Faiz Shaikh

Effect of water absorption on the mechanical properties of cotton fabric-reinforced geopolymer composites

Abstract Cotton fabric (CF) reinforced geopolymer composites are fabricated with fibre loadings of 4.5, 6.2 and 8.3 wt%. Results show that flexural strength, flexural modulus, impact strength, hardness and fracture toughness are increased as the fibre content increased. The ultimate mechanical properties were achieved with a fibre content of 8.3 wt%. The effect of water absorption on mechanical and physical properties of CF reinforced geopolymer composites is also investigated. The magnitude of maximum water uptake and diffusion coefficient is increased with an increase in fibre content. Flexural strength, modulus, impact strength, hardness and fracture toughness values are decreased as a result of water absorption. Scanning electron microscopy (SEM) is used to characterise the microstructure and failure mechanisms of dry and wet cotton fibre reinforced geopolymer composites.

Tensile Strain Hardening Behavior of PVA Fiber-Reinforced Engineered Geopolymer Composite

AbstractThis paper is aimed to improve the mechanical properties (namely compressive and tensile strengths) of a recently developed fly ash-based engineered geopolymer composite (EGC) with relatively low-concentration activator combinations. In this regard, four different activator combinations (including two Na-based solutions and one K-based activator solution, and one lime-based activator combination in the form of powder) were used to develop the fly ash-based EGCs exhibiting strain hardening behavior under uniaxial tension. Randomly oriented short polyvinyl alcohol (PVA) fibers (2% v/v) were used to reinforce the relatively brittle low-calcium (Class F) fly ash-based geopolymer matrix. The matrix and composite properties of the developed fly ash-based EGCs [including workability of the fresh matrix, density, compressive strength, matrix fracture properties (comprising elastic modulus, fracture toughness, and composite crack tip toughness), and uniaxial tensile behavior] were evaluated. A counterpart ...

Effect of nano-clay on mechanical and thermal properties of geopolymer

Abstract The effect of nano-clay platelets (Cloisite 30B) on the mechanical and thermal properties of fly ash geopolymer has been investigated in this paper. The nano-clay platelets are added to reinforce the geopolymer at loadings of 1.0%, 2.0%, and 3.0% by weight. The phase composition and microstructure of geopolymer nano-composites are also investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques. Results show that the mechanical properties of geopolymer nano-composites are improved due to addition of nano-clay. It is found that the addition of 2.0 wt% nano-clay decreases the porosity and increases the nano-composites resistance to water absorption significantly. The optimum 2.0 wt% nano-clay addition exhibited the highest flexural and compressive strengths, flexural modulus and hardness. The microstructural analysis results indicate that the nano-clay behaves not only as a filler to improve the microstructure, but also as an activator to facilitate the geopolymeric reaction. The geopolymer nano-composite also exhibited better thermal stability than its counterpart pure geopolymer.

Properties of concrete containing recycled construction and demolition wastes as coarse aggregates

The incorporation of mixed construction and demolition (C&D) wastes as a substitute to natural aggregates (NA) has many economic and environmental benefits. In this paper, the results of an investigation on the effect of recycled coarse aggregate (RCA) obtained from C&D wastes on mechanical and durability properties of concretes are presented and compared with concrete containing NA. Compressive, tensile, and flexural strengths are measured as part of mechanical properties and drying shrinkage, chloride ion permeability, water absorption, and sorptivity are measured as part of durability properties. The recycled aggregate concretes contain 25 and 50% RCA as replacement of NA. All samples are tested after 7, 28, 56, and 91 days of wet curing. The results show that the compressive strength of recycled aggregate concretes decreased with increase in RCA contents, however it improved with longer curing. Similar results are also observed in flexural and tensile strength of recycled aggregate concretes. The drying shrinkage of recycled aggregate concretes also increases with increase in RCA contents and time to drying exposure until 56 days. However, the rate becomes constant after 56 days of drying. The recycled aggregate concretes also exhibit poor sorptivity, water absorption, and chloride ion permeability compared to concrete containing NA. The result of poor durability performance of recycled aggregate concretes is relative to high porosity of constituents and interconnectivity of the pore system in the concrete. Correlations between different durability properties and compressive strength of recycles aggregate concretes are also established in this study.

Effects of steel fibre and silica fume on impact behaviour of recycled aggregate concrete

This paper presents the effects of silica fume and steel fiber on the mechanical properties and impact behavior of recycled aggregate concrete containing two types of recycled coarse aggregates (RCAs). In total, 20 series of concretes are considered and they are divided into 4 groups. The first group consisted of 1 control concrete containing natural coarse aggregate and 4 control recycled aggregates concretes containing 50 and 100% RCA of two types (A and B). The second and third series are similar to the first series in every aspect except the former contained 8% silica fume as partial replacement of ordinary Portland cement and the latter contained 1% steel fiber by volume. In the fourth series, both 8% silica fume and 1% steel fiber are used. Compressive and split tensile strengths of all concretes are measured in terms of mechanical properties evaluation and low velocity impact hammer test is conducted to evaluate the impact behavior of all concretes. Results show that the concrete containing RCA obtained from high strength parent concrete exhibited better mechanical properties than that containing RCA made low strength concrete. The addition of silica fume improved the split tensile and compressive strengths of recycled aggregate concretes containing both types of coarse aggregates. The addition of steel fibers significantly increased the compressive and split tensile strengths of all concretes, especially recycled aggregate concretes. The simultaneous use of silica fume and steel fibers had a significant effect on the compressive and split tensile strengths of all recycled aggregate concretes, probably due to better bond of steel fibers with mortar containing silica fume as well as improved ITZ between RCA and mortar. The addition of 100% RCA of both types significantly reduced the impact resistance of recycled aggregate concretes. The same is also true even when silica fume is added. The addition of steel fibers significantly improved the impact behavior of recycled aggregate concretes. The addition of silica fume, however, did not show any significant improvement in impact resistance of steel fiber-reinforced recycled aggregate concretes.

Effect of Nano Silica and Ultrafine Fly Ash on Compressive Strength of High Volume Fly Ash Mortar

This paper evaluates the effect of Ultrafine Fly Ash (UFFA) and nanoSilica (NS) on compressive strength of high volume fly ash (HVFA) mortar at 7 days and 28 days. Three series of mortar mixes are considered in the first part of this study. In the first series the effect of high content of class F fly ash as partial replacement of cement at 40, 50 and 60% (by wt.) are considered. While in the second and third series, the UFFA and NS are used as partial replacement of cement at 5%, 8%, 10%, 12% and 15% and 1%, 2%, 4%, 6% and 8% (by wt.) of cement, respectively. The UFFA and the NS content which exhibited highest compressive strength in the above series are used in the second part where their effects on the compressive strength of HVFA mortars are evaluated. Results show that the mortar containing 10% UFFA as partial replacement of cement exhibited the highest compressive strength at both 7 and 28 days among all UFFA contents. Similarly, the mortar containing 2% NS as partial replacement of cement exhibited the best performance. Interestingly, the use of UFFA in HVFA mortars did not improve the compressive strength. However, the use of 2% and 4% NS showed improvement in the compressive strength of HVFA mortar containing 40% and 50% fly ash at both ages. The effects of NS and UFFA on the hydration and strength development of HVFA mortar is also evaluated through X-Ray Diffraction (XRD) test. Results also show that the UFFA and NS can significantly reduce the calcium hydroxide (CH) in HVFA mortars.

Mechanical properties of cotton fabric reinforced geopolymer composites at 200–1000 ℃

Geopolymer composites containing woven cotton fabric (0–8.3 wt%) were fabricated using the hand lay-up technique, and were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. With an increase in temperature, the geopolymer composites exhibited a reduction in compressive strength, flexural strength and fracture toughness. When heated above 600 °C, the composites exhibited a significant reduction in mechanical properties. They also exhibited brittle behavior due to severe degradation of cotton fibres and the creation of additional porosity in the composites. Microstructural images verified the existence of voids and small channels in the composites due to fibre degradation.

Effects of curing conditions and sand-to-binder ratios on compressive strength development of fly ash geopolymer

AbstractThis paper investigates the effects of curing conditions on a high-strength geopolymer material synthesized by activating different combinations of Class F fly ash (FA), ground-granulated b...

Effect of nanoclay on durability and mechanical properties of flax fabric reinforced geopolymer composites

Abstract The main concern of using natural fibres as reinforcement in geopolymer composites is the durability of the fibres. Geopolymers are alkaline in nature because of the alkaline solution that is required for activating the geopolymer reaction. The alkalinity of the matrix, however, is the key reason of the degradation of natural fibres. The purpose of this study is to determine the effect of nanoclay (NC) loading on the mechanical properties and durability of flax fabric (FF) reinforced geopolymer composites. The durability of composites after 4 and 32 weeks at ambient temperature is presented. The microstructure of geopolymer matrices was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that the incorporation of NC has a positive impact on the physical properties, mechanical performance, and durability of FF reinforced geopolymer composites. The presence of NC has a positive impact through accelerating the geopolymerization, reducing the alkalinity of the system and increasing the geopolymer gel.

Microstructure and Nanoscaled Characterization of HVFA Cement Paste Containing Nano-SiO2 and Nano-CaCO3

AbstractThis paper presents the effects of nano-SiO2 and nano-CaCO3 on the microstructure of high-volume fly ash (HVFA) cement paste. The microstructures of HVFA cement pastes containing 40 and 60%...