"Proper compaction of unbound materials, such as soils, aggregate, and recycled materials, is a critical component in the performance of highway pavements and embankments. The most commonly used device to test for proper compaction is the nuclear density gauge. However, due to the costs associated with regulatory compliance and radiation safety training, there is an increased effort to find acceptable non-nuclear devices. This synthesis documents information on national and international experience with non-nuclear devices and methods for measuring compaction of unbound materials. Information used in this study was gathered through a literature review, a survey of state departments of transportation (DOTs) and Canadian provincial transportation agencies, and interviews with selected state DOTs. Munir Nazzal, Ohio University, Athens, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable with the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand."--Preface.