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Variation of flexural and split tensile strengths with compressive strength of GPC. [Colour online.]
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Use of ordinary portland cement contributes to environmental deterioration by releasing enormous quantities of CO2. To reduce use of cement, this research focuses on preparation of solely ground granulated blast-furnace-slag-based geopolymer binder, activated by a combination of sodium hydroxide and sodium metasilicate cured under ambient temperatu...
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Autoclaved aerated concrete (AAC) is one of the most common types of lightweight cellular concrete, having a density of approximately one-fourth of that of conventional plain cement concrete. The use of industrial waste materials in concrete as a replacement for cement has garnered a lot of attention in recent years as a way to reduce the environme...
The primary goal of the present research is to look into the rheological, mechanical as well as microstructural characteristics of flyash based self-compacting geopolymer concrete (SCGPC) comprised of the combination of fly ash and ground-granulated slag from blast furnaces (GGBS), that is cured at room temperature. GGBS is incorporated together wi...
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... Since the purpose of carbon neutrality was put forward in 2020 [1], metakaolin and clay [5][6][7][8]. The geopolymer formed by the above aluminosilicate precursors through chemical activation, mechanical activation or mechanochemical activation has the properties of cementitious binders [9][10][11][12][13]. However, geopolymer has a relatively less carbon footprint than conventional cementitious binders [14]. ...
This paper offers a comprehensive review of geopolymeric recycled concrete (GRC) research, particularly focusing on mechanical properties, durability, microstructure, and the interfacial transition zone (ITZ). The study emphasizes the influence of recycled aggregate (RA) content on GRC performance. Findings indicate that higher RA content leads to a gradual reduction in GRC’s compressive, tensile, and flexural strengths, elastic modulus, and toughness. The elastic modulus is most affected, followed by compressive strength, while tensile strength experiences the least decline. Moreover, increased RA content is associated with elevated water absorption, decreased resistance to chloride ion permeability, sulfate corrosion, acid, frost, and carbonization in geopolymer concrete. The integration of RA creates more intricate ITZs in geopolymer concrete, resulting in reduced bonding strength and a looser, more porous microstructure. However, the use of geopolymers can mitigate these effects by enhancing bonding in ITZs. The paper also presents a statistical analysis of compressive strength test results from various studies and proposes a preliminary method for estimating the compressive strength of geopolymer concrete with different RA replacement rates.
... For instance, the compressive strengths of the OPG binder samples without FA particles after 28 curing days can reach 8.03 MPa at 4 mol/L and gradually increase to 9.19 MPa at 5 mol/L, but then drop sharply to 7.67 MPa at 6 mol/L. This is because a proper molar concentration of NS (i.e., 5 mol/L) can accelerate the hydration reaction to some extent and promote the formation of hydrate gels, which substantially improves the OPG matrix [60]. However, under a high alkali concentration such as 6 mol/L, the rapid alkali activation may cause some of the precursors to quickly dissolve and polymerize into clumps [61]. ...
The application of geopolymers in ground improvement has garnered significant attention in recent years. However, most geopolymer preparations have focused on the two-part method, which not only has negative environmental impacts but also falls short of meeting practical requirements. This study aimed to address these limitations by employing solid sodium silicate (Na 2 O⋅nSiO 2 , n is the molar ratio, NS) to activate binary precursors (fly ash [FA] and ground granulated blast furnace slag [GGBFS]), along with water, to synthesize a one-part geopolymer (OPG) for soft clay stabilization. The primary factors on the properties of the OPG binder were firstly identified through macro-and micro-tests. Subsequently, the optimization of the OPG mixing proportion was achieved by reducing the molar concentration of NS, and was further used for soft clay stabilization. The effects of the FA/GGBFS ratio (0, 0.1, and 0.2), curing period (7, 14, and 28 days), and binder content (0.15, 0.20, and 0.25) on the mechanical properties of the OPG-stabilized soft clay were then evaluated using un-confined compressive strength (UCS) tests. Furthermore, mercury intrusion porosimetry (MIP), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), and X-ray diffraction (XRD) techniques were employed to examine the evolution of microstructure, hydrate composition, and mineral/phase of the OPG-stabilized soft clay samples. The experimental results indicated that an appropriate OPG stabilizer proportion was achieved with an FA/GGBFS ratio of 0.1, water/precursor ratio of 0.8, molar ratio of NS of 1.0, and molar concentration of 3 mol/L. The high-early-strength feature of OPG binder contributed to the rapid strength development of the stabilized soft clay at an early age. A noticeable pozzolanic reaction was observed in the OPG-stabilized soft clay sample with an FA/GGBFS ratio of 0.1. Additionally, a binder content of 0.20 was recommended for the stabilization of soft clay due to its optimal balance between economic benefits and meeting the required UCS criteria in soil stabilization. Finally, a reliable nonlinear relationship between UCS and porosity of OPG-stabilized soft clay was established to assess the mechanical properties and stabilization effects of the OPG-stabilized soft clay for practical applications. This study greatly enhances the scientific understanding of geo-polymerization in the OPG system by using a combination of the binary precursor of FA and GGBFS and the solid NS activator. It sheds light on the stabilization mechanism of OPG-stabilized soft clay. The outcomes of this study make a valuable contribution to the advancement of environmentally friendly soil stabilizers, promoting green and low-carbon practices in the field of ground improvement.
... However, the mixture of many factors affected our judgment on the dominant factors of the geopolymer mechanical properties, resulting in many inconsistent conclusions. This has hindered the scientific preparation and popularization of slag-based geopolymers [26,27]. In this paper, we choose to proceed from the two perspectives of the mix ratio of the alkali activator and the elemental composition of raw materials. ...
Blast furnace slag is one of the largest solid wastes in the world. The slag-based geopolymer obtained by alkali activation has many advantages, such as a high strength, a good corrosion resistance, low carbon and environmental protection. Existing studies have shown that the mechanical properties of slag-based geopolymers are related to the combined effects of many factors, but there is still a lack of reliable conclusions on the primary and secondary influence degree of each factor, which greatly affects the scientific preparation and application of slag-based geopolymers. In order to solve this problem, we choose to proceed from the two perspectives of the mix ratio of the alkali activator and the elemental composition of raw materials. Through the orthogonal analysis method, this paper studies the influence of the modulus of the alkali activator, the solid-to-liquid ratio of the activator, the water–cement ratio and the metakaolin replacement rate on the uniaxial compressive strength of a slag-based geopolymer. The results show that when the solid–liquid ratio is about 0.25, the modulus of the alkali activator is 1.3~1.5, the water–cement ratio is about 0.4 and the samples with higher strength can be prepared. With the addition of metakaolin, a new gel phase NASH was formed in the system, which significantly promoted the late strength and toughness growth of the sample. The research results comprehensively analyze the influence of different factors on the mechanical properties of the slag-based geopolymer, which can provide a valuable reference for the engineering application of alkali-activated slag materials.
... In the process of preparing geopolymer, aluminum-silicate material is readily dissolved in the alkaline solution to form AlO 4 and SiO 4 tetrahedral units [11]. These tetrahedral frameworks are linked to yield polymeric precursors (-SiO 4 -AlO 4 -, or -SiO 4 -AlO 4 -SiO 4 -, or -SiO 4 -AlO 4 -SiO 4 -SiO 4 -) by sharing all oxygen atoms between two tetrahedral units, while water molecules are released [12][13][14]. ...
The objective of this study is to use the geopolymer technique to solidify/stabilize heavy metal contaminated soil. There are over 739,700 square meters of heavy-metal-contaminated sites in Taiwan; most sites are soil farmlands. These heavy metal contaminants in soil can also infiltrate into groundwater and cause more serious pollution problems. This study explores the possibility of using the geopolymer technique to solidify heavy metal contaminated soil (CS), stabilize heavy metal, and produce good mechanical and physical properties. The ground granulated blast furnace slag (GGBFS) was activated by an alkali solution to form a geopolymer binder that can be used to solidify CS and stabilize the heavy metal. The effect of GGBFS and CS mixing ratio on the mechanical and physical properties and the TCLP test was investigated. The test results show that the compressive strength of specimens made with a 1.5 CS/GGBFS ratio can reach 46.61 MPa and 47.66 MPa after curing for 14 and 28 days, respectively. TCLP tests show only 2 ppm Cu was detected from a geopolymer-treated contaminated soil sample. The influence of alkali solution, such as the molarity of the NaOH, SiO2/Na2O, and SiO2/Al2O3 molar ratio, were also evaluated. The specimens prepared with 8 M NaOH, 0.96 SiO2/Na2O, and 1.28 SiO2/Al2O3 molar ratio alkali solution have a compressive strength of 51.74 MPa and 58.63 MPa after 14 and 28 days of curing. The TCLP tests show no heavy metal ions leached from the sample.
This research demonstrates the synthesis of GGBS-based ready-mix (one-part) geopolymer (RMG) utilizing MBS as partial replacement to GGBS (10, 20 and 30 % by-mass) in addition to solid-alkaline reagents (NaOH-flakes and Na2SiO3 powder) using thermal and mechanical treatments, resulting in the formation of “ready-to-use” geopolymer product, “just-add-water” alike cement. The RMG was characterized by analyzing mineral phases, functional-groups identification followed by surface-morphology and elemental analysis at multiple stages, and engineering properties such as setting-time, flowability, compressive strength and ultrasonic-pulse-velocity were evaluated under ambient curing condition. The results show that GGBS-MBS-based RMG has dense morphology, affirming the development of C-S-H and C(N)-A-S-H gels due to its amorphous nature with some crystalline phases (SiO2) which are in-linked to Si-O-Si and Al-O Si bonds. The dry-mix of GGBS with powdered-Na2SiO3 and 4 m molality NaOH (Na2SiO3/NaOH=1), pre-heated at 105±5◦C for 6 h, followed by 6 h ball-milling with 20 % MBS replacement, achieved the highest 28-day compressive strength of 72.8 MPa, 10 % higher than the referenced mix and had satisfactory UPV results. The RMG not only solves handling problems caused due to concentrated aqueous-alkaline reagents used in two-part geopolymer synthesis but also provides sustainability by utilizing industrial and agricultural waste/by-products, hence reducing Portland cement demand, carbon footprint and waste-disposal issues.