This research paper presents an experimental evaluation of the effect of water-cement ratio on the flexural strength of reinforced concrete beams made with 50% replacement of coarse aggregates with recycled concrete aggregates (RCA). 72 reinforced concrete beams were cast using 0.54, 0.6, 0.65 and 0.70 water-cement ratio. In each ratio, 12 beams were cast using RCA and 3 beams were cast using all-natural coarse aggregates (NCA). Beams were cured for 7 and 28 days. After curing, all beams were tested with central point load in a universal load testing machine. From the obtained results, it is observed that the maximum reduction in flexural strength of RCA beams is about 28% when compared to the 0.54 w/c ratio beams of the same group and 31.75% in comparison to NCA beams cast with same w/c ratio. The maximum deflection and average strain in beams remained within limits. The observed cracking pattern shows shear failure of all beams.
Self-weight of a structure comprises a major portion of the overall structural load which causes conservative structure design. Reduction of structures’ self-weight is an active area of research today. One of the options is to use lightweight concrete and no-fines concrete is one of its types. This type of concrete is made with coarse aggregates, cement, and water. From the density point of view, it is the lighter concrete compared to normal weight concrete but it exhibits less strength. Normally no-fines concrete is manufactured with uniform size aggregates. The performance of no-fines concrete depends on the cement-aggregate ratio and water-cement (w/c) ratio. This study focuses on investigating experimentally the effect of gradation of coarse aggregates and the w/c ratio on unit weight and compressive strength of no-fines concrete. NFC with two cement-aggregate ratios (1:6 and 1:8) having seven combinations of coarse aggregate gradations (10-5 mm, 16-13mm, 20-16mm, 20-13mm, 20-10mm, 16-10mm and 20-5mm) were studied. Two w/c ratios are considered 0.38 and 0.42. The effect of coarse aggregate gradation, cement-aggregate ratio and w/c ratio are studied in terms of unit weight and compressive strength of NFC. The results reveal the pronounced effect of aggregate gradation on the compressive strength and unit weight of the concrete. Also, a substantial effect on the unit weight and compressive strength is observed with the variation in cement-aggregate ration and the w/c ratio.
An experimental study on the shrinkage of recyclable aggregate concrete panels is presented in this paper. Recyclable aggregates are used in 50%, 60%, 70% and 80% replacement of natural coarse aggregates. For each replacement percentage, 3 panels were cast using 1:2:4 mix with 0.54 water-cement ratio and were cured for 28 days. In addition, 3 panels with the same parameters but using all-natural coarse aggregates were also cast to compare the results. Shrinkage in all panels was recorded for 3 months. Comparison of results reveals that with a 50% replacement, 8.33% increase in shrinkage was recorded. Along with shrinkage, cracks were also observed. At the end of the three month period, the widest crack had less width than 1mm, showing good resistance of the proposed material to shrinkage. Concluding, 50% replacement can be used in new concrete.
This study experimentally investigates the mechanical and durability performance of bacteria concrete in terms of density, compressive strength, split tensile strength, and water absorption capacity. The concrete specimens were produced with a ratio of 1:2:4, w/c ratio of 0.45, and having a bacteria dosage level ranging from 1 to 6% by weight of water. To investigate the usefulness of the bacteria dosage level, cubic and cylindrical specimens were cast and tested after 28 days of water curing in a Universal Testing Machine with a constant loading rate. The density of each specimen was also recorded soon after casting and after the curing period ended. Moreover, the water absorption test was similarly conducted on cube specimens at various time intervals to record the penetration depth. The test results of normal concrete (without bacteria) were compared with the ones of the specimens containing bacteria. The optimum level of bacteria was found to be 3.5%, which showed the highest values in terms of compressive strength, split tensile strength, and density. Bacteria tend to generate more crystalline materials inside the concrete mass due to reactions with the surrounding moisture which produces a compact surface, thus strength properties were improved and water penetration was blocked which suggests better durability of the concrete.
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