Portland Cement Fly ash portland cement refers to the combination of Portland cement clinker and fly ash, mixed with an appropriate amount of gypsum and then ground, codenamed P.F. Any hydraulic cementitious material made of Portland cement clinker, fly ash and an appropriate amount of gypsum ground is called fly ash Portland cement, codenamed P.F. The amount of fly ash added to the cement is 20%~40% by mass, and its strength grade and strength requirements at each age are the same as those of slag Portland cement. Raw material It is made of Portland cement clinker and fly ash, mixed with an appropriate amount of gypsum and then ground. Code P.F Any hydraulic cementitious material made of Portland cement clinker, fly ash and an appropriate amount of gypsum ground is called fly ash Portland cement, codenamed P.F. The amount of fly ash added to the cement is 20% to 40% by mass. It is allowed to participate in the granulated blast furnace slag not exceeding 1/3 of the total amount of mixed materials. At this time, the total amount of mixed materials can reach 50%, but the amount of fly ash should not be less than 20% or more than 40%. Features The structure of fly ash cement is relatively dense, the internal specific surface area is small, and the adsorption capacity for water is much smaller, and the water demand for cement hydration is small, so the dry shrinkage of fly ash cement is small, and the crack resistance is also low. good. In addition, similar to the general cement mixed with active admixtures, it has low hydration heat and strong corrosion resistance. Performance The unique properties of fly ash Portland cement are as follows: (1) The early strength is low, and the late strength increase rate is large: the early strength of fly ash cement is low, and the early strength decreases significantly with the increase of fly ash content. Because the vitreous body in fly ash is extremely stable, the fly ash particles are eroded and destroyed very slowly by Ca(OH)2 during the hydration process of fly ash cement, so the strength development of fly ash cement is mainly reflected in the later stage. , its late strength increase rate is large, and it can even exceed the late strength of the corresponding Portland cement. (2) Good workability and small dry shrinkage: Because most of the fly ash particles are closed and solid spherical, and the internal surface area and single-molecule adsorption water are small, the fly ash cement has good workability and small dry shrinkage. , has the characteristics of high tensile strength and good crack resistance. This is a clear advantage of fly ash cement. (3) Good corrosion resistance: fly ash cement has high corrosion resistance to fresh water and sulfate. Due to the combination of active SiO2 in fly ash and Ca(OH)2, calcium silicate hydrate is generated when balanced. The required limit concentration (i.e. liquid phase alkalinity) is much lower than that required for the equilibrium of calcium silicate hydrate in ordinary Portland cement, so the leaching rate in fresh water is significantly reduced, thereby improving the cement resistance. Fresh water corrosion ability and resistance to sulfate damage. (4) Low heat of hydration: The hydration speed of fly ash cement is slow and the heat of hydration is low, especially when the amount of fly ash added is large, the reduction of the heat of hydration is very obvious. Portland cement All Portland cement clinker mainly composed of calcium silicate, limestone or granulated blast furnace slag with less than 5%, and hydraulic cementitious material made of finely ground gypsum are collectively referred to as Portland cement. Internationally collectively known as Portland Cement. Classification Portland cement is divided into two types, the type I Portland cement without mixed material is called Portland cement, code P·I; the mixed material with limestone or granulated blast furnace slag not exceeding 5% of the cement mass is called II Type Portland cement, code P·Ⅱ. Mineral composition The main mineral composition of Portland cement is: tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium ferric aluminate. Tricalcium silicate determines the strength of Portland cement within four weeks; dicalcium silicate only exerts its strength after four weeks, and reaches the strength of tricalcium silicate for four weeks in about a year; the strength of tricalcium aluminate It exerts faster, but the strength is low, and it plays a certain role in the strength of Portland cement within 1 to 3 days or a little longer; The strength contribution of acid salt cement is small.