The effects of potassium and rubidium hydroxide on the alkali-silica reaction

Expansion of mortar specimens prepared with an aggregate of mylonite from the Santa Rosa mylonite zone in southern California was studied to investigate the effect of different alkali ions on the alkali-silica reaction in concrete. The expansion tests indicate that mortar has a greater expansion when subjected to a sodium hydroxide bath than in a sodium-potassium-rubidium hydroxide bath. Electron probe microanalysis (EPMA) of mortar bars at early ages show that rubidium ions, used as tracer, were present throughout the sample by the third day of exposure. The analysis also shows a high concentration of rubidium in silica gel from mortar bars exposed to bath solutions containing rubidium. The results suggest that expansion of mortar bars using ASTM C 1260 does not depend on the diffusion of alkali ions. The results indicate that the expansion of alkali-silica gel depends on the type of alkali ions present. Alkali-silica gel containing rubidium shows a lower concentration of calcium, suggesting competition for the same sites.     

Comparison of alkali-silica reaction products of fly-ash- or lithium-salt-bearing mortar under long-term accelerated curing

The alkali-silica expansion of mortar specimens bearing fly ash (FA), lithium carbonate, and lithium fluoride under long-term accelerated curing was investigated. ASTM C1260 standard test method was applied and expansions were recorded up to 56 days. The composition of alkali-silica reaction (ASR) products was also studied by environmental scanning electron microscopy (ESEM). It was observed that in Li-bearing mixtures, the expansions ceased beyond 28 days. However, in fly-ash-bearing mixtures, the reactions were continued and expansions were increased steadily throughout the test. No clear correlation was found between the composition of massive reaction products and expansion values. However, except for lithium-fluoride-bearing samples, good correlation was observed between the composition of crystallized reaction products and expansion values.     

Use of perlite powder to suppress the alkali-silica reaction

Reported below are the results from a study aimed at mitigating the deleterious alkali-silica reaction by using perlite powder as an admixture. The expansion of mortar bars containing various amounts of silica fume (SF), expanded perlite, and natural perlite was studied. Two kinds of reactive aggregates were used in the study: highly reactive river aggregate containing opal and marginally reactive monzo-diorite aggregate. Expanded perlite and silica fume were tested with both aggregate, separately; on the other hand, natural perlite was tested only with monzo-diorite aggregate. The bars were cast in accordance with ASTM C1260, accelerated mortar bar method, and were stored in NaOH solution for 30 days. Length changes were measured and reported. The results showed that both expanded and natural perlite powder (NPP) have potential to suppress the deleterious alkali-silica expansion.     

Alkali-silica reactivity of some frequently used lightweight aggregates

Lightweight aggregates (LWAs) are frequently used in concrete as well as in thermally insulating mortars and grouts, so that information on their alkali-silica reactivity (ASR) is very important. Four LWAs—expanded vermiculite, expanded clay, expanded glass and perlite—were studied regarding their ASR, using the following test methods: the accelerated mortar bar test (ASTM C 1260), the rapid chemical test (ASTM C 289) and the combined scanning electron microscopy-energy dispersive X-ray technique (SEM-EDX). According to these methods, neither the expanded vermiculite nor the expanded clay exhibited any potential ASR. On the other hand, in the case of the aggregates containing a glassy phase (expanded glass and perlite), the results of SEM-EDX analysis showed serious decomposition of aggregate texture due to ASR, although no deleterious expansion was observed in the accelerated mortar bar test. Therefore, suitable test criteria for ASR need to be defined for LWAs of this type when the AMBT method is used, as has already been suggested for slowly reactive aggregates in Australia.     

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.     

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.     

Alkali-silica reactivity of large silica fume-derived particles

Pozzolanic materials, including silica fume, are commonly added to concrete to reduce expansion due to alkali-silica reaction (ASR). It has been noted, however, that commercial silica fume is not always adequately dispersed, and large agglomerates may be present. These large particles have been hypothesized to act as amorphous silica aggregates, thereby participating in an expansive reaction with the alkalis present in cement paste pore solution. If such were the case, some silica fume particles would actually aggravate expansion due to ASR rather than suppress it. The present investigation characterizes the microstructure and morphology of agglomerated and sintered silica fume particles and compares their effects on alkali-silica-related expansion. While a 5% replacement of moderately reactive sand with sintered silica fume aggregates caused significant expansion under accelerated testing conditions (modified ASTM C1260), the replacement with large agglomerates of densified silica fume decreased expansion compared with control mortar bars containing only sand. Both the sintered aggregates and the agglomerates reacted with the pore solution; one reaction was expansive, while the other was not.     

废弃阴极射线管玻璃砂对砂浆性能的影响

废弃阴极射线管（cathoderaytubes,CRT）玻璃因其含有有害物质铅而导致严重环境问题,为此,使用粉煤灰、磨细矿渣作为矿物掺合料,研究了磨细阴极射线管玻璃（groundcathoderaytubeglass,MG）取代0、30％、60％、100％（质量分数,下同）河砂细骨料时砂浆新拌性能、力学性能、干缩性能、碱骨料反应（alkali-silicareaction,ASR）膨胀性能、金属铅浸出值。结果表明：随着MG取代比例从0变化到100％,砂浆初始流动度与容重不段增加,硬化砂浆抗压强度、抗折强度和静弹性模量、干缩性能先增加后逐渐减小;MG取代比例为60％时,砂浆具有较高力学性能和较大干缩值;砂浆ASR膨胀值和硬化砂浆金属铅浸出值随MG取代比例增加而增加,但仍在安全范围内;掺加矿物掺合料的MG砂浆作为循环材料可用于干燥环境下的建筑砂浆。     

Studies of alkali-silica reaction — part II effect of air-entrainment on expansion

From an extensive petrographic investigation of concrete samples suffering from alkali-silica reaction, it has been hypothesized that a deliberately introduced air-bubble system will reduce expansion due to alkali-silica reaction. The above hypothesis has been tested using mortar bars made from 35 sand types of differing degrees of alkali-silica reactivity. The results show that on the average the introduction of 4% air decreased the expansion by about 40%. A petrographic examination of mortar bars has shown that in the case of reactive sand the air-bubbles tend to get filled up by gel, but the air-bubbles remain empty in the case of unreactive sand. It has also been noted that this filling up of the air-bubbles will decrease their effectiveness in a freezethaw environment.     

Test methods for determining potential alkali-silica reactivity in cements

The ASTM C227 test can be modified to develop performance tests for predicting potential alkali-silica reactivity of both portland and blended portland cements. The two methods of test investigated here differed mainly on the choice of the standard reactive aggregate, one using pyrex and the other a naturally occurring reactive silica. Low water/cement and aggregate/cement ratios were found helpful in accelerating expansion of mortar bars stored at 110F (43C). A 14-day test period was considered by the writers to be adequate for the evaluation of relative alkali-silica reactivity of a cement in the methods developed. Test data in 17 portland cements and 10 blended portland cements are reported to show that for this purpose performance tests may be more suitable than chemical specification limits.     

Volcanic ash and pumice as cement additives: pozzolanic, alkali-silica reaction and autoclave expansion characteristics

This study reports the results of investigation to assess the suitability of volcanic ash (VA) and pumice (VP) powder to be used as cement additives. Pozzolanic activity of VA and VP was tested according to the Italian standard and found to be acceptable. The strength activity index with Portland cement and the effectiveness of VA and VP admixture in controlling alkali-silica reaction and autoclave expansion were tested according to ASTM standards. Mortar cubes were specially prepared as per ASTM standards for these studies using different mixes with varying percentages of VA and VP (0-40%) as cement replacement. The results are then compared with ASTM requirements to assess the suitability of VA or VP as cement additives.     

Effect of modified zeolite on the expansion of alkaline silica reaction

Effect of modified zeolite (MZ) on the ASR expansion was analyzed, and comparison between MZ and other mineral admixtures such as fly ash and ground blast furnace slag was made according to ASTM C441. It is shown that the modified zeolite derived from immersion of natural zeolite(NZ) in 2 N NH₄Cl solution might decrease the concentration of soluble alkalis in pore solution more effectively, as the alkali ions could be exchanged by NH₄⁺ existed in MZ with formation of NH₃·H₂O, as a result, the expansion due to alkali-silica reaction (ASR) was controlled consequently. In ASTM C441 test, the 14-day expansion of the specimen incorporating 5% of MZ was less than 0.1%, while the percentage of the fly ash and blast furnace slag with the same efficiency was about 25% and 40%, respectively. Physical properties of cement incorporating 5% of MZ, such as normal consistency, setting time, bending and compressive strength also met the requirement of the Chinese national standard.     

Studies on blended cements containing a high volume of natural pozzolans

This paper presents the results of an investigation on the characteristics of laboratory-produced blended portland cements containing 55% by weight volcanic tuffs from Turkey. Volcanic tuffs from two different resources were used. Using different grinding times, particle size distribution, setting time, compressive strength, and alkali-silica activity of the blended cements were investigated and compared with reference portland cements ground for the same time period. For the compressive strength test, a superplasticizer was used to obtain mortar mixtures of adequate workability at a constant water-to-cement (w/c) ratio of 0.45. Compared to portland cement, the blended cements containing 55% pozzolan showed somewhat lower strengths up to 91 days when the grinding time was 90 min. However, at 91 days, blended cements and portland cements ground for 120 min showed similar strength. Moreover, blended cements containing 55% natural pozzolans showed excellent ability to reduce the alkali-silica expansion.     

废玻璃粉作为辅助胶凝材料对砂浆性能影响及作用机理

作为辅助胶凝材料掺入混凝土是废弃玻璃回收利用的途径之一。研究废玻璃粉掺料对砂浆性能影响及作用机理,结果可为该类应用提供指导。本文研究0~0.075 mm、0.075~0.15 mm和0.15~0.3 mm这三组不同粒径废玻璃粉作为辅助胶凝材料对砂浆力学性能及碱硅酸反应(ASR)膨胀作用的影响。研究发现:掺入玻璃粉粒径为0~0.075 mm可将砂浆28 d抗压强度增加5%~15%,ASR膨胀率减小20.2%;掺入玻璃粉粒径为0.15~0.3 mm则使砂浆28 d抗压强度降低5%~8%,ASR膨胀率增加39.7%。采用热重分析、等离子电感耦合、扫描电镜及能谱分析试验对反应产物、孔溶液、微观结构及其元素分布进行检测。分析认为粒径粗的玻璃粉碱骨料活性强,易发生ASR,导致膨胀率增加;粒径细的火山灰活性强,发生火山灰反应生成了膨胀率低的低钙硅比水化硅酸钙凝胶,该产物不仅会吸收Na⁺、K⁺,从而减少用于发生ASR的反应物含量,而且更密实,有利于降低孔隙率,减少水的渗透,提高抗压强度并抵抗膨胀压。     

Long-term effectiveness and mechanism of LiOH in inhibiting alkali-silica reaction

A practical alkali reactive aggregate-Beijing aggregate was used to test the long-term effectiveness of LiOH in inhibiting alkali-aggregate reaction (AAR) expansion. In this paper, the most rigorous conditions were so designed that the mortar bars had been cured at 80 °C for 3 years after being autoclaved for 24 h at 150 °C. At this condition, LiOH was able to inhibit long-term alkali-silica reaction (ASR) expansion effectively. Not only was the relationship between molar ratio of n(Li)/n(Na) and the alkali contents in systems established, but also the governing mechanism of such effects was studied by SEM.     

The alkali-silica reaction in alkali-activated granulated slag mortars with reactive aggregate

The expansion of alkali-activated granulated blast furnace slag (AAS) cement mortars with reactive aggregate due to alkali-silica reaction (ASR) was investigated. The alkaline activator used was NaOH solution with 4% Na₂O (by mass of slag). These results were compared to those of ordinary portland cement (OPC) mortars. The ASTM C1260-94 Standard Test Method based on the NBRI Accelerated Test Method was followed. The nature of the ASR products was also studied by SEM/EDX. The results obtained show that the AAS cement mortars experienced expansion due to the ASR, but expansion occurs at slower rate than with OPC mortars under similar conditions. The cause of the expansion in AAS cement mortars is the formation of sodium and calcium silicate hydrate reaction products with rosette-type morphology. Finally, in order to determine potential expansion due to ASR, the Accelerated Test Method is not suitable for AAS mortars because the reaction rate is initially slow and a longer period of testing is required.     

Compatibility between ecocement produced from incinerator ash and reactive aggregates in ASR expansion of mortars

Recently, in Japan, two new-type hydraulic cements, high early strength type ecocement (HEC) and normal type ecocement (NEC), have been developed using incinerator ashes up to 50% of the raw materials. In this study, the compatibility of these ecocements with various types of reactive aggregates with respect to alkali-silica reaction (ASR) was studied. Ordinary Portland cement (OPC) and blast furnace slag cement (BFSC) were also used for a comparative study. Two types of the accelerated mortar bar expansion test, the JIS A1146 and the Danish methods, were used to clarify the expansion behavior of mortars made with the above cements. The influence of a combination of the chemical and mineralogical compositions of cement and the reactive components of aggregate on both the amount of ASR gel and the expansion rate of the mortar was also investigated. From the results, it was found that the expansion behaviors of mortars due to ASR varied significantly depending on a combination of both the mineralogical composition of cement and the reactive component of aggregate.     

Reactivity of reclaimed concrete aggregate produced from concrete affected by alkali-silica reaction

This paper presents results from a research program that focused on studying the reactivity of reclaimed concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The results showed that RCA produced from ASR-affected concrete causes significant expansion when used in new concrete. The expansion was similar to that produced in concrete containing the reactive aggregate used originally in the old concrete. It is believed that crushing the old concrete exposed fresh faces of the reactive aggregate which causes renewed reaction and expansion in the new concrete. The alkalis contributed from the RCA are also believed to contribute to the expansion. The amount of supplementary cementing materials required to mitigate the expansion in new concrete containing ASR-affected RCA was higher than those normally needed in concrete containing the virgin reactive aggregate. The results showed a good agreement between the 14-day expansion of accelerated mortar bars and the expansion of concrete prisms.     

Laboratory study of LiOH in inhibiting alkali-silica reaction at 20 °C: a contribution

At 20 °C, alkali-aggregate reaction (AAR) expansion of mortar incorporated zeolitization perlite could be long-term effectively inhibited by LiOH and the effect increased with the augment of Li/(Na+K) molar ratio. Mortar strength would decrease when LiOH was added. The more LiOH was added, the more the strength would decrease. In addition, there was more effect on 28 days' strength than 3 days', and the influence degree of LiOH to compressive strength was higher than that to flexural one. The initial and final setting times of cement were shortened when LiOH was added, and the more Li/(Na+K) molar ratio of LiOH was added, the more the setting time was cut down. Not only mortar bar expansion, the change in 20 °C, but also, the evidence of reaction and the composition of reaction products after 4-year curing was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that when both Li⁺ and K⁺ (Na⁺) were added, more Li⁺ reacted to form some matter that not as the same as normal alkali-silica reaction (ASR) gel, especially for its nonexpansive property. Such might be the main reason of the phenomenon that ASR expansion could be inhibited by adding lithium compounds.     

Prevention of alkali-silica expansion by using slag-Portland cement

A previously postulated hypothesis that concrete or mortar prisms devoid of free Ca(OH)₂ will not suffer from alkali-silica expansion has been tested. In this investigation high slag-Portland cements were used to make mortar prisms with a reactive sand. Storage of these prisms in a saturated NaCl bath at 50°C caused no expansion. At the end of the storage period in NaCl bath, the prisms were found to be free of Ca(OH)₂. The results are consistent with the proposed hypothesis.