3.1.2 The processes of structure formation in the ITZ "alkali-activated cement-natural sustainable aggregate"

The structure formation processes in the ITZ of the concretes made using real aggregates were studied on beam specimens (4 4 16 cm), which were subjected to continuous steam curing for 360 days at temperatures of 38 and 65 3°С.

Micro photos of the ITZs in different concretes made from various cements and aggregates are shown in Figures 2–7.

Thin plates for the examination with the help of an electron microscope were cut directly from the beam specimens (4 4 16 cm).

As it follows from Figure 2, significant signs of corrosion in the concretes from traditional (ordinary) Portland cement with crushed basalt rock are seen, the lowest corrosion being in the case with the metakaolin additive (Figure 2b).

The signs of corrosion in the concretes from traditional (ordinary) Portland cement with crushed perlite rock and expanded perlite are, respectively, lower in all cases than those in the case of the crushed basalt rock (Figure 2e, f). This can be attributed to the presence in perlite (both expanded and not expanded) of active Al2O3 with the glassy phase, which amounts to 90–97%, whereas a quantity of a glassy phase in the crushed basalt rock is only 8–12%. Thus, though a total quantity of Al2O3 in the crushed basalt rock and perlite is almost close (14.0% and 12.5– 13.2%, respectively) (Table 3), active Al2O3 is contained in the perlite in much higher amounts. Moreover, in compliance with [4, 41], it may be allowed that a part of the products of corrosion depose in a pore space of the perlite, thus eliminating a

SEM images of the ITZ concrete—"Portland cement-soluble silicate-agregate" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement paste; 2, ITZ; 3, aggregate. Curing conditions—90 days

The Influence of Interfacial Transition Zone on Strength of Alkali-Activated Concrete

DOI: http://dx.doi.org/10.5772/intechopen.90929

The compositions of the alkali-activated Portland cement with high-modulus soluble silicate as alkaline activator are given in Figure 3. Metakaolin was used as a modifying additive. Analysis of the micro photos showed that the hydration reaction products are mostly observed in the composition with the crushed basalt rock without additive (Figure 3a). The additive of metakaolin improves the picture. The

In the compositions with the crushed perlite rock and expanded perlite using alkali-activated Portland cement with soluble silicate some signs of corrosion are present in the ITZ in the additive-free compositions and are practically absent in the

little bit their deleterious action.

Figure 3.

11

of steam curing at t = 65°С.

ITZ became sharp and clear (Figure 3b).

compositions with the metakaolin additive (Figure 3c–f).

#### Figure 2.

SEM images of the ITZ concrete—"Portland cement-water-agregate" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement stone; 2, ITZ; 3, aggregate. Curing conditions—90 days of steam curing at t = 65°С.

## The Influence of Interfacial Transition Zone on Strength of Alkali-Activated Concrete DOI: http://dx.doi.org/10.5772/intechopen.90929

#### Figure 3.

The alkali-activated cement concrete with the artificial granular aggregate had a dense structure and was characteristic of high bond strength of the granules with the cement paste. A dense structure of the alkali-activated cement concrete under study, as well as the composition of the hydration products, determine high physical-mechanical properties of such concrete, which, in their turn, determine

3.1.2 The processes of structure formation in the ITZ "alkali-activated cement-natural

The structure formation processes in the ITZ of the concretes made using real aggregates were studied on beam specimens (4 4 16 cm), which were subjected to continuous steam curing for 360 days at temperatures of 38 and 65 3°С.

Micro photos of the ITZs in different concretes made from various cements and

Thin plates for the examination with the help of an electron microscope were cut

As it follows from Figure 2, significant signs of corrosion in the concretes from traditional (ordinary) Portland cement with crushed basalt rock are seen, the lowest

SEM images of the ITZ concrete—"Portland cement-water-agregate" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement stone; 2, ITZ; 3, aggregate. Curing conditions—90 days of steam

corrosion being in the case with the metakaolin additive (Figure 2b).

performance properties.

Compressive Strength of Concrete

Figure 2.

10

curing at t = 65°С.

sustainable aggregate"

aggregates are shown in Figures 2–7.

directly from the beam specimens (4 4 16 cm).

SEM images of the ITZ concrete—"Portland cement-soluble silicate-agregate" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement paste; 2, ITZ; 3, aggregate. Curing conditions—90 days of steam curing at t = 65°С.

The signs of corrosion in the concretes from traditional (ordinary) Portland cement with crushed perlite rock and expanded perlite are, respectively, lower in all cases than those in the case of the crushed basalt rock (Figure 2e, f). This can be attributed to the presence in perlite (both expanded and not expanded) of active Al2O3 with the glassy phase, which amounts to 90–97%, whereas a quantity of a glassy phase in the crushed basalt rock is only 8–12%. Thus, though a total quantity of Al2O3 in the crushed basalt rock and perlite is almost close (14.0% and 12.5– 13.2%, respectively) (Table 3), active Al2O3 is contained in the perlite in much higher amounts. Moreover, in compliance with [4, 41], it may be allowed that a part of the products of corrosion depose in a pore space of the perlite, thus eliminating a little bit their deleterious action.

The compositions of the alkali-activated Portland cement with high-modulus soluble silicate as alkaline activator are given in Figure 3. Metakaolin was used as a modifying additive. Analysis of the micro photos showed that the hydration reaction products are mostly observed in the composition with the crushed basalt rock without additive (Figure 3a). The additive of metakaolin improves the picture. The ITZ became sharp and clear (Figure 3b).

In the compositions with the crushed perlite rock and expanded perlite using alkali-activated Portland cement with soluble silicate some signs of corrosion are present in the ITZ in the additive-free compositions and are practically absent in the compositions with the metakaolin additive (Figure 3c–f).

#### Figure 4.

SEM images of the ITZ concrete—"GBFS-alkaline component-basalt rock" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement paste; 2, ITZ; 3, aggregate. Curing conditions—90 days of steam curing at t = 65°С.

The nature of flow of corrosion processes in the alkali-activated slag compositions with high-modulus soluble silicate is mostly similar to the compositions using alkali-activated Portland cement (Figure 4a, b).

Thus, taking into account micro photos of the cement paste/alkali-susceptible

SEM images of the ITZ concrete—"Portland cement-water-crushed basalt rock" (а, c, e) without metakaolin additive; (b, d, f) with metakaolin additive; 1, cement paste; 2, ITZ; 3, aggregate. Curing conditions at t = 20,

The Influence of Interfacial Transition Zone on Strength of Alkali-Activated Concrete

DOI: http://dx.doi.org/10.5772/intechopen.90929

depending upon a cement type and kind of aggregate, showed clear presence of

• At t = 38°С at an age of 90 days in additive-free compositions, except for those with perlite, in most cases there are fixed disturbance of sharpness and integrity of the ITZ. The addition of the metakaolin to the traditional

(ordinary) Portland cement and alkali-activated cements reduces a quantity of

At the temperature t = 65°С at an age of 90 days, disturbance of the ITZ is much more clearly expressed than that at t = 38°С, chiefly, in the concretes from cement without additives. Exceptions are the concretes with perlite, where the products of corrosion, probably, could distribute in a pore space of the aggregate and, above all, perlites are represented, chiefly, by a glassy phase with rather high contents of active alumina, which can bind rather effectively free alkalis, reducing, in this way, a risk of active silica-aggregate reaction. The metakaolin additive in all cases influences positively on reducing deposits of the products of corrosion in the ITZ.

• At t = 20°С at an age of 90 days, all concrete specimens under study, not

aggregate ITZ, the following conclusions can be drawn:

destructive processes in the ITZ.

38, 65°С 90 days after steam curing.

Figure 5.

13

undesirable reaction products in the ITZ.

Reducing of silicate modulus of soluble silicate down to Мs = 1 (sodium metasilicate) and the use of solution of sodium carbonate (Figure 4a, e) leads to decreasing of corrosion products in the ITZ in the additive-free compositions compared to compositions using high-modulus soluble silicate (Figure 4a). The metakaolin additive influenced positively on slowing of corrosion processes in the ITZ (Figure 4b, d, f).

The influence of the curing conditions of the specimens on the development of the corrosion processes is shown in Figures 5 and 6, where results of observation of compositions using traditional (ordinary) and alkali-activated Portland cement with crushed basalt rock are given, which cured for 90 days at t = 20, 38, and 65°С and RH =100%.

It is shown that in this period at t = 20°С, there are practically no any signs of corrosion in the ITZ "cement stone-aggregate" in both compositions, both with and without the metakaolin additive, being fixed (Figure 5a, b). ITZ в additive-free compositions at t = 38°С (Figures 5c, 6c) are a little bit less expressed and even less at t = 65°С (Figures 5e, 6e). The presence of the kaolin makes the ITZ more clearly expressed (Figures 5d, f and 6d, f).

The study on microhardness of the ITZ in the concretes with crushed basalt rock showed that the metakaolin additive within the alkali-activated cements intensifies constructive corrosion (Figure 7).
