Recycling of water treatment sludge in concrete: The role of water-binder ratio from a nanoscale perspective.

For eutrophic water bodies, potassium permanganate is an effective pre-oxidant to remove algae and its residue in water treatment sludge. Recycling water treatment sludge in concrete is an environmentally friendly and high-value utilization measure. However, little research has been done on the effect of manganese-rich drinking water sludge ash (DWSA) on concrete. The effect of water-binder ratio (w/b) on strength, shrinkage and microstructural characteristics of concrete containing DWSA was investigated, and the structural behavior was explained from a nanoscale perspective. The results show that recycling 10 % DWSA in concrete improved the strength and shrinkage resistance of the samples. Reducing the w/b effectively increased the strength of DWSA-modified concrete and reduced the shrinkage deformation. The paste with high w/b had higher contents of non-evaporated water and calcium hydroxide, as well as higher reaction degree of DWSA. Nanoscale characterization shows that reducing the w/b reduced the volume fraction of pore and unhydrated phases in the matrix and increased the proportion of high-density C-S-H. Meanwhile, reducing the w/b also reduced the interfacial transition zone width of DWSA-modified concrete. Recycling DWSA in concrete effectively reduced the total carbon footprint and cost of the mixture. The combined application of reducing the w/b and incorporating DWSA effectively improved the economic and environmental benefits of concrete material. For the concrete modified with 10 % DWSA (w/b = 0.3), its cost and carbon emissions are reduced by 14 %-21 % and 19 %-25 % compared with the reference sample, respectively. Overall, this study reveals the action mechanism of DWSA in cement system at different w/b from nanoscale perspective, and gives a new insight on determining the optimal w/b in full-scale application of DWSA concrete.

Experimental analysis of the stick-slip characteristics of faults at different loading rates.

In deep underground engineering, in a large spatial, high-stress environment, rapid excavation is likely to affect the loading rate of the fault structure and to cause stick-slip. In this study, an experiment was conducted to explore the stick-slip characteristics at different loading rates. A double-sided shear experiment and the digital speckle correlation method were used to analyze the evolution of the displacement field, the slip displacement, and the slip rate of the fault's stick-slip activity at different loading rates as well as their correlation with the loading rate. The loading rate, moment magnitude, and stress drop of the fault's stick-slip and their corresponding relationships were studied. The results show that the occurrence of stick-slip is inversely proportional to the loading rate. The evolution of the fault-slip displacement field at different loading rates is similar. At a given loading rate, the magnitude is positively correlated with the stress drop. The magnitude and stress drop are inversely related to the loading rate.