Influence of Water Content on Mechanical Strength and Microstructure of Alkali-Activated Fly Ash/GGBFS Mortars Cured at Cold and Polar Regions

Abstract

Negative temperature curing is a very harmful factor for geopolymer mortar or concrete, which will decrease the strength and durability. The water in the geopolymer mixture may be frozen into ice, and the water content is a crucial factor. The purpose of this paper is to explore the influence of water content on the properties of alkali-activated binders mortar cured at −5 • C. Fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as binders. Three groups of experiments with different water content were carried out. The prepared samples were investigated through uniaxial compression strength test, Scanning electron microscopy (SEM), and X-ray diffraction (XRD) for the determination of their compressive strength, microstructural features, phase, and composition. The results indicated that, the compressive strength of samples basically maintained 25.78 MPa at an age of 28 days; for 90 days, the values reached 33.4 MPa-34.04 MPa. The results showed that lower water content is beneficial to improving the early strength of mortar at −5 • C curing condition, while it has little impact on long-term strength. These results may provide references for the design and construction of geopolymer concrete in cold regions.However, most previous studies about the alkali-activated fly ash/GGBFS mortar and concrete were carried out by curing samples at elevated temperature or in ambient curing condition [13]. Many researchers believed that addition of GGBFS can significantly improve early and later age mechanical strength of fly ash based geopolymer concrete cured at room temperature [14,15]. Up to now, the research on the physical and mechanical properties of geopolymer concrete curing at negative temperature has not been reported.With the social development, cleaner and energy-saving building materials are needed in cold and polar regions of the world. For example, Figure 1 shows the mean annual air temperature distribution of China in 2015 [16], and the temperature in most areas is lower than 0 • C, however, many infrastructures were built in these areas, such as Qinghai-Tibet railway, Sichuan-Lasa Expressway, and Harbin Dalian high speed railway. These projects only have a very short construction period of positive temperature (above 0 • C) every year, which will extend the entire construction period and increase the cost. If the in-situ casting geopolymer concrete with better performance can be obtained under the condition of negative temperature curing, the construction period will be shortened and the cost will be saved. Materials 2019, 12, x FOR PEER REVIEW 2 of 16building materials, fire-retardant coatings, fiber-reinforced composite materials, and fixed solutions for chemical and nuclear industrial wastes. However, most previous studies about the alkali-activated fly ash/GGBFS mortar and concrete were carried out by curing samples at elevated temperature or in ambient curing condition [13]. Many researchers believed that addition of GGBFS can significantly improve early and later age mechanical strengt...

Strength, Shrinkage and Early Age Characteristics of One-Part Alkali-Activated Binders with High-Calcium Industrial Wastes, Solid Reagents and Fibers

“…The compressive strength development was associated with the formation of both binding phases (C-A-S-H and N-A-S-H) in FA/GGBFS binders, as observed from the matrix microstructure through SEM/EDS and XRD analyses. The formation of such binding phases was also observed in previous research studies on FA/GGBFS-based alkali-activated mortars and composites [9,[55][56][57][58]. The binders (without fibers) incorporating reagent 2 exhibited 2% to 18% higher 28 day compressive strength (between 39 and 57 MPa) than their reagent 1 counterparts (Figure 4a,b and Table 2) due to the formation of additional C-S-H gel formation associated with high calcium content in the system.…”

“…Polymerization occurs under highly alkaline conditions when reactive aluminosilicates are rapidly dissolved, and free [SiO 4 ]-and [AlO 4 ]-tetrahedral units are released in solution. The tetrahedral units are alternatively linked to polymeric precursors by sharing oxygen atoms, forming polymeric Si-O-Al-O bonds [1,9]. The development process of geopolymers uses 60% less energy and produces 80 to 90% fewer greenhouse gases than the synthesis of ordinary Portland cement (OPC)-based binders [7][8][9][10][11].…”

“…The tetrahedral units are alternatively linked to polymeric precursors by sharing oxygen atoms, forming polymeric Si-O-Al-O bonds [1,9]. The development process of geopolymers uses 60% less energy and produces 80 to 90% fewer greenhouse gases than the synthesis of ordinary Portland cement (OPC)-based binders [7][8][9][10][11].…”

Rice Husk Ash/Silicone Rubber-Based Binary Blended Geopolymer Coating Composite: Fire Retardant, Moisture Absorption, Optimize Composition, and Microstructural Analysis

“…However, due to the dominant geopolymer composite matrix and high water content (as compared to samples S17 and S18), cracks and corrugated wrinkles were developed during the curing and hot pressing process. The effect of water content on crack formation was proven by Wei et al [ 57 ], who concluded that the high water content in the geopolymer matrix resulted in a sudden shrinkage during the curing process, thus forming cracks. The cracks subsequently provided an opening which allowed heat to travel faster into the layers of coating and thus lower the fire retardant properties of the sample.…”

Alkali Activated Paste and Concrete Based on of Biomass Bottom Ash with Phosphogypsum

“…The chemical and mineral composition of BBA is appropriate for reusing in the production of new, low-carbon building materials. In this way, the replacement of traditional initial material [3,4] such as fly ash or slag in alkali activated materials (AAM) by BBA leads to important environmental benefits [5][6][7]. As demand for ecological alternatives to Portland cement like alkali 2 of 13 activated materials (AAM) is growing, there is interest to utilize phosphogypsum (PG) in AAM.…”