Preparation,Properties And Mechanism Of Cementitious Materials With Basalt

With the acceleration of infrastructure construction, new urbanization and in-depth promotion of the "the Belt and Road" in China, the increasing need for supplementary cementitious material in cement and concrete is prominent in southwestern China and related Southeast Asian countries. Basalt is mainly used for preparation of building stone and basalt fiber,both of which require strict screening of raw materials, resulting in a large number of tailings and waste. Tailings and waste may cause environmental pollution as well as waste of resources without reasonable utilization. At present, there are some practices and examples for the research and application of ground basalt as cement admixture. However, the composition, structure,properties and reaction mechanism of basalt is not well studied. Thus it is of great significance to investigate basalt powder as supplementary cementitious materials and its effect on hydration.Closely abounding the preparation of the basalt-cement composite and its cementing mechanism in this paper, aiming at the problem of basalt hard to grind, the preparation technology of the basalt-cement composite powder was researched, the essence cause of the high power consumption in the basalt grinding has been clear explained, the process of the grinding refinement of the basalt was also analyzed, and the grinding agent of basalt has been developed.The mechanical properties and durability of the cement mortar and concrete using the basalt-cement system were studied, and the solution of adaptability problem between the system and the water reducing agent was provided. The composite Portland cement and ordinary Portland cement products in accordance with the national standard were prepared, and the key preparation techniques of the basalt-cement system has been mastered and successfully transformed. The influence factors and the differences of the volcanic activity of the basalt compared with quartz powder, fly ash and metakaolin were revealed. The main conclusions and results are as follows:Grinding characteristics of basalt and development of grinding aid. The basalt-cement gel powder was prepared by separate grinding and hybrid grinding, using ball mill, planetary mill,agitating mill and so on. The influence laws of the powder fineness and particle size distribution by the different grinding process have been analyzed. Bond work index as the main reference index of power consumption in heat treatment basalt grinding was carried out. Combining with lithofacies analysis, the influence of the mineral composition and microstructure on the interaction mechanism of grinding process was explained, and the grinding process of basalt was analyzed. Furthermore, the effects of different organic and functional groups on the basalt grinding were studied. The results show that: (1) Grinding characteristics. The basalt could reach"grinding equilibrium" state by using the standard laboratory ball mill (feeding maximum particle size 4.75mm) for 1h, and the basalt has a certain "micro-grinding agent" effect because of its high hardness. (2) Grinding process. Basalt shows poor abrasiveness, and the particle size presents bimodal characteristics instead of normal distribution. The left peak was rapid release and refinement of vitreous in basaltic mineral structure,and the right peak was the main Contains feldspar, pyroxene-like minerals due to higher hardness. (3)Development of grinding aids. The results show that polyols and alkanolamines present significant grinding effect on basalt. The grinding efficiency decreased in the order: polyols (BS)>triethanolamine (T)> propylene glycol(BE) ? ethylene glycol (YE).Basic properties and industrial production practice of basalt-cement system. Basic physical properties of basalt-cement system under different grinding methods of preparation of the basalt powder,the fineness and dosage of basalt were studied. The adaptability between basalt-cement system and water reducing agent was studied by the Marsh cone, fluidity and free liquid phase method. The primary cause of instability was made clear by testing Zeta potential of basalt powder, clinker and fly ash, and appropriate solutions was put forward. The results show that: (1) Physical and mechanical properties. When the content of basalt powder is less than 15%,it can promote the early hydration of cement clinker and show better pozzolanic reactivity in the long term. (2) The adaptability of basalt-cement system and water reducing agent. When the content of basalt is less than 8% and the specific surface area of basalt-cement system powders is about 370m2/kg, the effect of basalt powder on the compatibility of the admixture was negligible.(3) Industrial production practice. When admixture (basalt: slag = 1:1) is fixed at 16%, with the increase of specific surface area of powders, the 3d strength is increased significantly. When the specific surface area is less than 370 m2/kg, the workability of concrete of C30 is good, otherwise the performance may be reduced. (4) Preliminary analysis of the durability of concrete prepared by basalt-cement. The sulfate attack resistance and carbonation resistance of concrete admixed with basalt or manufactured sand (basalt) are better than fly ash or slag. And it shows a complementation effect when admixing basalt with fly ash or slag.Microscopic tests of basalt-cement system and hydration process analysis. Using hydration hot analysis, XRD, TG-DSC, SEM, and ICP, the hydration heat, hydration radiated rate,hydration product type and relative content, morphology of the hydration product, and the law of silicon and aluminum ion dissolved out in strong alkaline environment were analyzed,compared with quartz powder, fly ash, and partial kaolin. Combining the characteristics of mineral composition of basalt and the microstructure of microcrystalline, the pozzolanic reaction process and mechanism of hydration between cement clinker and basalt was discussed. The results show that: The mechanical properties of basalt-cement paste present a good correlation with the results of mortar specific strength analysis. The active index of basalt is low because of the active elements content of silicon and aluminum is relatively few in basalt minerals. At early age, the metal cations exchange with H+ because of voids in the pore-like structure of basalt framework.The exchange rate can be accelerated in the overbased Portland cement hydration system and the surface structure begins to destroy and disintegrate, and this promotes the hydration of cement clinker. In later stage, the surface of the basalt powder particles would be further decomposed slowly, and small amounts of hydration products on the surface are beneficial to the long-term mechanical properties of concrete.