Experimental Study On Making Artificial Flood-Prevention Stone Using Silica Fume-Fiber Cement Mortar Of Yellow River Sand

The Yellow River is the mother river of the Chinese nation and the second largest river in China,but because it flows through the Loess Plateau and carries a lot of sediment,over time the sediment accumulates and raises the riverbed on both sides,causing serious harm to the people downstream.Therefore,it is urgent to manage the Yellow River sediment.The resource utilization of Yellow River sediment is an effective way to solve the problem of "hanging river on the ground",which can be divided into three aspects according to the role of flood control engineering,ecological restoration,construction and industrial materials,etc.One of the feasible methods in flood control engineering is to make artificial flood-prevention stone,but because the Yellow River sediment particles are very fine,also known as the Yellow River superfine sand,can not be used as fine aggregate alone to make mortar or concrete,thus limiting the resource utilization of the Yellow River sediment.In this study,the compressive strength,flexural strength,splitting tensile strength,water absorption,impact resistance,frost resistance and other working properties of cement mortar were investigated by different mud content of yellow river sand,different basalt fiber admixture and different silica fume admixture;and the microstructure of the composites was also characterized by SEM electron microscopy scanning and XRD diffraction experiments,and the reasons for the improvement of mortar strength by mud content,basalt fibers and silica fume were analyzed.The main research contents and conclusions of this thesis are as follows:(1)Mechanical strength tests and workability studies were conducted on yellow river sand cement mortars with different mud contents,and the results showed that the mechanical strength of yellow river sand cement mortars improved significantly with the decrease of mud content and improved fluidity;the mud content affected the water absorption of mortars,and the lower the mud content,the lower the water absorption rate and the better the durability.It was observed by SEM microanalysis that the internal hydration reaction of mortar with 0%mud content was more adequate and the C-S-H gel was more uniformly distributed.(2)The compressive strength and flexural strength of basalt fiber-silica fume mortar with75% mud content were determined experimentally,and the flexural ratio was calculated to obtain the optimum mixture of basalt fiber and silica fume.The compressive strength of basalt fiber-silica fume mortar with 55% mud content was also measured experimentally and compared with basalt fiber-silica fume mortar with 75% mud content,and the results showed that basalt fiber has a greater influence on the flexural strength of mortar,and the ultimate flexural load is gradually enhanced with the increase of basalt fiber admixture,but too high admixture affects the mortar strength instead;Silica fume has a significant effect on the compressive strength of mortar,with the increase of silica fume admixture,the compressive strength of mortar is gradually enhanced and reaches the best ratio at 15% admixture.Basalt fiber and silica fume were mixed into the mortar together,which effectively improved the mechanical strength of the mortar;the optimal content of fiber 1.5% and silica fume 20%increased the compressive strength by 44% compared with the common mortar containing75% mud,and the stress-strain curve graph found that the addition of basalt fiber and silica fume reduced the stiffness and increased the toughness of the mortar.Compressive strengths of 75% and 55% mud content were compared,showing that the effects of basalt fiber and silica fume on the strength of 55% mud content were basically the same as those on 75% mud content,but the compressive strength of 55% mud content was enhanced more significantly by basalt fiber and silica fume.The compressive strength of basalt fiber-silica fume mortar with 55% mud content increased by 15% compared with basalt fiber-silica fume mortar with75% mud content;from the microscopic analysis,silica fume enhanced the strength because it filled the mortar voids and generated additional C-S-H gel,and basalt fiber enhanced the flexural strength because of the mechanical occlusion effect.(3)The water absorption rate of basalt fiber-silica fume mortar was determined experimentally at 75% and 55% mud content,and the best basalt fiber and silica fume matching ratio was selected for 75% and 55% mud content to compare the working properties such as frost resistance and impact resistance.The results showed that basalt fiber had a small effect on the water absorption of mortar,while silica fume had a more significant effect on the water absorption of mortar.The joint addition of both basalt fiber and silica fume limited the number and width of cracks in the cement mortar,further reduced the water absorption capacity,and improved the durability of the cement mortar,with little difference in the effect on the water absorption rate at the two mud contents.The mortar made under the two mud contents meet the requirements of artificial flood-prevention stone for frost resistance and impact resistance.Comparing the XRD diffraction patterns,there is no significant difference in the mineral composition of basalt fiber-silica fume mortar compared with common yellow river sand.