Alkali-silica Research Articles

Structural assessment of an ASR-affected reinforced concrete bridge

ASR (alkali-silica reaction) has long been acknowledged as a key consideration when designing concrete structures in South Africa. This study raises awareness of the influence of ASR on the structural behaviour of reinforced concrete bridge structures. Aggregate type plays a role in how the ASR develops over the structural life cycle. Greywacke aggregate is found to be prominent in ASR-affected structures within the Western Cape region, and in the structure that was investigated. ASR decreases concrete tensile strength, compressive strength, and E-modulus over time. To develop a standardised approach that can be replicated on other bridge structures, a simply supported rectangular reinforced concrete bridge deck slab was analysed. The slab was modelled according to the construction drawings, including the reinforcement detailing, to determine the ultimate shear and moment resistance according to the code (BS 1972) used for the original design, and current Eurocode standards, for both unaffected and ASR-affected concrete. Traffic load was determined from the relevant TMH7 standard, and from weigh-in-motion data collected at a station on the high-traffic-volume route crossing the bridge. Due to compressive strength being the least affected material property by ASR deterioration, the ultimate resistance to original design loads was found to be sufficient.

Studying the effectiveness of sewage sludge ash and its combination with natural pozzolans in controlling alkali–silica reaction

AbstractSewage sludge ash (SSA), obtained by the incineration of sewage sludge, which is a byproduct of water treatment, could be used as a cement replacement material (CSR) to promote sustainability. SSA characteristics differ due to its different sources, compositions, and incineration methods. On the other hand, extensive investigations have highlighted the CSRs' ability to control alkali–silica reaction (ASR) as a destructive phenomenon, threatening durability. Hence, this study was conducted in order to study the ability of SSA with two finenesses, three replacement levels, and also its ternaries with trass or pumice, as natural pozzolans, to control ASR. The utilized SSA did not meet the requirements of a pozzolan at either finenesses. The results revealed that despite the fact that SSA generally reduced ASR expansion significantly, it only managed to control ASR at 50% replacement level. This was true for both finenesses. Furthermore, ternaries improved resistance against ASR expansion significantly, providing the ability to control ASR at lower replacement levels of SSA. The Si/Ca ratio was the key reason of SSA's ability to control ASR as it contained 1.5 and 2.5 times more SiO2 and Al2O3 than Portland cement respectively, and about one third of its CaO. Scanning electron microscopey (SEM), energy dispersive spectroscopy (EDS), and mapping confirmed that the relative amounts of Si, Al, and Ca in the SSA was crucial.

Using Autoclave Concrete Prism Testing to Evaluate ASR Reactivity in Concrete Using Laboratory Tests and Outdoor Exposure Blocks as Benchmark Data

Abstract The alkali–silica reaction (ASR) occurs in concrete that contains silica in a reactive aggregate, sufficient alkalis, and sufficient moisture. Although the most widely accepted tests for evaluating ASR potential are the concrete prism test (CPT) and the accelerated mortar bar test, each test has limitations. Because of the need to test concrete mixes within a short period of time, an accelerated autoclave test method (autoclaved CPT [ACPT]) was investigated using concrete prism samples boosted to 3.0 % total alkali content subjected to an exposure temperature of 271°F (133°C) with a corresponding pressure of 29 psi (0.2 MPa) for 24 hours. A suite of aggregates was evaluated by concrete prism specimens using both the ACPT and CPT methods. The ACPT was able to classify individual aggregate fractions for ASR reactivity with 97.2 % accuracy for the proposed limit of 0.09 % expansion for 36 tested mixtures and approximately 130 specimens. Data from this test suggest that a week-long test could be considered an effective screening tool for the alkali reactivity of coarse or fine aggregate fractions. In addition, miniature CPT (AASHTO T 380, Standard Method of Test for Potential Alkali Reactivity of Aggregates and Effectiveness of ASR Mitigation Measures (Miniature Concrete Prism Test, MCPT) and 12-year outdoor exposure block results are evaluated and compared with both CPT and ACPT results. Although the data suggest a general agreement between these methods, further testing is warranted along with multi-laboratory precision evaluation.

Effect of alkali-silica reaction on the flexural behavior of beams with tensile lap splices

A series of 19 beam specimens, with varying stirrup spacing and tensile lap splice lengths, were tested at the National Institute of Standards and Technology (NIST) under four-point loading to investigate the impact of alkali silica reaction (ASR) on the flexural strength and bond behavior of reinforced concrete members. The beams contained highly reactive aggregates, were cured in an environmental chamber at high relative humidity and temperature, and were tested in batches at regular intervals in time. The development of strains in the deformed bar reinforcement was monitored in five beam specimens to provide an assessment of the level of ASR expansion achieved prior to testing. The strain development in the tensile reinforcement bars and stirrups was generally similar between the specimens, despite differences in stirrup spacing and lap splice length. Strains in the transverse stirrups due to ASR-induced expansion at the time of testing were roughly twice the strains recorded in the longitudinal tensile reinforcement, reaching a maximum value of approximately 0.002 mm/mm prior to testing. The concrete mixture studied exhibited expansions in the range of 0.2% and the tested beams exhibited randomly oriented surface cracking with no localized spalling or general loss of section at the time of testing. The effects of ASR included reductions in the compressive strength and modulus of companion cylinders of up to 15% and 50%, respectively. A rigorous statistical analysis of the measured data was performed to quantify the influence of ASR-induced expansion, splice length, and stirrup spacing on the beams’ flexural capacity and the maximum achieved average bond strength. Results indicated that in the range of expansions, stirrup spacings, and lap splice lengths studied, there was no evidence that the moment capacity or the maximum average bond strength was reduced by the effects of ASR. Tested beams constructed with ACI 318 code compliant splice lengths achieved or exceeded the nominal flexural strength of the section, regardless of the degree of ASR-induced expansion observed.

Recycling of Aluminosilicate-Based Solid Wastes through Alkali-Activation: Preparation, Characterization, and Challenges

Recycling aluminosilicate-based solid wastes is imperative to realize the sustainable development of constructions. By using alkali activation technology, aluminosilicate-based solid wastes, such as furnace slag, fly ash, red mud, and most of the bio-ashes, can be turned into alternative binder materials to Portland cement to reduce the carbon footprint of the construction and maintenance activities of concrete structures. In this paper, the chemistry involved in the formation of alkali-activated materials (AAMs) and the influential factors of their properties are briefly reviewed. The commonly used methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), nuclear magnetic resonance spectroscopy (NMR), and X-ray pair distribution function technology, to characterize the microstructure of AAMs are introduced. Typical characterization results of AAMs are shown and the limitations of each method are discussed. The main challenges, such as shrinkage, creep, efflorescence, carbonation, alkali–silica reaction, and chloride ingress, to conquer for a wider application of AAMs are reviewed. It is shown that several performances of AAMs under certain circumstances seem to be less satisfactory than traditional portland cement systems. Existing strategies to improve these performances are reviewed, and recommendations for future studies are given.

Efficient inhibition of ASR by microbially induced calcium carbonate precipitation on aggregates at a low degree of saturation

Alkali-silica reaction (ASR) is a chemical reaction between alkaline ions (Na+, K+), silicon phases and aluminum phases in the aggregate, causing volume expansion and cracking of the concrete, leading to a deterioration in the mechanical properties of the structure. In previous studies, microbially induced carbonate precipitation (MICP) technology had been demonstrated to be effective in inhibiting ASR. In this study, in order to explore better inhibition effect, MICP treatments of alkali active aggregates under different saturation degrees were tested. The results showed that when treated at a low-saturation degree (35 %), the inhibition effect of ASR was better comparing with that obtained at higher saturation degrees in the presence of same CaCO3 content. When the CaCO3 content was about 6 %, mortar bar specimens made of low-saturation treated aggregates possessed a 75 % reduction in the expansion and a 37 % increase in the compressive strength compared to the control group. In addition, through microstructure and component analysis of the aggregate surface, it was found that under the low-saturation treatment, the CaCO3 layer could be formed on the surface of the aggregate more uniformly and efficiently, with a higher binding strength to the aggregate and a greater Vickers hardness. Thus, it could better block the invasion of external alkaline ions to react with the active SiO2 inside the aggregate, leading to a better inhibition of ASR.

Influence of engineered self-healing systems on ASR damage development in concrete

Supplementary cementing materials (SCMs) have proven effective in minimizing alkali-silica reaction (ASR) development. In addition, crystalline admixtures (CAs) have been identified as potential solutions to counteract damage in concrete. However, limited data on this topic is available in the literature. This study investigates the impact of CA on concrete damage and is divided into two phases: 1) the effectiveness of CA in self-healing cracks and restoring the mechanical properties of mechanically damaged concrete; 2) it explores concrete mixtures incorporating a wide range of binder compositions (i.e., general use type cement, silica fume, fly ash, slag and Metakaolin) and chemical admixtures (i.e., commercially available CAs and modified versions) in conditions enabling ASR development. Both phases involve microscopic/mechanical analyses to assess the effects of CA on damage, and comparisons with concrete mixtures without CAs are made. The results reveal that CA enhanced the self-healing of cracks up to 82 % of cracks in cement paste (115 % higher values than concrete mixtures without CA) and restored 69 % of compressive strength. Furthermore, although CAs could change the damage mechanism of ASR, they did not “safely” mitigate it. However, combining SCMs and CAs effectively reduces ASR-induced expansion.

Historical defects in buildings – No. 3: Alkali–silica reaction in concrete

Hugh Docherty continues this series by examining the potential damage caused by alkalis and silica reacting in concrete, and offering brief advice on identification and remediation.

Influence of recycled concrete, marble, glass, and limestone powder, and utilization ratios on the compressive strength and alkali–silica reaction performance of mortar mixtures

Influence of recycled concrete, marble, glass, and limestone powder, and utilization ratios on the compressive strength and alkali–silica reaction performance of mortar mixtures

Avaliação do pó de vidro na mitigação da reação álcali-sílica (RAS)

Abstract The alkali-silica reaction (ASR) is one of the problems that can compromise concrete durability, as the chemical reactions between the reactive aggregate and concrete pore solution, specifically sodium (Na+), potassium (K+), calcium (Ca2+) and hydroxyl (OH-) in the presence of moisture, trigger expansion and cracking of concrete elements. The use of pozzolanic materials, such as finely ground glass powder (particles smaller than 75μm), to partially replace cement has been widely studied and has demonstrated beneficial results. However, because the behavior of pozzolans towards ASR is not completely understood yet, this work evaluates the effect of incorporating ground glass powder into cementitious composites against ASR. To this end, 8% silica fume was used as a control admixture, and four levels of glass powder (10, 20, 30, and 50%) were incorporated into the cementitious mixture to partially replace cement. Expansion tests were carried out in accordance with NBR15577-4 (ABNT, 2018) on mortar bars using the accelerated test method to assess the mitigation of expansions. The results show that the expansions caused by ASR decreased with the increasing content of glass powder in the cement mixtures. Furthermore, only the 50% level reduced the expansions to a safe value according to the Brazilian standard.

Modelagem Numérica de RAA: um método semi-empírico atualizado

Abstract Alkali-silica reaction (ASR) is a deleterious expansion phenomenon affecting concrete structures worldwide. It occurs when a susceptible chemical composition of concrete components is present, and it is particularly rampant in inherently humid environments. This phenomenon is exacerbated when found in mass concrete structures such as dams and foundations. The amount of volumetric ASR strain used to be deemed as nearly constant, however, recent advances have shown that it is actually affected by the distribution of volumetric stresses. Therefore, this behavior demands an update in the numerical models that have been devised to simulate the anisotropic ASR-driven expansion. This paper deals with Saouma & Perotti’s thermo-chemo-mechanical coupled model, which has been applied in a solely mechanical manner, and updated to account for a varying volumetric strain. A simulation of the experiment that shed new light on the variation of ASR volumetric strain was then carried out with the finite element method package COMSOL. As a result, significantly smaller errors in predicted strains were attained by the updated model in comparison to the original one, and consequently, the new model poses a promising tool for a more accurate simulation of ASR expansion.

Experimental investigation on strength characteristics of autoclave aerated concrete block using natural pozzolanas

In this present study we have studied about the strength enhancement of autoclaved aerated block by using natural pozzolanas. Fly ash has been partially replaced with GGBS. GGBS has been used in place of fly ash at percentages of 6%, 12%, and 18% of the total amount of fly ash plus super plasticizer. GGBS improves resistance to damage from alkali silica reaction. It also reduces the thermal cracking. The role of super plasticizer is to reduce the water content in block.we have used 1% of super plastizer to the 1 litre of water. Each block's compressive strength is measured and computed for varying fly ash and GGBS ratios. It has been observed that replacing GGBS with 12% yields higher compressive strength than replacing it with 6% or 18%.

Random Finite Element Reliability Assessment of Existing Concrete Structures – Case Studies and Research Direction

The material properties of concrete and reinforcing steel in reinforced concrete structures vary spatially across the structural dimensions due to the inherent heterogeneous nature of concrete. The spatial variation is further affected by active deterioration mechanisms such as freeze thaw damage, alkali silica reactivity, and corrosion of the reinforcing steel as all of these mechanisms are random. The spatial variation of concrete mechanical properties (compressive strength, tensile strength, modulus of elasticity) and corrosion effect of reduced section loss influence the structural reliability, and hence, the structural risk. Random finite element (RFE) simulation has been recently employed in engineering consultancy to assess structures with spatially varying properties using reliability analysis. The objectives of this paper are to 1) document the application of RFE in real-life case studies of structural reliability assessment projects conducted by the authors in Canada, and 2) provide recommendations for future research to improve the practicality of analysis for consulting jobs. The paper will provide readers with insight into the application of advanced methods of analysis in consulting work for risk-based condition assessment of critical infrastructure. Recommendations for future research and analysis refinements are discussed.

Monitoring internal swelling reactions in concrete dams

Alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are the most common internal swelling reactions (ISR) in concrete dams. The swelling effects and concrete deterioration caused by ISR can be observed in several forms at the structural level, including relative movements between blocks, displacements and deformations, cracking, surface discoloration around the cracks, scaling or spalling as well as surface “pop-outs”.The detection and the assessment of these structural symptoms in large concrete dams is usually made through visual inspection and interpretation of the monitoring data, such as stress free strainmeters embedded in concrete, geodedic levelling, pendulums, rod extensometers and internal or external jointmeters. The strainmeters and the levelling data are also used for providing estimations of the dam concrete expansion.The Portuguese information system, designed to serve as a national database, has its own data structure and includes the monitoring systems data for large concrete dams of all structural types, including dams with over 60 years old. This information system is used by both the dam owners and the National Laboratory for Civil Engineering (LNEC) for dam safety assessment over the years.This work discusses the importance of the dam observed behaviour data provided by the monitoring system as a tool for ISR assessment. The progression of concrete expansion for several dams located in Portugal is presented. The presented observed results were based on data from stress free strainmeters, while others were calculated from geodetic levelling.

Analysis of the Resistance of Self-Compacting Concrete (SCC) with the Use of Granite Stone Waste to Alkali-Silica Reaction

Aggregates occupy ±70% of the concrete volume and their quality must meet specifications. Concrete surfaces submerged in water for a long time cause concrete failure due to the reaction between aggregate and cement to form silica gel. The wear value of granite is less than gravel, so this study used granite as a substitute for coarse aggregate. This study was conducted to assess the resistance of SCC concrete with 0%, 25%, and 30% granite stone variations to alkali-silica reaction attack. The experimental method was applied to the study with ACI method mix design as well as 25 MPa plan fc'. Concrete cylinder samples 150 mm x 300 mm aged 28 days were used in the compressive strength test, alkali-silica reaction expansion test used mortar block samples 285 mm x 25 mm x 25 mm in 80±2˚C NaOH solution bath for 14 days. The optimum compressive strength of 32.17 MPa and the lowest percentage change in length of 0.04% was obtained by sample BG.25-SCC, indicating that granite stone is not reactive to silica alkali reaction because the percentage change in length <0.10%. This study concludes that granite stone can improve the resistance of concrete to silica alkali reaction.

Replacing fly ash with a natural pozzolan in normal strength concrete and ultra-high performance concrete

Fly ash is a widely-used supplementary cementitious material (SCM) in concrete. Common reasons for using fly ash in normal strength concrete (NSC) are to reduce cement consumption and mitigate alkali-silica reaction. Additionally, fly ash is being used in ultra-high performance concrete (UHPC) to reduce use of silica fume which is more expensive than fly ash. Fly ash and silica fume are important SCMs in UHPC that provide a dense microstructure, improving UHPC strength and durability. However, fly ash is becoming less available because the energy industry has been investing in renewable energy production and removing coal burning power plants from operation. Therefore, there is a need to identify sustainable SCMs to replace fly ash in NSC and UHPC mixtures. Natural pozzolans are a diverse class of siliceous or siliceous and aluminous materials that can form compounds possessing cementitious properties in the presence of water. Since natural pozzolans are easily mined, they are usually considered to be more sustainable than Portland cement and nearly as sustainable as other SCMs such as fly ash and silica fume. This experimental study evaluated the effects of a natural pozzolan (pumicite) as a potential replacement for fly ash that can produce comparable rheological and mechanical properties in NSC and UHPC mixtures. Results indicated that workability of both NSC and UHPC mixtures containing pumicite was consistent enough to achieve the targeted workability in just a few trials. Additionally, NSC mixtures with 30% pumicite had comparable compressive strength compared to NSC mixtures with 30% fly ash. Modulus of rupture (MOR) for NSC mixtures containing 30% pumicite (greater than 4.10 MPa) exceeded the MOR for specimens containing 30% fly ash. For UHPC mixtures, results showed that up to 75% of the fly ash in the control mixture could be replaced with pumicite while still producing acceptable compressive and flexural strengths. Based on these results, it appears that pumicite can be a reliable alternative for fly ash in NSC and UHPC mixtures in terms of rheological and mechanical properties.

Corrigendum to: Analysis of the Resistance of Self-Compacting Concrete (SCC) with the Use of Granite Stone Waste to Alkali-Silica Reaction

Corrigendum to: Analysis of the Resistance of Self-Compacting Concrete (SCC) with the Use of Granite Stone Waste to Alkali-Silica Reaction

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.

Interacting Action of Alkali-Silica Reaction and Chloride-Induced Steel Corrosion on The Reinforced Concrete Structures – A Critical Review

Interacting Action of Alkali-Silica Reaction and Chloride-Induced Steel Corrosion on The Reinforced Concrete Structures – A Critical Review

Alkali thermal fusion: A prospective route to enhance the reactivity of low-grade clay and utilize as supplementary cementitious material (SCM)

Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and 29Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction.