Non-reactive Aggregate Research Articles

Effects of seawater on AAR expansion of concrete

Recently, AAR was identified in submerged piles of some bridges in tidal waters. Microstructural examination detected chloroaluminate salts in some cracks. To clarify whether seawater had influenced the deterioration an experimental program was planned to examine the effects of sodium chloride on AAR under various curing conditions. Concrete prisms containing either of highly-reactive, slowly-reactive or nonreactive aggregate, and either low or high alkali contents, were stored in saltwater (representing seawater) or at 100% RH, at temperatures of 38, 60 and 80 °C, for expansion measurement over 600 days, after which the temperature for those stored in saltwater was lowered to 23 °C, to check its effect on further expansion, which could be attributed to precipitation of ettringite and/or Ca-chloroaluminate. The results indicate that the type of aggregate and concrete alkali content had the greatest effect on AAR expansion. Exposure to saltwater did not have any significant effect on the AAR expansion.

Selection of an effective ASR-prevention strategy for use with a highly reactive aggregate for the reconstruction of concrete structures at Mactaquac generating station

Mactaquac Generating Station was constructed in the mid 1960's and is located in the province of New Brunswick in Eastern Canada. The effect of ASR expansion on the concrete structures of the station were first noticed approximately 10 years after construction and, ASR was conclusively diagnosed in 1986. Since 1985, various remedial measures have been undertaken to mitigate the effects of concrete expansion. Eventually reconstruction of the concrete structures will be necessary and current projections are that replacement should be complete by 2030. Due to the lack of any suitable locally-available non-reactive aggregate, consideration is being given to using the same source of reactive aggregate for reconstruction. This paper describes a research study to determine the optimum strategy for preventing deleterious ASR expansion with this aggregate. The options being evaluated include the use of pozzolans and slag, limiting the alkali content of the concrete, and the use of chemical admixtures. Methods of evaluation include accelerated laboratory tests and field exposure of large blocks.

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.

Measurement of alkali–silica reaction progression by ultrasonic waves attenuation

Development of non-destructive methods, developed specifically for assessing the damage induced by alkali–silica reaction (ASR) in concrete structures, is needed in order to carry out a systematic evaluation of the concrete condition. The aim of this study is to monitor the evolution of the ASR-damage in laboratory with concrete samples with ultrasonic pulse velocity and attenuation of ultrasonic waves methods. For this study, results of both methods were compared with expansion and mass variation.One reactive concrete mixture was made with reactive aggregate, and one other mixture, incorporating non-reactive aggregate, was made as a control. Specimens were kept at 38 °C in a 1 mol l−1 NaOH solution to accelerate the reaction. Attenuation of transmitted ultrasonic waves appeared to be more appropriate for the evaluation of ASR-damage compared with pulse velocity. The attenuation of accelerated reactive concrete cylinders increased by 90% after 1 year while it increased by 40% for the non-reactive concrete used as a control. Major part of the attenuation increase in the non-reactive concrete is due to liquid absorption.This work suggests that in-situ non-destructive techniques based on ultrasonic wave attenuation, like ultrasonic attenuation tomography, should be developed in order to evaluate the development of ASR in concrete structures. Petrographic examination confirmed that damage to concrete is associated with ASR.

Dual effectiveness of lithium salt in controlling both delayed ettringite formation and ASR in concretes

The influence of lithium nitrate on expansions due to delayed ettringite formation (DEF) and alkali-silica reaction (ASR) has been investigated. Effects of the lithium salt were examined in heat-cured mortars and concretes containing one or both damage mechanisms. The mortars and concretes made using reactive and/or non-reactive aggregates were subjected to heat treatment consisting of a hydration delay period of 4 h at 23 °C followed by steam-curing at 95 °C and then stored in limewater. Results showed that the lithium salt admixture was able to reduce the occurrence of deleterious expansion due to delayed ettringite formation in addition to controlling alkali-silica reaction in cementitious systems containing one or both mechanisms. In concretes made using non-reactive limestone aggregates, incorporation of lithium nitrate in a proportion of 0.74 M ratio of Li to (Na+K) was found to control delayed ettringite formation during the one-year period of this study.By analyzing the leaching properties of lithium and other alkalis from mortars during storage, it was found that a substantial amount of lithium was retained in the cementitious system in a slightly soluble form, and is expected to be responsible for reducing DEF.

Modified ASTM C 1293 Test Method to Investigate Potential of Potassium Acetate Deicer Solution to Cause Alkali-Silica Reaction

Following the recent investigations by FAA into premature deterioration of some airfield concrete pavements that were exposed to deicing chemicals, a comprehensive research study was undertaken to examine the role of deicing solutions in causing alkali-silica reaction (ASR) in mortar and concrete test specimens. It was conducted to evaluate the influence of a potassium acetate deicer and anti-icer in causing ASR distress in concrete specimens. A modified ASTM C 1293 test method was employed in this investigation, in which concrete prisms prepared with aggregates of known reactivity were exposed to 50% solution of potassium acetate (KAc) or 1 normal solution of sodium hydroxide (1N NaOH) during the course of testing. Expansion of the concrete test prisms was monitored periodically, along with changes in their dynamic modulus of elasticity. In addition, visual and scanning electron microscopic examinations were conducted on polished specimens at the conclusion of tests. The pH of the deicer soak solution was monitored to detect any changes caused by its interaction with the specimens. Findings from the study indicate that potassium acetate deicer solution is capable of causing significant ASR distress in concrete specimens containing reactive aggregates. A secondary reaction product, composed primarily of a potassium sulfate phase, was observed in prisms containing both reactive and non-reactive aggregates. This product was predominantly found as an infilling in cracks and voids. Additional research needs are identified to help to decipher the precise mechanisms involved in this attack.

Investigation into Potential of Alkali–Acetate–Based Deicers to Cause Alkali–Silica Reaction in Concrete

Recent investigations by the FAA into the condition of airfield pavements have indicated increased occurrence of premature deterioration in concrete pavements, particularly caused by alkali–silica reaction (ASR). On the basis of the evidence, it was suspected that certain deicing chemicals used on the pavements may have been responsible for the distress. This paper presents the results from a study conducted to investigate the effect of potassium acetate–and sodium acetate–based deicers on causing ASR in test specimens. A modified ASTM C 1260 test procedure was used in this study, in which mortar bars prepared with reactive aggregates were soaked in deicer solutions, instead of 1 N sodium hydroxide solution as in the standard ASTM C 1260 test. Tests were conducted on four reactive aggregate sources and one nonreactive aggregate, using a low-alkali and a high-alkali cement. In addition, standard ASTM C 1260 tests were conducted on all aggregates considered in this study. The effect of concentration and temperature of soak solutions on the observed expansions of mortar bars was also investigated. Length-change measurements, dynamic modulus of elasticity, scanning electron microscopy, and energy dispersive X-ray analyses were conducted on test specimens. The pH values of the soak solution were monitored to observe any interactions between the soak solution and the mortar bars. On the basis of this research, it was found that the two common airfield deicing chemicals—potassium acetate–and sodium acetate–based deicer solutions—have a significant potential to cause ASR in test specimens containing reactive aggregates.

Investigation into Potential of Alkali-Acetate-Based Deicers to Cause Alkali-Silica Reaction in Concrete

Recent investigations by the FAA into the condition of airfield pavements have indicated increased occurrence of premature deterioration in concrete pavements, particularly caused by alkali-silica reaction (ASR). On the basis of the evidence, it was suspected that certain deicing chemicals used on the pavements may have been responsible for the distress. This paper presents the results from a study conducted to investigate the effect of potassium acetate- and sodium acetate-based deicers on causing ASR in test specimens. A modified ASTM C 1260 test procedure was used in this study, in which mortar bars prepared with reactive aggregates were soaked in deicer solutions, instead of 1 N sodium hydroxide solution as in the standard ASTM C 1260 test. Tests were conducted on four reactive aggregate sources and one nonreactive aggregate, using a low-alkali and a high-alkali cement. In addition, standard ASTM C 1260 tests were conducted on all aggregates considered in this study. The effect of concentration and te...

Effects of aggregate size and angularity on alkali–silica reaction

The effects of reactive aggregate size and aggregate angularity on alkali–silica reaction (ASR) were studied. An all-in natural reactive aggregate was used. The coarse aggregate particles were crushed to obtain crushed fine particles. The angularity of the aggregate was determined using ASTM C1252 and EN 933-6 methods. ASTM C1260 accelerated mortar bar test was conducted to compare the ASR expansion caused by various aggregate size fractions. The effect of the size of the particles on ASR expansion was studied by replacing each size fraction of the non-reactive aggregate with the reactive aggregate of the same size. In spite of similarity of the chemical and mineralogical compositions, the crushed aggregate caused higher ASR expansion than the natural aggregate in all size fractions. The summation of the expansions of individual reactive size fractions of both aggregates was found to be higher than that of corresponding control mixtures.

A study on the alkali-aggregate reaction in high-strength concrete with particular respect to the ground granulated blast-furnace slag effect

The alkali-aggregate reaction (AAR) in high-strength concrete and the effect of ground granulated blast-furnace slag (GGBFS) were studied in this paper. From the results of this study, following conclusions can be drawn: (1) In high-strength concrete, because of high alkali content, the possibility of alkali-aggregate reaction is much higher than conventional concrete. (2) The occurrence of large expansion can be prevented by using nonreactive aggregate, which has been judged according to the mortar bar and chemical method's as specified in JIS A 5308, in high-strength concrete. (3) The replacement of cement by 30% of blast-furnace slag and using low-alkali cement can prevent the alkali-aggregate reaction from causing large expansion in high-strength concrete.

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.

A comparison of RTA T363 and ASTM C1260 accelerated mortar bar test methods for detecting reactive aggregates

Nowadays, bridge structures are designed for 100 years of service life, and care must be taken to avoid materials that would cause premature deterioration problems in the structures. This requires careful attention to structural design, selection of sound materials and manufacture of components, which would remain durable under the given environmental conditions (exposure and loading). One of the important concrete deterioration problems is the alkali–aggregate reaction (AAR), which can cause cracking and diminished strength properties in concrete, and the best method of avoiding it is to select nonreactive aggregates for the concrete or those that could safely be combined with mineral additives to suppress their reactivity. The purpose of this paper is to compare the expansion results obtained by the two test methods using a number of aggregates with known field performance and to assess the validity of their expansion limits in predicting the field performance of these aggregates. The paper also covers the comparison of the two test methods for the assessment of the effectiveness of fly ash in suppressing AAR expansion.

The effect of stress relaxation, self-desiccation, and water absorption on the alkali-silica reaction in low [formula omitted] ratio mortars

A device has been designed and tested for measuring the stress caused by the alkali-silica reaction (ASR) in mortars. Specimens were placed in a frame equipped with a load cell, allowing us to approximately fix the strain at zero and measure the total stress generated over time. The specimens and the frame were immersed in a 1-N NaOH solution at 50 °C. Even without ASR, the specimens expanded due to water absorption that relieves the shrinkage caused by self-desiccation. In addition, applied stresses, as well as stresses that were set up in the sample by expansion caused by ASR and/or water absorption, were subject to stress relaxation. By using companion samples having nonreactive aggregates, we were able to distinguish the stress caused by ASR from that caused by water absorption-driven expansion. The effects of stress relaxation could not be removed without further experimentation and theoretical analysis.

Evaluating the reaction of actual compositions of concrete with respect to alkali-aggregate reactions preliminary testing at 110°C and 150°C

Different curing methods at 110°C and 150°C were tested on concrete prisms of various compositions in order to develop a rapid expansion test to evaluate the risl of AAR in actual concrete compositions. While no significant expansion occurred at 110°C (in water or water vapour), we obtained expansion values in the range 0–0.35% for concrete prisms cured at 150°C in water or in alkaline solution during 3–5 weeks. For both curing methods at 150°C, the highest expansion values are obtained for potentially reactive aggregates and high alkali levels in the concrete, whereas the lowest expansions correspond to the concrete mixes containing only non-reactive aggregates or having a total alkali content of less than 2.5 kg m−3. However, alkaline treatment accounts better for the effectiveness of mineral admixtures and, in general, for the reactivity of the concrete compositions, than curing in water. From the correlations obtained with data at 38°C or 60°C and 100% RH after 12 and 4 months, respectively, alkaline curing for 3 weeks at 150°C shows a reasonable potential for predicting accurately the influence of the total alkali content, nature of the aggregates, water/cement ratio and effectiveness of mineral admixtures on concrete expansion.

Fused quartz as a reference reactive aggregate for alkali — silica reaction studies

The use of fused quartz as a reference reactive aggregate for alkali—silica reaction (ASR) studies was investigated on mortar bars made with Portland or blended cement, natural quartzitic sand as a non-reactive aggregate and fused quartz. The quartz glass varied from 0 to 75 % by mass of the total aggregate. The expansions of the bars were measured under different storage conditions (exposure at 38°C and 100% relative humidity (RH), immersion in a saturated NaCl solution at 50°C or in a IM NaOH solution at 80°C). The proportion of fused quartz in the overall aggregate was found to be strongly limited by the high water demand of fused quartz and by its abnormal expansivity with low-alkali cement in mortars stored at 38°C and 100% RH. A 4% dosage of fused quartz appears to be suitable for the preparation of mortar specimens with appropriate characteristics of workability and expansivity (workability requirements as specified in ASTM C227, high expansion with high-alkali Portland cement and insignificant expansion with low-alkali Portland cement in mortars stored at 38°C and 100% RH). This dosage also appears to be appropriate for investigation of the effects of mineral admixtures on ASR in mortars subjected to various storage conditions.

Phagocyte interactions in echinoid and asteroid echinoderms

Phagocytes of the starfishes Asterias rubens L., and Marthasterias ghcialis (L.) (Echinodermata: Asteroidea) phagocytose allogeneic and xenogeneic phagocytes in vivo, but form non-reactive aggregates or syncytia in vitro. The coelomocytes of the sea urchins Echinus esculentus (Mortensen) and Psammechimts miliaris (Gmelin), (Echinodermata: Echinoidea) also form aggregates or syncytia with allogeneic and xenogeneic cells in vitro. Mutual cy totoxicity could not be demonstrated either by enzyme-release or by decrease in numbers of viable cells in cultures of mixed origin as compared with autogeneic controls. The factors which may govern cell recognition and behaviour are discussed.

Digital simulation of the aggregate–cement paste interfacial zone in concrete

Researchers using backscattered scanning electron microscopy, along with quantitative image analysis techniques, have clearly demonstrated the existence of a highly porous interfacial region between aggregate particles and the cement paste matrix in ordinary Portland cement concrete. This paper presents the results of a digital-image-based simulation model of this interfacial zone. A dissolution-diffusion-reaction-like cycle of hydrating cement particles is directly simulated using cement particles packed around a simple nonreactive aggregate particle. The model is two-dimensional, as we are comparing to experimental results obtained on two-dimensional images of polished sections. The qualitative features seen experimentally, such as large amounts of porosity and calcium hydroxide in the interfacial zone, are accurately reproduced. A new mechanism, one-sided growth, is proposed, along with the more usual particle-packing ideas, as an explanation of the origin of the characteristic features of the interfacial zone.

Re-examination of AAR in an old concrete

Concrete from a dam which has been reported to have suffered AAR was re-examined to explore whether the damage was at least partly due to AAR. The re-examination of the concrete confirmed the previous identification of AAR. The phyllite aggregate that had been used in the concrete was also subjected to testing for alkali reactivity in comparison to known reactive and non-reactive aggregates, and provided further evidence that the damage was partially caused by the AAR.

安山岩のアルカリシリカ反応試験結果の比較

The mortar-bar expansion test (ASTM C227), chemical test (ASTM C289) and measurement of specific gravity were performed on the aggregates of which the mineral characteristics were discussed in the previous report. The cement used for the mortar bar test was an ordinary portland cement with an alkali content of 1.6% (equivalent Na2O) adjusted by NaCl reagent. The results of the tests on 27 mortar bars showed that the rate of expansion was in the range of 0.02-0.65% in 6 months. Twenty-one aggregates were classified as being reactive according to the ASTM criteria. In the chemical test, the determined concentration of silica in solution ranged from 190mmol/l to 670mmol/l. The reduction in alkalinity of the NaOH solution ranged from 65mmol/l to 290mmol/l. All of the 36 aggregates belonged to the reactive group. The specific gravity of the aggregates was in the range of 2.19-2.68. Although no relationship was observed between mortar bar expansion and the result of the chemical test, a negative correlation was found between mortar bar expansion and specific gravity. To prevent excessive expansion, the isopleth map of the rate of expansion was drawn based on the test results on a number of mortar bars to cover variables in alkali content of the cements and in mixing ratio of the reactive aggregate of andesite and the nonreactive aggregate of greywacke.

A rapid method for identification of alkali reactivity of aggregate

A rapid method for the identification of alkali reactivity of aggregate within two days has beeb achieved. 1×1×4 cm mortar bars with cement:aggregate = 10:1, w/c = 0.3, size of aggregate = 0.15−0.75mm were demolded after one-day curing and subjected subsequently to 100°C steam curing for 4 hours, after which they were immersed in 10% KOH solution and autoclave-treated at 150°C for 6 hours. After each stage of curing expansion measurements were carried out. From the data of more than thirty species of rocks, the authors arrived at the conclusion that the rapid method could be used to distinguish reactive and non-reactive aggregate. The results of microscopic observation made clear that the expansion of mortar bars was caused by alkali-silica reaction. This method cannot only be used to identify the alkali reactivity of aggregate, but when combined with the use of optic and electron microscope, can be also used to study the mechanism of alkali-aggregate reaction.