## 3 Fundamentals
### The Influence of the AAC Basicity
#### 3.1.2 Factor #2: Charge of Polar Groups of a Surfactant  
The subject of research was a concrete based on an AAC with M\({}_{\rm b}\) = 1.2-1.6 (Mixes 5-9) (see Table 2). The criteria for evaluating the effectiveness of a surfactant was the consistency (slump) and its retention time of fresh concrete, as well as thecompressive strength of concrete. The effectiveness of the combined action of anionic, nonionic, and cationic surfactants (1.0% by mass), each taken alone and in conjunction with NaLST, was evaluated. With the AAC basicity decrease from M\({}_{\rm b}\) = 2.4 to M\({}_{\rm b}\) = 1.6 (Mixes 5 and 6) (Figure 3a,b) and further to M\({}_{\rm b}\) = 1.3-1.2 (Mixes 7-9) (Figure 3c-e), higher contents of the alkaline component were required and, as a result, the effectiveness of anionic surfactants (PCE) decreased, resulting in a decrease of the plasticizing effect and consistency retention time. This effect can be attributed to a lower adsorption ability of surfactants due to the change of the mineral particles from positive to negative with the increase in GBFS content in AAC. Additionally, a shorter consistency retention time can be attributed to PCE destruction (hydrolysis) in a highly alkaline medium [63]. On the contrary to anionic surfactants, the effectiveness of cationic surfactants increased proportionally with the decrease in the AAC basicity and increased in the alkaline component content. The changes in the AAC basicity from M\({}_{\rm b}\) = 1.6 (Mixes 5 and 6) (Figure 3a,b) to M\({}_{\rm b}\) = 1.2 (Mixes 7 and 8) (Figure 3d,e), regardless of the anion of the alkaline component, were accompanied by the higher consistency and the longer consistency retention time. The higher adsorption ability of cationic surfactants can be attributed to the higher values of negative charge (zeta-potential) on the surface of mineral particles. With low AAC basicity, nonionic surfactants like polyethylene glycol exhibited a similar higher effect. These plasticizers were ineffective for the AAC with M\({}_{\rm b}\) = 1.6 (Mixes 5 and 6) (Figure 3a,b), even used in conjunction with NaLST, which should have provided the adsorption (Figure 3a,b). However, with the decrease in basicity (M\({}_{\rm b}\)) from 1.3 to 1.2 (Mixes 7-9) (Figure 3c-e), the consistency of fresh concrete during the first 60 min remained within one class in consistency. The consistency retention of AAC concrete mixes was attributed to the stability of the molecular structure of cationic and nonionic surfactants at the early stages of hydration. Figure 2: Compressive strength of the mortar based on the AAC with M\({}_{\rm b}\) = 2.4 (Mix 1) at 1 day (**a**) and 28 days (**b**) vs. the surfactant type (PCE1—blue, PCE2—red, PEG-M—yellow, and without admixture (reference)—black) and W/C (0.45, 0.47, and 0.65). Also, the influence of the AAC basicity on the action effect of surfactants under a criterion of strength of concrete produced with a constant W/C (Figure 4) was studied. The use of anionic surfactants in the AAC with M\({}_{\rm b}\) = 1.6 (Mixes 5 and 6) resulted in some retarded hardening of the AAC concretes at early ages (Figure 4a,b). However, after 28 days, the strength of modified concrete exceeded that of the reference concrete. The effectiveness of anionic surfactants decreased with the decrease in the AAC basicity and increased in the content of the alkaline component. This effect was accompanied by the retarded hardening of AAC concrete and can be attributed to the increase in the concentration of the alkaline component due to the hydrolysis of polyesters. On the contrary, the effectiveness of nonionic surfactants increased with the decrease in the AAC basicity and, respectively, the increase of the content of the alkaline component. So, PEG 400 decreased the strength gain in the AAC with M\({}_{\rm b}\) = 1.6 (Mixes 5 and 6)--based concrete both at the early stages of hardening and at 28 days (Figure 4a,b).