November 2017

An investigation on the behaviour of metakaoline based hybrid fiber reinforced concrete when subjected to acid attack
Shreepad Desai and Prakash K.B.

Combining fibres with different geometry and mechanical properties can improve the mechanical properties of fibre reinforced concrete. Often called hybrid fibre reinforced concrete (HFRC), these composites take advantage of different and synergistic effects on mechanical properties of each fibre type. Macrofibers of steel, due to their high modulus and improved bonding characteristics are known to improve toughness of concrete at relatively small crack openings; on the other hand, micro-fibres of polypropylene are expected to mitigate shrinkage cracking, improve the tensile strength of the matrix, improve the crack growth resistance and enhance strain capability. In this experimental work an attempt is made to study the strength characteristics of metakaoline based hybrid fiber reinforced concrete when subjected to acidic attack. Different fibers used in the work are steel fibers (SF), galvanized iron fibers (GIF), waste coiled steel fibers (WCSF), high density polyethylene fibers (HDPEF), waste plastic fibers (WPF) and polypropylene fibers (PPF). Different combinations of hybrid fibers used for the study are (SF+GIF), (SF+WCSF), (SF+HDPEF), (SF+WPF) and (SF+PPF).

Influence of various exposure conditions on the structural performance of sandwich wall panels
Vishnu B., Aditi Chauhan, Danie Roy and U.K. Sharma

The structural performance of concrete sandwich wall panels after having exposed to various environmental conditions was investigated in this study. Reinforced concrete expanded polystyrene core panels were subjected to exposures simulating corrosion, alternate wetting and drying and dry heat conditions. Post exposure, the panels were tested for their in plane shear and out of plane bending strengths. The degree of composite action for panels tested in flexure was calculated in terms of initial stiffness. No reduction in the composite action was noted after exposure to different chosen exposure conditions.

Prediction of compressive strength of concrete using electrical resistivity measurement on cement and fine aggregate replacement
R.K. Mishra and R.K. Tripathi

Performance and reliability of any part or whole structural unit depends up on the pre and post quality or aging and degradation. This phenomenon can also be observed on performance of ingredients. The properties of concrete core or any cementitious sample can be related with its density or strength. An electrical method of testing involves passing electrical current perpendicular to casting direction [1]. This helps in finding out denseness or packing due to compaction and development of hydration product [2]. This paper deals with the correlation between concrete bulk resistivity using parallel plate resistivity meter, compressive strength test results and setting empirical relation for the same. The tests have been conducted in the laboratory by varying ingredients in concrete.

Improving strength of recycled fine aggregate concrete using metakaolin
Krishnamurthy Pandurangan and Rajendiran Arunpandian

In India, traditionally river sand is used as fine aggregate in concrete production. However, due to continuous exploitation of river sand, its availability has become scarce. Construction industry has started using alternate materials as fine aggregate. Out of which manufactured sand is one of the popularly used material as fine aggregate. Materials such as quarry dust and recycled concrete aggregate have issues of dumping and environmental pollution. These materials are viable alternatives for replacement of natural river sand. Recycled concrete, if used as coarse aggregate has problems of water absorption and reduction in strength. Hence, an attempt has been made in this research to use recycled concrete aggregate (RCA) as fine aggregate in concrete. Further, use of RCA as fine aggregate in concrete may reduce the compressive strength of concrete. Hence, it is proposed to use metakaolin as a supplementary cementitious material in concrete with Recycled Fine Aggregate (RFA) as fine aggregate. This study investigates the effect of metakaolin and RFA on the mechanical characteristics of concrete mixtures. Mechanical properties such as compressive strength, split tensile strength, flexural strength at 7 and 28 days are determined. Metakaolin is added to cement in the range of 7.5% to 20% by weight of cement. Natural sand is replaced with RFA in the range of 0-100% by weight of sand. From the study it is found that RFA could be used as alternative material for natural sand. However, as complete replacement of RFA reduces the strength of concrete, metakaolin addition is mandatory. A minimum of 7.5% metakaolin is required to prevent strength loss in concrete. However, if RFA alone need to be used without addition of metakaolin, only 50% replacement of sand with RFA is recommended.