Evaluation of Thermal-Mechanical Behavior of Massive Self Compacting Concrete Containing Alkali-Activated Slag

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Evaluation of Thermal-Mechanical Behavior of Massive Self Compacting Concrete Containing Alkali-Activated Slag

ارائه دهنده: Provider: shahriar abdolahzade

اساتید راهنما: Supervisors: Mahmoud Nili (PhD)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Rahmad Madandoust (PhD)-Malek Ranjbar (PhD)-Mohamad Shooshtari (PhD)

زمان و تاریخ ارائه: Time and date of presentation: 13-11-2023

مکان ارائه: Place of presentation: Engineering Faculty

چکیده: Abstract: Concrete as the most widely used material in the world, plays a key role in construction projects. Thermal stress and damages caused by heat generation at an early age tend to be important challenges in constructing massive elements. On the other hand, one of the goals of sustainable development is decreasing CO2 production and preserving the environment which can be achieved by using by-product materials in order to reduce or even eliminate the cement from concrete. Therefore, it is necessary to use new concretes such as self-compacted concretes and new ways and materials like alkali- activated slag to improve mechanical properties and reduce the risk of cracking in massive elements. In this study, the use of alkali-activated slag in self-compacted concretes in massive elements has been taken into account to reduce the risk of cracking and improve mechanical properties. Given the variety of influential factors on mechanical and thermal properties of massive concretes and in order to specify the most influential parameter, the Taguchi method (L9 orthogonal array) was used to determine the concrete mixes. Moreover, four curing methods were considered to simulate the different conditions in massive concretes. Thus, concretes with binder content of 500, 600, and 700, water to binder ratio of 0.45, 0.465, and 0.48, sodium ion of 5,6, and 7% of binder content and coarse to fine aggregates ratio (C-F) of 35-65, 30-70, and 25-75 were taken into account. In the first section of this research, mechanical properties including compressive and tensile strength, modulus of elasticity, water absorption and thermal properties such as semi-adiabatic temperature history and coefficient of thermal conductivity of nine concrete mixes were evaluated. With respect to the experimental results, numerical analysis via Minitab software and simulation by 4C temp & stress software were conducted to assess the risk of cracking. In the second section, numerical relationships were presented in order to estimate the mechanical and thermal properties of alkali-activated self-compacted concretes and they have been verified by four random mix designs. In section three, thermal and mechanical properties of alkali-activated and cement-based self-compacted concretes were compared in three binder contents. The highest compressive and tensile strength and modulus of elasticity are related to mixes with 700 binder content and an alkaline solution with 7% Na2o. The thermal curing regime contributes to improving the mechanical properties of alkali-activated self-compacted concretes. Increasing the amount of binder content from 500 to 600 and 600 to 700 resulted in a 7.6 and 6.7 % rise in the compressive strength and 7.6 and 3.9% rise in tensile strength. It is possible to estimate the mechanical properties as well as the amount of heat produced as one of the most important thermal factors by regression relationships with high accuracy (R²=0.968). Lower modulus of elasticity in alkali activated concretes can be beneficial in reducing the risk of cracking in massive concretes because of their ductility. Generally, peak temperature and the amount of heat produced by cement-based concretes are 14% and 56% higher than that of alkali-activated ones, respectively. As a result, in software simulation, a higher risk of cracking in cement-based concretes compared to alkali- activated ones shows the better thermal and mechanical performance of alkali-activated mass concretes.

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