Potential Alkali-silica Reactivity Research Articles

Alkali-silica reaction in calcium aluminate cement mortars induced by deicing salts solutions

Calcium aluminate cement (CAC) mortars and concrete may be used as high-performance repairing materials for pavement restoration in airfields and roads. During recent years alkali-silica reaction (ASR) was reported in Portland cement concrete subjected to the action of organic deicers. Present paper reports the results of the investigation on the influence of organic and inorganic alkali deicers on ASR potential in CAC mortars containing fused silica as model reactive aggregate. It was shown for the first time, that concentrated solutions of sodium and potassium acetates, as well as sodium chloride, can cause ASR in CAC mortars. Sodium and potassium acetate resulted in much larger expansions comparing to sodium chloride and sodium hydroxide solutions used as a reference. Differences in alkali-silica gel were found depending on the solution which samples were soaked in. It was shown that ASR could proceed in a system without calcium hydroxide and an external source of hydroxyl ions.

Evaluation of the chemical index model for predicting supplementary cementitious material dosage to prevent the alkali-silica reaction in concrete

This study investigates the chemical index model effectiveness in predicting the minimum replacement of several types of Supplementary Cementitious Materials (SCMs) to mitigate the potential Alkali-Silica Reaction (ASR) in concrete. The experimental program results evaluating four natural aggregates (AF1, AF2, AF3, and AF4) and two Recycled Concrete Aggregates (RCA1 and RCA2), as presented here, were used in the model predictions. The SCMs used in this study consisted of fly ash class C (FA1), fly ash class F (FA2), ground granulated blast-furnace slag (SL), and silica fume (SF). For each SCMs, three levels of Portland cement replacements were used in the production of mortar bars: 15%-20%-25% for FA1-FA2; 20%-40%-60% for SL; and 5%-8%-10% for SF. The natural aggregates were tested according to the ASTM C1260 accelerated mortar bar test. For the RCA, an alternative preparation procedure was applied in the experimental phase to eliminate variability in the results given the RCA's high absorption.Further testing was then implemented for the aggregates classified as potentially reactive by evaluating different SCMs replacement levels to mitigate ASR using the accelerated mortar bar method, following the ASTM C1567. A Monte Carlo simulation was conducted to evaluate the chemical index prediction uncertainty, based on the model inputs statistical variation. The SCMs evaluated in this investigation were effective in mitigating ASR while used in sufficient proportion. The most effective SCMs in reducing ASR was silica fume, with a 10% replacement of Portland cement's weight, fly ash class F was next (15–25%), and finally ground granulated blast-furnace slag (40–60%). The chemical index has proven to give good results when predicting the minimum replacement of supplementary cementitious materials required to suppress ASR based on its chemical composition.

Alkali-silica reaction (ASR) - Investigation of crystallographic parameters of natural sands by backscattered electron diffraction

abstract: This study involved analyzing several natural sands to ascertain the possible causes for distress due to ASR. The analyses were performed using the following techniques: X-ray diffractometry, accelerated mortar bar tests (AMBT), electron backscattering diffraction and elementary chemistry analyses, by FEG-SEM/EBSD/EDS. These experiments allowed identifying the presence of several mineral composites (such as microcline, anorthite, among others), as well as the microstructural-crystallographic planes of quartz (such as the Dauphiné type). From the results it could be inferred that the multiple techniques used, especially the FEG-SEM / EBSD, proved to be promising in the analysis of the ASR potential of sands for use in Portland cement mortars and concretes.

Reliability of Miniature Concrete Prism Test in Assessing Alkali-Silica Reactivity of Moderately Reactive Aggregates

Alkali-silica reaction (ASR) is one of the most significant durability issues in concrete structures. Although there are a number of standardized test procedures to evaluate the aggregate reactivity, each method has its own drawbacks. Two of the most common tests that are employed widely are the accelerated mortar bar test (AMBT) (ASTM C1260) and the concrete prism test (CPT) (ASTM C1293). The major issue with the AMBT test is the number of false-positive results from this test associated with high test temperature, rendering the test method unreliable. CPT is one of the most reliable tests for assessing the potential for ASR, but its major disadvantage is the duration of the test involved, which takes one to two years. In this research, a novel test method called the miniature concrete prism test (MCPT) was developed and the effectiveness and reliability of the results assessed when compared with CPT and AMBT. Samples of 26 coarse aggregates and 16 fine aggregates with various reactivity levels were employed for the testing. The test results were compared for MCPT versus CPT, in which 23 out of 26 coarse aggregates and eight out of 16 fine aggregates either passed or failed in both MCPT and CPT. For MCPT versus AMBT, 16 out of 26 coarse aggregates and 13 out of 16 fine aggregates either passed or failed in both MCPT and AMBT. The sensitivity of false-negative and false-positive aggregate sources is discussed and explained briefly.

Hawaiian and Azorean volcanic aggregates: a preliminary study of the potential alkali-silica reaction

The alkali-silica reaction (ASR) is a chemical deterioration of concrete that involves reactive forms of silica. Volcanic glass is one of the potentially reactive forms of silica that can be present in volcanic rocks such as basalts. The aggregates used for concrete purposes from the Azores and Hawaiian Archipelagos are mainly of basic composition (basalts s.l.). In general, there is no report of ASR damaged structures in both archipelagos. However, in order to evaluate the behavior of these rocks regarding ASR and to compare the rocks from the two archipelagos, a set of methodologies were performed on a total of twenty-one volcanic aggregates. Geochemical analysis, total alkali-silica diagram, CIPW norm calculation, and petrographic analysis are some of the methods used for the assessment and analysis of rocks. The study was also complemented by electron probe microanalysis (EPMA) in order to identify the composition of volcanic glass and by X-ray diffractometry (XRD) for the Hawaiian aggregates. The results obtained from the studied aggregates showed that there are some differences between the two archipelagos. The rocks from the Azores are alkaline while the majority of the rocks from Hawaiian Archipelago are tholeiitic. The petrographic study revealed that the analyzed rocks from the Hawaiian Islands contain a higher quantity of interstitial volcanic glass than those from the Azores Archipelago. The EPMA carried out in some samples from the Hawaii showed that the volcanic glass has a composition of silica higher than 65%, value that is considered in the literature as potentially reactive.

Effective Utilization of Waste Glass as Cementitious Powder and Construction Sand in Mortar.

The purpose of this study is to investigate the availability of waste glass as alternative materials in sustainable constructions. Collected waste glass was ground into waste glass powder (WGP) with similar particle size distribution as Portland cement (PC) and waste glass sand (WGS) with similar grade as sand. The compressive strength was investigated through the Taguchi test to evaluate the effect of different parameters on WGP-blended mortar, which include WG-replacement rate (G/B, 0, 10%, 20%, 30%), water/binder ratio (w/b, 0.35. 0.40, 0.50, 0.60), cementitious material dosage (Cpaste, 420, 450, 480, 500 kg/m3), and color of powder (green (G) and colorless (C)). The alkali–silica reaction (ASR) expansion risk of WGS-blended mortar was assessed. The experimental results indicated that WGP after 0.5 h grinding could be used as substituted cement in mortar and help to release potential ASR expansion. The replacement rate played a dominant role on strength at both the early or long-term age. The water/binder ratio of 0.35 was beneficial to the compressive strength at three days and 0.50 was better for strength at 60 and 90 days. An optimal value of cementitious material dosage (450 Kg/m3) exited in view of its strength, while the effect of the color of WG was minor. WGS could be graded as standard construction sand and no ASR expansion risk was found even for 100% replacement of regular sand in mortar. Through the comprehensive reuse of waste glass, this study could provide basic knowledge and a concept for the sustainable development of building materials.

A Modified Chemical Index to Predict Fly Ash Dosage for Mitigating Alkali-Silica Reaction

Abstract It is well chronicled that coal fly ash can mitigate the risk of alkali-silica reaction (ASR) in concrete structures. However, the efficacy of individual fly ashes is highly dependent on their chemical composition. Prescriptive requirements for ASR mitigation have largely focused on whether the fly ash is classified as Class F or Class C per ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, whereas performance requirements may require extensive testing to satisfactorily demonstrate mitigation potential of a fly ash. Previous research established the need for an accurate model to predict required fly ash replacement rates for ASR mitigation based on the chemical constituents of cement and fly ash. Therefore, a new model is proposed to account for the availability of each chemical constituent from cement and fly ash separately, utilizing ASTM C1260, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method), and ASTM C1567, Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar Bar Method), test data. The successful development of models based on 14-day and 28-day expansion data from these tests is presented in this article.

The role of composition in the structure and water-binding in alkali-silica reaction sol and gel

The discrepancy between alkali cation (Na+) used in accelerated assessments of potential alkali-silica reactivity (ASR) and those predominant in portland cements (larger amounts of K+ than Na+) leads to questions regarding the reliability of standardized test methods to predict concrete field performance. To better understand the role of alkali cation type in ASR, this study investigates the influence of alkali cation type on the structure and water-binding ability of ASR sols and gels of varying composition. Results obtained by small-angle neutron scattering, 1H NMR relaxometry, and rheological measurements indicate the formation of densified agglomerate structures with increasing silica-to-alkali molar mass ratios (S/A). However, Na-based sols exhibit a greater tendency to agglomerate and a higher dynamic viscosity than K-based ones. Furthermore, at high S/A, 1H NMR relaxometry shows the greater ability of K-based gels to bind water, suggesting the better dispersion of siliceous structures and the development of finer porosities.

Mitigation of the potential alkali–silica reaction of FNS using ground FNS as a supplementary binder

Alkali–silica reactivity of granulated ferronickel slag (FNS) aggregate was evaluated by accelerated mortar bar tests. The test results showed noticeable expansions of the samples containing 50% FNS aggregate due to potential alkali–silica reaction (ASR). On the other hand, finely ground FNS (GFNS) exhibited pozzolanic property in the studies of compressive strength development, thermogravimetric analysis and X-ray diffraction analysis. Therefore, GFNS was used as a partial replacement of cement to study its effect on the reduction of ASR. It was found that the use of GFNS for at least 30% cement replacement reduced the 10 d and 21 d mortar bar expansions below the allowable limits. The consumption of portlandite by the pozzolanic reaction of GFNS is considered as the primary reason for the reduction of expansion. The ASR mitigation process of GFNS was further confirmed by scanning electron microscopy images and energy-dispersive X-ray spectroscopy of the reaction product.

Impact of pore solution concentration on the accelerated mortar bar alkali-silica reactivity test

The accelerated mortar bar test (AMBT), commonly used for evaluating the potential alkali-silica reactivity (ASR) of aggregates, is unreliable in some cases. Likely, this lack of reliability is due in part to the 80 °C temperature and the 1 N NaOH storage solution specified in the test differing significantly from field conditions. Therefore, the influence of temperature and storage conditions on pore solution composition was studied. The AMBT procedure was modified accordingly and improvements in the accuracy were assessed against the results of the concrete prism test at 38 °C (CPT) and the accelerated concrete prism test at 60 °C (ACPT), as well as known field performance. Modifying the temperature of the standard AMBT to 60 °C and the storage solution to 0.65 N KOH + 0.15 N NaOH, for more representative pore solutions was found to only improve the accuracy for aggregates exhibiting pessimum behaviour.

The use of micro and nano-sized particles in increasing concrete durability

The main objective of this research is to increase the concrete durability by reducing deleterious alkali-silica reactivity (ASR) which results in a substantial damage to concrete members due to induced internal stresses. ASR reaction is initiated when the silica content of the aggregate reacts with Alkali Hydroxide in the mix in the presence of relatively high moisture content. The expansive ASR reaction results in the formation of an expansive gel-like material which induces destructive internal stresses within hardened concrete. In this research, micro and nano-sized supplementary cementitious materials (SCMs) are used in producing concrete with potential ASR reactivity. The micro and nano-sized particles resulted in a reduced air content and smaller void ratio of the produced concrete. The reduced concrete voids resulted in a lower permeability; hence, reduced water content, for the produced concrete, which resulted in a substantial reduction in ASR reaction. Results showed that the reduced ASR reaction is directly correlated to the fineness of the incorporated particles. The outcomes of this research will help to maintain the conditions of ASR prone highway construction projects and reduce the maintenance, repair, and replacement budgets required for the highways network.

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.

Feasibility Study on Concrete Performance Made by Partial Replacement of Cement with Nanoglass Powder and Fly Ash

In this paper, the feasibility of using nanoglass as a partial replacement of cement in combination with fly ash was investigated. Three concrete mixtures made with fly ash and nanoglass as cement replacements were studied as a preliminary investigation. The first mixture contained 25% class F-fly ash (FA) and 0% nanoglass powder (NGP); the second mixture had 12.5% class F-FA with 12.5% NGP; while the third mixture had 0% class F-FA, with 25% NGP. In all the mixtures, the water-to-cementitious (w/cm) ratios were kept constant at 0.42. Fresh properties of each mixture were tested, which included air content and workability. Expansion due to potential alkali–silica reaction (ASR) was also tested, as well as mechanical properties such as compressive strength, tensile strength, and flexural strength. It was observed that the increase in NGP content beyond 12.5% in the presence of 12.5% class F-fly had a negative effect on the concrete fresh and mechanical properties. Overall, the addition of NGP enhanced the mechanical properties of the concrete, and the expansion due to ASR is less than 0.1% which is the threshold value.

A Literature Review on Alkali Silica Reactivity of Concrete

Deterioration of concrete structures with time is well understood. One of the major reasons of deterioration is reaction between cement paste and reactive siliceous aggregates which is known as alkali silica reaction (ASR). This article reviews the studies on ASR in concrete. Although a vast literature is available on mechanisms and preventive measures against ASR, however there are still a lot of deficiencies regarding the test methods to detect the ASR potential in concrete. The aim of this article is to discuss different factors affecting ASR, consequences of ASR and different challenges encountered by researchers in the detection of ASR. The study revealed that alkali content of cement, aggregates grading, mineralogical combinations, testing methods and testing conditions are all the challenges, researchers face during evaluation of ASR potential in concrete.

Potential alkali silica reaction expansion mitigation of ferronickel slag aggregate by fly ash

This study investigates the potential alkali silica reaction (ASR) of ferronickel slag (FNS) aggregate, which is a by‐product of nickel production. A class F fly ash was used as a possible ASR mitigation in accelerated mortar bar test (AMBT) specimens containing 50% FNS. There were visible surface cracks on the specimens using no fly ash or 10% fly ash. Use of 20% fly ash reduced expansion by 45% as compared to that with 10% fly ash. In accordance with the expansion limits of Australian Standard, the mixtures using 20 and 30% fly ash were categorized as slowly reactive and nonreactive, respectively. Thermogravimetric analysis (TGA) and microstructural observations confirmed the effectiveness of fly ash in reducing Portlandite content that reduced the ASR expansion. Therefore, the use of 20–30% fly ash as cement replacement is considered as an adequate ASR mitigating measure of FNS fine aggregate.

Field Evaluation of Concrete using Hawaiian Aggregates for Alkali Silica Reaction

Alkali Silica Reaction (ASR) occurs in concrete when the alkali hydroxides (Na+, K+ and OH-) from the cement react with unstable silica, SiO2, in some types of aggregate. The resulting gel will expand when it absorbs water, potentially leading to cracking and overall expansion of the concrete. Concrete aggregates available in Hawaii have not demonstrated a history of ASR, however, results of accelerated laboratory tests using ASTM C1260 indicated a potential for ASR with some aggregates. In order to assess the accuracy of the laboratory test results, a long-term field study of the potential for ASR in concretes made with Hawaiian aggregates was initiated in 2011. Forty concrete specimens were constructed of various concrete mixtures using aggregates from all Hawaiian aggregate sources, and some US mainland aggregates known to exhibit ASR expansion. The specimens are located in an open field site in Manoa valley on the Hawaiian Island of Oahu, exposed to relatively high humidity and frequent rainfall. A weather station at the site records the ambient conditions on a continual basis. This paper describes the field evaluation program and presents the results after six years of monitoring. Comparisons are made between the field observations and accelerated laboratory tests.

INVESTIGATION OF POTENTIAL ALKALI-SILICA REACTIVITY OF AGGREGATE SOURCES IN THAILAND

Since the first local evidence of alkali-silica reaction (ASR) was reported in Thailand in 2011,awareness of ASR was raised and the importance of aggregate performance database was recognized, thus anattempt to set up local aggregate database was initiated. As part of the effort to establish the database, a studyof potential ASR reactivities was carried out involving aggregates from several current industrial sources ineastern and central Thailand and the results were presented here. Aggregate samples were randomly collectedfrom various sources and tested by two methods; accelerated mortar-bar test (AMBT) and petrographicexamination. The types of aggregate sampled included limestone, greywacke, and rhyolitic tuff. The AMBTexpansion results indicated that several aggregate types had larger expansion than the threshold of potentiallydeleterious ASR behavior as suggested by ASTM C 1260 standard. Furthermore, it was found that samples ofsame aggregate type, although apparently had mineralogically similar compositions, had different reactivities,particularly when sampled from around geological fault zone compared with that taken from the surroundingarea and portions of parent rock were observed to be weathered in this area. Thin section analysis revealedevidence of ASR gel at the aggregates’ rim, inside the aggregates and in the matrix. These findings suggestpossible future ASR problems in Thailand as well as in neighboring countries where the continuity ofgeology pattern is observed.

ASR Potential and Mitigation Measures for Wyoming Aggregates

AbstractDiscovered in the 1940s, alkali-silica reaction (ASR) causes undesired expansions in concrete. If unmitigated, ASR may cause premature deterioration. Since its discovery, researchers have s...

The Investigation of Alkali – Silica Reactivity (ASR) of Lithuanian Aggregates

The potential alkali-silica reactivity (ASR) of Lithuanian aggregates from five quarries was investigated using national chemical method, accelerated mortar bar test method RILEM AAR-2 (specimens 40×40×160mm) and storage of specimens at 60°C and 100% RH conditions. It was found, that all aggregates are contaminated with reactive rocks (4.0% - 4.6% in sand and 1.5% - 2.4% in gravel). The most of aggregates can be assigned to Class II-S according AAR-0. “Pop-out” and ASR-gel were observed after 15 weeks in the mortar specimens stored at 60°C and 100% RH.

Evaluation of alkali–silica reaction potential of quartz-rich rocks by alkaline etching of polished rock sections

Rock sections mainly composed of quartz (coming from orthoquartzite, quartz metagreywacke, pegmatite quartz, vein quartz, chert, and flint) were subjected to experimental etching in 1 M NaOH solution at 80 °C. After 4 h–14 days, the rock sections were analysed using a scanning electron microscopy (SEM) combined with energy-dispersive spectrometer. Representative areas were documented in backscattering mode and analysed using fully automatic petrographic image analysis (PIA). Specific features connected to alkaline etching were observed on the surface of the rock sections: dissolution gaps, accentuation of pre-existing microcracks, etched out parts of aggregates, and the formation of altered silica-rich layer, and alkali–silica gels, all influencing the greyscale spectrum of the BSE microphotographs. Using SEM-PIA, it was possible to quantify the area affected by alkaline etching (etched area) and to express it as a percentage of the total area analysed. A very good correlation was found between the etched area and alkali–silica reaction potential of investigated rocks measured according to an accelerated mortar bar test.