Research on the Crack Risk of Early-Age Concrete under the Temperature Stress Test Machine.

Longlong Liu,Dahai Huang,Jianda Xin,Jianshu Ouyang,Shuling Gao,Feilong Li

doi:10.3390/ma11101822

Abstract

A new temperature stress test machine (TSTM) was developed to improve temperature control accuracy and efficiency. As there is no uniform standard for the threshold value of TSTM, quite different threshold values are used in the test, which results in the influences of the threshold value on the evaluation of thermal stresses and crack risk of concrete not being determined. To illustrate the importance of an appropriate threshold value, different threshold values were used to evaluate the influences on the thermal stresses and cracking resistance of concrete specimens under a complete restraint test with semi-adiabatic temperature development. The results show that the maximum compressive stress of a concrete specimen with a threshold value 3 με was slightly larger than that of 1.5 με when the growth rate of tensile stress of the concrete specimen with the threshold value 3 με was slightly greater than that of concrete specimen with the threshold value 1.5 με. Based on the combination of crack risk coefficient and restraint degree, a new system for evaluating the crack resistance of concrete was proposed, in which different threshold values were used to estimate their influences on the crack risk of concrete. Thus, an appropriate range of threshold values could be determined.

Highlights

Cracks in young concrete affect the appearance and performance of the structure, and the ability of the structure to resist external corrosive substances, which leads to the reduction of the durability of structures, ranging from dams, massive foundation slabs, bridge decks and piers, to beams used for buildings [1,2]
When the concrete expands during adiabatic temperature rise, compressive stresses arise if the structure is restrained [3]
After a series of improvements, the cracking frame evolved into a temperature stress test machine (TSTM) when the restraint degree and temperature development could be controlled in the test

Summary

Introduction

Cracks in young concrete affect the appearance and performance of the structure, and the ability of the structure to resist external corrosive substances, which leads to the reduction of the durability of structures, ranging from dams, massive foundation slabs, bridge decks and piers, to beams used for buildings [1,2]. When the concrete expands during adiabatic temperature rise (temperature increases during the exothermic chemical reaction between cement and water), compressive stresses arise if the structure is restrained [3]. The temperature starts to fall, and the concrete structure will contract, which gives rise to incremental tensile stresses (see Figure 1). After a series of improvements, the cracking frame evolved into a temperature stress test machine (TSTM) when the restraint degree and temperature development could be controlled in the test. The TSTM system has been developed with the design

Methods

Results

Conclusion