Mix Design And Performance Study Of High-strength Lightweight Aggregate Concrete

With the need of high-rising, large-span and heavy-loading-structures in civil engineering, normal weight concrete (NWC) prepared by normal weight aggregates (NWA) has shown its shortcoming of large self-weight more evidently. Lightweight aggregate concrete (LWAC) has been used successfully for many years. Lightweight aggregate concrete permits savings in dead load directly. In addition to lighter weight, Lightweight aggregate concrete is more resistant to seismic force and fire, and furthermore, Lightweight aggregate concrete has reliable durability and reasonable comprehensive economics. For Lightweight aggregate concrete, as for normal weight aggregates, there is a well-established trend toward using higher strength. Research on this area seems limited in China.Based on the experiments in preparing high-strength normal weight aggregates and Lightweight aggregate concrete in many countries, high-strength Lightweight aggregate concrete using high-strength lightweight aggregate (LWA) produced in china was obtained with the application of chemical admixtures. The physical and mechanical properties of high-strength Lightweight aggregate concrete have been investigated. The paper consists of six chapters totally. The emphasis parts are chapter three, chapter four and chapter five.Chapter one mainly talks about the study background, significance and contend. Along with the rapid change of the construction techniques, the development of the construction is to the long-span and high-level, in order to reducing the structural sections and support, improving the thermal insulation properties and so on, the demands of the concrete is high-strength and lightweight. Artificial light aggregate and lightweight aggregate concrete directly overcome the drawback of the normal weight aggregates, so wide attention of all countries in the world. United States, and Europe, Japan and other countries have been put the production of the artificial lightweight aggregate and the application of lightweight aggregate concrete and construction materials as the major civil engineering topics. In these countries and regions, the research and application of high-strength lightweight aggregate concrete has marched at the forefront of the world. In our country, the study of the lightweight aggregate and lightweight aggregate concrete began in the mid-1950s from the 20th century. But its scope and depth as compared to those of other developed countries, there is still a big gap.Chapter two mainly talks about the definition and classification of lightweight aggregate and lightweight aggregate concrete, fresh lightweight aggregate concrete and hardening lightweight aggregate concrete. The focus is formation characteristics of fresh lightweight aggregate concrete. Because of the density of the aggregate lower than that of cement, lightweight aggregate will go up, led to the segregation of lightweight aggregate concrete. This paper presents a mathematical model to analyze the speed of light aggregate float. In view of these factors, give out measures of control the segregation of the lightweight aggregate concrete. In hardening lightweight aggregate concrete, talks the intensity mechanism of lightweight aggregate concrete and characteristics of the damage which different from the ordinary concrete.Chapter three describes the study of the physical and mechanical properties of lightweight aggregate. Lightweight aggregate is critical for high-strength lightweight aggregate. The grading, special particle density, bulk density, water absorption, and Cylinder compressive strength of lightweight aggregate are investigated. The microstructure of lightweight aggregate mainly including the surface textures and internal pore structure are observed. The results shows using this kind of lightweight aggregate to preparing high-strength lightweight aggregate concrete is rational.Chapter four describes the mix proportion design of lightweight aggregate concrete. After determining the design parameters,"relax volumetric method"is used to calculate mix proportions, using lightweight aggregate of saturated-drinking. On the basis of the benchmarks mix proportion, using contrast experiments by changing one or more of the factors, analyze its effects on the concrete performance. In this factors, water-cement ratio, percentage of sand, lightweight aggregate whether saturated-drinking or not and the cylindrical compressive strength of lightweight aggregate are the major factor. Lower water-cement ratio, the increased intensity of concrete, but when the water-cement ratio lowered to a certain value, workability and density of the lightweight aggregate concrete will be reduced, thus reducing the intensity; higher the percentage of sand, increase the strength and density of the concrete, and when the percentage of sand beyond reasonable limits and excessive, the concrete will eduction, leading to uneven concrete structure, the strength of concrete reduced; for the same mix proportion, the lightweight aggregate which saturated-drinking will increase the strength of the concrete; for the same lightweight aggregate, the smaller the largest diameter, the higher the strength of concrete.Chapter five describes the study of the physical and mechanical properties of lightweight aggregate concrete. Density and mechanical properties are the two most important properties of lightweight aggregate concrete. Except several mix proportions, the cubic compressive strength at the age of 28d of most mix proportions exceeds 40 MPa with the correspond oven-dried density less than 1950 kg / m3. The mechanical properties including compressive strength, tensile strength and relationships between these properties are investigated. The experimental results are compared with normal weight concrete with same strength grade. In lightweight aggregate concrete, the ratio of the compressive strength with age of seven days and 28 days was slightly higher than the ratio of normal weight concrete. Light aggregate concrete shows early strength of concrete at a rate faster than the normal weight concrete. The axial compression ratio of lightweight aggregate concrete is higher than the same level of normal weight concrete, splitting tensile strength and flexural strength bending slightly bigger than the same level of ordinary concrete. The former was mainly due to the hoop effect of lightweight aggregate concrete is weak, the latter mainly because of the better interfacial bonding of lightweight aggregate concrete.Chapter six is summary of the paper in which the content and direction are also pointed out for further study.