Preparation Of High-Strength Lightweight Lytag And Its Concrete Performance

Lightweight aggregate concrete is characterized with a lightweight, low-cost, high-seismic resistance, high crack resistance, high durability and high fire resistance, heat insulation and so on. Lightweight aggregate concrete used in construction projects not only meet the strength and other performance requirements but also substantially relieve the weight of the structure, which are of some very important value. With the national policy of environment protection and sustainable development of economic and society, as well as the rising demand for energy-saving construction, the theory and application Technology using a variety of industrial waste to produce man-made lightweight aggregate and high-performance lightweight aggregate concrete plays an important research value and of practical significance.This paper firstly discussed the preparation of high-strength lightweight aggregate using fly ash in laboratory and in factory. Fly ash used as the main raw materials, incorporated with sintering additive and Ca(OH)2 in different ratio, was sintered a high-strength lightweight aggregate of fly ash(Lytag)in the laboratory-controlled electric furnace. The results show that in the sintering temperature range of 1200 to 1280℃, retaining time of 5 min ~ 10min, the bulk density and the apparent density and 24 h water absorption of Lytag decreased with the increase of sintering additive and the decrease of the amount of fly ash. The addition of Ca(OH)2 can significantly enhance the compressive strength of Lytag pellets, reduces its water absorption at 24h and improve internal pore-shape of inner structure. The coefficient of burnability Pk kept a good linear relationship with porosity and particle strength of Lytag. The optimal mix proportion to meet requirements of high-strength Lytag density of the three grades (600, 700, 800) Lytag was obtained. Three test pilots in QiQihar, Hulan and Daqing were performed and the optimal production process and technology was promoted.Rheometer used to examine the effect of the type and amount of mineral admixture on the rheological parameters of cement slurry. The development rule of Yield strength and plastic viscosity of the cement slurry with single-doped slag, fly ash, silica fume and zeolite powder, as well as the different multiple-doping proportion were obtained. Then the optimal single-doped or multiple-doped ratio of various mineral admixture were attained in order that the fresh Lytag concrete can arrive better workability and Lytag gain in a very uniform distribution in concrete. These have laid a theoretical foundation for preparation of a high-performance lightweight aggregate concrete.The uniaxial compression tests have been used to examine Lytag concrete with the different mineral admixture and normal concrete. The relationship between the compressive strength of prism specimens and cube specimens was set up. Peak strain, elastic modulus, Poisson's ratio and the cube compressive strength of these two concrete were compared. The results showed that the whole stress-strain curves of Lytag concrete and ordinary concrete were similar and the existing norms can meet the design requirement of Lytag concrete.In view of the bridge deck applied a large number of lightweight aggregate concrete in cold region, the European Union recommended standard (CDF) about frost resistance of concrete test was adopted in this paper to do a comparative study on frost resistance of Lytag concrete and ordinary concrete. The frost resistance of Lytag concrete adding mineral admixture is better than that of ordinary concrete. The order of frost resistance for single-doped mineral admixture after 56 cycles is: silica fume> fly ash> slag. The order of frost resistance for multiple-doped mineral admixture after 56 cycles is: silica fume +slag > silica fume+ fly ash > slag+ fly ash. The frost resistance of concrete for multiple-doped mineral admixture was much better than that of concrete with single-doped mineral admixture. The SEM-EDXA analysis indicated that the interface transition zone of lightweight aggregate and cement is about 5 ~ 20um, far less than the interface transition zone of ordinary concrete. The smaller the interface transition zone, the better mechanical properties and durability of concrete.A new testing device on concrete permeability under load was developed, which can make the concrete specimens bear the tensile stress or compressive stress of 0 to 70% and continue to examine the permeability of concrete specimens. The test method for permeability of concrete was conformed to ASTM C 1202 method of Cumulative electrical value. Regardless of loaded or unloaded, the permeability for the same level of intensity of the lightweight aggregate concrete was better than that of ordinary concrete aggregate. When the stress is greater than a certain threshold, the permeability of concrete increased significantly. In this test for permeability of concrete, the quadratic function relationship between concrete electric flux Q and the pressure (or pull) f stress can be demonstrated: Q = Af2 + Bf + C (A, B, C is a constant).