| In order to explore the early hydration characteristics of the low-heat Portland cement(hereinafter referred to as low-heat cement)-based cementitious system,the electrical resistivity tester and the electroacoustic Zeta potential analyzer were used to measure the water-binder ratio and different fly ash content.The resistivity and Zeta potential of low-heat cement and ordinary Portland cement(hereinafter referred to as ordinary silica cement)were tested for hydration,and combined with the ion concentration of the slurry pore solution and the volume of each phase of cement hydration simulated by GEMS,the resistivity and Zeta potential were compared and analyzed.The change rule of the solid phase volume fraction characterized by the Zeta potential test,the results show that:(1)Resistivity and Zeta potential methods can independently characterize the early hydration process of low-heat cement,but the electrical resistivity method focuses on the characterization of macroscopic properties,while the Zeta potential method focuses on the characterization of microscopic properties.Therefore,the two methods combination each other can better characterize the early hydration characteristics of low-heat cement.(2)The water-binder ratio has a significant influence on the early hydration characteristics of low-heat cement.In the rapid dissolution stage,the higher the water-binder ratio,the slower the rate of formation of ettringite(AFt)and hydrated calcium silicate(CSH)on the surface of cement hydration particles;in the setting period of the acceleration stage,the time for the gypsum to be consumed with the increase of the water-to-binder ratio,it is prolonged correspondingly,indicating that the higher the water-to-binder ratio,the later the transition from AFt to the monosulfide hydrated calcium sulfoaluminate(AFm)phase equilibrium is;in the deceleration period,the more the water-to-binder ratio is larger the K_mvalue of the slurry,the smaller the value,indicating that the increase in the water-binder ratio will reduce the number of cement particles participating in the reaction sealing per unit volume and reduce the structure compaction rate.(3)By comparing the early hydration process of ordinary Portland cement with different water-binder ratios,it is found that under the same water-binder ratio,the dissolution rate of low-heat cement is faster in the rapid dissolution stage,but the ion concentration in the slurry is still low;In the setting period of the acceleration stage,the time for the phase equilibrium conversion of AFt to AFm in the low-heat cement paste is delayed and the conversion process lasts for a short time;in the deceleration period,the K_mvalue of the low-heat cement paste is slightly lower,indicating that the low-heat cement paste There are slightly fewer cement particles involved in the reaction sealing per unit volume in the body,and the pore shortening rate is slightly slower.(4)The content of fly ash has a significant effect on the early hydration characteristics of low-heat cement.In the rapid dissolution stage,the more fly ash content of the cement paste,the later the formation of AFt and CSH in the body;in the induction period,the fly ash content of more than 30%of the cement paste,the content of AFt and CSH generated on the surface of the particles is reduced,and the end of the induction period is greatly affected by the osmotic pressure;during the coagulation period of the acceleration stage,the conversion of AFt to AFm phase equilibrium in the slurry with fly ash content greater than 30%is very weak,and under this condition,it is very weak.The hydration has not undergone the hardening acceleration stage,but directly enters the deceleration period,indicating that after the low-heat cement hydration reaches the final setting,the content of active mineral components involved in the reaction in the cement stone is lower;during the deceleration period of the hydration,the more fly ash content more cement pastes have a smaller K_mvalue,indicating that the more fly ash content of the paste enters the deceleration period,the slower the hydration rate and the lower the compactness of the cement stone structure. |
