Comparative Evaluation of Shrinkage and Temperature Behavior of Rapid-Set Belitic CSA Concrete for Sustainable Pavement Repairs: Outdoor vs. Laboratory Conditions

Concrete pavement repairs require materials that balance rapid strength gain, dimensional stability, and sustainability. This study evaluates two polymer-modified belitic calcium sulfoaluminate (CSA) concretes—CSAP (powdered polymer) and CSA-LLP (liquid polymer admixture)—against Type III Portland cement (OPC) concrete under both laboratory and field conditions. Early-age mechanical properties, shrinkage behavior, and temperature-induced strain development were assessed. Laboratory tests revealed that CSA mixes achieved compressive strengths exceeding 3200 psi at 4 hours. However, field-cast CSA specimens exhibited slower early strength gain under cool ambient conditions (~48°F), demonstrating thermal sensitivity. CSA-LLP exhibited the lowest drying shrinkage in laboratory testing (0.036% at 16 weeks), while large slabs cast in field conditions showed initial expansion, resulting in minimal shrinkage or net expansion (+200 µε at 16 weeks). Approximately 90% of outdoor strain development occurred within 24–48 hours due to autogenous and plastic effects. CSA mixtures maintained lower internal temperatures and reduced thermal strain amplitudes compared to OPC slabs, contributing to improved dimensional stability. These findings underscore the need for field validation of laboratory predictions, highlighting CSA’s shrinkage-compensating mechanisms and thermal sensitivity. When properly cured, polymer-optimized CSA concretes demonstrate superior dimensional stability and rapid strength development for durable pavement repairs.