*2.2. Concrete Composition and Properties' Test Methods*

Based on Portland multicomponent cements CEM II/C-M and multicomponent cements CEM VI, concrete mixes with the following composition, given in Table 4, were designed.


**Table 4.** Mix proportions of concrete mixtures.

Two types of concrete were prepared—type I containing 300 kg of cement in 1 m3 of concrete mix at a ratio w/c = 0.60 and type II, containing 340 kg of cement in 1 m<sup>3</sup> of concrete mix at a ratio w/c = 0.35. Natural gravel aggregate with a fraction up to 16 mm and sand 0–2 mm as fine aggregate were used in the concrete mixture. A superplasticizer (PCE) based on polycarboxylate ether was used in the composition of concrete with reduced water–cement ratio (w/c = 0.35).

The properties of concrete mixtures and hardened concrete were tested according to the methodology included in the standards, which are presented in Table 5.


**Table 5.** Procedures used to determine the properties of the concrete mixture and hardened concrete.

#### **3. Results and Discussion**

#### *3.1. Properties of CEM II*/*C-M and CEM VI Cements*

The properties of the cements are presented in Table 6. The density of the cements was lowest for those containing siliceous fly ash (Table 6). The specific surface area of ternary cements ranged from 4350 to 4750 cm2/g. Cement slurries with ternary cements did not show volume changes due to swelling (Table 6). The setting time of cements and other properties are closely related to their composition and the amount of mineral additives introduced (Table 6).


**Table 6.** Physical and mechanical properties of cements.

In most cases, the highest increases in strength of standard cement mortars can be observed between 7 and 28 days of curing (Figure 4). During this period, the strength increases quite significantly in the case of cements containing blast furnace slag (the slag is hydraulically active and begins to react with water a long time before the ash pozzolanic reaction begins). The highest strength increase in this period is observed in comparative slag cement C(55S) on Figure 4. Partial replacement of blast furnace slag, both with limestone LL and fly ash V, slightly reduces the strength increase between the 7th and 28th days of hardening. Omitting the small influence of limestone on the increase in early strength, it is a rather chemically inert component in the cement system, and therefore its addition to slag causes a decrease in later strength. Replacement of slag with fly ash also slows down the dynamics of strength growth. This can be explained by the fact that the pozzolanic reaction of fly ash begins intensify only after 28 days of curing (when the amount of Ca(OH)2 from cement hydration increases). The final strength (after 360 days) of multicomponent cement C(30S-10LL) is similar to that of comparative cement C(55S), while in the case of cement C(35S-20V) there is a slight decrease in the final strength, compared to cement C(55S) (Figure 4). This decrease can be explained by the lower activity of fly ash in relation to ground granulated blast furnace slag, which is a component with latent hydraulic activity (with a CaO content of approximately 40–44% and after heat treatment in a blast furnace under conditions similar to those in a rotary kiln for Portland clinker production).

The partial replacement of fly ash by limestone C(30V-10LL) in cement composition, allows a cement to be made with higher early strength (after 2 days) and higher final strength than the reference cements C(40V) and C(40LL). The higher early strength in the presence of limestone may result from the caulking effect as well as the small amount of carboaluminates formed. On the basis

of the results obtained, it can also be observed that the addition of LL limestone decreases the strength of cement mortars to a greater extent in combination with siliceous fly ash (C(30V-10LL)), while the use of limestone (even up to 20%) in combination with ground granulated blast furnace slag (cements: C(30S-10LL), C(35S-20LL)) gives a much smaller decrease, slightly less than in the case of using the S slag composition with fly ash V-cement C(35S-20V).
