[Show abstract][Hide abstract] ABSTRACT: Stress (compression/tension) leads to generate micro cracks in concrete matrix, which eventually forms visible cracks. Such formation of cracks is common and causes failure of structures. An experimental investigation was carried out to compare the self healing of partially cracked conventional mortar (prepared with ordinary Portland cement) and cement - fly ash mortar. 20 % OPC has been replaced by class F fly ash for cement - fly ash mortar. All mortar specimens were prepared with 1:3 binder to sand ratio (by weight) and with fixed 0.5 water/binder ratio. After curing in normal tap water for 28 days, specimens were subjected to direct compression (50% of corresponding 28 days compressive strength) to generate micro cracks in it. Healing environment was made (a) curing in normal tap water for 120 days and (b) curing in normal air for 120 days separately. The compressive strength, ultrasonic pulse velocity, water absorption and rapid chloride ion permeability test on mortar specimens (with/without fly ash) confirm self healing of cementitious composites in terms of recovery of its properties and the self healing property is more prominent for fly ash mortar. FESEM with EDAX and XRD of the white deposition in the crack opening was found to be calcite.
[Show abstract][Hide abstract] ABSTRACT: An experimental investigation was carried out to compare the compressive strength of zero slump and high slump concrete with high volume fly ash. 40% to 70% replacements of OPC (by weight) with class F fly ash have been incorporated. Superplasticizer was added at 1% of binder (cement + fly ash) to the zero slump mixture to get a slump in the range of 140 to 180mm and cubes were cast without compaction. The results showed that the apparent porosity and water absorption were higher for zero slump concrete than high slump concrete. Zero slump concrete showed better compressive strengths than superplasticized concrete with 40 to 60% fly ash addition for all curing times tested (3,7 and 28 days). Ultrasonic pulse velocity results categorized all mixes as of ‘EXCELLENT’ concrete quality. Based on the present experimental investigation, it can be concluded that high volume fly ash concrete is suitable for general construction applications.
Global Nest Journal 12/2013; 15(4):578-584. · 0.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An experimental investigation has been carried out to study the effect of variation of
compressive load on mortar specimens. Ordinary portland cement and river sand as fine aggregate was mixed with water/cement ratio of 0.45. Loads of 0, 30, 50 and 70% of compressive strength at 7 days were applied to the samples of age 7 days separately and released the load immediately. At higher loading range, cracks of up to 2 mm have been noticed on the surface of the samples. The stressed samples were tested for percentage apparent porosity and water absorption which showed increase in their values with the higher load application. Compressive strength and ultrasonic pulse velocity of the stressed samples confirm that the quality of concrete deteriorate with load application.