Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

7

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

about synthesis of sodium and mixed sodium- calcium aluminosilicate hydrates, what is 

confirmed by the analysis of the X-ray patterns (Fig. 3). The lines corresponding to 

Na

2

O Al

2

O

3

4SiO

2

2H

2

O (d = 0.560; 0.343; 0.293; 0.252; 0.174 nm), 

2Na

2

O 2

5Al

2

O

3

10SiO

2

10H

2

O (d = 0.654; 0.467; 0.353; 0.283; 0.270 nm) are clearly 

identified in Curve 5. The expansion of the interfacial transition zone due to formation of the 

above mentioned hydration products is clearly seen in the microphotos, thus, with account of 

physico- mechanical characteristics, testifying about a constructive corrosion of the basalt bar 

in the interfacial transition zone “cement stone   basalt bar”. Introduction of the metakaolin 

additive to pure portland cement (without alkaline activation) (Table 2, Composition 2) does 

not affect essentially a diffraction picture (Fig. 3, Curve 4). However, as it is clearly seen 

from, a content of 

 and, hence, of the hydroxide-ions tends to decline essentially in the 

interfacial transition zone, thus reducing considerably risk of flow of corrosion processes in 

the interfacial transition zone associated with destructive processes. 

 

 

Figure 3: X-ray patterns of the interfacial transition zone of the model system “cement stone   

basalt”: 1   initial system “portland cement + basalt”; 2   “portland cement + basalt + water”; 

3   initial system “portland cement + metakaolin + basalt”; 4   “portland cement + 

metakaolin + basalt + water”; 5   “portland cement + basalt + soluble glass”; 6   “portland 

cement + metakaolin + basalt + soluble glass” 

 

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8

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

This correlates well with a sharpness of the interfacial transition zone in the microphoto 

(Fig. 2a), as well as with the data given in [11], according to which the presence of active 

alumina in portland cement stone reduces considerably a concentration of alkalis in its pore 

space. The presence of alkalis does not exclude transformation of clay minerals of the 

interfacial transition zone into more stable minerals of the zeolite type [12, 13]. 

 

The introduction of the metakaolin into the alkali activated portland cement (Table 2, 

Composition 4) is found to suppress almost completely corrosion of the basalt bar. The line of 

contact in the microphotos is sharp and clear (Fig. 3). Zeolite-like hydration products of the 

Na

2

O Al

2

O

3

4SiO

2

2H

2

O (d = 0.569; 0.343; 0.293; 0.251; 0.174 nm), 

Na

2

O Al

2

O

3

3SiO

2

2H

2

O (d = 0.653; 0.587; 0.436; 0.286; 0.219 nm), 

2Na

2

O 2

5Al

2

O

3

10SiO

2

10H

2

O (d = 0.654; 0.467; 0.353; 0.285; 0.269 nm) types are 

clearly identified in the X-ray patterns (Fig. 3, Curve 6), what is confirmed by the increase of 

contents of Al

3+

and Na

+

 and decrease in the 

2+

 content in the interfacial transition zone.

 

 

 

5.  Mechanism of AAR prevention in the presence of metakaolin 

 

A mechanism of AAR in concrete is described in details in [14, 15]. The AAR in concrete 

takes place in case of alkali susceptible aggregates and when concrete works in high humidity 

service conditions. However, deterioration of concrete as a result of corrosion induced by 

AAR takes place only in cases when quantities of alkali in concrete exceed limit values. 

Alkalis can be formed both in the process of cement hydration according to the following 

scheme: Na

2

SO

4

+Ca(OH)

2

+2H

2

O 

 CaSO

4

·2H

2

O+2NaOH(Na

+

,OH

-

), and can be brought in 

from outside (for example, by alkaline activation of portland cement): 

Na

2

O·nSiO

2

·mH

2

O+Ca(OH)

2

CaO·nSiO

2

·mH

2

O+2NaOH. 

 

An alkali metal hydroxide enters into reaction with alkali susceptible silicon dioxide (SiO

2

) 

with the formation of silicic acid gel, which, by adsorbing water and calcium, will create 

expanding pressure, resulting in deterioration of concrete 

(2NaOH+nSiO

2

+mH

2

O

Na

2

O·nSiO

2

·mH

2

O). 

 

In the presence of Ca(OH)

2

, an alkali metal silicate gel can form  -S- – phase and this is 

accompanied by further release of greater and greater quantities of alkali metal hydroxide: 

Na

2

O·nSiO

2

·mH

2

O+Ca(OH)

2

+ mH

2

O

CaO·SiO

2

·mH

2

O(stands for  -S- )+2NaOH. 

 

Some portions of alkalis are bound by  -S- – phases; with decrease of Ca/Si ratio an ability 

of  -S-  – phase to binding alkalis increases [16]. With addition of metakaolin to cement 

composition an interaction mechanism will change. This can be attributed, first of all, to its 

(metakaolin) ability to bind the formed gel of Na

2

O·nSiO

2

·mH

2

O and free alkali metal 

hydroxide (NaOH) with the formation, as was shown by the studies, of alkaline 

aluminosilicate hydrates: Al

2

O

3

·2SiO

2

+2NaOH+mH

2

O

Na

2

O·Al

2

O

3

·2SiO

2

·mH

2

O; 

Al

2

O

3

·2SiO

2

+ Na

2

O·nSiO

2

·mH

2

O

 Na

2

O Al

2

O

3

·(n+2)SiO

2

·mH

2

O. 

 

Moreover, C-A-S-H– phases can be formed in a cement stone in the presence of Al

2

O

3

·2SiO

2

. 

These phases are able to bind greater quantities of alkalis compared to  -S- – phases [17] 

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