Quantity of cement required is based on what strength is required in combination of different aggregate and what type of workability is expected of the concrete. So any combination can be used similar to Ordinary Portland Cement missed with different pozzolona materials like flyash, metacaolin, silicafumes etc

It is perfectly possible to use two different types of cement ( as binder) in the same concrete mix; e.g. a portland cement CEM I in combination with a blast furnace slag cement CEM III/A.

I'm not familiar with the use of cement as a filler ("sealing the graining structure"). That could possibly be used in types of ultra high performance concrete.

you can do that, it will be binary or ternary system

but the kinematic hydration will be very complicated

Using two different cements in the same concrete mixture, while technically feasible, should be avoided. Why?

(1) The blend ratio needs be consistently maintained throughout the construction project.

(2) Lot-to-lot shipments of the same cement have have slight changes in reactivity. Now consider this situation with two cements. The cement reactivity problem, especially with use of chemical admixtures, becomes compounded.

(3) Concrete producer must now inventory two cements, which can be a problem if plant is located in an urban area and space is limited.

(4) Since there is such a wide range of cements available, hard to understand why two cements need to be used.

It is perfectly possible to use two types of cement simultaneously in one recipe for concrete composition provided that the rate of hydration (such as rapid hardening and low heat cement) and setting time is not in conflict.

yes it is possible and our need at that particular situation and my opinion try to mix coloured cement with other cements to get desired colour and you may try to mix different grades and watch

If want to achieve a specific color for the concrete, use a coloring admixture.

Two types of cements can be used simultaneously, especially when higher strengths are required. However, special care should be given on setting time, workability, and heat of hydration.

Yes, you can definitely use unless not recommended by the manufacturer. However, you need to match your requirements and capacities of the cements.

Yes, we can add two or more different types of cement (whether it is supplementary cementitious materials) in a single composite (binary, ternary and quaternary), and we need to add these materials selectively for the properties we required as mentioned by Dhanushka Kobbekaduwa. When these SCM's are finer than the base cement in the composite, they also act as filler materials and improve both strength and durability properties.

Yes we can , most of the concrete works can use two type of cement

Although it should be avoided for several reasons, it is actually possible to use two types of cement, substantially for reduced concrete volumes. However, it is important to compile the characteristics, in order to monitor relevant parameters such as: content and type of addition, fineness, setting time, heat of hydration etc.

Why using two types together? We have different types for specific purpose and use

Yes Pozzolans or scm can be added to cement to achieve improve strength and to increase durability.

Yes, most especially when working on water retaining structure, one works as a binder and the other a sealant, forinstance, OPC used together with water proof cement as an additive

Yes indeed, depending on the propeties of evry kind of cement, and the goal of your work.

maybe can but it is not recommended, it is better to use additives instead of using two different type of cement.