Issue 49

Y. Liu et alii, Frattura ed Integrità Strutturale, 49 (2019) 714-724; DOI: 10.3221/IGF-ESIS.49.64 719 table and vibrating rod, that is, the “shear-thinning” feature in fluid dynamics. Fly ash is a microscopic particle whose shape is similar to a globule. However, the shapes of cement particles are irregular. Therefore, when fly ash is added into the cement paste (with a fly ash content of less than 50%), the friction of cement mortar will be reduced under the rolling effect. Since less water is needed for the smooth surface of the fly ash sphere, the free water in the mortar will increase, diluting the cement mortar and increasing the shear thinning degree [31]. As a result, when the fly ash concrete is vibrated and the density difference between the top and the bottom becomes larger, the course aggregate moves downward faster. Effect of bending load on the carbonization resistance of concrete The carbonization depths of the reinforced concrete blocks in the bending-tension and bending-compression zones under different bending loads are shown in Tab. 3. Fly ash content Bending load stress level 7d 14d 28d Tension/compre ssion Tension/compre ssion Tension/compre ssion 0% 0% 4.74/4.50 5.48/5.34 6.64/7.93 20% 4.56/5.99 5.32/6.54 6.25/9.65 40% 4.01/7.32 4.88/8.56 5.33/10.28 60% 3.55/8.86 4.21/9.77 4.56/11.26 20% 0% 7.13/5.40 8.71/7.20 9.58/8.26 20% 6.02/7.55 6.57/8.38 8.23/9.95 40% 5.55/7.92 6.26/8.78 7.05/11.45 60% 4.55/9.57 5.32/10.95 5.88/12.50 30% 0% 7.61/5.90 8.76/7.30 9.98/8.60 20% 6.87/7.99 8.76/9.26 9.35/9.98 40% 6.74/8.45 7.44/9.87 8.05/12.00 60% 5.52/9.85 6.38/11.20 7.52/12.98 40% 0% 8.00/6.20 9.25/7.84 10.63/9.75 20% 7.50/8.24 9.24/10.24 10.25/12.99 40% 6.85/9.57 8.82/10.55 10.01/13.21 60% 6.02/10.45 7.22/11.98 9.00/13.90 Table 3: Carbonization depths of concrete test blocks under different bending loads/mm Effect of bending-compression load on the carbonization resistance of concrete The variation curve of the carbonization depth in the bending-compression zone of concrete with the bending load stress level is shown in Fig. 5. Fig. 5 shows that with the bending load stress increasing, the carbonization depth of the concrete in the bending- compression zone decreased under the same fly ash content. This indicates that the bending-compression load inhibits the erosion of CO 2 and improves the carbonization resistance of concrete. To quantify the effect of bending load stress on the carbonization depth of concrete blocks, the carbonization influence coefficient of bending-compression load stress was used, by reference to Niu Jiangang's method [16]. c c n X K X  (2) where K c is the carbonization influence coefficient of bending-compression load stress; X c is the carbonization depth of concrete under bending load in the compression zone; and X n is the carbonization depth of concrete without load in the compression zone. Through regression analysis, the fitting equation between the carbonization influence coefficient of bending-compression stress and bending load stress level under different fly ash contents can be determined, as shown in Tab. 4, where K C is the carbonization influence coefficient of bending-compression stress and S C is the bending load stress level. As shown in Tab. 4, the relationship between the carbonization influence coefficient of the bending-compression stress and the bending load stress level can be described using a quadratic polynomial. The coefficient of this formula is different from the results of the quadratic polynomial fitting in reference [16]. The main reason may be that the