Study On Tensile Properties Of High Strength Concrete At Early Ages

The properties of concrete at early ages, especially tensile propertiesare indispensable parameters to predict and model risks of early-agecracking due to volume changes, but have never received much attention.In this paper, tensile properties of high strength concrete (HSC) at earlyages were experimentally investigated with self-designed testing rig, andrelationships between early-age cracking and tensile properties werediscussed. Furthermore, methods for evaluating early-age cracking ofHSC were explored preliminarily.The conclusions based on the present research work can be drawn asfollows, (1) Testing rig adopted in this paper effectively evaluated tensileproperties of hardening HSC, (2) Tensile strain capacity (TSC) of HSCwas very high during hardening, which rapidly decreased with age andminimum value was reached somewhat later. Early-age TSC wassignificantly dependent on water-cement ratio (W/C), and lower W/Cleaded to higher TSC value. TSC after the age of 1 day does not varysignificantly with either mix proportions or ages, (3) Tensile strength andelastic modulus of HSC rapidly developed at early ages, and uniaxialtensile strength is about 0.96 times of splitting tensile strength, (4)Cracking tensile stress approximately equals to 70%-80% of tensilestrength at the age of cracking. When the restrained tensile strain is at thesame range of TSC, there is a rather high possibility of cracking, (5) Evaluation models based on CEB-FIP Model Code for early-age tensileproperties were established, and (6) The significant factor that must beconsidered to predict early-age cracking is the stress history, especially atvery early ages. Faster stress development leads to earlier cracking.