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Highlights • A temperature stress testing machine was employed. • Effect of temperature history and restraint degree was investigated. • A high-low cooling rate history improved the cracking potential of concrete. • The relationship between restraint degree and temperature difference was established. Abstract This study experimentally investigated the effect of temperature history and restraint degree on cracking behavior of early-age concrete, including cracking temperature, cracking stress/strength, creep/free deformation and cracking potential. The deformation, temperature and stress were measured with two different temperature histories and three different restraint degrees via a temperature stress testing machine (TSTM). The results show that, under different temperature histories, the magnitude of cracking potential of concrete was found to vary significantly. The concrete with a high-low cooling rate at early-age had better anti-cracking performance (improved by at least 13.1%) due to the more effective utilization of creep on reducing restrained stress. The high-low cooling rate history showed more outstanding effect on lowering cracking risk of concrete under higher restraint degree. Furthermore, an analytical method for establishing the relationship between the restraint degree and temperature difference was recommended for assessing cracking risk of concrete. [ABSTRACT FROM AUTHOR]

Two-graded roller compacted concrete (RCC) containing high volumes of fly ash has been widely used in anti-seepage structures of RCC dams in China. The crystalline additive as a self-healing addition is added to the grout enriched two-graded RCC to increase crack resistance. The effects of fly ash and crystalline additive on mechanical properties of two-graded RCC were investigated in this research. Tests were performed to measure plastic and hardened RCC properties. The results indicate that the vibrating compacted values and air contents of plastic RCC containing fly ash of up to 58% conform to the engineering requirements. As the fly ash content in RCC increases, the air content increases and the unit weight decreases. Adding crystalline additive to the concrete mixture has no apparent effect on the slumps of grout enriched two-graded RCC, but may increase the air content and reduce the unit weight. The cube compressive strength, splitting tensile strength, axial tensile strength, ultimate tensile strain, modulus of elasticity, and axial compressive strength of two-graded RCC all decrease with increasing amounts of fly ash content. At 90 days, the relations between these properties and two variables, fly ash to cementitious material ratio (F/CF) and water to cementitious material ratio (W/CF), between splitting tensile and cube compressive strengths, between axial tensile and cube compressive strengths, and between axial and splitting tensile strengths were analyzed. The values for these properties of two-graded RCC were lower than those of grout enriched two-graded RCC at the same age, F/CF and W/CF, and adding crystalline additive to the grout enriched two-graded RCC may produce higher values for these properties than that without crystalline additive in most cases. The results confirm the feasibility of using crystalline additive in two-graded RCC of high RCC arch dams. [ABSTRACT FROM AUTHOR]

• Application of uniaxial restraint test for cementitious systems is reviewed. • Newly developed uniaxial restraint test methods are discussed. • Insight into the current application rationalities is addressed. • Suggestions are made for standardization of TSTM. This paper provides a state-of-the-art review of uniaxial restraint tests for evaluation of behavior and cracking potential of early-age cementitious systems in the last five decades. Histories of design concept and improvement of uniaxial restraint tests (longitudinal-passive and longitudinal-active test) have been introduced. Particularly, analytical methods of restraint degree and restrained stress, sensitivity analysis of uniaxial restraint test parameter, as well as cracking potential evaluation with respect to their application rationalities are addressed, which are extended contents compared with the last review in early 2000s. Finally, challenges and perspectives of uniaxial restraint tests for evaluation of behavior and cracking potential of cementitious systems are given for future improvement. [ABSTRACT FROM AUTHOR]

• In the casting process of self-compacting concrete, the SSIT is prone to void defects. • As a novel structural, there are few studies on its millimetre-level defect detection. • An effective identification model based on elastic wave and decision tree was established. • The accuracy of the method is 90.83%, which has great potential in practical application. Void defects seriously threaten the overall force of the Sandwich-structured immersed tunnel (SSIT). Accurately identifying the location and evaluating the severity of the void defect through non-destructive testing methods to determine the overall structural health status can provide meaningful information for the grouting reinforcement repair of the immersed tunnel structure. This research has developed a method to identify void defects in SSIT by combining impact elastic wave technology with machine learning algorithms. Eleven eigenvalues including the waveform characteristics, frequency spectrum characteristics and structural location attributes of the impulse response waveform were integrated, and the different characteristics of the void defect area and the dense area were analyzed. Based on the full-size model experimental data, a sample database was established for model training and verification. The average accuracy of void-defect identification was 90.83%. The results show that this method has great potential for the detection and evaluation of void defects in SSIT structures. [ABSTRACT FROM AUTHOR]