This investigation centers on early concrete technology used in Seguin, Texas, during the mid-19th century. Over the course of fifty years, more than ninety concrete structures were built in Seguin. Over the last century, these have dwindled to twenty extant structures. Much of the previous Seguin concrete era research has focused on the historical narrative and architectural description. This study aims to answer questions that previous research has not — it investigated the raw materials used in making Seguin’s concrete. The results provide new information about the Seguin concrete structures, providing guidance for their long-term maintenance. The materials analysis uses instrumental techniques such as scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction to determine the chemical composition and crystalline structure of the cement binder from several extant structures in Seguin. Gathering both qualitative and quantitative data for the binder allowed us to identify the raw materials used in the concrete and better understand the construction methods. Studying the materials and methods increased our understanding of these historic structures and will inform future preservation efforts. / text