Study On The Preparation And Properties Of Alkali-Blast Furnace Slag-CFBC Bottom Ash Composite Cementitious Materials

Alkali activated composite cementitious materials is one of the popular non-metallic inorganic materials to study in recent years. This material has good mechanical properties and a wide source of materials, and it has broad prospects for development. Blast furnace slag is the residue of emissions in the steel smelting process, rich in CaO, and it has the potential of Self-hardening. The object of this thesis is Nanjing Meishan Iron and Steel Plant blast furnace slag. In this thesis, using adding grinding aids grinding to optimize their quality. On the basis of comprehensive analysis of its physical and chemical properties, using blast furnace slag powder and CFBC bottom ash powder as raw materials to prepare alkali-blast furnace slag-the CFBC bottom ash composite cementitious materials. This thesis studied the particle size distribution characteristics of blast furnace slag powder and the effect of grinding aids. Research on Alkali-blast furnace slag-the CFBC bottom ash composite binder macro-mechanical properties of the mineral phase composition and microstructure by the manners of micro-pressure test, X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrometer(FTIR).Firstly, the physical and chemical properties of the Nanjing Mei Shan Iron and Steel plant blast furnace slag is analysised. The results show that:the blast furnace slag are rich in CaO, total to36.84%, followed by SiO2and A12O3, the sum is50.07%. There is no quartz, mullite stone which is always found in the fly ash and other mineral phases in the blast furnace slag samples, but there are a large number of amorphous glassy substance. It can be seen from the IR spectrum, characteristic absorption peak is mainly caused by the glassy-related groups.Based on grinding experiments, this thesis analyzed the45μm sieve margin of slag powder after grinding, with characteristics specific surface area (Bertrand) and granularity characteristics. The results show that:the best slag grinding time is about40min. In this thesis, the effect of grinding aids were evaluated, the analysis results show that the promoting effect of grinding aids on grinding mainly in the first30minutes. When grinding20min, particles less than45μm of adding grinding aids slag grinding samples were significantly more than the blank. Optimization of45μm sieve margin and the surface area (Bertrand) is respectively24%and15%. At the same time, the compressive strength of cement mortar which obtained by using blast furnace slag powder is also improved.In the thesis, the physical and chemical properties of CFBC bottom ash powder was analyzed. CFBC bottom ash contains more SiO2and Al2O3, total to88%. Based on blast furnace slag powder and CFBC bottom ash powder, in the thesis, using cast molding technology to prepare Alkali-blast furnace slag-the CFBC bottom ash composite cementitious materials with liquid to solid ratio (0.5:1). The compressive strength of the samples which inspired by different modulus of water glass are1.5Modulus>1.2Modulus>2.0Modulus. The compressive strength of the samples which obtained by1.5Modulus water glass and in28days of conservation reached190MPa. Macroscopic mechanical properties of alkali-blast furnace slag-the CFBC bottom ash composite cementitious material excited by different concentrations is10M>7.5M>2.5M. The mechanical properties of the materials sprepared by KOH solution is superior to NaOH solution. The sample of10MKOH obtain the best mechanical properties. Its28-day compressive strength reached87.55MPa.Alkali-blast furnace slag-the CFBC bottom ash composite binder hydration products were also analyzed in this thesis. The XRD results showed that:there is a certain amount of calcium silicate hydrate crystals (CSH) besides quartz crystal minerals in the crystalline minerals of hydration products. This shows that the same or similar material in portland cement exist in the composite cementitious materials hydration products. SEM results show that the main hydration product is an amorphous aluminosilicate gel with a certain amount of CSH interspersed. The new generation of crystalline mineral phase is found in the local area of the microscopic structure, combined with the XRD results, these newly generated crystals of mineral content is less so it did not appear in the XRD.