Effect of Alkaline Activators on the Mechanical Properties of Geopolymer Mortar

"Geopolymerization is a process where silica and alumina rich source materials turn into excellent binding materials by the aid of alkali solutions. Materials such as fly ash are by-products in energy power plants. Fly ash is classified based on its constituent materials. Fly ash class F mainly consists of alumina and silica. Compressive strength of class F fly ash geopolymer mortar is influenced by many factors such as fluid to binder ratio, Na2SiO3/NaOH ratio, curing duration, curing temperatures and molarity of the activator solution. The present study investigates the effect of the fluid to binder ratio and Na2SiO3/NaOH ratio on the compressive strength of geopolymer mortar. The curing temperature was fixed to 80 °C. The curing durations investigated was 24h. For each combination, three cubes with dimensions of 50 x 50 x 50 mm were casted. After heat curing in the laboratory oven, the samples were tested on a universal testing machine for the compressive strength. The results showed very high early compressive strength of 66.39 MPa for samples cured at 80 °C and for a duration of 24 hr. The significance of the present study is that it will allow for establishing methods for production of high strength geopolymer mortar that can be used in civil engineering applications, in addition to the environmental advantages of using such source materials to produce binding materials with outstanding mechanical properties.

Evaluation of Bond Strength Between Carbon Fiber Reinforced Polymer (CFRP) Composites with Modified Epoxy Resins and Concrete

Rehabilitation and strengthening of concrete structures are becoming more significant in civil engineering applications. The use of externally bonded Fiber Reinforced Polymers (FRP) is one of the methods to strengthen and rehabilitate reinforced concrete members, providing noticeable improvement to their capacity in resisting load. Carbon Fiber Reinforced Polymer (CFRP) is used along with epoxy resins to evaluate the bond strength of two commercially available epoxies (EPON 828 and EPON 862) between CFRP and concrete. In addition, three new combinations that resulted from mixing the two epoxies were examined. The mechanical properties of epoxy resins are significantly weaker than this of the CFRP making the epoxy characteristics the determining factor in the quality of the bond strength. Three-point flexural test was conducted to examine the bond strength between the CFRP composites and concrete. Further, differential scanning calorimetry was conducted to examine the glass transition temperature of the resultant epoxies. The results showed that the optimum composition was a mixture of 70% of epoxy 828 and 30% of epoxy 862. Therefore, achieving better bond strength and high glass transition temperature, resulting in CFRP composite with higher fire resistance

Dosage Optimization of Polypropylene Fiber for Strength Enhancement of Cementitious Composites

"Concrete is the most commonly used materials for construction in Qatar as well as in the world. Exposure to sever environmental conditions causes physical deterioration of concrete structures and significantly affect the concrete’s strengths and modulus of elasticity. In the last decades, many improvements had been made in concrete technology. Most of these improvements focused on the weak point of concrete, which is tensile strength enhancement. One possible method to improve the tensile strength of cementitious composites is incorporation of fibers in the mix. Polypropylene fiber is widely used for this purpose due to their corrosion resistance and relatively low cost. Polypropylene fibers are usually incorporated in cement mortar to control cracks propagation thus enhance its tensile and flexural properties. This research focuses on Polypropylene fiber dosage optimization for strength enhancement of cementitious composites. Four dosages of Polypropylene microfibers; 0%, 0.05%, 0.1%, and 0.2% by weight of cement; were added into cement mortar to explore the optimum dosage that can lead to big enhancement in mechanical strengths of cementitious composites. The mechanical strengths were investigated in terms of compressive and flexural strengths. The results revealed that adding small amount of Polypropylene microfibers could enhance the compressive and flexural strengths of cement mortar. The maximum enhancement in the compressive and flexural strengths was equal to 26% and 19% and was achieved in the case of adding 0.1% and 0.05% by weight of cement, respectively.

Sustainable utilization of waste carbon black in alkali-activated mortar production

This article investigates the potential utilization of waste carbon black (WCB) resulting from the aluminum industry as a by-product material in the fly ash-based geopolymer composites production. Experimental study was conducted to evaluate the effect of WCB on the performance of the geopolymer. Different contents of WCB including 5%, 10%, 15%, 20%, 30%, and 40%,by weight of the fly ash, have been incorporated in the geopolymer mix as either additives or fly ash replacement. Life cycle assessment (LCA) has also been conducted to evaluate the landfills utilization and the environmental impact of the WCB incorporation. The experimental results reflected that the WCB could be used as additives in small quantities (5% of fly ash weight) to the geopolymer mix without negatively affecting its performance. Adding 5% of WCB insignificantly enhanced the compressive strength of the geopolymer by 5%, increased its workability and density by 3% and 4%, respectively, and did not affect its excellent thermal stability. Scanning electron microscopic (SEM) imaging showed more unreacted fly ash particles combined with more voids and cracks within the microstructure of the geopolymer with high WCB content. Finally, incorporating WCB in the geopolymer production improved the utilization of landfills use and reduced the global warming potential, acidification potential, eutrophication potential and abiotic depletion potential

Development of sustainable geopolymer composites for repair application: Workability and setting time evaluation

One of the most used construction materials worldwide is concrete. It has a lot of advantages over the other construction materials. However, the production process of concrete produces a huge amount of carbon dioxide. Geopolymer composites are gained attention as eco-friendly alternative to traditional cement. In this research an attempt has been done to optimize a sustainable geopolymer mortar made of ground-granulated blast furnace slag (GGBS) and fly ash (FA). The optimized geopolymer mortar is designed to be convenient and practical for repairing damaged reinforced concrete members. Accordingly, this research is focused on improving setting time and workability of an ambient cured geopolymer mortar. In this research an attempt has been done to study the impact of using different superplasticizer dosages, different GGBS percentages, and different alkaline activator solution ratios on the setting time and flowability of an ambient cured geopolymer mortar. The obtained findings of this study showed that, alkaline activator ratio is one of the most significant parameters that affect workability and setting time of the geopolymer mortar. In this study, fifteen different mixes were tested and evaluated. Modified Vicat apparatus and Flow Table test were used to evaluate setting time and workability for the mortars. The outcome of the optimization showed that, the most convenient and practical mix which provided the highest setting time and reasonable flowability contained of 25% GGBS, 75% FA and 5% superplasticizer. The obtained workability for the optimum mix was about 156.25 mm and the achieved setting time was about 30 min.Office of Research and Graduate Studies at Qatar University funded the work presented in this study under project (QUST-2-CAM-2022-700)

Industrial Waste Utilization of Carbon Dust in Sustainable Cementitious Composites Production

This paper experimentally investigates the effect of utilization of carbon dust generated as an industrial waste from aluminum factories in cementitious composites production. Carbon dust is collected, characterized, and then used to partially replace cement particles in cement mortar production. The effect of adding different dosages of carbon dust in the range of 5% to 40% by weight of cement on compressive strength, microstructure, and chemical composition of cement mortar is investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF) analysis are used to justify the results. Experimental results show that incorporation of carbon dust in cement mortar production not only reduces its environmental side effects but also enhances the strength of cementitious composites. Up to 10% carbon dust by weight of cement can be added to the mixture without adversely affecting the strength of the mortar. Any further addition of carbon dust would decrease the strength. Best enhancement in compressive strength (27%) is achieved in the case of using 5% replacement ratio. SEM images show that incorporation of small amount of carbon dust (less than 10%) lead to produce denser and more compact-structure cement mortar

Effect of elevated temperatures on mechanical performance of cement mortar with nanoclay

In this research, the effect of nanoclay addition on mechanical strengths of cement mortars subjected to elevated temperatures was investigated. Mortars with three different replacement dose of montmorillonite nanoclay (0, 1 and 2% of cement weight) were prepared and then subjected to 200 °C, 400 °C, and 600 °C for 2 hrs. Compressive and flexural strengths of the heated and unheated specimens were obtained. The results showed that nanoclay addition to cement mortar caused marginal enhancement in its compressive and flexural strengths at room temperature. But, the efficiency of nanoclay to enhance the flexural strength of cement mortar increased at higher temperatures. The maximum relative improvement in flexural strength due to 2% nanoclay addition was achieved at 400°C

The role of polypropylene microfibers in thermal properties and post-heating behavior of cementitious composites

This paper experimentally studied the effect of polypropylene (PP) microfibers on thermal and post-heating mechanical behaviors of cementitious composites. Cement mortars with small dosage of polypropylene fibers were prepared, heated at various temperatures (150 °C, 200 °C, 450 °C, and 600 °C), and then tested. The investigated parameters include residual compressive and flexural strengths, elastic modulus, fracture energy, stress intensity factors, failure modes, microstructure (scanning electron microscopy (SEM) imaging), thermal conductivity, heat flow (differential scanning calorimetry (DSC) test), mass loss (thermogravimetric analysis (TGA) test), and chemical composition (XRD analysis). The results showed the efficiency of PP fibers to enhance the post-heating behavior and the residual mechanical properties of cement mortar after heating. The presence of PP fibers did not affect the heat flow and the mass loss of cement mortar at room temperature. However, heating cement mortar at temperature beyond the melting point of the fibers negatively affected its thermal behavior. The presence of PP fibers played a major role in bridging the cracks and mitigating their propagation. Once the melting point of the polypropylene fibers is exceeded, the fibers melted and created extra voids in the microstructure of concrete.The APC was funded by Qatar National Library

Potential utilization of municipal solid waste incineration ashes as sand replacement for developing sustainable cementitious binder

This paper investigates the ability of recycling the municipality solid waste incineration (MSWI) ashes as sand replacement in cementitious binder production. Two types of MSWI ashes were considered in this study including fly ash and bottom ash. The ashes were characterized, and then incorporated into the mixes as sand replacement with different ratios: 0%, 10%, 20%, and 30%. Comprehensive experimental work was conducted to investigate the mechanical strengths, workability, density, water absorption, thermal conductivity, thermal stability, chemical composition, and heavy metals content of the prepared binders. The results reflected the ability of producing sustainable cementitious binder with low dosage of MSWI ashes (up to 10%) as sand replacement with good mechanical properties, and accepted workability, water absorption, and thermal stability. Partially substitution of sand with MSWI ashes enhanced the early (3-day) compressive strength of cement mortar. Optimum enhancements of 16% and 45% were achieved at 10% and 20% replacement ratios in the case of mortar with MSWIFA and MSWIBA, respectively. Using the MSWI ashes as sand replacement resulted in better compressive strength of the mortar compared to the common approach of using it as cement replacement. However, the chemical composition analysis showed the presence of heavy metals in the hydration products of the binder. The mobility and leaching of these metals should be taken into consideration before any possible application of these materials.The ICP-OES test was accomplished in the Central Laboratories unit, Qatar University, Qatar.Scopu

Ambient and Heat-Cured Geopolymer Composites: Mix Design Optimization and Life Cycle Assessment

The feasibility of producing sustainable cement-free composites and its environmental impact were investigated in this research. Experimental parametric evaluation was carried out in this regard to explore the optimum mix design of the composites. The effect of synthesis parameters and curing conditions on the behavior of the produced geopolymer composites was investigated. The studied parameters included the molarity of the sodium hydroxide solution (12 M, 14 M, and 16 M), the sodium silicate to sodium hydroxide ratio (1, 1.5, 2, and 2.5), the fluid to binder ratio (0.6, 0.65, and 0.7), and the age. The curing conditions included ambient curing and heat treatment at 40 °C, 80 °C, and 120 °C for 24 h, 48 h, and 72 h. In addition, life cycle assessment was performed to compare the environmental impact of geopolymer and cementitious composites. The results reflected the possibility of producing geopolymer composites with significant positive environmental impacts over traditional cementitious composites. The synthesis parameters played a major role in the behavior of the produced geopolymers. Heat curing was necessary for the geopolymer mortar to achieve high early strength. However, strength development with age was more obvious for ambient-cured specimens than heat-cured specimens. The optimum fluid to binder ratio used in this research was 0.6. For this ratio, the compressive strength increased as the molarity of the sodium hydroxide solution increased for all sodium silicate to sodium hydroxide ratios. Finally, SEM images showed that the higher the molarity and as the amount of reacted FA particles increased, the better the microstructure of the geopolymer mortar was and the fewer pores the matrix had