Risk Of Alkali-silica Reaction Research Articles

The alkali–silica reaction of seawater-mixed mortar

The application of seawater concrete is receiving increasing attention due to the advantage of using seawater in alleviating water scarcity. One concern with seawater concrete applications is the potential for alkali–silica reaction (ASR) due to the elevated alkali concentration. In this paper, the ASR risk induced by mixed seawater in cement mortar incorporating non-reactive or reactive aggregates (RAs) was studied through short-term and long-term experiments. Experimental results indicate that seawater only increased ASR in the presence of RAs due to the high alkali concentration. Replacing cement with 70% ground granulated blast-furnace slag (GGBS) prevented expansion, although very few ASR products may be observed. SEM results indicated that seawater decreases the (Na + K)/Si ratio and increases the Ca/Si ratio of ASR products slightly. Compared with cement mortar, C–S–H in GGBS blended cement mortar has a higher (Na + K)/Si ratio, which indicates its higher alkali binding capacity.

Influences of aggregate gradation on alkali-silica reaction of seawater and sea sand concrete

The application of seawater and sea sand concrete (SWSSC) is beneficial for marine engineering, but the impact of aggregate gradation on its alkali-silica reaction (ASR) remains poorly understood. This study aims to bridge this gap by analyzing ASR products, pore characteristics and expansion rate of specimens. The test results reveal that ordinary concrete (OC) exhibits an inhibitory effect on ASR in comparison with to SWSSC. The 14-day expansion of ordinary concrete and SWSSC with the same aggregate gradation are 0.130 % and 0.212 %, showing potential and high risk of ASR, respectively. Moreover, particle size and gradation of aggregate are the key factors influencing the ASR degree of SWSSC. Compared with coarser aggregate, specimens with finer aggregate consume more K+ and Ca2+ ions, generate more ASR-P1, form less porosity, and produce a larger expansion. Additionally, specimens with gap-graded aggregates, as opposed to those with uniform or continuous gradation, show greater consumption of K+ and Ca2+ ions, increased ASR-P1 formation, more harmful pore formation, and a larger expansion. These results offer insights into optimizing aggregate gradation to reduce ASR in SWSSC and improve its durability.

Effects of desalinated sea sand on the alkali–silica reaction of seawater and sea sand concrete

The application of seawater and sea sand concrete (SWSSC) can reduce the construction period and cost of island infrastructure, but it may also bring the risk of alkali–silica reaction (ASR) owing to the presence of alkali ions in seawater and sea sand. To compare the characteristics of ASR between SWSSC and seawater and desalinated sea sand (DSS) concrete, the properties and the ASR products of mortar bars with different DSS content were studied. When the DSS proportion increased from 0% to 100%, the sodium (Na+), potassium (K+) and calcium (Ca2+) ion concentration of the specimens decreased by 22.6, 2.0 and 45.1 mg L−1, respectively, the pH decreased by 0.05 and the expansion of mortar bars was reduced by 0.16%. Desalination of sea sand could not eliminate the risk of ASR of SWSSC completely. The 14 days expansion of mortar bars with 100% DSS was 0.13%, and the precursors of ASR-P1 were observed by SEM. The experimental results of micriscopic tests all showed that with the increase of DSS proportion, the content of Na-shlykovite and ASR-P1 were reduced. A small amount of magnesium (Mg) in ASR products was detected. This study can provide a basis for the application of SWSSC in island infrastructure.

Evaluation of Nepali Aggregates for Alkali-silica Reactivity Using Accelerated Mortar Bar Test Method

In many countries, large concrete structures needed to be replaced by new structures because treatment of Alkali Silica Reaction (ASR) was not feasible. Availability of amorphous or poorly crystalline silica is a necessary condition for ASR and it has been a common problem in several countries located in cold geographical regions. Some Nepali rocks also comprise amorphous silica as detected in Sanjen Hydropower Project (SHP) and Tanahu Hydropower Project (THP) during the examination of aggregate through various tests. ASR kinetics and the resulting expansion are observed to be enhanced with an increase in temperature and humidity. Accordingly, the risk of ASR is expected to be prominent in Nepal where temperature and humidity are relatively high. However, systematic research on ASR in Nepal is scarce and the possibility of ASR is little known. This paper determines the reactivity of potential aggregate sources considered for some large infrastructures in Nepal. Accelerated mortar bar test based on the guidelines of ASTM C1260 was performed on aggregate specimens collected from the Pokhara Regional International Airport Project (PRIAP), THP, and SHP. 14-day longitudinal expansion of the mortar bar prepared from the aggregated collected from PRIAP, THP, and SHP was 0.1%, 0.17%, and 0.06% respectively. The aggregate collected from THP is deleterious, whereas aggregate collected from PRIAP and SHP is non-reactive. This study demonstrates that Nepal may have many sources of aggregates that are reactive.

Mechanisms on the inhibition of alkali-silica reaction in supersulfated cement

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na+ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO42− in the pore solution of SSC can inhibit the diffusion of OH−. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk.

Internal alkali transport in recycling concrete and its impact on alkali-silica reaction

Recycling concrete (RC) produced with recycled aggregates (RA) obtained from demolished concrete structures bears the risk of an alkali-silica reaction (ASR). In this study, the interplay between aggregate reactivity and alkalis contributed by the cement and the RA is investigated. Three sets of concrete mixtures are produced using RA and natural aggregates, both reactive and non-reactive ones. Caesium either present in the RA or in the mixing water of the RC is used to trace the transport of alkalis and their incorporation in ASR products. The result shows that alkali released by RA can intensify ASR. On the other hand, ASR in RA with a low alkali content but reactive aggregate particles can be triggered by the alkali provided by the new cement paste of the RC. The highest risk of ASR in RC is caused by RA from a source concrete already affected by ASR.

Influence of seawater concentration on alkali-silica reaction of seawater sea-sand concrete: Mimicking through NaCl solution and recycled glass aggregate

Seawater sea-sand concrete (SSC) is one environment-friendly and promising construction material. Nevertheless, limited research shed favorable light on alkali-silica reaction (ASR) of SSC. This work provided a novel insight regarding the fast test method that (i) the recycled glass aggregate (RGA) was used for fast assessing the effect of seawater concentration on ASR, reusing its characteristic resource; (ii) the NaCl solutions with different concentrations were used to mimic different salinities of sea waters; and (iii) a modified curing method was adopted. The results showed that the NaCl solution could be used for assessing ASR risk of SSC instead of seawater. The specimens mixed with twice and above the sodium concentration of seawater would exhibit ASR expansion, strength reduction, coarsening of nanopore distribution, and the cracks on the macro and micro levels. However, the change of NaCl concentration scarcely affected the composition and content of hydration products. Additionally, with increasing the mixing Na+ concentration, the ASR crack would firstly appear in the interface between the cement paste layer and the glass layer, and then developed in the internal zone of RGA matrix with different hardness, elastic modulus, and Si contents based on the destroyed degree.

Efficiency of natural pozzolan and natural perlite in controlling the alkali-silica reaction of cementitious materials

Pozzolanic materials have generally been found to be useful in reducing the effects of alkali-silica reaction (ASR) in cementitious composites by reacting with hydroxyl ions and portlandite to produce new phases that trap alkali ions. The main objective of this study is to compare the effects of the same fineness natural pozzolan (PZ) and natural perlite (PR) on the physical, mechanical, and microstructural changes of mortars exposed to the risk of ASR. In addition, the experimental work aims to consider the relationship between the chemical compositions of these two locally available pozzolans and their ASR attenuation levels in cementitious materials. In this context, mortar mixes were prepared using Portland cement (PC) substituted at 0%, 10%, and 20% of PZ or PR and tested after immersion in alkaline sodium hydroxide (NaOH) solution based on ASTM C1567 recommendations. Changes in mortar length and mass, ultrasonic pulse velocity, flexural and compressive strengths, X-ray diffraction, and scanning electron microscopy were considered. The results demonstrated that PR was more effective than PZ in improving the resistance of cementitious composites against ASR. The ultrasonic pulse velocity and flexural strength test results are in good agreement with the ASR expansion of all mortar mixes. Interestingly, at the same fineness, the pozzolanic activity level, silica content, and calcium/silica ratio of natural pozzolans were confirmed as accurate parameters in estimating their effects on the ASR reductions of mortars.

Rheology and alkali-silica reaction of alkali-activated slag mortars modified by fly ash microsphere: a comparative analysis to OPC mortars

The poor workability and the risk of alkali-silica reaction (ASR) caused by alkaline activators restrict the wide range of applications of alkali-activated slag (AAS) cement. This paper presents a study on the effect of fly ash microsphere (FAM) on mitigating the rheological properties and ASR of AAS mortars for the first time. For comparison, the ordinary Portland cement (OPC) mortars blended with FAM are also prepared and investigated. The FAM addition is effective in decreasing the viscosity and meanwhile increasing the fluidity of the AAS pastes and mortars due to its ‘ball-bearings’ effect. According to the results obtained from the accelerated mortar bar test, the addition of more than 10% FAM reduces the ASR expansion effectively in both of the AAS and OPC mortars. Mineralogical studies demonstrate that for the AAS mortars, FAM promotes the formation of C-A-S-H gel phases with a better alkali binding capacity to mitigate ASR. The pozzolanic reaction of FAM consumes Ca(OH)2 in the OPC mortars, which is essential to the ASR development. In addition, minor ASR products are observed in the AAS or OPC mortars modified with FAM, and meanwhile there is a more strong bonding between the interface of aggregate-paste.

Accelerated test for assessing the potential risk of alkali-silica reaction in concrete using an autoclave

To rapidly assess the potential risk of alkali-silica reaction (ASR) in concrete, an accelerated test using an autoclave by adopting multi-cycle 80 °C steam warming at atmospheric pressure is proposed. The influence of autoclave steam warming temperature, cycles/duration, and alkali dosage on expansion of mortar bars and concrete prisms was evaluated. Mechanical properties of concrete under accelerated ASR test were investigated. Furthermore, SEM-EDS analysis confirmed ASR products and indicated that the expansion is caused by ASR. The expansion limits considered for classifying aggregates were discussed. The experimental results demonstrated that the period required for assessing the potential risk of ASR in concrete (dacite aggregate in this study) can be shortened to 37 days.

Laboratory investigations on fine aggregates used for concrete pavements due to the risk of ASR

The assessment of the aggregate suitability for concrete pavements applies mainly to coarse aggregate. However, even fine aggregate can significantly affect the long-term durability of concrete when it is susceptible to alkali-silica reaction (ASR). The sustainable use of available fine aggregates for the production of concrete, while reducing the effects of ASR, requires special preventive measures. The paper proposed different procedures to determine the chemical composition of aggregate and the related ASR risk. The study covers various properties of natural fine aggregates from glacial deposits. The experiments included determination of chemical composition by prompt gamma activation analysis (PGAA), quantitative mineralogical characterisation on thin sections using digital image procedure (DIP) and expansion measurements in mortar bar test (MBT). The strong correlation of sand origin and its susceptibility to ASR was observed. Content of micro- and cryptocrystalline quartz in siliceous sand was found to have a crucial effect on its performance in AMBT. Highlights The different testing procedures to determine the chemical composition of aggregate and the related ASR risk are proposed. The ASR expansion of a various origin sands was studied. The origin of the siliceous sand has a significant effect on its alkali-silica reactivity. The max. content of reactive quartz regarding ASR is determined.

Use of binary and ternary cementitious blends of F-Class fly-ash and limestone powder to mitigate alkali-silica reaction risk

The aim of this paper was to investigate the effects of binary and ternary cementitious systems including Portland Cement (PC), F-Class fly ash (FA) and limestone powder (LSP) to suppress expansion caused by alkali-silica reaction (ASR). Mortar prisms were prepared with potentially deleterious aggregates and tested by using Mortar-Bar Method according to ASTM C 1260. To evaluate the effect of FA and LSP on the suppression of ASR in mortar, ten different types of mortar were cast with combination of different dosages of FA and LSP as binary and ternary blend systems (partial replacement of PC) while the control mortar consisted of only PC as binder. Moreover, the Scanning Electron Microscopy (SEM) was carried out to interpret the microstructure. It was found that the reduction of ASR expansion rate due to increase in LSP content was more prominent compared to the increase of FA content in the binary blends system. Finally, the mixture containing ternary blends of 20% FA/LSP were in general more effective to mitigate the ASR risk for 14days compared to all mortars.

Effect of the inherent alkalis of alkali activated slag on the risk of alkali silica reaction

Alkali silica reaction (ASR) occurred in the alkali activated slag (AAS) concrete was evaluated by a revised mortar prism method. The mortars were made of blast furnace slags activated by alkali silicate solution possessing different modulus (0.5, 0.75, 1 and 2) as well as cations (sodium and potassium) and standard sand with a volume replacement of 25vol% by borosilicate glass beads. Their changes in length and dynamic elastic modulus were monitored up to 7months. The results showed that ASR has taken place among some mortars, which were evident under both light microscopy and electron microscopy with EDX analysis. The results also revealed that high alkali content did promote the risk of ASR but the degradation due to ASR was affected in a much more complex way.

Application of Electron Backscatter Diffraction to evaluate the ASR risk of concrete aggregates

Alkali-Silica Reaction (ASR) is a frequent cause of reduced concrete durability. Eliminating the application of alkali reactive aggregates would reduce the quantity of ASR concrete deterioration in the field.This study introduces an Electron Backscatter Diffraction (EBSD) technique to distinguish the ASR risk of slow-late reacting aggregates by measuring microstructural properties of quartz. Quantifying the amount of quartz grain boundaries and the associated misorientation of grains can thereby be used to differentiate microstructures bearing an ASR risk. It is also shown that dissolution of quartz in high pH environments occurs along quartz grain and subgrain boundaries.Results of EBSD analysis are compared with ASR performance testing on concrete prisms and optical light microscopy characterization of quartz microstructure. EBSD opens new possibilities to quantitatively characterize microstructure of quartz in concrete aggregates with respect to ASR. This leads to a better understanding on the actual cause of ASR.

Risk of ASR in coating mortars incorporating glass aggregates and a Portland–limestone cement

As the cement content is one of the parameters that control alkali–silica reaction (ASR), this study examined its influence on the expansion of glass mortars. The mortars had volumetric ratio of 1:4 (cement: aggregate) and various aggregate compositions, obtained using replacement ratios of natural sand with waste glass, of 0, 20, 50 and 100%. A volumetric ratio 1:4 was chosen because it is a current composition for cementitious coating mortars. In fact, mortar mixes with increased cement content can lead to erroneous conclusions for in situ mixtures with reactive aggregates. It is concluded that it is feasible to produce glass mortars without deleterious ASR expansion depending on the amount of cement used. For normal cement/aggregate ratios for coating mortars (1:4, in volume), a CEM II/B-L 32.5 N mortar with glass incorporation has a low ASR risk.

Application of ASR tests to recycled concrete aggregates: Influence of water absorption

Concrete is one of the most abundant construction and demolition wastes. It can be crushed to produce Recycled Concrete Aggregates (RCA) that can eventually be recycled for the manufacture of new concrete. However, the presence of adherent cement paste leads to higher alkalis content in these aggregates that could increase the risk to observe Alkali Silica Reaction (ASR). Moreover, the origin of natural aggregates in the RCA is generally unknown and these aggregates can potentially be reactive concerning ASR. Among standards which qualify the risk of ASR for natural aggregates, two main tests are used in this paper to evaluate the risk of ASR of RCA: tests on mortars and tests on microbars. In these tests, the water absorption of aggregates is not taken into consideration for the effective water calculation. However, in the case of absorbing aggregates like RCA, absorption water cannot be neglected. It could change significantly the effective water to cement ratio, and then influence the measured expansion. The first aim of this paper is to study the influences of absorption water and initial saturation state of RCA on the expansion of mortars and microbars. The second objective is to propose a new simple method for the assessment of water absorption coefficient of the fine granular fraction 0.16/0.63mm used for the manufacture of microbars. It is shown that absorption water has a strong influence on the expansion of mortars and microbars made with RCA, and that it has to be taken into account in the composition of the mixes. The initial state of saturation of RCA is less influential. The proposed method for the water absorption coefficient determination of fraction 0.16/0.63mm is based on the correlation between water absorption and cement paste content. The estimation of the latter from the mass loss between 105 and 475°C for two fractions of RCA, allows for an accurate determination of the water absorption coefficient of the fine fraction.

Inhibitory Effect of Waste Glass Powder on ASR Expansion Induced by Waste Glass Aggregate.

Detailed research is carried out to ascertain the inhibitory effect of waste glass powder (WGP) on alkali-silica reaction (ASR) expansion induced by waste glass aggregate in this paper. The alkali reactivity of waste glass aggregate is examined by two methods in accordance with the China Test Code SL352-2006. The potential of WGP to control the ASR expansion is determined in terms of mean diameter, specific surface area, content of WGP and curing temperature. Two mathematical models are developed to estimate the inhibitory efficiency of WGP. These studies show that there is ASR risk with an ASR expansion rate over 0.2% when the sand contains more than 30% glass aggregate. However, WGP can effectively control the ASR expansion and inhibit the expansion rate induced by the glass aggregate to be under 0.1%. The two mathematical models have good simulation results, which can be used to evaluate the inhibitory effect of WGP on ASR risk.

The risk of alkali–silica reaction in concrete made with non-conforming cement

A cement plant had supplied large quantities of cement into the market and the actual alkali contents were in excess of the manufacturer's declared mean. When the correct cement alkali levels were used to recalculate the amount of alkali, it was found that in some concretes the total alkali contents were above industry-recommended limits designed to minimise the risk of deleterious alkali–silica reaction (ASR). Given the large number of projects in which the concrete alkali content did not comply with the available guidance, it was necessary to develop a quick initial method of assessing the risk that concrete performance would be unacceptable. The unusual aspect of the investigations was that although the concretes did not conform to the recommended limits for minimising ASR risk, they had not shown any external symptoms or signs of damage. However, better information than is normal was available on the materials used, structural details and exposure of the concrete. The project-specific information was considered in the initial assessments using a severity ranking classification developed for the purpose. Subsequently, some of the projects were subject to more detailed physical investigation to establish more definitive conclusions. The investigations concluded that there was a general conservatism in the current guidance on minimising risk of ASR, but found greater degrees of uncertainty than expected in the base data used to underpin normal industry guidance. In addition, the level of record keeping on a number of sites was not sufficient to identify and locate concrete that was subsequently determined to be non-conformant. This work will help those investigating structures potentially affected by ASR and inform the future consideration of guidance for minimising the risk of ASR.

Utilizing Waste Recycled Glass as Sand/Cement Replacement in Concrete

The potential use of waste recycled glass in concrete as recycled glass sand (RGS) and pozzolanic glass powder (PGP) was examined in this study. No major difference was found in compressive strength of concrete with the presence of RGS as sand replacement. While, the compressive strength of concrete reduced by 16 and 10.6% at 28 and 364 days respectively when 20% of Portland cement was replaced by PGP. The potential expansion of concrete due to alkali-silica reaction (ASR) was monitored according to the procedure of British Standard BS 812 Part 123:1999. As a siliceous material, the use of RGS as sand replacement in concrete possesses high risk of ASR expansion. Therefore, cracks were observed when RGS was used as sand replacement in concrete without any precautions to minimize this risk. Different materials were used as ASR suppressors to mitigate the potential risk of ASR, such as: ground granulated blastfurnace slag, metakaolin, PGP, and lithium nitrate (LiNO3). The expansion associated with ASR was significantly reduced when the ASR suppressor was used in concrete.

Durability of mechanically loaded engineered cementitious composites under highly alkaline environments

Durability of mechanically loaded Engineered Cementitious Composites (ECC) is investigated in this paper. ECC offers significant potential for durable civil infrastructures, due to its high tensile strain capacity of more than 3%, and controlled micro-crack width of less than 80 μm. An experimental study was designed to investigate the durability of ECC material with regard to cracking and healing under combined mechanical loading and environmental loading conditions. ECC coupon specimens were firstly pre-loaded under uniaxial tension to different strain levels, and then exposed to an alkaline environment up to 3 months at 38 °C and reloaded up to failure. The reloaded specimens showed slight loss of ductility and tensile strength, but retained the multiple micro-cracking behavior and tensile strain capacity of more than 2% (about more than 200 times that of normal concrete and normal fiber reinforced concrete). The test results indicated strong evidence of self-healing of the micro-cracked ECC material, which can still carry considerable tensile stress and strain and restore nearly the original stiffness. The phenomenon of self-healing effectively closes the micro-cracks even after one month exposure period. In addition to coupon specimens, ECC bar specimens were also immersed in alkali solution at 80 °C in accordance to ASTM C 1260 to determine their length change due to alkali silica reaction (ASR). The ECC bar specimens did not show any expansion at the end of 30 days soaking period. Therefore, these test results indicated that ECC, both virgin and micro-cracked, remain durable despite exposure to a high alkaline environment. The risk of ASR in ECC is determined to be low.