A Comprehensive Investigation into the Influence of Prolonged Mixing on the Properties of Concrete Incorporating Different Types of Portland Cement

Prolonged concrete mixing can occur due to transportation delays or logistical issues on construction sites, potentially affecting the material's properties. This study investigates the effects of extended mixing times on concrete's fresh and hardened properties utilizing four different types of Portland cement: PC-32, PC-40, PC-RS-32, and PC-LF. An experimental program involved materials characterization, concrete mix design, and systematic testing procedures. Fresh concrete properties, including slump, temperature, specific mass, and air content, were evaluated hourly for up to 8 hours of mixing. Hardened concrete tests encompassed electrical resistivity, dynamic modulus of elasticity, and compressive strength measurements. Prolonged mixing led to a significant loss of slump and plasticity, particularly for PC-LF cement. Specific mass and apparent density decreased with mixing time, while electrical resistivity declined hourly, indicating increased porosity and susceptibility to chemical attacks. The dynamic modulus of elasticity remained relatively constant, except for PC-LF cement. Compressive strength was maintained or slightly increased up to 7 hours but decreased for PC-32 and PC-LF cements at 8 hours. The study demonstrates the feasibility of prolonged mixing for up to 8 hours with proper precautions. The choice of cement type played a crucial role, with PC-40 cement exhibiting the best overall performance. Further research is recommended to investigate durability aspects, porosity characteristics, and methods to maintain workability during extended mixing times.