Effect of 12-hour fire on Flexural Behavior of Recyclable Aggregate Reinforced Concrete Beams

Fire being one of the hazards causes external and internal adverse effects on concrete. On the other hand, demolishing waste causes numerous environmental issues due to lack of proper disposal management. Therefore, this research work presents experimental evaluation of effect of 12-hur fire on flexural behavior of reinforced concrete beams made with partial replacement of natural coarse aggregates with coarse aggregates from demolished concrete. The model beams are prepared using both normal and rich mix. Natural coarse aggregates are replaced in 50% dosage. Also, the beams without recyclable aggregates are prepared to check the results of proposed beams. After 28-day curing all the beams are exposed to fire for 12-hour at 1000°C in purpose made oven, followed by testing in universal load testing machine under central point load. During the testing deflection, load, and cracks are monitored. Analysis of flexural behavior and cracking reveals that after 12-hour fire residual strength of the beams is 52%. This shows loss of the strength of reinforced concrete beams thus requires appropriate retrofitting decision before putting again the structure in service after fire. Observation of cracks shows that most of the beams failed in shear with minor flexural cracks. In comparison to the results of control specimen the proposed beams show good fire resistance. The outcome of the research will prove landmark for future scholars and help the industry personals in understanding the behavior of the material in fire

Effect of Mould Size on Compressive Strength of Green Concrete Cubes

This paper is aimed to evaluate the effect of mould size on compressive strength of concrete cubes made with recyclable concrete aggregates. Natural coarse aggregates were replaced with 50% recycled aggregates from old demolished concrete. Five different mould sizes were used to cast 420 concrete cubes using 1:2:4 mix and 0.55 water/cement ratio. In each size equal number of cubes was cured for 3, 7, 14 and 28-day. After curing, weight of cubes was determined followed by testing for compressive strength in universal load testing machine with gradually increasing load. From the obtained results the strength correction coefficients were computed keeping 28-day cured standard size cubes as control specimens. Also, numerical expression based on regression analysis was developed to predict the compressive strength using weight of cube, area of mould and curing age as input parameter. The numerical equation predicts the compressive strength very well with maximum of 10.86% error with respect to experimental results.

Workability and Flexural Strength of Recycled Aggregate Concrete with Steel Fibers

This study examined how concrete workability and flexural strength are affected by steel fibers and recycled aggregates. Steel fibers were used in doses between 1-5%, with an increment of 0.5%, and 50% of the natural coarse aggregates were replaced by recycled. Two mixes of conventional and recycled aggregate concrete without steel fibers were used as control mixes. Concrete mixes were prepared using 1:2:4 and 0.45 water-to-cement ratios. Workability was determined using the slump cone. Three prism specimens sized 500×100×100mm were prepared for each batch and cured for 28 days in potable water. After curing, the specimens were air-dried in the laboratory and tested to evaluate their flexural strength under two-point loading. The load and deflection were monitored at regular intervals until failure. A comparison of results with control mixes showed that as the percentage of steel fiber increased, flexural strength increased by 69% and deflection decreased by 66%. The use of steel fibers improved the flexural strength of the recycled aggregate concrete by 59%

Assessment of the Flexural Strength of Binary Blended Concrete with Recycled Coarse Aggregates and Fly Ash

This study investigated the effect of blending fly ash and recycled aggregates as replacements for cement and conventional coarse aggregates, respectively. Recycled concrete helps to reduce waste management issues and protect the environment. Fly ash was used in percentages from 0% to 10% with an increment of 2.5%, whereas demolition debris was used in a proportion of 50% with conventional aggregates. The 1:2:4 mix with a 0.5 w/c ratio was used to make six concrete mixtures, one of them made entirely of congenital aggregates. Slump tests were performed for all mixtures. A total of 30 prisms of size 500×100×100mm were made and cured for 7 and 28 days. The flexural strength of the specimens was assessed under a two-point bending test till failure. The 5% fly ash and 50% Recycled Coarse Aggregates (RCA) mixture produced better results than the other mixes, showing a decrease in flexural strength of 10.74% and 15.75% after 7 and 28 days of curing, respectively. The small reduction in flexural strength compared to preserving conventional deposits and reducing the hazardous environmental impact of cement production and debris waste makes this mix suitable for use in structural members