There is an increasing demand for maximizing the economic, environmental, and social value of our infrastructure systems as a means for developing sustainable infrastructure. Sustainable infrastructure development requires collaborative planning and coordination among key stakeholders. Project stakeholders have usually varied - and possibly conflicting - definitions and prioritization of values. Joint understanding and alignment of values among stakeholders is essential to avoiding potential conflicts, improving cooperation, and facilitating joint decision-making that maximizes the collective value of our infrastructure systems. In the context of collaborative sustainable infrastructure development, an axiology is a model that represents and reasons about values and valuation. It addresses core questions, such as: What are the processes or products that add or may add value? How to valuate the values of these processes or products? Formal axiology is a branch of axiology that uses mathematical formalism to define value and value systems. It attempts to model value principles with mathematical rigor. Modeling axiologies in a formal format is a key to semantic (computer-understandable) axiologies. Semantic representations facilitate intelligent reasoning for the development of intelligent decision-support systems. This paper starts by discussing the need for a formal axiology to support collaborative sustainable infrastructure development. It follows by providing a brief overview of the meaning of axiology and the approaches previously used to develop axiologies in other domains. The paper, then, discusses a set of potential applications of formal axiologies in the infrastructure domain. Finally, the paper presents the initial modeling efforts towards a formal axiology for the infrastructure domain. The formal axiology is a semantic model that conceptualizes and reasons about values and valuation, considering different stakeholder perspectives.