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The early-age cracking of concrete is one of the most critical parameters affecting the performance of concrete structures. It is attributed to both the internal and external influences such as early age restrained shrinkage, thermal deformation as well as the applied load. In this paper, a detailed review of the causes of early-age cracking is first presented, followed by the factors affecting the concrete cracking including raw materials quality problems, improper construction measures, external environmental influences and structural design flaws. Then the preventive measures for concrete cracking are summarized. The potential for the application and development of structural health monitoring and artificial intelligence techniques for early-age cracking of concrete is also discussed. Through the comprehensive review of the early-age cracking of concrete, the research direction for the subsequent research on early-age cracking of concrete is pointed out. The current problems and concerns of concrete cracking are also prospected.

The treatment and disposal of sewage sludge ash (SSA) have emerged as crucial environmental concerns. This study delves into the profound impact of substituting SSA for sand in cement mortar, examining fresh and mechanical properties, drying shrinkage, and high-temperature resistance. Analyzing the SSA-modified mortar through X-ray diffraction (XRD) and scanning electron microscopy (SEM), the research reveals that the porous nature of sludge ash marginally influences the hydration rate and degree by adsorbing ions or encapsulating cement particles. While the SSA leaching solution has only a neglectable impact on the hydration rate. The workability is enhanced with the increase of the addition of excess water. Meanwhile, although the presence of excess water indirectly increases the w/c ratio of mortar, mortar with 5 % and 10 % SSA exhibit superior mechanical performance due to denser microstructure. Porous structures of SSA and more excess water in higher SSA content result in the rise of mortar drying shrinkage. When the sintering temperature reaches 800 °C, the high-temperature resistance of mortar with 20 % SSA is greater than that of the control group. The rough surface of SSA effectively fills cracks induced by elevated temperatures and improves the friction reaction, contributing to enhanced performance.

The application of reinforced concrete has been used in various engineering and architecture fields. Stress relaxation and creep are two crucial time-dependent behaviours of concrete. The influence of two behaviours is closely related to the service life of the reinforced concrete structure. However, the research on experimental relaxation behaviour has rarely been extensively studied because of the complicated procedures. Meanwhile, fly ash is commonly utilised to partially replace cement to reduce the greenhouse effect. As a result, this study is committed to examining the creep and relaxation behaviour of fly ash concrete. The concrete creep and relaxation tests were designed to maintain a constant stress and strain levels, respectively. The creep and relaxation tests were conducted at the same time to minimise the shrinkage and ageing effects. The stress and strain levels were selected as 20% and 60% of concrete compressive strength to investigate creep and relaxation in linear and nonlinear cases. By comparing computed values of relaxation from the inverse of the compliance function, the estimated relaxation function showed good agreement using the inverse of the compliance function. However, the existing creep model showed a difference in predicting the creep of fly ash concrete. As a result, the existing model is amended to improve the estimation of creep and relaxation of fly ash concrete.