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Dynamic splitting tensile performance of new and old concrete after high temperature treatment

Cao Hai

Archives of Civil Engineering

2021

Vol. 67, nr 4

79--89

In order to study the dynamic splitting tensile properties of new and old concrete after high temperature treatment, the effects of different impact velocities and temperatures on failure modes, dynamic splitting strength and energy absorption of new and old concrete were analyzed by impact dynamic splitting tensile test use of variable cross-section Φ 74 mm split Hopkinson pressure bar apparatus. The results show that: Impact velocity and temperature not only affect the dynamic splitting strength of new and old concrete bonding specimens, but also affect the failure modes and degree of breakage. The dynamic splitting strength of new and old concrete increases with the increase of impact velocity, but the increase rate decreased with the increase of temperature. The dynamic splitting strength first increases slowly and then decreases dramatically with the increase of temperature. In the dynamic splitting test of new and old concrete, the energy absorption increases with the increase of impact velocity and decreases with the increase of temperature.

Badanie wpływu warstwy przejściowej starego i nowego betonu na odporność betonu na pękanie

Kubiszyn J.

Zeszyty Naukowe Politechniki Rzeszowskiej. Budownictwo i Inżynieria Środowiska

2000

z. 32[180], cz.1

311-318

The article presents a possibility of using fracture mechanics methods for investigation the effect of the contact zone of old and new concrete on the fracture toughness of concrete elements. The investigation according Mode 1 (tension at bending) was carried out on beams formed by mixing several years old concrete and new 28 days old concrete. The research work involved beams with two substantially different contact surfaces: the surface obtained due to natural fracture and the ground one. The results of fracture toughness investigations according Mode 1 using RILEM draft recommendations and guidelines contained in the ASTM STP 410 have been presented. The critical stress intensity factor K slc and K lc as well as critical crack tip opening displacement CTODc have been determined. Based on the obtained investigation results the following conclusions were drawn: *The values of the critical load PQ and those of the stress intensity factor Klc from for secondary beams with a ground contact surface were on average by 35 % lower than those for the beams with a contact zone obtained due to a natural fracture. *The values of the critical factors of stress intensity for secondary beams with natural fracture, calculated according to and were, on average, 30% lower than for the primary beams. *The value of stress intensity factors calculated according to the RELEM draft recommendation is many times as much (3 times) as the values obtained from the Brown and Srawley's formula published so far can not be treated as data of comparison but as those of only visual value. *Based on the comparison of the values of the investigated parameters, one can find out that even in laboratory conditions, where the samples were carefully prepared (cleaned and wetted before the tacking layer was put on) the contact zone of the new and old concrete was the weakest element of the tested beams.