Field-Curing Methods for Evaluating the Strength of Concrete Test Specimens

The purpose of this combined laboratory and field study was to evaluate field-curing methods of concrete specimens for estimating the early opening strength of an in-place concrete item. One Illinois Department of Transportation (IDOT) class PV mix was used to cast cylinders, beams, and in-place concrete slabs in October 2021 and February 2022. Concrete cylinders were cured using three methods: ambient air (method #C1), an insulated box/cooler (method #C2), and a power-operated box (method #C3). Beams were cured using two methods: ambient air (method #B1) and an insulated plywood box (method #B2). The cast-in-place specimens from each slab and cylinder were tested for compressive strength, and beams were tested for flexural strength after 1, 3, and 7 days of curing. One cylinder and one beam in each curing method along with slabs were embedded with sensors to collect temperature variation with time. Only methods #C1, #C2, and #B1 were selected for evaluating further in the field, and data were collected from the IDOT District 5 box culvert demonstration project. Laboratory results showed that the insulated box (method #C2) estimated early (1–3 days) and ambient air (method #C1) estimated the 7-day compressive strength of an in-place concrete item within an acceptable range. Field results showed that method #C2 cylinders mimic the in-pour temperature better than method #C1 cylinders. Further statistical analyses supported the results observed in the laboratory and field.