Salim Barbhuiya

Effect of Pakistani bentonite on properties of mortar and concrete

Abstract Bentonite is composed primarily of montmorillonite and is useful in a wide range of applications. This paper presents the results of an experimental investigation carried out to evaluate the possibility of using a Pakistani bentonite (from Jehangira, Swabi District) as a cement replacement material in mortar and concrete. The cement in mortar and concrete was replaced with the bentonite at 0%, 20%, 30%, 40% and 50% by cement mass. The strength activity index of bentonite was determined ‘as received’ (20°C) and ‘heated’ (treatment at 500°C and 900°C). The test results indicated that the strength activity index of bentonite conformed to the ASTM Standard C618 specifications, except for the ‘900°C heated’ bentonite. The water absorption decreased for mortar containing up to 30% bentonite and then steadily increased at higher bentonite loadings. When immersed in 5% Na2SO4 and 2% MgSO4 solution, the greatest compressive strength was observed for mortar containing 30% bentonite. The water demand of concrete increased with increasing bentonite content. Although the compressive strength of concrete decreased progressively as the substitution level of bentonite was increased, the compressive strength of concrete containing 30% ‘as received’ bentonite was found to be 70% of the control concrete, whereas for concrete containing 30% ‘500°C heated’ bentonite, the strength was found to be 79% of the control concrete. It can be concluded that this Pakistani bentonite can be used to replace up to 30% of cement to produce concrete with sufficient compressive strength for low-cost construction resistant to sulphate attack.

PVA, PVA Blends, and Their Nanocomposites for Biodegradable Packaging Application

ABSTRACT This review exclusively addresses material systems primarily based on poly(vinyl alcohol) (PVA), one of the most popular water-soluble biopolymers, for their use in packaging applications with the primary objective of reducing petrobased plastic waste. In addition, some typical PVA blends and nanocomposites are discussed as comparative studies for material packaging. Structural characteristics, mechanical, thermal, and barrier properties, in addition to biodegradation of these multiple material systems are summarized in a systematic manner. Finally, associated fabrication processing methods together with the most popular theoretical models used for the permeability of PVA nanocomposites are also reviewed in detail. GRAPHICAL ABSTRACT

Electrospinning: Current Status and Future Trends

With the emerging nanotechnology, nanoscaled materials have drawn much attention to wide research communities for many years. Nanoscaled fibrous materials offer a multitude of fascinating features such as high surface area-to-volume ratio and tuneable porosity, making them attractive for widespread applications. Among different methods for nanofibre fabrication, electrospinning is a simple and versatile process for generating ultrathin fibres from a variety of polymeric materials or composites. This chapter gives a holistic review on current approaches and developments in electrospinning and its future trends in manufacturing advanced materials.

Nanoscaled Mechanical Properties of Cement Composites Reinforced with Carbon Nanofibers

This paper reports the effects of carbon nanofibers (CNFs) on nanoscaled mechanical properties of cement composites. CNFs were added to cement composites at the filler loading of 0.2 wt % (by wt. of cement). Micrographs based on scanning electron microscopy (SEM) show that CNFs are capable of forming strong interfacial bonding with cement matrices. Experimental results using nanoindentation reveal that the addition of CNFs in cement composites increases the proportions of high-density calcium-silicate-hydrate gel (HD-CSH) compared to low-density CSH gel. It was also found that the inclusion of CNFs increases the compressive strength of cement composites.

Effects of metakaolin on nanomechanical properties of cement paste

Metakaolin (MK) is a pozzolanic material, which is a dehydroxylated form of the clay mineral kaolinite. It is obtained by calcination of kaolinite clay at a temperature between 500 °C and 800 °C. In cement matrix, MK reacts with Ca(OH)2, to produce calcium silicate hydrate (CSH) gel. MK also contains alumina that reacts with Ca(OH)2 to produce additional alumina-containing phases, including C4AH13, C2ASH8 and C3AH6. This research aims to provide a better understanding of the effects of MK on the nanomechanical properties of the main phases present within the cement paste. Two different mixes were prepared, one control mix and the other one with 10 % MK (by cement weight). A constant water-binder ratio of 0.4 was used for both the mixes. Fraction volumes determined from nanoindentation testing show an increase in the amounts of high-density CSH at the cost of low-density CSH gel in cement pastes containing 10 % MK.

Anti-corrosion behaviour of VE/GF coatings on mild steel

Abstract In this study, the properties of vinyl ester/glass flake (VE/GF) coating on mild steel plates was investigated to determine its anti-corrosion performance. The corrosion penetration rate of VE/GF coated and uncoated mild steel was evaluated using immersion tests for 20 days. Corrosion resistance of the coating was evaluated in various corrosive environments viz. 5% HCl, 8% HCl, 5% NaOH and 7% NaOH. The mild steel plates were coated with four different thicknesses of VE/GF coating and a comparative analysis was carried out to evaluate the corrosion protection efficiency. Scanning electron microscopy was carried out before and after the immersion test to study the morphological changes and products of corrosion.

A review on the use of nanoindentation technique in characterizing cement-based materials

In this paper an attempt has been made to provide an overview on the use of nanoindentation technique in characterizing cement-based materials. The basic principle of nanoindentation is described. The mathematical formulation to determine the mechanical properties fro nanoindentation is vividly discussed. A discussion is also made on the nano-mechanical properties of different phases in cement paste. Finally, the challenges in using the nanoindentation technique in characterizing cement-based materials are highlighted.

Characterisation of Asphalt Concrete Using Nanoindentation

In this study, nanoindentation was conducted to extract the load-displacement behaviour and the nanomechanical properties of asphalt concrete across the mastic, matrix, and aggregate phases. Further, the performance of hydrated lime as an additive was assessed across the three phases. The hydrated lime containing samples have greater resistance to deformation in the mastic and matrix phases, in particular, the mastic. There is strong evidence suggesting that hydrated lime has the most potent effect on the mastic phase, with significant increase in hardness and stiffness.

Effective Surface Preparation Technique for Cementitious Samples in Nanoindentation Testing

The nanomechanical properties of cementitious materials determined by nanoindentation largely depend on the surface roughness and intrinsic material porosity of the samples. Studies have shown that high surface roughness causes an overall reduction in the measured indentation modulus and hardness. Therefore, it is important to reduce the surface roughness to a desirable value by means of polishing. However, polishing causes damage to the cement matrix. Thus, the most challenging task is to obtain a reasonable surface roughness with minimum disturbance to the microstructure of the samples. This paper discusses an effective surface preparation technique that would meet the roughness criteria for nanoindentation. With the application of Taguchi method, the optimum parameter combinations and relative contributions of various controlling factors such as force, speed, and time of polishing were determined. A second-order response surface model was developed based on signal to noise ratio to establish the relationship between the controlling factors and surface roughness. Finally, the predicted surface roughness values from both Taguchi method and response surface model were compared with the experimental values of the optimized confirmation runs and a good agreement was achieved.

Strength recovery of lightweight concrete under elevated temperature

This research is aimed at investigating the effect of elevated temperature, curing duration and curing methods on the strength recovery of lightweight concrete. Concrete specimens were subjected to elevated temperatures ranging from 300 to 600°C in a controlled heating environment. The specimens were subjected to three types of curing conditions: continuous water curing at 27°C, curing in a relative humidity of 95% at 27°C and curing in water at 60°C for three days and then curing in water at 27°C. The curing duration ranged from 7 to 56 days. The results indicated that the re-curing of concrete for the recovery of compressive strength is most effective in the temperature range from 300 to 500°C. For temperatures outside the range of 300 to 500°C, re-curing was either not effective or had limited application.