Experimental Investigation of the Influence of Sand Fineness Modulus on Rebar Corrosion in Recycled Concrete

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Experimental Investigation of the Influence of Sand Fineness Modulus on Rebar Corrosion in Recycled Concrete

ارائه دهنده: Provider: Navid Ommi

اساتید راهنما: Supervisors: Ebrahim Ghiasvand (Ph. D)

اساتید مشاور: Advisory Professors: Mohammad Mahdi Rastegar (Ph. D)

اساتید ممتحن یا داور: Examining professors or referees: mojtaba Nili (PHD)- mohammad Sadegh Ketabi (PHD)

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: آمفی تأتر دانشکده مهندسی

چکیده: Abstract: The use of recycled concrete is a key method for conserving natural aggregate resources and promoting sustainable development. However, because recycled aggregates have higher water absorption and porosity compared to natural aggregates, recycled concretes generally have inferior mechanical and durability properties. This is particularly important for recycled concrete, as its weaker mechanical and durability properties make rebar corrosion a significant concern. Understanding the type and severity of this corrosion can help in applying preventative and restorative measures to concrete structures. This study presents the results of an experimental investigation into the effect of recycled aggregate fineness modulus on the mechanical properties, durability, and corrosion process. The concretes in this study were made with sand fineness moduli of 2.5, 3.0, and 3.5, and the results were compared to a natural concrete control mix. The mix design used recycled aggregates with a maximum nominal size of 2.36 mm and Type 2 cement. The water-to-cement ratios were 0.74 for the recycled concrete mixes and 0.65 for the natural concrete mix. Tests for compressive strength, volumetric water absorption, and capillary water absorption were performed on each mix. Samples for these tests were cured in water until they reached the specified age. Three samples from each mix were used for evaluation, and their average was reported as the final result. Furthermore, electrochemical methods, including half-cell potential, linear polarization resistance, and potentiodynamic polarization resistance tests, were used to assess rebar corrosion. Samples for the electrochemical tests were cured in a lime-water solution for 28 days and then subjected to five 2-week cycles. In each cycle, the samples were kept in open air for one week and then in a 10% salt solution for one week to simulate a chloride environment. The test results showed that for recycled concretes with a similar water-to-cement ratio but different sand fineness moduli, reducing the fineness modulus decreased the compressive strength of the samples. This also led to an increase in volumetric and capillary water absorption. The electrochemical test results further indicated that a lower sand fineness modulus in recycled concrete samples led to a reduced half-cell potential. Moreover, due to the weaker mechanical and durability properties of recycled concrete, the passive layer that forms on the steel rebars breaks down quickly, significantly increasing the rate of corrosion.