ارزيابي ميداني روش هاي نوين تعيين دانسيته لايه هاي روسازي

چگالي بهترين معيار سنجش و كنترل كيفيت روسازي اجرا شده مي باشد. تعيين چگالي مخلوط آسفالتي در حين عمليات تراكم و پس از آن، از دو جهت تعيين ميزان تراكم و زمان اتمام عمليات داراي اهميت مي باشد . در حال حاضر متداول-ترين و البته دقيق ترين روش‌ تعيين دانسيته در محل مخلوط آسفالتي، روش مغزه گيري مي باشد. روش معمول براي انجام اين كار استفاده از مغزه گير و انجام آزمايش تعيين چگالي بر روي مغزه هاي بدست آمده در آزمايشگاه مي باشد. اما اين روش داراي معايبي شامل ايجاد خرابي در سطح روسازي، هزينه نسبتاً بالا، عدم تكرارپذيري و پايش دانسيته براي يك نقطه خاص و صرف زمان زياد مي باشد. زمان بر بودن انجام اين آزمايش، منجر مي‌شود كه نقاط ضعف لايه ناشي از عدم تراكم لازم به سرعت مشخص نشوند و لذا اقدامات اصلاحي در زمان مناسب صورت نگيرند. در سال هاي اخير استفاده از آزمايش هاي غير مخرب تعيين دانسيته، با استقبال زيادي مواجه شده است . اين نوع آزمايش ها در سطح روسازي ايجاد خرابي نمي كنند، هزينه انجام آنها كمتر از مغزه گيري مي باشد و بعلت عدم ايجاد خرابي بوسيله آنها تكرارپذيرند، كه شامل دو روش غيرمخرب هسته اي و غيرهسته اي مي باشند. در اين تحقيق ارزيابي ميداني دستگاه الكترومغناطيسيPQI مدل 301 و دستگاه هسته اي Troxler مدلHS-5001EZ انجام گرديد كه بعد از انجام تحليل هاي آماري مشخص شد كه دستگاهPQI مناسب براي تعيين دانسيته لايه هاي آسفالتي و دستگاه هسته اي براي تعيين دانسيته لايه هاي سنگدانه اي مناسب مي باشند.

One of the most applicable methods to control the quality of performed pavements is to measure asphalt concrete and granular layers densities. Determining asphalt mixture density while compaction and after finishing it, is important from compaction ratio and project accomplishment time aspects. The most common and precise method of measuring asphalt mixture density in situ is using cores. It is done by coring from asphalt mixture and performing density test on these samples in laboratory. The problem with this method is being destructive, expensive and results cannot be validated by repeating the test for a specific point while a lot of time is needed for a full project. The last problem makes it impossible to recognize bad compaction condition of layer and perform modifications on time. Using nondestructive density determination tests turned popular so much in recent years. These tests don’t destroy pavement, are less expansive than core method and are repeatable since can be used in a specific point for several times. Nondestructive test are divided to nuclear and non-nuclear tests. Nuclear device is used to determine density and moisture content in site based on ASTM D2922 – D3017 which is rapid and nondestructive. Gamma ray and Neutron particles are used in this device for determining density and moisture content respectively. On the other hand, radioactive substances which are radiated from these devices are the most important problem with them. Non-Nuclear NDT devices has the advantages of nuclear instruments while hasn’t the noticed problem. In this research electromagnetic PQI301 and nuclear Troxler HS-5001EZ device is evaluated in the field. Firstly the devices were calibrated and after that, 60 points in Tehran-Pardis freeway were selected in a lane with 3.65 width and at a spacing of 7 meters, each section divided to 6 parts and 10 sections were chosen totally. Both nuclear and nonnuclear devised were used for determining density of each point and for each group, one core were excavated and density were measured too. For granular layers, a detour for Latian Dam Road was selected and density determination were performed by sand bottle method and nuclear device. SPSS software was used to analyze the results of study. It was concluded PQI is useful in determining asphalt layer density, while nuclear device isn’t appropriate in measuring asphalt mixture density and it is convenience in determining granular layers density. It should be noted PQI is a good device to determine points with low compaction, even in pavement edges. Since density in edge of roller path is less than this parameter exactly under roller, quality control points should be selected not from edge points, otherwise the results contain a considerable error.