Abstract: This paper introduces development and application of ultra-high strength/high performance concrete in construction of the Xita tower high-rise building at Zhujiang New City of Guangzhou, China. The goal of the concrete construction in the Xita Tower project will be realized via research of mix proportion and optimization of pumping equipment. In regard to mix proportion of concrete, low water/cement (W/C) ratio, low water content lower than 150 kg/m3 and employment of superplasticizer are essential to acquire high strength. A series of parameters have been measured to research workability of concrete from C70 to C90, such slump, slump flow, flow time from inverted cone, L-box flow, and bleeding under pressure et al. Properties of hardened concrete should also be considered, including durability, autogenous shrinkage caused cracking, and fire resistance.
Abstract: In this paper, the technical problems are discussed, and a couple of countermeasures are proposed. To solve the problems of HPC, such as autogenous-shrinkage caused cracking, cracking caused by swelling, and high plastic viscosity, the key parameters are water content and cement content in mix proportion. Coarse aggregate should comprise of two grades. Such HPC can inhibit autogenous-shrinkage caused cracking, cracking caused by swelling, and lower plastic viscosity and improve pumping performance. Incorporate polypropylene fiber can prevent explosive spalling under high temperature.
Abstract: Mineral powders play positive role in improving the durability of concrete subjected to alkaline and saline corrosion, where sulphate ion and chloride ion coexisted may cause serious deterioration to the reinforced concrete structures. Metakaolin, slag, fly ash and natural zeolite mixed in appropriate proportion were tested in inhibiting the deterioration. It is found that the composite powder might decreased AAR and the charge passed of concrete effectively，the while the 7d and 28d strength of cement and concrete are improved as well.
Abstract: Durability of C100 concrete in Shenyang WAN XIN Hotel engineering including long-term mechanical properties, dynamic modulus of elasticity, and chloride ion resistance was tested and analyzed. Test results appeared that C100 concrete had very good density and extremely good durability. Simultaneously we suggest improving the evaluation method to test the durability of super-high strength concrete in order to enhance the evaluation level effectively. It will provide one according of durability to apply super-high strength concrete.
Abstract: Performing the superposition effect of multi-elements mineral admixtures, high performance concrete (HPC) with 3% of silicon fume, 20% of fly ash and 40% of ground granulated blast-furnace slag (GGBS) was prepared, and its physical and mechanical properties and durability were studied systematically. The compressive strength and tensile strength of HPC are better than those of ordinary concrete. HPC has high compactness with smaller gas diffusion coefficient and relative permeability coefficient. Adding volume stabilizer and controlling the contents of SO3 in the GGBS and volume stabilizer at 3%, can reduce dry shrinkages effectively. Large mount of mineral admixture was used to make the concentrations of K+ and Na+ in the pore solution and the expansion caused by alkali-silica reaction depress greatly. So the alkali-silica reaction gets controlled markedly. The effective diffusion coefficient of chloride ion is 1.96×10-12 m2/s, which means HPC has a favorable chloride ion penetration resistance. After 15 times of wet-dry cycle, the rates of the rust area and quality loss of the reinforcing steel bars in HPC are only 4.1% and 0.05% respectively, so HPC has better performance of steel protection. The mortar bar did not expand in corrosive sodium sulfate solution, and it means HPC has better performance of sulfate resistance. The performances of frost resistance and carbonation resistance of HPC are also favorable. It’s proved in tests that the superposition effect of multi-elements mineral admixtures can enhance the physical and mechanical properties and durability of concrete greatly.
Abstract: The high-moisture quick-concreting material is a special type of cement which can be quick-concreting and full solidifying under the condition of high water cement ratio (2.5 : 1 ) . Thus , the mechanical performances of high-moisture quick-concreting material are as follows : 1) The grout fluidity is better and the penetrability is strong ; 2)The volume of concretion is tiny expansion in favor of solid filling in steel tube and exiguous gap ; 3) Concreting speed is rapid and the early strength is big , and the concreting speed may be also adjusted ; 4)The water cement ratio and the mixing ratio can be changed to meet requirement of different strengths ; 5)There is a good plasticity . The residual strength of concreting body may account for about 50% of the peak value strength if the uniaxial compressive strain reaches to 15% ; 6) As a result of the big water cement ratio , little dosage of the unit volume and low price , the cost for using high-moisture quick-concreting material to reinforce the foundation pit wall and ground base and to fill the steel tube is lower. In this study , the mechanical property and concreting mechanism of high-moisture quick-concreting material to reinforce the loose coal body are studied and analysed by the field test and laboratory test . The test results indicated that there is a notable effect to consolidate roadway , foundation pit wall and ground base by grouting of high-moisture quick-concreting material . Finally , the engineering example of grouting by using the high-moisture quick-concreting material is presented.
Abstract: According to the theory of dense packing of particle, the theoretical particle size distribution of raw materials of RPC (Reactive Powder Concrete) was calculated. On the basis, the ratio of raw materials with different range of particle sizes of the RPC was determined by mechanical experiments. According to the determined ratio, a new type RPC was prepared by using flying ash and slag to replace part of cements and quartz flour, respectively. The workability, mechanical properties of the new RPC with different mix proportion and its shrinkage, cured at the normal temperature and 60°C, respectively, were studied. The results show that when water-binder ratio is 0.23, fly ash replaces 30% cements, slag replaces 50% quartz flour and superfine steel fibers percentage in volume is 2%, the compressive and flexural strength of prepared RPC are 160.1MPa and 25.3MPa, respectively, and after 3days heat curing (60°C), the dry shrinkage of it in 28days age reaches 299um/m. In addition, the fluidity of the new RPC is 258mm and meets requirements of workability of the pump concrete.
Abstract: The paper discussed the mix principle, performance target and the technical demands for the underground high performance concrete combined the Shenzhen side-connection item of Shenzhen-Hong Kong West Channel project. The better mix proportion of underground high performance concrete is brought forward, which can direct the construct units and the concrete servers to produce the high quality concrete that fit for the underground project.
Abstract: Guangzhou Xita Project uses a special exterior frame which consists of huge inclining concrete-filled columns. To ensure the engineering quality and select the suitable concrete-filled steel tube column structure, two concrete-filled steel tube column structure experiments have been carried out. To ensure the quality of the concrete-filled steel tube column structure experiment, the C100, C90 and C70 high performance concrete experimental research have been done specially, and the result of the experimental researches has been used in concrete-filled steel tube column structure sample successfully. The raw materials, mixture proportions and performance of the high performance concrete were discussed in this paper.
Abstract: This paper reports the tensile properties of a new class of engineered cementitious composite with characteristic of low drying shrinkage. Experimental results show that drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, while the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain at 28 days is only 10910-6 to 24210-6 for low shrinkage ECCs. For traditional ECC, the shrinkage strain at 28 days is nearly 120010-6. The average tensile strain capacity after 28 days curing is 2.5% of the low shrinkage ECC with tensile strength of 4-5MPa.