Potential Alkali Reactivity Of Aggregates Research Articles

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.

Tapas de sílice - a smörgåsbord of reactive mineralogies and textures.

A source of sand is proposed as an educational tool to aid in the identification of silica mineralogies and textures susceptible to alkali-silica reaction. This particular silica sand originates in the southern portion of the state of Veracruz, Mexico, and exhibits a wide variety of lithologies, A thin section produced from a cross-section through a mortar bar subjected to ATSM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) exhibits plentiful examples of reactive silica.

Evaluation of Current ASTM Standards for ASR Prevention When Fine Lightweight Aggregates Are Used

Abstract Previous research has shown that using fine lightweight aggregate (FLWA) can be a promising strategy to mitigate alkali-silica reaction (ASR) in mortar and concrete. However, limited studies focused on assessing current ASTM standards for their applicability in evaluating the efficacy of ASR mitigation using FLWAs. In this study, three commercially used FLWAs (expanded shale, clay, and slate) were investigated in mortar and concrete mixtures with reactive aggregates of different levels of reactivity. ASTM test methods, including ASTM C289-07, Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method) (Withdrawn 2016); ASTM C1260-14, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) (Superseded); and ASTM C1293-18, Standard Test Method for Determination of Length Change of Concrete due to Alkali-Silica Reaction (Superseded), were completed. Fine normal-weight aggregates were replaced by the FLWA at 25 % and 50 % by volume in the concrete mixtures, and 25 %, 50 %, and 100 % in mortar mixtures. Results showed that ASTM C1260-14 and ASTM C1293-18 can be used to evaluate the mitigation efficacy when pre-wetted FLWAs were used. The ASTM C289-07 test is not a reliable test method to study the reactivity of the FLWAs, but the results can be used to indicate the alkali-consuming ability of the FLWAs. All three FLWAs were effective in reducing ASR-induced expansion in both ASTM C1260-14 and ASTM C1293-18. The investigated FLWAs were especially effective in the concrete when moderately reactive aggregates, as classified by ASTM C1778-14, Standard Guide for Reducing the Risk of Deleterious Alkali-Aggregate Reaction in Concrete (Superseded), were used. For concrete with a highly reactive aggregate or very highly reactive aggregate, other mitigation strategies may need to be combined with FLWAs to effectively mitigate ASR.

Development of a new short-term concrete prism test method (SCPT) to improve predictability for potential alkali reactivity of aggregates

This experimental study basically aims to come up with a new method [SCPT], which would be a reliable accelerated performance for predicting potential alkali reactivity of aggregates, because available test methods whether long or accelerated, have some drawbacks such as long test duration in the CPT [concrete prism test] and false tests results in the AMBT [accelerated mortar bar test]. The new method called as short-term concrete prism test [SCPT] has been designed with analysing the degree of correlation between the designed new methods and available test method by examining 32 types of aggregate, whosefield performances can be observable. Common specifications of the SCPT includes 50 mm x 50 mm x 200 mm concrete prisms, 16 mm maximum aggregate size, storage temperature at 60 °C and soak solution with 0.35N NaOH + 1% CaCl 2 and takes only 28 days.

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.

EFFECTS OF ALUMINIUM ADDITION ON INHIBITION OF CONCRETE EXPANSION RESULTED FROM ALKALI SILICA REACTION (ASR)

Alkali-silica reaction (ASR) is one of the major causes of expansion, which ultimately leads to failure in concrete. When reactive concrete is subjected to humidity, alkali silicate hydrate gel (ASR gel) is formed. The swollen ASR gel exerts pressure and creates cracks in the concrete structure. This study, thus, aimed at inhibiting concrete expansion which was caused by the ASR reaction, by creating pores. To achieve pore formation, aluminium powder was used as an air entrainment agent. Mortar bars with aluminium content of 0.05, 0.1, 0.15 and 0.2 weight percent of cement was tested according to the ASTM C1260: Standard Test Method for Potential Alkali Reactivity of Aggregates. The results indicated that a larger quantity of entrained pores was achieved at higher aluminium content. The results also showed that when tested according to the ASTM C1260, concrete expansion was reduced as the aluminium content was increased. Microstructural analysis revealed that the entrained pores accommodated spaces for ASR gel, resulting in the decline of concrete expansion.

Assessment of Potential Alkali Aggregate Reactivity for Siliceous and Carbonate Aggregates: A Case Study

Alkali-aggregate reactivity (AAR) involves a reaction between the pore solution of concrete and certain minerals found in some aggregates. To assess the potential AAR various physical and chemical tests are available and extensively used. The petrographic examination is the initial assessment that decides the further investigation for potential reactivity of an aggregate. A chemical approach is another option to assess the aggregate for potential AAR. The accelerated mortar bar method and concrete prism tests are other very important tests for determination of potential AAR of aggregates samples. However, a combination of the results of all the techniques provides most reliable results for potential AAR in aggregates. Moreover, each test represents the stepwise investigation and provides the decision for the test of next approach. Petrographic examination and chemical test methods are the quick decision-making methods for the estimation of potential AAR. In some cases, by these two methods, the aggregate can be selected and rejected confidently. However, for critical values or doubtful aggregates, further tests are necessary to develop a higher confidence level of the results. The present study comprises of the assessment of the alkali-reactivity of siliceous and carbonate aggregates using petrographic and chemical approaches. X-ray diffraction analysis was used as a complementary method to the petrographic evaluation. Moreover, under chemical approach, two separate test methods were used for siliceous and carbonate aggregates. The study also included a comparison between the petrographic examination and chemical analysis for the same aggregate samples and found significant results.

Five-Hour Autoclave Test for Determining Potential Alkali-Silica Reactivity of Concrete Aggregates: A Multi-Laboratory Study

Abstract Alkali-silica reaction (ASR) is a deleterious chemical reaction that can lead to expansion and cracking of concrete structures. The reaction occurs between alkali hydroxides in the pore solution and reactive forms of silica present in some aggregates. To successfully mitigate ASR in new structures, the potential alkali reactivity of the aggregates must be known. Standardized test methods for this purpose are sometimes too time-consuming for rapid military construction operations. To assess the viability of a five-hour autoclaved mortar bar test method for ultra-rapid identification of aggregate reactivity, researchers in five laboratories participated in a multi-laboratory study led by the U.S. Army Engineer Research and Development Center (ERDC). The test method uses fine aggregate in mortar bars like those used in ASTM C1260, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method), but the equivalent alkali content of the mortar is boosted to 3.5 % by mass of cement. Mortar bars are cured for 48 hours prior to autoclaving at 130°C for five hours at peak temperature. This paper details the test procedure, expansions, comparisons with the accelerated mortar bar test and the concrete prism test, within- and multi-laboratory precisions, and investigation into the amount of alkali leaching during the test. For 85 % of the 20 aggregates tested, there was agreement between the autoclave test and ASTM C1260 in determining whether or not an aggregate was reactive to some degree. The agreement between the autoclave test and ASTM C1293, Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction, was 100 % for ten of the aggregates for which ASTM C1293 data were available. The average within- and multi-laboratory coefficients of variation were 5.9 and 20.0 %, respectively. Results showed alkali leaching to be between 6 and 9 % per mortar bar. This study demonstrated the viability of the five-hour autoclave test for rapidly assessing aggregate reactivity in military construction operations.

Evaluation of the concrete prisms test method for assessing the potential alkali-aggregate reactivity of recycled concrete aggregates

The concrete prism test (CPT) is a widely used method for assessing the potential alkali-aggregate reactivity of any given natural aggregate. This paper presents the evaluation of the current method and its applicability to assess the alkali-silica reactivity of recycled concrete aggregates (RCA). The testing was carried out on two different types of RCA: manufactured from >15years old blocks disposed outdoors and from a demolished overpass infrastructure. Following the analysis of the different parameters that make RCA different than original aggregates, it has been found that the residual mortar content of the RCA particles and their absorption condition prior to their addition to mixtures are considerably important. The CPT is reliable to access RCA reactivity, however it is therefore recommended to use saturated RCA as higher expansion is obtained under these conditions. It is also recommended to use the aggregate dry rodded bulk density to determine the coarse aggregate-to-sand ratio, instead of using a fixed 60 to 40 ratio. Moreover, no pessimum effect was observed using RCA; in fact, the expansion of the test prisms was increasing with increasing RCA content. The extent of damaged suffered by the concrete from which the RCA are manufactured and the geology of the original virgin aggregates incorporated in the RCA are also important parameters to consider while using the CPT to assess correctly each RCA reactivity.

Influence of grinding method and particle size distribution on the properties of Portland-limestone cements

The benefits of using limestone as a partial replacement of Portland cement (PC) are well established in the literature. Economic and environmental advantages by reducing CO2 emissions are well known. This paper describes the influence of the producing method (intergrinding or separate grinding) and particle size distribution on properties of Portland-limestone cements (PLC). Experiments were carried out on cement paste including normal consistency, time of setting, and heat of hydration, on cement mortar including compressive and flexural strength, and potential alkali reactivity of aggregates, and on concrete including compressive strength, sorptivity, electrical resistivity, and rapid chloride permeability. In this study, ten types of cements including two types of PC, and eight types of PLC were used. The results show that mechanical and durability properties of PLC were not affected significantly by grinding method. In addition, the use of cements with high fineness is not very effective on improvement of durability properties.

Effect of Portland Cement Fineness on ASTM C1260 Expansion

Abstract The present study is aimed at investigating the effect of portland cement fineness on the results of ASTM C1260 tests—Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method). The effects of clinker alkali content, aggregate reactivity, and sodium hydroxide (NaOH) solution concentration on the mortar expansion test results were also studied. In this study, high and low alkali portland cement clinkers were selected and ground with gypsum in a laboratory ball mill to three fineness levels: 300, 400, and 500 m2/kg (Blaine). Moderately- and highly-reactive aggregates were tested with these cements according to ASTM C1260. In addition to the standard 1 N NaOH solution, a 0.5 N NaOH soak solution was also used. The results show that mortar-bar expansion was promoted with increased cement fineness regardless of clinker alkali, aggregate reactivity, or soak solution normality. Clinker alkali had no or little effect on moderately reactive aggregate; whereas it had considerable effect on highly reactive aggregate. Highly reactive aggregate tended to be more sensitive to cement fineness and alkalinity. Although cement fineness and clinker alkali content did not affect the classification in terms of potential reactivity of the aggregates used in this study, they might change the classification for the aggregates near the boundary between reactive and nonreactive aggregates. Specification of fineness and alkali content of cement, or both, might be beneficial to further improve the reliability and reproducibility of ASTM C1260.

Application of Modified ASTM C1260 Test for Fly Ash-Cement Mixtures

The ASTM C1260 accelerated mortar-bar test is a commonly used method for rapid identification of potential alkali-aggregate reactivity and may also be used for assessing the effectiveness of supplementary cementitious materials in suppressing alkali–silica reactivity (ASR). A general criticism of this test method is the severity of test conditions. It is not uncommon for aggregates with a good field-performance track record and no history of ASR to test reactive by this method. The purpose of this study was to evaluate the effectiveness of fly ash in controlling expansion due to ASR, using a modified ASTM C1260 test. Three different strengths of NaOH solution were used to test reactive, potentially reactive, and nonreactive aggregates in the presence of Class F and Class C fly ash at 20% and 35% replacement by mass of cement. The other variables included high- and low-alkali cement, extended curing time, and a longer testing period of 28 days. A correlation was drawn between additional evaporable water and expansion due to ASR.

Alkali-aggregate reactivity in Québec (Canada)

In the province of Québec, due to the particular geology and the historic use of high-alkali cements, a large number of concrete structures are affected by alkali-silica reactivity (ASR). Consequently, tremendous effort was made in this province during the last 20 years on (1) the determination in the laboratory (testing methods) as well as in the field (inspection of structures) of the potential alkali-aggregate reactivity (AAR) of concrete aggregates, (2) the prevention of AAR in new structures, and (3) the management of existing structures affected by this problem. For new structures, the most popular measure used in Québec in the presence of potentially reactive aggregates consists of limiting the alkali contribution by the cement to 3 kg/m3 of concrete (Na2Oeq). Also, blended silica fume cements were used on many occasions against ASR; ternary cements containing fly ash and silica fume, which proved in the laboratory to be effective against ASR, are presently available. As concerns the existing structures affected by ASR, many of them were repaired using various techniques ranging from the simple application of a penetrating sealer to the application of post-constraints or slot cutting.Key words: aggregate, alkali-aggregate reaction, cement, concrete, diagnosis, management, preventive measures, prognosis, Québec, testing.

A critical review of ultra-accelerated tests for alkali-silica reactivity

A large number of ultra-accelerated test procedures, for determining the potential alkali reactivity of aggregates, have been developed, particularly in the past 15 years. An ultra-accelerated test method is defined as one which yields results within a few days or, at most, a few weeks. A number of ultra-accelerated test methods have been adopted as ‘standard tests’, but few have been adequately evaluated. The rapid globalization of the construction industry will require the harmonization of National Standard Test Methods. The major requirement of ultra-accelerated test methods is that they should correctly predict the potential reactivity of aggregates in greater than 95% of the cases. Due to the complexity and variability in the composition and grain size of aggregates, it is improbable that a single test method will be developed which would be appropriate for evaluating all types of aggregates. Another major requirement for ultra-accelerated test methods is that the interlaboratory coefficient of variation should be low, preferably less than 12%. At present, only the NBRI accelerated mortar bar method has been subject to adequate inter-laboratory evaluation. However, a more limited inter-laboratory investigation showed that the autoclave mortar bar test also shows considerable potential, as a satisfactory ultra-accelerated test method. Further refinement of the NBRI and autoclave methods is required to improve their performance with a wide variety of aggregates.

Aggregate expansivity due to sulfide oxidation — I. Reaction system and rate model

Oxidation and hydration of sulfides in aggregate materials can yield to expansive reactions that affect the durability of concrete. This process is, in principle, independent from the potential alkali-aggregate reactivity and the oxidation of the sulfide is the rate-limiting reaction. A model is presented to evaluate the kinetic evolution of expansion due to sulfide oxidation and subsequent sulfate attack on the paste.

Use of the NBRI accelerated test to evaluate the effectiveness of mineral admixtures in preventing the alkali-silica reaction

The NBRI accelerated test for determining the potential alkali reactivity of aggregates can also be used to assess the ability of mineral admixtures to prevent deleterious expansion in concrete, which is caused by the alkali-silica reaction of quartz-bearing aggregates. Results from the accelerated test, the ASTM C227 mortar prism test, and tests undertaken on concrete beams and cubes exposed outdoors, are compared and discussed.

Re-evaluation of standard mortar bar and concrete prism tests for alkali-aggregate reactivity

The effectiveness of the mortar bar ASTM C227 and concrete prism CSA A23. 2-14A tests for evaluating the potential alkali-aggregate reactivity of classical alkali-silica, late expansive siliceous and alkali-carbonate aggregates is discussed. It is emphasized that petrographic examination is an essential preliminary step in the evaluation of potential alkali reactivity of all aggregates. The expansion limits set to differentiate between deleteriously expansive and innocuous cement-aggregate combinations by ASTM, CSA, U.S. Corps of Engineers, U.S. Bureau of Reclamation and by the author are evaluated for use with classical alkali-silica, late-expanding siliceous and alkali-carbonate reactive aggregates.