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Article

Effect of Mix Design Parameters on the Properties of Dam Sediment/Slag-Based Geopolymer Mortars

by
Mohamed Salah Mouaissa
1,*,
Hafida Marouf
1,
Tewfik Ali-Dahmane
2,3,4,
Ahmed Soufiane Benosman
4,5 and
Walid Maherzi
6,7,*
1
Smart Structures Laboratory (SSL), Departement of Civil Engineering and Publics Works, University of Ain Temouchent, P.B.284, Ain Temouchent 46000, Algeria
2
Laboratory of Organic Electrolytes and Polyelectrolytes Application (LAEPO), University Abou Beker Belkaid, Tlencen BP119, Tlemcen 13000, Algeria
3
Laboratory of Chemistry of Materials (L. C. M), University of Oran1 Ahmed Ben Bella, BP 1524, El-Mnaouer, Oran 31000, Algeria
4
Ecole Supérieure en Sciences Appliquées de Tlemcen, ESSA—Tlemcen, BP 165 RP, Bel Horizon, Tlemcen 13000, Algeria
5
Laboratory of Materials LABMAT, Department of Civil Engineering, ENPO Maurice Audin, BP1523, El Mnaouer, Oran 31000, Algeria
6
IMT Nord Europe, Institut Mine-Télécom, Centre for Materials and Process, F-59000 Lille, France
7
Laboratory of Civil Engineering and Geo-Environment, University of Lille, ULR 4515—LGCgE, F-59000 Lille, France
*
Authors to whom correspondence should be addressed.
Buildings 2025, 15(6), 886; https://doi.org/10.3390/buildings15060886
Submission received: 3 February 2025 / Revised: 5 March 2025 / Accepted: 10 March 2025 / Published: 12 March 2025
(This article belongs to the Topic Green Construction Materials and Construction Innovation)
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Abstract

This study focuses on the use of dredged sediment (SD) from the dam for the synthesis of a geopolymer. The samples investigated in this work were prepared by mixing micronized and calcined sediment and ground granulated blast furnace slag (GGBFS), at different percentages (10%, 20%, 30%, 40%, and 50%). Furthermore, the influence of the molarity of the NaOH solution, which was used as an activator, as well as the impacts of the (SD/GGBFS) and (SiO2/Al2O3) ratios, and the use of different activator solutions, were also examined. In addition, the effects of the curing temperature and porosity were explored The results revealed that among the NaOH concentrations studied (6M, 8M, 10M, 12M, and 14M), 12M was identified as the optimal concentration, and the optimum SD/GGBFS ratio was 70/30. In addition, variation of the ratio (SiO2/Al2O3) allowed the identification of specific proportions for different binders. Indeed, a ratio (SiO2/Al2O3) equal to 4.45 offered an optimum compressive strength of 24.86 MPa, which is significantly higher than the 13.7 MPa obtained for the geopolymer based on sediment with a SiO2/Al2O3 ratio of 3.12 and 12M NaOH. Moreover, the curing temperature of 40 °C, for a period of 48 h, gave a mechanical strength value that was higher than that obtained at room temperature. Similarly, the optimal formulations led to a significant reduction in total porosity, especially when the molarity of the NaOH solution was high, with a GGBFS percentage of 30% achieving an optimal porosity value of 12.5%. Likewise, the X-ray diffraction, infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses confirmed the formation of geopolymers with a compact structure, which paves the way for the development of innovative and sustainable eco-construction materials with a low-carbon footprint.

1. Introduction

In the face of current environmental concerns, cement production is one of the most polluting industrial sectors, and in fact poses major environmental challenges, such as the over-exploitation of natural resources and considerable greenhouse gas emissions. Indeed, it has been reported that the production of one ton of cement requires on average around 1.7 tons of raw materials [1], which directly generates around 0.8 tons of CO2 which is launched into the atmosphere [2]. It should be highlighted that the cement industry consumes a significant amount of fossil fuels, accounting for around 12–15% of the energy consumption of all industrial sectors. Furthermore, on a global scale, the production of ordinary cement (OC), due to its clinker content, results in the release of 1.35 billion tons of greenhouse gases per year, representing between 6% and 9% of the planet’s CO2 emissions [3].
Another worrying environmental issue concerns waste management, particularly waste from dam maintenance work. Most of Algeria’s dams have been affected by the reduction in storage capacity due to silting; therefore, dredging operations are carried out on a regular basis and large volumes of sludge are extracted and stored in settling areas. The storage of dredged sediments in settling basins poses challenges because of the cost of constructing these basins and also due to the large surface areas that these structures require for their installation [4]. These dredged sediments are often composed of clay, limestone, and silt.
In order to reduce the environmental impact of cement, a number of research projects have looked at the formulation and use of alternative binders, such as geopolymers or activated binders. Studies have shown that binders based on various mineral wastes, such as sediments and granulated blast furnace slag, can be a sustainable solution that can certainly help to reduce the environmental and socio-economic impact of the production of construction materials. Geopolymers are aluminum silicate-based cementitious materials formed through a polycondensation reaction in an alkaline medium [5,6,7,8]. In this regard, Mehsas et al. [9] synthesized a geopolymer mix, using three ratios of (metakaolin (MK)/ground granulated blast furnace slag (GGBFS), i.e., 50/50, 80/20, and 100/0 by weight. They also used activating solution (Na2SiO3·nH2O), with densities equal to 1.3 and 1.4, and found that the best performance of the synthesized geopolymer was obtained for an activator density of 1.4 and a GGBFS content of 20%. Moreover, they observed that the mechanical strength of the geopolymer increased with curing time. Youssef et al. [10] studied the possibility of reusing wastes of bricks (BW) for the mix design of new geopolymer bricks. They concluded that the best compressive and flexural strength was obtained for a mix (GGBFS/BW) ratio of 80/20, a (sodium silicate/sodium hydroxide) ratio of 2, and a molarity of the NaOH solution of 8 M. In another study, Youssef et al. [11,12] compared seven formulations of geopolymer bricks with traditional, fired bricks, and concluded that clay-based geopolymer bricks exhibited better performance, with a compressive strength of 20 MPa, a reduction in CO2 emissions of up to 55% compared to fired bricks, and a cost saving of 5%.
The activation and curing parameters play a crucial role in the synthesis and performance of geopolymers. Factors such as the type and concentration of the alkaline activator, the curing temperature, and the raw material composition significantly influence the mechanical properties, durability, and microstructural development of geopolymer materials. Understanding these parameters is essential for optimizing geopolymer formulations and tailoring them for specific applications, including construction and 3D printing.
Furthermore, Youssef et al. [13] explored a new approach to manufacturing clay-based geopolymers for 3D printing applications, and successfully demonstrated that a clay-based geopolymer can replace cement mortar in this process. Moungam et al. [14] developed geopolymer formulations using rice husk ash (RHA) combined with sodium hydroxide (NaOH) as an activating solution. Their study demonstrated that the RHA-NaOH gel could effectively replace the conventional Na₂SiO₃ activator in the geopolymerization process, offering similar or even superior properties. The characteristics of this gel are similar or even better than those of commercial Na2SiO3. Likewise, Kejkar et al. [15] conducted a study to examine the effect of the curing temperature of geopolymer bricks based on fly ash and fired clay. They suggested that the desired compressive strength was obtained with a 4 M alkaline solution, at a curing temperature of 400 °C. Rezzoug et al. [16] synthesized geopolymers derived from sanitary ceramic waste. By optimizing the curing temperatures (60, 80, and 100 °C) and the NaOH concentrations (10 and 16 M), they achieved a compressive strength of up to 11.25 MPa and a significant reduction in porosity. However, they highlight that for a high alkali concentration, the thermal stability of the prepared samples decreased in the long term.
Furthermore, a number of studies have investigated various geopolymer optimization methods, focusing on the effect of sediment calcination and using different materials and activators. In this context, Ferone et al. [17,18] investigated the effect of calcination on sediments from southern Italy, at temperatures ranging from 400 to 750 °C. They also reported that higher temperatures helped to improve the polycondensation and mechanical strength of the samples. Molino et al. [19] reported that the use of a sodium aluminate solution as an activator reduces the calcination temperature to 650 °C and optimizes the mechanical properties of geopolymers. Merabtene et al. [20] synthesized a geopolymer binder from Algerian kaolin and dam sediments, then showed that better mechanical performances could be obtained after calcination at 800 °C. Likewise, Mostefa et al. [21] demonstrated that calcination for 5 h, with an 8 M NaOH solution, optimized the mechanical performance of geopolymers based on sediments from the dam of Fergoug located in the Wilaya of Mascara, in Algeria. On the other hand, Lirer et al. [22] demonstrated that the addition of fly ash to dredged marine sediments enhanced the mechanical properties of the material obtained, and classified it as non-hazardous. Regarding Karam et al. [23], they reported that the replacement of slag with sediments delays the initiation of alkaline activation in the short term. However, this effect diminishes after 28 days. It should be highlighted that a low water-to-solid ratio causes the mechanical resistance to decline. In addition, Hosseini et al. [24] showed that mechanical-chemical activation strengthened the chemical bond between particles, reduced pore surface area, and increased compressive strength, for a substitution rate of fly ash by sediment up to 25%. Similarly, Mahfoud et al. [25] conducted a study showing that the replacement of fly ash with sediment enhances the mechanical performance of the geopolymer, even at high substitution percentages, and results in a decrease in pore diameter. These encouraging findings open promising avenues for the optimization of geopolymers, with the aim of developing sustainable and high-performance construction materials.
On the other hand, Mahfoud et al. [26] examined the effect of carbonation on the mechanical and microstructural properties of geopolymers based on fly ash and dredged sediment. A number of tests were then carried out and the results showed that accelerated carbonation (CO₂ concentration of 3%) produced carbonates (nahcolite, natron, and calcite) that densified the matrix, reduced porosity, and significantly improved the mechanical strength by more than 200% for certain mixtures.
This innovative study explores the use of dredged sediment, an abundant waste material, for geopolymer synthesis, with a focus on optimizing formulations while promoting sustainability and the circular economy. Unlike previous research that relies on high curing temperatures, this study employs reduced curing conditions (40 °C and 20 °C), lowering the energy footprint and enhancing applicability under real construction site conditions. The research aims to develop high-performance geopolymers by incorporating other mineral wastes, such as granulated blast furnace slag, to improve mechanical properties and durability.
The approach involves using locally sourced waste materials, including sludge from the Bouhanifia dam in the Wilaya of Mascara and granulated blast furnace slag, to define optimal geopolymer formulation conditions. To enhance material reactivity, the sediment was calcined before use. The study investigates the impact of different NaOH molarities on mechanical properties, the influence of slag addition while varying the (CaO/SiO2) ratio, and the effect of modifying the (SiO2/Al2O3) weight ratio by incorporating sodium silicate (Na2SiO3) in the activating solution. Additionally, the effects of curing temperature (40 °C and 20 °C) on geopolymer formation and compressive strength were examined. The optimal formulations were further characterized using mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).
This study demonstrates that the optimal mechanical performance and lowest porosity in sediment-based geopolymers were achieved using sodium silicate combined with 12 M NaOH and a 30% substitution of sediment with GGBFS. Additionally, thermal curing at 40 °C for 48 h further enhanced strength. These findings underscore the potential of dredged sediment as sustainable raw materials for geopolymer binders in civil engineering.

2. Materials and Test Methods

2.1. Materials

The materials used in this experimental study were dredged sediment (SD), standardized sand, and ground granulated blast furnace slag (GGBFS). This sediment came from the dam of Bouhanifia which is located in the commune of Bouhanifia, in the Wilaya of Mascara. This sediment was dried in an oven at 105 °C, with mass measurements taken every 24 h until stabilization, meaning that the mass difference between two consecutive measurements was zero. Once drying was complete, the sediment was pre-ground using a cutter, then further refined in a grinder until a very fine powder was obtained. Finally, this powder was sieved through an 80 µm in order to obtain a fairly fine powder and, therefore, to improve its reactivity [27,28]. Afterwards, the resulting product was then calcined at 750 °C, for 5 h. This temperature was chosen based on the thermogravimetric analysis (Figure 1), while the calcination time was determined on the basis on the results reported in previous research works [21].
The GGBFS was supplied by the Hadjar-Soud cement plant, located in the Wilaya of Skikda (east of Algeria). The CEN standardized silica sand, compliant with [29], with a grain size of 0/2, was used as aggregate for the manufacture of several geopolymer specimens.
Furthermore, three distinct alkaline solutions were used as alkaline activating solutions (AS):
  • The first component was NaOH granules with a purity of 98%, supplied by HEX-Static. These granules were dissolved in demineralized water to prepare NaOH solutions of different concentrations (6M, 8M, 10M, 12M, and 14M).
  • The second solution was a mixture of sodium silicate and sodium hydroxide, with a concentration of 12 M (Na2SiO3 + NaOH 12 M) and a mass ratio (silicate/hydroxide) equal to 2 (S/H = 2).
  • The third one was composed only of sodium silicate (Na2SiO3), which was supplied by the company Sarl Ginie Chimie, with the following proportions: SiO2 = 28.3%, Na2O = 14.85%, and H2O = 56.75% (% by weight).

2.1.1. Specific Surface Area and Density of Raw and Calcined Sediment, and GGBFS

The specific surface area and density of three powders, namely raw sediment (SD), calcined sediment (calcined SD), and ground granulated blast furnace slag (GGBFS), were measured; they are presented in Table 1. In addition, the density of solid particles was determined using a water pycnometer. The basic principle consists of measuring the volume using the pycnometer, and to obtain the mass of solid particles by weighing, in accordance with the [30]. The specific surface area was evaluated using a fineness determination method, in accordance with the [31]. The values of the specific surface area of raw sediment (SD) and calcined sediment (calcined SD) were, respectively, found equal to 24.031 m2/g and 24.755 m2/g. These values are in conformity with the conditions required for geopolymer formulation. The specific surface area is required to be between 16 and 29 m2/g [32,33,34].

2.1.2. Particle Size Distribution of the Materials

The particle size distribution of raw dredged sediment and that of the calcined sediment used in our study were determined using a Mastersizer V3.81 laser granulometer. The principle of this particle size analyzer is based on the diffraction of a laser beam by the suspended particles. This particle size analysis was carried out at the laboratory of the Lafarge Holcim Cement Plant, in the Wilaya of M’sila, in Algeria. The fine particle sizes of raw sediment (SD) and calcined sediment (SD CAL), ranging from 0.3 μm to 100 μm, as shown in Figure 2, improved the mineral activity and facilitated the geopolymerization process.

2.1.3. Chemical Composition of Solid Materials

The information on the chemical composition of raw sediment, calcined sediment, and ground granulated blast furnace slag (GGBFS) is presented in Table 2. These data were obtained by energy dispersive X-ray fluorescence spectrometry, using the Bruker S8 TIGER spectrometer. The technique adopted allows for an accurate determination of the chemical composition of SD, SD CAL, and GGBFS used in the formulation of geopolymers. The analysis of raw sediment (SD) revealed a SiO2 content of 42.34% and an Al2O3 percentage of 13.59%, with a weight ratio (SiO2/Al2O3) of 3.11. After calcination, the chemical analysis of the calcined sediment revealed silica and alumina contents of 46.23% and 16.18%, respectively, for a weight ratio of approximately 2.86. On the other hand, it was found that GGBFS mainly consisted of 41.3% SiO2 and 11.8% Al2O3, with a remarkable proportion of calcium oxide (CaO) of 18%. This high CaO content could contribute to improving the mechanical properties of geopolymers, especially by enhancing their compressive strength [35].

2.1.4. X-Ray Diffractometry

The three powders, i.e., SD, SD CAL, and GGBFS, were characterized by X-ray diffraction (XRD) using a Bruker D4 Endeavor X-ray diffractometer that uses CuKα radiation. The diffractograms were recorded over a 2θ range of 5° to 70° with a step size of 0.008°, in order to identify the existing mineralogical phases (Figure 3). The approach adopted here was selected so as to obtain high-quality diffractograms, and achieve usable and accurate results during the analysis of the mineral phases. Based on the above, the bulk sediment (BS) exhibited three dominant phases: silicates (14.82% silica), carbonates (25.9% calcite), and clays (8.66% kaolinite, 1.18% albite, 5.87% muscovite, and 30.91% illite). After heat treatment at 750 °C, calcite, illite, and kaolinite disappeared, giving rise to amorphous phases, along with the appearance of new minerals, such as gehlenite and rankinite (Figure 3). These changes occurred as a result of thermal reactions between calcium oxide (CaO), silicon oxide (SiO2), and aluminum oxide (Al2O3) present in the materials [20].
Likewise, the XRD patterns of GGBFS, which are shown in Figure 4, indicate the presence of an amorphous hump in the XRD spectrum, between 25° and 35°, which confirms the existence of a significant amount of glass [36].

2.1.5. Fourier Transform Infrared Spectroscopy

Fourier transform infrared spectroscopy (FTIR) was also used to identify the functional groups and analyze the structural modifications of raw sediment, calcined sediment, and ground granulated blast furnace slag (GGBFS), as illustrated in Figure 5. This FTIR analysis was performed using a Bruker spectrophotometer, in absorbance mode, covering a wavenumber range from 4000 to 400 cm⁻1. FTIR measurements were conducted at the Chemistry Laboratory of the University of Tlemcen, Algeria. The results revealed the presence of functional groups, such as Si–O–Al, Si–O–Si, and O–H, in the raw materials (raw and calcined sediment). The presence of quartz in raw and calcined sediment was confirmed by the presence of symmetrical bending vibrations of the Si–O bonds that were observed around 695 cm⁻1 (Figure 5) [37]. In addition, a broad band centered at 1443 cm⁻1, corresponding to the vibrational stretching of the carbonate groups present in calcite, was also detected in the raw sediment [21]. Furthermore, a band centered on 3696 cm⁻1, attributed to the stretching of hydroxyl groups (O–H) of the internal surface, was also observed [21,38]. The presence of this last band and that at 798 cm⁻1 indicates that the studied sediment contained kaolinite [21]. Furthermore, FTIR analysis highlighted not only the minerals present, but also the degradation or transformation of the crystalline structure after calcination, which is crucial for understanding the chemical reactions involved in the geopolymerization processes and the enhancement of mechanical properties

2.2. Geopolymer Mix Design

Geopolymers were prepared by mixing solid precursors in a weight ratio of 50% standardized sand and 50% aluminosilicate source. The aluminosilicate source consisted either of sediment alone or a mixture of sediment and granulated blast furnace slag (GGBFS). All mixing ratios, including those in Table 3, are expressed by weight. For this, (SD)n(GGBFS)m formulations were prepared. These formulations consisted of sediment and slag, with n representing the percentage of sediment (SD) (n = 100, 90, 80, 70, 60, and 50%) and m corresponding to the percentage of slag (GGBFS) (m = 0, 10, 20, 30, 40, and 50%). Note that GGBFS, which is rich in aluminosilicates, was incorporated into the geopolymers in order to increase the mechanical strength and enhance the development of this strength at room temperature [39]. Moreover, the activation solutions (AS) were used with the aim to improve the geopolymerization process and enhance the formation of geopolymeric gels, due to the high reactivity of the activation solution and the rapid dissolution of the raw materials as well [40]. For the purpose of achieving a homogeneous mixture, the solid materials were dry-mixed, manually for 10 min, before the alkaline solution was added. The resulting mixture was then put into an auto-mortar mixer (Controlab Equipment company- Saint-Ouen-l’Aumône, France) with a capacity of 5 L, set at a variable rotational speed, with 1 min at low speed and 4 min at high speed. The liquid/solid (L/S) ratio was maintained at 0.85 by weight, where L represents the mass of the alkaline activation solution (AS) and S corresponds to the mass of the aluminosilicate source. The resulting mixture was used for the preparation of nine cylindrical samples for each formulation, using molds of dimensions (26 × 52) mm2. These samples were then placed in an oven for 48 h at curing temperatures of 40 °C and 20 °C. Once demolded, the samples were kept at room temperature until their compressive strength test at different ages (7, 14, and 28 days). This number of samples was selected to ensure reproducibility of the results, with three samples per formulation and age. The final results obtained correspond to the average of the values obtained from these tests.
It is worth emphasizing that, in this study, four main parameters were taken into consideration during the formulation of geopolymers. These are as follows:
  • The molar concentration of NaOH;
  • The amount of added GGBFS and the (SD/GGBFS) ratio;
  • The (SiO2/Al2O3) ratio (in the presence of sodium silicate);
  • The curing temperature of geopolymer mortars at early age.
These four factors were then analyzed to assess their impact on the mechanical performance of the prepared geopolymers, particularly their compressive strength.
  • SD-NaXM with (X = 6, 8, 10, 12, 14): geopolymer based on (100% sediment), with X representing the concentration of the NaOH activator solution and the 40 °C/48 H cure.
  • SDnGGBFSm with n = 90, 80, 70, 60, 50 and m = 10, 20, 30, 40, 50: geopolymer based on sediment and slag, with n and m representing the percentage of sediment and slag, respectively, the NaOH activator solution with a concentration of 12M, and the 40 °C/48 h cure.
  • SDnGGBFSm-1 with n = 100, 90, 80, 70, 60, 50 and m = 0, 10, 20, 30, 40, 50: geopolymer based on sediment and slag, with n and m representing the percentages of sediment and slag, respectively, the activator solution based on (Na2SiO3 + NaOH 12M), and the cure 40 °C/48 h.
  • SDnGGBFSm-2 with n = 100, 90, 80, 70, 60, 50 and m = 0, 10, 20, 30, 40, 50: geopolymer based on sediment and slag, with n and m representing the percentages of sediment and slag, respectively, the activator solution based on Na2SiO3, and the cure 40 °C/48 H.
  • SDnGGBFSm-3 with n = 100, 90, 80, 70, 60, 50 and m = 0, 10, 20, 30, 40, 50: geopolymer based on sediment and slag, with n and m representing the percentages of sediment and slag, respectively, the Na2SiO3-based activator solution, and the 20 °C/48 H cure.

2.2.1. Synthesis of Geopolymers with Different NaOH Concentrations (SD-NaXM)

The NaOH concentration in the activation solution is a crucial factor as it directly affects the geopolymerization process [41]. In this study, NaOH molarities ranging from 6 M to 14 M were investigated to optimize the dissolution of the aluminosilicate source (Table 3) and evaluate their impact on the compressive strength of geopolymer mortars with a (Ca/Si) ratio of 0.33. The samples were exclusively prepared using calcined sediment as the aluminosilicate source, combined with standardized sand. The mixtures were then molded into cylindrical specimens (26 × 52 mm2) while maintaining a fixed solution-to-binder mass ratio of 0.85. The primary objective of this approach was to assess the influence of the NaOH concentration on the mechanical properties of geopolymers.

2.2.2. Synthesis of Geopolymers with the Addition of GGBFS and Optimization of the (SD/GGBFS) Ratio

Optimization of the (SD/GGBFS) ratio, in the formulation of geopolymers, was achieved by measuring the variation in the compressive strengths as a function of this ratio, while varying the (Ca/Si) ratio between 0.21 and 0.38. The tests were carried out on cylindrical specimens of dimensions (26 × 52) mm2, using the second activation solution that was composed of Na2SiO3 and 12M NaOH, with a mass ratio (Na2SiO3/NaOH) of 2, and the third activation solution that contained only sodium silicate (Na2SiO3), as indicated in Table 3.
On the other hand, Nath et al. [42] conducted a study to show that the addition of calcium, which is present in the granulated blast furnace slag, plays a crucial role in the geopolymerization process. It was indeed found that calcium promotes the formation of intermediate phases, thus significantly increasing the compressive strength of geopolymers following reactions between calcium compounds and the geopolymer binder.

2.2.3. Synthesis of Geopolymers with an Optimized (SiO2/Al2O3) Ratio, with the Presence of Sodium Silicate in the Activator Solution

For each binder formulation (SD100, SD90GGBFS10, SD80GGBFS20, SD70GGBFS30, SD60GGBFS40, and SD50GGBFS50), a particular weight ratio (SiO2/Al2O3) was determined. This ratio varied according to the composition of the selected formulation. The ratio (SiO2/Al2O3) was adjusted by gradually adding sodium silicate into the activation solution. For each formulation, three cylindrical specimens of dimension (26 × 52) mm2 were prepared in order to conduct the compressive strength tests at different ages of 7, 14, and 28 days, with the aim of assessing the evolution of mechanical performances over time.
The results presented in Table 3 show that the ratio (SiO2/Al2O3) ranges from 3.12 to 5.19. This ratio is very important in the geopolymerization process, in the formation of the three-dimensional network of aluminosilicate bonds, as well as in the final microstructure of the material [43,44].

2.2.4. Influence of Curing Temperatures on Geopolymer Synthesis

The compressive strength of geopolymers can reach up to 70% of its maximum value within the first four hours after their placement. However, conventional concrete can attain that level of strength after several days [45]. The choice of the curing temperature is highly important because it allows acceleration of the geopolymerization process. It is important to specify that the curing temperature has a direct influence on the development of the compressive strength of geopolymers. In addition, it was revealed that increasing the curing temperature, with a prolonged application time, can significantly improve the compressive strength of geopolymers [46].
Two curing temperatures were used in this study. The first one was 40 °C, applied for 48 h before the demolding of the cylindrical specimens, and the second, 20 °C (room temperature), was applied for the same duration. This adopted approach aimed to assess the impact of the curing temperature on the hardening of geopolymer materials and on the geopolymerization process as well. It also allowed for a better understanding of the effect of curing temperature on the mechanical properties of geopolymers.

2.3. Test Method

2.3.1. Compressive Strength

A number of compressive strength tests were performed on cylindrical samples of dimensions (26 × 52) mm2, at different ages (7, 14, and 28 days). These tests were performed by means of a PA Hilton Ltd HSM44 mechanical press (Andover, Hampshire, United Kingdom) that is capable of supporting a maximum load of 50 kN. It should be noted that these tests were conducted with the purpose to monitor the evolution of the mechanical properties of the samples over time, and to determine the optimal formulation for each preparation scenario by varying the NaOH molarity, the ratio (SD/GGBFS), the ratio (SiO2/Al2O3), and the curing temperature. The method used here aimed to optimize the mechanical performance of geopolymers by identifying the most important parameters for their hardening.

2.3.2. Mercury Porosity

It was revealed that porosity is an essential factor that must be taken into account in order to ensure the durability of the prepared materials. Indeed, porosity has a direct influence on their permeability and their interactions with the external environment. Moreover, excessive porosity can lead to increased vulnerability to aggressive agents, thus reducing the durability of geopolymers. Therefore, in addition to the evaluation of mechanical performance, it is also essential to characterize the pore size distribution in mortar samples. This characterization is performed on fragments of the selected optimal formulations dried at 40 °C, using a Micromeritics Autopore V 9600 Porosimeter, manufactured by Micromeritics Instrument Corporation, headquartered in Norcross, GA, USA, in accordance with [47]. This analysis provides valuable information on the internal structure of the materials, including size, shape, and connectivity between pores.

2.3.3. Geopolymer Microstructure

The five optimal formulations of geopolymers (SD-Na12M, SD70GGBFS30, SD70GGBFS30-1, SD60GGBFS40-2, and SD60GGBFS40-3) were characterized by XRD, FTIR, and SEM techniques. Scanning electron microscopy (SEM) was carried out by means of a Hitachi S-4300SE/N microscope, manufactured by Hitachi High-Technologies Corporation, headquartered in Tokyo, Japan to achieve a detailed analysis of the morphology of the geopolymers.

3. Results and Discussion

3.1. Compressive Strength

3.1.1. Effect of NaOH Molarity on the Compressive Strength of Geopolymers

Figure 6 depicts the effect of NaOH solution molarity (6M, 8M, 10M, 12M, and 14M) on the compressive strength of geopolymers. It is observed that the maximum strength of 13.7 MPa was obtained for the NaOH concentration of 12 M. This strength value of 13.7 MPa is comparable to, and sometimes even higher than, that reported by several other research teams [15,19,21]. The minimum strength value of 7.4 MPa was found for a molarity of 6 M. The intermediate molarities 8M, 10M, and 14M produced moderate strengths, respectively, equal to 9.8, 11.5, and 10.7 MPa. The slight decrease in strength observed at 14M can be attributed to the excessive concentration of NaOH, which disrupts polycondensation by promoting the formation of soluble secondary products and limiting the growth of the geopolymeric network. This may also lead to a loss of workability, affecting the overall microstructure and mechanical properties of the material. These findings indicate that the NaOH concentration has a significant influence on the mechanical strength of geopolymers. They also confirm the role of the activating solution as well. Indeed, it was found that increasing the NaOH molarity accelerates the geopolymerization process, which may certainly be attributed to the more efficient dissolution of aluminosilicate minerals in the solution. This does in fact facilitate the formation of a greater number of oligomers [48], and consequently leads to an increase in the compressive strength.

3.1.2. Effect of the (SD/GGBFS) Ratio

Figure 7 illustrates the evolution of the compressive strength as a function of the ratio (SD/GGBFS). It is observed that when this ratio is equal to (90/10), the compressive strength reaches the value 13.75 MPa, with a (CaO/SiO2) weight ratio equal to 0.34, exceeding that of geopolymers containing only sediment (100% SD). In addition, it is noticed that the strength value increases as the percentage of GGBFS in the formulation of sediment-based geopolymers rises. For example, for a (SD/GGBFS) ratio equal to (80/20), with (CaO/SiO2) = 0.35, the strength is 14.26 MPa, and it increases to 14.9 MPa when the (SD/GGBFS) ratio is (70/30), with the (CaO/SiO2) ratio = 0.36. Beyond that ratio value (SD70GGBFS30), the strength value starts to decrease gradually to reach 13.7 MPa, with (CaO/SiO2) = 0.38, for a (SD/GGBFS) ratio (50/50). This therefore allows the conclusion that the optimal value of the (SD/GGBFS) ratio is (70/30).
The compressive strength improvement is mainly attributed to the incorporation of GGBFS into the geopolymer matrix. It was revealed that GGBFS acts simultaneously as a cementitious binder and a geopolymer binder. Furthermore, the calcium oxide (CaO) content in the GGBFS plays a crucial role in improving the mechanical properties of the cured geopolymer [1]. This contributes significantly to the performance enhancement of the specimens under study.

3.1.3. Effect of the (SiO2/Al2O3) Ratio, in the Presence of Sodium Silicate

Figure 8A,B present the results of the compressive strength investigations. A maximum strength of 24.86 MPa was obtained for the geopolymer (SD70GGBFS30-1) that is characterized by a mass ratio equal to 4.45, a (CaO/SiO2) ratio of 0.26, and an activating solution (AS) composed of Na2SiO3 and NaOH 12M. This compressive strength is very close, and even similar, to those previously reported in other research works [22,27]. The mechanical test results also indicate a progressive mechanical compressive strength increase, between 7 and 28 days of curing. This progression depends on the type of binder used and the ratio (SiO2/Al2O3). These findings corroborate those reported in the literature [49,50,51,52]. In this regard, Davidovits [53] recommends a (SiO2/Al2O3) ratio between 3.5 and 4.5 for the synthesis and improvement of geopolymers, while Kioupis [51] points out that the addition of silica in sufficient quantity enhances the mechanical strength. As for Duxson et al. [50], they assert that the additional silicon ions promote the formation of the geopolymer matrix, although an excess of silica can have an adverse effect because it can restrain the dissolution of the aluminosilicate precursor [51].

3.1.4. Curing Temperature of Geopolymer Mortars

The temperature applied for 48 h before demolding the specimens, at 20 °C (room temperature) and 40 °C, had a significant impact on the formation of geopolymers. With an activation solution prepared from sodium silicate (AS), formulation 21, as shown in Table 3, displays a compressive strength of 21.2 MPa after a curing temperature of 40 °C, and a maturation of 28 days. This strength is significantly higher than that of the geopolymer corresponding to formulation 27, which was subjected to curing at 20 °C, and which exhibits an acceptable strength of 16.24 MPa, as depicted in Figure 9.
The above findings suggest that a curing temperature above 20 °C accelerates the polymerization reaction, which promotes faster hardening of the geopolymer material. This is particularly beneficial in applications where a short curing time is required, as it allows the reaching of optimal mechanical strength values more quickly. In addition, previous research has also demonstrated that using a 40 °C curing temperature contributes to obtaining dredged sediment-based geopolymers with good mechanical properties [20].

3.2. Mercury Intrusion Porosimetry

Mercury intrusion porosimetry (MIP) was performed for two series of formulations.
Formulations with the best mechanical strengths.
  • Formulations with activation solution (Na2SiO3 + NaOH 12M). A mass ratio (silicate/hydroxide) equal to 2 was employed for the formulations (SD100GGBFS0-1), (SD90GGBFS10-1), (SD80GGBFS20-1), (SD70GGBFS30-1), (SD60GGBFS40-1), and (SD50GGBFS50-1). The total porosity percentages were measured and found equal to 14.00% for (SD100-1), 13.2% for (SD90GGBFS10-1), 14.40% for (SD80GGBFS20-1), 12.50% for (SD70GGBFS30-1), 14.60% for (SD60GGBFS40-1), and 16.2% for (SD50GGBFS50-1), as shown in Figure 10.
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Figure 10. Pore size distributions of formulations with different (Si/Al) ratios, with the activation solution (Na2SiO3 + NaOH 12M).
Figure 10. Pore size distributions of formulations with different (Si/Al) ratios, with the activation solution (Na2SiO3 + NaOH 12M).
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Formulations with the lowest mechanical resistances.
  • Formulations with various NaOH molarities. The formulations studied include (SD-Na6M), (SD-Na8M), (SD-Na10M), (SD-Na12M), and (SD-Na14M). The total porosity percentages for the different formulations are 29.7% for (SD-Na6M), 24.3% for (SD-Na8M), 24.5% for (SD-Na10M), 24.03% for (SD-Na12M), and 24.60% for (SD-Na14M), as shown in Figure 11. It is worth noting that for the formulations with different NaOH molarities, the total porosity remains relatively stable for concentrations ranging from 8M to 14M (Figure 11). In contrast, formulations using the activating solution (Na2SiO3) exhibit some variation in porosity of approximately (±2%) between formulations, with a minimum of 12.5% for (SD70GGBFS30-1), which corresponds to an optimum compressive strength of 24.86 MPa, after 28 days (Figure 10).
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Figure 11. Pore size distributions of formulations with different NaOH molarities.
Figure 11. Pore size distributions of formulations with different NaOH molarities.
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Furthermore, Figure 12 illustrates the pore size distributions of the formulations using different NaOH molarities. It is worth highlighting that two pore sizes were identified for each formulation which correspond to the dominant pore size distributions, i.e., 40 µm and 0.05 µm for (SD-Na6M), 35 µm and 0.04 µm for SD-Na8M, 25 µm and 0.032 µm for (SD-Na10M), 26 µm and 0.05 µm for SD-Na12M, and 28 µm and 0.07 µm for (SD-Na14M). Beyond 8 M, the increase in NaOH molarity induced a decrease in the peak of fine porosity (diameter < 0.1 µm) as well as a decline in the size of fine pores.
Figure 13 suggests that the pore diameters for the formulations with activation solution (Na2SiO3 + 12M NaOH) are 18 µm and 0.009 µm for formulation (SD100GGBFS0-1), 19 µm and 0.009 µm for (SD90GGBFS10-1), 20 µm and 0.009 µm for (SD80GGBFS20-1), 27 µm and 0.017 µm for (SD70GGBFS30-1), 24 µm and 0.009 µm for (SD60GGBFS40-1), and finally, 32 µm and 0.05 µm for (SD50GGBFS50-1). As the substitution rate of sediment with granulated blast furnace slag (GGBFS) increases, the fine porosity peak increases, while the size of fine pores decreases.
The porosity, which depends on the diameter of pores, is an indicator of durability. There are four types of porosities: harmless porosity (<20 nm), less harmful porosity (20–50 nm), harmful porosity (50–200 nm), and very harmful porosity (>200 nm) [54]. Figure 11 indicates a reduction in very harmful porosity as the NaOH molarity goes up. Likewise, Figure 10 reveals a pore size decrease as the sediment replacement rate by GGBFS increases up to 30%. This is probably due to the formation of a C-A-S-H geopolymer gel as a result of the presence of calcium in the slag [55,56]. For a substitution rate beyond 30%, the pore size increases. Hence, E. Mahfoud et al. [25] found almost identical results by replacing sediments with fly ash in the synthesis of geopolymers. Figure 14 and Figure 15 show the critical pore diameters as well as the pore size distribution for the optimal formulations. The 30% substitution rate of sediment with GGBFS reduces the most harmful pore diameters (>1000 nm), which is attributed to the pozzolanic effect of GGBFS and to its high calcium content. This reduction in total porosity, i.e., 24.07% for (SD-Na12M) and 12.5% for (SD70GGBFS30-1), resulted in a mechanical strength increase, particularly the compressive strength.

3.3. Microstructure and Morphology

3.3.1. X-Ray Diffraction

Figure 16 presents the XRD diffractograms of five optimized geopolymer formulations (SD-Na12M, SD70GGBFS30, SD70GGBFS30-1, SD60GGBFS40-2, and SD60GGBFS40-3) after 28 days of curing. The results regarding the observed crystalline phases, especially quartz (SiO2), are in agreement with those reported in several studies found in the literature [57,58]. The recorded spectra show that quartz, which is present in the calcined sediment (Figure 3), remained unchanged after the geopolymerization process, suggesting that this process was mainly due to the amorphous phase of the aluminosilicate source [27,59]. Indeed, many researchers have confirmed that geopolymer binders result from the curing of an amorphous aluminosilicate gel [60,61]. Moreover, the presence of a calcite peak (CaCO3) in the optimal formulations is attributed to the calcium content of the sediments. The calcium content was particularly increased after the addition of blast furnace slag, which enhanced the mechanical strength of geopolymers [55,62]. Furthermore, the XRD analysis suggests the presence of rankinite (Ca3Si2O7) and gehlenite (Ca2Al2SiO2), which typically appear in calcium-rich geopolymers. Similarly, the XRD diffractograms revealed the coexistence of the hydrated phases of sodium aluminum silicate (N-A-S-H) and calcium aluminum silicate (C-A-S-H), especially in the case of the (SD70GGBFS30-1) formulation, due to the high rate of substitution of sediments with slag. The amorphous phases, especially (C-A-S-H) and (N-A-S-H), which are more abundant in the (SD70GGBFS30-1) formulation, explain the superior compressive strength of this formulation quite well [28].
It is worth highlighting that these phases are poorly visible on the DRX diffractograms due to the high presence of quartz due to the addition of standardized sand and the high crystalline quartz content in these geopolymer formulations.

3.3.2. Fourier Transform Infrared Spectroscopy

Figure 17 displays the Fourier transform infrared spectrometry (FTIR) results, in transmission mode, of the five optimal geopolymer formulations (SD-Na12M, SD70GGBFS30, SD70GGBFS30-1, SD60GGBFS40-2 and SD60GGBFS40-3) after 28 days. The band observed at 470 cm⁻1 corresponds to the bending vibration of the Si-O-Si and O-Si-O bonds. In addition, the broad band at 3445 cm⁻1, accompanied by the band at 1645 cm⁻1, indicates the presence of geopolymerization products associated with the vibrations of the H-OH groups [59], thus signaling the presence of H2O molecules in the geopolymers.
In addition, the band at 1445 cm⁻1, which is attributed to the functional group (O-C-O), suggests the presence of the carbonation phenomenon, which is confirmed by the existence of calcite in the geopolymer, and is also corroborated by the X-ray diffraction analysis [63]. Likewise, the interval between 1350 and 800 cm⁻1 corresponds to the asymmetric stretching vibration mode of T-O-T bonds (where T denotes tetrahedral Si or Al) [64]. Furthermore, the band observed at 990 cm⁻1 represents the Si-O-T vibrations that are associated with the geopolymer network [60]. These nanostructural changes resulted in a shift of the bands to lower wavenumbers at the early stages of the reaction, suggesting the potential formation of an N-A-S-H geopolymer gel [65]. This shift resulted from changes in the Si-O-T bond lengths and angles. These changes were induced by the formation of non-bridging oxygen atoms and the involvement of aluminum in the geopolymer gel network as well [57,66].
In addition, the band at 1055 cm⁻1 underwent a shift to lower wavenumbers over time, suggesting the formation of a more aluminum-rich gel [60]. The detection of a band near 1455 cm⁻1, in different formulations, indicates the presence of an O-C-O functional group and suggests the existence of CO₃2⁻ bonds originating from sodium carbonate [67]. Finally, the band at 687 cm⁻1 is attributed to the presence of quartz, already observed by XRD [24,68]. Thus, the presence of all these FTIR bands indicates the formation of a geopolymer structure.

3.3.3. Scanning Electron Microscopy

Figure 18 and Figure 19 depict the scanning electron microscopy (SEM) photos of (SD-Na12M) and (SD70GGBFS30-1) geopolymers. They show that the grains of these two geopolymers are homogeneously distributed; however, the texture presents pores in the structure of the geopolymers. Further, it was observed that the structure of (SD-Na12M) geopolymer, which is shown in Figure 18A, is less dense than that of (SD70GGBFS30-1) geopolymer, which is depicted in Figure 19A. This can be attributed to the choice of starting materials and the specific activation method employed in the geopolymerization process. In fact, the (SD-Na12M) formulation revealed a low reactivity in the geopolymerization process in the absence of additives, such as slag, which promotes the formation of aluminosilicate gels (N-A-S-H and C-A-S-H). It is important to mention that the lack of uniformity in the matrix of the (SD-Na12M) formulation resulted in the appearance of a greater number of pores and cracks in the (SD-Na12M) geopolymer which were probably caused by the excessive evaporation of water during the curing process at temperature 40 °C, which is not the case for the (SD70GGBFS30-1) geopolymer that is characterized by a fairly dense and homogeneous microstructure, with fewer pores and cracks. The values obtained for the compressive strength confirm these observations quite well.

4. Conclusions

This work aims first and foremost to study the possibility of valorizing sediment from the dredging of the Bouhanifia dam for the formulation and characterization of geopolymers. It also seeks to investigate the effect of replacing sediment with granulated blast furnace slag. In addition, the weight ratio (SiO2/Al2O3) and the curing temperature (40 °C and 20 °C) were varied to determine the optimal ratio (SiO2/Al2O3) and the optimal curing temperature for each binder.
The findings allow us to draw the following conclusions:
  • The molarity of NaOH in the activator solution plays a crucial role in the mechanical strength of geopolymers. Moreover, the NaOH concentration of 12 M turned out to be optimal, as it provided the best compressive strength of the formulations under study. This can be explained by the maximum dissolution of aluminosilicate minerals in the NaOH solution, thus favoring the formation of geopolymers with higher mechanical strength.
  • The substitution of sediment with GGBFS improves the mechanical strength of geopolymers. Moreover, the optimal SD-to-GGBFS ratio in the geopolymer formulation was determined to be 70/30. The improvement in the mechanical performance of geopolymers was essentially due to the presence of calcium oxide which promotes the geopolymerization reaction and strengthens the geopolymer binder.
  • It turned out that, by varying the ratio (SiO2/Al2O3), some specific optimal ratios were found for different types of binders. Indeed, the (Si/Al) ratio of 4.45 was found for the formulation of geopolymer composed of 70% sediment and 30% slag, activated with a Na2SiO3 + NaOH 12M solution, and cured at 40 °C for 48 h, with a compressive strength of 24.86 MPa and a (Ca/Si) ratio of 0.26. Both ratios were optimal for this geopolymer.
  • The curing temperature of geopolymers also has a significant impact on their mechanical strength. In addition, the thermal curing at 40 °C for 48 h produced geopolymers with compressive strength values greater than those of geopolymers cured at room temperature (20 °C), highlighting that the curing temperature accelerates the geopolymerization process and improves the mechanical performance as well.
  • The mercury intrusion porosimetry (MIP) results show that the optimal formulations exhibit low total porosity, especially when using NaOH at high molar concentrations with a GGBFS percentage of 30%. A decrease in total porosity is associated with an increase in mechanical strength.
Finally, the XRD and FTIR analyses confirmed the formation of geopolymers with a clearly defined structure, highlighting the presence of C-A-S-H and N-A-S-H gels. Furthermore, SEM analysis revealed that the geopolymer with the optimal sediment-to-slag ratio exhibited a denser and more homogeneous microstructure, with fewer pores and cracks, which is not the case for the sediment-based geopolymer activated with 12 M NaOH and cured under the same conditions. These results explain its superior mechanical strength. In addition, the addition of slag and sodium silicate promoted the formation of gels and improved the reactivity of the material.
This study provides valuable insights into the key parameters that affect the mechanical and structural properties of sediment-based geopolymers. Sediment from dam dredging can be a source of aluminosilicates in a geopolymer eco-binder, which paves the way for the development of low-carbon and more resistant, sustainable construction materials for various civil engineering applications.

Author Contributions

Conceptualization, M.S.M. and H.M.; methodology, T.A.-D., A.S.B. and W.M.; writing—original draft preparation, M.S.M. and W.M.; writing—review and editing, A.S.B., T.A.-D. and W.M.; visualization, M.S.M., H.M. and W.M.; supervision, A.S.B. and T.A.-D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Thermogravimetric analysis (TGA) of raw sediment (SD).
Figure 1. Thermogravimetric analysis (TGA) of raw sediment (SD).
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Figure 2. Particle size distributions of raw and calcined sediment.
Figure 2. Particle size distributions of raw and calcined sediment.
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Figure 3. X-ray diffraction analysis of raw and calcined sediments (SD and SD CAL).
Figure 3. X-ray diffraction analysis of raw and calcined sediments (SD and SD CAL).
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Figure 4. X-ray diffraction analysis of ground granulated blast furnace slag (GGBFS).
Figure 4. X-ray diffraction analysis of ground granulated blast furnace slag (GGBFS).
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Figure 5. Fourier transform infrared spectrometry (FTIR), in transmission mode, of raw sediment (SD), calcined sediment (CAL SD), and (GGBFS).
Figure 5. Fourier transform infrared spectrometry (FTIR), in transmission mode, of raw sediment (SD), calcined sediment (CAL SD), and (GGBFS).
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Figure 6. Progression of the compressive strength of geopolymers at different NaOH concentrations (6, 8, 10, 12, and 14M) for curing at 40 °C for 48 h.
Figure 6. Progression of the compressive strength of geopolymers at different NaOH concentrations (6, 8, 10, 12, and 14M) for curing at 40 °C for 48 h.
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Figure 7. Progression of compressive strength of geopolymers for different ratios (SD/GGBFS).
Figure 7. Progression of compressive strength of geopolymers for different ratios (SD/GGBFS).
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Figure 8. (A) Progression of compressive strength of geopolymers for different (SiO2/Al2O3) ratios, with the activation solution AS (Na2SiO3 + NaOH 12M). (B) Progression of compressive strength of geopolymers for different (SiO2/Al2O3) ratios, with the activation solution AS (Na2SiO3).
Figure 8. (A) Progression of compressive strength of geopolymers for different (SiO2/Al2O3) ratios, with the activation solution AS (Na2SiO3 + NaOH 12M). (B) Progression of compressive strength of geopolymers for different (SiO2/Al2O3) ratios, with the activation solution AS (Na2SiO3).
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Figure 9. Compressive strength of geopolymers at room temperature (T° = 20 °C).
Figure 9. Compressive strength of geopolymers at room temperature (T° = 20 °C).
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Figure 12. Pore size structures of formulations with different NaOH molarities [µm].
Figure 12. Pore size structures of formulations with different NaOH molarities [µm].
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Figure 13. Pore size structures of formulations with different (Si/Al) ratios, with the activation solution (Na2SiO3 + NaOH 12M).
Figure 13. Pore size structures of formulations with different (Si/Al) ratios, with the activation solution (Na2SiO3 + NaOH 12M).
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Figure 14. Pore size structures of optimal formulations (µm).
Figure 14. Pore size structures of optimal formulations (µm).
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Figure 15. Pore size distributions for the optimal formulations.
Figure 15. Pore size distributions for the optimal formulations.
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Figure 16. DRX analysis of the optimal geopolymer formulations (SD-Na12M), (SD70GGBFS30), (SD70GGBFS30-1), (SD60GGBFS40-2), and (SD60GGBFS40-3).
Figure 16. DRX analysis of the optimal geopolymer formulations (SD-Na12M), (SD70GGBFS30), (SD70GGBFS30-1), (SD60GGBFS40-2), and (SD60GGBFS40-3).
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Figure 17. FTIR spectra of optimal geopolymer formulations (SD-Na12M), (SD70GGBFS30), (SD70GGBFS30-1), (SD60GGBFS40-2), and (SD60GGBFS40-3).
Figure 17. FTIR spectra of optimal geopolymer formulations (SD-Na12M), (SD70GGBFS30), (SD70GGBFS30-1), (SD60GGBFS40-2), and (SD60GGBFS40-3).
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Figure 18. SEM photos of the geopolymer (SD-Na12M).
Figure 18. SEM photos of the geopolymer (SD-Na12M).
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Figure 19. SEM photos of the geopolymer (SD70GGBFS30-1).
Figure 19. SEM photos of the geopolymer (SD70GGBFS30-1).
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Table 1. Absolute density and specific surface area of different powders.
Table 1. Absolute density and specific surface area of different powders.
Density (g/cm3)Specific Surface Area (m2/g)
SD2.5224.031
Calcined SD2.7824.755
GGBFS2.794.863
Table 2. Chemical compositions in weight percent of SD, calcined SD (SD CAL), and GGBFS.
Table 2. Chemical compositions in weight percent of SD, calcined SD (SD CAL), and GGBFS.
CompositionsSiO2Al2O3Fe2O3CaOMgOSO3K2ONa2OTiO2ClL.O.I
SD42.3413.595.77142.640.251.180.50-0.02518.96
Calcined SD46.2316.185.68154.060.183.040.410.680.0136.3
GGBFS41.3011.804.3185.70.100.830.251.660.0014.7
Table 3. Different geopolymer formulations.
Table 3. Different geopolymer formulations.
MixSampleSD
(%)		GGBFS
(%)		ASCure ConditionSiO2/Al2O3 Weight RatioCaO/SiO2
Weight Ratio
1SD-Na6M1000NaOH 6M40 °C/48 h3.120.33
2SD-Na8M1000NaOH 8M40 °C/48 h3.120.33
3SD-Na10M1000NaOH 10M40 °C/48 h3.120.33
4SD-Na12M1000NaOH 12M40 °C/48 h3.120.33
5SD-Na14M1000NaOH 14M40 °C/48 h3.120.33
6SD90GGBFS109010NaOH 12M40 °C/48 h3.150.34
7SD80GGBFS208020NaOH 12M40 °C/48 h3.180.35
8SD70GGBFS307030NaOH 12M40 °C/48 h3.220.36
9SD60GGBFS406040NaOH 12M40 °C/48 h3.260.37
10SD50GGBFS505050NaOH 12M40 °C/48 h3.290.38
11SD100GGBFS0-11000(Na2SiO3 + NaOH 12M)40 °C/48 h4.290.23
12SD90GGBFS10-19010(Na2SiO3 + NaOH 12M)40 °C/48 h4.340.24
13SD80GGBFS20-18020(Na2SiO3 + NaOH 12M)40 °C/48 h4.390.25
14SD70GGBFS30-17030(Na2SiO3 + NaOH 12M)40 °C/48 h4.450.26
15SD60GGBFS40-16040(Na2SiO3 + NaOH 12M)40 °C/48 h4.50.27
16SD50GGBFS50-15050(Na2SiO3 + NaOH 12M)40 °C/48 h4.560.28
17SD100GGBFS0-21000Na2SiO340 °C/48 h4.890.21
18SD90GGBFS10-29010Na2SiO340 °C/48 h4.940.22
19SD80GGBFS20-28020Na2SiO340° C/48 h50.22
20SD70GGBFS30-27030Na2SiO340° C/48 h5.060.23
21SD60GGBFS40-26040Na2SiO340° C/48 h5.120.24
22SD50GGBFS50-25050Na2SiO340 °C/48 h5.190.24
23SD100GGBFS0-31000Na2SiO320 °C/48 h4.890.21
24SD90GGBFS10-39010Na2SiO320 °C/48 h4.940.22
25SD80GGBFS20-38020Na2SiO320 °C/48 h50.22
26SD70GGBFS30-37030Na2SiO320 °C/48 h5.060.23
27SD60GGBFS40-36040Na2SiO320 °C/48 h5.120.24
28SD50GGBFS50-35050Na2SiO320 °C/48 h5.190.24
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MDPI and ACS Style

Mouaissa, M.S.; Marouf, H.; Ali-Dahmane, T.; Benosman, A.S.; Maherzi, W. Effect of Mix Design Parameters on the Properties of Dam Sediment/Slag-Based Geopolymer Mortars. Buildings 2025, 15, 886. https://doi.org/10.3390/buildings15060886

AMA Style

Mouaissa MS, Marouf H, Ali-Dahmane T, Benosman AS, Maherzi W. Effect of Mix Design Parameters on the Properties of Dam Sediment/Slag-Based Geopolymer Mortars. Buildings. 2025; 15(6):886. https://doi.org/10.3390/buildings15060886

Chicago/Turabian Style

Mouaissa, Mohamed Salah, Hafida Marouf, Tewfik Ali-Dahmane, Ahmed Soufiane Benosman, and Walid Maherzi. 2025. "Effect of Mix Design Parameters on the Properties of Dam Sediment/Slag-Based Geopolymer Mortars" Buildings 15, no. 6: 886. https://doi.org/10.3390/buildings15060886

APA Style

Mouaissa, M. S., Marouf, H., Ali-Dahmane, T., Benosman, A. S., & Maherzi, W. (2025). Effect of Mix Design Parameters on the Properties of Dam Sediment/Slag-Based Geopolymer Mortars. Buildings, 15(6), 886. https://doi.org/10.3390/buildings15060886

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