Basic research on layered geopolymer composites with insulating materials of natural origin.

New restrictions on carbon dioxide emissions and electricity consumption are currently being introduced around the world. Innovative solutions are being adopted in many countries to reduce CO2 emissions and material and energy consumption. The present work is related to the study of innovative binders based on geopolymers for the production of layered building envelopes. The binders are reinforced with composite bars and containing fibers of natural origin. The natural materials used to produce the samples are completely biodegradable. A 10-mol sodium hydroxide solution with an aqueous solution of sodium silicate was used for alkaline activation of geopolymers. The purpose of the study was to compare and determine the insulating properties of natural fiber-based materials such as coconut mat, jute felt, hemp felt, flax felt, flax wool, hemp wool, flax-jute wool, and to determine the effect of these materials on geopolymer composites, in which 4 layers of natural insulating materials were used, and the composites were reinforced by fiberglass bars. The publication presents the results of physicochemical studies of geopolymerization precursors and natural insulating materials, studies of thermal properties of fibers, mats, felts and wools, morphology of fiber structure and texture, as well as physical and thermal properties of finished multi-layer partitions. The results indicate the great potential of these materials in prefabrication and structural-insulation applications. The fabricated composites using 4 layers of natural fibers showed improved thermal conductivity by as much as 40% (reduced thermal conductivity from 1.36 W/m × K to about 0.8 W/m × K). The work may have future applications in energy-saving and low-carbon construction.

Application of Industrial Waste Materials by Alkaline Activation for Use as Geopolymer Binders.

The purpose of this study is to synthesize geopolymer binders as an environmentally friendly alternative to conventional cement using available local raw materials. Waste materials such as chalcedonite (Ch), amphibolite (A), fly ash from lignite combustion (PB), and diatomite dust (D) calcined at 900 °C were used to produce geopolymer binders. Metakaolin (M) was used as an additional modifier for binders based on waste materials. The base materials were subjected to fluorescence X-ray fluorescence (XRF) analysis and X-ray diffractometry (XRD) to determine chemical and phase composition. A laser particle size analysis was also performed. The various mixtures of raw materials were activated with a 10 M solution of NaOH and sodium water glass and then annealed for 24 h at 60 °C. The produced geopolymer binders were conditioned for 28 days under laboratory conditions and then subjected to microstructural analysis (SEM) and flexural and compressive strength tests. The best compressive strength results were obtained by the Ch + PB samples-more than 57 MPa, while the lowest results were obtained by the Ch + D+A + M samples-more than 20 MPa. On the other hand, as a result of the flexural strength tests, the highest flexural results were obtained by D + A + M + PB binders-more than 12 MPa, and the lowest values were obtained by binders based on Ch + D+A + M-about 4.8 MPa.

Surface Modification of Synthetic Zeolites with Ca and HDTMA Compounds with Determination of Their Phytoavailability and Comparison of CEC and AEC Parameters.

Zeolites obtained from fly ash are characterized by very good anion- and cation-exchange properties and a developed porous structure. This paper presents the results of surface modification studies of synthetic zeolites obtained from calcined coal shale (clay materials). Calcium compounds and hexadecyltrimethylammonium bromide (HDTMA) were used as modifying substances. The characteristics of the raw material and the zeolite obtained as a result of its synthesis are presented. The surface modification method is described. Furthermore, the results of sorption and desorption of NO3, PO4, and SO4 from raw and modified samples are presented. The results of anion- and cation-exchange capacities for other zeolite types were also compared. Modification of the materials with Ca ions and HDTMA surfactant only improved the sorption of sulfates. The 90% desorption of nitrates, phosphates, and sulphates from the zeolite material without modification indicates a good release capacity of these compounds and their potential use as fertilizer additives.

Optimizing the L/S Ratio in Geopolymers for the Production of Large-Size Elements with 3D Printing Technology.

Geopolymer concretes can be a viable alternative to conventional Portland cement-based materials. In their design, it is important to maintain an appropriate liquid-to-solid ratio (L/S), which affects several properties, such as the compressive strength, water absorption, and frost resistance. The objective of this paper is to analyze the influence of the fly-ash and metakaolin precursor types for three different L/S ratios: 0.30, 0.35, and 0.45. The results of the physical and mechanical properties, including the apparent density and compressive strength, as well the durability parameters, including frost resistance and water penetration depth, are presented in this paper. It was found that as the L/S ratio decreased, the average compressive strength increased for all materials. After freeze-thaw cycles, decreases in the compressive strength properties were observed for all types of materials-metakaolin- and fly ash-based-irrespective of the L/S ratio. Moreover, the frost resistance of geopolymers increased with the increase in the L/S ratio. The printability of the mixes was also verified in order to confirm the application of the developed materials to additive manufacturing processes.

3D Printing of Concrete-Geopolymer Hybrids.

In recent years, 3D concrete printing technology has been developing dynamically. Intensive research is still being carried out on the composition of the materials dedicated to innovative 3D printing solutions. Here, for the first time, concrete-geopolymer hybrids produced with 3D printing technology and dedicated environmentally friendly building construction are presented. The concrete-geopolymer hybrids consisting of 95% concrete and 5% geopolymer based on fly ash or metakaolin were compared to standard concrete. Moreover, 3D printed samples were compared with the samples of the same composition but prepared by the conventional method of casting into molds. The phase composition, water leachability, compressive, and flexural strength in the parallel and perpendicular directions to the printing direction, and fire resistance followed by compressive strength were evaluated. Concrete-geopolymer hybrids were shown to contain a lower content of hazardous compounds in leaches than concrete samples. The concentration of toxic metals did not exceed the limit values indicated in the Council Decision 2003/33/EC; therefore, the materials were classified as environmentally neutral. The different forms of Si/Al in fly ash and metakaolin resulted in the various potentials for geopolymerization processes, and finally influenced the densification of the hybrids and the potential for immobilization of toxic elements. Although the compressive strength of concrete was approximately 40% higher for cast samples than for 3D printed ones, for the hybrids, the trend was the opposite. The addition of fly ash to concrete resulted in a 20% higher compressive strength compared to an analogous hybrid containing the addition of metakaolin. The compressive strength was 7-10% higher provided the samples were tested in the parallel direction to the Z-axis of the printout. The sample compressive strength of 24-43 MPa decreased to 8-19 MPa after the fire resistance tests as a result of moisture evaporation, weight loss, thermal deformation, and crack development. Importantly, the residual compressive strength of the hybrid samples was 1.5- to 2- fold higher than the concrete samples. Therefore, it can be concluded that the addition of geopolymer to the concrete improved the fire resistance of the samples.

The Influence of Short Coir, Glass and Carbon Fibers on the Properties of Composites with Geopolymer Matrix.

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their high mechanical properties. Natural fibers have been chosen because of their mechanical properties as well as for the sake of comparison between their properties and the properties of the artificial ones. Fourth series of fly ash-based geopolymers for each fiber was cast: 1, 2, and 5% by weight of fly ash and one control series without any fibers. Each series of samples were tested on flexural and compressive strength after 7, 14, and 28 days. Additionally, microstructural analysis was carried out after 28 days. The results have shown an increase in compressive strength for composites with fibers-an improvement in properties between 25.0% and 56.5% depending on the type and amount of fiber added. For bending strength, a clear increase in the strength value is visible for composites with 1 and 2% carbon fibers (62.4% and 115.6%). A slight increase in flexural strength also occurred for 1% addition of glass fiber (4.5%) and 2% addition of coconut fibers (5.4%). For the 2% addition of glass fibers, the flexural strength value did not change compared to the value obtained for the matrix material. For the remaining fiber additions, i.e., 5% glass fiber as well as 1 and 5% coconut fibers, the flexural strength values deteriorated. The results of the research are discussed in a comparative context and the properties of the obtained composites are juxtaposed with the properties of the standard materials used in the construction industry.

Process Design for a Production of Sustainable Materials from Post-Production Clay.

Alkali activated cement (AAC) can be manufactured from industrial by-products to achieve goals of "zero-waste" production. We discuss in detail the AAC production process from (waste) post-production clay, which serves as the calcium-rich material. The effect of different parameters on the changes in properties of the final product, including morphology, phase formation, compressive strength, resistance to the high temperature, and long-term curing is presented. The drying and grinding of clay are required, even if both processes are energy-intensive; the reduction of particle size and the increase of specific surface area is crucial. Furthermore, calcination at 750 °C ensure approximately 20% higher compressive strength of final AAC in comparison to calcination performed at 700 °C. It resulted from the different ratio of phases: Calcite, mullite, quartz, gehlenite, and wollastonite in the final AAC. The type of activators (NaOH, NaOH:KOH mixtures, KOH) affected AAC mechanical properties, significantly. Sodium activators enabled obtaining higher values of strength. However, if KOH is required, the supplementation of initial materials with fly ash or metakaolin could improve the mechanical properties and durability of AAC, even c.a. 28%. The presented results confirm the possibility of recycling post-production clay from the Raciszyn II Jurassic limestone deposit.

An Efficacy Assessment of Phosphate Removal from Drainage Waters by Modified Reactive Material.

Phosphates may pose a threat to the aquatic ecosystem when there is a connection or a path between the soil and the aquatic ecosystem. Runoff and drainage ditches connect arable land with the waters of the receiver. Phosphates in the runoff and the ditches contribute to the negative phenomenon of surface water eutrophication. In order to prevent it, certain reactive materials are used which are capable of the selective removal of compounds by way of sorption or precipitation. Zeolites can be distinguished among the many reactive materials. Within the present analysis, the modification of a reactive material containing zeolites was carried out using calcium hydroxide solutions of different concentrations. A certain concentration of calcium hydroxide was created for use in further studies. In order to characterise the new material, an analysis was done of the chemical and mineral composition, as well as the porous texture and morphology. The efficacy of phosphate removal for its typical concentrations in drainage waters in Poland was confirmed by way of an experiment. Using a modified reactive material as an element of landscape structures may reduce the negative impact of phosphates on the quality of surface water.

Mechanical Properties of Short Fiber-Reinforced Geopolymers Made by Casted and 3D Printing Methods: A Comparative Study.

The main objective of this article is to develop ceramic-based materials for additive layer manufacturing (3D printing technology) that are suitable for civil engineering applications. This article is focused on fly ash-based fiber-reinforced geopolymer composites. It is based on experimental research, especially research comparing mechanical properties, such as compressive and flexural strength for designed compositions. The comparison includes various composites (short fiber-reinforced geopolymers and plain samples), different times of curing (investigation after 7 and 28 days), and two technologies of manufacturing (casted and injected samples-simulations of the 3D printing process). The geopolymer matrix is based on class F fly ash. The reinforcements were green tow flax and carbon fibers. The achieved results show that the mechanical properties of the new composites made by injection methods (simulations of 3D technology) are comparable with those of the traditional casting process. This article also discusses the influence of fiber on the mechanical properties of the composites. It shows that the addition of short fibers could have a similar influence on both of the technologies.

Decreasing of Leaching and Improvement of Geopolymer Properties by Addition of Aluminum Calcium Cements and Titanium Oxide.

The article presents the latest results of the leaching of alkali from geopolymers depending on the introduced additions in the form of aluminum calcium cement and nanometric titanium oxide. Aluminum calcium cements were introduced in two variants: G40 (>40% Al2O3) and G70 (>70% Al2O3) in amounts of 0%, 2%, and 4% by weight. Titanium oxide was also incorporated in amounts of 2% and 4% by weight. The results of conductivity tests of solutions in which geopolymers were immersed were carried out. On this basis, it was found that geopolymers cured in the aquatic environment have a lower risk of efflorescence in the later periods of their use due to leaching of compounds at the stage of aquatic curing. In addition, it was found that the addition of calcium aluminum cements decreases the leaching of substances from geopolymers. It was also found that geopolymers based on an 8 M NaOH solution have greater leaching than when using a 10 M solution. The results of the compressive strength tests for the tested samples were also presented.

Alkali Activation of Waste Clay Bricks: Influence of The Silica Modulus, SiO2/Na2O, H2O/Na2O Molar Ratio, and Liquid/Solid Ratio.

This study was conducted to investigate the influence of various reaction conditions, namely the silica modulus SiO2/Na2O, H2O/Na2O molar ratio, and liquid/solid ratio on the geopolymerization reaction of the waste fired clay bricks (Grog). The starting raw material and the generated geopolymer specimens produced by different geopolymerization reaction conditions have been characterized using different techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal analysis. Furthermore, physico-mechanical characterization has been carried out through the determination of bulk density, porosity, water absorption, and compressive strength for each sample at interval curing times of up to 28 days. The results indicated that the geopolymerization system of the waste fired clay bricks is influenced by the investigated reaction conditions at room temperature. The compressive strength of the geopolymer sample produced at optimum conditions increased significantly by up to 37.5 MPa, in comparison with 4.5 MPa for other conditions. Finally, an optimum recommendation and useful conclusions concerning the recycling and utilization of this waste material through the geopolymerization process are made for compatibility with construction applications.

Optimal Design of Ph-Neutral Geopolymer Foams for Their Use in Ecological Plant Cultivation Systems.

We have calculated that with the world population projected to increase from 7.5 billion in 2017 to 9.8 in 2050, the next generation (within 33 years) will produce 12,000-13,000 Mt of plastic, and that the yearly consumption will reach 37-40 kilos of plastic per person worldwide. One of the branches of the plastics industry is the production of plastics for agriculture e.g., seed trays and pots. In this paper, novel metakaolin-based geopolymer composites reinforced with cellulosic fibres are presented as an alternative to plastic pots. Materials can be dedicated to agricultural applications, provided they have neutral properties, however, geopolymer paste and its final products have high pH. Therefore, a two-step protocol of neutralisation of the geopolymer foam pots was optimised and implemented. The strength of the geopolymer samples was lower when foams were neutralised. The reinforcement of geopolymers with cellulose clearly prevented the reduction of mechanical properties after neutralisation, which was correlated with the lower volume of pores in the foam and with the cellulose chemical properties. Both, neutralisation and reinforcement with cellulose can also eliminate an efflorescence. Significantly increased plant growth was found in geopolymer pots in comparison to plastic pots. The cellulose in geopolymers resulted in better adsorption and slower desorption of minerals during fertilisation. This effect could also be associated with a lower number of large pores in the presence of cellulose fibres in pots, and thus more stable pore filling and better protection of internal surface interactions.

Calcined Post-Production Waste as Materials Suitable for the Hydrothermal Synthesis of Zeolites.

The zeolite production process is currently being very intensively researched. Due to environmental protection, as well as issues related to the guidelines of a zero-waste economy, all activities aimed at obtaining such materials from post-processed waste are extremely important. This article presents an innovative method of utilising calcined carboniferous shale in order to produce synthetic zeolites. The raw material for testing came from two Polish hard coal mines. Both the chemical and phase composition of the coal shale were characterised. Based on the recorded thermal analysis results coupled with the mass spectrometer, the processes occurring during the heating of raw materials were interpreted and the calcination temperatures were determined. The changes in the phase composition of raw materials resulting from the calcination process used were also analysed. The heat-treated raw materials were subjected to the synthesis of zeolites in an aqueous solution of sodium hydroxide by means of the hydrothermal method at a concentration of 2.75 M. The results of water leaching and structural parameters are presented for both raw materials, as well as the produced synthesis. The conducted research confirmed that after the application of the synthetic process on coal shale, a zeolite with a surface area of SBET equal to 172 m2/g can be obtained.

Geopolymers as a material suitable for immobilization of fly ash from municipal waste incineration plants.

This paper discusses the possibility of using the process of geopolymerization to immobilize ash from municipal waste incineration plants. Fly ash used in the related research came from the same incineration plant, one of the biggest in Poland. The examination was conducted on the waste samples labeled as 190107* and 190113*. The comparison included such properties of waste as chemical composition, dioxin content, and size and morphology of particles. The waste was solidified in geopolymer matrix made from (i) fly ash from the combustion of bituminous coal or (ii) metakaolin. The waste percentages were 50 mass% and 70 mass%, respectively. Moreover, leaching tests were carried out and mechanical properties of the geopolymers materials containing immobilized ashes were analyzed. It was proved that geopolymerization process allows for the high-level immobilization of compounds and elements such as chlorides, sulfates, fluorides, barium, and zinc. Additionally, it was observed that in the case of the geopolymer samples containing 70 mass% of 190107* waste, the average compressive strength exceeded 18 MPa. Implications: A novel aspect of the results presented in this paper is the comprehensive investigation of the immobilization of large amounts of hazardous waste by means of the synthesis of geopolymers from metakaolin or coal fly ash. According to these results, it was determined that the level of immobilization is much higher in the case of the geopolymers based on metakaolin in comparison with geopolymers made from coal fly ash. On the basis on the obtained results, investigated geopolymers may be successfully used, e.g., as barriers or linear drains in landfills.