Analysis of Mix Design Variability and Carbon Emission Characteristics in Ready-Mixed Concrete Based on Actual Production Data

Ready-mixed concrete (RMC) produced under commercial conditions exhibits substantial variation in mix proportions that may not be fully represented by environmental assessments based on representative or average mixtures. This study investigated the relationship between actual mix design variability and carbon emissions using approximately 13,000 production records collected from 25 RMC manufacturers in South Korea. Carbon emissions were calculated for a functional unit of 1 m3 at the raw material production stage using the Korean national Life Cycle Inventory database. Variations associated with compressive strength, geographical region, company size, seasonal production conditions, and supplementary cementitious material (SCM) replacement ratio were evaluated using descriptive statistics and regression analysis. Substantial emission variability was observed within the same compressive strength grade, with average emissions ranging from 236.17 kg CO2-eq/m3 for 21 MPa concrete to 299.36 kg CO2-eq/m3 for 30 MPa concrete. Cement content exhibited a strong relationship with calculated carbon emissions (R2 = 0.996–0.998), although this relationship partly reflects the calculation framework in which cement quantity is directly used as an input to the GWP calculation. SCM replacement ratio showed a consistent negative relationship with calculated carbon emissions across the investigated strength grades (R2 = 0.735–0.863). Descriptive differences in carbon emissions were also observed across geographical regions, company-size groups, and seasonal production periods. Field-scale validation at two commercial batch plants showed that mixtures incorporating approximately 35% SCM replacement satisfied the specified requirements for slump, air content, and 28-day compressive strength under the evaluated production conditions. These findings demonstrate the importance of incorporating actual production variability and distribution characteristics into carbon assessment of commercially produced RMC and provide a basis for improving low-carbon mix design and environmental performance assessment.