Summary,of,Research,on,Use,of,Sediment,in,Building,Materials

Lidan CAI, Chen WANG, Wenkun ZOU, Chenhao LIANG, Qi LI

Jiangxi University of Technology, Nanchang 330098, China

Abstract Based on the recent research at home and abroad, this paper summarizes the preparation of cement clinker, baking-free brick, subgrade filler and ceramsite from sediment, and puts forward relevant suggestions and prospects for the future research direction of sediment.

Key words Low carbon cycle, Sediment, Green building materials, Resource utilization

At present, some water treatment plants, rivers, lakes,etc.need to treat tens to hundreds of tons of acidic sediment every year. Some of the waste sediment is used as self-circulating slurry, and the rest is directly discharged to the sediment yard. Such sediment storage occupies a lot of land resources and will also cause damage to the ecological environment. According to the development requirements of China’s 14thFive-Year Plan, the construction of ecological civilization plays an increasingly important role in promoting the deep integration of green and low carbon and ecological environment protection, and promoting the sustainable development. In order to make comprehensive and full use of sediment, scholars at home and abroad have studied and analyzed sediment.

Governments at all levels thoroughly implement Xi Jinping’s ecological civilization thought, unswervingly follow the road of ecological priority and green development, and make every effort to create a beautiful China. At present, the industrial structure is imbalanced and it is in the critical period of kinetic energy conversion. Resources and environment have become the key factors restricting the sustainable development of economy. Building materials industry is an important part of the traditional industrial system. Under the requirement of dual-carbon goal, promoting the green development of building materials industry is the only way to speed up the establishment and improvement of a green and low-carbon circular economic system, realize the recycling of resources and achieve the purpose of turning waste into wealth.

This paper mainly expounds the utilization of sediment in building materials, so as to achieve the purpose of resource utilization. The main components of sediment are silicon dioxide and aluminum oxide, and the treated sediment can be used as raw materials for building materials. This can not only protect the ecological environment, reduce mining, but also solve the secondary pollution caused by sediment stacking and a large amount of land occupation, and achieve the goal of carbon neutrality and carbon peaking.

TheReportofthe20thNationalCongressoftheCommunistPartyofChinapointed out that it is necessary to speed up the green transformation of development mode and develop green and low-carbon industries. Against the background of dual carbon goals, the state makes every effort to promote green and low-carbon construction, promote green building materials, encourage local governments to develop green building materials according to local conditions, promote the coordinated development of green building materials and green buildings, and enhance the use of green building materials in the renovation of new and existing building projects. Especially in modern technology, the cost of construction and materials accounts for more than 60% of the whole project cost, and the demand for materials in the construction industry is large, which leads to a large amount of mining. Therefore, it is a development trend to recycle the solid waste in the construction industry.

2.1 Cement clinkerSediment contains a large amount of organic matter. Before preparing cement clinker, the sediment is heat-treated and sintered. In this process, the sediment will decompose and produce micropores, thus reducing the bulk density and improving the air permeability. Sediment is used as the raw material of cement clinker[1]. At present, the technology of using sediment as cement clinker has been well applied at home and abroad. Some scholars use sediment as the main raw material for the preparation of cement clinker. From the aspects of sediment drying technology and mixture ratio, it is found that the toxicity of the sediment is greatly reduced after resource application, and the sediment used for preparation of cement clinker is less harmful to the environment. It can make full use of the sediment as the raw material of cement clinker, which brings good ecological, economic and social benefits.

2.2 Preparation of baking-free bricksAt present, there are many cases of preparing pavement bricks from sediment at home and abroad, which mainly adopt direct blending process and sintering method. The disadvantages of using sintering for brick-making are high energy consumption and generation of a large amount of CO2,etc.In order to solve the energy consumption and strength problems of preparing pavement bricks from sediment, relevant scholars[2]made the sediment into modified sintering-free aggregate, which was then mixed with cementitious materials and pressed into waterproof aggregate bricks and shell aggregate bricks. The wet process is adopted in this study, and the raw sediment does not need to be dried. It has the characteristics of low cost, simple process, energy saving and environmental protection, which can not only effectively solve the problem of sediment treatment, but also replace the current pavement bricks, reduce the development and utilization of mineral resources in China, and comprehensively utilize the waste sediment as resources.

2.3 Preparation of cementitious materialsMany years ago, some relevant scholars[3]explored the cement production process from sediment. They dried the sediment, ground it, mixed it with 10% fly ash and 20% sediment as new cementitious materials, and molded and cured it after stirring. The stability of the cementitious materials obtained was qualified after testing, and the strength and setting time met the specification requirements. Some scholars[4]prepared three different types of cementitious materials according to different amount of sediment instead of 0%, 10% and 20% cement. According to the curing time (3, 7, 28 d), with the increase in the mixing amount, the compressive strength and flexural strength of the cementitious materials showed different changes. By analyzing the test data, it was concluded that the sediment with substitution rate of 10% had the greatest compressive strength and flexural strength, followed by no sediment, and the sediment with substitution rate of 20%. The results showed that higher substitution rate was not conducive to the preparation of cementitious materials, and proper substitution rate of sediment was beneficial to the strength, compressive strength and slump of cementitious materials.

3.1 Subgrade fillerIf sediment is used as subgrade filler, bearing ratio, compactness and unconfined compressive strength[5]must meet the corresponding requirements. The water content of sediment is high, but the dehydrated and solidified sediment is not easy to settle and permeate, and has high strength. At the same time, relevant additives, such as limestone and fly ash, are added, so the sediment can be used as a good subgrade filler. Some foreign scholars mixed sediment with ordinary Portland cement and fly ash, tested and analyzed the compressive strength, flexural strength and corresponding indicators of the sample after a series of processes such as test, sampling and maintenance. It was found that adding fly ash effectively improved its mechanical properties, and the maximum values of these indicators could be obtained under the combination of 5% ordinary Portland cement and 10% fly ash, which reached the subgrade filling standard of the national highway. This test proved that sediment could be used as a good road subgrade filler.

3.2 Preparation of ceramsite from sedimentThe sintering of ceramsite mainly includes three stages: drying, preheating and roasting. In the whole process, controlling preheating and roasting conditions is the key to preparing high-quality ceramsite[6]. The main properties of sediment samples are measured and analyzed, and different additives are added at the same time. At present, in the method of preparing ceramsite with sediment as the main raw material, the selected additives are coal gangue, fly ash and so on. Sediment contains a large amount of organic matter, direct roasting will produce a large amount of CO2, and cracking will occur in the roasting process, so preheating is needed to remove excess organic matter before roasting. In the whole process of preparing ceramsite from sediment, controlling preheating and roasting is the key to preparing high-quality ceramsite.

According to the requirements of sustainable development of green building materials, people’s awareness of ecological environment protection and green building materials is getting higher and higher, waste resource utilization technology is also rapidly advancing, and sediment treatment technology is constantly developing. The environmentally friendly dredging of sediment and its resource utilization have been comprehensively applied, especially the utilization of sediment in building materials and resource application of sediment, as well as the utilization of sediment as subgrade filler and the preparation of ceramsite from sediment, which can not only bring ecological and environmental benefits, but also create better economic and social benefits. In recent years, the recycling technology of sediment is more and more advanced, so the recycling technology of sediment can avoid the high energy consumption in traditional sediment treatment, and can also solve the problem of secondary pollution to the environment, and greatly reduce the treatment cost, with a good application prospect.

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