Impact toughness and dynamic constitutive model of geopolymer concrete after water saturation

The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress-strain curves.

Experimental investigation on the behavior of fly-ash based geopolymer reinforced concrete beams strengthened with CFRP

Recently, the demand for strengthening and rehabilitation of existing RC structures has increased due to the corrosion of internal steel reinforcement, variations in temperature, and increasing loading. As a result, several experimental studies have been performed to investigate the structural behaviour of strengthening RC beams with CFRP sheets, but few for GPC beams; therefore, this investigation focuses on the behaviour of strengthening GPC beams with CFRP sheets. In this experimental work, a set of ten specimen beams with the same cross section of 100 × 250 mm and 850 mm length with a 750 mm clear span were cast in two groups of five beams each. First group (flexural group) to study the flexural behavior, and the second one for the shear behaviour (shear group). In each group, the first beam was carried out as an RC control beam and the second as a GPC control beam without strengthening, while the other three beams were cast as GPC beams and strengthened with various schemes of CFRP sheets. All specimens were tested up to failure under two-sided static loading (four-point bending). The first cracking, yielding, and ultimate failure loads, the deflection values at midspan, the longitudinal bar strain, and the concrete strain were recorded for all tested specimens. The experimental results indicated that the Flextural Strengthening of GPC with CFRP sheet increased the First Cracking, yield and ultimate load capacity by 25.33%, 15.3% and 15% respectively, as well as, deflection was decreased by 16% on average while ductility and toughness have improved by 10% and 12% on average compared to R.C Beam.On the other side, the Shear Strengthening of GPC with CFRP strips increased the First Cracking, yield and ultimate load by 43%, 70% and 68% respectively, as well as, shear ductility has improved by 8% on average compared to R.C Beam. Overall, the different schemes of externally bound CFRP sheets have improved the flexural and shear behaviour of GPC beams.

A comparative cradle-to-gate life cycle assessment of geopolymer concrete produced from industrial side streams in comparison with traditional concrete

Traditional concrete production is a major contributor to global warming. Industrially produced geopolymer concrete is a viable substitute to limit the negative impacts of concrete production. Thus, this study developed novel geopolymer concrete mix designs using industrial side streams, such as bark boiler ash, construction and demolition waste (CDW), fibre waste, and mine tailings. A cradle-to-gate life cycle assessment (LCA) methodology was conducted to evaluate the potential impacts of these different geopolymer concrete (GPC) mix designs in comparison with traditional concrete. The results showed that industrial-based geopolymer concrete with lower amounts of sodium silicate and metakaolin exhibited better environmental performance. Specifically, a 10 % reduction in metakaolin content reduces the global warming impact by 16 % compared with traditional concrete. The processing and curing of industrial waste for concrete formulations has an environmental impact of less than 1 %. From a sustainability perspective, the environmental performance of geopolymer concrete produced from industrial side streams can be further improved by increasing the concentration of recycled waste in the concrete mixes. In addition, the effective use of industrial side streams can improve the waste management, sustainability, and strength of concrete.

Mechanical and durability assessments of steel slag-seashell powder-based geopolymer concrete

Globally, an increasing carbon footprint has had a negative effect on the ecosystem and all living things. One of the sources that produces these footprints is the cement manufacturing process. Therefore, it is crucial to produce a cement substitute to reduce these footprints. The production of a geopolymer binder (GPB) is one of these possibilities. In this study, sodium silicate (Na₂SiO₃) was used as an activator in the production of geopolymer concrete (GPC) together with steel slag and oyster seashell as precursors. The materials of the concrete were prepared, cured, and tested. Workability, mechanical, durability and characterization test were conducted on the GPC. The results showed that adding a seashell increased the slump value. The optimum GPC compressive strength on a 100 × 100 × 100 mm³ cube for 3, 7, 14, 28, and 56 curing days was obtained with 10% seashell, while seashell replacement exceeded 10% declined in strength. Portland cement concrete achieved better mechanical strength when compared to steel slag seashell powder geopolymer concrete. However, steel slag seashell powder-based geopolymer gained better thermal properties than Portland cement concrete at 20% seashell replacement.

Proposing several model techniques including ANN and M5P-tree to predict the compressive strength of geopolymer concretes incorporated with nano-silica

Geopolymers are innovative cementitious materials that can completely replace traditional Portland cement composites and have a lower carbon footprint than Portland cement. Recent efforts have been made to incorporate various nanomaterials, most notably nano-silica (nS), into geopolymer concrete (GPC) to improve the composite's properties and performance. Compression strength (CS) is one of the essential properties of all types of concrete composites, including geopolymer concrete. As a result, creating a credible model for forecasting concrete CS is critical for saving time, energy, and money, as well as providing guidance for scheduling the construction process and removing formworks. This paper presents a large amount of mixed design data correlated to mechanical strength using empirical correlations and neural networks. Several models, including artificial neural network, M5P-tree, linear regression, nonlinear regression, and multi-logistic regression models, were utilized to create models for forecasting the CS of GPC incorporated with nS. In this case, about 207 tested CS values were collected from literature studies and then analyzed to promote the models. For the first time, eleven effective variables were employed as input model parameters during the modeling process, including the alkaline solution to binder ratio, binder content, fine and coarse aggregate content, NaOH and Na₂SiO₃ content, Na₂SiO₃/NaOH ratio, molarity, nS content, curing temperatures, and ages. The developed models were assessed using different statistical tools such as root mean squared error, mean absolute error, scatter index, objective function value, and coefficient of determination. Based on these statistical assessment tools, results revealed that the ANN model estimated the CS of GPC incorporated with nS more accurately than the other models. On the other hand, the alkaline solution to binder ratio, molarity, NaOH content, curing temperature, and ages were those parameters that have significant influences on the CS of GPC incorporated with nS.

A comparative study on environmental performance of 3D printing and conventional casting of concrete products with industrial wastes

3D printing construction techniques are believed to have potential sustainability benefits, including improved resource efficiency, increased construction productivity, and construction of complex geometries without supporting structures. 3D printable concrete materials, when introducing industrial wastes such as fly ash, silica fume, and slag, may also bring additional sustainability benefits. These advantages need to be verified quantitatively. This study investigated the environmental impact of 3D printable concrete materials using industrial wastes compared with the conventional ones via life cycle assessment (LCA). Two types of concrete materials applied in concrete casting or 3D printing were compared, that is, cement-based concrete and geopolymer concrete. The results indicate that using waste materials as cement replacement could bring environmental benefits; however, such environmental benefits might be diminished with increasing activator content in geopolymer concrete for 3D concrete printing. Based on the material-level LCA results, this study further conducted an LCA study at the component level, which investigated the life-cycle environmental impact of concrete components of different shapes constructed by Contour Crafting method. Results show that the potential environmental benefit of 3D concrete printing increases with the level of building complexity while decreases with the reuse times of formwork, which leads to the conclusion that 3D concrete printing method is more desirable for constructing non-repetitive freeform concrete structures.

Durability and life prediction of fly ash geopolymer concrete in corrosion environments caused by dry and wet circulation

The use of tailings, waste rock, fly ash, and slag to prepare geopolymer concrete can effectively solve the problems of land resources occupied by tailings and waste rock, low utilization rate, and environmental pollution. Using a dry-wet circulation method, fly ash for a different corrosion solution to geopolymer concrete (referred to as TWGPC) was analyzed. Through an appearance change, the corrosion resistance coefficient of the compressive strength, relative dynamic elastic modulus, tensile splitting strength, relative mass, and durability were investigated, using scanning electron microscopy (SEM) analysis of the microstructure, The life of TWGPC was predicted based on the GM(1,1) prediction model of grey system theory. The test results show that with an increase in the number of dry-wet cycles, the surface of the specimen crystallizes, cracks, spalls, and exhibits other phenomena. The compressive strength corrosion coefficient, relative dynamic elastic modulus, crack tensile strength, and relative mass show a trend of increasing first and then decreasing, finally reaching the peak value after 40 cycles. The erosion products generated by the early reaction fill the slurry aggregate pores and improve the strength of TWGPC. In a later stage, a large number of erosion products absorb water and expand; the internal pores of TWGPC are connected, leading to a decrease in strength. Cl^- inhibits the corrosion of SO₄^2- in concrete and improves the durability of concrete.

Taguchi optimization of geopolymer concrete produced with rice husk ash and ceramic dust

Metakaolin, fly ash, and mostly granulated blast furnace slag (GBFS) are traditionally used in the production of geopolymer. This study, adding to the knowledge base on geopolymer concretes as an alternative to cement mixtures, explored an experimental approach that investigates the use of ceramic dust (CD) and rice husk ash (RHA) with high SiO content instead of GBFS in the production of geopolymers. For this purpose, instead of GBFS, RHA at proportions of 0, 5%, 10%, and 15% and CD at proportions of 0, 10%, 20%, and 30% were used in the production of geopolymer concrete. In addition, groups were determined with a Taguchi L16 matrix with NaOH (an important material in geopolymer production) at 12, 14, 16, and 18 molality. Varying combinations of flow diameter, density, porosity, and water absorption rate were used, and their performance under high temperatures in terms of compressive strength was evaluated. The use of RHA in geopolymer concretes produced using CD and RHA had a negative effect on the flow and water absorption rates. However, the use of CD had a positive effect, and geopolymer concretes with high density and porosity were obtained. In addition, it was determined that strengths > 70 MPa could only be obtained if 5-20% CD were used at 14-16 molality. The resistance of geopolymer concretes to high temperatures is lower than normal concretes. However, when comparing RHA and CD, it was determined that the use of CD would be more effective on geopolymer materials, and special measures should be taken at temperatures > 450 °C.

Strength curve data for slender geopolymer concrete columns with GFRP, steel and hybrid reinforcement

This article provides a wide range of circular columns strength values under different loading conditions. The provided strength values are dependent on various parameters including the longitudinal and transverse reinforcement ratios. Results for GFRP, steel and hybrid reinforcement configurations are provided. The results were collected from analysis output files of more than 60,000 columns, and tabulated in a form that is suitable for generating analytical strength curves. The provided data format allows the generation of strength curves for a wide range of slenderness ratios and the applied load eccentricities. Inspecting the analytical strength curves could provide insights on the slenderness limits for maintaining specific strength thresholds. Also, further investigations of data could provide a group of recommendations to avoid longitudinal and transverse reinforcement underutilization. Additional data processing could provide axial load-bending moment interaction diagrams for different columns` configurations taking into consideration the slenderness effects. The use of interaction diagrams in inspecting slender columns behavior is a ubiquitous subject that has been utilized in many recent research papers. Moreover, the results of a sensitivity analysis are provided within the article.

Novel approach to microscopic characterization of cryo formation in air voids of concrete

Portland Cement Concrete (PCC) production is one of the major contributor to atmospheric Carbon Dioxide (CO₂) emission. Geopolymer Concrete (GPC) as an alternative construction material has the potential to reduce CO₂ emissions while creating durable structures. Freezing and thawing is an exemplary concrete deterioration mechanism that can cause widespread damage in concrete structures. Concrete structures exposed to freeze-thaw cycles delaminate due to expansive stresses induced when liquid converts to ice. There are numerous theoretical studies that have been done focused on capturing the effect of freeze-thaw cycles on microstructure of PCC. However, there is limited and no experimental work reported on cryo formation inside the air voids of PCC and GPC respectively. The main issue here is that most of the scanning electron microscopic devices cannot maintain the low temperature required to capture an image from a frozen sample. The amount of internal stress due to cryo formation and temperature range of cryo formation can be determined by investigation of morphology of the cryo products. Hence, in this study attempts have been made to investigate the morphology of the cryo formation inside the microstructure of GPC using a 4-D Low Temperature Scanning Electron Microscopic (4D-LTSEM). GPC specimens were frozen at -180 °C and were slowly sublimated to capture cryo creation in the paste. According to ASTM C666, nominal freezing temperature for PCC is -18 °C. So, the microstructure of GPC at -18 °C was investigated to find the applicability of ASTM C666 for paste tense. The results show that rate of cryo formation is slow from 0 °C to -18 °C indicating sufficient resistance of GPC when exposed to cold climates.