Article

PETROGRAPHI C FEATURES OF ALKALI-SILICA REACTIVE AGGREGATES IN HOKURIKU DISTRICT AND COMAPATIBILITY BETWEEN VARIOUS TEST METHODS DETERMINING ALKALI-SILICA REACTIVITY OF AGGREGATE

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... In an example of Japanese andesites, analyzed for bulk chemical composition by standard-less EDS analysis with BSI imaging of polished rock specimens [91], the obtained compositions were unrealistic for andesite, i.e. 11-12 wt.% of Na 2 O, 18-24 wt.% of Al 2 O 3 , somewhat resembling a plagioclase (albite-oligoclase) but with SiO 2 10 wt.% lower. This inconsistency was due to less quantitative standard-less analysis, as well as small number of analyses (N5 points) applied to inhomogeneous textures of andesites. ...
Article
Typical examples of so-called alkali-carbonate reaction (ACR) in the Canadian field concretes in Ontario, CSA concrete prism, RILEM concrete microbars and RILEM mortar bar containing Pittsburg aggregate, were examined petrographically based on polarizing microscopy, SEM observation and quantitative SEM-EDS analysis of the reaction products. It was revealed that ASR gel was the main product responsible for the crack formation in concretes, and that this gel had a common nature to that in the typical ASR. That is, ASR gel presented distinctive compositional trend lines, passing from low-Ca ASR gel at [Ca/Si] = 1/2–1/6, [Ca]/[Na + K] = 1.0 to the “convergent point” with [Ca/Si] = 1.3–1.8, [Ca]/[Na + K] = 100 at which chemical equilibrium is attained with CSH gel. The so-called ACR is a combination of deleteriously expansive alkali-silica reaction (ASR) of cryptocrystalline quartz, and harmless dedolomitization which produces brucite and carbonate halo. In laboratory specimens, fine dolomitic aggregate undergoes dedolomitization, and brucite and ASR gel react to form non-expansive Mg-silicate gel on the dolomite crystals. This explains why the mortar bar produces smaller expansion than the concrete microbar, and why the reaction products are so minute that they escape attention by optical microscopy. As a crystalline counterpart, mountainite is a candidate for low-Ca ASR gel, while sepiolite is one for Mg-silicate gel. Concealed ASR was detected in ACR-affected field concretes undergoing ingress of deicing salt which formed Friedel's salt and Cl-doped CSH gel. Compositions of ASR products, methods of sample preparation and analysis for correct identification of ACR, and artifacts were critically reviewed.
Chapter
The replacement of bridge RC slabs has marked the start of expressway renewal work. On the snowy Hokuriku expressway, the deterioration caused by the combination of alkali–silica reaction (ASR) with steel corrosion is accelerated by the application of de-icing salts. Therefore, it is imperative to identify and determine the leading cause of deterioration of each bridge when planning maintenance. In this study, a survey on the amount of chloride penetration into concrete, and the degree of ASR of concrete was investigated using cores taken from RC slabs in a viaduct in the Kanazawa City area. Based on this survey, a new cathodic protection method was applied, and titanium wire sensors monitored its effectiveness. Finally, it was determined that the new cathodic protection method effectively controlled the corrosion of steel bars of reinforced concrete slabs in a saline environment with de-icing salts.
Article
The brittle fracture of steel bars in ASR-affected concrete bridge piers has recently been reported in various places in Japan. At present, the development of maintenance and rehabilitation techniques for such severely damaged concrete piers becomes a great concern for civil engineers. The authors have carried out the series of investigation on both the deterioration of concrete and the fracture of steel bars in concrete piers which were severely deteriorated again after the surface coating had been applied. This report describes the survey on the deterioration of ASH-damaged concrete bridge piers, and the reconstruction method of piers proposed based on the survey.
Article
In order to investigate the possibility of occurrence of alkali silica reaction (ASR) in concrete containing lightweight aggregates, the alkali-silica reactivity of six artificial lightweight aggregates and one natural lightweight one, which are now produced in Japan, was comparatively examined according to the chemical method, JIS A 1145, and three types of mortar bar methods, JIS A 1146, ASTM C 1260 and Danish method, along with their mineralogical properties. From the results of ASR, assessment test, it was found out that the alkali-silica reactivity of all lightweight aggregates was determined as “Not Innocuous” by the chemical method, JIS A 1145, but that it was determined as “Innocuous” by three types of mortar bar methods. Furthermore, although ASR gel was actually formed around the shell or in the voids of some lightweight aggregates in concrete, the expansion behavior of concrete bar was not so significant because the internal voids in lightweight aggregate may eliminate the expansion pressure due to ASR. Furthermore, the appropriate test procedure for ASR assessment of the concrete containing lightweight aggregates was discussed and proposed
Article
In Japan, by the application of countermeasures against alkali aggregate reaction, ASR, such as the restriction of total alkalis in concrete and the use of blended cement with the combination of evaluation methods of alkali reactivity of aggregate such as a chemical method and a mortar-bar method, the majority of ASR has been controlled. However, some problems have remained in these methods when the wide variations of real aggregate, sever conditions for ASR, and increasing usage of alternative aggregates are considered. Besides, the foreign standards that are the basis of Japanese evaluation methods of aggregate are now changing. In this article, recent activities of RILEM TC 191 - ARP, reaction mechanisms of ASR, evaluation methods of aggregate including petrographic evaluation, and problems in these methods are outlined. Based on the information, “Kyushu Standard” in which the application of blended cement is recommended as a standard mitigating method from a realistic point of view is introduced and reasonable countermeasures against ASR are proposed.
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