Authors
Katarzyna Łaskawiec | Piotr Gębarowski | Piotr Zając | Jarosław Stankiewicz
Łukasiewicz – Institute of Ceramics and Building Materials
katarzyna.laskawiec@icimb.lukasiewicz.gov.pl
Aim of the project
The aim is to present the possibility of using artificial aggregates for AAC elements. The technology offered is a process for obtaining a product with the expected properties within a narrow range of values. The project result is mainly the knowledge allowing further use of the technology in the disposal processes of various waste groups. Developing an effective AAC production technology based on aggregates from raw waste materials will bring economic benefits and contribute to the protection of the natural environment.
Currently developed concrete-based construction in a large-size modular system focuses on a material that should be characterized primarily by high strength, suitable for the intended transport and method of installation, and high values of thermal insulation.
Developing an aggregate that will improve relevant functional properties of the final products will guarantee greater production efficiency and competitiveness of such products on the market.
Short description of the problem addressed by this project
AAC, as a lightweight material, seems to be advantageous for the purpose of modular prefabrication but it has significant limitations resulting from relatively low strength and production technology that includes growing in forms.
AAC used in the construction of single-family houses and low-rise buildings has sufficient strength and is characterized by thermal insulation capabilities that limit the formation and minimize the impact of thermal bridges.
In terms of prefabricates for small construction sites, large-scale prefabricates from AAC should use blocks dimensions and weights of which will allow transport by non-specialized trucks and assembly using cranes with small overhang and low carrying capacity. The construction of buildings made from factory-made, high-quality elements should be attractive to investors in an era when investment execution time is critical and the rising cost of construction need to be considered.
On the materials engineering side, innovative binders and low-clinker cements are expected. Utilization of waste materials is a natural trend in the development of prefabricates, which is part of the sustainable construction industry development. It involves both the use of by-products and the recycling of waste from the prefabrication process.
Main results and achievements
Based on the analysis of the results of the AAC elements properties on a laboratory scale, two recipes were selected according to the produced modular elements.
Aggregate – ground sand to slurry in a ball mill in an aqueous environment forms 60% or 50% of the mass, and Gransil aggregate (fraction with grain sizes: 0-0.1; or 0.1-2) accounts for another 10% to 20%.
The remaining 30% is binder – mixed cement and lime (balance). The autoclaving process:
The duration of the first phase (autoclave purging) is set at 5-7 minutes.
The duration of pressure increase to its maximum value (phase II) and pressure decrease (phase IV) to the level of atmospheric pressure depends on the maximum pressure of the cycle. It should be approx. 120–180 minutes.
The duration of the third phase, when a constant pressure of 1.1 MPa of saturated steam is maintained will be approx. 480 minutes.
Conclusion
The project results demonstrated that AAC strength parameters using Gransil are equal to those of AAC using sand. The shrinkage of AAC using Gransil aggregate is lower than in the reference concrete, and the thermal conductivity coefficient λ of AAC is favorably lower.
General construction assumptions:
- assumed exposure class according to EC2 – XC1;
- corrosion source – carbonation;
- RC2 reliability class;
- ABK 550 class (to be finally agreed during the implementation phase at the production plant);
- Reinforcement in the form of X2CrNi12 stainless steel reinforcing grids or standard concrete reinforcing bars with characteristic strength of min. 450 MPa (anti-corrosion coated) or non-metallic fiberglass bars;
- It is expected that the element in the wall will be experiencing primarily vertical load, the eccentricity will be small, and the resultant force will most often not extend beyond the core of the section.
Acknowledgements
This project elaborated with the financial support R&D project from ŁUKASIEWICZ grants.
