The function of a carbon nanofiber aggregate, henceforth referred to as the invention, is to sense strain in reinforced concrete (RC) and prestressed concrete (PC) structures. The invention consists of a small mortar cube containing carbon nanofibers that can be placed in an RC or PC structure during concrete casting. This technology is important because it has the potential to gauge the ability of a structure to perform its intended function despite aging, degradation, or disasters. Short-fiber composites, such as the invention, are a class of strain sensor based on the concept of short electrically conducting fiber pUll-out that accompanies slight and reversible crack opening, allowing dynamic monitoring. Current commonly used strain sensors, including strain gages, fiber optic sensors, and piezoelectric sensors, all suffer from high cost, poor durability and the need for expensive peripheral equipment including electronics and lasers. Because of this, the use of sensors in civil structures is uncommon. The invention is low-cost, much more durable than competing products, and only requires resistance measurements that do not require expensive peripheral equipment.