Strength Characteristics Of Hardened Cement Paste At Low Water Binder Ratio

High-strength and high-performance concretes are mostly formulated with low water-to-binder ratio.In the case of low water-to-binder ratio,the research on the strength change of cement paste mixed with fly ash and other admixtures is not perfect.This paper aims to explore the general law of strength change of cement paste with low water-to-binder ratio,and provide a theoretical basis for the preparation of cement-based composite materials.In this paper,the cement paste with a water-cement ratio of 0.26 to 0.46 is first used to measure the compressive strength and chemically bound water of the cement slurry.Explain the reason for the strength change from the perspective of degree;then,choose four water-binder ratios of 0.42,0.38,0.34 and 0.30,and mix different amounts of fly ash to replace cement while keeping the water-binder ratio unchanged,and study The effect of fly ash content on strength,and CT tomography technology was used to further study the cause of strength change.Research indicates:(1)The strength development of cement paste with low water-cement ratio depends on the normal hydration of the cement and the degree of hydration.When the cement can be fully hydrated,the strength increases with the decrease of the water-cement ratio;when the cement cannot be fully hydrated,its strength development does not increase with the decrease of the water-cement ratio;when the outside can provide moisture,the As the water-cement ratio decreases,the strength continues to increase;when the outside world cannot provide water,the strength will not develop further,and the unhydrated cement can only serve as a filling effect.(2)For the low cement paste mixed with fly ash,the water-cement ratio is still the main factor affecting the strength of the hardened cement paste.When the water ash is relatively high,the cement can be fully hydrated,and the compressive strength decreases with the increase of the fly ash content at the same water-to-binder ratio.The early hydration strength is mainly caused by the cement hydration.The activity is only stimulated and has a certain contribution to the strength;when the water-cement ratio is low to a certain degree,the cement in the slurry cannot be fully hydrated,and the compressive strength of the slurry is determined by the water-cement ratio that can be hydrated,so the same water The compressive strength under the glue ratio did not change significantly with the increase of fly ash content,because the unhydratedcement and fly ash were only used as fillers.(3)The results of chemical combined water determination and CT tomography show that the reason for the strength change of cement paste and fly ash cement paste depends on the degree of hydration of cement and fly ash in the cement paste.