Waste Materials From Industry And Agriculture Reused In Concrete

The concepts of green concrete and sustainable development of materials were attracting more and more researchers’attentions recent years. To achieve the green and sustainable concrete, reducing the content of cement is an important and efficient way, which is also favourable for our environment, to recycle of un-rebirth resources and decrease the discharge of harmful materials. Some existing researches prove that fly ash, silica fume and blast furnace slag from industry can be used as mineral admixtures to reduce the cost of concrete and lessen the pollution to environment and soil. They can also improve the performance of cement concrete and satisfy the design demands of modern concrete engineering. Therefore, some interesting tests were carried out in this paper to study the physical and mechanical properties, durability, and microscopic structure of concretes mixed with different percentages of rice husk ash, fine rice husk ash, steel slag and red mud by mass substituting10%～30%cement. At the same time, some parallel experiments were done to study the physical and microscopic properties of concretes mixed with two kinds of mineral admixtures by the residue mentioned above and fly ash or silica fume.Experimental results indicate that blended concretes containing fine rice husk ash (FRHS) have lower specific surface area and higher porosity than that of ordinary Portland cement concrete. Chloride permeabilities of concretes decrease with the increasing replacement rate of rice husk ash because of the increasing closed pore in concrete. The mechanical properties and durability of concrete are improved simultaneously when the cement replacement by FRHS is10%, due to its micro-aggregate effect and pozzolanic effect.The test results obtained in this study reveal that the steel slag can be used in concrete as cementing material with lower activity than cement. Steel slag substituting10%cement by mass improves mechanical properties and durability of concrete. Even up to20%, the steel slag could be advantageously blended with cement without adversely affecting the performance of concrete. When the mixture uses equal weight portion of rice husk ash and silica fume, or steel slag and silica fume, the strength and the durability of concrete are improved dramatically.The test results from red mud concrete prove that red mud can be utilized as a concrete pigment. Both mechanical properties and durability decrease when the concrete mixes with red mud because of the high alkalinity which increases the content of calcium hydroxide in hydration products. In addtion, Red mud has an effect of excitation to the activity of secondary reaction of silica fume and fly ash because of its high alkalinity. The use of a blended mineral admixture of red mud and silica fume, or red mud and fly ash improves the directed orientation of calcium hydroxide, therefore, enhances the mechanical strength and durability of concrete. The most efficient mixing ratio of red mud and fly ash is1:3according to the improvements of mechanical strength and chloride permeability resistance.To reveal the modification mechanism, the micro-structure of concrete was studied by the SEM scanning method. The test results show that the physical and mechanical properties of concrete are controlled by the microscopic changes in the material, and the changing regularity of the microstructure has a good agreement with the macroscopic properties.