Issue 49

Y. Liu et alii, Frattura ed Integrità Strutturale, 49 (2019) 714-724; DOI: 10.3221/IGF-ESIS.49.64 715 found to be greater than that of the bottom at the same position. To a certain extent, with the increasing bending-load stress, different carbonization resistances were observed in the bending-tension zone and the bending- compression zone of the concrete test blocks. Meanwhile, to study the relationship between the carbonization damages in the bending-tension zone and the bending-compression zone of concrete test blocks, a carbonization influence coefficient of bending tension-compression load was proposed, which provides a convenient and scientific guidance for the detection and evaluation of concrete carbonization damages in practical engineering. K EYWORDS . Reinforced concrete; Bending load; Pouring surface; Carbonization depth; Carbonization influence coefficient of bending tension- compression load. which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION he replacement of cement with fly ash as the admixture of concrete can not only reduce cement consumption but also effectively improve various properties of concrete [1-3]. Therefore, fly ash has been used more and more widely in concrete buildings. On the other hand, due to the deterioration of the natural environment and the increase of the CO 2 concentration in the atmosphere, carbonization damage has become one of the most significant factors affecting the durability of fly ash concrete. However, the effect of load on the carbonization resistance of fly ash concrete was rarely discussed [4-10]. In practical engineering, the structure of a building is subject to the combined action of both load and environment, especially the former, so studying the environment alone cannot fully solve the carbonization problem in practical engineering [11-15]. Most of the building components such as beams and slabs are mainly subjected to the bending load in concrete structures. So the carbonization analysis under bending loads is still the focus of the durability study on fly ash concrete. However, the current research conclusions cannot be directly compared as they were obtained from different experimental platforms. What is more, most of the research focused on plain concrete, without considering the influence of steel bars on its carbonization, which cannot provide very helpful reference for the actual engineering, as studies [16-18] have shown that steel bars make the concrete more compact on the setting and hardening process of the concrete, which inhibits the carbonization damage of the concrete. This paper performed a rapid carbonization test to investigate how the bending load affects the properties of reinforced concrete blocks with varying fly ash contents. Then it analyzes the effects of the pouring surface and the bending tension and compression loads on the carbonization resistance of concrete and the relationship between the tension and compression loads with respect to their effects on the carbonization resistance of concrete. Furthermore, it proposed a carbonization influence coefficient of bending tension-compression load with respect to reinforced concrete. In summary, this study can provide convenient and scientific guidance for the detection and evaluation of carbonization damages in concrete structures in practical engineering. E XPERIMENT Experimental materials .O 42.5 ordinary Portland cement and Grade II fly ash (type F) were used in the experiment. River sand was used as fine aggregate, with a fineness modulus of 2.74 and good gradation. The continuously graded crushed stone with a particle size of 5-20mm was adopted as coarse aggregate. In this experiment, polycarboxylates high- performance water reducing admixture was adopted. The strength of the concrete blocks was C30, and four fly ash contents (the mass ratio of fly ash) were selected, namely, 0%, 20%, 30% and 40%. The concrete mix proportions are listed in Tab. 1. The test blocks were divided into several groups, each of which contains 51 blocks. In each group, 3 blocks were subjected to the measurement of ultimate bending load, and 48 underwent the carbonization test. T P