Title: Impact of Extremely Hot Weather and Mixing Method on Changes in Properties of Ready Mixed Concrete during Delivery
Author(s): Abdulaziz I. Al-Negheimish and Abdulrahman M. Alhozaimy
Publication: Materials Journal
Appears on pages(s): 438-444
Keywords: admixtures; compressive strength; hot weather; mixing; ready mixed concrete; slump loss; temperature
Changes in concrete temperature, slump, and compressive strength during delivery of ready mixed concrete (RMC) were investigated under the extremely hot, dry environment of Riyadh in central Saudi Arabia. A total of 80 delivery trucks were tested representing three plants using a central-mixing method and three plants employing a truck-mixing method in their operations. The results indicate that changes in the properties of RMC during delivery under the extremely hot, dry environmental conditions characterizing summer months in the region were not significantly different than those for a much milder summer typical in the midwestern U.S. The study shows that concrete temperature increased by an average of 1.1 °C (2.0 °F) and slump lost 37% of its initial value during delivery in the summer time. The compressive strength at the site was slightly higher than at the plant and was not significantly affected by long travel times. The use of waterreducing and retarding admixtures plus controlling concrete temperature and avoiding delivery during noon hours, as per ACI 305R recommendations, are shown to be effective in controlling the adverse effects of hot weather on the production and delivery of concrete, even under the extremely hot weather conditions prevailing in the region. The anticipated problem of increased rate of slump loss associated with the use of water-reducing and retarding admixtures in hot weather was not observed in this study.