**5. Physicochemical studies of the composition of the obtained foam concrete and its porous structure**

At the next stage of the work, physical and chemical studies of samples of foam concrete with medium density D500, prepared on the basis of stabilized foam and NaCl additives, were carried out: X-ray phase and differential thermal analysis. Three samples of foam concrete were studied: No. 1, control; No. 2, based on the foam stabilized with SiO2 sol and with the addition of NaCl; and No. 3, based on the foam stabilized with Fe(OH)3 sol and with the addition of NaCl.

In all samples X-ray phase analysis showed the presence of reflexes corresponding to β-SiO2 with d/n (interplanar spacing) = (3.337, 2.447, 2.280, 2.119, 1.657; 1.539) Å, as well as reflexes corresponding to Ca(OH)2, d/n = (3.114, 2.625, 1.926, 1.675) Å, low-basic hydrosilicate C6S6H d/n = (3.030, 2.033, 1.95) Å, and hydrosilicate C2SH2 (d/n = (3.030, 2.765, 1.830, 1.565) Å). In the X-ray spectra of samples No. 2 and No. 3, new lines belonging to the low-basic hydrosilicate C3S2H3 (d/n = 2.88; 2.766; 2.152; 1.973; 1.793; 1.627 Å) appear. The radiographs of samples No. 2 and No. 3 show the lines characterizing the dolomitized limestone. Alite analytical line (C3S, d/n = 1.76 Å) is present only in the control sample; in other samples, it does not manifest itself, which indicates a deeper degree of cement hydration in them. The formation of additional low-basic hydrosilicates with increased strength, as well as the absence of an analytical line of alite on the radiographs, can explain the increase in the strength of foam concrete samples No. 2 and No. 3.

The derivatographic analysis, **Table 8**, confirmed the data of X-ray phase analysis and showed that the total mass loss of samples based on the stabilized foam and NaCl additives increases by 20%; besides that, a new phase of low-basic hydrosilicate C3S2H3 (endothermic effect in the region of 350–400°C) appears in the samples, which also confirms the increase in the strength of the foam concrete samples.

Then, in order to assess the porous structure of foam concrete based on the foam stabilized with SiO2 sol, porosity of the samples was investigated by means of mercury porometry (**Figure 10**).

The figure shows that the specific surface area of the pores in the sample based on the stabilized foam is twice that of the control sample. This may be due to the fact that such a foam is more stable in preparing a foam concrete mixture and in subsequent hardening the fine porous structure of the material is retained. The studies of the macroporous structure of foam concrete confirm this conclusion, as shown in **Figure 11**.


**Figure 11.**

**Figure 12.**

**117**

*Macroporous structure of samples: (a) a control sample and (b) a sample based on the stabilized foam.*

*The Improvement of the Quality of Construction Foam and Non-Autoclave Foam Concrete…*

*DOI: http://dx.doi.org/10.5772/intechopen.88234*

*Distribution of macropores according to their size for the control sample of foam concrete.*

**Table 8.**

*Derivatographic analysis of foam concrete samples of average density D500.*

**Figure 10.**

*The total specific surface of pores of foam concrete with average density of D500: (1) a control sample, (2) a sample based on the foam stabilized with SiO2 sol.*

*The Improvement of the Quality of Construction Foam and Non-Autoclave Foam Concrete… DOI: http://dx.doi.org/10.5772/intechopen.88234*

**Figure 11.** *Macroporous structure of samples: (a) a control sample and (b) a sample based on the stabilized foam.*

NaCl additives increases by 20%; besides that, a new phase of low-basic

samples.

mercury porometry (**Figure 10**).

*Foams - Emerging Technologies*

**Additive (130–**

NaCl

NaCl

**Table 8.**

**Figure 10.**

**116**

*sample based on the foam stabilized with SiO2 sol.*

**170)**

shown in **Figure 11**.

hydrosilicate C3S2H3 (endothermic effect in the region of 350–400°C) appears in the samples, which also confirms the increase in the strength of the foam concrete

stabilized with SiO2 sol, porosity of the samples was investigated by means of

**No. Stabilizer Endothermic effects, °C Total mass**

**(520– 580)**

1. — 88 — 24 14 — 126 179 2. Fe(OH)3 sol 86 16 20 33 28 183 213

3. SiO2 sol 90 18 19 40 30 197 227

*The total specific surface of pores of foam concrete with average density of D500: (1) a control sample, (2) a*

**(350– 400)**

*Derivatographic analysis of foam concrete samples of average density D500.*

Then, in order to assess the porous structure of foam concrete based on the foam

The figure shows that the specific surface area of the pores in the sample based on the stabilized foam is twice that of the control sample. This may be due to the fact that such a foam is more stable in preparing a foam concrete mixture and in subsequent hardening the fine porous structure of the material is retained. The studies of the macroporous structure of foam concrete confirm this conclusion, as

> **(750– 880)**

**loss on the effects, mg**

**sample, mg Mass loss, mg**

**(930– 960)**

**The total mass loss by the**

corresponds to the foam concrete the class of which is one class lower by the average density. At the same time, the duration of the cutting strength attainment reduces by 7 hours, which significantly speeds up the technological process.

*The Improvement of the Quality of Construction Foam and Non-Autoclave Foam Concrete…*

**Additive The time of cutting**

*DOI: http://dx.doi.org/10.5772/intechopen.88234*

**strength attainment, hour**

D500 — 17 0.117/100 3.4

*Physical and technical characteristics of industrial samples of non-autoclaved foam concrete of average density*

*The number of concrete products of the first quality category: (1) control products, (2) products based on the*

*Foam concrete products based on the stabilized foam and NaCl additives.*

NaCl 10 0.094/80 2.8

in **Table 9**.

**Class by average density**

**Table 9.**

**Figure 14.**

**Figure 15.**

**119**

*stabilized foam and NaCl additives.*

*D500.*

In addition, the shrinkage value of the foam concrete samples was estimated in drying. It was stated to decrease by 18% compared to the control sample, as shown

> **Thermal conductivity, λ, W/(m∙°C)/%**

**Shrinkage in drying, mm/m**

**Figure 13.**

*The distribution of macropores according to their size for the foam concrete sample on the basis of foam stabilized with SiO2 sol.*

**Figures 12** and **13** show the distribution of large pores according to their size for the foam concrete samples of average density D600; the study was conducted by means of the electron microscopy.

As it can be seen from the figures, the peak of the pore distribution according to their size in the case of a foam concrete sample based on a stabilized foam is shifted toward a smaller pore diameter (Dav = 520 μm). The number of such pores is 18%, the half-width of the peak is 0.44 mm. For the control sample, the peak corresponds to Dav = 600 μm, the number of pores of the average diameter is 15%, and the halfwidth of the peak is 0.52 mm.

Thus, it can be concluded that the stabilization of foam with SiO2 sol influences both the micro- and macropores of foam concrete. This increase in the foam concrete pore dispersion during the stabilization of foam explains the decrease in its thermal conductivity (**Table 5**).
