A New Method for Investigating thr Effect of Alkali-Silicate Reaction on Cement-based Products Containing Slag

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: A New Method for Investigating thr Effect of Alkali-Silicate Reaction on Cement-based Products Containing Slag

ارائه دهنده: Provider: soran dehghani

اساتید راهنما: Supervisors: ebrahim ghiasvand

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: s mahdi hoseinian - javad tahery nejad

زمان و تاریخ ارائه: Time and date of presentation: October, 09, 2022

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: Alkali-silica reaction is a harmful internal reaction that occurs in concrete. This reaction is the result of the reaction between active and reactive silica in some aggregates and alkalis in cement paste, which leads to the production of a hydrophilic gel. The gel moves in empty spaces and fills them. Due to having hydrophilic groups in its structure, it absorbs the surrounding water, which causes its expansion and volume increase. This increase in volume is not harmful as long as it does not completely occupy the empty holes in the concrete and does not put pressure on the surrounding walls. If the conditions are favorable and the gel has a destructive expansion, new cracks will be produced and spread, which can have destructive effects. These cracks cause internal weakening of concrete, which can ultimately affect the mechanical properties of concrete. To evaluate the reactivity of aggregates and also to evaluate the intensity of silica-alkaline reaction in concrete, there are many standard tests, many of which are obsolete and some of which are still used. . The most important of them are the ASTM C1260 and ASTM C 1293 standard tests. The ASTM C 1260 standard test does not give accurate and reliable results due to the short duration of the test, and since the silica-alkaline reaction occurs over a long period of time, therefore, short-term tests do not perform well in evaluating this reaction. And in some cases, the result of aggregate reactivity evaluation is negative or false positive. On the other hand, the ASTM C 1293 standard test has a good performance in evaluating the reaction, but due to the long duration of the test (one year), it has little use and practically loses its use in projects that must be executed at a high speed. On the other hand, many researchers have tested many materials and materials in order to find a suitable alternative to Portland cement in concrete and to reduce the consumption of cement and consequently to reduce the environmental damage caused by it. Among these materials, the slag of the slag furnace, which is considered an industrial waste, has shown good performance as a substitute for cement, as well as controlling the alkali-silica reaction. In this research, an attempt is made to propose a new method for evaluating the reactivity of aggregates in concrete mixed with cement (cement + slag). For this purpose, slag has been replaced with 10, 20, 35 and 50 percent of cement. Since the development of destructive silica-alkaline reactions is associated with the expansion of wide cracks inside and on the surface of concrete, the weakening of mechanical properties appears. Therefore, it is possible to know whether the aggregates are reactive or not by examining the changes in the mechanical properties of cement-based products. The new method proposed in this research is based on examining changes in compressive strength, bending strength, length, and electrical resistance of mortar and concrete samples. The results indicate that by increasing the amount of slag, the expansion caused by the alkali-silica reaction decreases and also all the resistance and durability properties are improved. The consistency of the mentioned results proves that the newly introduced method can be used as a basis for the evaluation of the silica-alkaline reaction.

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