## 4 Conclusions  
In this study, the compressive strength of hardened alkali activated past and fine-grained concretes was determined. To improve the reaction degree of BBA calcium promoter such as PG was used. The following observation were made:  
Figure 7: The porosity of alkali activated fine-grained concrete samples. P—total porosity; Pa—open porosity; Pu—closed porosity.  
* The higher values of compressive strength were detected when SiO\({}_{2}\)/Na\({}_{2}\)O molar ratio was three compared with the samples where samples had SiO\({}_{2}\)/Na\({}_{2}\)O = 2. When SiO\({}_{2}\)/Na\({}_{2}\)O molar ratio was two, the samples containing 20% PG substitute had the highest compressive strength (24.3 MPa) after 28 days, while compressive strength of the samples with SiO\({}_{2}\)/Na\({}_{2}\)O molar ratio three peaked after 28 days at 30.0 MPa;
* Overall, paste samples activated with NaOH/Na\({}_{2}\)SiO\({}_{3}\) solution were weaker compared activated with NaOH. The compressive strength peaked at 23.0 MPa after seven days with 15% PG substitute, but after 28 days was reduced to 8.0 MPa. The reduction could be attributed to the cracking caused by the drying shrinkage. In addition, SEM images showed a higher degree of microcracking and unreacted the particle of BBA were detected when NaOH/Na\({}_{2}\)SiO\({}_{3}\) solution was activator;
* The amount of PG substitute was 15%-20% of BBA mass and it is recommended not to exceed 25%. The higher amount of PG significantly reduced the compressive strength;
* In contrary to paste samples, fine-grained concrete samples have shown different tendencies. When BBA with 15% PG was activated with NaOH/Na\({}_{2}\)SiO\({}_{3}\) solution compressive strength reached 15.4 MPa after 28 days, but when the same precursors were activated with NaOH compressive strength was reduced by 16% (12.9 MPa). The higher compressive strength could be related with the higher amount of active silicon;
* Even though total porosity of fine-grained concrete activated by NaOH and NaOH/Na\({}_{2}\)SiO\({}_{3}\) solution was nearly the same -27.5% and 27.7% respectfully, there is difference in open and closed porosity. When sodium silicate was present the open porosity was reduced from 16.8% to 14.1%. Hence, the fine-grained concrete activated with the NaOH and Na\({}_{2}\)SiO\({}_{3}\) solution should have higher freeze-thaw resistance;
* After 28 days of hydration the highest compressive strength reached 30.0 MPa the samples activated NaOH solution and by using 15% of BBA substitution to PG. The possibility of potential use of BBA (silicon and aluminum sources) and PG (calcium source) as binder precursor for production of AAMs was confirmed. This can suggest a solution for both alkaline binders industry to provide a new precursor and fertilizers industry to solve the storage problems of PG.  
We all authors: [PERSON], [PERSON], [PERSON] ([PERSON]), [PERSON] and [PERSON]. ([PERSON]) declare that we contributed to this article in equal parts about 20% everybody: [PERSON] and [PERSON] prepared the introduction part. Characterization of initial materials and the part of experimental procedures was prepared by [PERSON] and [PERSON]. ([PERSON]). The parts of \"Results and discussion\" and \"Conclusion\" were written and evaluated by all authors. All authors have read and agreed to the published version of the manuscript. This research received no external funding. This research work was supported by the Lithuanian Science Council project \"The utilization of industrial waste in alkali-activated concrete\", project code P-MIP-17-363. The authors declare no conflicts of interest.