malaysia. Majority of construction aggregate are produced from granite. Developing regions of Johor Bahru, Kuala Lumpur, Penang and Selangar utilize granite aggregates. Normally it is considered aggregates as non-alkali reactive. Geological study can identify various rock types, geological structures, and reactive minerals which contribute to Alkali Silica Reaction (ASR). Deformed granites formed through faulting results in reduction of quartz grain size. Microcrystalline quartz and phyllosilicates are found in granites in contact with country rocks. Secondary reactive minerals such as chalcedony and opal may be found in granite. Alkali Silica reaction is slow chemical reaction in concrete due to reactive silica minerals in aggregates, alkalis in cement and moisture. For long term durable concrete, it is essential to identify potential alkali silica reactive aggregates. Lack of identifying reactive aggregates may result spalling, cracking in concrete and ultimately ASR can result in hazard to concrete structure. This paper deals with geological study of any aggregate quarry to identify rock type and geological structures with laboratory test –petrographic analysis and bar mortar test can identify type of aggregates being produced. Mine plan with Surpac software can be developed for systematic working for aggregate quarry to meet construction aggregate demand.

Potential alkali silica reactivity of various rock types in an aggregate granite quarry

Generally, alkali–silica reaction (ASR) is considered as an internal chemical reaction between the alkaline components in the cement and active silica–silicate based mineral constituents of some aggregates. The use of aggregates susceptible of ASR in concrete can cause a severe degradation of the concrete structures because of several reasons e.g. high humidity and sea saline water. Utilization of potentially alkali–silica reactive aggregates needs to conduct reliable tests for evaluating their alkali–silica reactivity. The objective of this study is to identify the potential alkali–silica reactivity of several aggregate rock types. To achieve this objective, a granite quarry which is operated to produce aggregates was selected and investigated. Six samples of five igneous rock types were collected from the mentioned site and an extensive laboratory tests consisting of petrographic examination and accelerated Bar Mortar test were conducted on these samples to assess the potential alkali–silica reactivity. According to ASTM C 1260 suggested method, three Bar Mortar tests were performed on each sample. Based on the obtained results, it was found that five samples of all six samples were considered as innocuous due to their average expansion rates which are less than 0.1%. Only one sample which was collected from the fault zone considered as reactive with average expansion rate of 0.2404% which is more than 0.2%.

Experimental investigations to evaluate the alkali-carbonate reactivity and alkali-silica reactivity of aggregates

The objective of this paper was to evaluate the alkali-silica reactivity (ASR) and alkali-carbonate reactivity (ACR) of the 14 aggregate groups quarried from different locations. In order to serve the stated purpose, the investigated aggregate groups were tested in determining their alkali-silica reactivity using the ASTM C 1260 at the ages of 2, 4, and 8 weeks, and the modified ASTM C 1293 (prisms submerged in the 1N NaOH at 80°C) at the test durations of 4, 8 and 13 weeks. The aggregate prone to the alkali-carbonate reactivity was accessed using the ASTM C 1105 at the ages of 3, 6 and 12 months. The study revealed that the aggregates susceptible to alkali-carbonate reactivity were also shown to be reactive due to the alkali-silica reactivity.

Reliable quantification of AAR damage through assessment of the Damage Rating Index (DRI)

This paper presents the results of the condition assessment of twenty concrete mixtures incorporating ten different reactive aggregates through the Damage Rating Index (DRI), a microscopic and semi-quantitative petrographic tool, with the aim of verifying the development of distress due to alkali-aggregate reaction (AAR) as a function of the specimen's expansion (i.e. from 0.05 to 0.30%). The DRI was found to provide a reliable assessment of the degree of damage in the concretes incorporating reactive fine or coarse aggregates. An envelope of DRI damage assessments against the expansion level of the affected materials is proposed. For all alkali–silica reactive aggregates investigated, the progress in counts and proportions of opened cracks in the aggregate particles and in the cement paste, with and without gel, as well as the crack density parameter, were found to be diagnostic petrographic features for quantifying ASR progress. Moreover, a qualitative ASR distress model in concrete was defined.

A kinetic-based ASR aggregate classification system

A kinetic approach which as-received aggregates were immersed in alkaline solution of varying concentrations and allowed to react at different temperatures was proposed in this study to calculate ASR compound activation energy (CAE) as a measure of alkali silica reactivity of aggregate. The tested aggregates were categorized based on the measured CAE to form an ASR aggregate classification system. The classification system (i) overcomes the limitations and drawbacks of the current test methods, (ii) correctly identifies the aggregates that belong to false positive and negative categories (i.e., failed by ASTM C 1260 but passed by ASTM C 1293 and vice versa), (iii) has the ability to test field aggregates and determine reactivity matching with the field level of alkalinity, and (iv) can serve as an alternative to the current ASR test methods.

Alkali–silica reactivity of alkali volcanic rocks

The purpose of this study is to determine the alkali silica reactivity (ASR) of alkali volcanic rocks (from basalt to rhyolite) that have different mineralogical, chemical compositions and textures. For this purpose, nine different alkali volcanic samples, located in seismically active Lake Van region, were collected from five different volcanic area named as Etrüsk volcano, Girekol volcano, Timar, Yüksektepe and Bendimahi. Petrographical analysis, chemical method and accelerated mortar bar test results showed that intermediate and acidic alkali volcanic rocks are deleterious but basic alkali volcanic rocks are innocuous in terms of ASR. It is concluded that the products resulted from alteration processes, amount of volcanic glass in the aggregate and magma-mixing processes of the magma chamber in which rocks are formed may be effective in ASR of aggregates.

USE OF PUMICE AND SCORIA AGGREGATES FOR CONTROLLING ALKALI SILICA REACTION

Turkey has important potential pumices reserves (68% of the reserve of the world) and especially, 56 % of pumice reserve of Turkey is in the East Anatolia Region. It is important to assess huge mine, pumice, reserve in Eastern Turkey for its use in the cement and concrete industry. Use of acidic pumice and basic pumice (scoria) as cement additive or aggregate are gaining popularity because of their proven structural/durability properties. This paper presents the results of an investigation to assess the effectiveness of pumice and scoria aggregates in controlling alkali silica reaction (ASR) of alkali silica reactive aggregate using the following test methods: the accelerated mortar bar test (ASTM C 1260) and the scanning electron microscopy technique (SEM). The morphologies, structures and properties of the samples were determined by XRD, ICP-MS, XRF and thin section study. Mortar cubes were specially prepared as per ASTM standards using 10, 20 and 30% pumice or scoria aggregate as alkali silica reactive aggregate replacement. The results are then compared with ASTM requirements to assess the suitability of pumice or scoria for preventing alkali silica reactivity. According to the results of these methods, pumice aggregates control the alkali silica reaction whereas scoria aggregates decrease expansion but is not as effective as pumice in preventing ASR. The results of SEM analysis showed alkali silica gel formation and serious decomposition of aggregate texture due to ASR in scoria added mortar bars.

Alkali–silica reactivity of some common rock types. A global petrographic atlas

The correct identification of potentially alkali–silica reactive aggregates is important for the prevention of alkali–silica reaction (ASR) in concrete. Although a number of standards for assessment of concrete aggregate by petrography are available, distinction of potentially deleterious from innocuous rock types can be problematic. The application of geological nomenclature alone is insufficient, as the geological history and hence mineralogical texture of a given rock type may strongly influence its performance in concrete. One of the goals of RILEM TC 219-ACS is to develop a worldwide photo atlas as a guide for petrographers in the identification of the mineral compositions and textures that are characteristic of alkali-reactive rocks. The atlas is based on micrographs of rock types recognized as potentially deleterious by field performance and/or laboratory expansion testing. It is intended to serve as an independent reference work and aims to unify rock terminology so as to improve the petrographic characterization of aggregates. The mission of RILEM, the International Union of Laboratories and Experts in Construction Materials, Systems and Structures (Reunion Internationale des Laboratoires et Experts des Materiaux), is to advance scientific knowledge in the field of construction. Its Technical Committee TC 219-ACS focuses on alkali reactions and their effects on concrete.

An Improved Test Method for the Detection on Alkali-Silica Reactivity of Aggregate

Test the alkali-silica reactivity of slate aggregate in Guizhou using mortar-bar method in JTG E42-2005of China and accelerated mortar-bar method in TB/T2922.5-2002 of China. The results show that the six months expansion is 0.11% with mortar-bar method, the aggregate has low alkali activity. The 14-days expansion exceeds 0.30% with accelerated mortar-bar method, according to the TB10005-2010, the aggregate has high alkali reactivity. Obviously, the accelerated mortar-bar method is safer than the mortar-bar method, but the test parameters and test conditions of accelerated mortar-bar method have some differences with the aggregate physical environments. According to the accelerated mortar bar method, the thesis proposes an improved test method for evaluating the alkali-silica reactivity of slate aggregate.

Twenty-Year Field Evaluation of Alkali-Silica Reaction Mitigation

To evaluate measures to prevent alkali-silica reaction (ASR) in concrete and to correlate short-term laboratory tests to long-term performance, an outdoor exposure site was established in Kingston, ON, Canada, in 1991. Alkali-silica reactive aggregate was combined into six concrete mixtures using various cements and supplementary cementitious materials (SCMs). Both unreinforced and reinforced 0.6 x 0.6 x 2 m (24 x 24 x 79 in.) beams, and 0.2 x 1.2 x 4 m (8 x 48 x 158 in.) pavement slabs were instrumented and have been monitored for 20 years. The high-alkali cement concrete cracked at 5 years and low-alkali cement cracked after 12 years. The high-alkali cement was replaced with various amounts of SCMs. Two concretes, containing 50% ground granulated blastfurnace slag (GGBFS) and a ternary blend of 25% slag plus 3.8% silica fume interground with a high-alkali portland cement, have neither expanded nor cracked. After 14 years, cores were examined petrographically, chloride penetration profiles were made, and chloride diffusion as well as rapid chloride permeability tests, were performed.

Study of autoclave methods for evaluating the alkali-silica reactivity of aggregates

This research focuses on the feasibility of employing the mortar bar autoclave test (MBAT) and the concrete prism autoclave test (CPAT) for the evaluation of alkali-silica reactivity in 22 aggregates. ASTM C289, C227, C1293, AFNOR P 18-588, and JIS A 1804 tests were also conducted for purposes of comparison. Expansions of 0.05% for the MBAT, and the 0.04% CPAT method are suggested as criteria for the differentiation of non-reactive aggregate. Without underestimation, more than 90% of the results obtained from the MBAT were consistent with the ASTM tests. Each result obtained by the CPAT was similar to the ASTM tests. The ASTM C289, MBAT, and CPAT methods are recommended as effective tools for identifying non-reactive aggregate in routine or screening tests.

Role of Potassium Acetate Deicer in Accelerating Alkali–Silica Reaction in Concrete Pavements

About 15 years after the introduction of alkali–acetate and alkali–formate deicers, premature deterioration was observed on some airfield pavements that had been exposed to the deicers. A characteristic map cracking pattern was observed on pavement surfaces that had experienced repeated applications of these deicers, and the suspected cause of this cracking pattern was accelerated alkali–silica reaction (ASR). Laboratory-based research indicated that alkali–silica reactive aggregates may undergo active deterioration when intimately exposed to such deicers under conditions promoting accelerated reaction. Investigations were conducted on cores collected from an airport whose deicing operations involved repeated applications of potassium acetate deicer. Detailed microscopic investigation indicated that uniform distress existed throughout the depth of the pavement, although in one, the distress resulted from alkali-carbonate reaction rather than from ASR. However, investigations on the depth of penetration of deicer into these pavement cores showed only limited incursion. A companion laboratory study estimated the extent of deicer penetration under different laboratory exposure conditions. Even in a relatively aggressive wetting and drying exposure regime, ingress of the deicer was limited. Thus, it was concluded that although the potassium acetate deicer can induce severe ASR under aggressive laboratory conditions, penetration into field airport pavements may be so limited in some cases that the potassium acetate deicer does not seem to aggravate the ASR distress should one already exist.

Effect of fly ash on the expansion of concrete due to alkali-silica reaction – Exposure site studies

Abstract In this study 45 concrete blocks (915 × 915 × 815 mm or 350 mm cubes) containing alkali-silica reactive aggregates, and various levels of high-alkali cement and fly ash were placed on an outdoor exposure site in S.E. England for a period of up to 18 years to determine the efficacy of fly ash in controlling damaging alkali-silica reaction (ASR). The reactive aggregates used included a variety of flint sands and a crushed greywacke combined coarse and fine aggregate. Length-change measurements were conducted periodically throughout this period. All concrete blocks without fly ash showed excessive expansion and cracking within 5–10 years of production and in many cases the ultimate expansion exceeded 1.0% after 15–18 years. Fly ash used at replacement levels of 25% and 40% was effective in significantly reducing expansion and cracking with all three flint aggregates at all levels of alkali. Of the 27 blocks containing fly ash and flint sand only two blocks showed evidence of damage after 16–18 years. The expansion of these blocks was significantly lower than similar blocks with the same Portland cement content without fly ash. None of the blocks with greywacke aggregate and fly ash exhibited cracking (expansion data were not available for these blocks). Collectively the data confirm that fly ash, when used at levels of 25–40%, does not effectively contribute alkalis to the alkali-silica reaction.

Effect of environmental conditions on expansion in concrete due to alkali–silica reaction (ASR)

The environmental conditions to which a concrete element incorporating alkali–silica reactive aggregates is exposed play a major role in dictating the progression and manifestation of the reaction. This paper reports and analyses the results of research programs investigating the comparative evaluation of the effect of environmental conditions on the development of alkali–silica reaction (ASR) in concrete specimens stored in outdoor exposure at the authors' respective laboratories. This data is compared to samples subjected to laboratory testing (controlled environmental conditions). Concrete mixtures that incorporate reactive aggregates with varying reactivity levels are compared. The focus of this paper is on control concretes e.g. 100% opc + reactive aggregate (coarse or fine).

Alkali-silica reactivity of different aggregates from mineral and textural characteristics

To identify the aggregates causing the alkali-silica reaction, and the reactivity of rocks in different parts of China, the mineral and texture characteristics of some typical coarse aggregates and the alkali reactivity of these aggregates were systematically investigated. On one hand, petrographic examination of aggregates, combined with X-ray diffraction analysis, chemical analysis, scanning electron microscopy, was conducted for analyzing their mineralogy and texture. It was found that not only mineral characteristics, but also their interior structure would affect their potential alkali-silica reactivity. Furthermore, the alkali-silica reactivity of aggregates is due to their mineral compositions, such as containing different alkali-reactive minerals, while, different stuctures of those aggregates with similar minerals affect their reactivity to some extent. There are some amount of micro-aperture and cracks across the quartz in the aggregate, which may become the natural accesses for Na+, K+, and OH− ions to intrude in the mortar or concrete during the process of alkali-silica reaction. Alkali-silica reactivity of the aggregates was detected by the accelerated mortar bars test. It was revealed that all the aggregates tested were alkali-silica reactive and the results were also in accordance with their mineral and structure analysis.