ساخت و تحليل حسگر بتني سنجش خرابي سازگار با خصوصيات مكانيكي رويه بتني راه

Construction and Evaluation of Damage Detection Sensor Consistent with Concrete Pavement

تكنولوژي نظارت و كنترل سلامت ساخته هاي مهندسي (SHM ) با تامين راهي جهت ارزيابي ايمني و دوام رويه بتني در طول عمر آن، اين امكان را به وجود مي آورد تا بتوان از ميزان سلامت، رويه بتني درهرحال باخبر بود. به منظور عملياتي نمودن سيستم SHM لازم است كه زيرساخت آن از قبيل ايجاد حسگر در نقاط مختلف رويه بتني به منظور برداشت لحظه به لحظه اطلاعات مربوطه عملياتي گردد. يكي از مهم ترين و اقتصادي ترين حسگرها، حسگرهايي از جنس خود رويه بتني راه مي باشند كه از اختلاط نانولوله كربن با بتن توليد مي شوند. هدف از اين تحقيق، تشريح چگونگي ساخت حسگرهاي بتني از جنس رويه بتني راه به گونه اي كه خواص مكانيكي (مقاومت فشاري و خمشي) حسگر توليدشده نزديك به رويه بتني راه باشد. در اين راستا تعيين مقدار بهينه و كيفيت پخش نانولوله هاي كربني با توجه به تاثير مواد فعال كننده سطحي مختلف به عنوان اصلي ترين پارامتر تاثيرگذار در خواص حسگر موردبررسي قرار گرفت. براي اين منظور از دو نوع ماده فعال كننده سطحي و مقادير متفاوت نانولوله كربن براي ساخت حسگرهاي مختلف بتني استفاده شد. براي سنجش خصوصيات مكانيكي حسگر بتني، دو آزمايش مقاومت فشاري و خمشي مورداستفاده قرار گرفت و همچنين به منظور ارزيابي الكتريكي پاسخ حسگر نيز دو معيار حساسيت حسگر و انحراف معيار از خطاي پيش بيني مورداستفاده قرار گرفت. نتايج نشان دادند كه حسگر ساخته شده با نانولوله كربن به مقدار 0.15% وزني سيمان، به همراه فعال كننده سطحي تركيبي فوق روان كننده و SDS داراي خواص مكانيكي سازگار با رويه بتني راه و پاسخ الكتريكي مناسبي است.

Structural Health Monitoring (SHM) provides a way to evaluate safety and durability of a structure during its service life in order to ensure the serviceability and sustainability. Therefore, the sensor technology is a critical part to operate SHM system for recording relevant data through its lifespan. Sensor is a device capable of identifying the probability or the value of parametric changes and showing them as a relevant output (typically electrical or optical signal). Making materials electrically conductive may be useful in many different ways such as creating piezoresistive sensors with the ability to acquire stress-strain or load-displacement data or creating sensors with the ability to acquire data on the extent of damage to the concrete. The piezoresistive sensor is capable of detecting the applied forces to the structure based on the changes in the electrical resistance. But the damage detection sensor operates based on the contacting conduction of CNTs. This means that by increasing the amount of CNTs in concrete, a three-dimensional contacting network of CNTs is built. When the amount of CNTs exceeds the percolation threshold, the contacting conduction will affect the electrical conduction of nano-composites. One of the most significant and economical types of the sensor is the damage detection sensor which is provided by mixing conductive fibers (such as carbon nanotubes (CNT)) with concrete. For preparing damage detection sensor, CNTs and surfactants were mixed in the water for 10 minutes using a magnetism stirrer at 5000 rpm. Then, the mix was prepared at one ultrasonic energy dispersion. The cement and CNTs were added to high-speed mixer to be uniformly mixed. After adding aggregate to the mixer, the concrete was placed in pre-oiled molds and by applying appropriate vibration, any trapped air was released. The specimens were cured for 28 days and they were tested under the static loading by Instron-Tech. test equipment. In order to remove the effect of polarization - which is due to the movement of free ions in the concrete sensor during the measurement - an alternating current generator was used to nullify this phenomenon. After preparing the sensors, two main factors affecting the performance of concrete sensors are the amount of CNTs and their dispersion quality in the mixture. The goal of this study is to determine the optimum amount of CNTs with regard to the combined effects of the surfactant and the CNTs dispersion quality on the performance of the sensor. In this regard, various criteria such as sensitivity of the sensor (Se), the Absolute prediction errors as electrical criteria and flexural strength as mechanical criteria are involved. The results demonstrate that the sensor provided by 0.15 wt% CNTs, superplasticizer and SDS as a surfactant has the best performance. Also, the static criteria indicates that the quality of the dispersion (using proper surfactant material) and the amount of CNTs are effective on the sensitivity and the Absolute of the prediction errors, respectively.