Papers by Author: Mohammad Iqbal Khan

Abstract: The implementation of nanotechnology in concrete has led to an active incorporation of nano silica in concrete in a global level. Different methods of nano silica production are available and vary from expensive to cost-effective routes. Nano silica particle sizes and their chemical and physical nature depend on the method of production. Several types of dispersed nano silica are recommended to be used in concrete due to practical reason. However, the dry powders of nano silica particles are difficult to be dispersed in concrete and require special types or family of nano superplasticizers. The effective addition of nS leads to C-S-H with improved cementitious properties.

Abstract: The evaluation of the tensile strength and determination of the tensile stress-strain curve using indirect tests becomes approximate hence there is a necessity for exploring direct tensile strength measurement. This investigation is part of ongoing research on the development of direct tensile strength measurement. In this paper direct tensile strength test has been proposed and the results obtained have been compared with compressive strength and flexural strength. It has been found that results obtained are well comparable and relationships are similar to that proposed in earlier findings.

Abstract: High strength concrete consisting of binary and ternary blended cementitious systems based on ordinary Portland cement, pulverised fuel ash and silica fume were investigated for carbonation. PFA up to 40% was used and to these blends 0, 5, 10, and 15% SF was incorporated as partial cement replacement. Results of carbonation of concrete cured in mist and air are reported. It was found that carbonation linearly increases with an increase in PFA content. Concrete with OPC only and concrete with 10% SF content showed insignificant change in carbonation when comparing air cured and mist cured concrete. The maximum carbonation depth observed for air cured concrete (containing 40% PFA) was less than 4 mm while in the case of mist cured concrete it was less than 2 mm. This depth is still far less than the cover of reinforced steel bars to cause corrosion.

Abstract: This paper reports the results of an investigation of chloride ion penetration and diffusion for high performance concrete. Concrete was prepared incorporating pulverised fuel ash (PFA) and silica fume (SF) with various water-binder ratios. Chloride ion penetration was measured at various ages using rapid chloride permeability test in accordance with ASTM C1202-91. Based on experimentally obtained results, isoresponse contours for chloride permeability were developed showing the interactive and optimized effect between the various parameters investigated. Diffusion coefficient of concrete was determined applying Fick’s law of diffusion. The results show that the inclusion of PFA and SF reduced both chloride permeability and chloride concentration of concrete. It was found that rapid chloride permeability values were consistent with diffusion coefficient of concrete.

Abstract: The most common form of rehabilitation for a deteriorated structure is to remove the deteriorated concrete and replace it with a new material, thus increasing the design life of the structure. Good adhesion of a repair material to concrete is of vital importance in the application and performance of concrete repairs. A major factor that influences the durability of the repair is the bond strength between the new material and the substrate. In this investigation, the most common repair materials, produced by international reputed manufactures, available in the local market were selected from cementitious repair mortars and cementitious polymer modified mortars. The performance of these materials were evaluated in terms of compressive strength, tensile strength, bond strength in tension and bond strength in modulus of rupture.