稻壳灰应用于水泥混凝土的研究进展

Research Progress on Application of Rice Husk Ash in Cement and Concrete

稻壳是21世纪最有潜力的再生资源之一,通过低温燃烧制备的稻壳灰(RHA)含有高纯度的非晶态SiO 2,具有较高火山灰活性,可作为水泥基材料的辅助性胶凝材料,这不仅提高了稻壳的附加值,也符合可持续发展绿色建筑的理念。相比于粉煤灰、硅灰、矿渣等市场成熟的掺合料,稻壳灰有两大优势:(1)原材料稻壳储备量大,价廉;(2)非晶质SiO 2含量高达90%,火山灰活性可比肩硅灰。然而稻壳灰对生产燃烧设备要求较高,燃烧控温技术难关及副产物回收技术未完全被攻破,只能用流化床小规模生产,市场供应量低。未来在酸处理后的污水的回收利用方面,流化床设备的改进仍需进一步探索。同时稻壳灰的Si-O键会与减水剂的官能团发生配位反应,削弱减水效果,影响水泥混凝土的相容性,与之匹配的高性能减水剂仍需进一步研发,才有望实现稻壳灰在水泥混凝土中高效且规模化的应用。稻壳灰由细度约50 nm的SiO 2凝胶粒子疏松地粘聚形成,且含有大量纳米尺度的孔隙,这是其具有高火山灰效应的内在原因。通过酸处理的稻壳先经低温燃烧后再高温燃烧,在低于750℃的燃烧制度下可获得优质的稻壳灰。稻壳灰比表面积高达50~100 m 2/g,使其具有吸附性,吸附自由水会降低混凝土的流动性,提高粘聚性;当稻壳灰的平均粒径小于水泥且掺量为10%~20%时,可以提高混凝土的后期强度及其与钢筋的粘结强度,其耐久性也能得到显著改善。本文系统梳理了稻壳灰用于水泥基材料的国内外文献,对稻壳灰的理化性质、微观结构、生产制备工艺及其对水泥混凝土各项性能的影响等方面的研究进展进行了介绍,揭示了稻壳灰用于水泥混凝土的工作机理,厘清了该领域尚待进一步探索的问题,旨在为将来稻壳灰再生利用形成完整的生产链提供理论依据和技术支撑。

R ice husk is one of the most promising renewable resources in the 21st century,which contains high purity amorphous SiO 2 by low-temperature combustion.It has high pozzolanic activity and can be used as an auxiliary cementitious material of cement material.As a substitute for mineral admixture,rice husk ash(RHA)is used in concrete,which conforms to the concept of sustainable development.Compared with fly ash,silica ash,slag,RHA has two advantages:(1)high yield and low price;(2)amorphous SiO 2 is up to 90%.On the other hand,RHA need strict requirements for combustion equipment,and the difficulties of combustion temperature control and by-product recovery technology have not been completely broken,so it can only be produced in fluidized bed on a small scale,and the market supply is low.In the future,the improvement of fluidized bed equipment should be further explored for the recovery and utilization of sewage after acid treatment.At the same time,the Si-O bond will coordinate with the functional group of water reducer.RHA is formed by loose cohesion of SiO 2 gel-particles with fineness of 50 nm and contains a large number of nanometeral pores.The best physicochemical properties of RHA can be obtained by the combustion system of"low temperature before high temperature"after acid treatment.The specific surface area of RHA is as high as 50—100 m 2/g,which makes it adsorbable.The adsorption will reduce the mobility of concrete and improve the cohesion of concrete.When the average particle size of RHA is smaller than that of cement and the content of rice husk ash is 10%—20%,the later strength of concrete and its bond strength with steel bar can be improved,and its durability can also be significantly improved.In this paper,massive literatures of RHA used in cement materials is systematically combed,and the physical and chemical properties,microstructure,production and preparation technology of RHA and its influence on the properties of concrete are introduced.This paper reveals the working mechanism of RHA used in cement concrete,clarifies the problems that need to be further explored in this field,and points out the direction for the research of RHA used in concrete,besides it provides theoretical basis and technical support for the regeneration and utilization of RHA to form a complete production chain in the future.