Study On Early Performance And Application Of Geopolymer Cement

Geopolymer cement can be considered as a new class of inorganic cementitious materials,which has advantages such as early strength and fast hardening,and there is still great room for improvement.However,compared with ordinary portland cement,the early setting and hardening mechanism and parameter design of geopolymer cement are still immature and lack of systematic research.According to the different preparation process parameters,the setting and hardening process is difficult to control and the early strength varies greatly during preparation at room temperature.At the same time,the lack of fracture toughness and easy cracking of the early hardened geopolymer cement has greatly limited its development and application.In this paper,metakaolin was used as the raw material of silicoaluminum to prepare geopolymer cement material.The effects of alkali equivalent,n（SiO₂/Al₂O₃）and water-binder ratio on the early rheological properties,setting and hardening properties and mechanical properties of geopolymer cement were systematically studied.A geopolymer cement material product with controllable setting and hardening process,good workability,and high early strength and fracture toughness was attianed by the optimization and adjustment of the mix ratio parameters and the composite modification of mortar.The results of the main research work were as follows:（1）The range and variance analysis of orthogonal test showed that the interaction between the basic factors cannot be ignored.Considering the reasonable mix ratio parameters was of great significance to obtain better rheological parameters of geopolymer cement pastes.At the same time,combined with the analysis of the influencing factors of the rheological parameters under time-varying,it was initially determined that the selection direction of the mix ratio parameters was high alkali equivalent,low n（SiO₂/Al₂O₃）and moderate water-binder ratio.（2）The setting and hardening properties of geopolymer cement pastes varied with different proportion parameters.The initial setting time ranged from 250 to445min,the final setting time ranged from 300 to 525min,the 1d flexural strength was between 3.6 and 5.0MPa and the 1d compressive strength was between 23.6 and43.8MPa.Reasonable selection of mixing parameters had important significance for adjusting the setting time and early hardening strength of paste.The analysis of the variation of ultrasonic velocity showed that the ultrasonic velocity test can be considered as an effective method for monitoring the early setting and hardening of geopolymer cement paste.（3）Taking alkali equivalent,n（SiO₂/Al₂O₃）and water-binder ratio as variables,the second-order response surface optimization models of 1d flexural strength and compressive strength of geopolymer cement paste were established by response surface method experimental design.And the effect of basic factors on the1d flexural strength and compressive strength were analyzed.In the case of comprehensively obtaining better 1d flexural strength and compressive strength of the geopolymer cement paste,the proportion parameters can be reasonably selected according to the actual situation.Alkali equivalent was 16%～17.5%,n（SiO₂/Al₂O₃）was 2.6～2.74,and water-binder ratio was 0.48～0.51.（4）When the alkali equivalent is constant,the strength of geopolymer cement mortar with lower n（SiO₂/Al₂O₃）developed faster with age,but the strength was relatively low.Additionally,higher n（SiO₂/Al₂O₃）can guarantee the development of compressive strength in early and late stage,but it can inhibit the development of early flexural strength.Adding boron oxide（B₂O₃）can effectively improve the early strength and toughness of geopolymer cement mortar.When the B₂O₃content was 1%,the flexural strength at 12h and 24h increased by 90%and 32.4%,and the compressive strength at 12h and 24h increased by 140%and 19.4%,respectively,compared to the blank group.At the same time,it can better maintain fluidity and the gel time is moderate.Therefore,adding 1%B₂O₃can effectively make up for the deficiency of sodium silicate and improved the early performance of geopolymer cement mortar.This provided a certain reference for the application of maintenance and reinforcement materials and 3D printed building materials.