Effects of improper moist curing on flexural strength of slabs cast under hot weather conditions

• Effects of inadequate curing in hot weather on flexure in RC slabs are investigated.
• Inadequate curing adversely affected concrete mechanical and structural properties.
• Flexural strength was reduced by 6–29% and deflections were considerably increased.
• Compressive strength of cores drilled from slabs was reduced by 12–39%.
• Calculations using strength of cores do not capture reduction in flexural strength.

Inadequate moist curing can have adverse effects on the properties of concrete, especially during hot weather concreting (HWC). This research aims at gaining a better understanding of the effects of inadequate moist curing on the flexural behavior of reinforced concrete (RC) slabs cast during severe HWC. Five RC slabs and field-cured cylinders and cubes were cast and cured under peak temperatures as high as 50 °C, relative humidity as low as 6%, and relatively strong winds. Two additional slabs were control specimens which were cast and cured under lab conditions. The slabs were tested in a four-point loading setup to study their flexural behavior. The experimental results showed a general reduction in the properties of the concrete cast and cured outdoors, especially the concrete which did not receive adequate moist curing. The flexural strengths of the slabs cured outdoor were smaller than those of the lab-cured slabs by 6–29%. In addition, considerable decreases in the flexural stiffness were observed. The compressive strength of cores drilled from the slabs cast outdoors and not cured with moisture was smaller than that of the lab-cured control slab by 39%. The flexural strength of the slabs was calculated using the flexure theory and ACI code equations based on the compressive strength of the drilled cores and the field-cured cylinders. Using the reduced compressive strengths for the outdoor slabs did not lead to capturing the actual reduction in the flexural strength. However, the strength calculations remained conservative for all slabs, with strain hardening in the tension reinforcement being one of the contributors to this conservatism.