Properties and printability evaluation of three-dimensional printing magnesium oxychloride cement by fully utilizing aeolian sand

Three-dimensional concrete printing(3DCP)is increasingly being applied in harsh environments and isolated regions.However,the effective utilization of aeolian sand(AS)resources and by-products derived from arid zones for 3DCP is yet to be fully realized.This study developed a three-dimensional(3D)printing composite using AS and magnesium oxychloride cement(MOC)from local materials.The effects of the mole ratio of MgO/MgCl_(2)and sand/binder(S/B)ratio on the mechanical properties such as water resistance,drying shrinkage strain,rheology,and printability,were investigated systematically.The results indicated that the optimal mole ratio of MgO/MgCl_(2),was 8,which yielded the desired mechanical performance and water resistance.Furthermore,the S/B ratio can be increased to three within the desired printability to increase the AS utilization rate.The rheological recovery and buildability of the 3D-printed MOC with AS were verified.These findings provide a promising strategy for construction in remote deserts.

Effects of background fertilization followed by co-application of two kinds of bacteria on soil nutrient content and rice yield in Northeast China

With the improvement of living standards,people pay more and more attention to the quality and safety of rice.Microbial agents are favored by the public because they can activate the nutrient supply in the soil,and reduce the residue and application amount of chemical fertilizers and pesticides.Based on the conventional fertilization in the field,Bacillus mucilaginosus and Aspergillus niger were applied,Bacillus mucilaginosus was inoculated at four levels in the paddy soil in the cold region of Heilongjiang Province of China.The effects of different proportions of Bacillus mucilaginosus and Aspergillus niger on the number of soil microorganisms,enzyme activity,microbial biomass,soil biochemical intensity,soil nutrient content,plant nutrient content and yield were studied,and the effects on the plant nutrient content of rice and the nutrient dynamics were discussed.The results showed that a 2.62%-21.20%higher yield of rice obtained from co-application treatments compared with that of the control-blank treatment.Furthermore,the highest yield obtained(10736±65 kg/hm^(2))suggested that the optimized values for the two bacteria applied were 120×10^(11) CFU/hm^(2) for Bacillus mucilaginosus and 15×10^(11) CFU/hm^(2) for Aspergillus niger.Bacillus mucilaginosus can decompose minerals in soil,dissolve potassium and silicon,decompose apatite and release phosphorus into soil.Aspergillus niger can transform the phosphate which cannot be absorbed by plants into soluble phosphate which can be directly absorbed by plants by producing non-volatile acids.In particular,Bacillus mucilaginosus and Aspergillus niger have synergistic effect,and their combined application effect is greater than that of two bacteria alone.Co-application promoted the release of soil soluble silicon,and then increased the silicon content of plants.At the same time,soil microorganism,microbial biomass,enzyme activity and biochemical activity all increased significantly.This study provides an effective way to reduce the amount of chemical fertilizer applied in rice production in cold regions of China.